辽东桓仁西部古元古代侵入岩年代学及岩石地球化学

华北克拉通东部辽东地区出露古元古代侵入岩,为准确认识辽东地区古元古代构造演化过程,选取北沟岩体、正岔岩体和树柳林子岩体的岩相学、岩石地球化学及年代学特征,探讨了岩体的形成时代、岩石成因及其构造环境。锆石SHRIMP U-Pb年代学研究表明,柳林子岩体年龄为(2 490±8) Ma,北沟岩体年龄为(2 457±11) Ma。北沟岩体高硅富钾,富集Rb、U、Th、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,为过铝质高钾钙碱性I型花岗岩,Nb/Ta平均值5. 75,Rb/Nb平均值4. 21,源于太古宙古老地壳的部分熔融;正岔岩体高硅富钾,富集Rb、Ba、U、Th、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,为弱过铝质高钾钙碱性A型花岗岩,Nb/Ta平均值16. 06,Rb/Nb平均值4. 81,源区可能由幔源岩浆底侵带来的热量加热地壳,导致其重熔并与之混合后形成的。柳林子岩体为变质角闪辉长岩,呈亚碱性,富集Rb、Ba、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,显示其岩浆可能形成于受陆壳微弱混染的软流圈地幔或岩石圈地幔。认为研究区古元古代侵入岩形成于东、西陆块碰撞拼合后的后造山挤压向板内伸展转换的构造环境,为构造体质转换的产物。

Geochronology and Geochemistry of Paleoproterozoic Intrusive Rocks in Western Huanren Area,Eastern Liaoning Province

Paleoproterozoic intrusive rocks are widespread in the Eastern Liaoning Province (ELP), which is located in the eastern North China Craton (NCC). This paper reported the petrography, geochemistry and geochronology of the Beigou, Zhengcha and Liulinzi plutons in the Kaiyuan area of the eastern part of the northern NCC margin. We discussed the formation age, petrogenesis and tectonic environment of these plutons. Zircon U-Pb dating shows that both the Liulinzi (2,490±8 Ma) and Beigou (2,457±11 Ma) plutons were formed in the Early Paleoproterozoic. The Beigou intrusive rocks have higher SiO₂ and K₂O contents, and are enriched in large ion lithophile elements (LILEs, e.g., Rb, K, U and Th) but depleted in high field strength elements (HFSEs, e.g., P, Nb and Ti), with Nb/Ta=5.75 and Rb/Nb=4.21. These features indicate that the Beigou pluton is metaluminous calc-alkaline I-type granite, which was likely originated from the partial melting of lower crust. The Zhengcha pluton samples have higher SiO₂ and K₂O contents. They are also enriched in LILEs and depleted in HFSEs, with Nb/Ta=16.06 and Rb/Nb=4.81. These features indicate that the Zhengcha pluton is metaluminous calc-alkaline A-type granite, which was most likely originated from the partial melting of lower crust with minor mantle-derived input. The Liulinzi meta-gabbro is sub-alkaline, enriched in LILEs and depleted in HFSEs, indicating that the magma may have derived from the depleted mantle with crustal contamination in an intracontinental extension setting. Combined with previous studies, magmatic rocks of the study area may have formed under a compressional to extensional tectonic transition regime after the collision between the Eastern block and the Western block of the NCC.