本文根据INDEPTH-Ⅳ剖面所做的地质?地球物理探测所取得的资料,进行综合研究,提出了一个新的昆仑山造山模式,论述了:(1)在早二叠世松潘—甘孜洋向昆仑—柴达木地块下俯冲使地块南缘形成陆缘弧和弧后拉张区,使昆仑—柴达木地块在持续碰撞挤压过程中,分别形成了造山带与古近—新近纪盆地的不同构造演化特征;(2)昆仑地段老结晶基底在地块对挤中不断向上抬升成山,同时又受到强烈剥蚀,使老结晶基底及深成岩呈现在地表;南昆仑地块则沿昆仑地块中央断裂向北逆冲到北昆仑地块之上,断裂深10 km;昆仑地块没有发生向北逆冲推覆到柴达木地块上;(3)昆仑地块地壳增厚主要发生在中地壳(6.2~6.6 km/s),是中基性岩石层的增厚;(4)柴达木盆地作为昆仑弧弧后拉张地带,随昆仑造山隆升而下沉,新生界陆相沉积达12~14 km厚,由“沉积”与“挤入”两个作用造成了地壳增厚;结晶基底发生断陷形成新裂谷,裂谷宽度约12 km,深度约4 km,导电带显示裂谷通过断裂与深部发生热流体联系;(5)再次确定了,柴达木盆地莫霍界面深52 km,昆仑山的莫霍界面深65~70 km,莫霍界面台阶位于格尔木附近(185 km距离处);(6)松潘—甘孜地体复理石层厚度为10~14 km,其下面的6.2~6.3 km/s 均匀速度层(同时有高导电性显示)是本地块所特有,推测为残留洋壳的堆积,约15 km厚;浅层通过古近—新近系风火山推覆系增厚,另在中地壳部位挤入了15 km厚岩层;(7)否定了亚洲岩石圈地幔向柴达木地块地幔岩石圈之下俯冲的模式,提出印度大陆地幔岩石圈从高喜马拉雅下拆离成两层,并沿高原地壳底部向北伸展,直到中祁连山之下,成为高原南北对挤过程中岩石圈地幔长度调节的新方式?
Abstract:According to the information obtained by geological and geophysical work along INDEPTH- Ⅳ profile, the authors formulated a new model for the Kunlun Mountains orogeny based on detailed comprehensively studies. Some main viewpoints heldby the authors are as follows: (1)In the Early Permian, the subduction of Songpan - Ganzi Ocean toward the Kunlun- Qaidam block resulted in the formation of continental margin arc and extension area of arc. With the continuous collision and squeezing of Songpan - Ganzi and Kunlun-Qaidam blocks, there occurred different tectonic evolutions. (2)Old crystalline basement of Kunlun region was lifted up to form mountains and subjected to strong erosion during the face-to-face squeezing of the land masses, and hence the old crystalline basement and the plutonic rocks were exposed on the surface due to denudation. Kunlun terrane did not overthrust northward to the Qaidam. South Kunlun block thrust over the North Kunlun block, with the breaking depth reaching10 km. (3)The crustal thickening of Kunlun occurred mainly in the lower crust (6.2-6.7 km/s), mainly mafic lithosphere. (4)As the back- arc extension zone of the Kunlun Mountains, the Qaidam Basin was uplifted and experienced subsidence with the Kunlun orogenic uplift, and Cenozoic sedimentary thickness was 12- 14 km resulting from two sorts of actions (deposition and compression). Crystalline basement underwent rifting and formed a new rift, with the width of rift being about 12 km and the depthbeing about 4 km. The conductive zone implied that the rift was connected with the deep thermal fluids through the fracture. (5)The Moho depth of the Qaidam Basin is 52 km, that of the Kunlun Mountains is 65-70 km, and the Moho level lies near Golmud (with a distance of 185 km). (6)The flysch layer thickness of Songpan-Ganzi terrane is 10-14 km. Shallow layers were thickened by Tertiary Fenghuoshan thrusting. The underlying uniform velocity layer (with high conductivity display) is 6.2-6.3 km/s, which is a unique phenomenon of the terrane. The thickness of the accumulation of residual oceanic crust was 15 km, the shallow layer was thickened through Tertiary volcanic nappe system, and 15 km of thick rock bed squeezed into middle crust. (7)The model that Asian lithospheric mantle subducted into the Qaidam mantle lithosphere was denied. The authors hold that the Indian continental lithosphere mantle was separated into two layers, stretching northward along the bottom of the plateau and was subducted over the lithosphere mantle of Qaidam. That is a new way of length adjustment caused by the squeezing process of the north and south of the plateau.
赵文津 吴珍汉 史大年 薛光琪 宿和平 Karplus M S Mechie J 宋洋 杨宏伟 刘志伟. 昆仑山深部结构与造山机制[J]. 中国地质, 2014, 41(1): 1-18.
ZHAO Wen-jin, WU Zhen-han, SHI Da-nian, XUE Guang-qi, SU He-ping, Karplus M S, Mechie J, SONG Yang, YANG Hong-wei, LIU Zhi-wei. Deep structure and orogenic mechanism of the Kunlun Mountains[J]. Geology in China, 2014, 41(1): 1-18(in Chinese with English abstract).