柴北缘欧龙布鲁克微陆块西段原“达肯大坂岩群”的沉积时代、源区及其对冈瓦纳大陆重建的制约

Depositional age and source analysis of the Late Neoproterozoic-Early Paleozoic metamorphic strata identified from the Dakendaban Group in the western Oulongbuluke microcontinent of the North Qaidam Basin:Constraints on the Gondwana continental reconstruction

柴北缘欧龙布鲁克微陆块西段原古元古代达肯大坂岩群中新识别出一套新元古代晚期-早古生代早期浅变质地层,其原岩沉积时代、沉积物质来源研究可为欧龙布鲁克微陆块在冈瓦纳大陆重建中的古地理位置提供有效约束。岩石学、碎屑锆石U-Pb年代学研究表明,该浅变质地层主体为一套发育绿片岩相-低角闪岩相变质的石英片岩组合,最大沉积年龄为548~563Ma,并具有~2486Ma、~1594Ma、~1108Ma、~936Ma、~776Ma及~548Ma等6个碎屑锆石年龄峰值,与发育高角闪岩相-麻粒岩相变质的古元古代达肯大坂岩群存在明显差异。此外,通过与周边其他地块同时代地层的碎屑锆石年龄谱系的综合对比,认为欧龙布鲁克微陆块在新元古代晚期-早古生代早期主要接受了来自印度板块东北部的沉积物质;在冈瓦纳大陆重建中,该陆块与南祁连、阿拉善、羌塘等微陆块均位于印度板块东北缘。

A newly identified Late Neoproterozoic-Early Paleozoic low-grade metamorphic strata,which has been disintegrated from the Palaeoproterozoic Dakengdaban Group(DG)in the western segment of the Oulongbuluke microcontinent(OLB),is a key object to understand the paleogeography of the Early Paleozoic Gondwana.Petrological study of this strata indicates that it is predominantly composed of various quartz schists that experienced a greenschist to lower amphibolite facies metamorphism,exhibiting significant difference from the DG which underwent an upper amphibolite to granulite facies metamorphism.A comprehensive detrital zircon U-Pb dating analysis of 382 zircon grains from four samples of the strata yielded a minimum age peak of 548~563Ma,suggesting that its maximum sedimentary age is not earlier than the Late Neoproterozoic.Additionally,the detrital zircons are characterized by six prominent age peaks at approximately 2486Ma,1594Ma,1108Ma,936Ma,776Ma and 548Ma,respectively.These features indicate that the newly identified strata are markedly distinct from the DG.The age spectra for the OLB,in combination with those of the OLB s surrounding microcontinents,exhibits similarities to those of the South Qilian,Alashan,Qiangtang and North India,but distinctively differs from those of the Tarim Block,South China Block and Australian Plate.Our interpretation suggests that the OLB should primarily receive sediments from northeastern part of the India Plate during the Late Neoproterozoic-Early Paleozoic.Moreover,the comparable age spectra also imply a close affinity between the OLB,South Qilian,Alashan,Qiangtang and North India in the Gondwana supercontinent,and the location of these microcontinents in the reconstruction of Gondwana should lie on the northeastern margin of the Indian Plate.