1. 中国科学院地质与地球物理研究所, 北京, 100029; 2. 美国麻省理工学院地球、大气及行星科学系 Cambridge MA 02139
THE LAJISHAN FAULT BELT IN QINGHAI PROVINCE: A MULTI-STAGED UPLIFTING STRUCTURAL WINDOW
Wang Erchie1, Zhang Qi1, Clark B. Burchfiel2
1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029; 2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, 02139 USA
The Qilian Shan fold belt constitutes the northeastern margin of the Tibetan plateau and can be divided into three major tectonic elements, among which the northern and central parts are characterized as a suture zone of Early Paleozoic age and a metamorphic belt of Proterozoic age, respectively, whereas the southern part is composed of a set of deposits formed in passive continental margin with age ranging from Silurian to Triassic . Marked by a high mountain range, the Lajishan fault belt extends within the eastern part of the central Qilian Shan in a NW-SE direction. Our recent field studies show that the Qilian Shan orogenic belt was shortened in N-S direction in the Middle Paleozoic along the Qilian Shan central thrust fault, along which the ophiolite and island arc volcanic rocks of Early Paleozoic age of the northern Qilian Shan subducted southward for a long distance under the high-grade metamorphic rocks of Proterozoic age of the central Qilian. Resulted from intracontinental convergence of the Tibetan plateau occurred in the Late Paleozoic and Late Mesozoic, the ophiolite and volcanic rocks overlain by the high-grade metamorphic rocks of the central Qilian Shan were folded and exhumed to the surface along the Lajishan fault belt. By the Late Cenozoic, trigged by collision between the Indian plate and Eurasia, the Lajishan fault belt underwent rapid uplift along its northern and southern boundary thrust faults, divided the central Qilian Shan into two parts. We suggest here that the Early Paleozoic ophiolite and island arc volcanic rocks along the Lajishan fault belt are the allochthon within a structural window, instead of an continental rift, as some previous studies proposed.