Geochronological And Geochemical Characteristics Of The Minettes From Taiping Area, Centre Jiangxi Province

The Minette dyke swarms are located in Taiping area, Le'an County, Jiangxi Province. It distributes mainly along the fault?its orientation is NE, NNE and NW? to region which is surrounded by Shenhuashan-Guanfang-Yaojiangshang-Xingzishan in the area of Taiping. China's largest volcanic type uranium ore field—Xiangshan uranium polymetallic ore field is the northern of Taiping area and the distance is about 30 km. This paper selects Taiping area Minette as the main research object, and studies its formation age, origin, material source and tectonic environment through the research of the petrology, U-Pb zircon geochronology and geochemical characteristics.The LA-ICP-MS U-Pb zircon age of Taiping area Minette is 223.7±1.5Ma?n=15, MSWD=1.17?.The SHRIMP zircon U-Pb age of Minette is 231.6±2Ma?n=10, MSWD=1.5?. Both ages are consistent within the allowed error range, it indicates that the Minette is formed in the late Triassic?Indosinian?.The Minette possesses lamprophyric structure. The phenocryst is biotite and the matrix main are potash feldspar and biotite, the contents of which are 60%⁷0% and 25%³5%. The electron probe data shows that the mica is phlogopite and the feldspar is orthoclase. The accessory minerals can be seen in the Minette is apatite, zircon and a small amount of chromites. The common alterations are carbonatization and chloritization. The content of Si O₂ in Minette is 43.18%⁴5.90% and the content of an alterative sample is reaching up to 62.12%. Total content of alkalis?K2O+Na2O? is 3.42%⁸.38% and the ratio value of K2O/Na2 O is large. It is obvious enrichment of potassium. The content of Fe OT is 7.27%⁸.2% and Mg# is 56.55⁸3.21, the average is 77.11. The ratio of Fe OT/Mg O is low and the volatiles are rich. It belongs to parlkaline and ultra-potassic Minette. The REE is extremely rich and ?REE is 1253³944.12 ppm. The distribution plots is sharply to the right tilt. The differentiation of LREE and HREE is strong and the values of LREE/Hree and?La/Yb?n are large, respectively 15.88²0.01 and 27.04⁷8.45. The value of ?Eu is 0.56⁰.81 and it shows weak-medium negative anomalies. There is not anomaly of Ce. Rb, Ba, K, Th, Pb?LILE? is obvious enrichment in the Minette and Ta, Nb, P, Zr, Hf, Ti?HFSE? is loss. It shows TNT?Ta, Nb, Ti? loss model and illustrates that the source area has affinity with the continental crust and subduction zone.According to petrology, mineralogy and geochemical characteristics and tectonic environment discrimination diagrams of Minette, combined with regional geological background, suggesting that early subduction zone components is dehydrated to form enriched fluid and it has metasomatism with lithospheric mantle forming the enriched mantle in South China. It is a stretching post-orogenic environment in late Triassic. Due to lithospheric and crustal stretching and thinning, the asthenosphere upwells and the enriched lithospheric mantle occurs partial melting and rise to the near surface along the structural weak zone, resulting in the formation of Minette dyke swarms in the Taiping area.