海南岛中新元古代花岗质岩类的成因及其构造意义

报道了海南岛中新元古代(~1000Ma)花岗质岩类的地球化学和Sm、Nd同位素分析结果。海南岛中新元古代花岗岩类属于钙碱性系列,具有富硅(SiO2含量为67.78%~75.04%),准铝或弱过铝(A/CNK=0.96~1.08),低Mg#值(0.24~0.44)及较低Cr(5.82~13.42μg/g)、Ni(2.74~7.23μg/g)含量,强烈亏损Y(2.85~13.70μg/g)和HREE(Yb为0.26~1.22μg/g),以及较高的Sr/Y(23.75~173.38)和La/Yb(32.11~88.12)比值等特点,类似于TTG或低Mg埃达克岩。结合其低的正εNd(t)值特征,可以认为海南岛中新元古代花岗岩类是底侵玄武质下地壳部分熔融形成的,源区残留相以石榴子石为主,并可能有少量角闪石,其源岩很可能是古中元古代高钾和低Cr、Ni的斜长角闪岩。海南岛中新元古代花岗岩类形成于格林威尔造山作用晚期,这一结果支持华南统一大陆形成于~1000Ma的观点。

PETROGENESIS OF THE MESO-NEOPROTEROZOIC GRANITOIDS IN HAINAN ISLAND AND THEIR TECTONIC SIGNIFICANCE

Geochemical and Sm-Nd isotopic data are reported for the Meso-Neoproterozoic (ca. 1000Ma) granitoids in Hainan Island. The Meso-Neoproterozoic granitoids in Hainan Island are calc-alkaline,characterized by enrichment in silicon (SiO2 contents are 67.78%~75.04%),being metaluminous or weakly peraluminous(A/CNK=0.96~1.08),lower Mg# values(0.24~0.44)and Cr (5.82~13.42μg/g) and Ni(2.74~7.23μg/g)contents,intensively depletion in Y(2.85~13.70μg/g)and HREE(Yb contents are 0.26~1.22μg/g),and with high Sr/Y(23.75~173.38)and La/Yb(32.11~88.12)values,which are similar to TTG or low-Mg adakites. Combined with their slighty positive εNd(t),the Meso-Neoproterozoic granitoids in Hainan Island might be generated by partial melting of underplated basaltic lower crust,with garnets and possible few amphiboles as residues in source region,and the source rocks are most likely the Paleo-Mesoproterozoic amphiboles with high K and low Cr and Ni contents. The Meso-Neoproterozoic granitoids in Hainan Island were generated in the late stage of the Grenvillian orogeny,and this result supports the idea that a coherent South China Craton was formed during the ca. 1000Ma.