CAJ | 학술논문

对蚌埠地区的荆山和涂山花岗岩进行了详细的年代学和岩石地球化学研究,分析结果表明:花岗岩的SiO_2含量较高,介于71.22%～73.76%之间,富K_2O、Na_2O,贫TiO_2、CaO、MgO,为弱过铝质岩石.K_2O-Na_2O图解上,所有数据点都落在"I"型花岗岩区域,结合呈右倾的微量元素标准化蛛网图,可知该区富集大离子亲石元素,同时具有明显的U、Pb、Ba、Sr正异常,Ti的负异常,暗示蚌埠岩体的形成背景可能为造山后的伸展环境.Cameca IMS 1280 SIMS锆石U-Pb年龄分析表明,主要有800Ma左右的新元古代年龄、三叠纪相关的220Ma和晚侏罗世的165Ma这三种主体年龄.根据上述地球化学资料,推断蚌埠岩体的母岩浆来源于火成岩的部分熔融,岩浆源区为与华北板块碰撞后继续向北伸展的部分扬子板块下地壳火成岩物质,其中,800Ma左右的新元古代年龄解释为扬子板块下地壳物质的继承锆石年龄,三叠纪的继承锆石理解为三叠纪时期华南、华北板块的碰撞导致,晚侏罗世的岩浆活动推测由于古太平洋板块北西向的斜向俯冲诱发扬子板块下地壳的物质部分熔融所致.
대방부지구적형산화도산화강암진행료상세적년대학화암석지구화학연구,분석결과표명:화강암적SiO_2함량교고,개우71.22%～73.76%지간,부K_2O、Na_2O,빈TiO_2、CaO、MgO,위약과려질암석.K_2O-Na_2O도해상,소유수거점도락재"I"형화강암구역,결합정우경적미량원소표준화주망도,가지해구부집대리자친석원소,동시구유명현적U、Pb、Ba、Sr정이상,Ti적부이상,암시방부암체적형성배경가능위조산후적신전배경.Cameca IMS 1280 SIMS고석U-Pb년령분석표명,주요유800Ma좌우적신원고대년령、삼첩기상관적220Ma화만주라세적165Ma저삼충주체년령.근거상술지구화학자료,추단방부암체적모암장래원우화성암적부분용융,암장원구위여화북판괴팽당후계속향북신전적부분양자판괴하지각화성암물질,기중,800Ma좌우적신원고대년령해석위양자판괴하지각물질적계승고석년령,삼첩기적계승고석리해위삼첩기시기화남、화북판괴적팽당도치,만주라세적암장활동추측유우고태평양판괴북서향적사향부충유발양자판괴하지각적물질부분용융소치.
The Bengbu uplift is located on the southeastern margin of the North China block, about 200km north of the Dabie orogen in the southwest of the Su-Lu orogen, east of the Tan-Lu Fault Zone. The genesis and geochronology of the Bengbu granites can reveal the deep-subduction direction of the Dabie-Sulu ultrahigh-pressure metamorphic belt and influence scope and help to realize the tectonic evolution of the eastern North China block in the Mesozoic. Considering these, we particularly analyze the Bengbu Jingshan and Tushan granitic rocks by geochronology and geochemistry methods. The Jingshan and Tushan granites in this area are mainly biotite monzonitic granites, which have very high SiO_2 (71.22%～73.76%), relatively high K_2O and Na_2O, and low TiO_2, CaO and MgO contents, belonging to slight peraluminous rocks. All samples are projected onto the area of I-type granites in the diagram of K_2O-Na_2O, combining with a right-deviating trace elements spider diagram, with obviously positive anomalies of U, Pb, Ba, Sr and negative Ti anomaly, which all prove that the Bengbu granites could be formed under the post-orogenic extensional environment. Furthermore, Cameca IMS 1280 SIMS zircon U-Pb dating shows that there are three major age groups:～800Ma,～220Ma and ～165Ma. According to the above-mentioned geochemical data, we believe the parent magmas of the Bengbu granites were originated from the partial melting of igneous rocks and magma source of lower crust of the Yangtze craton. As for ages, new Proterozoic ages of about 800Ma are interpreted as the inherited zircon ages of the Yangtze craton lower crust,～220Ma Triassic ages are due to the Triassic collision of the South China block and North China block, and late Jurassic magmatism are presumed owing to partial melting of the Yangtze craton lower crustal materials induced by oblique subduction of the paleo-Pacific plate.