地质学报2018，Vol.92Issue(5)：887-907,21.
鞍山地区始—古太古代花岗质地壳的形成及演化——深沟寺杂岩的岩石学、年代学及地球化学证据
Formation and Evolution of Eo-Paleoarchean Granitic Crust in the Anshan Area: Evidence from Petrology, Geochronology and Geochemistry of the Shengousi Complex
摘要
Abstract
Anshan is the only area in the North China Craton which preserves one complete set of Archean geological record (3.81 ～ 2.5 Ga).In this paper,detailed petrological,chronological and geochemical studies were carried out on the typical Archean Shengousi complex to further understand the formation and evolution of the early granitic crust.Petrologic and occurrence analysis of the Shengousi complex section determined two major rock units:Eoarchean trondhjemitic gneiss and Paleoarchean migmatitic gneiss complex.SIMS zircon U-Pb ages demonstrate that the trondhjemitic gneiss formed at 3803± 9 Ma,which represents the Eoarchean trondhjemitic crust.The migmatitic gneiss complex has an age of 3311～3335 Ma,representing a Paleoarchean tectonic-metamorphic thermal event.The Eoarchean trondhjemite is characterized by high Si and Na and poor K,weakly fractionated rare earth element (REE) patterns ((La/Yb)N =6.76～35.96)with negative Eu anomalies (δEu=0.57～1.43),and rich in Rb,La,Hf and Zr,poor in Nb,Ta,Sr and Ti,low Sr/Yratios (8～29),Mgnumbers (21～30),Cr (8.81×10-6～28.00×10-6) and Ni (0.881×10-6～18.55 ×10-6) concentrations,indicating that the magmas formed relatively shallow,no mantle material was involved,and not balance reaction occurred within garnet and plagioclase,with plagioclase remained within the source area.Combined with the fact that ～3.8 Ga zircon of the Anshan area has a positive εHf(t) value,the Eoarchean trondhjemite may derive from a juvenile crust by partial melting of aqueous basaltic rocks (amphibolite) at the bottom crust due to mantle magma upwelling.The main mineral assemblages of the Paleoarchean migmatitic gneiss complex are quartz+plagioclase+biotite,without non-uniform phase minerals (e.g.,potassium feldspar,sillimanite and garnet),indicating that no dehydration reaction occurred within hydrous minerals and the melting reaction is Qtz+ Pl±H2O=melt.Moreover,neither aluminous mineral nor clastic structure has been found in the migmatitic gneiss complex,indicating that it should be orthogneiss with protolith rock likely being trondhjemite or tonalite.A large amount of Eoarchean inherited zircons has been found in the Paleoarchean migmatitic gneiss complex,and εHf(t) of the ～3.3 Ga zircons are mostly negative,suggesting that it formed from remelting of the Eoarchean trondhjemitic crust.This study results suggest that evolution of the Eo-Paleoarchean granitic crust in the Anshan area can be divided into two main stages:Eoarchean trondhjemitic juvenile crust growth (～3.8 Ga) and Paleoarchean granitic crust re-melting event (～3.3 Ga).关键词
太古宙/锆石U-Pb定年/部分熔融/地壳演化/鞍山Key words
Archean/zircon U-Pb dating/partial melting/crustal evolution/Anshan引用本文复制引用
张家辉,金巍,王亚飞,李斌,蔡丽斌..鞍山地区始—古太古代花岗质地壳的形成及演化——深沟寺杂岩的岩石学、年代学及地球化学证据[J].地质学报,2018,92(5):887-907,21.基金项目
本文为中国科学院岩石圈演化国家重点实验室自主研究课题(编号Z1005)和中国地质调查局二级项目(编号DD20160042)资助成果. （编号Z1005）
