U-Pb zircon age, geochemical and Sr-Nd isotopic data as constraints on the petrogenesis and emplacement time of andesites from Gerze, southern Qiangtang Block, northern Tibet----Institute of Geochemistry Chinese Academy of Sciences

Mesozoic post-collisional andesites occur in the Gerze area within the Qiangtang Terrane of northern Tibet, China. Geochronological, geochemical, and whole-rock Sr-Nd isotopic analyses were performed on this suite of volcanic rocks to characterize their petrogenesis. Laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon analyses yielded consistent ages ranging from 122.4 +/- 0.4 Ma to 124.4 +/- 0.4 Ma for two andesite samples (JC01 and GZ01). The andesites belong to the alkaline and sub-alkaline magma series in terms of K2O + Na2O contents (4.7-10 wt.%), and belong to the high-K calc-alkaline and calc-alkaline series on the basis of their high K2O contents (1.0-3.3 wt.%). The volcanic rocks are further characterized by the enrichment of light rare earth elements [(La/Yb)(N) = 7.4-11.5] and large-ion lithophile elements (e.g., Rb), slightly negative Eu anomalies (Eu/Eu* = 0.79-0.94), and negative anomalies in high field strength elements (e.g., Nb, Ta, and Ti) relative to primitive mantle. The samples show slightly elevated (Sr-87/Sr-86)(i) values that range from 0.7049 to 0.7057, and low epsilon(Nd)(t) values of -3.4 to 0.7. These results suggest that the rocks were derived from a compositionally heterogeneous mantle source and that their parent magmas are basalt magma. The parent mafic magmas may have undergone fractional crystallization of olivine, pyroxene, hornblende, and to a lesser extent, plagioclase during ascent through the thickened crustal pile, with minor or no crustal contamination, before the finally erupting as andesites. (C) 2011 Elsevier Ltd. All rights reserved.

　 Publication name JOURNAL OF ASIAN EARTH SCIENCES　Volume:45　Pages:150-161　Published:FEB 2 2012

　 Author(s)
Liu, Shen; Hu, Ruizhong; Gao, Shan; Feng, Caixia; Coulson, Ian M.; Feng, Guangying; Qi, Youqiang; Yang, Yuhong; Yang, Chaogui; Tang, Liang

Corresponding author　
LIU Shen
liushen@vip.gyig.ac.cn
Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550002, Peoples R China 　

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