云南保山东缘早古生代高Si花岗岩的成因及构造意义

对保山地块东缘高Si花岗岩开展矿物化学、岩石地球化学及锆石U Pb Hf系统研究，结果表明该高Si花岗岩为具钙碱性、强过铝质特征的S型花岗岩。锆石U Pb同位素分析表明，高Si花岗岩侵位于454 Ma，并含有800~1 100 Ma的继承锆石。锆石Hf同位素分析表明其岩浆锆石具有与青藏高原及东南缘同时代长英质侵入体相似的Hf同位素组成，暗示其相似的岩浆起源。矿物化学、同位素组成及Melts模拟计算结果表明，保山东缘高Si花岗岩为一系列复杂作用的结果：高硅花岗岩母岩浆起源于该区沉积岩部分熔融；熔体形成后经高度分异演化，在侵位过程中同化混染围岩；岩浆冷凝至固相线下部分矿物再平衡。保山东缘高Si花岗岩体与平河花岗岩体具相似年龄和地球化学特征，暗示它们之间可能存在类似的成因机制。

Origin and Tectonic Implications of the Early Paleozoic High-Si Granite in the Eastern Baoshan Block,Yunnan

Integrated mineral chemistry, geochemistry and zircon U Pb Hf isotopic analyses were carried out on the high Si granite in the eastern Baoshan block.Results show that the high Si granite is S type and shows calc alkaline, strongly peraluminous features. Zircon U Pb isotopic analyses show that the high Si granite emplaced at 454 Ma with 800 to 1,100 Ma inherited zircon grains. Magmatic zircons from the high Si granite in the eastern Baoshan show similar Hf isotope compositions with those from coveal felsic intrusions in the Tibetan Plateau and its southeastern margin, implying their similar magmatic origin. Lines of evidence including mineral chemistry, zircon Hf isotopes, and geochemical simulation show a complex history of the high Si granite in eastern Baoshan: the parental magmas of the high silica granite originated from partial melting of the regional sedimentary rocks; the melts underwent high degree differentiation, and then assimilated wall rock during emplacement; some minerals experienced solid state re equilibration after cooling. Similarities of the high Si granite in eastern Baoshan and the coeval Pinghe batholithin geochemical features imply their parallel processes of their petrogenesis.