松辽盆地西缘断裂带中花岗质糜棱岩的锆石SHRIMP和云母氩-氩年龄及其构造意义

松辽盆地西缘发育大型的北北东走向韧性断裂带,该韧性断裂带的性质、活动时限一直存在争议,制约了对松辽盆地构造成因的认识以及松辽盆地西缘油气勘探开发的进展。腾克、金星及嘎拉山地区是松辽盆地西缘韧性断裂带的代表性出露区,主体岩石组合为条带状花岗质糜棱岩、眼球状花岗质糜棱岩等。腾克、金星及嘎拉山地区发育一组糜棱面理和线理,其中面理为110°~135°∠45°~65°、线理为倾伏向10°~25°,倾伏角10°~35°;其运动性质均显示左行走滑特征。确定韧性断裂带活动时限的样品采自构造带内花岗质糜棱岩的锆石和同变形云母,其中锆石SHRIMP谐和年龄为296.9~299.4 Ma;黑云母⁴⁰Ar-³⁹Ar年龄为(123.0±0.7)Ma,白云母的⁴⁰Ar-³⁹Ar年龄为(124.4±0.9)Ma。松辽盆地西缘韧性断裂带应该属于嫩江断裂带的北段。年龄结果表明该韧性断裂带中花岗岩侵位于晚石炭世,大型北北东向韧性构造变形发生于早白垩世。腾克金星嘎拉山剪切带控制松辽盆地西缘,同时表明松辽盆地在早白垩世经历了走滑挤压盆地演化阶段,这种大型北北东向韧性断裂带的形成可能与当时西太平洋伊泽纳崎板块向欧亚大陆俯冲发生转向有关。

SHRIMP U Pb Zircon Dating and Mica Laser 40 Ar 39 Ar Ages of the Granitic Mylonites in Ductile Fracture Belt in the Western Songliao Basin and Its Tectonic Implication

The large NNE trending ductile shear zone extends along the western boundary of Songliao basin.Its kinematics and movement age have not been thoroughly studied,which limits the study of the tectonic evolution and the oil and gas exploration of Songliao basin.Tengke,Jinxing, Galashan are typical outcrops of the ductile shear zone and they consist of banded granitic mylonite and augen granitic mylonite.There is one set of mylonitic foliation and lineation in Tengke,Jinxing and Galashan ductile shear zones.The foliation is ca.1 10° 135°∠45° 65°with a lineation of ca.10° 25°to 10° 35°.The motion indicates that the three ductile shear zones are left-lateral strike-ship faults.In this study,the SHRIMP zircon U Pb dating from a granitic mylonite gives an age of 296.9 299.4 Ma,the biotite laser 40 Ar 3 9 Ar dating of the same rock samples yields an age of (123.0 ±0.7)Ma,while the muscovite laser 40 Ar 3 9 Ar dating of the same rock samples yields an age of (124.4 ± 0.9 )Ma.The ductile fracture belt in the western Songliao basin should belong to the northern Nenjiang fault.The age indicates that the protolith of the granitic mylonite is formed in Late Carboniferous and its deformation from the same sample was in Early Cretaceous.These ages show that Songliao basin experienced transgression evolution,and the western boundary was controlled by the Tengke Jinxing Galashan shear zone during Early Cretaceous.In consideration of the regional tectonic setting of the Northeastern China,we believe that the formation of this large-scale ductile shear zone with NNE trending might be related to the subduction of Izanagi plate under Eurasian plate.