摘要
利用新近完成的1∶25万区域地质调查资料和其他相关的研究成果,编制了第一张冈底斯带中生代岩浆岩分布图,初步厘定了中生代岩浆作用的分布特点和时空框架,并利用已有的地球化学数据重点分析了早白垩世花岗岩类的岩浆作用性质。将冈底斯带中生代岩浆活动置于时空框架内分析发现,南冈底斯和北冈底斯在侏罗纪和白垩纪时主要受俯冲作用的影响,而冈底斯弧背断隆带和中冈底斯自早侏罗世以来除了受到俯冲作用的影响外,还受到了自东向西逐步扩展的碰撞作用的影响,结合构造和地层研究的新资料,提出冈底斯带中生代岩浆活动可用班公湖-怒江洋壳向南、新特提斯洋壳向北的双向剪刀式(剪刀口向西张开)俯冲模式来解释。建议将传统的"拉萨地块"解体为以古—中元古代地壳物质组成为特色的真正意义上的"拉萨地块"(可能包括冈底斯弧背断隆带和中冈底斯)及其南北两侧通过岛弧增生拼贴形成的以新元古代地壳物质为特色的南冈底斯岛弧带和北冈底斯岛弧带。提出二叠纪时期冈底斯带可能为一个在古特提斯洋盆中呈条块状"漂浮"的冈瓦纳碎片。新发现和厘定的由狮泉河-拉果错-永珠-纳木错-嘉黎混杂岩带所代表的弧后洋盆的消减和闭合可能在中冈底斯和北冈底斯岩浆成因中并未起到主导作用。
The authors used the latest 1：250000 regional geological survey data and other relevant research results to compile the first map of distribution of Mesozoic magmatic rocks of the Gangdise belt, Tibet, and preliminarily define the distribution characteristics and tempo-spatial framework of Mesozoic magmatism and discuss the nature of magmatism of Early Cretaceous granitoids. When an analysis is performed by placing the Mesozoic magmatism of the Gangdise belt in a tempo-spatial framework, we may find that the Southern Gangdise and Northern Gangdise were mainly affected by subduction during the Jurassic and Cretaceous, while since the Early Jurassic the Gangdise back-arc fault uplift and Central Gangdise also underwent the effects of collision that extended from east to west in addition to the effects of subduction. Based on the aforesaid study, combined with new data of stmctura） and stratigraphic studies, the authors suggest that Mesozoic magmatism in the Gangdise belt may be explained by the model of bidirectional scissors-style subduction （the scissors open toward the west）, with the Bangong Co-Nujiang oceanic crust subducted southward and the Neo- Tethys oceanic crust northward. The authors suggest that the conventional ＂Lhasa block＂ should be disassembled into the real ＂Lhasa block＂ characterized by Paleo- and Mesoproterozoic crustal materials （possibly including the Gangdise back-arc fault uplift and Central Gangdise） and the Southern Gangdise island-arc belt and Northern Gangdise island-arc belt consisting mostly of Neoproterozoic crustal materials that accreted to the south and north sides of the real ＂Lhasa block＂ by island-arc accretion during Mesozoic time, respectively. They propose that during the Pernfian the Gangdise belt might be a fragment of Gondwana that floated in the Paleo-Tethyan Ocean. The subduction and closure of the back-arc oceanic basin represented by the Shiquan River-Lagkor Co-Yunzhug- Nam Co-Lhari ophiolitic melange zone may not have played a dominant role in the generation of Mesozoic magmas in the Central Gangdise and Northern Gangdise.
出处
《地质通报》
CAS
CSCD
北大核心
2008年第9期1535-1536,I0001,I0002,1537-1550,共18页
Geological Bulletin of China
基金
国土资源部百名优秀青年科技人才计划项目<西藏南西部二叠纪玄武岩的区域对比及意义>
国家自然科学基金项目(编号:40503005
40572051
40473020)
中国地质调查局青藏高原基础地质综合研究项目(编号:1212010610101)资助。
关键词
双向剪刀式俯冲模式
向西扩展的碰撞作用
岛弧型岩浆作用
中生代岩浆岩
西藏冈底斯带
bidirectional scissors-style subduction model
westward propagating collision
island-arc magmatism
Mesozoic magmatic rocks
Gangdise belt, Tibet
