【摘要】 东特提斯构造域北界的确定不仅可以约束构造域的范围及演化,而且对于约束中国各陆块的原始构造归属也有着非常重要的意义。本文将从地球化学角度对这一科学问题进行探讨。祁连造山带早古生代蛇绿岩单元内枕状玄武岩的元素、Sr-Nd-Pb同位素组成系统研究表明:其地幔源区的Nd和Pb同位素组成均表现出印度洋MORB型同位素组成特征;枕状玄武岩(△²⁰⁷Pb/²⁰⁴Pb)_?变化范围为9．1～24．3（平均值为14．7）,(△²⁰⁸/²⁰⁴Pb)_?变化范围为9．1～101．1（平均值55．3）;与古特提斯和新特提斯蛇绿岩具有一致的同位素组成。因此,祁连造山带古洋幔应属于原特提斯构造域。纵观中国境内的特提斯构造域蛇绿岩的分布特征可知:该构造域表现出自北而南变年轻的时空演化规律,从而说明中央造山带的动力学过程也应纳入冈瓦纳大陆裂解和亚洲增生的总动力学系统之中。更多还原

【Abstract】 It is very important to discovery the northern boundary of eastern Tethyan tectonic domain not only for constraining its range and evolution,but also for establishing the tectonic affinity of microcontinents or terranes in China.Early Paleozoic ophiolitic suites preserved in Qilian orogenic belt give very great opportunities to emphasize insights into this scientific problem.This paper provides geochemical constraints on it.Systematic elements Sr-Nd-Pb isotopic compositions for pillow basalts from these ophiolitic complexes are presented in this article.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-,Ceno-Tethys and Indian Ocean.(Δ²⁰⁷pb/²⁰⁴Pb),of these basalts ranges from 9.1 to 24.3（Average:14.7）;(Δ²⁰⁸/²⁰⁴pb),is between 9.1 and 101.1（Average:55.3）.The age-corrected Nd and Pb isotopic characteristics indicate that these ophiolitic units were derived from the mantle source that had the Indian MORB-type isotopic signature.Therefore,we have suggested that ancient oceanic mantle for these Early Paleozoic ophiolitic complexes was an important branch of Proto-Tethys.It could be summarized that the ancient oceans developed in eastern Tethyan tectonic domains become progressively younger from north to south in China.Further,the evolution of Central cordillera is the epitome of tremendous geodynamics setting that some continental slivers were rifted from the northern margin of Gondwanaland and amalgamation（or accretion）of these to form proto-East and SE Asia.更多还原