Subjects -> MINES AND MINING INDUSTRY (Total: 82 journals)
Showing 1 - 42 of 42 Journals sorted alphabetically
American Mineralogist     Hybrid Journal   (Followers: 16)
Applied Earth Science : Transactions of the Institutions of Mining and Metallurgy     Hybrid Journal   (Followers: 4)
Archives of Mining Sciences     Open Access   (Followers: 3)
AusiMM Bulletin     Full-text available via subscription   (Followers: 1)
BHM Berg- und Hüttenmännische Monatshefte     Hybrid Journal   (Followers: 2)
Canadian Mineralogist     Full-text available via subscription   (Followers: 7)
CIM Journal     Hybrid Journal  
Clay Minerals     Hybrid Journal   (Followers: 9)
Clays and Clay Minerals     Hybrid Journal   (Followers: 5)
Coal Science and Technology     Full-text available via subscription   (Followers: 4)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 14)
Environmental Geochemistry and Health     Hybrid Journal   (Followers: 3)
European Journal of Mineralogy     Hybrid Journal   (Followers: 14)
Exploration and Mining Geology     Full-text available via subscription   (Followers: 3)
Extractive Industries and Society     Hybrid Journal   (Followers: 2)
Gems & Gemology     Full-text available via subscription   (Followers: 2)
Geology of Ore Deposits     Hybrid Journal   (Followers: 5)
Geomaterials     Open Access   (Followers: 3)
Geotechnical and Geological Engineering     Hybrid Journal   (Followers: 9)
Ghana Mining Journal     Full-text available via subscription   (Followers: 3)
Gold Bulletin     Hybrid Journal   (Followers: 2)
Inside Mining     Full-text available via subscription  
International Journal of Coal Geology     Hybrid Journal   (Followers: 4)
International Journal of Coal Preparation and Utilization     Hybrid Journal   (Followers: 2)
International Journal of Coal Science & Technology     Open Access   (Followers: 1)
International Journal of Hospitality & Tourism Administration     Hybrid Journal   (Followers: 16)
International Journal of Minerals, Metallurgy, and Materials     Hybrid Journal   (Followers: 12)
International Journal of Mining and Geo-Engineering     Open Access   (Followers: 4)
International Journal of Mining and Mineral Engineering     Hybrid Journal   (Followers: 8)
International Journal of Mining Engineering and Mineral Processing     Open Access   (Followers: 6)
International Journal of Mining Science and Technology     Open Access   (Followers: 4)
International Journal of Mining, Reclamation and Environment     Hybrid Journal   (Followers: 6)
International Journal of Rock Mechanics and Mining Sciences     Hybrid Journal   (Followers: 9)
Journal of Analytical and Numerical Methods in Mining Engineering     Open Access  
Journal of Applied Geophysics     Hybrid Journal   (Followers: 18)
Journal of Central South University     Hybrid Journal   (Followers: 1)
Journal of China Coal Society     Open Access  
Journal of China University of Mining and Technology     Full-text available via subscription   (Followers: 1)
Journal of Convention & Event Tourism     Hybrid Journal   (Followers: 6)
Journal of Geology and Mining Research     Open Access   (Followers: 10)
Journal of Human Resources in Hospitality & Tourism     Hybrid Journal   (Followers: 9)
Journal of Materials Research and Technology     Open Access   (Followers: 2)
Journal of Metamorphic Geology     Hybrid Journal   (Followers: 17)
Journal of Mining Institute     Open Access  
Journal of Mining Science     Hybrid Journal   (Followers: 5)
Journal of Quality Assurance in Hospitality & Tourism     Hybrid Journal   (Followers: 6)
Journal of Sustainable Mining     Open Access   (Followers: 3)
Journal of the Southern African Institute of Mining and Metallurgy     Open Access   (Followers: 6)
Lithology and Mineral Resources     Hybrid Journal   (Followers: 4)
Lithos     Hybrid Journal   (Followers: 11)
Mine Water and the Environment     Hybrid Journal   (Followers: 6)
Mineral Economics     Hybrid Journal   (Followers: 2)
Mineral Processing and Extractive Metallurgy : Transactions of the Institutions of Mining and Metallurgy     Hybrid Journal   (Followers: 14)
Mineral Processing and Extractive Metallurgy Review     Hybrid Journal   (Followers: 5)
Mineralium Deposita     Hybrid Journal   (Followers: 4)
Mineralogia     Open Access   (Followers: 2)
Mineralogical Magazine     Hybrid Journal   (Followers: 1)
Mineralogy and Petrology     Hybrid Journal   (Followers: 5)
Minerals     Open Access   (Followers: 2)
Minerals & Energy - Raw Materials Report     Hybrid Journal   (Followers: 1)
Minerals Engineering     Hybrid Journal   (Followers: 14)
Mining Engineering     Full-text available via subscription   (Followers: 7)
Mining Journal     Full-text available via subscription   (Followers: 4)
Mining Report     Hybrid Journal   (Followers: 3)
Mining Technology : Transactions of the Institutions of Mining and Metallurgy     Hybrid Journal   (Followers: 4)
Mining, Metallurgy & Exploration     Hybrid Journal  
Natural Resources & Engineering     Hybrid Journal  
Natural Resources Research     Hybrid Journal   (Followers: 5)
Neues Jahrbuch für Mineralogie - Abhandlungen     Full-text available via subscription   (Followers: 1)
Physics and Chemistry of Minerals     Hybrid Journal   (Followers: 4)
Podzemni Radovi     Open Access  
Rangeland Journal     Hybrid Journal   (Followers: 4)
Réalités industrielles     Full-text available via subscription  
Rem : Revista Escola de Minas     Open Access  
Resources Policy     Hybrid Journal   (Followers: 4)
Reviews in Mineralogy and Geochemistry     Hybrid Journal   (Followers: 5)
Revista del Instituto de Investigación de la Facultad de Ingeniería Geológica, Minera, Metalurgica y Geográfica     Open Access  
Rock Mechanics and Rock Engineering     Hybrid Journal   (Followers: 9)
Rocks & Minerals     Hybrid Journal   (Followers: 5)
Rudarsko-geološko-naftni Zbornik     Open Access  
Transactions of Nonferrous Metals Society of China     Hybrid Journal   (Followers: 9)
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Lithos
Journal Prestige (SJR): 2.67
Citation Impact (citeScore): 4
Number of Followers: 11  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0024-4937 - ISSN (Online) 1872-6143
Published by Elsevier Homepage  [3304 journals]
  • Contrasting whole-rock and mineral compositions of ore-bearing (Tongchang)
           and ore-barren (Shilicun) granitic plutons in SW China: Implications for
           petrogenesis and ore genesis
    • Abstract: Publication date: 15 July 2019Source: Lithos, Volumes 336–337Author(s): Lei-Luo Xu, Xian-Wu Bi, Rui-Zhong Hu, Yong-Yong Tang, Xin-Song Wang, Ming-Liang Huang, Ying-Jing Wang, Rui Ma, Gong Liu A common perception is that oxidized magma is critical for the formation of a porphyry Cu ± Mo ± Au ore deposit. We have used an ore-bearing pluton (Tongchang) and an ore-barren pluton (Shilicun) in the western rim of the South China block to test this idea and to determine other important controls on ore genesis. Zircon UPb ages indicate that the Tongchang and Shilicun plutons were emplaced at 36.3 ± 0.2 Ma and 35.2 ± 0.4 Ma, respectively, broadly coinciding with strike-slip faulting in the region and continental collision that occurred ~300 km to the west. These two plutons are all characterized by significant light REE enrichments and pronounced negative NbTa anomalies, similar to the bulk crust. Apatite separates from these two plutons all have elevated initial 87Sr/86Sr (Tongchang, 0.70690 to 0.70796; Shilicun, 0.70703 to 0.70726) and negative εNd(t) (Tongchang, −6.2 to −7.3; Shilicun, −4.5 to −5.8). The mean εHf(t) and δ18O of zircon from these plutons are −1.4 and 6.8‰ for Tongchang, and −0.3 and 6.5‰ for Shilicun. The Sr-Nd-Hf isotope compositions are all within the ranges of the Neoproterozoic mafic arc lower crust in the region. Whole-rock U-Nb-Ta systematics indicate that the Tongchang and Shilicun plutons originated from an amphibole-bearing source and a garnet-bearing source, respectively, implying a shallower and more H2O-rich mafic source for the former than the latter. Quartz trace element data indicate that the Tongchang pluton was emplaced at a shallower depth than the Shilicun pluton. Zircon Ce4+/Ce3+ and whole-rock V/Sc ratios, and apatite SO3 and MnO contents indicate that the parental magmas of both plutons are as oxidized as those of some porphyry Cu deposits in northern Chile, but the parental magma of the Tongchang pluton is less oxidized than that of the Shilicun pluton. Apatite Cl-F-OH systematics and higher abundant hydrous silicate minerals such as amphibole and biotite in the Tongchang pluton than the Shilicun pluton indicate that the parental magma of the Tongchang pluton has higher Cl and H2O content than that of the Shilicun pluton. Our results show that oxidized magma is important but this alone cannot make a porphyry Cu ± Mo ± Au ore deposit. High contents of H2O-Cl in magma and shallow depth of emplacement are also important.
       
