Chao Teng’s scientific contributions

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Publications (2)


Geochronology and Geochemistry of the Uhelchulu Quartz Diorite-Granodiorite in Inner Mongolia of China: Implications for Evolution of the Hegenshan Ocean in the Early-Middle Devonian
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August 2024

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14 Reads

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1 Citation

Minerals

Tianshe Cheng

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Wenjing Yang

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Chao Teng

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[...]

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Deng Xiao

The Uhelchulu quartz diorite-granodiorite intrusions in Xiwuqi, Inner Mongolia, are exposed along the northwestern margin of the Xilinhot microcontinental block, located within the central and eastern parts of the southeastern Hegenshan suture zone. LA-ICP-MS zircon U-Pb dating yielded crystallization ages of (396 ± 8) Ma for the quartz diorite and (385 ± 5) Ma for the granodiorite, indicating an Early-Middle Devonian magmatic event. The quartz diorite exhibits I-type granite features, characterized by elevated Al2O3 (14.33–15.43 wt%), MgO (3.73–5.62 wt%), and Na (Na2O/K2O = 1.04–1.44), coupled with low P2O5 (0.15–0.20 wt%) and TiO2 (0.73–0.99 wt%). Trace element patterns show relative enrichments in Rb, Th, U, and Pb, while Nb, Ta, Sr and Ti are relatively depleted. Total REE contents are relatively low (123–178 ppm), with significant LREE enrichment (ΣLREE/ΣHREE = 4.75–5.20), and a non-obvious Eu anomaly (δEu = 0.75–0.84). In contrast, the granodiorite displays S-type granite characteristics, with high SiO2 (70.48–73.01 wt%), K (K2O/Na2O = 1.35–1.83), Al2O3 (A/CNK = 1.16–1.31), and a high differentiation index (DI = 76–82). Notably, MgO (1.44–2.24 wt%) contents are low, and significant depletions of Ba, Sr, Ti, and Eu are observed, while Rb, Pb, Th, U, Zr, and Hf are significantly enriched. Total REE contents are relatively low (178–314 ppm), exhibiting significant LREE enrichment (LREE/HREE = 6.17–8.36) and a pronounced negative Eu anomaly (δEu = 0.34–0.49). The overall characteristics point towards an active continental margin arc background for the Uhelchulu intrusions. Previous studies have suggested that the Hegenshan ocean continuously subducted northward from the Early Carboniferous to the Late Permian, but there is a lack of evidence for its geological evolution during the pre-Early Carboniferous. Therefore, this paper provides a certain basis for studying the geological evolution during the pre-Early Carboniferous in the Hegenshan ocean. We preliminarily believed that the Hegenshan ocean underwent a southward subduction towards the Xilinhot microcontinental block in the Xiwuqi area, at least from the Early Devonian to the Middle Devonian and the Hegenshan ocean may might have undergone a shift in subduction mechanism during the Late Devonian or Early Carboniferous.

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Figure 1. (a) Tectonic subdivision of the Tibetan Plateau [11,15]. Age data are from Zhu et al. (2012), Zhang et al. (2012), and Peng et al. (2020) [11,15,26-32]. (b) Geological map of the study area [26,33].
Figure 4. Zircon 206 Pb/ 238 U vs. Zircon εHf(t) and diagrams of the Burshulaling Granites and A (or A2)-type granites, rhyolites, and Early Cretaceous granites along the BNSZ [21,28,29,31].
Figure 7. (K2O + Na2O) vs. 10,000Ga/Al (a), Y vs. 10,000Ga/Al (b), and Nb vs. 10,000Ga/Al (c) diagrams of the Burshulaling Granites and A(or A2-)-type granites, rhyolites along the northern margin of the Lhasa Block [7,28,29,31,32].
Figure 8. Rb/Nb vs. Y/Nb (a), Nb vs. Y vs. 3Ga (b), and Nb vs. Y vs. Ce (c) diagrams of the Burshulaling Granites and A(or A2-)-type granites, rhyolites along the northern margin of the Lhasa Block [10,28,29,31,32].
Figure 9. Al2O3 + MgO + TiO2 + Fe2O3 T vs. Al2O3/(MgO + TiO2 + Fe2O3 T ) (a) and Sr/Y vs. La/Yb (b) diagrams of the Burshulaling Granites and A(or A2)-type granites, rhyolites along the northern margin of the Lhasa Block [27-32,69,71]. Abbreviations: Grt = garnet, PI = plagioclase.

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Early Cretaceous A-Type Acidic Magmatic Belt in Northern Lhasa Block: Implications for the Evolution of the Bangong–Nujiang Ocean Lithosphere

June 2024

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64 Reads

Minerals

A-type granites have been the subject of considerable interest due to their distinct anorogenic geological background. The A-type and arc-related granites are crucial in deciphering the evolution of the ocean closure and continental collision in the Tibet Plateau. The demise of the Bangong–Nujiang suture zone (BNSZ) and the Yarlung–Tsangpo suture zone was accompanied by the emplacement of volumes of syn-collisional and post-collisional granites. Controversy has persisted regarding the contribution of the collisional granites within the Lhasa Block to the growth of the Tibetan Plateau. This study provides key evidence about the evolution of the Lhasa Block and Bangong–Nujiang Ocean (BNO) by the newly documented 1200 km long, Early Cretaceous A-type acidic magmatic belt. The resolution was achieved through the utilization of petrology, whole-rock geochemistry, zircon U-Pb geochronology, and in situ zircon Hf isotope analysis of the Burshulaling Granites in the eastern segment and previous existing data in the central and western segment of the Lhasa Block. The Burshulaling Granites are characterized as peraluminous, high-K calc-alkaline series, indicating a post-collision setting with high temperature and low pressure. The zircon grains from two granite samples yield 206Pb/238U ages of 115–113 Ma. In situ zircon Hf analyses with 206Pb/238U ages give εHf(t) of −6.2–0.6, showing prominent characteristics of crust-mantle interaction. Granites from east to west exhibit whole-rock geochemical and geochronological similarities that fall within the well-constrained Early Cretaceous time frame (117–103 Ma) and track post-collisional A-type acidic magmatic belt along BNSZ. We argue that this magmatism resulted from slab break-off or orogenic root detachment, leading to melting and mixing of the lower crust. Meanwhile, this study indicates the existence of the Bangong–Nujiang Ocean southward subduction or a collapse following an Andean-type orogen.

Citations (1)


... I-type granites are magmatic products from the melting of unweathered igneous rocks [50], exhibiting two genetic models: the crystallization differentiation of intermediatemafic magmas [51] and the partial melting of crustal rocks with the contribution from mantle-derived materials [52]. The granite samples from the Chazangcuo mining area were relatively enriched in LILEs and LREEs but depleted in HFSEs and HREEs. ...

Reference:

Granites of the Chazangcuo Copper–Lead–Zinc Mining Area in Tibet, China: Magma Source and Tectonic Implications
Geochronology and Geochemistry of the Uhelchulu Quartz Diorite-Granodiorite in Inner Mongolia of China: Implications for Evolution of the Hegenshan Ocean in the Early-Middle Devonian

Minerals