造山后构造岩浆作用研究评述  

Post-Orogenic Tectono-Magmatism and Its Implications for Evolution of Orogenic Belts

作　　者：李晓勇[1] 郭锋[1] 王岳军[1] 

机构地区：[1]中国科学院长沙大地构造研究所,湖南长沙410013

出　　处：《高校地质学报》2002年第1期68-78,共11页Geological Journal of China Universities

基　　金：中国科学院知识创新工程项目 (KZCX1 10 7和KZCX2 10 4) ;国家自然科学基金项目 (4 0 0 730 11)

摘　　要：综合造山后岩浆作用的主要岩石学特征包括 :a、双峰式火山岩组合 ;b、高钾钙碱性甚至钾玄岩系列 ;c、巨量花岗岩。由于其熔融源区受到早期的陆 /洋壳俯冲作用的影响 ,它们在地球化学特征上总体表现出类似岛弧型火山岩的微量元素特征。如LILE ,LREE富集和HFSE亏损 ;但比岛弧型火山岩具有更高的K2 O +Na2 O含量、ω(Fe2 O3 +FeO) /ω(MgO)和ω(K2 O) /ω(Na2 O)比值以及较高的Sr含量和Zr/Y比值。其Sr-Nd同位素比MORB和OIB富集。这些特征表明同位素组成受控于LILE、LREE富集作用的时间和俯冲地壳的性质。在岩石成因方面 ,造山后岩浆作用的源区受到了年青地幔或地壳组分的改造 ,其岩浆形成机制与深大断裂的大规模走滑作用和造山后岩石圈的伸展 -减薄作用密切相关。The traditional plate tectonics and its derivative plate collision theory have been successfully applied in explaining the plate motion and formation of orogenic belts. However, they are now in the face of many difficulties in explaining many geological phenomena after the final convergence of plates, such as rapid uplifting of orogenic belts, exhumation of high to ultra high pressure metamorphic rocks and extensive magmatism, and so on. Post orogenic magmatism, as one of the most important manifestations to reflect the adjustment and transition of thermal stress structure in orogenic belts, its petrogenesis is crucial for understanding the entire evolution of orogenic belts. It generally shows lithological associations characterized by: (a) bimodal volcanism; (b) high K calc alkaline to shoshonitic characters; and (c) massive granitic plutons. Due to their melting sources having been modified by previously subducted continental/oceanic crust, the post orogenic basaltic magmas generally exhibit similar geochemical characteristics to those of island arc volcanic rocks. For instance, strong LILE and LREE enrichment and significant HFSE depletion. Comparing with those of IAB, they usually possess higher K 2O+Na 2O and ((Fe 2O 3+FeO)/((MgO), ((K 2O)/ ((Na 2O) ratios as well as higher Sr contents and Zr/Y ratios. Additionally, they exhibit enriched Sr and Nd isotopic ratios in relation to those of MORB and OIB, which are determined by the degree of LILE and LREE enrichment as well as the characters of subducted crust. For the basaltic magmas, they are derived from decompressional melting of metasomatized continental lithospheric mantle formed during previous plate subduction in response to unrooting of the thickened lithosphere, whereas the felsic magmas can be generated either by means of differentiation of basaltic melts in crust level magma chamber, or remelting of lower/middle crust as a result of basaltic underplating. The mechanism for extensive melting during post orogenic stage is closely related

关 键 词：岩浆作用 地球化学特征 伸展-减薄作用 造山后阶段 火山岩 形成机制 

分 类 号：P542.36[天文地球—构造地质学]