  • Chlorine and lithium behavior in metasedimentary rocks during prograde
           metamorphism: A comparative study of exhumed subduction complexes
           (Catalina Schist and Schistes Lustrés)
    • Abstract: Publication date: 15 July 2019Source: Lithos, Volumes 336–337Author(s): Jaime D. Barnes, Sarah C. Penniston-Dorland, Gray E. Bebout, William Hoover, Grace M. Beaudoin, Philippe Agard Lithium and chlorine concentrations and isotopic compositions of well-characterized metasedimentary suites from the Schistes Lustrés and Lago di Cignana (Western Alps) and the Catalina Schist (southern California, USA) were compared to determine Li and Cl behavior during prograde subduction-zone metamorphism. New data were obtained for Cl from both suites and for Li from the Western Alps. The Catalina Schist contains lawsonite-albite to amphibolite grade rocks recording peak temperatures of 200 to 750 °C and depths of 15 to 45 km, with the higher-grade units representing relatively warm subduction P-T paths. Bulk Cl concentrations decrease from ~100–500 μg/g to ~10–25 μg/g across metamorphic grades, largely due to Cl loss from chlorite and white mica, with most of this loss occurring at the lower grades. This loss mirrors the previously documented decreases in N, B, Cs, As, and Sb concentrations, with relatively little loss at higher metamorphic grade, and contrasts with the behavior of Li showing only modest loss and change in δ7Li values across all grades. Metapelitic rocks from the Western Alps representing a relatively “cool” geothermal gradient of ~8 °C/km, record peak temperatures of 350 to 550 °C and depths of up to 90 km. In this suite, both Cl and Li concentrations are uniform across grade, showing no obvious change in concentration. Lithium concentrations range to somewhat higher values compared to those previously measured in the Catalina Schist. Chlorine isotope compositions of the Schistes Lustrés overlap with those measured in the Catalina Schist, whereas Li isotope compositions of the Schistes Lustrés samples range to somewhat higher values than those from the Catalina Schist. Both suites show significant isotopic heterogeneity within single metamorphic grades and no systematic change in δ37Cl or δ7Li values with increasing grade. These heterogeneities are interpreted to be inherited from the protolith. Lithium isotope compositions correlate well with the chemical index of alteration (CIA), an observation also supporting minimal metamorphic alteration of the isotopic composition reflecting the protolith. These data demonstrate that, although some Cl is retained to great depths during subduction, most Cl is lost from metasedimentary rocks at shallow depths, similar behavior to that of B, Cs, As, and Sb. In contrast, Li loss is minimal across the full range of grade, more similar in behavior to Rb, Ba, and K.
       
  • Zircon perspectives on the age and origin of evolved S-type granites from
           the Cornubian Batholith, Southwest England
    • Abstract: Publication date: 15 July 2019Source: Lithos, Volumes 336–337Author(s): W.D. Smith, J.R. Darling, D.S. Bullen, S. Lasalle, I. Pereira, H. Moreira, C.J. Allen, S. Tapster Granite stocks across southwest England have played a significant role in the genesis of world-class polymetallic mineralisation. This study presents the first geochemical and geochronological dataset for the composite Crownhill stock, placing it into the newly emerging geochronological framework for the Cornubian Batholith. The Crownhill stock comprises kaolinised two-mica granite in the north and variably-grained biotite granite in the south that encloses pods of tourmaline granite. All granites are peraluminous (A/CNK > 1) and the biotite (BG) and tourmaline granites (TG) are related by the replacement of biotite by tourmaline and secondary muscovitization. Integrated LA-ICP-MS and CA-ID-TIMS geochronology indicate two-phase magmatism, where zircon cores yield 288.9 ± 5 Ma and 286.4 ± 5 Ma and rims yield 277.74 ± 0.33 Ma and 278.35 ± 0.35 Ma, for BG and TG respectively. The zircon cores crystallised during initial magmatism, that formed the two-mica and muscovite granites (e.g., Carnmenellis, Bodmin, and Hemerdon) exposed in the north of the Crownhill stock. The zircon rims crystallised from the second phase of magmatism that formed the biotite and tourmaline granites (e.g., Dartmoor and St. Austell). This indicates that zircon crystals were assimilated from older two-mica and muscovite granites and entrained in the second phase of magmatism. Trace element compositions of zircon grains suggest that the rims crystallised from a more evolved magma, where zircon grains hosted in tourmaline granites are broadly more evolved than those from biotite granites. This is likely a result of elevated volatile concentrations delaying zircon fractionation. Trace cassiterite has been observed within interstitial tourmaline in the tourmaline granites, where crystallisation was likely induced by the removal of boron through tourmaline fractionation, coupled with the addition of Sn sourced from the alteration of biotite. The assimilation and over-printing of older granites by second-stage magmatism suggests that the initial phase of magmatism could be more widespread than initially thought and that tourmalinisation may have been responsible for leaching and remobilising Sn from the biotite-rich granites.
       
  • Sr–Nd–Hf isotopic compositions of lamprophyres in western Shandong,
           China: Implications for the nature of the early cretaceous lithospheric
           mantle beneath the eastern North China Craton
    • Abstract: Publication date: 15 July 2019Source: Lithos, Volumes 336–337Author(s): Hao-Tian Yang, De-Bin Yang, Mao-Song Mu, An-Qi Wang, Yi-Kang Quan, Le-Ran Hao, Wen-Liang Xu, Dong-Hong Yang This paper presents new zircon UPb ages and Hf isotope data, and whole-rock geochemical and SrNd isotopic data, for lamprophyres in the western Shandong area of China. These data provide new insights into the nature of the lithospheric mantle beneath the eastern North China Craton (NCC) during the Early Cretaceous. The lamprophyres are divided into low-Ti (TiO2  370) suites, where the Xiaya and Jingziyu minettes are defined as low-Ti lamprophyres and the Jingziyu pyroxene lamprophyres are defined as high-Ti lamprophyres. The igneous zircons yield weighted-mean ages of 126, 132, and 130 Ma for the low- and high-Ti lamprophyres, respectively, indicating these units formed during the Early Cretaceous. The inherited zircons within the Xiaya and Jingziyu minettes define six (2517, 1852, 725, 375, 276, and 236 Ma) and two (2523 and 462 Ma) main age populations, respectively. In comparison, the inherited zircons from the Jingziyu pyroxene lamprophyres yield two main age populations (2523 and 1848 Ma). The low-Ti lamprophyres are enriched in the light rare earth elements (LREE) and large-ion lithophile elements (LILE), depleted in the heavy REE (HREE) and high-field-strength elements (HFSE), and have small negative Eu anomalies. In comparison, the high-Ti lamprophyres are enriched in the LREE but are slightly depleted in the HFSE. The low-Ti lamprophyres also have high 87Sr/86Sr(t) ratios (0.7121–0.7123), low εNd(t) values (−18.81 to −18.62), and contain igneous zircons with relatively high εHf(t) values (generally between −9.94 and −3.36). In comparison, the high-Ti lamprophyres have 87Sr/86Sr(t) ratios of 0.7066–0.7068, εNd(t) values from −5.01 to −4.64, and contain igneous zircons with εHf(t) values from −11.77 to −8.50. These data indicate the low-Ti lamprophyres formed from primary magmas generated by the partial melting of an enriched region of the lithospheric mantle that was previously strongly modified jointly by subduction breakoff of the downgoing Yangtze Craton basement material and delamination of the lower continental crust within the NCC. In comparison, the magmas that formed the high-Ti lamprophyres were generated by the partial melting of an enriched region of the lithospheric mantle that was weakly modified by interaction with the lower continental crust of the NCC. Both the low- and high-Ti lamprophyres formed in an extensional tectonic environment during lithospheric thinning, and the presence of these two suites of lamprophyres indicates that lithospheric thinning of the eastern NCC peaked during the Early Cretaceous.
       
  • An effect of reduced S-rich fluids on diamond formation under mantle-slab
           interaction
    • Abstract: Publication date: 15 July 2019Source: Lithos, Volumes 336–337Author(s): Yuliya V. Bataleva, Yuri N. Palyanov, Yuri M. Borzdov, Ivan D. Novoselov, Oleg A. Bayukov Experimental study, dedicated to understanding the effect of S-rich reduced fluids on the diamond-forming processes under subduction settings, was performed using a multi-anvil high-pressure split-sphere apparatus in Fe3C-(Mg,Ca)CO3-S and Fe0-(Mg,Ca)CO3-S systems at the pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–60 h. At the temperatures of 900 and 1000 °C in the carbide-carbonate-sulfur system, extraction of carbon from cohenite through the interaction with S-rich reduced fluid, as well as C0-producing redox reactions of carbonate with carbide were realized. As a result, graphite formation in assemblage with magnesiowüstite, cohenite and pyrrhotite (±aragonite) was established. At higher temperatures (≥1100 °C) formation of assemblage of Fe3+-magnesiowüstite and graphite was accompanied by generation of fO2-contrasting melts - metal-sulfide with dissolved carbon (Fe-S-C) and sulfide-oxide (Fe-S-O). In the temperature range of 1400–1600 °C spontaneous diamond nucleation was found to occur via redox interactions of carbide or iron with carbonate. It was established, that interactions of Fe-S-C and Fe-S-O melts as well as of Fe-S-C melt and magnesiowüstite, were С0-forming processes, accompanied by disproportionation of Fe. These resulted in the crystallization of Fe3+-magnesiowüstite+graphite assemblage and growth of diamond. We show that a participation of sulfur in subduction-related elemental carbon-forming processes results in sharp decrease of partial melting temperatures (~300 °C), reducting the reactivity of the Fe-S-C melt relatively to FeC melt with respect to graphite and diamond crystallization and decrease of diamond growth rate.
       
  • Mineralogical and geochemical constraints on the origin and evolution of
           albitites from Dmytrivka at the Oktiabrski complex, Southeast Ukraine
    • Abstract: Publication date: 1 June 2019Source: Lithos, Volumes 334–335Author(s): Magdalena Dumańska-Słowik, Tomasz Powolny, Magdalena Sikorska-Jaworowska, Wiesław Heflik, Vyacheslav Morgun, Ban To Xuan Albitites from Dmytrivka quarry form veins like bodies within fenitized alkali granites of the Oktiabrski complex. They are mainly composed of albite, and subordinately K-feldspar, zircon, aegirine, astrophyllite, pyrochlore and ilmenite. Albitites are characterized by high alkalies (Na2O + K2O) content coupled with low MgO, CaO, and SiO2 concentrations relative to host alkali granites. They show inversion of REE patterns (negative slopes for LREE and positive slopes for HREE), enrichment in HFSE (i.e. Zr, Nb, Ta), and strong Eu anomalies. The existence of rare composite of M-type and W-type REE tetrad effect in albitites indicates their complex genesis, i.e. formation during the coexistence of the melt with aqueous phase, later being superimposed by further alterations with hydrothermal solutions. The magmatic origin of albitites (evolved from highly differentiated A-type magma and emplaced at shallow depths) is documented by the presence of flow and snowball textures, zircon-aegirine glomerocrysts, no traces of replacement interfaces and reaction zones between K-feldspar and albite as well as no smooth, gradual changes in bulk-rock compositions between alkali granite, fenite vs albitite. On the contrary, the strong influence of pervasive, post-magmatic high-temperature (381–392 °C evidenced by CM geothermometer), and highly-oxidizing alkaline-bearing metasomatizing fluids on albitites is revealed by the occurrence of polygonal textures of albite laths, red CL luminescence of feldspars typical of fenitized rocks as well as crystallization of astrophyllite at the expense of arfvedsonite. Additionally, the presence of fluid-mineral interactions is evidenced by the development of secondary porosity and patchy zoning within zircon crystals coupled with the presence of blue (Dy3+-Tb3+-activated) and yellow (SiO4-Tb3+-activated) domains within them. All these textural, mineralogical and geochemical features observed in albitites from Dmytrivka suggest complex, magmatic-hydrothermal nature of the rocks.
       
