| A 2000km NE trending orogenic belt as well as a huge sedimentary basin formed during the late early Paleozoic owning to a strong tectono-thermal event. The sedimentary basin provides important materials for the study of the nature of the early Paleozoic tectono-thermal event and the evolution of orogenic belt.Through the comprehensive study of sedimentology, sandstone grain framework, and detrital zircon geochronology as well as geochemistry study of basinsediment, we are trying to discuss the nature, morphology, provenances and the spatial-temporal evolution of the basin, to investigate the relationship between the basin evolution and the orogenic uplift and denudation, to reveal the regional tectonic evolution. The main conclusions are listed as follows:1. Sediments in the late early Paleozoic basin mainly consist of coarsening up terrigenous clastic rock, with the lower part being grayish, caesious, greenishgray and the upper part being yellow green, fuchsia and khaki. And the sedimentary facies change from the lower neritic facies to the upper delta facies. The basin morphology is asymmetrically wedge-shaped in transverse cross-section, with the steep, thick part adjacent to the orogenic belt and gentling and thinning crantonward. The narrow subsidence center of the basin parallels the orogenic belt and migrates crantonward. And the development of the sedimentary basin coupled the uplift of the orogenic belt. All these features indicate that the late early Paleozoic sedimentary basin is a foreland basin.2. On the Dickinson Diagram, the sedimentary rocks shed from the recycled orogenic belt. The provenance of the foreland basin sediments are post-Archean granites and/or granodiorites or upper crust as evidenced by the low Eu/Eu* ratio, Gd/Yb(N) ratio and La/Th ratio, as well as the high LREE/HREE ratio. The chondrite-normalized curve of REES reveals an enrichment of LREE and deficit of heavy one, with Eu negative abnormality. According to the detrital zircon geochronology study, the northern part of the basin sediments mainly recycled from the underlying late Neoproterozoic rift sequences and southern part of the basin sediments mainly recycled from the Sinian to middle Ordovician strata.3. The SiO2/Al2O3, Zr/Ti and Zr/Sc ratios of the contemporarysamples increase dramatically from the proximal Lin’an section to the distal Huangshan section, and then decrease to the northwesternmost Chaohu section. Samples from theLin’an section show Th/Sc, La/Sc, Co/Th, Eu/Eu* and Cr/Th ratios lower than that from the Huangshan and Chaohu sections, indicating that the later are more felsic than the formation. The geochemical and paleocurrent evidences prove that the foreland basin receive materials both from the orogenic belt and the forebulge.4. The boundary between the wedge-top and the foredeep through the Changshan County and extends westward to Wuyuan-Jingdezhen-Poyang-Xiushui (Jiangxi procince), and tend southwest to Changde-Huaihua (Hunan province)-Huitong-Dushan (Guizhou province) according to the contact relationship of strata between the Upper Paleozoic and the underlying strata.5. The mudstone-dominated, neritic facies Changwu Formation indicatesa rapid tectonic subsidence and represents starved evolution stage of the foreland basin. The supplied sediments coarsened up as the increasing uplift and cratonward progradation of the orogenic belt during the Wenchang Formation. A small number of 460-420 Ma detrital zircon in the Gaojiabian Fomation indicates that the synorogenic magmatic rocks, as well as the country rock and cover were exposed to provide materials. And the synorogenic magmatic rocks continunously exposed during the middle Silurian, as evidenced by the increasing 460-420 Ma detrital zircon presented in the Fentou Formation and Tangjiawu Formation. |
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