Subjects -> MINES AND MINING INDUSTRY (Total: 82 journals)
 Showing 1 - 42 of 42 Journals sorted alphabetically Applied Earth Science : Transactions of the Institutions of Mining and Metallurgy       (Followers: 4) Archives of Mining Sciences       (Followers: 1) BHM Berg- und Hüttenmännische Monatshefte       (Followers: 1) Canadian Mineralogist       (Followers: 5) CIM Journal Clay Minerals       (Followers: 8) Contributions to Mineralogy and Petrology       (Followers: 11) Environmental Geochemistry and Health       (Followers: 2) European Journal of Mineralogy       (Followers: 12) Extractive Industries and Society       (Followers: 2) Gems & Gemology       (Followers: 1) Geology of Ore Deposits       (Followers: 3) Geomaterials       (Followers: 2) Geotechnical and Geological Engineering       (Followers: 8) Ghana Mining Journal       (Followers: 3) Gold Bulletin International Journal of Coal Geology       (Followers: 2) International Journal of Coal Preparation and Utilization       (Followers: 1) International Journal of Coal Science & Technology       (Followers: 1) International Journal of Hospitality & Tourism Administration       (Followers: 14) International Journal of Minerals, Metallurgy, and Materials       (Followers: 8) International Journal of Mining and Geo-Engineering International Journal of Mining and Mineral Engineering       (Followers: 5) International Journal of Mining Engineering and Mineral Processing       (Followers: 5) International Journal of Mining Science and Technology       (Followers: 4) International Journal of Mining, Reclamation and Environment       (Followers: 4) International Journal of Rock Mechanics and Mining Sciences       (Followers: 6) Journal of Analytical and Numerical Methods in Mining Engineering Journal of Applied Geophysics       (Followers: 15) Journal of Central South University       (Followers: 1) Journal of China Coal Society Journal of Convention & Event Tourism       (Followers: 4) Journal of Geology and Mining Research       (Followers: 11) Journal of Human Resources in Hospitality & Tourism       (Followers: 8) Journal of Materials Research and Technology       (Followers: 2) Journal of Metamorphic Geology       (Followers: 15) Journal of Mining Institute Journal of Mining Science       (Followers: 2) Journal of Quality Assurance in Hospitality & Tourism       (Followers: 5) Journal of Sustainable Mining       (Followers: 2) Journal of the Southern African Institute of Mining and Metallurgy       (Followers: 5) Lithology and Mineral Resources       (Followers: 3) Lithos       (Followers: 9) Mine Water and the Environment       (Followers: 4) Mineral Economics Mineral Processing and Extractive Metallurgy : Transactions of the Institutions of Mining and Metallurgy       (Followers: 11) Mineral Processing and Extractive Metallurgy Review       (Followers: 4) Mineralium Deposita       (Followers: 4) Mineralogia       (Followers: 2) Mineralogical Magazine       (Followers: 1) Mineralogy and Petrology       (Followers: 2) Minerals Minerals & Energy - Raw Materials Report Minerals Engineering       (Followers: 9) Mining Engineering       (Followers: 5) Mining Journal       (Followers: 3) Mining Report       (Followers: 2) Mining Technology : Transactions of the Institutions of Mining and Metallurgy       (Followers: 2) Mining, Metallurgy & Exploration Natural Resources & Engineering Natural Resources Research       (Followers: 8) Neues Jahrbuch für Mineralogie - Abhandlungen       (Followers: 1) Physics and Chemistry of Minerals       (Followers: 4) Podzemni Radovi Rangeland Journal       (Followers: 1) Réalités industrielles Resources Policy       (Followers: 4) Reviews in Mineralogy and Geochemistry       (Followers: 4) Revista del Instituto de Investigación de la Facultad de Ingeniería Geológica, Minera, Metalurgica y Geográfica Rock Mechanics and Rock Engineering       (Followers: 6) Rocks & Minerals       (Followers: 2) Rudarsko-geološko-naftni Zbornik Stainless Steel World       (Followers: 17) Transactions of Nonferrous Metals Society of China       (Followers: 9)
Similar Journals
 Contributions to Mineralogy and PetrologyJournal Prestige (SJR): 2.747 Citation Impact (citeScore): 3Number of Followers: 11      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1432-0967 - ISSN (Online) 0010-7999 Published by Springer-Verlag  [2469 journals]
• Exhumation of a migmatitic unit through self-enhanced magmatic weakening
enabled by tectonic contact metamorphism (Gruf complex, Central European
Alps)

