摘要
早古生代原特提斯洋在祁连造山带的分支本文称为古祁连洋。其洋内及邻区存在中祁连、阿拉善、柴达木、华北、扬子、塔里木等多个陆块、微陆块,处在一个复杂的多岛洋的环境中。祁连地区早古生代经历了较为复杂的俯冲拼合、碰撞造山过程。本文探讨了祁连造山带的几个构造单元构造属性,认为早古生代阿拉善微陆块南缘为被动大陆边缘,中祁连北缘为活动大陆边缘。阿拉善南部与之平行的龙首山构造单元为俯冲造山形成的增生楔体;北祁连构造带为一套俯冲增生杂岩,包含高压变质岩带、蛇绿岩带、岛弧岩浆和部分洋壳残片等,记录了古祁连洋壳从大陆裂解,洋壳形成,俯冲拼合,碰撞造山的造山过程。495Ma左右南祁连南部柴达木微陆块向北俯冲的影响,古祁连洋壳俯冲受阻,俯冲带向北后退,形成大岔大坂岛弧。弧前地区发生洋-洋俯冲事件,堆积增生大岔大坂、白泉门、九个泉等SSZ型北祁连蛇绿岩北带,并伴随第二期清水沟、牛心山、野牛滩等地岩浆事件。460Ma左右阿拉善微陆块和中祁连微陆块开始碰撞拼合,古祁连洋开始闭合。值得注意的是拼合过程不是均一的,存在自西向东斜向"剪刀式"的拼合方式,产生了由西向东年代变新的"S"型同碰撞岩浆岩。约440Ma古祁连洋闭合,进入陆内造山阶段。440Ma之后,拼合陆块处在一种拉伸的构造环境之下,金佛寺、牛心山、老虎山等地产生碰撞后岩浆岩。422~406Ma发生俯冲折返、高压榴辉岩和高压低温蓝片岩退变质作用,形成以紧闭不对褶皱为特征的第二幕变形。根据各陆块、微陆块碎屑锆石年龄谱分析对比,中祁连基底应与华北不同,而可能与扬子有关。Rodinia超大陆聚合之前,中祁连微陆块作为一个独立的微陆块与华北、扬子保持一定距离。1.0~0.8Ga Rodinia超大陆聚合过程中祁连微陆块与冈瓦纳北缘拼贴在一起,而距华北较远。随着Rodinia超大陆裂解,中祁连微陆块远离冈瓦纳,逐渐向华北靠近,500~400Ma原特提斯洋闭合,华北、阿拉善与中祁连拼合,并整体拼合到冈瓦纳大陆北缘。
The branch of the Proto-Tethys Ocean in the Qilian Orogen is known as the Paleo-Qilian Ocean during the Early Paleozoic. Many eontinents/microcontinents, such as the Central Qilian, the Alxa, the Qaidam, the North China, the Yangtze and the Tarim blocks, located in and near the Paleo-Qilian Ocean, generating a complex archipelagic ocean. The Qilian area experienced a complex subduction-collision process in the Early Paleozoic. This paper discusses the tectonic attribute of the units in the Qilian Orogen. It is suggested that the southern Alxa Microcontinent was a passive continental margin, while the northern Central Qilian was an active continental margin during the Early Paleozoic. The Longshoushan tectonic unit, resulted from the subduction-collision process, is an accretionary wedge parallel to the southern Alxa. The North Qilian tectonic unit is a subduction accretionary complex composed mostly of high-pressure metamorphic rock, ophiolite, arc magmatite and some oceanic fragments. It records the evolution of the Paleo-Qilian Ocean from continental rifting, oceanic crnstal growth, subduction and collision. The subduction zone of the Paleo- Qilian Ocean retreated northward due to the northward subduction of the Qaidam Microcontinent at about 495Ma, forming the Dachadaban Arc. There was a subduction event occurring in the fore-arc area, forming the SSZ-type North Qilian ophiolite belts in the Dachadaban, the Baiquanmen and the Jiugequan, and a second magmatic event in the Qingshuigou, the Niuxinshan and the Yeniutan. The Paleo-Qilian Ocean began to close at 460Ma due to the collision between the Alxa and the Central Qilian microcontinents. The collisional process did not occur at the same time. The ＂ scissor-like＂ collision model from west to east is more reasonable, accompanied by ＂S＂ type collision-related magmatite with the age younging from west to east. The closure of the Paleo-Qilian Ocean terminated at 440Ma. Then the intracontinental orogenic stage started. Under an extensional environment after the collision, the magmatite formed in the Jinfosi, Niuxinshan, Laohushan and other places after 440Ma. The retrograde metamorphism of HP eclogites and HP-LT blueschists occured as a result of the exhumation of the subducted plate during 422 - 406Ma, forming the second episode of deformation characterized by asymmetric tight fold. According to the analysis of the detrital zircon age spectra of different continents or microcontinents, it could be concluded that the basement of the Central Qilian Microcontinent is different form that of the North China Block, but may be associated with that of the Yangtze Block. The Central Qilian Microcontinent was far away from the North China and the Yangtze blocks as an independent microcontinent before the assembly of the Supercontinent Rodinia. Then the Central Qilian Microcontinent assembled to the Yangtze Block due to the formation of the Supercontinent Rodinia during 1.0 - 0. 8Ga, still far away from the North China Block. After the breakup of the Supercontinent Rodinia, the Central Qilian Microcontinent drifted away from the Gondwana, and gradually approached the North China Block. The Proto-Tethys Ocean closed during 500 - 400Ma, and the Alxa, the North China and the Central Qilian blocks assembled again to the northern margin of the Gondwana.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第6期1633-1652,共20页
Acta Petrologica Sinica
基金
国家自然科学基金重大项目(41190072
41190070)
国家杰出青年基金项目(41325009)
泰山学者特聘教授项目
鳌山卓越科学家计划(2015ASTP-0S10)联合资助
关键词
原特提斯
早古生代
构造变形
微陆块
构造演化
Proto-Tethys Ocean
Early Paleozoic
Deformation
Microcontinent
Tectonic evolution
