Growth of the Qaidam Basin during Cenozoic exhumation in the northern Tibetan Plateau: Inferences from depositional patterns and multiproxy detrital provenance signatures
Growth of the Qaidam Basin during Cenozoic exhumation in the northern Tibetan Plateau: Inferences from depositional patterns and multiproxy detrital provenance signatures
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DOI：
10.1130/l449.1
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发表时间：
2016-02-01
期刊：
影响因子：
2.4
通讯作者：
Nie, Junsheng
中科院分区：
文献类型：
--
作者：
Bush, Meredith A.;Saylor, Joel E.;Nie, Junsheng
青藏高原北部柴达木盆地的沉积学和物源分析有助于阐明盆地边界地区初始变形和折返的地层特征。该盆地记录了几个不同物源区的抬升和剥离的沉积转变。在东北缘盆地边缘，大红沟背斜6200m厚的新生代层序中保存了折返和盆地隔离的碎屑记录。从轴向河流和边缘湖相沉积向横向河流沉积的上切面转变，反映了地壳变形的活化和推进，反映了进积作用和日益接近的沉积物来源。砂岩岩石学、U-Pb年代学和重矿物分析结果表明，古新世晚期-始新世早期起源于火成岩、变质岩和沉积源，与以南部(昆仑山)或西南(祁门塔格)盆地边缘为主的二叠纪-三叠纪弧岩一致。沉积物成分和碎屑锆石U-Pb年龄分布在剖面上的变化可归因于始新世-渐新世来自祁连山中北部下古生界和中生界的火成岩和变质岩。火成岩源区的消失和变质源区的残留与南山-南山早-中新世早期沿南山-柴达木冲断带前缘缩短形成的南祁连山-南山相一致。这些结果得到了古水流分析的支持，该分析揭示了始新世沉积物从大致E向(轴向)向西南向(横向)扩散的转变。岩石相、组分、U-Pb年龄和古流体的变化与昆仑山晚古新世-早始新世-祁连山-南山中始新世-中中新世折返一致。诊断U-Pb年龄组的上切面消失和重现可能与多个逆冲断块的逐步剥离、沉积和岩浆源的连续输入以及祁连山-南山向南侵位进入柴达木盆地有关。本文提供的沉积记录表明，在古近纪，统一的柴达木-塔里木盆地在并入不断增长的青藏高原时发生了分离和隆升。与青藏高原及周边盆地的对比表明，基底强度和横向均质性以及同沉积构造坝的形成是大型沉积盆地形成的主要控制因素。
Sedimentologic and provenance analyses for the Qaidam Basin in the northern Tibetan Plateau help to elucidate the stratigraphic signatures of initial deformation and exhumation in basin-bounding ranges. The basin recorded sedimentary transitions in response to uplift and unroofing of several distinctive source regions. Along the NE basin margin, a detrital record of exhumation and basin isolation is preserved in the 6200-m-thick Cenozoic succession at the Dahonggou anticline. An up-section shift from axial fluvial and marginal lacustrine deposition to transverse fluvial sedimentation suggests progradation and increasingly proximal sediment sources, reflecting activation and advance of crustal deformation. Provenance results from sandstone petrology, U-Pb geochronology, and heavy mineral analyses indicate initial late Paleocene-early Eocene derivation from igneous, metamorphic, and sedimentary sources, consistent with Permian-Triassic arc rocks dominating the southern (Kunlun Shan) or southwestern (Qimen Tagh) basin margins. Up-section variations in sediment composition and detrital zircon U-Pb age distributions are attributed to Eocene-Oligocene derivation from lower Paleozoic and Mesozoic igneous and metamorphic rocks of the central to northern Qilian Shan-Nan Shan. Disappearance of igneous sources and persistence of metamorphic sources are consistent with derivation from the southern Qilian Shan-Nan Shan during early-middle Miocene shortening along the frontal Nan Shan-North Qaidam thrust belt. These results are supported by paleocurrent analyses revealing an Eocene shift from roughly E-directed (axial) to SW-directed (transverse) dispersal of sediment. Variations in lithofacies, composition, U-Pb ages, and paleoflow are consistent with late Paleocene-early Eocene exhumation in the Kunlun Shan followed by middle Eocene-middle Miocene exhumation in the Qilian Shan-Nan Shan. The up-section disappearance and reappearance of diagnostic U-Pb age populations can be associated with progressive unroofing of multiple thrust sheets, successive input of sedimentary and magmatic sources, and southward encroachment of Qilian Shan-Nan Shan shortening into the Qaidam Basin. The sedimentary record presented here indicates that during the Paleogene, the unified Qaidam-Tarim Basin was partitioned and uplifted as it was incorporated into the growing Tibetan Plateau. Comparison with basins on and surrounding the Tibetan Plateau suggests that basement strength and lateral homogeneity, and formation of syndepositional structural dams are among the primary controls on formation of giant sedimentary basins.