摘要
有关阿尔泰造山带中变质岩形成时代问题,目前仍有争议。特别是中国-哈萨克斯坦联合地质科学考察队将其绝大部份均划为古元古-中元古代变质岩系后,更引起诸多地质学家的关注。本文研究的青河片麻岩出露在青河县西南地区,在构造上处于额尔齐斯剪切带。青河片麻岩的元素地球化学和Nd-Sr同位素组成特征表明其原岩形成于岛弧构造环境。应用精确的SHRIMP锆石U-Pb定年,获得该变质岩系中英安质片麻岩中锆石的年龄为281±3(2σ)Ma,代表其片麻岩的形成年龄。研究中未发现有任何前寒武纪古老锆石或相关的年龄信息,因此研究结果不支持该区变质岩为“前寒武纪”的观点。结合片麻岩中锆石阴极发光图像特征,说明该地区的变质作用和岩浆作用的时间范围在293±6Ma～271±5Ma期间。因此,该项研究结果确定了阿尔泰造山带发生在二叠纪早期一次重要地质热事件的可靠时限。额尔齐斯构造剪切带中青河片麻宕的锆石U-Pb年龄,以及各种变质岩中角闪石和黑云母的^(40)Ar/^(39)Ar年龄,记录了阿尔泰造山带晚古生代时期一次重要的构造、变质作用、快速隆升的动力学过程,为研究晚古生代古亚洲洋的闭合或大陆的回返时限提供了初步的证据。
Formation age of metamorphic rocks occurred in Altai orogen of China has been questioned up to now, especially, since most part of metamorphic rocks were designated to be Paleo Proterozoic to Meso-Proterozoic metamorphic rocks by the geoseientific survey team of China-Kazakstan. Qinghe gneiss studied in this paper occurs in the southwest area to Qinghe County and locates in Erqishi shearing zone. Geochemical characteristics and Nd-Sr isotopic compositions of gneisses show formation in island arc setting. SHRIMP U-Pb analyses for zircons from an andesitic gneiss yield a precise age of 281 ± 3（2σ）Ma, representing formation age of the gneiss. Any older zircons or related Precambrian ages from the Qinghe gneiss have been never found in this study, consequently this result does not support opinion about formation of Qinghe gneiss in Precambrian. Combined with characteristics of cathodoluminescence images of zircons from this gneiss, it is indicated that metamorphism and magmatism could be happened during period of 293 ± 6Ma - 271 ±5Ma. The available data confirm the time limit of a significant geological thermal event in the Ahai Orogen during the early Permian. To combine zircon U-Pb SHRIMP age of Qinghe gneiss and ^40Ar/^39Ar ages of hornblende and biotite from Erqishi shearing zone, important kinetic events, including tectonics, metamorphism and fast cooling or rapid uplifting in Ahai orogen during late Paleozoic were reveulled. This precise and credible zircon SHRIMP age of the Qinghe gneiss possibly provides a primary evidence for study on time limit of closure of Paleo-Asia Ocean and continental thrust during the late Paleozoic.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第1期1-10,共10页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划项目"中亚造山与成矿研究"(编号:2001CB409805)
国家自然科学基金项目(40173026)
中国科学院广州地球化学研究所创新项目(A15-041107)资助成果.