Abstract: Abstract The Central Alpine lower crustal migmatitic Gruf complex was exhumed in contact to the greenschist-grade Chiavenna ophiolite and gneissic Tambo nappe leading to a lateral gradient of ~ 70 °C/km within the ophiolite. The 14 km long, E-W striking subvertical contact now bridges metamorphic conditions of ~ 730 °C, 6.6 kbar in the migmatitic gneisses and ~ 500 °C, 4.2 kbar in the serpentinites and Tambo schists 2–4 km north of the contact. An obvious fault, mylonite or highly sheared rock that could accommodate the ~ 8.5 km vertical displacement is not present. Instead, more than half of the movement was accommodated in a 0.2–1.2 km thick orthogneiss of the Gruf complex that was heterogeneously molten. Discrete bands with high melt fractions (45–65%) now contain variably stretched enclaves of the adjacent MOR-derived amphibolite. In turn, the adjacent amphibolites exhibit tonalitic in-situ leucosomes and dikes i.e., were partially molten. The H2O necessary for fluid-assisted melting of the orthogneiss and amphibolites was likely derived from the tectonic contact metamorphism of the Chiavenna serpentinites, at the contact now in enstatite + olivine-grade. U–Pb dating of zircons shows that partial melting and diking occurred at 29.0–31.5 Ma, concomitant with the calc-alkaline Bergell batholith that intruded the Gruf. The major driving forces of exhumation were hence the strong regional North–South shortening in the Alpine collisional belt and the buoyancy provided by the Bergell magma. The fluids available through tectonic contact metamorphism led to self-enhanced magmatic weakening and concentration of movement in an orthogneiss, where melt-rich bands provided a low friction environment. Continuous heating of the originally greenschist Chiavenna ophiolite and Tambo gneisses + schists by the migmatitic Gruf complex during differential uplift explains the skewed temperature profile, with intensive contact heating in the ophiolite but little cooling in the portion of the now-exposed Gruf complex.
PubDate: 2022-05-17

• The formation of three-grain junctions during solidification. Part I:
observations

Abstract: Abstract The thermodynamic equilibrium dihedral angle at grain junctions in crystalline rocks is set by the grain boundary interfacial surface energies, but the long times required to attain equilibrium mean that the observed dihedral angles in igneous rocks are generally set by the kinetics of crystallisation. We distinguish three types of augite–plagioclase–plagioclase dihedral angle in mafic igneous rocks. In the first, augite grows in the pores of a pre-existing plagioclase framework accompanied by little to no inwards-growth of the plagioclase pore walls. In the second, the plagioclase pore walls grow inwards simultaneously with the augite, and the dihedral angle is generally larger than the original angle at which the two plagioclase grains impinged except when the impingement angle itself is large. The first type is seen in rapidly crystallised rocks, whereas the second is observed in slowly cooled rocks. The third type is highly asymmetric and resembles (and so we call) an eagle’s beak: it is only seen in slowly cooled rocks. It is common in gabbroic cumulates, and is also present in strongly orthocumulate troctolites. Using the mode of interstitial phases to calculate the amount of interstitial liquid present in a series of mafic cumulates from the Rum and Skaergaard layered intrusions, we show that the asymmetry of three-grain junctions in troctolites increases as the rocks progress from adcumulate to orthocumulate (i.e. as the olivine–plagioclase crystal mush becomes more liquid-rich), with eagles’ beaks becoming the dominant three-grain junction geometry for troctolitic mushes containing ∼ 12 vol.% interstitial material (corresponding to ∼ 30 vol.% liquid in the mush). The geometry of three-grain junctions in mafic rocks is thus a function not only of cooling rate, but also of the progression along the liquid line of descent during fractionation. The first two types of junction are formed in relatively primitive liquids, during which the crystal mushes on the margins of the solidifying magma body are formed predominantly of plagioclase and olivine, whereas the eagle’s beak geometry occurs once augite forms an important component of the crystal framework in the accumulating mush, either because it is a framework-forming primocryst phase or because it grows from highly abundant interstitial liquid.
PubDate: 2022-05-11

• Garnet EoS: a critical review and synthesis

Abstract: Abstract All available volume and elasticity data for the garnet end-members grossular, pyrope, almandine and spessartine have been re-evaluated for both internal consistency and for consistency with experimentally measured heat capacities. The consistent data were then used to determine the parameters of third-order Birch–Murnaghan EoS to describe the isothermal compression at 298 K and a Mie–Grüneisen–Debye thermal-pressure EoS to describe the PVT behaviour. In a full Mie–Grüneisen–Debye EoS, the variation of the thermal Grüneisen parameter with volume is defined as $$\gamma = {\gamma }_{0}{\left(\frac{V}{{V}_{0}}\right)}^{q}$$ . For grossular and pyrope garnets, there is sufficient data to refine q which has a value of q = 0.8(2) for both garnets. For other garnets, the data do not constrain the value of q and we therefore refined a q-compromise version of the Mie–Grüneisen–Debye EoS in which both γ/V and the Debye temperature θ D are held constant at all P and T, leading to $$\left( {{\raise0.7ex\hbox{\({\partial C_{{\text{V}}} }$$} \!\mathord{\left/ {\vphantom {{\partial C_{{\text{V}}} } {\partial P}}}\right.\kern-0em} \!\lower0.7ex\hbox{$${\partial P}$$}}} \right)_{{\text{T}}} = 0\) , parallel isochors and constant isothermal bulk modulus along an isochor. Final refined parameters for the q-compromise Mie–Grüneisen–Debye EoS are: Pyrope Almandine Spessartine Grossular V0 (cm3/mol)a 113.13 115.25 117.92 125.35 K0T (GPa) 169.3 (3) 174.6 (4) 177.57 (6) 167.0 (2) $$K^{\prime}_{{0{\text{T}}}}$$ 4.55 (5) 5.41 (13) 4.6 (3) 5.07 (8) θ D0
PubDate: 2022-05-06

• Links between continental subduction and generation of Cenozoic
potassic–ultrapotassic rocks revealed by olivine oxygen isotopes: A case
study from NW Tibet

