辽宁本溪地区新太古代晚期钾质花岗岩的发现及其地质意义

The Discovery and Geological Implications of Late Neoarchean Kaligranites in Benxi Area,Liaoning Province

辽宁本溪地区位于华北克拉通东部陆块东北部,区内广泛发育新太古代深成侵入岩和变质表壳岩,尚无钾质花岗岩的报道。钾质花岗岩的形成过程是早期陆壳发育成熟和稳定的重要标志,本次钾质花岗岩的发现对系统的研究华北克拉通早期陆壳的形成与演化具有重要的价值。本文对本溪地区马家沟的钾质花岗岩进行了岩石学、成岩年代学、岩石地球化学的研究,探讨了岩石成因和形成的构造背景。马家沟岩体为片麻状中细粒黑云母二长花岗岩。锆石U-Pb测年数据显示,岩石^(207)Pb/^(206)Pb加权平均年龄为(2490±21)Ma,形成于新太古代晚期。该岩体属弱过铝质、高钾钙碱性系列钾质岩石;主要富集高场强元素La、Zr、Th及大离子亲石元素K、Nd等元素,亏损P元素、高场强元素Nb和大离子亲石元素Sr、Ti等;REE曲线为右倾型,负Eu异常,属于S型花岗岩。研究区钾质花岗岩岩浆主要来源于地壳,是变质泥岩部分熔融的产物,形成于活动大陆边缘碰撞造山后的伸展环境,代表华北太古宙克拉通固结基底形成之前的最后一次岩浆活动,标志着在新太古代晚期本溪地区微陆块已拼贴完成,并与其他地区一起构成稳定的华北太古宙克拉通。

The Benxi area of Liaoning Province is located in the northeastern part of the eastern North China craton,where Neoarchean plutonic intrusive rocks and metamorphic supracrustal rocks are widely developed,but no kaligranites have been reported.The formation process of kaligranites is an important symbol of the maturation and stability of the early continental crust.The discovery of kaligranites is significant for the systematic study of the formation and evolution of the early continental crust in the North China craton.In this paper,the petrology,diagenetic age,and petrogeochemistry of kaligranites in Majiagou,Benxi area are studied,and the petrogenesis and tectonic setting of formation are discussed.Majiagou pluton is a gneissic medium-fine-grained biotite monzogranite.The zircon U-Pb dating data show that the^(207)Pb/^(206)Pb weighted average age is(2490±21)Ma,suggesting the kaligranites formed in the Late Neoarchean.The granite is weakly peraluminous and high potassium calc alkaline kaligranite.The high field strength elements La,Zr,Th and large ion lithophile elements K,Nd are enriched,while high field elements P,strength elements Nb and large ion lithophile elements Sr,Ti are depleted.The REE partition curve is rightward with negative Eu anomalies,indicating S-type granite.The magma originated from the crust and the product of partial melting of metamorphic mudstone,which formed in an extensional environment after collisional orogenesis at active continental margins.It represents the last magmatic activity before the formation of the consolidated basement of the Archean craton in North China,and marks the completion of the collage of micro-blocks in Benxi area in the Late Neoarchean,and together with other regions,forming a stable North China Archean craton.