The Tarim Large Igneous Province Driven By Mantle Plume:Evidence From Sedimentary Record

The Early Permian Tarim Large Igneous Province, located in the southern part of Xinjiang Uygur Autonomous Region of the northwestern China, is another most important Large Igneous Province genetically linked with a mantle plume after the finding and study of the Emeishan Large Igneous Provincein China by the geologists. It has an important scientific significance and a good support on the exploration of mineral resources and oil and gas.The Early Permian Tarim Large Igneous has been related to a mantle plume mostly constrained by perology and geochemistry. However, the crustal uplift/erosion related to a mantle plume has rarely been addressedwhich can provide some good information to better understand the magma dynamics of the TLIP. In this thesis, combined with the study of Carboniferous — Lower Permian stratigraphic and sedimentary facies, and detrital zircon U-Pb age spectrum of Devonian— Lower Permian in Sishichang outcrop, to explore the sedimentary response of the Early Permian Tarim Large Igneous Province brfore it erupted. The conclusions are summarized as follow:Carboniferous-Permian unconformity has been documented by significant strata absence and exposed features such as dissolved poers and caves. Carboniferous strata in the Tarim Basin can be divided into six members on the basis of their lithology. In order to improve our understanding of crustal uplift/erosin we have studied the stratigraphy and sedimentology of eighty-five boreholes/outcrops and two seismic profiles. The results indicate a regional unconformity and onlap contact between the earliest Permian and Carboniferous strata, with denudation of Carboniferous and deposition of earliest Permian strata. The denudation of Carboniferous strata has been divided into three types of erosion:deep, partial and weak, with a deep erosion zone located in Northern Tarim region (east of Keping and west of Northern Tarim) which gradually weakens towards the south. This unconformity represents a spatial distribution of denudation forced by doming uplift/erosion at the end of the Carboniferous, after Xiaohaizi formation deposition, before Xiaoyiaoan stage (-302Ma), with minimum estimation of its vertical and lateral extent of 1000 m and ～300 kmrespectively.Through the analysis of detrital zircon U-Pb age spectrum of Devonian—Lower Permian in Sishichang outcrop, two important issues have been comfirmed. One is the finding that, Tarim Basin was characterized by stable structures and no magmatism (except Early Permian Tarin Large Igneous Province) between Devonian and Early Permian. The other is the finding of large number of detrital zircons, of which U-Pb ages in 300-290Ma, in the Sample SSC07 and SSC05 in the bottom of Permian. We have ruled out the possibility that these detrital zircons (U-Pb ages in 300-290Ma) came from Tarim plate peripheral magmatism, by analysising the sedimentary facies of Lower Permian in the north and the south edge of Tarim Basin. We deduce thatthese detrital zircons came from the centre of doming uplift at the end of Carboniferous (east of Keping and west of Northern Tarim), from the evidence of the landscape feature at Early Permian and the sampling point location. The tuff section under the bottom basalt in Kupukuziman has been founded based on the comprehensive interoretation of boreholes, logging and seismology. The tuff was generated in the early stage of volcanic eruption, mostly located at the north of the Tarim Basin. In conclusion, tephra had been erputed before the Kupukuziman basalt erputed, and these detrital zircons (U-Pb ages in 300-290Ma) most likely came from the tephra.The uplift was short-term and approximately dome-shaped, occurring immediately before the Tarim LIP (-290 Ma). Through the analysis of the theory of crustal uplift and LIP (mantle plume), the time interval between the crustal uplift and TLIP, the geological background of Tarim basin during late Carboniferous to early Permian, this paper confirmed that there is close relationship between late Carboniferous crustal uplift of the Tarim plate and Early Permian Tarim Large Ignous Province. These result provide new sedimentological constrains on the role of a mantle plume in the formation of Early Permian Tarim Large Ignous Province.