| This study discusses the petrological characteristics,petrogenesis,source of diagenetic materials and diagenetic dynamics background of four typical granitic pluton in the research area in the indosinian,which is based on the systematic collection and analysis of the basic geological data of the Wollonggang-Huangyangling area in the northwesternern margin of Songpan-Gerze Continental Block?The four typical granitic pluton are named respectively Redhill,Two-tigers,5328-highland,Wollongang.Meanwhile,the petrology,elemental geochemistry,U-Pb isotope chronology of zircons,and Lu-Hf isotope tracer and other research methods or technical means were conducted.The paper comes to the following conclutions:(1)According to the petrology and petrographic studies,the intrusive rocks of the late indosinian in the northwesternern margin of Songpan-Gerze Continental Block are medium-acidic granite,and the lithology is mainly fine-grained diorite,diorite porphyrite,fine-grained quartz diorite and granite porphyry.(2)In the northwesternern margin of Songpan-Gerze Continental Block,the typical granitic pluton in the indosinian are Quasi-aluminum-peraluminous calc-alkaline series with rich silicon and alkali,and have medium aluminum content;LREE is enriched and HREE is lost,and the heavy and light rare earth fractionation is obvious,while the heavy rare earth fractionation was lower than the former.LILE(K,Rb,Th,La,Ce,U,etc.)was enriched relatively.The difference is that Redhill,Two-tigers,5328-highland plutons all have high Sr(mean 371ppm>300ppm),low Y and Yb(mean Y content 18.12 ppm <20ppm,the average content of Yb is 2.00ppm),indicating that there were garnet phase crystallization or residual in the source area.(3)The study of LA-ICP-MS U-Pb chronology of zircons shows that the diagenetic age was 210.4±1.7Ma of diorite porphyrite of Redhill pluton;213.5±1.0Ma of the diorite and 212.4±1.3Ma of the diorite-porphyrite of Two-tigers pluton;216.78±0.80 Ma of the quartzdiorite and 211.3±1.3Ma of the diorite-porphyrite of 5328-highland pluton;200.9±1.2Ma of the granite-porphyry of Wolonggang pluton.In conclusion,the formation age was 210~216Ma of the neutral granitic plutons,and about 201 Ma of the acidic granitic poluton..(4)The Lu-Hf isotope analysis results of four typical pluton show that the magmatic source area of the late indosinian neutral granitic pluton were dominated by crustal sources,meanwhile,a very small amount of mantle material is added,indicating a weak degree of crust-mantle mixing.The magma source area of acid granitic pluton was characterized by the ancient crust.(5)Through this article research,combining previous research results,with comprehensive analysis,there is a insights that the neutral granitic pluton of Songpan-Gerze Continental Block(Redhill,Two-tigers,5328-highland pluton)were formed in the magmatic arc tectonic environmentancient of the ancient tethys ocean(the southern branch)diving and cutting towards to Songpan-Gerze Continental Block;the acidic pluton(Wollongang pluton)was formed in the syn-collision tectonic environment of Qiangtang Continental Block diving and cutting towards to Songpan-Gerze Continental Block after the ancient tethys ocean(the southern branch)closed.(6)According to the study of the paper,combined regional data analysis,the paper considers that at the end of the Permianthe,the oceanic crust between Songpan-Gerze Continental Block and Qiangtang Continental Block started to diving and cutting towards to Songpan-Gerze Continental Block;At about 210 ~216 Ma(Norian in late Triassic),the tectonic movement was in the late stage,at the same time,formed the magmatic arc neutral intrusive rock in late indosinian.Around 201Ma(late Triassic Rietene),the ancient tethys ocean(the southern branch)was completely closed and the indosinian acid intrusive rock was formed.From then on,Qiangtang Continental Block and Songpan-Gerze Continental Block were connected together,and the activity continental margin of Bayankala was transformed into the foreland basin. |
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