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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