松辽盆地变质核杂岩和伸展断陷的构造特征及成因

文中讨论了松辽盆地北部中央基底隆起变质核杂岩和徐家围子伸展断陷的构造特征、成因和演化 ,重点讨论了下列问题 :( 1)中央基底隆起变质核杂岩具有科迪勒拉变质核杂岩的许多特征 ;( 2 )识别出组成中央基底隆起变质核杂岩的多层次、低角度韧性拆离体系 ,它们是使中地壳的中深变质岩层抽拉至上地壳的主要原因 ;( 3)穹窿状火山岩台地于晚侏罗世 ( 145.7±6.2 )Ma形成 ,受顶部拆离断层控制的伸展断陷于早白垩世 ( 133～ 12 0Ma)形成 ,而邻近顶部拆离断层的糜棱岩年龄为 ( 12 6.7± 1.54)Ma。这表明变质核杂岩的形成始于晚侏罗世。早白垩世递进的伸展构造与变质核杂岩较深部的部分上拱至地表相伴生 ,推测该变质核杂岩的上拱和剥露、火山岩台地和伸展断陷盆地的形成可能是由伊泽奈奇和亚洲板块陆陆碰撞后的地幔拆沉作用、地幔的岩浆底侵作用以及伸展垮塌作用联合造成的。

STRUCTURAL CHARACTERISTICS, ORIGIN AND EVOLUTION OF METAMORPHIC CORE COMPLEX IN CENTRAL BASEMENT UPLIFT AND XUJIAWEIZI FAULTED DEPRESSION IN SONGLIAO BASIN, NORTHEAST CHINA

The structural characteristics, origin and evolution of the metamorphic core complex of the central basement uplift and Xujiaweizi faulted depression in northern Songliao basin are discussed and several points have been emphasized as follows: (1) The central basement uplift metamorphic core complex displays many of the structural characteristics of Cordillerian metamorphic core complex; (2) Multi-layered low-angle ductile detachment systems which consist of the central basement uplift are recognized, and they have been the main factors enabling middle grade metamorphic rocks to be brought from middle crust to upper crust;(3) The volcanic dome-shaped platform were formed during the Late Jurassic (145.7±6.2)Ma, the extensional faulted depressions controlled by top-detachment fault were formed the Early Cretaceous (133～120 Ma), while the age of mylonites near top-detachment fault in Well Fang deep-3 is (126.7±1.54)Ma. These imply doming and exhumation of the central basement uplift were also generated since the Late Jurassic. Progressive extension tectonics was associated with upwarping of the deeper parts of this core complex to the surface during the Early Cretaceous. It is suggested that doming and exhumation of this core complex, formation of extensional faulted depression, are driven by mantle delamination, magmatic underplating of mantle and extensional collapse following the continental collision of Izanazi plate and Asia plate.