论博格达俯冲撕裂型裂谷的形成与演化  

Initiation and evolution of the Bogda subduction-torn-type rift.

作　　者：顾连兴[1] 胡受奚[1] 于春水[1] 吴昌志[1] 严正富[1] 

机构地区：[1]南京大学地球科学系

出　　处：《岩石学报》2001年第4期585-597,共13页Acta Petrologica Sinica

基　　金：国家"九.五"攻关305项目(No.96-915-05-03-01);国家自然科学基金项目(No.49172094)合作研究成果;南京大学现代分析中心测试基金;南京大学成矿作用国家重点实验室开放课题的资助.

摘　　要：博格达裂谷带位于准噶尔与吐-哈两个前寒武纪地块之间,呈东-西走向,东端与克拉麦里-哈尔里克泥盆-石炭纪火山弧呈大角度相交。该裂谷于早-中石炭世启动和沉降,在盆地中堆积了巨厚的陆源碎屑岩夹双峰式火山岩。裂谷的闭合发生于中石炭世末至晚石炭世。在裂谷闭合后区域构造由挤压向拉张的转折时期,发生了以辉绿岩为主的侵入活动,并伴有少量中-酸性分异产物。博格达裂谷东、西两段的演化特征有着显著差异。东段早石炭世就已开始裂离,裂离过程的火山岩以玄武岩为主,仅有少量流纹岩,裂谷盆地强烈沉降,形成深海-半深海环境,裂谷在中石炭世未至晚石炭世初即已闭合,裂谷岩系因强烈褶皱,与上覆二叠系呈明显角度不整合,显示了“突变”式闭合特征。与此不同的是,西段至中石炭世才开始明显裂离,裂软过程的火山岩以英安岩和流纹岩为主,玄武岩量较少,火山-沉积岩系均形成于浅海环境,裂谷至晚石炭世末才发生闭合,裂谷岩系因未发生强烈褶皱,故与上覆二叠系为平行不整合接触。显示了“渐变”式闭合特征。该裂谷的形成是古亚洲洋壳向先存的准-吐-哈陆块斜向俯冲,将其东南端撕裂的产物,因而可称为俯冲撕裂型裂谷。演化过程沿走向的明显不均一性是这类裂谷的重要特点。The W-E trending Bogda rift is situated between the Junggar and the Turfan-Hami Precambrian blocks. It extends with the east and is connected with the Devono-Carboniferous Kelameili-Harlik volcanic arc at a large angle. Following the Early and Middle Carboniferous initiation of rifting, a thick sequence of terrestrial clastics with bimodel volcanites was accumulated in the Bogda basin. Rift closure took place towards the end of Middle Carboniferous or during the Late Carboniferous time. Magmatism characterised by widespread diabase with minor intermediate-acidic differenciates represents post-closure tectonic conversion from compression to extension. The eastern and western sections of the rift are distinct in their evolution history. Rifting of the eastern section was commenced during early Carboniferous and featured by volcanism dominated by basalts with minor rhyolites. Intense subsidence of this section led to a bathyal or abyssal environment, and closure of the rift was accomplished by the end of middle Carboniferous or early at the late Carboniferous time. On intense folding, rift sequence of the eastern section is overlain unconformably by the Permian strata, exhibiting 'abrupt' closure of the rift. By contrast, rifting of the western section did not become prominent until middle Carboniferous epoch. Rift volcanites are dominated by dacites and rhyolites with minor basalts, and the volcanic-sedimentary sequence was accumulated in a shallow-sea environment. It was not until late Carboniferous that the western section of the rift closed. Without intense folding, rift sequence of this section passes into the overlying Permian strata through a parallel unconformity, exhibiting 'gradational' closure of the rift. This rift was initiated by the tearing force induced by oblique subduction of the ancient Asian oceanic crust beneath the ancestral Junggar-Turfan-Hami continental block, and could, therefore, be designated as a subduction-torn-type rift. Conspicuously non-uniform evolution along strike is an essential

关 键 词：造山带 裂谷 板块俯冲 岩浆活动 火山作用 

分 类 号：P542.4[天文地球—构造地质学]