Petrogenesis and tectonic implications of Palaeocene (ca. 54 Ma) rhyolites in the western Lhasa Terrane, south Tibet: Constraints from geochemistry and Sr–Nd–Hf isotope compositions,Geological Journal

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Petrogenesis and tectonic implications of Palaeocene (ca. 54 Ma) rhyolites in the western Lhasa Terrane, south Tibet: Constraints from geochemistry and Sr–Nd–Hf isotope compositions
Geological Journal ( IF 1.8 ) Pub Date : 2020-08-31 , DOI: 10.1002/gj.3976
Xiang‐Li Ding _{1,

2,

3} , Lin Ding _{1,

2,

3} , Chao Wang ₁ , Hou‐Qi Wang _{1,

3} , Xu‐Dong Guo _{1,

2}

Affiliation

The widespread Linzizong volcanic successions (LVS) in the Lhasa Terrane was a magmatic response to the tectonic transition from Neo‐Tethyan oceanic subduction to the India–Asia collision, which has been the subject of many studies; however, studies on the LVS in the western Lhasa Terrane are scarce compared to those in the east, limiting our understanding of the tectonic transition. Zircon U–Pb ages of two rhyolitic samples from the Shiquanhe region in the west of the Lhasa Terrane indicate that at least part of the Zenong Group, previously thought to have formed during the Early Cretaceous, was actually erupted during the Late Palaeocene (ca. 54 Ma) and belongs to the LVS. The rhyolites are characterized by high SiO₂ and Al₂O₃, moderate K₂O and Na₂O, and low MgO, CaO, and FeO contents, enrichment in Rb and Th, depletion in Sr, Ba, Eu, Nb, and Ta, and have relatively uniform whole‐rock ε_Nd(t) (−1.90 to −0.89) and zircon ε_Hf(t) (+0.95 to +5.03) values. These geochemical characteristics indicate that they were formed by the partial melting of juvenile continental crust with subsequent plagioclase, biotite, amphibole, and Fe–Ti oxide fractionation. Combined with the results of previous studies, our data show that the western Lhasa Terrane underwent intensive Early Cenozoic crustal growth, similar to what occurred in the east, due to underplating of mantle‐derived magma resulting from the roll‐back and eventual break‐off of the Neo‐Tethys slab after the initial continental collision.

更新日期：2020-08-31

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