Abstract: Abstract Tibetan Cenozoic syn-collisional potassic–ultrapotassic igneous rocks provide unique insights into the processes and origins of metasomatism in the upper mantle, as well as continental subduction and plateau uplift. Crustal recycling in the magma source of the Tibetan potassic–ultrapotassic rocks has been well-documented. However, the nature of the metasomatic agents and the timing of mantle metasomatism are still disputed. Oxygen isotopes are a powerful tracer for identifying any recycled crustal material in the mantle due to the significant fractionation caused by surface water–rock interaction. Here we present an integrated in-situ study of oxygen isotopes and the major/trace elements of olivine in the Cenozoic potassic–ultrapotassic rocks and mantle xenoliths from the western Kunlun area of the northwestern Tibet. Olivines from mantle xenoliths have oxygen isotope compositions that range from elevated δ18O values (5.83 ± 0.78–5.97 ± 0.40‰) to values (5.09 ± 0.56–5.10 ± 0.46‰) that are indistinguishable from typical mantle olivine values of 5.18 ± 0.28‰ (Mattey et al., Earth Planet Sci Lett 128:231–241, 1994). Elevated olivine δ18O values reflect mantle metasomatic processes by an 18O-rich agent, although a few olivine rims show higher δ18O values caused by reactions with host lavas. In contrast, olivine oxygen isotope compositions of potassic–ultrapotassic rocks are higher than typical “mantle” values and those of the mantle xenoliths (6.51 ± 0.74–7.52 ± 0.24‰). There is no sign of crustal contamination, and fractional crystallization did not change the isotopic compositions of the studied potassic–ultrapotassic igneous rocks, thus their high-δ18O signature reflects the nature of the primary melts and their source region. Enrichments in olivine 18O and clinopyroxene Sr isotopic compositions, as well as the enriched trace element compositions of clinopyroxene and orthopyroxene in the mantle xenoliths, indicate that they have been highly metasomatized by silicate materials with a minor carbonate component from recycled Indian continental crustal component, and the enriched lithospheric mantle is the magma source of potassic–ultrapotassic rocks. High olivine δ18O values are a common feature of Tibetan Cenozoic potassic–ultrapotassic rocks, consistent with the mantle metasomatic agents that were derived directly from recycled continental crust material via Indian continental subduction. Our study reinforces the profound link between continental subduction, mantle processes and generation of Tibetan Cenozoic potassic–ultrapotassic rocks.
PubDate: 2022-05-03

• An empirical H2O solubility model for peralkaline rhyolitic melts

Abstract: Abstract The H2O solubility in peralkaline haplogranitic melts has been experimentally determined as a function of pressure (27–200 MPa) and temperature (1123–1523 K). The compositions were based on Ab38Or34Qz28 (AOQ) with 4 and 8 wt% Na2O in excess. H2O solubility experiments were performed in an internally heated pressure vessel and quenched to glasses for analysis. For quantification of H2O contents in the glasses using FTIR analysis, the linear molar absorption coefficients as a function of Na2O excess with respect to AOQ composition were determined, as well as the glass densities as a function of H2O concentration. The H2O solubility increases with increasing pressure, decreasing temperature, and with increasing peralkalinity. A linear dependence between Na2O excess (wt%) and H2O solubility (wt%) was found. It has been previously shown that on a molar basis the different alkalis contribute similarly to the H2O solubility increase so that H2O solubility increases linearly with excess alkali (difference between mole fractions of alkalis and that of alumina). Thus, the dependence of H2O solubility on pressure, temperature and excess alkali obtained from the new data of this study allow a simple prediction of H2O solubility for peralkaline rhyolitic melts based on the excess alkali content. This new empirical model was tested with H2O solubility data from literature for peralkaline haplogranitic and natural peralkaline rhyolitic melt compositions, yielding good agreement (< 10% deviation) between predicted and observed H2O solubility, which is an improvement compared to previous models. The model can be applied to natural peralkaline rhyolitic melts that occur, e.g. on Pantelleria, Gran Canaria, or the East African Rift.
PubDate: 2022-04-24

• Mantle sources and melting processes beneath East Antarctica: geochemical
and isotopic (Sr, Nd, Pb, O) characteristics of alkaline and tholeiite
basalt from the Earth’s southernmost (87° S) volcanoes

Abstract: Abstract Mount Early and Sheridan Bluff (87° S) are the above-ice expression of Earth’s southernmost volcanic field and are isolated by > 1000 km from any other exposed Cenozoic volcano in Antarctica. These monogenetic, Early Miocene volcanoes consist of olivine-phyric basaltic pillow lavas and breccias (Mount Early) and pāhoehoe lavas (Sheridan Bluff) whose differentiation is controlled by the fractional crystallization of olivine with lesser quantities of clinopyroxene, plagioclase and magnetite. Fractional crystallization or contamination by crust cannot account for the coexistence of olivine tholeiite and alkaline compositions but their relationship can be explained by change from higher (5–6%) to lower (1.5–2%) degrees of partial melting concurrent with a decrease in peridotite‒melt reaction in a mantle that is heterogeneous on a small-scale. Both magma types have geochemical and isotopic signatures that differentiate them from most of the volcanism found within the West Antarctic rift system. Data trends in Sr–Nd–Pb isotope space indicate mixing of at least two-distinct mantle sources: (1) a relatively depleted component similar to sources for mid-ocean ridge basalt from the extinct Antarctic–Phoenix spreading center, and (2) an enriched component similar to sources for mafic magmas of the Jurassic Karoo‒Ferrar large igneous provinces. The availability of these mantle source types was facilitated by the detachment, sinking and heating of metasomatized continental lithosphere (enriched source) that released volatiles into the surrounding asthenosphere (depleted source) to promote flux melting. Volcanism triggered by lithospheric detachment is, therefore, explicitly applied to Mount Early and Sheridan Bluff to explain their isolation and enigmatic tectonic setting but also to account for source heterogeneity and the ephemeral change in degree of mantle partial melting recorded in their mafic compositions.
PubDate: 2022-04-17

