Research On The Late Paleozoic-Early Mesozoic Orogeny In East Kunlun Orogen

East Kunlun Orogen is a compound orogenic belt having a long geologicalhistory, overprinted by different orogenic phase and different type orogeny. Theirdeveloped an ocean system relating to Prototethys Ocean and its evolution process isintact, and is controlled by the Paletethys Ocean lying in the southern margin of theEast Kunlun tectonic belt in late Paleozoic-Mesozoic. Thus, East Kunlun Mountain isa unique area in which we can detaidly study the compound orogeny and formationevolution. This thesis mainly focus on the composition, sedimentary filling sequences,basin protype, magmatic arc attribute, structure of orogenic belt, tectonic deformationcharacteristics with comprehensive research of structure, sedimentary, petrology,zircon U-Pb geochronology and geophysics, on basis of which we rebuild theevolution history in late Paleozoic-early Mesozoic and discuss the orogenic process.Until now, some new points have been achieved as follows:1、On the basis of depositional filling sequence of East Kunlun orogen(easternsegment) in late Paleozoic-early Mesozoic, this thesis restore the basin protype andevolution sequence. According to the results of basin depositional system, combiningseveral important unconformity and other regional geological data, we realized thatthe protype basins are faulted basin developed on the Palo-continent in Devonian,shallow-water basin developed on the continental margin in Carboniferous toearly-middle Permian, forarc basin in late Permian to middle Triassic, forland basin inlate Triassic and fault basin in early Jurassic, respectively in East Kunlun area. EastKunlun is located in the passive continental margin, as Buqingshan location in thelimited ocean basin in the south of which developed some seamounts. In other words,the passive continental margin system indicated by the depositional characteristic ofEast Kun area formed in the background of the Paleotethys Ocean extension regime.East Kunlun orogen evoluted passively with the Buqingshan-Anemaqen Ocean, thisconclusion is significant to reconstruct the late Paleozoic framework and study thecompound orogeny of East Kunlun Orogen.2、Halagatu granite in eastern segment of East Kunlun Orogen consists of granodiorite, monzonitic granite, potassium granite, with large quantities of dioriticenclaves in general. The major element and rare element characteristics show that itwas formed in volcanic arc or continental arc setting. The granite intruded in thePrecambrian strata between256Ma and247Ma in age. The chronology andgeochemical characteristic indicated that Buqingshan-Anemaqen Paleotethys Oceanbegan to subduct in late Permian, and the polarity of subduction is northward.Helegangxilikete granite mainly consists of granodiorite with many dioritic enclaves.The geochemical feature and the other geological data prove that the granite formedin post-collision setting, and the petrogenesis is related to the breakoff of subductioncrust. It is obtained that the granite age is225Ma, belong to middle stage of lateTriassic. The ascertainment of Helegangxilikete granite can provide new constraint topost-collision orogeny in middle stage of late Triassic.3、According to the tectonic deformation feature, statistic results of someattitudes, regional unconformity, and difference deformation style, the latePaleozoic-early Mesozoic strata were divided into three important tectonic layer andfour tectonic deformation sequence. The first phase of deformation is characterized byfold deformation in the shallow tectonic level of the earth’s crust in subduction stage,and the fold style is relatively wide. The second phase of tectonic deformation ischaracterized by tight fold accompanying the fault structure in the shallow tectoniclevel, and this deformation is related to the collision orogen in the late stage of middleTriassic to early stage of late Triassic. The third phase of deformation is characterizedby wide fold and thrust structure in upper tectonic level of crust, and closely related tothe intro-continent orogeny. The fourth phase of deformation is characterized bycrritle fault in surface-seated tectonic level, closely related to the inhomogeneousuplift of Qing-tibet plateau and eastward lateral extrusion escape in Cenozoic.4、 By comprehensive research of basin filling sequence, basin protype,magmatic response to orogeny, tectonic deformation sequence, we draw a preliminaryconclusion that East Kunlun Orogen suffered several tectonic movement in latePaleozoic-early Mesozoic, i.e, subduction orogeny in late Permian to middle Triassic,collision orogeny in middle Triassic to early stage of late Triassic, post collision in middle-late Triassic, intro-continent orogeny in late-middle Jurassic, in which thecollision orogeny is the most strongly tectonic movement forming the main tectonicframework in East Kunlun and adjacent area.5、 East Kunlun developed a small Ocean basin system represented byQingshuiquan ophiolite, Wutuo ophiolite, and Kekekete mafic-ultramafic rocks in latestage of Neoproterozoic to early Cambrian. From middle Cambrian on, the oceaniccrust began to subduct and collide followly, and produced some arc magmatic granitesand collision-type granites with the peak time being490～411Ma. It is concludes thatthe post-collision event taken place in the late Silurian in which the main tectonicframework formed. From late Paleozoic on, East Kunlun began to breakup on thebasis of early-middle Proterozoic crystalline basement and metamorphic foldbasement formed by Caledonian orogen, and turned into another tectonic evolutionstage related to Buqingshan-Anemaqen Paleotethys Ocean closely. Subductionorogeny in late Permian to middle Triassic, collision orogeny in middle Triassic toearly stage of late Triassic, collision orogeny in middle-late Triassic, intro-continentorogeny in late-middle Jurassic followly overprinted on the Pre-Caledonian orogeny,and form the present main tectonic framework. In a word, East Kunlun Orogen is acontinental compound orogenic belt having a long geological history, overprinted bydifferent orogenic phase and different type orogeny. So research on these issues inEast Kunlun has important theoretical value and actual significance to discuss thecompound orogenic regime and orogenic dynamics.