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前人研究表明,扬子陆块存在广泛的太古代结晶基底,但是目前除在宜昌黄陵穹窿一带有确切证据显示有太古代高级变质地体(崆岭群下部)以外,还未见其他地区有出露的报道.为进一步了解扬子克拉通的基底组成及其形成演化过程,本文对钟祥胡集地区杨坡群及侵入其中的钾质花岗岩进行了岩石学、同位素年代学和岩石地球化学研究.研究显示,胡集钾质花岗岩的SHRIMP锆石U-Pb年龄为2655±9Ma,属于新太古代中期.同时该套花岗岩主量元素富硅和碱,贫Ca,Mg,P和Ti;微量元素富Rb,Th,Ga,Y和Zr,亏损Sr,Ba,Nb和Ta,强烈亏损Eu,高FeO*/MgO(=32.0~58.7)和104Ga/Al(=3.19~3.41)比值,表现出明显的具有陆壳源区的铝质A型花岗岩特征.因此,杨坡群沉积岩石组合和侵入其中的高分异A型花岗岩均证明,在新太古代中期以前,扬子克拉通已经发育有较为成熟的陆壳了.这一突破性发现为深入研究扬子克拉通陆块基底的形成演化过程开辟了新的窗口.
Previous studies have shown that there is a wide range of Archean crystalline basement in the Yangtze block. However, at present except for the evidence of the Archean high-grade metamorphic body (lower part of Gulingling group) in the vicinity of the Huangling vault in Yichang, no other areas have been found In order to get a better understanding of the basement composition and evolution of the Yangtze craton, this paper studied the petrology, isotopic chronology and geochemistry of the Yangpo Group and the intrusive potassic granites in the Wuji area of Zhongxiang. The study shows that the SHRIMP zircon U-Pb age of Huji potash granulite is 2655 ± 9Ma, belonging to the Neo-Archean Mesozoic, and the main elements of this granite are rich in silicon and alkali, depleted in Ca, Mg, P and Ti. Trace elements Rich Rb, Th, Ga, Y and Zr, depleted in Sr, Ba, Nb and Ta, strongly depleted in Eu with high FeO * / MgO (= 32.0-58.7) and 104Ga / Al (= 3.19-3.41) Of continental A-type granites characterized by continental crustal origin.Therefore, both the sedimentary rock assemblage of Yangpo Group and the highly-differentiated A-type granite intruded into it have proven that the Yangtze craton has developed more maturely before the Neo-Mesozoic Of the continental crust .This breakthrough discovery for further study of Yangtze cratonic land Formation and evolution of substrates opens up a new window.