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  This is an Open Access Journal Open Access journal
ISSN (Print) 1941-8264 - ISSN (Online) 1947-4253
Published by Geological Society of America Homepage  [4 journals]
  • Mesozoic-Cenozoic Topographic Evolution of the South Tianshan (NW China):
           Insights from Detrital Apatite Geo-Thermochronological and Geochemical

    • Abstract: AbstractThe present-day topography of Tianshan is the product of repeated phases of Meso-Cenozoic intracontinental deformation and reactivation, whereas the long-term Mesozoic topographic evolution and the timing of the onset of Cenozoic deformation remain debated. New insights into the Meso-Cenozoic geodynamic evolution and related basin-range interactions in the Tianshan were obtained based on new detrital single-grain apatite U-Pb, fission-track, and trace-element provenance data from Mesozoic sedimentary sequences on the northern margin of the Tarim Basin. Detrital apatite U-Pb age data from Early-Middle Triassic clastic rocks show two prominent age populations at 500–390 Ma and 330–260 Ma, with a paucity of ages between 390 and 330 Ma, suggesting that sediment source is predominantly from the northern Tarim and South Tianshan. From the Late Triassic to Early Jurassic, the first appearance of populations in the 390–330 Ma and 260–220 age ranges indicates that the Central Tianshan-Yili Block and Western Kunlun Orogen were source regions for the northern margin of Tarim Basin. In the Cretaceous strata, south-directed paleocurrents combined with the decrease in the 390–330 Ma age population from the Central Tianshan-Yili Block imply that South Tianshan was uplifted and again became the main source region to the Baicheng-Kuqa depression during the Cretaceous. Our new apatite fission-track data from the southern Chinese Tianshan suggest that rapid cooling commenced at c. 30 Ma along the southern margin, and the Early Mesozoic strata exposed on the southern flank of the Tianshan underwent c. 4–5 km of late Cenozoic exhumation during this period. This age is approximately synchronous with the onset of exhumation/deformation not only in the whole Tianshan but also in the interior of the Tibetan Plateau and its margins. It suggests that far-field, N-directed shortening resulting from the India-Asia collision was transmitted to the Tianshan at that time.
      PubDate: Fri, 15 Sep 2023 00:00:00 GMT
  • The Late Paleocene–Eocene Extension and Differential Denudation in the
           Eastern Daqingshan Mountains Around the Northeastern Margin of the Ordos
           Block, Western North China Craton, Constrained by Apatite (U-Th)/He

    • Abstract: AbstractThe initial timing of extension during the Cenozoic around the northeastern margin of the Ordos Block, western North China Craton (NCC), is still poorly constrained. Apatite (U-Th)/He low-temperature thermochronology was thus applied on eight pre-Cenozoic granitic and gneissic samples transecting the eastern Daqingshan Mountains, northeastern margin of the Ordos Block, to investigate the denudation and cooling event related to the onset of extension therein. Four mean corrected AHe ages in the southern part are overlapped within the standard deviations of 50.0 ± 0.4 to 45.0 ± 8.0 Ma. However, three mean corrected AHe ages in the northern part are prominently older of 99.2 ± 11.0 to 86.6 ± 17.1 Ma, with the rest one of 56.1 ± 8.6 Ma. Altogether, they show a younger-older-younger-older pattern along the transect correlated with the normal faults. AHe thermal history modeling results further demonstrate extensive cooling during the Late Cretaceous but differential cooling during the Late Paleocene–Eocene. The Late Cretaceous extensive cooling in the eastern Daqingshan Mountains, as well as the contemporaneous deposition hiatus in both the eastern Daqingshan Mountains and the Hohhot Depression, together indicates overall denudation in the northeastern margin of the Ordos Block at that time. The Late Paleocene–Eocene differential cooling is probably induced by the tilting of the eastern Daqingshan Mountains as a result of the extension suggested by the distribution of AHe ages. It corresponds to the syn-tectonic subsidence in the Hohhot Depression, indicating a basin-mountain coupling. Regional comparative analysis manifests similar extension around the Ordos Block and more widely across the NCC during the Late Paleocene–Eocene. Temporally, kinematically, and dynamically coupled with this regional extension event, the subduction of the Izanagi-Pacific plate probably plays a major role. However, the contribution of the India-Asia collision could not be ignored.
      PubDate: Mon, 11 Sep 2023 00:00:00 GMT
  • Mesozoic Thermo-Tectonic Evolution of the Western Altai Orogenic Belt (NW
           China): Insights from Low-Temperature Thermochronology

    • Abstract: AbstractThe Meso-Cenozoic tectonic activities of the Central Asian Orogenic Belt (CAOB) played an important role in controlling the present-day topography of Central Asia. The Altai orogenic belt is a key component in the southern CAOB; so far, there is still a lack of sufficient constraints on the time and mechanism of its tectonic reactivation since the Mesozoic. In this contribution, we present new zircon and apatite (U-Th)/He and apatite fission track thermochronological data from granitoid samples in the Habahe area, western Altai orogenic belt. Therein zircon (U-Th)/He ages range from ~230 to ~238 Ma, apatite fission track central ages are ~140–157 Ma, and apatite (U-Th)/He ages vary from ~134 to ~149 Ma. Based on the associated thermal history modeling results, the Habahe area underwent a moderate cooling during the Late Triassic to Middle Jurassic (~230–170 Ma) with a cooling rate of ~0.8–1.1℃/Ma and a subsequent moderate to slightly rapid cooling stage during the Middle Jurassic to Early Cretaceous (170–130 Ma) with a cooling rate of ~1.5–2.3℃/Ma. We propose that this prolonged cooling stage occurred under a long-lasting contractional tectonism in the western Altai throughout the early Mesozoic, which was produced by multiplate convergence in East Asia during this period, mainly including the consumption of the Mongol-Okhotsk Ocean in the northeast and the Meso-Tethys Ocean in the south. The region experienced rather limited Late Cretaceous-Cenozoic cooling and exhumation due to insufficient reactivation and weak surficial erosion.
      PubDate: Mon, 17 Jul 2023 00:00:00 GMT
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