• Hydrous mafic–ultramafic intrusives at the roots of a proto-arc:
implications for crust building and mantle source heterogeneity in young
forearc regions

Abstract: Abstract The New Caledonia ophiolite represents a rare example of proto-arc section originated during subduction infancy. The sequence is dominated by refractory harzburgites overlain by ultramafic (dunites and wehrlites) and mafic (gabbronorites) lithologies. In this contribution, we report the first occurrence of amphibole-bearing intrusives in the New Caledonia forearc sequence. This study deals with a petrological and geochemical investigation of a pyroxenite intrusion cut by mafic–ultramafic dikes. The intrusion consists of medium grain websterites, composed of orthopyroxene (30–75 vol %), clinopyroxene (20–50 vol %) and amphibole (2–30 vol %), which occurs as interstitial or poikilitic phase. Whole rocks display moderate Mg# (71–82) and concave downward REE patterns, bearing depleted to flat LREE (LaN/NdN = 0.5–1) and flat HREE segments (DyN/LuN = 0.8–1.1). Bulk rocks mirror clinopyroxene at higher absolute values. Fluid mobile element (FME) enrichments, coupled to Zr–Hf depletion, are observed for both clinopyroxene and bulk rock. Mineral major element variations and textural relationships indicate that the investigated lithotypes derived from hydrous magmas, which underwent extensive fractional crystallisation and post-cumulus processes. Geochemical modelling shows that the parental melts in equilibrium with the pyroxenites share remarkable similarities with the New Caledonia CE-boninite. However, they significantly differ from the equilibrium melts previously reported for the other intrusive rocks of the sequence. As a whole, our new results highlight a greater compositional variability for the liquids ascending into the Moho transition zone and lower crust. This may be also related to the involvement of a highly heterogeneous mantle source during subduction initiation.
PubDate: 2022-04-16

• Constraining the isotopic endmembers contributing to 1.1 Ga Keweenawan
large igneous province magmatism

Abstract: Abstract Continental flood basalt lavas often contain deeply-sourced, thermo-chemically anomalous material that can provide a potential probe of inaccessible reservoirs. However, continental flood basalts interact with geochemically diverse domains within the continental lithosphere, which may complicate interpretations of deep mantle signatures. We examine the role of continental lithospheric mantle in continental flood basalts erupted as part of the 1.1 Ga Keweenawan large igneous province, centered on the Lake Superior region of North America. We show that flood basalts at Mamainse Point exhibit a range of εHf 1100 from −14.1 to +6, plotting along the global εHf—εNd mantle array. Lithospheric mantle melts represented by alkaline rocks from the Coldwell and Seabrook Lake Complexes yield positive εNd 1100 (+0.7 to +4.3) and εHf 1100 from −6.9 to +2.4, placing them below the mantle array. Mamainse Point lavas are interpreted to be variably crustally contaminated melts of the Keweenawan plume and ambient upper mantle; there is no clear evidence for contributions from an enriched lithospheric mantle.
PubDate: 2022-04-13

• Genetic implications from textures, mineralogy, and geochemistry: the case
of Zona Basal–a singular polymetallic occurrence in the Quadrilátero
Ferrífero, Brazil

Abstract: Abstract High-temperature conditions for ore deposition and anomalous abundances of base metals in orogenic gold deposits are frequently attributed to magmatic-hydrothermal fluids instead of metamorphic orogenic fluids. Zona Basal is a shear zone-related gold and base metals-rich mineral occurrence recently discovered in the northwestern portion of the Quadrilátero Ferrífero mining district in southeast Brazil. Mineralogical and geochemical characterization has revealed a two-stage mineralizing system. An Au-W-As stage is marked by a late- to post-tectonic arsenopyrite-pyrrhotite-pyrite assemblage (crystallized from ca. 491 to 404 °C), associated with native gold and scheelite, which was formed during the transition from the peak of greenschist facies metamorphism to retrograde metamorphism. A following, clearly post-tectonic stage comprises a pyrrhotite-pyrite-sphalerite-chalcopyrite-galena-ullmannite ± meneghinite ± fahlore ± miargyrite ± pyrargyrite assemblage crystallized from ca. 400 to < 170 °C, corresponding to the Ag and base metals stage. Fahlores from the Zona Basal mineral occurrence have been found to be sufficiently enriched in Ag, due to the Ag–Cu cation-exchange reaction 13PbS (galena) + 10AgSbS2 (in galena) = 3Ag3SbS3 (pyrargyrite) + Ag(Cu)−1 (exchange in fahlore) + CuPb13Sb7S24 (meneghinite), to jump across the (Cu, Ag)10(Fe,Zn)2Sb4S13 miscibility gap. Two mechanisms may explain the abrupt chemical change between the two mineralization stages: (1) participation of magmatic-hydrothermal fluids of relatively low temperature (acting mostly as a chemical source for fluids) associated with a syn- to late tectonic granite intrusion; or (2) local re-concentration of base metals by unmixing of an early metamorphic orogenic fluid due to fluid immiscibility after the transition from ductile to brittle conditions, generating coexisting fluids with different salinities (i.e., extremely low and moderate salinity). The findings in this paper illustrate the importance of considering retrograde or cooling reactions and mineral re-equilibrium while addressing complex ore-formation.
PubDate: 2022-04-12

