The Stipulation Of TTG In The Area Of Cunqian Yongfeng County, Jiangxi Province And Its Geological Significance

In recent years, a survey carried out in the Lugang amplitude 1:50000 region found that granite in the area of Cunqian Yongfeng county, Jiangxi province belongs to the stipulation of TTG. What’s more, through access to relevant literature review, it is also found that some Caledonian granites in South China have the characteristics of TTG rock series. Since the Southern China Caledonian TTG rock series is put forward for the first time, the the research done on genesis and tectonic significance is still few. Therefore, choosing the Cunqian granite plutons mass as the main object in order to carry out detailed field geology, petrology, mineralogy and zircon SHRIMP and LA-ICP-MS U-Pb geochronology, whole rock major and trace elements, Sr-Nd-Pb isotope geochemistry of, determining the rock types and exact age rocks, finding out the geochemical characteristics, studying the genesis of rocks and the formation of tectonic background is a good way to add the new data for the study of the South China Caledonian tectonic environment.Cunqian granite plutons of Jiangxi Yongfeng county exposed in the area in Cunqian-Shuidongwei with the exposed area of 60 km2. The lithology is mainly gneissic micro-fine(containing spot) biotite granodiorite, locally with fine micro-fine biotite tonalite of the xenoliths. In addition, it also contains a small amount of medium-fine tourmaline-muscovite trondhjemite together constitute the TTG rock series. Through precise LA-ICP-MS U-Pb and SHRIMP U-Pb dating of zircon from Cunqian granite plutons of biotite granodiorite, the crystallization age of the intrusion was determined to be 434.9Ma±4.6Ma and 442.2Ma±3.2Ma, which indicates that the pluton is Cunqian granites formed in the Early Silurian era.The main rock forming minerals of rock is quartz, feldspar, plagioclase, biotite, muscovite. Micro-fine biotite granodiorite and micro-fine biotite tonalite of the rock mineral chemical analysis showed that:(1) Mica is an iron-black mica and primary dolomite,feldspar is oligoclase and orthoclase;(2) The chemical composition of rocks the Si O2 content low(the average is 68.95%), K2 O content low(average of 2.38%), low content of total alkali(average of 6.24%), higher content of CaO, K2O/Na2 O lower(average of 0.64, less than 1), belonging to the sodic series. With SiO2 content increased, CaO、MgO、TFeO、Al2O3、P2O5、Ti O2 reduced overall, K2 O content increased significantly, Na2 O content decreased slightly, the linear relationship between the components is relatively good, the source area is uniform, the evolution is relatively simple, mainly to the separation of crystallization;(3) The total amount of rare earth elements of Cunqian granite plutons is low, REE distribution curve right oblique type. Light rare earth enrichment, light and heavy rare earth differentiation is more obvious, moderate negative Eu anomaly;(4)The trace element distribution model for right deviation curve, with Ta、Nb、Ti negative anomalies( "Valley"), indicating that the source rocks in the crust or subjected to subduction fluid metasomatism of the mantle material;(5) Sr-Nd-Pb isotopic characteristics show that(87Sr/86Sr)i value is higher, 0.7099~0.7121, εNd(t) values for-6.04~-7.92, average of-6.82. Calculation of the second stage Nd model ages of T2 DM 1664~1817Ma, average of 1728 Ma, potassium feldspar of 206Pb/204 Pb is low, 18.116~18.137(average of 18.123); potassium feldspar of 207Pb/204 Pb is medium, 15.568~15.637(average of 15.603); medium of 208Pb/204 Pb, 38.233~38.516(average of 38.375). In the Rb-(Y+Nb) diagram, the projection points of all the rocks fall into the post collision zone, which conforms to the characteristics of the post collision granite. Cunqian granite plutons formed in Wuyi and Xiang-gui-gan plots the background of post-collision(collision orogenic collapse), main source of the mature degree lower crustal material, the base of the lower crust of amphibole rich the formation of dehydration partial melting under high pressure, separation and crystallization occurred in the process of the upper intrusion, and a small amount of upper crustal material was mixed.