中亚造山带伊犁北缘早古生代海相斑脱岩地质意义  

Age, Origin and Geological Implications of Early Paleozoic Marine Bentonites,Northern Yili Block of Central Asian Orogenic Belt

作　　者：曹胜楠 王博[1] Cao Shengnan;Wang Bo(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)

机构地区：[1]南京大学地球科学与工程学院,内生金属矿床成矿机制研究国家重点实验室,江苏南京210023

出　　处：《地球科学》2021年第8期2804-2818,共15页Earth Science

基　　金：国家自然科学基金项目(Nos.41772225,41390445,41172197,41222019);南京大学内生金属矿床成矿机制研究国家重点实验室自主研究课题(ZZKT-201603)。

摘　　要：伊犁地块位于西天山北部,通常认为其北缘经历了晚古生代活动陆缘的演化,但对其早古生代构造沉积演化(尤其是同位素定年)的研究仍较为薄弱.在伊犁北缘果子沟地区的奥陶系黑色硅质页岩中发现多层斑脱岩(蚀变凝灰岩)夹层,奥陶系发生了强烈褶皱变形,在其中一个倒转向斜的核部和翼部选取两层斑脱岩进行了锆石U-Pb测年. 2个斑脱岩样品中的锆石显示岩浆锆石的特征,其加权平均年龄分别为458±2 Ma和460±2 Ma.结合前人研究成果,认为该斑脱岩的沉积时代为中奥陶世末期(达瑞威尔阶顶部),该时代与温泉地区大陆弧岩浆岩年龄基本一致,是准噶尔洋在中-晚奥陶世向伊犁地块之下俯冲的又一证据;该斑脱岩与全球范围内的大规模火山活动时代一致,该期火山活动可能是中-晚奥陶世全球气候变化与生物大灭绝的重要原因.The Yili Block, a part of the Central Asian Orogenic Belt(CAOB), is located in the northern part of Chinese western Tianshan. It is generally believed that the northern Yili Block was an active continental margin during the Late Paleozoic.However, the study of sedimentary and tectonic evolution(especially the isotopic dating) of the Early Paleozoic in the northern Yili Block is relatively weak. Several bentonite(altered tuff) horizons within the Ordovician black siliceous shale sequences in the Guozigou area were recognized. The Ordovician strata were intensively folded. Two bentonite samples were collected from the core and limb of a syncline for zircon U-Pb dating. Both samples indicate their magmatic origin. They yielded consistent and concordant apparent ages, and weighted average ages of 458±2 Ma and 460±2 Ma, respectively. The previous and newly obtained data implies that the bentonites were deposited at the end of Middle Ordovician(Darriwilian Stage). The timing of the bentonites in this study is in agreement with the age of the continental arc-type magmatism in the Wenquan area, both were likely derived from subduction of the Junggar Ocean beneath the northern Yili Block. The bentonites are also coeval with the worldwide intense volcanism, and are likely one of the main causes of the Late Ordovician global climate change and mass extinction.

关 键 词：伊犁地块 奥陶系 斑脱岩 准噶尔洋 俯冲增生 造山作用 构造地质学 

分 类 号：P541[天文地球—构造地质学]