  • Coupled laser Raman spectroscopy and carbon stable isotopes of graphite
           from the khondalite belt of Kerala, southern India
    • Abstract: Publication date: 1 June 2019Source: Lithos, Volumes 334–335Author(s): Cun Zhang, M. Santosh Graphite in high grade meta-supracrustal rocks provide an important proxy to characterize biogenic and abiogenic carbon sources. Here we investigate graphite in various associations within the granulite facies metapelites (khondalites) of Kerala in southern India with a view to characterize the textural varieties and their genesis through the application of laser Raman spectroscopy and carbon isotopes. We trace the increasing intensity of metamorphism from the Raman spectra of the different graphite types. The δ13C values of the graphite show two distinct origins; the relatively lighter values in the range of −17.5‰ to −20.7‰ represent a mixture of biogenic and magmatic carbon, whereas the heavier isotopes in the range of −11.7‰ to −13.8‰ are suggested to present graphite precipitation from CO2-rich fluids from sub-crustal magmatic sources. Our study provides insights on the spectral properties of graphite in relation to the intensity of metamorphism and also reveals both biogenic and abiogenic sources of carbon.Graphical abstractUnlabelled Image
       
  • Sources and petrogenesis of Late Triassic Zhiduo volcanics in the
           northeast Tibet: Implications for tectonic evolution of the western Jinsha
           Paleo-Tethys Ocean
    • Abstract: Publication date: Available online 6 April 2019Source: LithosAuthor(s): Yan Liu, Jun Tan, Junhao Wei, Shaoqing Zhao, Xiaoyang Liu, Jinrong Gan, Zhihua Wang The western Jinsha suture, representing a branch of the Paleo-Tethys, makes the junction between the Songpan-Ganzi Complex and the North Qiangtang Block (NQB). However, the Triassic tectonic evolution of the western Jinsha Paleo-Tethys Ocean is poorly constrained. This paper shows new LA–ICP–MS zircon U-Pb geochronology, major and trace elements, and Sr–Nd–Hf isotopic compositions of the Zhiduo dacitic volcanic rocks in the northern margin of the NQB. LA–ICP–MS zircon U-Pb dating displays that they erupted between 227 ± 2 and 228 ± 1 Ma. These rocks exhibit high silica, medium-K calc-alkalic signature, and low MgO, TiO2, P2O5, Cr, and Ni compositions. They are enriched in light rare earth elements and large-ion lithophile elements with moderate to strong negative Eu anomalies (Eu/Eu* = 0.24–0.56), and depleted in heavy rare earth elements and high field strength elements. They possess relatively low initial 87Sr/86Sr ratios (0.7055–0.7084), positive whole rock εNd(t) (+0.2 to +1.4), and magmatic zircon εHf(t) values (focus on 9.2 ± 2.7) with young Nd and Hf model ages (T2DM (Nd) = 885–983 Ma; T2DM (Hf) = 467–1035 Ma). These features are comparable to those of typical arc volcanic rocks and indicate that they were probably derived from partial melting of a juvenile crust source. The eruption of these volcanic rocks could be attributed to southward subduction of the western Jinsha Paleo-Tethys Ocean. In combination with previous studies, we propose that the subduction of the western Jinsha Paleo-Tethys Ocean initiated at the beginning of the Late Triassic (ca. 228 Ma) and closed at the end of the Late Triassic (ca. 208 Ma). In addition, there is a universal northeastward-younging trend of arc magmas in the northern margin of the NQB, which may indicate a model involving the initial shallow subduction and subsequent slab roll-back.
       
  • Polymineralic inclusions in kimberlite-hosted megacrysts: Implications for
           kimberlite melt evolution
    • Abstract: Publication date: Available online 5 April 2019Source: LithosAuthor(s): Adam Abersteiner, Vadim S. Kamenetsky, Karsten Goemann, Alexander V. Golovin, Igor S. Sharygin, D. Graham Pearson, Maya Kamenetsky, Marina A. Gornova Megacrysts are large (cm to>20 cm in size) mantle-derived crystals, which are commonly entrained by kimberlite magmas, comprising of olivine, orthopyroxene, clinopyroxene, phlogopite, garnet, ilmenite and zircon as common phases. Numerous studies have shown megacrysts to contain polymineralic inclusions, which have been interpreted to represent entrapped kimberlite melt. To constrain the origin of these inclusions in megacrysts and their relationship to kimberlite magmatism, we present a detailed petrographic and geochemical study of clinopyroxene and olivine megacrysts and their hosted inclusions from the Diavik, Jericho, Leslie (Slave Craton, Canada) and Udachnaya-East (Siberian Craton, Russia) kimberlites. The studied megacrysts are between 1 and 3 cm in size and representative of both the Cr-rich and Cr-poor suites. Megacrysts contain two types of inclusions:i) Large (
       
  • Calcic garnets as a geochronological and petrogenetic tool applicable to a
           wide variety of rocks
    • Abstract: Publication date: Available online 5 April 2019Source: LithosAuthor(s): Ekaterina B. Salnikova, Anton R. Chakhmouradian, Maria V. Stifeeva, Ekaterina P. Reguir, Alexander B. Kotov, Yulia D. Gritsenko, Anatoly V. Nikiforov This contribution presents UPb geochronological data for Ca-Fe-Ti garnets from compositionally diverse alkaline and carbonatitic intrusive rocks ranging from Neoarchean to Permian-Triassic (Cinder Lake and Eden Lake in Manitoba, Canada; Belaya Zima and Odikhincha in Siberia, Russia; Afrikanda in the Kola Peninsula, Russia) obtained using isotope-dilution thermal-ionization mass spectrometry (ID-TIMS) and their trace-element compositions measured by laser-ablation inductively-coupled-plasma mass spectrometry (LA-ICP-MS). The studied garnets yield UPb concordant or subconcordant ages obtained with a precision of
       
  • Origin and duration of late orogenic magmatism in the foreland of the
           Variscan belt (Lesponne — Chiroulet — Neouvielle area, french
           Pyrenees)
    • Abstract: Publication date: Available online 4 April 2019Source: LithosAuthor(s): Baptiste Lemirre, Bryan Cochelin, Stéphanie Duchene, Michel de Saint Blanquat, Marc Poujol During the late stage of the Variscan orogeny, the pyrenean segment underwent intense magmatism and regional high temperature – low pressure metamorphism. In the Lesponne – Chiroulet – Neouvielle area, a granodioritic pluton was emplaced in the upper crust while dioritic to granitic magmas were emplaced in metamorphic domes. Magmatism was contemporaneous with the regional crustal partial melting recorded in the core of the domes. The area is therefore a key target in the Pyrenees to discuss potential magmatic sources as well as the age and duration of the late Variscan magmatism. Geochemical data on representative magmatic rocks highlight two distinct sources of magma: a mantle source and a metasedimentary crustal source that produced respectively metaluminous and peraluminous magmas. Geochronological results show that magmatism took place over a period of about 10 My from ca. 303 to ca. 290 Ma. During this period, the middle to lower crust was composed of partially molten metasediments intruded by mantle and crustal magmas that crystallized in a final pulse at ca. 290 Ma. Late Variscan metamorphism and magmatism recorded in the Pyrenees have to be related to a significant and rapid heating from the underlying mantle rather than to crustal processes such as the maturation of a thickened continental crust. We propose that the initiation of metamorphism and bimodal magmatism at ca. 305 Ma in the Pyrenees is the expression of the delamination of the Gondwanan lithospheric mantle at a global scale in the Variscan belt.
       
  • Petrogenesis and metallogenic significance of multistage granites in
           Shimensi tungsten polymetallic deposit, Dahutang giant ore field, South
           China
    • Abstract: Publication date: Available online 4 April 2019Source: LithosAuthor(s): Xianke Fan, John Mavrogenes, Zengqian Hou, Zhiyu Zhang, Xianyuan Wu, Jialiang Dai The Shimensi tungsten polymetallic deposit, situated in the Dahutang ore field, South China, is one of the largest tungsten deposits in the world, with an estimated WO3 reserve of 0.74 million tons. Coarse-grained porphyritic biotite granite (CPBG), fine-grained porphyritic biotite granite (FPBG), fine-grained biotite granite (FBG) and biotite granite porphyry (BGP) are all ore-related, but their diagenetic relationships and contributions to W-Cu-Mo mineralization are still in dispute. LA-ICP-MS monazite UPb dating of the CPBG, FPBG, FBG and BGP yield emplacement ages of 147.9 ± 1.1 Ma, 146.4 ± 1.1 Ma, 138.6 ± 0.98 Ma and 142.8 ± 1.7 Ma, respectively. Whole-rock geochemical results indicate that the four granites should be classified as S-type granites, but BGP has distinct features transitional between S- and I-type granites. They were possibly generated by partial melting of upper crustal pelites and basic volcanic rocks with different proportion from the Neoproterozoic Shuangqiaoshan Group in the source. Proportional variation in the magmatic source (clay and basic basalts) induces the change of geochemical compositions of the Shimensi granites. Geochemical characteristics suggest that they were derived from two magma chambers (the CPBG, FPBG and FBG vs. the BGP) and experienced different evolutionary processes and experienced different degree of magmatic differentiation during magmatic evolution. Chondrite-normalized REE patterns for the four granites display low total REE contents, variable and strongly enriched LREE relative to HREE and medium-strong negative Eu anomalies. They are enriched in Rb, Th, U, Ta and depleted in Ba, Nb, Sr, P, Ti. Biotites are iron-rich and aluminum-poor, and can be classified as ferro-biotite (CPBG, FPBG and FBG) and siderophyllite (BGP). The partial melting of tungsten-rich metasediments of the Shuangqiaoshan Group and high degree of fractional crystallization led to enrichment in tungsten in the magma suites. Oxygen fugacities of the CPBG and FPBG declined from early (most above the NNO buffers) to late stages of fractional crystallization (between the NNO and QFM buffers) because of the higher degree of magmatic differentiation in the late stages. In the early stages of fractionation, tungsten accumulated in the residual melts rather than partitioning into accessory minerals. In the late stages, lower oxygen fugacities and high fluorine contents promoted the removal of tungsten from the residual magma into reduced hydrothermal fluids. On the other hand, the FBG and BGP remained constant (above the NNO buffers) over the entire process of crystallization owning to the stable degree of magmatic differentiation, promoting retention of tungsten in the melt and resulting in low grade tungsten mineralization. Tungsten mineralization in the Shimensi deposit is greatly controlled by the redox states of the associated magma. The two porphyritic granites (the CPBG and FPBG) are most likely the main contributors of tungsten, while the FBG and BGP are mainly responsible for copper and molybdenum in the Shimensi deposit. Prolonged multiphase magmatism and prolonged W-Cu-Mo mineralization play important roles in the formation of Shimensi large tungsten polymetallic deposit.
       
