岩浆弧火成岩构造组合与洋陆转换  

Magmatic Arc and Ocean—Continent Transition:Discussion

作　　者：邓晋福[1] 冯艳芳[2] 狄永军[1] 刘翠[1] 肖庆辉[2] 苏尚国[1] 赵国春[1] 孟斐[1] 马帅[1] 姚图 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,岩石圈构造、深部过程及探测技术教育部重点实验室,北京100083 [2]中国地质调查局发展研究中心,北京100037

出　　处：《地质论评》2015年第3期473-484,共12页Geological Review

基　　金：国家自然科学基金会和中国科学院"板块构造与大陆动力学"学科发展战略项目"侵入岩大地构造重大关键地质问题研究"(编号:中地调研合同[2014]第169号);"全国侵入岩成矿地质背景研究"(编号:中地调研合同[2012]第107号);中国地质调查局项目"内蒙古东部-黑龙江西部燕山期火成岩特征及其成矿意义"(编号:12120114020901);"内蒙古中东部-黑龙江中生代岩浆作用与金(银)铜(钼)矿成矿作用研究"(编号:1212011121075)的成果

摘　　要：本文从岩浆弧的火成岩构造组合、主要地质特征和弧地壳成熟度几个方面,讨论洋陆转换作用及其过程。表征洋俯冲环境的火成岩构造组合主要有英云闪长岩—奥长花岗岩—花岗闪长岩(TTG)组合,高镁安山岩组合,镁安山岩组合,Adakite组合(即高锶低钇中酸性岩)与富铌弧玄武岩组合等。基于火成岩构造组合的配置,讨论了4种可能的洋俯冲壳的壳幔结构:(1)热的年轻的俯冲洋壳与上覆冷的幔楔岩石圈;(2)冷的老的俯冲洋壳与冷的幔楔岩石圈;(3)冷的老的洋壳与热的幔楔软流圈;(4)热的年轻的俯冲洋壳与上覆幔楔软流圈。讨论了弧岩浆前锋作为结构标志以及空间组成极性的构造意义;讨论了弧火山作用的时间极性与弧成熟度及其地壳厚度之间的正相关关系,提出岩浆弧地壳双层结构的模型,下地壳主要为玄武质的基性麻粒岩和角闪岩,上地壳为长英质的TTG片麻岩,相当于大陆壳形成的第一阶段,即新生陆壳。岩浆弧及其洋—陆过渡性的弧地壳是洋俯冲作用形成的洋陆转换带(或增生造山带)的最重要的记录。This paper discusses the ocean—continent transition of the magmatic arc and its processes in terms of the igneous petrotectonic assemblage,the geologic characteristics,and the arc maturity. The major igneous petrotectonic assemblages characterized the oceanic subduction may be tonalite—trondhjemite—granodiorite（ TTG）,high-Mg andesitic,Mg andesitic,adakitic and Nb-enriched arc basaltic assemblages. Based on the disposition of the petrotectonic assemblages,four possible models of oceanic subducted crust—mantle structure are discussed：（ 1） the warm young subducted oceanic crust and the above-situated cool mantle-wedge lithosphere;（ 2） both the cool older subducted oceanic crust and the mantle-wedge lithosphere;（ 3） the cool older subducted oceanic crust and the above-situated warm mantle-wedge asthenosphere;（ 4） both the warm oceanic crust and the mantle-wedge asthenosphere. The tectonic indications of the arc magmatic front as the structure markers and the special compositional polarity are also discussed. A model of two-layered arc crust is suggested,the lower arc crust may be composed of the mafic granulites and amphibolites,and the upper crust consists of the felsic TTG gneisses.The petrologic structure of the arc crust may have a typical transitional character between the ocean crust and the continental crust or may be regarded as the first stage of the continental crust,the juvenile continental crust. The magmatic arc and the transitional character of the arc crust are regarded as the most important record for the ocean—continent transitional belts（ or the accretional orogenic belts） derived by the oceanic subduction.

关 键 词：岩浆弧 岩浆前锋 组成极性 弧成熟度 弧地壳 新生陆壳 

分 类 号：P588.1[天文地球—岩石学]