柴达木盆地北缘新元古代-前中生代几个重要不整合面地质特征及其构造意义

Geological Characteristics of Unconformities in Neoproterozoic to Pre-Mesozoic Sequences in the North Qaidam Area and their Tectonic Implications

地层不整合接触是研究地质发展历史中构造演化及鉴定地壳运动特征的重要依据。通过大范围的野外露头观察与分析,根据不整合面(包括风化铝土层及铁质层)的发育特征,不整合面上下地层的岩性、产状、变质与变形程度等地质信息,在柴达木盆地北缘(简称"柴北缘")地区前中生界沉积地层中共识别出新元古界全吉群-达肯大坂群、下寒武统欧龙布鲁克组-全吉群、泥盆系牦牛山组-下古生界以及中生界-前中生界4个大的区域性角度不整合接触面(即4个Ⅰ级构造层序界面)。这4个角度不整合面的形成均对应着区域性的构造反转事件,与周边大地构造边界的汇聚事件密切相关。在此基础上,根据不同构造带内地层、不整合的发育及分布特征,结合古生物、同位素年代学资料明确4个构造层序界面以及其制约的3个构造层序的时间跨度,建立地层(包括不整合面)-时间对应关系,并与前人建立的构造-岩浆-热年代格架进行对比,以此限定俯冲作用和碰撞造山的时限。

Stratigraphic unconformity is an important basis for the study of tectonic evolution and crustal movement in geological history. Through large-scale outcrop observations and analyses, four large regional angular unconformities have been identified in the Pre-Mesozoic sedimentary strata in the northern Qaidam margin, according to the development characteristics of unconformities(including the weathering aluminous layer and ferruginous layer) and the geological information such as lithology, occurrence, and metamorphism and deformation degrees of the unconformity strata. The four regional unconformities include those occur at boundaries between the Neoproterozoic Quanji Group and the Dakendaba Group, the lower Cambrian Oulongbuluke Group and the Quanji Group, the Devonian Maoniushan Formation and the Lower Paleozoic, and the Mesozoic and Pre-Mesozoic sequences. Formation of the four angular unconformities are correspond to regional tectonic inversions which are closely related to converge events. Considering the occurrences of the strata and unconformities in different tectonic belts, as well as the paleontology and isotopic geochronological data available, we redefined the regional history of subduction and collisional orogeny.