  • Protracted evolution of the Marañón Valley Au Belt magmatic complex in
           the Peruvian Andes using zircon oxygen isotopes, Lu-Hf and U-Pb analyses
    • Abstract: Publication date: Available online 4 April 2019Source: LithosAuthor(s): F. Voute, S.G. Hagemann, A.I.S. Kemp, N. Thebaud, N.J. Evans, C. Villanes The Marañón Valley, located in the Eastern Cordillera of the northern Peruvian Andes, represents a 160-km-long section of the continental margin that was mainly active during the Paleozoic. A combination of whole rock geochemistry, and U-Pb, O and Hf isotope microanalysis of zircon on selected igneous rocks, reveals the timing and magmatic source variations along and across-strike of the Paleozoic proto-Andean margin. The igneous rocks exhibit a typical arc-related continental margin signature, with strong enrichment in LILE (e.g., Cs, Rb and Th), depletion of HFSE (e.g., Nb) and a negative Ti anomaly. The overlapping Hf-O isotopic compositions, together with similar inherited zircon ages, are consistent with the Lavasen Volcanics, the Esperanza Subvolcanic Complex and the Pataz Batholith sharing the same crustal source components, in about the same proportion. A genetic relationship is further supported by the strong depletion in Sr, Nb, Ta, Ti and Eu in the subvolcanic and volcanic rocks from the Esperanza Subvolcanic Complex and Lavasen Volcanics compared to the intrusive rocks from the Pataz Batholith, which is consistent with evolution of the erupted magmas by fractional crystallization. The new zircon U-Pb (LA-ICP-MS) age determinations, in combination with previously published geochronological data, suggest that the Pataz Batholith, the Esperanza Subvolcanic Complex and the Lavasen Volcanics were emplaced contemporaneously between ca. 342 Ma and 332 Ma. The new Mississippian U-Pb (zircon U-Pb LA-ICP-MS) age determination for the Lavador Pluton (336–332 Ma) and the Callangate-Enaben Pluton (341–337 Ma) suggest that magmatism was coeval with the emplacement of the Pataz Batholith. The Lavador Pluton is aligned with the main N-NW trend of the Pataz Batholith, and shares a similar range of Hf-O isotopic values (i.e., εHf (t) values from −5.3 to −1.3 and δ18O values from 6.4 to 7.1‰), and is therefore believed to represent a northern extension of the Pataz Batholith. The isotopic geochemistry and lithogeochemistry record in the Marañón Valley illustrates the regional scale tectonic switches that occurred during arc formation, from syn-collisional and compression in the Pataz-Parcoy district between ca. 342 Ma and 332 Ma, to post-collisional and extensional in the Montañitas district between ca. 332 Ma and 319 Ma. The delineation of the timing and location of tectonic regime switches in the Marañón Valley may provide a basis for future mineral exploration.
       
  • Genesis of porphyry Mo deposits linked to gradually dehydrating
           subcontinental lithospheric mantle metasomatised by previous subduction in
           northeastern China
    • Abstract: Publication date: Available online 3 April 2019Source: LithosAuthor(s): Yifei Liu, Leon Bagas, Sihong Jiang Many Mesozoic Mo-bearing granites, present along the northern margin of the Precambrian North China Block (NCB) and Phanerozoic Xing'an-Mongolian Belt (XMB) within the Central Asian Orogen (CAO) have hydrated sources. These granites are temporally and spatially related to biotite-rich mafic, alkali syenitic plutons, are highly evolved, have an arc-like trace element geochemical pattern, and were emplaced between ca. 245–129 Ma bracketed by A2- and A1-type granites. This conflicts temporally with the current model involving the westward subduction of the Pacific oceanic plate. We use Sm/Nd and Th/Yb ratios of Mesozoic nepheline-bearing pyroxene-biotite syenites (biotite-syenites), mantle-peridotite xenoliths from Palaeozoic diamondiferous kimberlites, and Mesozoic to Cenozoic alkali basalts to define a hydrous melt-extraction trend. The results indicate a Palaeozoic mantle-peridotite source that is more metasomatised than the lower continental crust and the source of the Mesozoic (
       
  • Magmatic evidence for middle-late Permian tectonic evolution on the
           northern margin of the North China Craton
    • Abstract: Publication date: Available online 3 April 2019Source: LithosAuthor(s): Hai Zhou, Guochun Zhao, Jianhua Li, Yigui Han, Jinlong Yao, Bo Wang Late Paleozoic tectonic evolution of the northern margin of the North China Craton (NCC) remains controversial, especially for the mechanism and time during the late-stage oceanic consumption of the Paleo-Asian Ocean (PAO). We address this issue through geochronological, geochemical and Lu-Hf isotopic studies on felsic-mafic volcanic rock suites and granite plutons from the Damao area in the western segment of the NCC's northern margin. Zircon U-Pb dating reveals that the volcanic suites, with eruptive unconformities in-between, erupted primarily at ~275–260 Ma while the granites emplaced later at ~255 Ma. The volcanic rocks contain rhyolites and dacites having an A-type affinity with high FeOt/MgO, (K2O + Na2O)/CaO and Ga/Al ratios, enriched Th, U, Zr, Hf and depleted Ba, Sr and Eu contents. The basaltic rocks display low MgO and TiO2 contents, negative Nb, Ta, Ti anomalies, as well as negative ƐHf(t) values. We suggest that the ~275–260 Ma volcanic suites were generated in a post-collisional setting, with the dominant rhyolites and dacites derived from the mixing between mantle and crustal magmas and subordinate basalts from the partial melting of enriched sub-continental lithospheric mantle. The sudden and intensive occurrence of these ~275–260 Ma felsic-dominant bimodal post-collisional magmatism and their sudden increase of zircon ƐHf(t) values imply a significant mantle contribution to their sources, possibly due to the slab breakoff of the subducting PAO plate. The ~255 Ma granites also have an A-type affinity and a large spread of negative ƐHf(t) values (−3.6 to −30.5), indicating a prominent involvement of continental crust materials that was likely related to crustal reworking after the slab breakoff. Overall, these ~275–255 Ma magmatic suites document a significant post-collisional crustal extension at the western segment of the northern NCC. In this region the southward subduction of the PAO likely ceased prior to ~275 Ma on the basis of a regional comparison.
       
  • Different melting conditions and petrogenesis of peraluminous granites in
           western Qinling, China, and tectonic implications
    • Abstract: Publication date: Available online 3 April 2019Source: LithosAuthor(s): Jingzhao Dou, Wolfgang Siebel, Jianfeng He, Fukun Chen The Qinling orogen records the prolonged amalgamation history between the North China Block (NCB) and the South China Block (SCB) accompanied by major granitoid intrusions during the Triassic. However, the petrogenesis of these granitoids, especially that of the peraluminous granites, remains a matter of debate. Detailed study of these peraluminous granites, which are the products of crustal melting, will give insights into the melting process and petrogenesis of peraluminous magmas and will further constrain the regional geological evolution. In this study, Xiahe (XH) tourmaline-bearing two-mica granite and Baijiazhuang (BJZ) two-mica granite were selected for systematic analysis of their mineralogy, petrology, zircon U-Pb geochronology, and geochemistry. The zircon U-Pb dating showed that the XH and BJZ granites were emplaced at approximately 242 Ma and approximately 214 Ma, respectively. The presence of muscovite and tourmaline, high peraluminosity at>1.1, low oxygen fugacity (ƒO2) conditions below the fayalite–magnetite–quartz (FMQ) buffer, and low zircon saturation temperatures indicate sedimentary protolith (S-type) granitic affinity. The low CaO/Na2O ratios
       
  • Constraints on the formation of the Baogutu reduced porphyry copper
           deposit (West Junggar, NW China): Assessing the role of mafic magmas in
           mineralization
    • Abstract: Publication date: Available online 3 April 2019Source: LithosAuthor(s): Chu Wu, Tao Hong, Xing-Wang Xu, Ming-Jian Cao, Hao Li, Qiang Ke, Hang Li, Lian-Hui Dong The Baogutu porphyry copper deposit is a typically reduced porphyry copper deposit (RPCD), characterized by reduced, calc-alkaline, felsic shallow intrusions. A newly discovered gabbro, which contains 1182–1260 ppm Cu, provides an ideal window to reveal the genesis and formation of the Baogutu RPCD. A combined study of the petrological, geochronological, geochemical and isotopic characteristics of the Cu-bearing gabbro and granitoids in the Baogutu RPCD has been completed. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) UPb dating of zircons from a gabbro, diorite and porphyritic diorite are 318.2 ± 0.8 Ma (MSWD = 0.01, n = 16), 315.8 ± 1.0 Ma (MSWD = 1.50, n = 16), and 314.9 ± 0.6 Ma (MSWD = 0.12, n = 20), respectively. The geochemical and isotopic characteristics of the gabbro, diorite, and porphyritic diorite at Baogutu RPCD are all metaluminous, calc-alkaline series rocks with depletion in Nb, Ta, and Ti and enrichment in light rare earth elements (LREE) and large ion lithophile elements consistent with an arc-related setting. The relatively high Nd and Hf isotopes (εNd(t) = +6.9 to +7.5, εHf(t) = +8.8 to +14.4) and wide variations of major and trace elements suggest that the gabbro and diorite in the Baogutu RPCD were all derived from a mixture of melts of metasomatized mantle wedge, the hydrous slab, and old crustally derived materials. The high Mg andesites (HMA)/sanukite features (high Mg#, Cr and Ni content) of the gabbro suggest it was derived mainly from a metasomatized mantle-hydrous slab-derived melt source with only slightly contamination by the old crustal materials, whereas adakitic features of the diorite (high Al2O3 and Sr contents and Sr/Y ratios) suggest a greater role the melting of residual subducted oceanic crust with juvenile mantle materials. The porphyritic diorite, which inherited the geochemical characteristics of diorite, was probably derived from a similar parental magma but the low εNd(t) of +1.4, old T2DM (Nd) age of 961 Ma and enrichment in Zr and Hf suggest a greater degree of crustal contamination. The high content of Cu and high oxidation state of the gabbro is consisted with it having formed early from an unusually Cu-rich parental magma. This magma would have provided abundant metal and sulfides which would have been mobilized and reconcentrated by later ore bearing fluids linked to the intermediate to acid porphyry intrusions in the Baogutu RPCD.Graphical abstractUnlabelled Image
       
