武当地区新元古代岩浆岩地球化学特征及其对南秦岭晋宁期区域构造性质的指示

Geochemical features of the Neoproterozoic igneous rocks from the Wudang region and their implications for the reconstruction of the Jinning tectonic evolution along the south Qinling orogenic belt.

对南秦岭武当地区武当群火山岩、基性侵入岩墙群和耀岭河群火山岩系统的元素和Nd同位素地球化学研究表明,武当群火山岩为形成于约1.0～0.9Ga的新元古代陆缘岛弧火山岩,而耀岭河群火山岩与武当地区基性侵入岩墙群为0.82～0.78Ga形成的大陆裂谷型同源岩浆岩;它们分别可与扬子克拉通北缘西乡群和南秦岭陕西境内的镇安磨沟峡火山岩、扬子克拉通北缘的火地垭群铁船山组碱性火山岩和望江山基性侵入岩群相对比,揭示出南秦岭与扬子克拉通北缘于晋宁期属统一的陆块。扬子克拉通北缘和南秦岭大量的新元古代岩浆岩所具有的1.2～0.9Ga Nd同位素模式年龄和较高的εNd正值等特征表明,晋宁期是扬子克拉通地壳增生和大陆岩石圈演化的重要时期之一。

A comprehensive study of geochemistry was made on a series of the Jinning period (1.0similar to0.75Ga) igneous rocks from the Wudang region, South Qinling Orogenic belt (SQOB). It shows that the volcanics of Wudang Gp, aged ca. 1.0similar to0.95 Ga, have the affinities of arc magmas, and could be compared, in terms of geochemistry and ages, with those from the adjacent Xixiang Gp located at the northern margin of the Yangtze craton (NMYC) and Mogouxia volcanics from SQOB in Shanxi province. Yaolinghe volcanics and Wudang mafic dikes, which emplaced into both Wudang and Yaolinh Gps, share the magma characteristics of the continental rift, and are thought to be the equivalents of Tiechanshan alkaline volcanics and Wangjiangshan mafic swarms from the NMYC, which were radiometriolly dated as ca. 0.82similar to0.78 Ga. The similar experience in tectonic evolution from subduction zone transforming to continental rifting in the two regions indicates that the NMYC and SQOB belong to a unigue continental block, even though the later one is earmarked of strong deformation due to the Phanerozoic orogeny. T-DM model ages of ca. 1.2similar to0.9 Ga and high positive epsilon(Nd) values for the Neoproterozoic igneous rocks of the Wudang region demonstrate that the Jinning events played extremely significant role in both crust growth and lithosphere evolution of the regiona.