• Boron isotopes of white mica and tourmaline in an ultra-high pressure
metapelite from the western Tianshan, China: dehydration and metasomatism
during exhumation of subducted ocean-floor sediments

Abstract: Abstract Boron geochemistry can track fluid–rock interaction during metamorphic evolution and provides important insights into mass transfer processes in subduction zones. This study presents boron concentration and isotopic data for white mica (phengite and paragonite) and tourmaline in an ultra-high pressure (UHP) metapelitic schist from the western Tianshan (Xinjiang Province, China). The pelitic schist experienced dehydration during heating related to the onset of exhumation, which is recorded by phengite and tourmaline formed during this stage. Boron isotope ratios in phengite decreased from – 8.5 to – 16.0 ‰ (relative to NIST SRM 951) with increasing temperature from 525 to 575 °C. This is recorded in a correlated decrease of 11B/10B ratios, B content and Si content of phengite. Thus, the B isotopes of released fluids during decompression–heating evolved from 0 to – 6.9 ‰, consistent with a preferential loss of isotopically heavy B during dehydration. The formation of BSE-dark zones in tourmaline with relatively light δ11B values (– 9 to – 6‰) and high Mg# (0.65–0.68) could be related with fluids released during this stage. In a second stage, paragonite formed in a rehydration process during advanced exhumation. During interaction with external fluids, boron concentrations and isotopic values in paragonite increased: B concentration range from 72 to 232 μg/g, and δ11B increased from – 15.6 to – 2.5 ‰. Fluid-fractionation modeling demonstrates that the external fluid [(B) = 340 ± 20 μg/g; δ11B =  + 8 ± 2 ‰] may have been derived from high-δ11B serpentinites that occur in the study area (δ11B between – 1 and + 8 ‰). In response to hydration, tourmaline likely developed BSE-light zones with heavier δ11B values (− 4 to − 2‰) and lower Mg# (0.62–0.64). Boron geochemistry of white micas and tourmaline improve our understanding of mass transfer during metamorphic processes in subduction zones; it allows us to identify the influence of both closed-system recrystallization events and the effect and likely source of externally derived fluids.
PubDate: 2022-04-11

• High-temperature water–olivine interaction and hydrogen
liberation  in the subarc mantle

Abstract: Abstract Oxidized fluids in the subduction zone may convert polyvalent elements in the mantle to their higher valence states. The most abundant polyvalent element in the mantle is Fe, a significant part of which is contained in olivine as Fe2+. Results of the study of arc mantle xenoliths, in lab high-pressure–high-temperature experiments, and thermodynamic modeling have shown that at pressures of ~ 50–2000 MPa and temperatures of 1000–1250 °C, well above the serpentine stability field, Fe2+ from olivine reacts with free aqueous fluid according to the following simplified reaction: 3Fe2SiO4 + 2H2O ⇆ 3SiO2 + 2Fe3O4 + 2H2. The resulting ferric iron is preserved in spinel of a certain composition, $$\left( {{\text{Mg,Fe}}_{{}}^{{2 + }} } \right){\text{Fe}}_{{2}}^{{3 + }} {\text{O}}_{{4}}$$ , whereas new high-Mg olivine, with magnesium number up to 96 in natural samples and 99.9 in experiments, forms in the reaction zone. SiO2 produced in the reaction either dissolves in the fluid or, with a small amount of water, reacts with olivine to form orthopyroxene as follows: (Mg,Fe)2SiO4 + SiO2 = (Mg,Fe)2Si2O6. The released H2 may decrease the oxidation state of polyvalent elements present in the fluid (e.g., S4+, S6+). Traces of high-temperature water–olivine interaction appear as swarms of fluid-spinel inclusions and are ubiquitous in olivine from ultramafic arc xenoliths. The described process is similar to serpentinization but occurs at higher pressure and temperature conditions and yields different reaction products. The reducing capacity of olivine is relatively low; however, given the large volume of mantle (and crustal) peridotites, the overall effect may be significant.
PubDate: 2022-04-11

• Geochronological and geochemical characteristics of continental basalts of
the eastern North China Craton: insights into crust–mantle interaction
induced by continental subduction