  • Magmatic differentiation at La Poruña scoria cone, Central Andes,
           northern Chile: Evidence for assimilation during turbulent ascent
           processes, and genetic links with mafic eruptions at adjacent San Pedro
           volcano
    • Abstract: Publication date: Available online 31 March 2019Source: LithosAuthor(s): Osvaldo González-Maurel, Benigno Godoy, Petrus le Roux, Inés Rodríguez, Carolina Marin, Andrew Menzies, Daniel Bertin, Diego Morata, Marina Vargas La Poruña (21°53′S; 68°30′W) is a 140 m high scoria cone composed of pyroclastic material and an extensive basaltic-andesite to andesite lava flow that is up to 8 km in length. Automated mineralogical analysis describes a suite of porphyritic mafic samples, comprising olivine- and pyroxene-bearing rocks. Well-defined major element compositional trends, as well as trace and rare earth element characteristics (e.g. Sr/Y 
       
  • Adakite-like parental melt generation by partial fusion of juvenile lower
           crust, Sakarya Zone, NE Turkey: A far-field response to break-off of the
           southern Neotethyan oceanic lithosphere
    • Abstract: Publication date: Available online 28 March 2019Source: LithosAuthor(s): Orhan Karsli, Abdurrahman Dokuz, Raif Kandemir, Faruk Aydin, Axel K. Schmitt, E. Yalçin Ersoy, Cihangir Alyildiz The timing of major tectonic events and the driving mechanisms for magma generation during Late Cenozoic convergence and collision between Arabia and Eurasia still remain unknown. The Sakarya Zone (SZ) in northeastern Turkey is a critical member of this collisional assemblage. In the easternmost part of the SZ, we have recognized a Late Miocene volcanic suite termed the Çağirankaya volcanics which displays characteristic post-collisional geochemical features. Here, we report a new data set of zircon UPb ages, whole-rock major and trace element, as well as SrNd isotope analyses for dacite and andesite samples from the Çağirankaya volcanics. Zircon UPb ages for a selected dacitic lava sample average 5.16 ± 0.11 Ma (mean spare of weighted deviates, MSWD = 0.45, n = 35), confirming a late Miocene age of this volcanic episode. The high-K calc-alkaline andesites and dacites exhibit an adakite-like geochemical signature, and are characterized by high Sr (424 to 552 ppm), Sr/Y ratios (31–43), and low Mg# (42 to 46) values, along with low Y (12–14 ppm) and heavy rare earth element (HREE) concentrations, that resemble those in adakites formed by partial melting of hot oceanic slab during subduction. Isotopic compositions are near bulk Earth (87Sr/86Sr(t) = 0.70482 to 0.70489, εNd(t) = +1.08 to +1.33), which rules out a solely asthenospheric origin. Elevated Nb/Ta (14 to 17) and K2O/Na2O (0.6–1.0) imply a juvenile mafic lower crustal source composed of ~20% garnet-bearing amphibolite. Geochemical modeling suggests that adakite-like parental melts were generated in the absence of subduction and without large-scale delamination of lower continental crust. Instead, our findings suggest that Late Miocene adakite-like volcanic rocks in the SZ formed in a post-collisional intra-continental setting, which experienced far-field extension after the subducted slab of the southern Neotethyan branch became detached in the collision zone. Asthenospheric upwelling and underplating of basaltic magma provided the heat for partial melting of lower crustal amphibolite, forming minor amounts of adakite-like melts in the SZ.
       
  • Temporal, Spatial and Geochemical Evolution of Late Cenozoic
           Post-Subduction Magmatism in Central and Eastern Anatolia, Turkey
    • Abstract: Publication date: Available online 23 March 2019Source: LithosAuthor(s): Fabien Rabayrol, Craig J.R. Hart, Derek J. Thorkelson Indentation of the Arabian platform into the eastern domain of the Anatolide-Tauride Block (ATB) led to sub-horizontal rupture and break-off of the Arabian segment of the subducting southern Neotethyan oceanic slab beneath ATB in the late Cenozoic. Although this rupture has been well-defined by seismic tomography and numerical modeling, its relationship with concomitant magmatism in central and eastern Anatolia has not been firmly demonstrated. To address this issue, we compiled, integrated and interpreted an extensive database of previously-published age and geochemical data. Our analysis shows that late Cenozoic magmatism in both eastern and central Anatolia was nearly continuous over a distance of ~1000 km, and is herein named the Eastern Anatolian Magmatic Belt. Magmatism initiated at 23 Ma in response to rupturing of the north-dipping subducting oceanic slab below eastern Anatolia and upwelling of hot asthenospheric mantle. The onset of initial rupture-related magmatism is ~12 Ma older than previously proposed. The magmatic belt migrated westward from eastern Anatolia (23-15 Ma) to central Anatolia (12 Ma-present) and is a proxy for the westward progression of the slab rupture and related asthenospheric infiltration. Magmatism generated from the shallow melting of the previously-metasomatized Anatolian subcontinental lithospheric mantle and asthenosphere by decompression due to the impingement of the Arabian sub-slab asthenospheric mantle. In eastern Anatolia, slab-rupture magmatism was followed by a second phase of magmatism that formed in response to destabilization and convective removal of the thick Anatolian lithospheric root (13 Ma-present). This new magmatic model emphasizes that the geochemical signature of post-subduction magmatism, as recorded by primitive basalts that constantly evolved through time and space. Magmatic sources recorded the shifting of mantle melt source domains that were controlled by slab segmentation and induced mantle flow.
       
  • Tracing magma mixing and crystal–melt segregation in the genesis of
           syenite with mafic enclaves: Evidence from in situ zircon Hf–O and
           apatite Sr–Nd isotopes
    • Abstract: Publication date: 1 June 2019Source: Lithos, Volumes 334–335Author(s): Jin-Feng Sun, Ji-Heng Zhang, Jin-Hui Yang, Yue-Heng Yang, Shi Chen Alkaline rocks contain essential information on post-collisional/intraplate extensional magmatic processes within the continental lithosphere. The Erhulai syenitic pluton in the Liaodong Peninsula, North China Craton, consists of quartz syenite, mafic enclaves, and porphyritic K-feldspar granite. Field observations and zircon U–Pb dating reveal that the quartz syenite and the hosted mafic enclaves were coeval (with identical emplacement ages of 129–126 Ma), and slightly older than the porphyritic K-feldspar granite (ca. 123 Ma). The mafic enclaves have relatively low SiO2 and high MgO contents (up to 3.0%), and lack Ba or Eu anomalies. Whole-rock analyses of the mafic enclaves and accessory minerals in the enclaves show relatively low initial 87Sr/86Sr ratios (0.7056 to 0.7078) and variable εNd(t) (−11.2 to −2.0) and εHf(t) (−15.8 to −5.5) values. Large proportion of zircons from the mafic enclaves possess mantle-like δ18O values. These geochemical features suggest an enriched mantle source, with the addition of crustal material. The quartz syenites have relatively high SiO2 and low CaO and MgO contents, as well as significantly positive K, Ba, and Eu anomalies. All the quartz syenites show variable (87Sr/86Sr)i ratios (0.7073 to 0.7081) and εNd(t) values (−10.4 to −8.6) for the whole-rocks and apatites, εHf(t) values of −12.4 to −3.6 for the zircons, and zircon δ18O values of +4.4‰ to +7.0‰ (mainly greater than +5.3‰). All these features can be isotopically produced by the partial melting of ancient crustal material, with the involvement of mantle-derived magma. Crystal fractionation process, such as K-feldspar crystallization and accumulation, played an important role in the formation of the quartz syenite. The porphyritic K-feldspar granites possess relatively evolved geochemical compositions with high silica contents (SiO2 > 69 wt%) and remarkable negative Ba and Eu anomalies, which are chemically complementary to the quartz syenite. A crystal mush model was employed to establish the genetic link between the porphyritic K-feldspar granite and the quartz syenite, with the granite representing the interstitial melt extracted from the crystal mush and the quartz syenite representing the residual accumulation of crystals. The variable isotopic compositions of the quartz syenite and the porphyritic granite were mainly the result of extensive interaction of isotopes between mantle- and crust-derived magmas during magma mixing.In situ analyses of the Sr, Nd, Hf, and O isotopes of accessory minerals, coupled with field observations and whole-rock geochemical data for the Erhulai syenitic pluton, indicate a complex multi-stage magmatic process involving magma mixing, crystal–melt segregation, and wall-rock assimilation. Our study also shows that in situ isotopic analyses of accessory minerals provide unique information on, and are powerful geochemical tracers of, mantle–crust interactions and magmatic processes.
       
  • Dunites in the mantle section of the Oman ophiolite – The boninite
           connection
    • Abstract: Publication date: 1 June 2019Source: Lithos, Volumes 334–335Author(s): Hugh Rollinson Dunites in the mantle section of the Oman ophiolite contain olivines which show both a wide range of compositions (Fo86.2 to Fo94) and very high magnesium numbers. These data are combined with experimental liquidus olivine-melt data to show that the range of olivine compositions requires that the dunites formed from a range of melt compositions and that some of these melts were very magnesian, with MgO concentrations up to MgO = 18–20 wt%. These observations are consistent with the finding of MgO-rich melt inclusions from chromitites in the mantle section of the Oman ophiolite (Rollinson et al., Lithos, 2018). It is proposed that the high Mg-olivines formed in equilibrium with high-Ca boninites, found in the upper section of the pillow lavas sequence of the ophiolite. A model is developed whereby high MgO boninites fractionated olivine through a process of melt-rock reaction/fractionation with the enclosing harzburgite to create a range of dunitic compositions and evolved boninitic lavas. Field evidence shows that the emplacement of boninites was late in the evolution of the Oman ophiolite indicating that the mantle dunites of boninitic origin formed late in the history of the ophiolite. High-Ca boninites form through the shallow, hydrous melting of the mantle wedge in a subduction setting and the presence of boninitic dunites and lavas further supports the view that the Oman ophiolite formed in a fore-arc setting through subduction-induced spreading.
       
