中亚造山带南蒙古地区石炭纪 : 二叠纪岩浆活动及其构造意义

Translated title of the contribution: Carboniferous-Permian Magmatism of Southern Mongolia, Central Asian Orogenic Belt and Its Tectonic Implications

吴妍蓉, 周海*, 赵国春, 韩以贵, 张东海, 王盟, 赵少伟, 裴先治, 赵千, Narantsetseg TSERENDASH, 耿红燕, Enkh-orshikh ORSOO

*Corresponding author for this work

Research output: Journal PublicationsJournal Article (refereed)peer-review

Abstract

中亚造山带作为显生宙以来全球最大的增生型造山带,记录了古亚洲洋俯冲、增生、闭合的全过程。南蒙古地区位于中亚造山带南缘中段,其晚古生代先后发育弧岩浆活动以及与伸展活动相关的岩石组合,是研究陆壳增生和改造的热点区域。笔者结合区域地质特征及前人研究对南蒙古地区石炭纪—二叠纪这一关键时期的岩石组合做出系统梳理和总结,研究区石炭纪—二叠纪岩浆活动大致可以分为早石炭世(350~325 Ma),晚石炭世(320~305 Ma)和早二叠世(300~280 Ma)3 个阶段。早石炭世(350~325 Ma)发育典型的弧岩浆岩且具有向南变年轻的趋势。此外,全岩 Nd 和锆石 Hf 同位素显示其主体具有显著的地幔贡献。综合前人认识,笔者认为这是古亚洲洋主洋盆以北多个次生的弧后洋盆俯冲后撤的结果。晚石炭世(320~305 Ma)以高硅花岗岩为主,尤其 315~310 Ma 的碱长花岗岩、碱长正长岩等是年轻弧地体重熔的产物,是俯冲大洋板片显著消耗的结束。早二叠世(300~280 Ma)发育伸展相关的岩石组合(如 A 型花岗岩、双峰式火山岩和基性岩墙),这些岩浆活动显示高温特征,且具有显著的地幔物质贡献。结合前人工作,特别是笔者的前期工作,上述岩浆活动是由石炭纪板片后撤之后高角度俯冲诱发的俯冲板片断离所造成,且前人研究成果表明南蒙古东西两侧均有类似的岩石、构造和沉积记录。因此,笔者提出,古亚洲洋主洋盆泥盆纪—二叠纪多期次的俯冲后撤导致了其北侧一系列次生的弧后洋盆的开启、俯冲至闭合,上述过程伴随了中亚造山带最后一次大规模侧向及其结束后板片断离诱发的垂向地壳增生。

As the largest Phanerozoic accretionary orogenic belt in the world, the Central Asian Orogenic Belt (CAOB) records the whole process of subduction, accretion and closure of the Paleo-Asian Ocean (PAO). The southern Mongolia, in the central segment of the southern CAOB, has successively developed rock associations of arc-magmatic activity and later extensional activity during the late Paleozoic, which is a key area for studying the accretion and transformation of continental crust. Combined with regional geological characteristics and previous studies, this paper systematically sorted out and summarized the rock association of the key period of Carboniferous-Permian in Southern Mongolia and the magmatic activity can be roughly divided into three stages: Early Carboniferous (350~325 Ma), Late Carboniferous (320~305 Ma), and the early Permian (300~280 Ma). During Early Carboniferous (350~325 Ma), the Southern Mongolia developed typical arc-type magmatic rocks having a southward migration trend. Whole-rock Nd and zircon Hf isotopes show that these rocks have significant mantle contribution. Combined with previous works, this resulted from slab retreating of a series of secondary back-are oceans of the PAO on the north of its main ocean basin. During Late Carboniferous (320~305 Ma), The southern Mongolia was dominated by high silica granites, especially the alkaline feldspar granites and syenites (315~310 Ma), which were produced by the remelting of earlier arc crusts, indicating the cessation of significant consumption of subducted oceanic plates. During the early Permian (300~280 Ma), extension-related magmatic rocks, such as A-type granite, bi-model volcanic rocks and basic dikes, were developed. The above magmatic activities showed the characteristics of high temperature and significant contribution of mantle materials. Therefore, we support that it was caused by the slab breakoff by high-angle subduction resulted from the aforementioned Carboniferous slab retreating. Previous studies show that there are similar rocks, structure and sedimentary records on both sides of Southern Mongolia. Therefore, we propose that the Devonian-Permian subduction and slab retreating of the main basin of the PAO caused the opening, subduction and closure of a series of secondary back-arc basins on the northern side of the PAO, which were accompanied by the last large-scale lateral crustal accretion and its cessation with subsequent slab-breakoff-induced vertical crustal accretion.
Translated title of the contributionCarboniferous-Permian Magmatism of Southern Mongolia, Central Asian Orogenic Belt and Its Tectonic Implications
Original languageChinese (Simplified)
Pages (from-to)1-19
JournalNorthwestern Geology
Volume57
Issue number3
DOIs
Publication statusE-pub ahead of print - 22 Mar 2024

Keywords

  • Central Asian Orogenic Belt
  • Carboniferous-Permian
  • magmatic activity
  • tectonic evolution
  • Southern Mongolia region

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