| There is a late Paleozoic-Early Mesozoic giant alkali-rich intrusive rock belt in the southern margin of the Central Asian orogenic belt and the northern margin of the Tarim-North China Craton.In particular,the Permian Crabtun northern margin and the Tianshan-Beishan area mainly develop Permian alkaline rocks.The A-type granite,which is distributed in the east-west direction and extends over a thousand kilometers,systematically summarizes the A-type granites and alkaline rocks formed in the extended background,which will contribute to the evolution of the structural magma in the area.The evolution of the late Asian Pacific Ocean.In this paper,the petrographic,mineralogy,geochemistry,isotopic geochemistry,chronological rock mass genesis and tectonic significance of the porphyritic porphyry in the Hollerzadg ring rock mass in the northern part of Beishan Mountain were studied and collected.The data of a large number of A-type granites and alkaline rocks in the northern margin of Tarim-Tianshan-Beishan area were compared and the differences between chronology and geochemical sources were studied.The results show:1.The LA-ICP-MS zircon U-Pb dating of the southeastern plaque-like granite sample of the Hollerzad-Gap is shown as 237.5±1.2 Ma(MSWD=0.14),which is the activity of the Early Triassic magmatism.The geochemical characteristics indicate that the plaque-like granite is quasi-aluminum,and the rare earth element distribution diagram shows a typical right-dip mode,enriched with light rare earth elements and depleted heavy rare earth elements.The light and heavy rare earths are distinct and have weak Eu negative anomalies;?Hf(t)=10.12?11.93,with an average of 11.12.The calculated age of Hf isotope model is 616.48?781.25Ma,and the average value is 690.39Ma.The trace element analysis of zircon shows heavy rare earth enrichment,light rare earth loss is serious,and it shows strong Eu negative.The anomaly,the zircon saturation temperature is calculated to be 827.8 ?,which represents the temperature of the magma near liquidus of the plaque-like granite.The tectonic environment is shown as an intraplate environment,indicating that the area has been transferred to the intraplate environment during the Early Triassic,which further defines the Triassic tectonic setting in the Beishan area2.A large number of Late Paleozoic-Early Mesozoic A-type granites(415-252.7Ma)and alkaline rocks(285.9-224Ma)are developed in the northern margin of Tianshan-Beishan-Talimu.In time,it can be divided into four stages:the first stage(415-292Ma),there is A2 type granite,no A1 type granite and alkaline rock are exposed;the second stage(292-285.9Ma)begins to have A1 type granite emplacement,and also A2 type granite appears,but there is no such period The alkaline rock;the third stage(285.9-252.7Ma),both the A1 type granite and the A2 type granite,as well as the alkaline rock in place,it is important that the Tarim mantle plume also developed during this period(280-275Ma)The fourth stage(247.5-224Ma),during which a certain amount of alkaline rock appeared,but only developed in the east,and there is no A-type granite in this period3.The A-type granite and alkaline rock in the northern margin of the Tianshan-Talimu-Beishan Mountains have appeared since the Early Paleozoic,until the Triassic,but mainly formed in the Late Paleozoic(Permian)development.The A2 type granite can be the earliest At this time,the Ai type granite and the alkaline rock did not appear.During this period,the area experienced the stage of collisional orogeny after the collision,indicating the granite formation and post-orogenic environment during this period.Related;the formation of Ai type granite is accompanied by A2 type granite,the early alkaline rock and A2,Ai type granite appear at the same time,and it is also the activity period of the Tarim mantle column,indicating that the study area has entered the plate from the post-orogenic environment.The system may be affected by the mantle plume activity,or directly the product of the mantle plume activity(alkaline rock);while the late alkaline rock alone,it should be related to the mantle-derived magmatism.From early to late,the evolution of time from A2? A2+A1?>A2+A1+alkaline rock?alkaline rock clearly shows the tectonic setting,from the later orogenic(late Carboniferous-Early ?)The dynasty)? post-orogenic-intraplate transition(Early Permian)?non-orogenic(in-plate,mid-late Permian)?intra-continental(Triassic)environmental transformation.This provides a very good indication of regional tectonic evolution,revealing that the southwestern part of ancient Asia was closed at least before the Permian4.The tectonic setting of the A2 type granite needs to be carefully screened.It is the A2 type granite that does not always represent the post-orogenic extension background.The A2 type granite can be formed in the post-orogenic environment or in the plate environment,and the A2 type The formation of granite is probably the result of multiple systems working together. |
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