Provenance Analysis And Tectono-paleogeography Of Western Cathaysia Block: Insight From The Sinian-Cambrian Sedimentary Rocks

With the assembly and breakup processes of the global supercontinents,the South China Block(SCB)has experienced multiple tectonic-thermal events since the Neoproterozoic,which results a very complex tectonic and sedimentary evolution histories for the SCB.The Cathaysia Block,as an important part of the SCB,is becoming a research hotspot.When the Cathaysia Block and the Yangtze Block joining together forming the unified SCB and what is the palaeo-position of SCB in the Rodinia supercontinent and the relationship between the Cathaysia Block and the Gondwana supercontinent after the breakup of Rodinia?There exist many tectonic paleogeographic models proposed for these questions.In this paper,we present the updated data of whole-rock elemental geochemistry,detrital zircon U-Pb geochronology and Hf isotopic analysis on the Sinian-Cambrian sedimentary rocks from the Chongyi and Jinggangshan area in western Cathaysia Block,aiming to clear the provenance and tectonic setting of the sedimentary rocks,and offering new constraints on the relationship between the Cathaysia Block and Yangtze Block and the palaeo-position of Cathaysia Block in the Gondwana supercontinent during the Sinian and Cambrian eons.The whole-rock geochemical characteristics indicate that the sedimentary rocks in the Chongyi and Jinggangshan areas of western Cathaysia Block had experienced a moderate to strong weathering history.Together with the whole-rock major and trace element systematics on discrimination diagrams,it shows that the studied sedimentary rocks were mostly sourced from felsic-intermediate materials and deposited in a relatively stable intracratonic basin after experiencing long-distance transport,rather than in an active basin associated with proximal sources.The source of the sedimentary rocks should come from a large-scale continent-continent collisional orogenic belt,which has a complex tectonic background and involves different materials forming in passive continental margin,active continental margin and continental island arc.The Sinian sedimentary rocks show the source area has experienced a relatively weak weathering degree,and in a relative activity of tectonic environment.The Cambrian sedimentary rocks show the source area has experienced a relatively strong weathering degree and in a relatively stable tectonic environment,which contains more recycled materials from the old passive continental margins.This may be caused by the Kuunga orogenic movement in the late Neoproterozoic,leading to the collision among the India,Antarctica and Australia.During the Cambrian,the Gondwana supercontinent is gradually formed and the tectonic setting of source area is becoming stabilized.On the other hand,the stronger weathering degree experienced by the Cambrian sedimentary rocks,to some extent,is a reply to the global warming and the elevated chemical weathering rates during the Neoproterozoic-Cambrian interval.Basing on the zircon morphology,Th/U ratios and rare earth elements,nearly all of the detrital zircons from studied sedimentary rocks in Chongyi and Jinggangshan areas are igneous origin.The U-Pb-Hf isotopic element system of detrital zircons from the studied samples shows that the Sinian-Cambrian sedimentary rocks from the Cathaysia Block,India and Qiangtang should be derived from a same source,and the main source area should be the East African Orogen formed in the assembly of Gondwana supercontinent,and the Prince Charles Mountains and Eastern Ghats Belt formed in the assembly of Rodinia supercontinent.Detrital zircon U-Pb ages of the studied sedimentary rocks in the western Cathaysia Block record five major age populations at 2676-2221 Ma,1987-1276 Ma,1220-886 Ma,870-715 Ma and 697-532 Ma.Each age population provides a record of global tectonic and magmatic event.The 2676-2221 Ma is consistent with the global Neoarchean continental crust growth,most probably deriving from the India and east Antarctica.The 1987-1276 Ma correlates with the period of assembly and breakup of Columbia supercontinent,most probably deriving from the SCB itself and some other blocks adjacent to the SCB in the Columbia supercontinent.The prominent 1220-886 Ma corresponds to the Grenvillian orogenic event associated with the assembly of Rodinia supercontinent,most probably deriving from the Eastern Ghats Belt in India and the Prince Charles Mountains in east Antarctica.The 870-715 Ma is consistent with the breakup of the Rodinia supercontinent,most probably deriving from the Nanhua Basin between the Cathaysia and Yangtze Blocks.The distinct 697-532 Ma population corresponds to the Pan-African orogenic event associated with the assembly of the Gondwana supercontinent,most probably deriving from the East African Orogen in east Gondwana.Similar age distributions between the Cathaysia Block and the southeastern Yangtze Block suggest that these two blocks derived from a similar provenance across the Jiangshao Fault during the Sinian-Cambrian period.Combining with the distribution and geochemical characteristics of granite in the SCB during this period,as well as the comparison of sedimentary facies and biofacies between the Cathaysia and Yangtze blocks,it suggests that the Cathaysia Block and Yangtze Block should share a common continent without an open ocean between during the Sinian and Cambrian eons,in which supposed to be an intracontinental basin on the basement of stable continental crust.Meanwhile,our data reveal prominent detrital zircon age distributions which correlates well with the Grenvillian and Pan-African orogenic events,although no obvious geological evidence for these events have been found within the SCB.Qualitative comparison of age spectra of the Cathaysia Block with the potential neighboring blocks during the Sinian and Cambrian time,such as Qiangtang,northeastern India,Lhasa Terrane and Western Australia,shows that the Cathaysia Block might have a closer relationship with the Qiangtang and the northeastern India,instead of having a direct connection with the western Australia and Lhasa Terrane during the Sinian and Cambrian.In addition,different part of the northeastern India shows different characteristics of detrital zircon age distribution.The age distribution of Cathaysia Block was more similar to the western part of northeastern India,suggesting that the Cathaysia Block seemed to be nearer Qiangtang and the western part of northeastern India in the Gondwana reconstruction during the Sinian and Cambrian eons.