摘要
通过对海西期以来幔源岩石化学成分 (特别是高度不相容元素对比值和具有相似性质的元素对比值 )研究并与相邻构造单元 (扬子板块北缘、华北板块南缘、北秦岭带、南秦岭带 )地幔特征对比表明 ,大别造山带中海西期春秋庙 -王母观辉长岩、碰撞后晚燕山早期镁铁 -超镁铁质岩体 (包括南、北大别造山带 )以及产于大别造山带南部和扬子地块北缘的晚燕山晚期碱性玄武岩源区地幔 ,均具有富Sc、Cu ,贫MgO ,低Zr/Hf和高Rb/Sr、Ba/Sr、Ba/La、Nb/Ta、Yb/Hf等特征。源区地幔的这些特点与元古宙以来扬子地幔特征相似 ,而与华北地幔特征存在显著区别 ,反映大别造山带发育在扬子地幔上。根据大量的地质学、构造地质学、岩石学、地球物理及地球化学等研究结果 ,指出桐柏 -商城 -磨子潭 -晓天断裂带是秦岭造山带中商丹断裂带的东延。综合研究证实大别造山带主体属南秦岭的组成部分。
Qinling Dabie orogenic belt(DOB) represents the composite convergence zone between the North China and the Yangtze blocks (NCB and YB). It is in doubt that Qinling orogenic belt (QOB) is composed of the southern margin of NCB (SNCB), northern QOB (NQOB), southern QOB (SQOB) and the northern margin of YB (NYB); Shangdan fault zone between NQOB and SQOB was a megasuture between NCB and YB during Neoproterozoic-Paleozoic period; and the Mianlue fault zone, a subsuture between SQOB and NYB, was formed within the Yangze plate during the Late Paleozoic. The geochemical characteristics of mantle derived rocks provide some new evidence for DOB subdivision in the present paper. Actually, there are abundant mafic ultramamic rocks distributed in different units of Dabie orogenic belt since the Late Paleozoic. For example, along the Tongbai Shangcheng fault zone occur the Chuqiumiao Wangmuguan gabbros of the Hercynian; in both northern and southern Dabie complex outcrop many post collisionally mafites and ultramafites of the early Late Yanshanian; and in central and southern Dabie orogenic belt present volume number of the basalts of the late Late Yanshanian. Geochemical research indicates that these mantle derived rocks are featured by enrichment of Sc and Cu, depletion of MgO, with higher Rb/Sr, Ba/Sr, Ba/La, Nb/Ta and Yb/Hf ratios, as well as lower Zr/Hf ratio. These characteristics are similar to those of the mantle in Yangtze block, and can be further compared to those of the mantle in southern Qinling orogenic belt. This result has been supported by the results, obtained from the research in geology, structural geology, petrology, geophysics and isotopic geochemistry for DOB, which suggests that Tongbai-Shangcheng-Mozitan-Xiaotian fault zone in DOB be an eastern extension of the Shangdan fault zone in Qinling orogenic belt. Based on the synthetic information, it is concluded that Dabie orogenic belt developed from Yangtze mantle and belongs to the eastern part of southern Qinling orogenic belt.
出处
《高校地质学报》
CAS
CSCD
2002年第2期129-140,共12页
Geological Journal of China Universities
基金
国家自然科学重大基金项目 (No .497940 43)
"壳幔相互作用
组成和动力学开放实验室"联合资助
