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Source rocks control the geochemical diversity of granite: The Lincang pluton in the western Yunnan Tethyan belt, SW China
Lithos ( IF 3.5 ) Pub Date : 2020-12-26 , DOI: 10.1016/j.lithos.2020.105950
Xi-Guang Huang , Jing-Zhao Dou , Guang-Hui Wu , Jun He , Wolfgang Siebel , Fukun Chen

The present study of the Lincang pluton in the western Yunnan Tethyan belt reveals that its compositional variation is largely inherited from a mixed igneous–sedimentary source. Geochemical composition analyses show that this pluton has a wide range of normative corundum values (0.5–3.1 %). With increasing mafic character [molar (FeO + MgO)/100g], the A/CNK values decrease at mafic character < 0.09; and they start to increase at mafic character > 0.09. As silica increases, P2O5 contents become less scattered and decrease at SiO2 > 69 wt.%. These characteristics indicate the transitional I-S-type affinity of this pluton, which is further supported by zircon trace element and oxygen isotopic features. Inherited zircons from the Lincang pluton display similar age–εHf(t) distributions to those of zircons from metavolcanic and metasedimentary rocks of the Lancang Group, suggesting that the Lancang Group served as source rock for the granite. Variable melting proportions of metavolcanic rocks, meta-arkoses, and mica schists of the Lancang Group can explain the positive correlation between 1000/Sr and initial 87Sr/86Sr ratios for the Lincang pluton. The melting of such mixed igneous–sedimentary source rocks is also in line with the negative correlation between CaO/Na2O and initial 87Sr/86Sr ratios as well as with the transitional I-S-type affinity of the Lincang pluton. Modeling of Sr–Nd ternary mixing shows that generation of the Lincang pluton requires the admixture of ~30–70 % metavolcanic rocks and variable proportions of meta-arkose and mica schist. The protracted emplacement period (ca. 30 million years) and heterogeneous initial 87Sr/86Sr ratios of the Lincang pluton suggest an incremental assembly of magmas. It is likely that individual magma batches were derived from a mixed igneous–sedimentary source, emphasizing the importance of source lithology on the compositional diversity of the granite.

更新日期:2021-01-02
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