  • Early Paleozoic magmatism along the northern margin of East Gondwana
    • Abstract: Publication date: 1 June 2019Source: Lithos, Volumes 334–335Author(s): Li-E Gao, Lingsen Zeng, Guyue Hu, Yaying Wang, Qian Wang, Chunli Guo, Kejun Hou Zircon UPb analyses of granitic gneisses from the gneiss domes (Xiaru, Mabja, Lhagoi Kangri, and Kangmar)within the Tethyan Himalaya and from the High Himalaya (Gyirong, Yadong, and Namche Barwa)yield that their protolith ages range from 509 Ma to 429 Ma. Similar to the Himalayan Cenozoic leucogranites, the Paleozoic granites are characterized by (1) high SiO2 (69.9–77.0 wt%), Al2O3 (12.4–16.1 wt%), K2O + Na2O (5.8–10.3 wt%) with K2O/Na2O > 1.0 and A/CNK > 1.0; (2) large variations in Rb (166–851 ppm), Sr (20–172 ppm), Ba (27–1474 ppm) and Rb/Sr ratios (1.0–38.3); (3) low degrees of LREE over HREE fractionation with (La/Yb)N 
       
  • Early Cretaceous subduction of Paleo-Pacific Ocean in the coastal region
           of SE China: Petrological and geochemical constraints from the mafic
           intrusions
    • Abstract: Publication date: 1 June 2019Source: Lithos, Volumes 334–335Author(s): Bo Zhang, Feng Guo, Xiaobing Zhang, Yangming Wu, Guoqing Wang, Liang Zhao The Mesozoic tectono-magmatism in SE China has widely been considered to relate to subduction of the Paleo-Pacific Ocean. However, there lacks robust petrologic and geochemical evidence from subduction-related mafic igneous rocks to reconstruct the architecture of the subduction zone. This paper presents a comprehensive geochemical dataset (petrography, mineral chemistry, zircon U-Pb age, in-situ Sr and Pb isotope compositions of plagioclase and whole-rock major, trace element and Sr-Nd-Pb-Hf isotope data) of three early Cretaceous (Pingtan, Daiqianshan and Quanzhou) mafic intrusions from the coastal region in SE China, with aims to understand their petrogenetic link with subduction of the Paleo-Pacific Ocean. The mafic rocks comprise predominantly calcic hornblende and Ca-rich plagioclase and show varying degrees of crystal accumulation. Petrological observations and mass balance calculation indicate their parental magmas are hydrous and calc-alkaline with typical arc-type trace element features. These rocks are also characterized by “crust-like” isotopic signatures, i.e., moderately radiogenic Sr, unradiogenic Nd and highly radiogenic Pb compositions. The narrow variations of in-situ plagioclase Sr and Pb isotope ratios and the nearly identical isotope compositions between the plagioclase and bulk rock in each intrusion indicate a minor role of crustal assimilation during magmatic evolution. Instead, such “crust-like” isotopic signatures were largely resulted from source enrichment through an input of subducted sediment. Further element-isotopic modeling results suggest that the parental magmas were likely produced by melting of a depleted mantle source metasomatized via the subducted sediment-derived melt. Generation of the early Cretaceous mafic intrusions can thus be explained by subduction of a relatively hot oceanic slab, during which melt derived from the subducted sediment acted as a predominant agent to enrich the mantle wedge. Our results provide powerful petrological and geochemical constraints on the early Cretaceous subduction of the Paleo-Pacific Ocean beneath the SE China and suggest that addition of subducted sediment-derived melt may be an important mechanism for mantle enrichment in relatively hot subduction zones.
       
  • Tectono-metamorphic evolution of subduction channel serpentinites from
           South-Central Chile
    • Abstract: Publication date: Available online 21 March 2019Source: LithosAuthor(s): Gaëlle Plissart, José M. González-Jiménez, Leonardo N.F. Garrido, Vanessa Colás, Julien Berger, Christophe Monnier, Hervé Diot, José Alberto Padrón-Navarta This work provides the first comprehensive petrological and multi-scale structural investigation of a suite of ultramafic bodies and enclosing metasediments from the Late Paleozoic accretionary prism of South-Central Chile. The targeted outcrops are located in the La Cabaña area and are characterized by the presence of three main types of ultramafic rocks: (1) partially serpentinized massive peridotites, (2) antigoritic schistose serpentinites, and (3) antigoritic mylonitic serpentinites. Partially serpentinized massive peridotites and schistose serpentinites recorded a common first hydration event with the formation of Fe2+ porous rim in chromites (at ~500 °C), followed by static partial transformation of olivine to lizardite (below ~300 °C) and formation of rims of Fe3+-rich chromite and magnetite around chromites. A second event of serpentinization linked to fluid passage through zones with focused deformation resulted in the partial transformation of partially lizarditized massive peridotites into antigoritic schistose serpentinites (at ~320–400 °C). This second event took place within the shallower portion of the serpentinitic subduction channel, near the base of the accretionary prism and was characterized by the formation of tubular folds made up of lenses of olivine-lizardite massive rocks embedded in a matrix of schistose serpentinites. Antigoritic mylonitic serpentinites encountered in the matrix of schistose serpentinites may locally contain metamorphic olivine (i.e., olivine-bearing mylonitic serpentinites), registering higher temperature conditions at medium pressures (~600 °C, 11 kbar) that prevailed during the initial immature stage of development of the subduction system. Moreover, some mylonitic serpentinites containing Ti-clinohumite, Ti-chondrodite and metamorphic olivine still record higher pressure conditions (> 15 kbar, i.e.,> 50 km depth for ~500 °C), which are related with a deformational event taking place when the subduction system had already cooled. These medium- and high-P mylonitic serpentinites preserved kinematic indicators of burial, whereas their exhumation along the subduction channel towards the shallower schistose serpentinites near the base of the accretionary prism could take place through discrete shear zones possibly aided by large sheath folds. Once incorporated in the accretionary prism (c. 285 Ma ago), the serpentinites shared metamorphism and deformation with the enclosing metasediments. Subvertical shortening related to uplift processes within the accretionary system took place in the stability field of antigorite (> 300 °C) and, later, a subhorizontal E-W shortening prevailed in more superficial conditions.
       
  • Thermodynamic modelling of phosphate minerals and its implications for the
           development of P-T-t histories: A case study in garnet - monazite bearing
           metapelites
    • Abstract: Publication date: Available online 19 March 2019Source: LithosAuthor(s): Sudip Shrestha, Kyle P. Larson, Erik Duesterhoeft, Mathieu Soret, John M. Cottle Accessory phosphate minerals, such as monazite and xenotime, are commonly used as geochronometers to provide timing constraints on tectonometamorphic events recorded by the host rocks within which they occur. However, the formation and recrystallization of accessory minerals, and their interaction with major mineral phases, are still poorly understood. As a consequence, linking ages obtained from accessory minerals to the metamorphic pressure-temperature (P-T) paths obtained primarily from major mineral phases, such as garnet, remains challenging. While there have been studies that have advanced our understanding of the behaviour of various accessory minerals through thermodynamic modelling, limited examples are available to test their reliability in natural metamorphic rocks.This study incorporates phosphate minerals into one of the most commonly used thermodynamic data sets for phase equilibria modelling. This refined methodology is tested by modelling the detailed P-T-time (t) paths for rocks from two different regions of the Himalaya, one subsolidus and one that experienced suprasolidus conditions. The results obtained from our integrated models yield direct information on the behaviour of monazite and xenotime growth/breakdown along the calculated P-T paths. This allows us to tie different age populations obtained from the accessory minerals directly to the P-T paths derived from major mineral phases and facilitates a refined understanding of the P-T-t histories of those rock specimens.
       
  • Calcium amphibole exsolution lamellae in chromite from the Semail
           ophiolite: Evidence for a high-pressure origin
    • Abstract: Publication date: Available online 19 March 2019Source: LithosAuthor(s): Tao Chen, Zhenmin Jin, Junfeng Zhang, Lu Wang We report here for the first time aluminous Ca-amphibole exsolution lamellae in an anhydrous chromite host of podiform chromitite from the Nakhl massif of the Semail Ophiolite. Transmission electron microscopy observations show that the Ca-amphibole lamellae have a crystallographic topotaxy and d-spacing relationship with the host chromite, i.e., [103]am//[11–8]chr, (020)am//(2−20)chr and d060am ≈ d220chr {note to typesetting, the minus signs are overbars on top of the 8 and 2, hereafter}, that indicate an exsolution origin. The presence of Ca-amphibole exsolution implies the incorporation of Si4+ and Ca2+ cations and hydroxyl in the host precursor chromite. The reconstructed precursor chromite had SiO2 concentrations of 0.33–0.58 wt%, suggesting upwelling from a minimum pressure of 8 GPa (depth of ~250 km). Hydroxyl groups occupy octahedral vacancies, which can be introduced in high-pressure chromite by substituting 4 Cr3+ by 3 Si4+ and a vacancy. During upwelling, vacancies decrease when Si4+ cations exsolve stepwise from chromite. It leads to a coupled decrease of OH occupied vacancies and exsolution of Ca-amphibole lamellae at pressures below 3 GPa. Our results provide new evidence for a deep origin of the chromitite-bearing mantle section of the Semail ophiolite.
       