Abstract: Abstract Crust–mantle interaction induced by continental subduction occurs through metasomatic reaction of continental crust-derived materials with mantle wedge peridotite in continental subduction channels. Mantle-derived igneous rocks above continental subduction zones can provide insights into the nature of crust–mantle interaction and the types of metasomatism. The Laixi region is located on the southeastern margin of the North China Craton adjacent to the Sulu orogen. Here, we present K–Ar dating, whole-rock major and trace elements, Sr–Nd–Pb isotopes, and olivine and clinopyroxene major and trace elements of the Laixi basalt to investigate the nature of metasomatism at the crust–mantle interface. These basalts exhibit geochemical inheritance of island arc basalt (IAB)-like trace-element patterns, moderately enriched Sr–Nd isotopic compositions, and variable Pb isotopic compositions from upper-crustal materials of the subducted South China Block. The olivine and clinopyroxene contents of the Laixi basalts indicate a mixed source composed of ~ 51% pyroxenite and ~ 49% peridotite which is the result of carbonate metasomatism. On the basis of the typical differences in MgO, CaO and Al2O3 contents between the Laixi basaltic magmas and experimental melts, the metasomatic agents are identified as carbonated eclogite-derived melts. These features of the IAB-like basalts suggest metasomatic reaction of mantle-wedge peridotite with carbonated silicate melt derived from the subducted upper crust in the continental subduction channel, with olivine being consumed to generate ultramafic metasomatites enriched in pyroxene.
PubDate: 2022-04-08

• COH-fluid induced metasomatism of peridotites in the forearc mantle

Abstract: Abstract Devolatilization of subducting lithologies liberates COH-fluids. These may become partially sequestered in peridotites in the slab and the overlying forearc mantle, affecting the cycling of volatiles and fluid mobile elements in subduction zones. Here we assess the magnitudes, timescales and mechanism of channelized injection of COH-fluids doped with $${\mathrm{Ca}}_{\mathrm{aq}}^{2+}$$ , $${\mathrm{Sr}}_{\mathrm{aq}}^{2+}$$ and $${\mathrm{Ba}}_{\mathrm{aq}}^{2+}$$ into the dry forearc mantle by performing piston cylinder experiments between 1–2.5 GPa and 600–700 °C. Cylindrical cores of natural spinel-bearing harzburgites were used as starting materials. Based on mineral assemblage and composition three reaction zones are distinguishable from the rim towards the core of primary olivine and orthopyroxene grains. Zone 1 contains carbonates + quartz ± kyanite and zone 2 contains carbonates + talc ± chlorite. Olivine is further replaced in zone 3 by either antigorite + magnesite or magnesite + talc within or above antigorite stability, respectively. Orthopyroxene is replaced in zone 3 by talc + chlorite. Mineral assemblages and the compositions of secondary minerals depend on fluid composition and the replaced primary silicate. The extent of alteration depends on fluid CO2 content and fluid/rock-ratio, and is further promoted by fluid permeable reaction zones and reaction driven cracking. Our results show that COH-fluid induced metasomatism of the forearc mantle is self-perpetuating and efficient at sequestering $${\mathrm{Ca}}_{\mathrm{aq}}^{2+}$$ , $${\mathrm{Sr}}_{\mathrm{aq}}^{2+}$$ , $${\mathrm{Ba}}_{\mathrm{aq}}^{2+}$$ and CO2aq into newly formed carbonates. This process is fast with 90% of the available C sequestered and nearly 50% of the initial minerals altered at 650 °C, 2 GPa within 55 h. The dissolution of primary silicates under high COH-fluid/rock-ratios, as in channelized fluid flow, enriches SiO2aq in the fluid, while CO2aq is sequestered into carbonates. In an open system, the remaining CO2-depleted, Si-enriched aqueous fluid may cause Si-metasomatism in the forearc further away from the injection of the COH-fluid into peridotite.
PubDate: 2022-04-05

• Characterization of biotite and amphibole compositions in granites

Abstract: Abstract Accessory and minor phases are frequently used to infer the composition and intensive parameters of magmas. In granites, the most common ferromagnesian phases are biotite and amphibole, which raises the question as to what compositional domains are present among these phases and how do those domains relate to granite composition. Here we present a characterization of biotite and amphibole compositions from S-, I-, and A-type granites. A database of biotite (1215 data points) and amphibole (525 data points) compositions from previously classified S-, I-, and A-type granites has been compiled. Three characteristics can be used to describe the variations in biotite composition including $${X}_{\mathrm{Annite}}^{\mathrm{Bt}}$$ (fraction of Fe2+ in the octahedral site), $${X}_{{\mathrm{Fe}}^{\mathrm{VI}*}}^{\mathrm{Bt}}$$ (fraction of total iron in the octahedral site), and total aluminum (apfu). Three characteristics can also be used to describe variations in amphibole composition including, NK/CNK [i.e., (Na + K)/(Ca + Na + K)], Fe/(Fe + Mg), and total aluminum. Utilizing, for the first time, a random forest (machine learning) model the three characteristics for biotite and amphibole could discriminate the inferred source region of the granites with 82 and 96% accuracy, respectively. Biotite composition can also be used to broadly characterize $${f}_{{\mathrm{O}}_{2}},$$ $$\frac{{f}_{{\mathrm{H}}_{2}\mathrm{O}}}{{f}_{\mathrm{HF}}}$$ , $$\frac{{f}_{{\mathrm{H}}_{2}\mathrm{O}}}{{f}_{\mathrm{HCl}}}$$ , and $$\frac{{f}_{\mathrm{HF}}}{{f}_{\mathrm{HCl}}}$$ of each granite type at a given temperature and pressure. Thus, biotite and amphibole compositions can be used to further characterize granites; however, biotite and amphibole should not solely be used to infer the source of a granite.
PubDate: 2022-04-02

