Geological Characteristics And Significance Of The Hongshan Paleozoic Granitoids In The East Of South Tianshan

There are a large number of late Paleozoic granitic plutons in the South TianshanOrogenic belt. This rocks are important products of the South Tianshan orogenic belt of latePaleozoic tectonic evolution. On the basis of the theory of modern rock formation, from thispaper we can know the ages, genetic type, source characteristics, petrogenesis and tectonicenvironment about the Hongshan granitic plutons in the study by detailed studying its rockmineralogy, geochemistry and zircon U-Pb geochronology.Hongshan granitic pluton has high content of SiO2, K2O, Al2O3, but relatively low MgO,The values of A/CNK vary from1.02to1.15, C-norm is greater than1%, suggesting thegranite belongs to high-K calc-alkaline. The Al2O3/TiO2ratio of Hongshan granitic pluton isless than100, indicates that the melting temperature of part of the source region of is greaterthan875℃, so it belongs to the high temperature over peraluminous. The CaO/Na2O ratio ofHongshan granitic pluton are greater than0.3, only a few sample of CaO/Na2O ratio is lessthan0.3,(0.23-0.63, the average is0.48). This suggests that the source area of material maybe mostly sandstone, not rule out the possibility of mixed with a small amount of argillaceousrock. In the rock mass of the magma source rock discrimination diagram shows the sameresul.Hongshan granitic pluton has obvious negative Eu anomaly, CaO, P2O5, TiO2content islow, suggested that the granite source area has a rich residual plagioclase, ilmenite, and apatite.Th/U ratios is higher than the earth’s crust averages3.8which suggest that diagenetic processmay have to join the mantle source material.Enrichment of Rb, Th, K and other large ionlithophile elements (LILE), apparent loss of Nb, Ti high field strength elements (HFSE)geochemical characteristics. It has crustal granite features from that REE patterns showed aright-wing type, enriched in LREE, lack of HREE, negative Eu anomalies apparent.We canknow that the Hongshan granitic pluton which exposed in eastern of the South Tianshanformation in the early Early Permian from that its age of zircon U-Pb is297±3Ma.According to the age of magma intrusion and related tectonic environmentdiscrimination diagrams, and combining with the south tianshan other granite formation ageand the comparison of environment,we know that Hongshan granitic pluton forming tectonic system in the late collision transformation to post-collision,which belongs to the post collisiongranites.According to the research results, we think that the south tianshan orogenic belt has beenformed in front of the early Permian, the south tianshan late Paleozoic residual basin in earlyPermian before has been closed. Combined with the basis of forefathers’ research, we think ofthe south tianshan orogenic collision time began in the early carboniferous, ended in earlyPermian.