辽东营口—辽阳地区古元古代花岗岩和变质基性岩形成时代及意义

Paleoproterozoic Granites and Meta-mafic Rocks from Yingkou-Liaoyang Area of the Eastern Liaoning and Their Significance

辽东地区保存有较为完好的古元古代地质记录。对位于辽东营口—辽阳地区古元古代花岗岩(建一花岗岩)和变质基性岩(隆昌变质辉绿岩和蒜盘峪变质辉长岩)进行了锆石U-Pb定年、地球化学和岩石成因学研究。结果表明:建一花岗岩形成于(2 322±18)Ma,隆昌变质辉绿岩形成于(2 335±21)Ma,蒜盘峪变质辉长岩形成于(2 353±22)Ma;建一花岗岩源自太古宙古老地壳部分熔融,属于准铝质钙碱性I型花岗岩,富集Rb、Ba、U等大离子亲石元素,亏损Nb、Ta、Zr、Hf等高场强元素,具有俯冲带岩浆特征;隆昌变质辉绿岩和蒜盘峪变质辉长岩均具有富集型洋中脊玄武岩(E-MORB)特点,并显示岛弧地球化学特征;隆昌变质辉绿岩源自新太古代富集程度不高的地幔部分熔融,并在上升过程中受到年轻地壳的改造,蒜盘峪变质辉长岩是古太古代—中太古代富集地幔部分熔融的产物;古元古代早期,辽吉地区处于大陆弧后盆地构造环境,弧后伸展作用导致大陆岩石圈部分熔融产生花岗岩和基性岩,在后期的地体拼贴过程中,两者遭受到不同程度的变质变形,进而形成了条痕状花岗岩和变质基性岩。

Paleoproterozoic geological records are well preserved in the eastern Liaoning.The zircon U-Pb dating,geochemical and petrogenesis of Paleoproterozoic granites（Jianyi granite）and meta-mafic rocks（Longchang meta-diabase and Suanpanyu meta-gabbro）in YingkouLiaoyang area of the eastern Liaoning were studied.The results show that LA-ICP-MS zircon UPb ages of Jianyi granite,Longchang meta-diabase and Suanpanyu meta-gabbro are（2 322±18）,（2 335±21）,（2 353±22）Ma,respectively;Jianyi Granite forms from partial melting of Archean crust,and belongs to metaluminous-calcalkaline I-type granite,and is enriched in large ion lithophile element（LILE）,and is depleted in high field strength element（HFSE）,showing the characteristics of magma in subduction zones;Longchang meta-diabase and Suanpanyu metagabbro belong to enriched mid-ocean ridge basalts（E-MORB）and have the geochemicalcharacteristics of island arc;Longchang meta-diabase is generated from partial melting of Neoarchean mantle which is not very enriched,and the diabase is contaminated by juvenile crust during upwelling;Suanpanyu meta-gabbro is produced from partial melting of PaleoarcheanMesoarchean enriched mantle;Liaoning-Jilin region is a continental back-arc basin in Early Paleoproterozoic,and the strong extension in the back-arc region results in partial melting of continental lithosphere,which generates the granites and meta-mafic rocks;these rocks are later metamorphosed,deformed and pushed together in later processes of terrane amalgamation.