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Durham University

Department of Earth Sciences

Profile

Publication details for Professor Yaoling Niu

Zhao, Z.D., Mo, X.X., Dilek, Y., Niu, Yaoling, DePaolo, D.J., Robinson, P., Zhu, D.C, Sun, C.G., Dong, G.C., Zhou, S., Luo, Z.H. & Hou, Z.Q. (2009). Geochemical and Sr-Nd-Pb-O isotopic compositions of the post-collisional ultrapotassic magmatism in SW Tibet: Petrogenesis and implications for India intra-continental subduction beneath southern Tibet. Lithos 113: 190-212.

Author(s) from Durham

Abstract

Ultrapotassic lavas having distinct geochemical compositions (K2O/Na2O>2, K2O>3%, and MgO>3%)
32 are common and widespread on the Tibet Plateau, where they are closely linked to N-S-trending
33 normal faults. The Tibetan ultrapotassic rocks range in age from ~8 to 24 Ma, slightly older than the
34 spatially associated potassic rocks (10-22 Ma). These lavas consist mainly of trachyte, trachyandesite,
35 basaltic trachyandesite, phonolite and tephriphonolite. They have high light rare earth element (LREE)
36 and large ion lithophile element (LILE) concentrations, but are low in high field strength elements
(HFSE). They are characterized by having extremely radiogenic Sr (87Sr/8637 Sr(i)=0.710719 to 0.736451)
and Pb isotopes (206Pb/204Pb=18.449-19.345, 207Pb/204Pb=15.717-15.803, 208Pb/20438 Pb=39.443-40.168)
39 with unradiogenic Nd isotopes (εNd(0)= -7.6 to -15) and old Nd model ages (TDM=1.3-2.1 Ga), similar in
40 character to the Himalaya basement. Their isotopic character is believed to reflect subduction of the
41 Indian plate beneath the Lhasa terrane, leading to a highly contaminated mantle source. Delamination
42 of the subducted oceanic/continental materials may have played an essential role in the genesis of the
43 ultrapotassic rocks in the Lhasa terrane. The available geological, geochemical and geophysical data
44 favor a model in which the Indian plate was subducted under southern Tibet.