山西五台群变质砂岩的物源和构造环境

华北克拉通中北部五台杂岩中出露一套变质砂岩,归属于上太古界五台群,其物质来源和构造环境分析对理解本区新太古代末期的地壳演化具有重要意义.该变质砂岩主要由石英、长石和粘土质胶结物组成,岩相学特征显示为杂砂岩,利用主量、微量元素判别的结果与岩相学观察一致.岩石地球化学分析结果显示,样品的SiO2含量变化较大(64.51％～...

Provenance and tectonic setting of metamorphosed sandstones of the Wutai Group of Shanxi Province, China

A suit of metamorphosed sandstones of the Wutai Group in the Wutai Complex,North Central North China Craton was recognized recently.Their provenance and tectonic setting are vital for further understanding on the Late Neoarchean crust evolution in this area.The metamorphosed sandstones are mainly composed of quartz,feldspar and clay cement.The petrographic characteristics show that they are greywackes,which is consistent with the result distinguished by their major and trace elements compositions.The geochemical features show that they have relatively large variation of SiO₂content(64.51%~71.80%),and relatively low maturity(SiO₂/Al₂O₃=3.98~4.73).Their chemical index of alteration(CIA),chemical index of weathering(CIW)and plagioclase index of alteration(PIA)are 60~76,63~91 and 61~89,respectively,which indicate that the protolith of the metamorphosed sandstones was formed by rapid transportation and deposition of near-source weathered clasts.Compared with ratios of immobile elements(such as Th/La,Sm/La,Zr/Hf,Y/Ho)of the potential source rocks,the provenances of metamorphosed sandstones are mainly from acidic volcanic rocks.This result is highly similar to those of sedimentary materials of the continental island arc which were mainly derived from acidic volcanic rocks.The discrimination results of trace elements on tectonic setting also show that the characteristics of the sandstones assemble those of the continental island arc.Consequently,we consider that the metamorphosed sandstones of the Wutai Group,North China Craton,were formed in a continental island arc setting in the Late Neoarchean.