Precambrian Tectonic Of South Margin Of Tarim Basin, NW China

Precambrian time covers approximately 90% of geologic time of the Earth's history, starting with the Earth's creation about 4.5 billion years ago and ending with the initial formation to the beginning of life almost four billion years later. During this time range, the Earth, Sun and Moon formed. As the Earth cooled, it developed its initial atmosphere and ocean, and life in the end period. Studies on early stage of the evolution of the Earth are important for us to implore the formation and evolution of earth and its planetary neighbours.In China, there are three old cratons:the North China craton, the Yangtze craton and the Tarim craton. Tarim craton is located in the northwest of China. In the past time, lesser work of Precambrian research has been done on the Tarim craton than that of the North China craton and the Yangtze, owning to the adverse environmental and poor traffic conditions.In this paper we subject previously proposed correlations for Precambrian terrains (Tiekelike and Altyn) of south margin of Tarim to a series of rigorous geochronological, geochemical and metamorphic petrology tests, based on new LA-ICP-MS U-Pb ages on granites, volcanics and sedimentary successions. This study provides insight into the timing nature of the magmatism of the Tarim during the Precambrian. Base on the detrital provenance study from clastic sedimentary rocks in the Tiekelike and Altyn, I hope to infer the Neoproterozoic tectonic evolution and palaeogeography of the south margin of Tarim relative the formation and the break-up of Rodinia. Additionally, I hope to clarify the crust evolution of the south margin of Tarim and its nature, whether by juvenile accretion, or by reworking of the rocks involved in the Precambrian.The main viewpoints and conclusions in this thesis are as follows:(1) Five U-Pb zircon age groups from South margin of Tarim show the Archaean-Palaeoproterozoic evolutionary history between 2.7 and 1.8 Ga:ca.3.6 and 2.7 Ga continental growth events at ca. Archean; the cratonization at ca.2.6-2.4 Ga; and the 2.0-1.83 Ga metamorphic event, suggest that the remnants of Paleoproterozoic orogens relative to the assembly of Columbia supercontinent.(2) Our study also places tight constraints on the age of Precambrian sedimentation. The youngest zircon population would represent a good approximation of the maximum age of sedimentation. In this studies, the Precambrian sequences in Tieleleke, the namely Paleoproterozoic-Mesoproterozoic Ailiankete Group, Kalakashi Group and Sailajiazitage Group, Mesoproterozoic-Neoproterozoic Sukuluoke Formation and Nanhua System Qiakemakelike Formation were defined to the Neoproterozoi strata. These strata are mainly composed by the clastic rocks deposited at ca.834-849 Ma and volcanic rocks emplaced between 780 and 789 Ma. Granitoids were intruded at different times during 787-845 Ma in Tieleleke. In Altyn Tagh, the namely Archean-Paleoproterozoic Altyn Group. Jixian System Taxidaban Group and Changcheng System Bashikuergan Group were defined to Neoproterozoic sequences by new detail LA-ICP-MS zircon dating. In this region, the Precambrian granitoids yielded mainly 900-930 Ma ages.(3) The nature and time of Neoproterozoic (930-700 Ma) mamgamtic rocks in the south margin of Tarim Block were identified. This study presents data for ca.787 Ma intraplate volcanic rocks and A-type granites in Tiekeleke. In Altyn, there are syn-collision granites at 900-930 Ma and post-collision granites at ca.703 Ma. These mamgatism probably reflect supercontinent Rodinia assembly and break-up in the south margin of Tarim Block.(4) Danshuiquan Ky-Grt-bearing felsic HP granulite and Jianggelesayi UHP Grt peridotites suggest the Altyn Group underwent the HP-UHP metamorphism. The Altyn Group represents the Neoproterozoic crust exprenced Early Paleozoic reworking at-500 Ma related to the subduction and exhumation.The peak metamorphic mineral assemblage in garnet-kyanite-bearing felsic gneiss from Altyn Group of Danshuiquan, indicates that the gneiss is a suit of high-pressure granulite, and the metamorphic condition is T=950-1000℃, P=2.42-2.49 Gpa according to the GASP barometers. Petrology and P-T estimations of the Yinggelesayi garnet peridotites recorded the transformation from early spinel peridotite into garnet peridotite (peak stage at 4.2-6.0 GPa and 920-990℃) into amphibole garnet peridotite stage into spinel peridotite stage. The P-T evolution is interpreted as a result of subduction and exhumation processes. Combined with information on compositions of whole rocks and minerals, P-T estimations and field relationships, the UHP garnet peridotites from the South Altyn Tagh is assumed to have been formed as cumulates crystallized from a mantle-derived magma intruded the continental crust, and was then subducted to depths of more than 100 km, and then metamorphosed in ultra-high-pressure conditions at-500 Ma.(5) U-Pb ages of detrital zircons from the new defined Neoproterozoic part of Tiekelike and Altyn were used to constrain the palaeogeography and provenance on the southern margin of Tarim during the Neoproterozoic. At the Late Neoproterozoic, the southern margin of Tarim representing an extension rift basin or extension continental sea basin. There are some significant differences in zircon age populations have been found in the sequences of the two tectonic units, although they show the same dominant age populations and even the same minor peaks in the late Neoproterozoic input.The Altyn Group deposits with a large input of early Paleozoic, early Neoproterozoic and Mesoproterozoic zircons while no peaks of cratonic Paloproterozoic ages, and records the Grenvillian magmatism and age surce, suggesting an active margin arc setting. The Bashikuergan Group, with the age peaks of 647 Ma,770 Ma,843Ma,905Ma,1350 Ma,1900Ma和2600Ma, show the older detritus from the cratonic Paloproterozoic Milan Group and the relative proportions of early Neoproterozoic and late Mesoproterozoic zircons from the Altyn Group. The Bashikuergan Group are preserved may have been located at the back-arc basin, attached to the arc-system.The sediments preserved in Tiekelike show the same dominant age populations: 2500-2700 Ma,2200-2300 Ma,1800-1950 Ma,835-850,787-800 Ma. But the Sukuluoke Formation and Qiakemake Formation from the northern of Tiekelike have its youngest detrital zircon population is 830 Ma, however the southern of Tiekelike has a younger depositional age constraint of 744-780 Ma which is younger than northern units of Tiekelike. Combined with the extensional magmanism in Tiekelike, we interpreted the Tiekelike as an south-ward deeping extension continental sea basin at Neoproterozoic.(6) Zircon Hf isotope analyses indicate that the Paleoproterozoic basement of Tiekeleke is a consequence of juvenile addition and Archean crust-reworking; And the Neoproterozoic crust display a contribution of Paleoproterozoic components reworking.Heluositan Group indicates the gneisses formed by melting of Archean crust (2.8 Ga) at 2.33 Ga. The second and third stage at ca.2.27-2.21 Ga and 2.08 Ga represent the reworked crust during compressive stresses. Zircon Hf isotopic data from Sailajiazitage Group show that older zircons (-1994 Ma) have crustal model ages are 2272-2784 Ma, suggesting an ancient crustal growth and reworking. The-787 Ma zircons have-2000 Ma crustal model ages, suggesting derivations from recycled Paleoproterozoic material.