摘要
西秦岭-松潘构造结是中国大陆中重要的构造转换域,为探讨不同陆块及古洋幔的构造归属提供了非常有利的条件。该构造结早古生代蛇绿岩单元内变质玄武岩的地球化学特征表明:其源区不具有高场强元素(HFSE)相对于大离子亲石元素(LILE)亏损的特征;稀土元素(REE)及其它不活泼元素特征表明蛇绿岩形成于与岛弧无关的环境。变质玄武岩的 Sr 同位素组成受到海水热液蚀变或后期变质作用的影响而有所改变。Nd-Pb 同位素组成特征表明其地幔源区具有典型的印度洋MORB 型同位素组成特征(传统意义上的"Dupal"异常),从而说明其地幔源区属于原特提斯构造域。西秦岭-松潘构造结古洋幔构造归属的研究不仅为研究该构造结内各微陆块构造归属提供重要的约束,也为研究有关陆块间造山带的性质、发展与演化提供了动力学背景。
The Weatem Qinling-Songpan tectonic node situated in the central China continent is the key geological area for unraveling the relationship between different continents and ancient mande. This paper is devoted to an exploratory geochemical study of ophiolites outcropped in the tectonic node in order to place important constraint on the tectonic affinity of the ancient oceanic mantle and microcontinents. The geochemical information conveyed by metabasalts in Early Paleozoic ophiolitic m^langes indicates that the mantle source did not be depleted in High field Strength elements （HFSE） related to Large ion lithophile elements （LILE）. The distribution features of rare earth elements and other immobile elements do confirm that these ophiolites formed in the tectonic setting without island-arc imprint. Sr isotopic compositions for the basalts were affected by hydrothermal alteration or metamorphism. It is shown that the Nd and Pb isotopic compositions of mantle sources for them are similar to those of mantle sources for the MORB-type basalts in the Palaeo-, Neo-Tethys and Indian Ocean. （classically named ＂Dupal＂ anomaly）. Thus, we have suggested that ancient oceanic mantle for these Early Paleozoic ophielitic complexes was an important branch of Proto-Tethys. It will provide important constraints for tectonic affinities of numerous microcontinents in the tectonic node, and geodynamics settings for the characteristics, developments and evolutions of the orogenic belts.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第12期2901-2909,共9页
Acta Petrologica Sinica
基金
国家自然科学基金项目资助(Nos.40234052
40603011)
高等学校学科创新引智计划(ED7011).
关键词
蛇绿岩
特提斯
西秦岭-松潘构造结
构造属性
地球化学
Ophiolites, Tethys, Western Qinling-Songpan tectonic node, Tectonic affinity, Geochemistry
