Geochemical Characteristics And Tectonic Significance Of The Early Paleozoic-Early Mesozoic Granite In Huaniushan Area,Beishan

Beishan orogenic belt is located in the Tarim,North China and Kazakhstan plate docking parts,belonging to the southern edge of the Central Asian orogenic belt,experienced early Paleozoic to early Mesozoic long-term multi-stage,complex dive-collage history,,East of Alashan,with two strike-slip faults(Star Gap and Algin)as the boundary,in a tectonic wedge,the geological structure is very complex.In this study,LA-ICP-MS zircon U-Pb chronology,petrology and geochemical studies were established to determine the rock formation,which provided evidence for inversion of tectonic evolution in Beishan area.The altered dacite is formed in the early Paleozoic(late Ordovician)of about 454.7 ± 0.87 Ma(MSWD = 0.28),Which provides a new basis for determining the depositional age of the Huaniushan Formation,limiting the age of the formation to Late Ordovician.At the same time,which is an over aluminum,high potassium calc-alkaline-potassium metamorphic granite,Ba,Nb,Ta,Ti,strongly enriched Pb,Th content changes,Zr,Hf with a weak positive anomaly-normal,rich rare earth elements,with high Yb content,showing significant arc properties,subduction of subduction fluid.The quartz diorite is formed in the late Paleozoic(late Late Devonian)of about 362.5 ± 1.1 Ma(MSWD = 0.075).It is an aluminous,calcareous granite,right in the spider diagram,strongly enriched with Pb,Zr and Hf are positive anomalies,weakly enriched large ion lithophile Sr,relative loss strong incompatible element Ba,weak negative Eu anomaly,and its weak element,the formation of the structural environment for the plate before the collision or the reduction of the active continental margin for the volcanic arc granite.Indicating that the finite oceanic basin represented by the Hongliuhe-Niujuanzi ophiolite belt in the southern part of the northern part of the mountain has begun to subduction to the south in the early stage of the Late Devonian,and the subduction has not yet ended until early Carboniferous,subduction effect of the end of the area occurred in the ocean basin closed.The granite porphyry is formed in the Early Mesozoic(Middle Triassic)of 232.4 ± 0.55 Ma(MSWD = 1.8).The emplacement time of the veins is basically the same as that of the Re-Os model(221.0 ± 3.4 Ma)of the molybdenum ore in the ore of the Huaniushan molybdenum deposit,indicating that the two are the products of the magma-hydrothermal action in the same period,coupling relationship.Which exhibits Ba,Sr,P,Eu,Ti is strongly depleted,Nb and Ta are weaker depleted,and Zr and Hf are not obvious enriched.Pb,Th,U are strongly positive,Sr and Yb are low and have strong negative Eu anomaly,plagioclase residues in source region,and the sample has high Nb content,it is presumed that a large amount of deep enriched mantle material is added during the magma melting process,so the rock mass is thought to be formed in the extensional settings and the deep enrichment mantle material upwelling.The porphyritic granite formed in the Early Mesozoic(Late Triassic)218.2 ± 1.8 Ma(MSWD = 1.7),which is enriched in Rb,Th,U,K,Pb and other strong incompatible elements,depleted of Nb,Ta,Ti etc.high field strength elements,while Zr,Hf is positive anomaly,with a strong negative Eu negative,while the rock has a high Sr,Yb,Nb,low Y/Nb and slightly lower Ga/Al,with A1-A2 transitional characteristics,the formation of signs of mantle invasion is gradually strong,for the area to bring a lot of heat,stretching tend to be more intense.In the study,it is believed that: since the late ordovician,the Hongliuhe-Niujuanzi ophiolite belt represented by the subduction of ocean basin to the south,to the late devonian subduction is still on,closed in the middle of the early carboniferous,early-and then entered the stage of intracontinental evolution,in the late Triassic,beishan area stretching tend to be more intense.