Precambrian And Early Paleozoic Magmatism,Mineralization And Tectonic Evolution Of The Eastern Central Tianshan,Nw China

Located between the Turpan-Hami and Tarim blocks,The Central Tianshan zone is an important component of the Tianshan tectonic belt and the Central Asian orogenic belt(CAOB).It is a crucial linkage between the Siberian,Kazakhstan,Turpan-Hami and Tarim blocks and a key for understanding the complex crustal evolution and collisional tectonics of the CAOB.This has enthused a number of studies dealing with Phanerozoic,especially post-late Paleozoic magmatism,tectonic framework and evolution and mineral deposits of the Central Tianshan zone and made numerous fruitful achievements.However,due to the scattered outcrops,high-dgree metamorphism,inconvenient transportation as well as the limitation of the previous research methods,little is known about the Precambrain and early Paleozoic magmatism,mineralization and tectonic evlution of the Central Tianshan.This has triggered various controversies on the tectonic affinity of the Central Tianshan basement and the early Paleozoic tectonic setting and tectonic evolution of the Central Tianshan.This dissertation started from the poorly studied Precambrian magmatism and mineralization events,combined with cases studies of the widely distrubited early Paleozoic granites and related metal deposits in the Central Tianshan,the Precambrian and early Paleozoic magmatism and mineralization of the Central Tianshan have been explored and discussed.Together with the previous studies,this dissertation also investigated the tectonic affinity of the Central Tianshan and constrained the earlyPaleozoic magmatism and mineralization of the Central Tianshan.On the basis of detailed field survey and petrograhic studies,the field contact relations,geological characteristics and mineral paragenesis were depicted.The formation ages of metal deposits and related magmatic rocks were determined using high-precision LA-ICP-MS zircon U-Pb dating.Integrated study of mineralogy,petrography,whole-rock geochemistry and Sr-Nd isotopes and zircon Hf isotope was carried out to discuss the source rock characteristics,petrogenesis and tectonic setting of the ore-bearing magmatic rocks.Moreover,comprehensive analysis and study of the geological characteristics,ore source and ore-forming prosses of the related metal deposits,combined with comparative study,the relevant metalligenesis and the tetonic context of these metal deposits were investigated,which also provide theoretical basises for further regional resourse prospecting.This thesis presents a series of the Neoproterozoic rift-related magmatic activties and mineralization evidence in the Central Tianshan.It is first time reported the Neoproterozoic Hongliujing alkaline granite and metamorphosed volcanic rocks of Shalong iron deposit with precise isotopic age in the Central Tianshan.The Neoproterozoic rare metal mineralization associated with alkaline granite was confirmed.Comparative study of the global Neoproterozoic iron formations,combined with the REE(rare earth elements)characteristics of the ores,it is suggested that the Shalong iron deposit of the Central Tianshan is part of the Cryogenian global iron ore-forming event,which may be accomplied by the breakup of the Rodinia supercontinent and bimodal volcanic activity.Volcanic hydrothermal was indicated to involve in the iron ore-forming process of the Shalong iron deposit.During the early Paleozoic,the Central Tianshan is considered to be a magmatic arc tectonic settting and occurred mineralization related to the arc magmatism according to studies of the early Paleozoic magmatic rocks and related metal deposits in the Central Tianshan.LA-ICP-MS zircon U-Pb dating of the ore-hosting metavolcanic rock shows that the Tianhu iron deposit(the only large iron deposit in Central Tianshan)was formed in the early Paleozoic rather than the Neoproterozoic of previous thought.It is suggested that the Tianhu iron ore deposit should be a volcanic-sedimentary iron ore deposit formed in the background of island arc,and was subjected to the Caledonian metamorphism and the Indosinian magmatic hydrothermal overprint.Furthermore,the study of the Tianhudong porphyry Mo deposit in the Central Tianshan,together with the widely distributed Caledonian calc-alkaline granitoids in the Central Tianshan indicate that it is potential to find porphyry molybdenum deposits in the Central Tianshan area.Combined with the available studies and data,the preliminary framework of the Precambrian-early Paleozoic geological evolution of Central Tianshan could be proposed through a number of the LA-ICP-MS zircon U-Pb geochronology studies.The Central Tianshan preserves records of the Paleoproterozoic and Mesoproterozoic tectonic-magmatic event,the Central Tianshan also preserves the important imprints of Neoproterozoic rift-related magmatism and mineralization related to the breakup of the Rodinia supercontinent.The Precambrain tectonic-magmatic events and tectonic evolution of the Central Tianshan can be well comparable to the adjacent Tarim block.Furthermore,these two blocks show a number of common features,indicating the Central Tianshan zone may be a part of the Tarim block,and was separated from it during Early Paleozoic due to pull-apart caused by the southward subduction of the Paleoasian Ocean to the north of the Central Tianshan zone.The early Paleozoic arc calc-alkaline granitoids in the Central Tianshan zone should be the product of the southward subduction of the Paleoasian Ocean.However,due to the limitations of natural conditions of the study area and time constraints,the metallogenesis of the studied metal deposits is not fully investigated in this dissertation,which will be an important composition of the author's future work.