摘要
华北克拉通北缘渣尔泰-白云鄂博-化德元古宙裂谷带,是一条重要的成矿带,发育一系列大型、超大型矿床。裂谷带自西向东分别沉积了中元古代渣尔泰群、白云鄂博群和化德群。最近的研究表明,分布在狼山地区的渣尔泰群中火山岩夹层锆石U-Pb年龄及碎屑锆石年龄将其时代限定为新元古代,而渣尔泰山一带的渣尔泰群碎屑锆石年龄最小峰值大于1 700 Ma,二者很可能不是同一套地层。前者被从原渣尔泰群中解体出来,称为狼山群。但由于狼山群与渣尔泰群岩石组合的相似性,以及地层展布在区域走向上相连,特别是它们都是华北北缘重要的含矿层,矿化特征也具相似性,导致目前为止这两套地层的叠置关系还不清楚,这对于认识华北北缘中新元古代裂谷发育特征和演化,以及对认识相关矿化规律造成了一定的混乱和难度。本文对发育于狼山地区平行山体走向的韧性剪切变形带进行了研究。结果表明狼山韧性剪切带内变形岩石糜棱面理走向NE-SW,向NW或SE陡倾,矿物拉伸线理向SW或NE缓倾,野外及显微运动学标志显示为左行走滑韧性剪切带。剪切带内两个糜棱岩化云母石英片岩样品中变形白云母的40Ar/39Ar坪年龄分别为(356.7±2.5)Ma和(379±4.7)Ma,表明剪切带形成于晚泥盆世。狼山韧性剪切带很可能是古亚洲洋闭合过程中导致阿拉善地块与鄂尔多斯地块发生相对滑动所形成的。该剪切带晚泥盆世的左行走滑导致新元古代狼山群和中元古代渣尔泰群叠置到一起。因此,在渣尔泰山北侧和狼山南部及阿拉善块体北缘的覆盖层之下,很可能分别存在隐伏的新元古代成矿带和中元古代成矿带。
The Zhaertai-Bayan Obo-Huade Proterozoic rift, located in the northern margin of the North China Craton, is an important metallogenic belt that includes a series of large scale ore deposits. In this rift zone, from the west to the east, developed the Mesoproterozoic Zhaertai, the Bayan Obo and the Huade Group. Recently researchers have discovered that the Zhaertai Groups dispersed in the Lang Shan and Zhaertai Shah areas are in different strata according to their isotopic age. The former, named the Lang Shang Group, belongs to the Neoproterozoic in terms of zircon U-Pb ages of the intercalary volcanic and meta-sedimentary rocks~ the later belongs to the Mesoproterozoic owing to the minimum zircon peak ages （bigger than 1700 Ma）. However, the relationship between the two Groups is still unclear because of the similarities in their lithology composition, strike connection of stratigraphy distribution and especially mineralization, which has resulted in the difficult of understanding the development of Meso- to Neoproterozoic rifting and formation of the ore deposits. In this paper, we studied the ductile shear zone parallel to the extension of Lang Shan. The Lang Shan ductile shear zone is characterized by a steeply NE-SW-trending, a NW- or SE-dipping shearing foliation, and subhorizontal SW- or NE-plunging stretching lineations. Mesoscopic and microscopic kinematic indicators show sinistral shearing. Two ^40Ar/^39Ar plateau aged 356.7±2.5 Ma and 3794±4.7 Ma were obtained from the deformed muscovites in two mylonitic muscovite quartzite schist samples, indicating that this ductile shear zone was formed in the Late Devonian. Thus, the Lang Shan ductile shear zone likely resulted from the relative movements of the Alxa and Ordos blocks caused by the closure of the Paleo Asian oceam consequently the sinistral ductile shearing of the Lang Shan ductile shear zone likely resulted in the superposition of the Neoproterozoic Lang Shan and Mesoproterozoic Zhaertai Group. Therefore, it is plausible to hypothesize that
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2017年第3期263-275,共13页
Earth Science Frontiers
基金
中国地质科学院地质力学研究所基本科研业务费项目(DZLXJK201502)
国家自然科学基金项目(41472211
41502199)
