Exposures of enclave-bearing granitoids can provide rare opportunities to directly evaluate the connection between compositional variability and the depth of origin of arc magmatic rocks. The ∼1000 km long Gangdese batholith is a composite batholith with composition from mafic to felsic; SiO2 ranges from 51 wt% to 70 wt%. New zircon U−Pb dating of the Nyemo plutons, Renbu plutons, and Xigaze plutons in the Gangdese batholith is consistent with their emplacement and crystallization in the Late Cretaceous (ca. 90−85 Ma). Mafic magmatic enclaves (MMEs) in the plutons are characterized by low SiO2 (50.9−56.0 wt%) and Nb/U, Ce/Pb, and Nb/La ratios coupled with enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements. These geochemical features, combined with depleted whole-rock εNd(t) (+4.2 to +4.7) and zircon εHf(t) (+9.0 to +13.8), suggest that they were derived by partial melting of a depleted mantle source associated with subduction-related fluids. The granitoids with high SiO2 (55.6−66.9 wt%) display adakitic geochemical characteristics, such as low Y and Yb contents, and high Sr/Y and La/Yb ratios. Their positive whole-rock εNd(t) (+4.0 to +5.5) and zircon εHf(t) (+6.9 to +14.3) values, as well as enrichment of incompatible elements, indicate that the granitoids were derived from partial melting of the juvenile lower crust. Geochemical modeling suggests that the compositional diversities of MMEs and adakitic granitoids were inherited from heterogeneous sources. This genetic relationship indicates that the underplated basaltic magmas could have supplied sufficient heat to trigger the melting of the thickened crust and thus formation of the enclave-bearing granitoid. In this regard, the origin of arc rocks can mirror the evolution of crustal thickness. Our results reveal that the crust was thickened to ∼50 km during the Late Cretaceous (90−85 Ma) and provide a magmatic record of crustal thickening prior to the Cenozoic Indo-Asia collision.
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Research Article|
January 10, 2023
Origin of Late Cretaceous, enclave-bearing granitoids in southern Tibet: Implications for magma recharge and crustal thickening
Ding-Jun Wen;
Ding-Jun Wen
1
State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
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Xiumian Hu;
Xiumian Hu
1
State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
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Jin-Hai Yu;
Jin-Hai Yu
1
State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
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Xiao-Lei Wang;
Xiao-Lei Wang
1
State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
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Timothy Chapman;
Timothy Chapman
2
Earth Science, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia
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Rui-Qiang Wang
Rui-Qiang Wang
3
School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China
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GSA Bulletin (2023)
Article history
received:
28 Mar 2022
rev-recd:
14 Sep 2022
accepted:
17 Oct 2022
first online:
11 Jan 2023
Citation
Ding-Jun Wen, Xiumian Hu, Jin-Hai Yu, Xiao-Lei Wang, Timothy Chapman, Rui-Qiang Wang; Origin of Late Cretaceous, enclave-bearing granitoids in southern Tibet: Implications for magma recharge and crustal thickening. GSA Bulletin 2023; doi: https://doi.org/10.1130/B36530.1
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