摘要
蛇绿岩套是运用板块构造理论解释造山带构造演化的关键,合理理解蛇绿岩套的形成、演化有助于构建与板块构造理论吻合的造山带演化模型。经典的蛇绿岩套发育由地幔橄榄岩、堆晶辉长岩、枕状玄武岩-深海沉积岩组成的“三位一体”岩石组合,与现代洋中脊新形成的大洋岩石圈具有相同的岩石组合及岩石空间分布样式。地球化学家们在经典蛇绿岩套定义基础上,根据玄武质岩石地球化学特征的变化,提出了“俯冲带之上(SSZ)蛇绿岩套”概念,并对其划分亚类、构建相应的概念性成因模型,从而引发了“在俯冲汇聚阶段能否发生岩石圈裂解、形成新生洋壳”的“蛇绿岩难题”。针对阿尔卑斯-喜马拉雅造山系内的两个典型SSZ型蛇绿岩套的详细解剖表明,部分SSZ型蛇绿岩套的定义可能存在玄武质岩石“年代误植”、“构造背景误植”问题。前人定义的伊朗克尔曼沙赫弧前蛇绿岩套、巴基斯坦拉斯科赫弧间蛇绿岩套均由两部分组成:下部为形成于洋中脊环境、时代较老的大洋岩石圈残片;其上分别被年轻的弧前盆地和岛弧相关火山-沉积岩组合不整合覆盖。显然,大部分SSZ型蛇绿岩套是经典洋中脊蛇绿岩套残片与形成于其他构造环境(如大陆裂谷、俯冲带)的火山-沉积岩序列的组合体,并不存在蛇绿岩难题。合理解释造山带内的基性-超基性岩组合的成因需要详细的野外调查以确定不同岩石单元之间的时空关系。
Ophiolite suite is a key to unlock tectonic evolution of any orogenic belt in term of plate tectonics,which depends on our understanding of the formation and evolution of ophiolite suite.A classic ophiolite suite consists of peridotite in the lower,massive or layered gabbro in the middle,and pillow basalt and pelagic sedimentary rocks in the upper.They form the Steinmann trinity,an analogy to the petrological architecture of an oceanic lithosphere segment formed in middle oceanic ridge.Geochemists proposed the term“suprasubduction zone”ophiolite suite according to development of basalts with non N-MORB affinity in some classic ophiolite suites.This leds to the“ophiolite conundrum”concerning whether sea-floor spreading can occur in plate convergence settings.They further subdivided the SSZ ophiolite suite into several sub-types and proposed conceptive models to interpret their formation processes.Detail anatomy of two typical SSZ ophiolite suites from the Alps-Himalayan orogenic system demonstrated that the definition of SSZ ophiolite suite is likely problematic that contains incorrect interpretation in timings as well as in tectonic settings of some basaltic rocks.Both the Kermanshah forearc ophiolite suite in Iran and the RashKoh intra-arc ophiolite suite in Pakistan are made of two portions,an older oceanic lithosphere fragment in the lower and a younger volcanoclastic successive in the upper.The volcanoclastic succession in Kermanshah represents forearc basin fillings,while that in RashKoh is subduction-related.It is highly probable that most SSZ ophiolite suites contain a fragment of the classic ophiolite suite that form in middle oceanic ridge and a volcanoclastic succession formed in other tectonic settings such as continent rift or subduction zone.As such,the“ophiolite conundrum”disappears.Understanding the formation mechanism of a mafic to ultramafic assemblage in any orogenic belt requires detail field study to reveal the temporal and spatial distribution of these rocks.
作者
杨天南
信迪
YANG Tiannan;XIN Di(Institute of Geology,Chinese Academy of Geological Science,Beijing 100037,China)
出处
《东华理工大学学报（自然科学版）》
2023年第6期537-546,共10页
Journal of East China University of Technology(Natural Science)
基金
国家自然科学基金重点项目“定量、半定量重建扎格罗斯造山带的新特提斯洋-陆俯冲过程”(92055206)。
关键词
蛇绿岩套
俯冲带之上
构造背景
玄武岩地球化学
时空分布样式
ophiolite suite
suprasubduction zone
tectonic settings
basalt geochemistry
temporal and spatial distribution
