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The Diagenesis Of Fanchang Basin And Ore Mineralization Of Taochong, Anhui Province, China

Posted on:2011-08-16Degree:MasterType:Thesis
Country:ChinaCandidate:Y M HuangFull Text:PDF
GTID:2120360308973068Subject:Mineralogy, petrology, ore deposits
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The Fanchang basin is one of the important continental volcanic fault basins in the Middle-Lower reaches of Yangtze River, where the volcanic rocks can be generally subdivided into four Formations, i.e., Zhongfencun Formation, Chisha Formation, Kedoushan Formation and Sanliangshan Formation. The LA-ICPMS U-Pb ages of zircons from trachyandesite of Zhongfencun Formation, biotite trachytic porphyry of Chisha Formation, rhyolite of Kedoushan Formation and biotite trachyte of Sanliangshan Formation are 134.4±2.9Ma,131.3±1.8Ma,130.8±2.2Ma and 128.1±3.1Ma respectively. Hence, the ages of volcanic rocks in the Fanchang basin range from 134-128Ma, corresponding to the Early Cretaceous. Many inherited or captured zircons occur in the volcanic rocks, the oldest one is 2894Ma age which may correspond to the 2.7Ga peak age of global magma activities and continental developments. It is implies the existence of Archean basement under the Fanchang basin. The forming period of volcanic rocks in the Fanchang basin is nearly similar to those in the other continental volcanic basins in Middle-Lower reaches of Yangtze River, and the four volcanic circles of Fanchang basin can entirely correspond with those of Luzong basin and Ningwu basin. The four formations of volcanic rocks of Fanchang Basin had homologous magma, which is from the enrichment mantle. Magma evolution included the magmatic differentiations, fractional crystallizations and assimilation of contaminations. The early Zhongfencun Formation and Chisha Formation was relatively low level of magmatic differentiation, but there were high level during the late Kedoushan Formation and Sanliangshan Formation. Early magmatic rocks formed in compression-extensional tectonic setting, while the late magmatic rocks were formed in the typical extensional tectonic setting at about 130.8Ma. Comparison shows that Fanchang basin and Luzong Basin may have similar geological processes, diagenetic processes and tectonic setting. The 135Ma is considered as the beginning of the early Cretaceous volcanic activities in the continental volcanic fault basins in Middle-Lower reaches of Yangtze River. The period of Mesozoic volcanic activities,135-128 Ma, in the Fanchang basin, correspond to the fastigium of the lithospheric thinning in eastern China, which constrained the volcanic activities in the Fanchang basin.The studies of lithogeochemistry on Taochong iron ore have shown that skarns were different with wall rocks.The inclusions shown the mineral characteristics had high temperature and high salt,and isotope datas show the magmatic hydrothermal formed related with the early skarn, the mixture of magmatic arid hydrothermal water related to the later mineralization forming. Therefore, the Taochong iron ore deposit is stratabound skarn deposit. Quartz sulfide mineralization stage relatively mixed magmatic-meteoric fluids.
Keywords/Search Tags:LA-MC-ICPMS dating, zircon, lithogeochemistry, magmatic rock, iron ore, Taochong, Fanchang Basin, Anhui Province
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