• Linking titanite U–Pb dates to coupled deformation and
dissolution–reprecipitation

Abstract: Abstract Titanite U–Pb geochronology is a promising tool to date high-temperature tectonic processes, but the extent to and mechanisms by which recrystallization resets titanite U–Pb dates are poorly understood. This study combines titanite U–Pb dates, trace elements, zoning, and microstructures to directly date deformation and fluid-driven recrystallization along the Coast shear zone (BC, Canada). Twenty titanite grains from a deformed calc-silicate gneiss yield U–Pb dates that range from ~ 75 to 50 Ma. Dates between ~ 75 and 60 Ma represent metamorphic crystallization or inherited detrital cores, whereas ~ 60 and 50 Ma dates reflect localized, grain-scale processes that variably recrystallized the titanite. All the analyzed titanite grains show evidence of fluid-mediated dissolution–reprecipitation, particularly at grain rims, but lack evidence of thermally mediated volume diffusion at a metamorphic temperature of > 700 °C. The younger U–Pb dates are predominantly found in bent portions of grains or fluid-recrystallized rims. These features likely formed during ductile slip and associated fluid flow along the Coast shear zone, although it is unclear whether the dates represent 10 Myr of continuous recrystallization or incomplete resetting of the titanite U–Pb system during a punctuated metamorphic event. Correlations between dates and trace-element concentrations vary, indicating that the effects of dissolution–reprecipitation decoupled U–Pb dates from trace-element concentrations in some grains. These results demonstrate that U–Pb dates from bent titanite lattices and titanite subgrains may directly date crystal-plastic deformation, suggesting that deformation microstructures enhance fluid-mediated recrystallization, and emphasize the complexity of fluid and deformation processes within and among individual grains.
PubDate: 2022-03-22

• Early magmatic history of the IBM arc inferred from volcanic minerals and
melt inclusions from early–late Oligocene DSDP Site 296: a
mineral–melt partition approach

Abstract: Abstract The magmatic history of the early Izu-Bonin-Mariana (IBM) arc forms a gap between a growing understanding of Eocene subduction and IBM arc initiation in the western Pacific, and Miocene- recent IBM arc processes. Fresh volcanic minerals in lapilli tuffs drilled at DSDP Site 296 on the northern Kyushu Palau Ridge (KPR) provide an opportunity to understand the early–late Oligocene magmatic evolution of the IBM arc leading up to arc rifting and opening of the Shikoku back-arc basin. In this study, we use major and trace element compositions of feldspar, amphibole and pyroxene, with melt inclusions, to infer KPR magma compositions, crystallization temperatures and pressures, and temporal sequence. A major finding of this approach is that inferred magma compositions span a wider range of trace element variation than that inferred from basaltic to dacitic glass shards within the tuffs. Elemental and thermobarometric data for clinopyroxene indicate the presence of mafic, incompatible element-depleted (Nb/Yb < 0.3 and La/SmN < 1.4) magmas that crystallized at shallow depths, and incompatible element-enriched (Nb/Yb = 8.1 and La/SmN = 6.5), mafic, amphibole-bearing arc magmas that either crystallized over a range of pressures or without reaching plagioclase saturation. We interpret the incompatible element-depleted magmas as decompression melts of a shallow BABB source mantle and the incompatible element-enriched type as mature, water-rich arc magmas. The occurrence of both types of magma in several lapilli tuff intervals in the drilled section suggests that arc extension and rifting was a gradual process leading to multiple events of decompression melting interspersed with the eruption of mature arc magma.
PubDate: 2022-03-21

• MafiCH: a general model for H2O–CO2 solubility in mafic magmas

Abstract: Abstract The solubility of CO2 in mafic magmas is strongly dependent on magma composition, which ultimately affects magma storage conditions and eruptive behavior. Recent experimental work showed that previously published volatile solubility models for mafic magmas are not well calibrated at mid-crustal pressures (400–600 MPa). Using a simple thermodynamic model, here we construct a general CO2 solubility model for mafic magmas by establishing the compositional dependence of two key thermodynamic parameters. The model is calibrated using experimental data from 10 magma compositions that span a range of pressures as well as silica (44–53 wt.%) and total alkali (2–9 wt.%) contents. We also survey the experimental literature for relevant H2O solubility data to determine how to model H2O solubility for these magmas. We combine these separate CO2 and H2O solubility models into a single general model for mixed-fluid (H2O–CO2) solubility in mafic magmas called MafiCH. We test the MafiCH model using experiments from three compositions that fall both within and beyond the calibrated range, and find that the model accurately constrains the CO2 solubility of depolymerized magmas. Sensitivity tests identify that Na, Ca, and Al have the largest effect on CO2 solubility while Si and Mg do not play a strong role in CO2 solubility in mafic, depolymerized melts. Overall, saturation pressures calculated using the new model presented here are typically lower than those predicted by previous models. The model provides a new framework to interpret volcanic data from mafic magma compositions for which no experimental data is available.
PubDate: 2022-03-19

• Eoarchean subduction-like magmatism recorded in 3750 Ma
mafic–ultramafic rocks of the Ukaliq supracrustal belt (Québec)

