辽西台里地区新太古代片麻岩杂岩的形成时代、岩石成因和地质意义

Geochronology, petrogenesis and geological significance of the Neoarchaean gneiss complex in Taili area of western Liaoning Province

辽西台里地区片麻岩杂岩主要由片麻状花岗岩、黑云斜长片麻岩、角闪斜长片麻岩组成.锆石U-Pb定年结果表明,该套杂岩形成于2 510～2 559 Ma,与“绥中花岗岩”时代相同,同属华北克拉通新太古代结晶岩石.野外产状和岩石组构特征显示,本区片麻岩杂岩为一套同变形的深熔型混合岩.其中,角闪斜长片麻岩代表低度熔融的“古成体”,其间分布少量具“浅色体”特征的长英质岩脉;黑云斜长片麻岩为熔融程度较低的“残留体”;片麻状花岗岩为部分熔融程度最高的“新成体”.它们在矿物组成和地球化学上呈现良好的递变关系.结合前人Hf同位素研究资料,本文认为台里地区片麻岩杂岩可能记录了一期重要的陆壳再造事件.

The Taili gneiss complex is exposed in the western Liaoning Province and mainly composed of gneissic granites,biotite plagioclase gneisses and hornblende plagioclase gneisses.Zircon U-Pb dating of these rocks indicates that the gneiss complex was formed in the late Neoarchaean （2 510～2 559 Ma）,with ages similar to those of the ＂Suizhong granite＂.This suggests that the Taili gneiss complex is an important part of Archean basement of the North China Craton.Field occurrences and rock textures suggest that the gneiss complex is a suite of migrnatites derived from syn-deformational anatexis,of which the hornblende plagioclase gneiss represents the ＂palaeosome＂,which was generated by a very low degree of partial melting with a few felsic veins inside.The felsic veins show the general characteristics of ＂leucosome＂.The biotite plagioclase gneiss represents the ＂residuum＂ after the low degree of partial melting,whereas the gneissic granite is the ＂neosome＂ characterized by the highest degree of melting.These rocks display a good gradational relationship in mineral content and geochemistry.In combination with previous zircon Hf isotopic data,the authors have reached the conclusion that the Taili gneiss complex originated from the anatexis of Mesoarchean ancient crust 2.8～3.0 Ga in age and recorded an important regional magmatic event of crustal reworking.