  • Early subduction dynamics recorded by the metamorphic sole of the Mt.
           Albert ophiolitic complex (Gaspé, Quebec)
    • Abstract: Publication date: Available online 18 March 2019Source: LithosAuthor(s): Benoît Dubacq, Mathieu Soret, Ella Jewison, Philippe Agard The metamorphic sole of the Mt. Albert ophiolitic complex (Gaspé peninsula, Quebec, Canada) is a sliver of Ordovician oceanic crust accreted to the base of an incomplete ophiolitic sequence, along a suture zone throughout the north-eastern Appalachians linked to the Taconian orogeny. A detailed mineralogical study of the rocks in the metamorphic section of the sole is provided in this publication: these rocks record valuable information in terms of petrological processes and conditions of accretion, with limited retrogression. The petrology of the metamorphic sole shows that it originates from ocean floor and that it is the equivalent of the Shick-Shock volcanics group, metamorphosed to granulite / higher amphibolite facies. Presence of alumino-silicate bearing metapelites allows constraining pressure conditions in a more robust way than in the case of the famous Semail ophiolite (Oman). Thermobarometric estimates for peak metamorphic conditions for the metamorphic sole of the Mont Albert ophiolitic complex indicate temperatures above 800 °C close to the contact with the overlying peridotite, decreasing to ~650 °C within
       
  • Origin and tectonic implications of early cretaceous high- and low-Mg
           series rocks and mafic enclaves in the Bomi–Chayu Fold Belt, SE Tibet
    • Abstract: Publication date: Available online 16 March 2019Source: LithosAuthor(s): Xiaohan Dong, Touping Peng, Weiming Fan, Guochun Zhao, Jingyi Zhang, Bingbing Liu, Jianfeng Gao, Bingxia Peng, Xirong Liang, Wen Zeng, Linli Chen Early Cretaceous granitoids are widespread on the Tibetan Plateau and record the tectonic evolution of several Tethyan oceans. We describe Early Cretaceous high-Mg (Mg# > 50) and low-Mg (Mg# 
       
  • Onset of the North-South Gravity Lineament, NE China: Constraints of late
           Jurassic bimodal volcanic rocks
    • Abstract: Publication date: Available online 16 March 2019Source: LithosAuthor(s): Jinlong Dong, Shuguang Song, Li Su, Yanguang Li, Liming Yang, Chao Wang, Bei Xu The North-South Gravity Lineament (NSGL) is an important geophysical boundary within NE China. Gravity anomaly, heat flow, crustal and lithospheric thickness, terrain and altitude all change dramatically across the NSGL. However, the timing of onset of the NSGL remains enigmatic, and the Mesozoic lithospheric thinning mechanism to the east of the NSGL is still unclear in NE China. Here we study a Late Jurassic bimodal volcanic suite located on the NSGL including N-MORB-like basalts, which constrains the initial formation of the NSGL. The bimodal volcanic rocks consist mainly of basalts and basaltic andesites with subordinate rhyolites. Our results show that the bimodal volcanic rocks are products of crust-asthenosphere interaction. Calculations indicate that lithospheric thicknesses in NE China have significantly changed from ~90–100 km in the west to 49–62 km in the east since the Late Mesozoic. The variation of lithospheric thicknesses on both sides of the NSGL could be ascribed to lithospheric delamination. Zircons from the bimodal volcanic rocks yield Late Jurassic ages of 147 Ma, nearly synchronous with the onset of the Songliao Basin and marking the start of extensional tectonics in NE China. Combined with previous studies, we confirm that the delamination induced by Paleo-Pacific subduction gave rise to the formation of the NSGL, which initiated at the Late Jurassic in NE China.Graphical abstractUnlabelled Image
       
  • Volcanic record of continental thinning in Baffin Bay margins: Insights
           from Svartenhuk Halvø Peninsula basalts, West Greenland
    • Abstract: Publication date: Available online 16 March 2019Source: LithosAuthor(s): Arnaud Agranier, René C. Maury, Laurent Geoffroy, François Chauvet, Bernard Le Gall, Adriano R. Viana We report major, trace elements and Pb, Hf, Nd and Sr isotopes in 61–54 Ma old basalts from Svartenhuk Halvø Peninsula (Greenland). This area corresponds to the northernmost exposure of the West Greenland volcanic province, of which the emplacement marks the continental thinning and breakup process leading to the opening of Baffin Bay during the Eocene. Its wedge structure displays typical characteristics of inner seaward-dipping-reflectors (SDR) with an exposed volcanic sequence thicker than 7 km. Our results cover the entire volcanic sequence starting with an earliest V1 unit reflecting rather low degree partial melts (transitional basalts), which are geochemically imprinted by continental crust contamination. This unit is followed by much thicker and mainly tholeiitic V2 and V3 basaltic lava piles, and ends with a rather thin V4 unit, consisting of alkali basalts and associated trachytes. Pressures and temperatures of melt extraction were estimated based on major element concentrations and rare earth elements patterns. Our results suggest that melts were extracted from the garnet-spinel transition zone at greater depths for the initial V1 and the final V4 lavas (alkali to transitional basaltic compositions) than for the main V2 and V3 mostly tholeiitic lava piles (at 2 ± 0.5 GPa and 1350 ± 100 °C). Isotope signatures suggest that mantle sources of the melts were controlled by the mixing of ambient upper mantle and Icelandic plume-type materials. The proportion of ambient upper mantle involved in the lava source appears to increase together with melting rates and the upward propagation of melting zone during V3 emplacement, suggesting that melting in this area progessed as follows: 1. Initiation of partial melting (low degrees) of deep-seated Icelandic plume-type material (V1 and V2); 2. Upward propagation of the melting area within the shallower mixed upper mantle (V3); 3. Progressive decrease of “ambient upper mantle” involvement, deepening of magma extraction and decrease of partial melting associated with the emplacement of V4 lavas. We show that these changes are consistent with the tectonic stages of continental thinning that preceded the Eocene breakup in Baffin Bay.
       
  • Late Triassic ridge subduction of Paleotethys: Insights from high-Mg
           granitoids in the Songpan-Ganzi area of northern Tibet
    • Abstract: Publication date: Available online 15 March 2019Source: LithosAuthor(s): Yin Liu, Wenjiao Xiao, Brian F. Windley, Rongshe Li, Wenhua Ji, Kefa Zhou, Miao Sang, Yichao Chen, Xiaoliang Jia, Liang Li, Haidi Zhang The time of final closure of the Paleotethys Ocean is still hotly debated in particular regarding the Jinsha Ocean in northern Tibet. This study reports new geochronologic and geochemical data of six granodiorites-diorites, which intrude the Mid-Late Triassic Songpan-Ganzi complex (SGC). LA-ICP-MS zircon U-Pb analyses of three quartz diorites (214.9 ± 2.2, 211.0 ± 1.3, 205.8 ± 1.4 Ma) and three granodiorites (210.8 ± 2.7, 206.7 ± 3.3, 205.9 ± 3.5 Ma) gave a Late Triassic age range (214.9–205.8 Ma). These granodiorite-diorite rocks have relatively high MgO (up to 9.1%) and Mg# (up to 70.2), Al2O3, Cr, Ni, but low TiO2, and high magnesium andesite/diorite (HMA) chemical signatures. Also, low Sr and Y content, slight-moderate negative Eu anomaly, together with captured coeval Late Triassic detrital zircons (as young as 208 Ma) and dioritic enclaves, demonstrate that the HMA magmas were probably derived from a reaction between subducted marine sedimentary siliceous melts and peridotites from a mantle wedge.From the eastward-younging (from northern Qiangtang to southern SGC), and the linear distribution of Late Triassic HMA rocks in combination with the contrasting distribution of volcanic rocks in the northern Qiangtang terrane, we suggest that a slab window opened in the downgoing oceanic crust with two diverse slab angles during oblique subduction. Accordingly, the final closure of the Paleotethys Ocean was later than 205 Ma, and most likely in the end of the Late Triassic to Early Jurassic.
       
  • Petrogenesis of the 1.85 Ga Sonakhan mafic dyke swarm, Bastar
           Craton, India
    • Abstract: Publication date: Available online 15 March 2019Source: LithosAuthor(s): J.G. Shellnutt, K.R. Hari, A.C.-Y. Liao, S.W. Denyszyn, N. Vishwakarma, S.D. Deshmukh The NNW trending tholeiitic Sonakhan mafic dyke swarm of the Northern Bastar Craton has variable compositions from basalt to basaltic andesite (SiO2 = 46.3 wt% to 55.3 wt%; Mg# = 37 to 70). A single basaltic dyke yielded a weighted-mean 207Pb/206Pb baddeleyite age of 1851.1 ± 2.6 Ma. The Sr and Nd isotopes (87Sr/86Sri = 0.70396 to 0.70855; εNd(t) = −5.7 to +2.0) are variable but can be explained by assimilation-fractional crystallization. Trace element modeling suggests the dykes were likely derived by partial melting of a spinel-bearing mantle source. The Sonakhan dykes are 30 million years younger than the 1.88 Ga Bastar-Cuddapah dykes (Bastanar-Hampi swarm) of the southern and central Bastar Craton indicating they represent a distinct period of magmatism. However, much like the 1.88 Ga dykes, the Sonakhan dykes appear to be correlative with dykes from the Yilgarn Craton (Yalgoo dyke = 1854 ± 5 Ma) of Western Australia. The temporal and compositional similarity of the Sonakhan dykes with the Yalgoo dyke is evidence that they are petrologically related and may represent different branches of the same dyke swarm. The existence of two distinct Paleoproterozoic dyke swarms in the Bastar Craton that each have a correlative unit in the Yilgarn Craton is supportive of a link between India and Australia before 1.9 Ga. Moreover, it suggests that the break-up of India and Western Australia was protracted and lasted for at least 30 million years.Graphical abstractUnlabelled Image
       
  • Seismicity and mineral destabilizations in the subducting mantle up to
           6 GPa, 200 km depth.
    • Abstract: Publication date: Available online 15 March 2019Source: LithosAuthor(s): Thomas P. Ferrand In the subducting oceanic lithosphere, a significant part of the seismicity is triggered in the mantle, especially along the upper and lower Wadati-Benioff planes. Several studies have investigated the potential involvement of dehydration reactions in the triggering mechanism of mantle earthquakes. Recent experimental results reveal that, under subduction conditions, mechanical instabilities nucleate in strong stable mineral aggregates during the destabilization of minor amounts of antigorite, i.e. the high-temperature serpentine, through a stress transfer, without any fluid overpressure. Here I confront these laboratory results to seismological observations. On one hand, most of the natural hydrous magnesium silicates seem to be known, with experimentally-deduced stability limits up to 7 GPa, at least, available as relatively accurate estimates. On the other hand, recent achievements in thermal structure of subduction zones combined with precise hypocentre relocation give access to pressure and temperature conditions at earthquakes hypocentres. A series of P-T diagrams summarizes the stability limit of minerals that may be part of natural peridotites or serpentinites with variable compositions at pressures from 0.5 to 6 GPa and temperatures from 200 to 950 °C, and compares it with seismicity. Both hydrous and anhydrous phases are considered. A myriad of minor metamorphic reactions could participate in a transformation-driven stress transfer, even if the stability limits of serpentine minerals seem to correlate with most of the observed seismicity.Graphical abstractUnlabelled Image
       