Abstract: Abstract Our understanding of the nature of crustal formation in the Eoarchean is limited by the scarcity and poor preservation of the oldest rocks and variable and imperfect preservation of protolith magmatic signatures. These limitations hamper our ability to place quantitative constraints on thermomechanical models for early crustal genesis and hence on the operative geodynamic regimes at that time. The recently discovered ca. 3.75 Ga Ukaliq supracrustal enclave (northern Québec) is mainly composed of variably deformed and compositionally diverse serpentinized ultramafic rocks and amphibolitized mafic schists whose metamorphic peak, inferred from phase equilibria modeling, was below 720 °C. Inferred protoliths to the Ukaliq ultramafic rocks include cumulative dunites, pyroxenites, and gabbros, whereas the mafic rocks were probably picrites, basalts, and basaltic andesites. The bulk-rock and mineral chemistry documents the partial preservation of cumulative pyroxenes and probably amphiboles and demonstrates the occurrence of a clinopyroxene-dominated, tholeiitic suite and an orthopyroxene-dominated, boninite-like suite. Together with the presence of negative μ142Nd anomalies in the boninitic basalts, two liquid lines of descent are inferred: (i) a damp tholeiitic sequence resulting from the fractionation of a basaltic liquid produced by mantle decompression; and (ii) a boninitic suite documenting the evolution of an initially primitive basaltic andesite liquid produced by flux melting. Petrographic observations, thermodynamic modeling, bulk-rock and mineral chemistry, and 142Nd isotopic compositions identify the Ukaliq supracrustal belt as the remnant of an Eoarchean arc crust produced by the recycling of Hadean crust in a similar way as modern-style subduction.
PubDate: 2022-03-14

• Direct nanoscale observations of degassing-induced crystallisation in
felsic magmas

Abstract: Abstract Water degassing plays a major role in magma transport and eruption by increasing liquidus temperatures, bubble and crystal volume fractions, and strongly affecting the viscosity of bulk magma. High spatial resolution textural analysis detailing the dynamics of bubble and crystal growth is key to unravelling the swift changes in magma crystallinity and gas content that affect the conditions of magma flow, fragmentation, and eruption. Ex situ observation of samples from a previous experimental study of magma degassing reveals that vesicles are surrounded by chemically heterogeneous residual glass that may be produced by newly formed minerals that are not observable at the microscale. Here, we present new in situ high-temperature (500–1100 °C), time-elapsed (every ~ 20 min at 200–800 °C, ~ 10 min at 900–1000 °C, and ~ 5 min at 1100 °C) observations of degassing of synthesised, hydrous (4.2 wt.% H2O) dacite glasses using scanning transmission electron microscopy at 0.4 nm resolution. The experiments reproduce degassing of a silicic melt by high-temperature heated stage mounted in the analytical instrument. We monitor the dynamics of nucleation and growth of nanobubbles that experience coalescence and formation of microbubbles and trigger the nucleation and growth of nanolites of plagioclase, clinopyroxene, Fe-Ti oxides, and quartz, at the expense of the residual melt. The ability to image degassing and crystallisation at nanoscale reveals a sequence of complex physical and chemical changes of the residual melt and shows that the kinetics of crystallisation in silicic melts is modulated by the melt’s ability to exsolve fluids that help form mineral nuclei and nanolites. Finally, we highlight that the competition between gas retention and crystallisation is initiated at the nanoscale and may anticipate the role of microlites in controlling rates of magma ascent in a volcanic conduit and modulating the style of the consequent volcanic eruption.
PubDate: 2022-03-12

• The solubility of titanite in silicate melt determined from growth and
dissolution experiments

Abstract: Abstract The solubility of titanite (CaTiSiO5) in Si-rich melts was measured experimentally through growth experiments at 800–1000 °C, 0.5–1.0 GPa, log fO2 ~ CCO–0.8, t = 72–168 h, and H2O = 0 to 4 wt.%, and in dissolution experiments at 925–1300 °C, 0.8 GPa, t = 18–118 h, and H2O = 1–10 wt.% in a piston-cylinder apparatus. Run product glasses in growth experiments were homogeneous, and iron loss suppressed ilmenite crystallization. Saturation concentrations in dissolution experiments were estimated by fitting measured diffusion profiles. Titanite solubility increases with increasing temperature and melt composition parameter $$M = {\text{ molar }}\left( {{\text{Na }} + {\text{ K }} + {\text{ 2Ca}}} \right)/\left( {{\text{Al }} \times {\text{ Si}}} \right)$$ . Multiple linear regression of glass composition data from growth and dissolution experiments (n = 29) plus 39 experiments from the LEPR database (Hirschmann et al. 2008) yielded the titanite solubility equation (adj. r2 = 0.95): $$\left( {TiO_{2} } \right)^{melt} \left( {wt.\% } \right) = 0.978 \times M + 0.0048 \times T\left( K \right){-}5.90$$ . This model correctly predicted undersaturation in 95% of 2344 experiments from the LEPR database that did not have titanite or rutile. Application to natural rocks yields saturation temperatures that are similar to independent temperature estimates. This equation should be useful for constraining the temperatures of titanite-saturated melts, for determining whether titanite saturation in magmatic source regions is likely, and for determining when titanite can crystallize and begin to exert an influence on melt geochemistry.
PubDate: 2022-03-07
DOI: 10.1007/s00410-022-01902-z

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