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本文对东秦岭造山带内27个花岗岩类岩体48件长石样品进行了铅同位素成分的测定。结果表明,本区的南秦岭不同时代花岗岩类以贫铀铅和钍铅为特征,具有明显的铅同位素块体效应,反映它们属于同一个铅同位素构造-地球化学省;而本区的北秦岭花岗岩类从晚元古代到早古生代,长石铅同位素组成以富铀铅和钍铅为特征,但从晚古生代开始,花岗岩类长石铅同位素组成明显发生变化,以贫铀铅和钍铅为特征,反映晚古生代及其后形成花岗质岩浆的源区明显发生改变,指示在北秦岭有着不同块体间的相互作用。南秦岭和北秦岭相近时代花岗岩类长石铅同位素组成比较,在晚古生代以前,铅同位素组成存在明显差异,说明它们分属两个不同的构造单元;但自晚古生代开始,南、北秦岭具有非常相似的铅同位素组成,反映该时期以后,南、北秦岭已焊结在一起,形成花岗质岩浆的源区相似,同时指示南秦岭陆壳物质俯冲垫托于北秦岭陆块之下。
In this paper, the determination of Pb isotopic composition of 48 feldspar samples from 27 granitoids in the East Qinling orogenic belt has been carried out. The results show that the granites from different ages in the South Qinling of this area are characterized by depleted uranium (Pb) and thorium (Pb), with obvious Pb isotopic mass effect, indicating that they belong to the same Pb isotopic tectono-geochemical province. The North Qinling granites From the Late Paleozoic to the Early Paleozoic, the feldspar Pb isotopic composition is characterized by the enrichment of uranium and thorium. However, since late Paleozoic, the lead isotopic composition of feldspar in granite has obviously changed, characterized by depleted uranium and thorium lead, The source areas reflecting the Late Paleozoic and the subsequent formation of granitic magma evidently changed, indicating the interaction between different blocks in the North Qinling. The Pb isotopic composition of granodiorite feldspar in the Late Qinling and Early Qinling Mountains is similar to that of Pb isotopes in the Late Paleozoic, indicating that they belong to two different tectonic units. However, since the Late Paleozoic, The similar Pb isotopic composition indicates that the source rocks of the southern and northern Qinling mountains have been welded together to form the granitic magma after this period, indicating that the subducted continental crust beneath the Qinling Mountains is under the Qinling ridge.