Geochronology And Geochemical Of Chengshang Complex Pluton In Central Jiangxi Province And Its Geological Significance

Chengshang complex pluton is located in the Meiyuan-Luotian area, which is to the east Wugong Mountain in central Jiangxi Province, and 10 kilometers to west of Xiajiang County. It has a significant indication to the analysis of the tectonic and magmatic evolutions in this area and even South China for the characteristics of several stages and various causes. Based on previous research and field geological investigation, this paper discusses its forming physicochemical conditions, genetic type, the nature of the source region, tectonic environment and relationship with mineralization by petrography, mineral chemistry, LA-ICP-MS zircon U-Pb dating and element geochemistry analysises.The northern Meiyuan intrusion is medium fine grained biotite granodiorite. The plagioclase and biotite of medium fine grained biotite granodiorite are pseudoalbite and magnesia biotite, with zircon LA-ICP-MS age of 436.2±2.4Ma. Its formation temperature is about 650℃~725℃, oxygen fugacity 10-11.4bar~10-12.2bar. Its diagenesis pressure 68Mpa~234Mpa, the corresponding depth 2.6km~8.9km, and the formation temperature of its initial magmaabout 759℃, based on which, this can be categorized as high-potassium calc-alkaline series and weak aluminum I-type granite. The rock was mainly formed by magma mixing between a few tholeiitic magmas and the poor clay sand metamorphic complex sand generated by partial melting of basic lower crustal material,when the collision orogeny of the Early Paleozoic Yangzi and Cathaysia block transformed from squeezing tectonic to extension tectonic. This is late collision granites. Xinyu iron deposit was damaged in space and indicate the upper time limit of deformation in originally by Mei-yuan rock mass. It does not have the metallogenic time and genesis relationship with the surrounding ores.The evolution of the intrusion of southern Indosinian Luotian intrusion can be divided into three stages, i.e. big-phenocryst medium coarse grained biotite adamellite, mid- phenocryst medium fine grained biotite adamellite and medium grained two-mica granite.The diagenetic age of medium grained two-mica granite is 239.0±1.0Ma, with the initial temperature of magma is 682℃~773℃. It belongs to high-potassium calc-alkaline to alkaline series and strongly peraluminous S-type granites. The rock was mainly formed by the melting of rich clay metamorphic mudstone, but possible to bring a number of metagreywacke in the process of magma rising and emplacement.The plagioclase of medium coarse grained porphyritic biotite adamellite is mainly oligoclase and pseudoalbite. Its flesh red giant phenocrysts is pure orthoclase. Its biotite belong to ferruginous biotite. Its diagenetic age is 227.0±1.2Ma. Its crystallization temperature and oxygen fugacity are about 625℃~725℃ and 10-13.8bar~10-15.1bar. Its diagenetic pressure is 265MPa~377MPa, corresponding at 10.0km~14.2km. The formation temperature of its initial magma is about 745℃~809℃. The medium coarse grained porphyritic biotite adamellite is high-potassium calc-alkaline series, weakly peraluminous to strongly peraluminous S-type granite. It was formed by the partial melting of the rich clay metasan- dstone, but may be mixed with a small amount of basic and argillaceous components material.The plagioclase of medium fine grained porphyritic biotite adamellite is mainly albite and a few oligoclase. Its biotite belong to siderophyllite-ferruginous biotite. Its diagenetic age is 222.1±1.1Ma. Its crystallization temperature and oxygen fugacity are about 600℃~650℃ and 10-15.6bar~10-16.6bar. Its diagenetic pressure is 417MPa~559MPa, corresponding at 15.8km~21.1km. The formation temperature of its initial magma is 698℃~722℃. The medium fine grained porphyritic biotite adamellite is high-potassium calc-alkaline series, strongly peraluminous S-type granite. It was formed by the partial melting of the rich clay felsic mudstone.All the three stages of granites have the similar element geochemical characteristics. They are characterized by high Si, Al, K and low Ca, Mg, P and strong negative Eu anomaly. They also have rich Rb, Cs, U, Nd, LREE and poor Ba, Sr, Ti and high fractional crystallization. The first stage rock may be the result of the collision between the South China block and the North China block. This is syn-collisional granite, influenced later by stretching structure of Wugong Mountain. The second and third stage rocks were both formed in Intracontinental extension tectonic environment after the collisional orogeny by the South China block and the North China block. They are post-collision granite. It has no time relationship with the surrounding minerals, but it is spatially and originally related to the granite.