满加尔坳陷北部早古生代中晚期沉积-物源体系及其构造动力学控制因素

The North Mangar Depression experienced sharp transformation on sedimentary face during the middle-late Early Paleozoic, and the filling properties of the basin changed from starvation to compensation. However, the tectonic-dynamics mechanism of the sedimentary transformation remains hot controversial. With the aim to decipher the focus issues on the paleogeographic framework and basin-range coupling process in the North Mangar Depression during the middle-late Early Paleozoic, this study will select Quruqtagh area as the key study window, firstly, establish refined isochronal stratigraphic framework, then combine the previous studies, analyse the sedimentary facies and environment. Based on the facies-analysis results, as the crucial research method of this study, we will conduct high resolution provenance and tectonic attribute analysis on detrital sedimentary records, revealing sedimentary provenance spatial configuration and paleogeographic framework. Using the provenance path as the clue, we will study the coupling or decoupling relationships between the sedimentary records inside the basin and oceanic subduction or ocean-continent collision events occurred in the tectonic active belts both south and north side of the basin, figuring out the tectonic-dynamics source which lead to the rapid filling and leveling-up event in the North Mangar Depression during middle-late Ordovician and Silurian. Eventually, we will discuss further the type of prototype basin of the Mangar Depression and basin-range coupling process and mechanism.

满加尔坳陷北部早古生代中晚期沉积面貌发生急剧转变，盆地充填性质由饥饿状态快速转变为补偿状态，而对导致这次沉积剧变的构造动力学机制存在诸多争议。针对满加尔坳陷北部在古地理格局及其盆山转换过程等认识上的焦点问题，本项目拟选取库鲁克塔格地区为主要研究窗口，在精细的等时地层格架搭建的基础上，结合前人研究成果，首先进行沉积相（体系）与沉积环境分析，之后作为本项目的重中之重，开展多指标、多尺度的高分辨率碎屑沉积记录的物源和构造属性分析，揭示中晚奥陶世-志留纪期间满加尔坳陷北部沉积物源空间配置型式和古地理格局；以物源供给途径为线索，进行盆内沉积记录与盆地南、北两侧构造活动带发生的洋壳俯冲、洋陆拼合等事件耦合或脱耦的对比、匹配研究，据此解析导致满加尔坳陷北部当时发生剧烈沉降和快速填平补齐事件的构造动力学来源。在此基础上，进一步探讨满加尔坳陷早古生代原型盆地类型及与邻区的盆山作用过程和机制。

按照项目研究计划，项目开展了四个方面的研究：1）等时地层格架与沉积相分析；2）高精度碎屑沉积物源示踪分析；3）沉积-物源体系及古地理格局恢复；4）古构造演化及动力学控制因素分析。. 项目研究主要取得了三个方面的重要研究成果，分别为：1）满加尔坳陷上奥陶统碎屑物源。库鲁克塔格南区上奥陶统砂岩碎屑锆石U-Pb年龄记录了527-694Ma、713-870Ma、904-1090Ma、1787-2094Ma和2419-2517Ma共5期构造热事件，并以新元古代（峰值为760Ma）和晚古元古代（峰值为1975 Ma）两期年龄为主体，通过与所有可能的物源区构造热事件年龄对比，其与塔里木克拉通基底构造热事件年龄具有最高的吻合度，表明中晚奥陶世库鲁克塔格南区及满加尔东北部碎屑物源主要来自于盆地内部古隆起，如库鲁克塔格北部隆起或塔北古隆起，而非盆地南侧的阿尔金造山带；2）库鲁克塔格南区上志留统砂岩碎屑样品中也存在少量420-430Ma的年龄，跟样品沉积时代很接近，锆石CL图显示岩浆振荡环带和较好的自形晶，说明来自近源的岩浆岩，库尔勒一带出露的花岗岩类年龄为约420Ma，认为这些420-430Ma的年轻年龄来自塔里木东北缘陆缘弧岩浆带。塔北地区上志留统砂岩碎屑锆石U-Pb年龄也检测到420Ma的次峰值，可以得出跟库鲁克塔格南区上奥陶统砂岩类似的结论。因此，综合起来表明塔里木东北缘晚志留世已经由被动陆缘转变为活动陆缘；3）晚奥陶世桑比阶至凯迪阶早期，南侧的北阿尔金地区发生洋壳俯冲、消减甚至碰撞造山作用，北侧的Terskey洋向塔里木克拉通下发生南向俯冲，由于南、北两侧活动带构造作用的叠加影响，满加尔坳拉槽及碳酸盐台地发育呈现出不同于经典模式的“个性”特征。晚志留世，南天山洋形成并向南俯冲导致塔里木东北缘陆缘弧岩浆带的产生，该岩浆弧为库鲁克塔格和塔北地区都提供了碎屑物源，但两地碎屑主体物源仍来自南侧阿尔金造山带，复杂的物源供给体系也是满加尔坳拉槽的“个性”之一。