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| Petrogenesis of the Taihe Granites in the Emeishan Large Igneous Province and Its Tectonic Implications |
| ZHONG Hong1, XU Gui-wen1,2, ZHU Wei-guang1, HU Rui-zhong1, HE De-feng1,2 |
1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
2. Graduate School of Chinese Academy of Sciences, Beijing 100049, China |
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Abstract The late Permian Taihe granitic stock in the Pan-Xi area,SW China,showing spatial association with the giant Fe-Ti-V deposit-bearing gabbroic intrusion,is genetically related to the upwelling Emeishan plume head.This granitic intrusion consists mainly of peralkaline alkali-feldspar granite and quartz syenite with subordinate syenite.These granitic rocks have a distinctive A-type chemistry characterized by elevated high-field-strength elements(HFSE) contents and high Ga/Al ratios(3.74 to 5.63).Nb/Ta and Zr/Hf ratios of the granitic rocks and gabbros are similar to those typical of oceanic island basalt(OIB).The granitoids have relatively low initial 87Sr/86Sr ratios(0.7025-0.7049),positive εNd(t) values(+1.9 to +3.5),which are comparable to those of the gabbros [(87Sr/86Sr)i=0.7049-0.7052;εNd(t)=2.4-3.3].The positive εNd(t) values of the Taihe granitic intrusion indicate a significant contribution of plume-derived basaltic underplating to magma genesis.The similarity of the Nd isotopic compositions of the gabbroic and granitic rocks suggests that their parental magmas were derived from a common reservoir.We propose that the Taihe granitic intrusion was predominantly generated by the emplacement of granitic melts from differentiation of newly underplated,basaltic magmas ponded at depth and subsequent fractional crystallization.It is therefore demonstrated that the growth of juvenile crust through mantle-derived underplating during the late Permian was significant in the inner zone of the Emeishan large igneous province.
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Received: 10 January 2009
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