  • Deciphering the Mesoarchean to Neoarchean history of crustal growth and
           recycling in the Caochang region of the Eastern Hebei Province, North
           China Craton using combined zircon U–Pb and Lu-Hf isotope analysis
    • Abstract: Publication date: Available online 15 March 2019Source: LithosAuthor(s): Liou Peng, Jinghui Guo In Archean cratons, the end of the Archean aeon (3.0–2.5 Ga) is marked by a considerable diversification in both the nature and petrogenesis of granitoid rocks. We reported the studies of a series of Mesoarchean-Neoarchean diorite and tonalite–trondhjemite–granodiorite (TTG) and granitic gneisses in the Caochang area, Eastern Hebei region of the North China Craton. Combined zircon U-Pb and Lu-Hf isotope analyses and CL imaging analysis reveal three major magmatic events (3.2-3.0 Ga, 2.9-2.8 Ga, ~2.5 Ga) and one major metamorphic overprint (~2.5 Ga). The close temporal relationship for different zircon domains reveals that the late-Neoarchean crustal materials were recycled or reworked immediately after their formation, immediately followed by ~2.5 Ga recrystallized metamorphism.The voluminous mantle-derived mafic rocks indicate that the 2.5-2.6 Ga is an important period of crustal addition in the Eastern Hebei region. The peak of Hf model age and the widespread Mesoarchean or Paleoarchean crustal materials in Eastern Hebei may point to another important period of crustal addition before the Neoarchean.
       
  • Distributed deformation along the subduction plate interface: The role of
           tectonic mélanges
    • Abstract: Publication date: Available online 7 March 2019Source: LithosAuthor(s): Hugues Raimbourg, Vincent Famin, Giulia Palazzin, Asuka Yamaguchi, Romain Augier, Yujin Kitamura, Arito Sakaguchi Recent geophysical monitoring of subduction zones has unraveled a complete spectrum of plate coupling behaviors, from coupled portions rupturing during earthquakes to decoupled portions slipping aseismically. However, the deformation mechanisms and the exhumed rock corresponding to these contrasted behaviors are not yet identified. Tectonic mélange zones are thought to play a major role in the deformation of the plate interface as they represent remnants of the subducted plate scraped off by the overriding plate. In this work we examine several tectonic mélange zones (Hyuga, Okitsu, Mugi) from the Shimanto Belt, an accretionary prism in southwest Japan connecting to the active Nankai subduction zone. These tectonic mélange zones have a block-in-matrix structure, with lenses of sandstones and basalts within a metapelitic matrix, and their deformation is distributed over zones of hundreds of meters in thickness. In addition, the examples of mélange considered here are bounded by sharp faults, some of them bearing pseudotachylyte layers, so that distributed deformation within the mélange and localized deformation on its boundary are juxtaposed. Distributed deformation involves the development of a foliation, as well as of a pervasive network of macroscopic and microscopic shear zones. Along with slip on this network, strain proceeds by fracturing and precipitation of quartz, in long veins parallel to the foliation or in smaller cracks perpendicular to stretching and forming in the neck of competent lenses of sandstones or former quartz veins. The analysis of shear band kinematics shows in all three examples a dominant, top-to-the-trench sense of shear, consistent with deformation along the plate boundary during subduction. Moreover, most shear zones, when foliation is restored back to syn-subduction position, are extensional structures. Finally, the geometry and kinematics of the mélange-bounding faults, as well as radiometric constraints, show that in most cases the faults (=localized structures) were formed during a later stage than mélange internal deformation. These findings bear several consequences on the structure and dynamics of the subduction plate boundary at seismogenic depths. First, there is no support for a model of plate boundary fault zone composed simultaneously of localized slip zones and domains of more distributed deformation. Second, rather than proposed models of underplating, where all deformation is localized into the thrusts bounding the tectonic sheets, we suggest that underplating was to a large extent accommodated by distributed deformation within the mélange sheets. This underplating model accounts for (i) the large amount of strain within the mélange, (ii) the absence of contractional structures during underplating, (iii) thinning of the mélange required by the network of extensional shear bands and stretched boudins. Third, mélanges appear as likely candidates for portions of the plate interface deforming by aseismic slip. The seismic vs. aseismic character of the plate interface might depend on the ability of sediments on top of the subducting plate to undergo distributed strain, which in turn depends on the efficiency of pressure solution to operate.
       
  • Volcanic shutdown of the Panama Canal area following breakup of the
           Farallon plate
    • Abstract: Publication date: Available online 2 March 2019Source: LithosAuthor(s): David M. Buchs, Henry Coombs, Derek Irving, Jian Wang, Anthony Koppers, Roberto Miranda, Romie Coronado, Arkin Tapia, Samuel Pitchford The Panama Canal area is a significant part of the Panama Isthmus, where prominent volcanic fronts of eastern Central America are interrupted by a topographic low of unclear tectonic and magmatic origin. Determining why no prominent volcanic system occurs along the Canal is essential to understand the formation of the Isthmus in an area believed to have hosted one of the last inter-American straits between the Atlantic and Pacific Oceans. We provide here new geochronological and geochemical constraints from volcanic units of the Panama Canal that belong to the recently-identified Central Panama Volcanic Field. Whole rock and mineralogical geochemical compositions document a secular magmatic change from ca. 25 to 16 Ma, with a progressive change from calc-alkaline to tholeiitic and possibly alkaline/transitional geochemical affinities. The age of the youngest volcanic unit of the Canal is similar to that of the youngest documented arc volcanism in eastern Panama ca. 18 Ma. We propose based on these observations and consistency with regional geological constraints that the Canal volcanism represents a unique example of magmatic cessation along a volcanic arc. This cessation occurred shortly after the breakup of the Farallon plate ca. 23 Ma, suggesting a causal link between volcanic shutdown and transition from orthogonal to oblique subduction along Central and Eastern Panama. We suggest that this tectonic event suppressed hydrous melting in the subduction zone and led to regional magmatic waning in Central and Eastern Panama ca. 16 Ma. The pre-existence of a transisthmian fault system in Central Panama probably facilitated extraction of the last supra-subduction melts during volcanic shutdown. Our results suggest that the end of volcanism, combined with transisthmian faulting, impeded the development of high topography in the Panama Canal area. Without this unusual tectono-magmatic evolution, the occurrence of a late inter-oceanic strait in Central Panama and the construction of the Panama Canal would not have been possible.
       
  • Boron isotope variations of Franciscan serpentinites, northern California
    • Abstract: Publication date: Available online 1 March 2019Source: LithosAuthor(s): Chinatsu Yamada, Tatsuki Tsujimori, Qing Chang, Jun-Ichi Kimura Serpentinites and serpentinized mantle peridotites with various tectonic origins occur in the Franciscan Complex of the Northern California Cordillera, USA. Boron isotopes of serpentinites differentiate with fluid-mediated processes, and have great potential for key geologic markers in convergent margins. To understand boron isotope behavior within the Franciscan subduction zone system, we apply a newly developed ablation volume correction (AVC) method for in-situ isotope/elemental analyses using a laser-ablation multiple collector inductively-coupled-plasma mass spectrometry (LA-MC-ICPMS) on seventeen different Franciscan serpentinites (sensu lato) collected from eight separate areas. Boron abundances and isotope compositions of the studied serpentinites show large variations B = 1.6–239 μg·g−1, δ11B = −12.0 to +24.4‰, which allow to discriminate the serpentinites into two groups: (1) a lighter δ11B of −12.0 to +8.8‰ with a lesser B  ~2 GPa. Preferential partitioning of 11B into fluids released from the subducted slab at shallow leaves lighter δ11B in the slab resulting in lighter δ11B in the deep slab fluids. In contrast, the blueschist-absent serpentinites with heavier δ11B may have formed at a shallow environment where shallow slab or hydrothermal fluids with heavier 11B were present. Lesser versus greater amounts of B in the deep versus shallow serpentinites are also consistent with the dehydration profile of B from a slab. Our results show the versatility of boron isotopes and composition for identification of the origin of serpentinite in Pacific-type orogenic belts.
       
  • A-type volcanic–intrusive complex in the Huanggangshan Basin:
           Implications for early cretaceous crust–mantle interaction in the
           Gan-Hang Belt and adjacent areas, South China
    • Abstract: Publication date: Available online 29 January 2019Source: LithosAuthor(s): Huang Hui, Wang Kai-Xing, Pan Jia-Yong, Liu Xiao-Dong, Sun Yue The origin and petrogenesis of Early Cretaceous A-type volcanic–intrusive complexes in the Gan-Hang Belt and adjacent areas of South China remain controversial. An A-type volcanic–intrusive complex in the Huanggangshan Basin of North Wuyi Mountain comprises syenite porphyry, granite porphyry, granite, and tuffaceous volcanic and pyroclastic rocks. These rocks were subjected to geochronological, geochemical, and isotopic analyses in order to investigate their age and petrogenesis, and crust–mantle interactions in South China. Field observations reveal that this A-type volcanic–intrusive complex contains abundant mafic microgranular enclaves. Zircon UPb dating of the various rock types yielded ages between 136 and 128 Ma. Geochemically, the rocks have A-type affinities, including high large-ion lithophile and high-field-strength element contents, Ga/Al ratios, and zircon saturation temperatures. (87Sr/86Sr)i values vary from 0.702704 to 0.711298, and εNd(t) = −10.63 to −7.28 and εHf(t) = −13.26 to −7.70. Three stages of magmatism are proposed to explain the petrogenesis of the A-type volcanic–intrusive complex in the Huanggangshan Basin: (1) syenitic magmas formed by mingling of crustally derived silicic and mantle-derived mafic magmas; (2) fractional crystallization of anorthitic plagioclase + biotite + ilmenite from the syenitic magmas generated A-type igneous rocks with SiO2  71 wt%. Combined with previous studies, we suggest that the Early Cretaceous A-type igneous rocks in the Gan-Hang Belt and adjacent areas might have been generated by crust–mantle-derived magma mixing, and the crust–mantle interaction was more intense from southwest to northeast. This increased crust–mantle interaction may have been a response to the Early Cretaceous back-arc extensional environment, possibly as a result of the rollback of the Paleo-Pacific Plate.
       
 
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