| Author's Name: ZHANG Jianyong1,2,3, XU Qiang4,5, CAO Yu4, XIONG Shaoyun1,2,3,
LIU Siqi1,2,3, TAN Xuanyu6, TAN Xiucheng4,5 |
| Institution: |
| Abstract: |
| The Bangong Lake-Nujiang suture zone is an extreme important tectonic boundary in the Tibetan Plateau
which is not only closely related to evolution of the Tethyan tectonic domain, but also directly controls the formation and
inversion of the Mesozoic southern Qiangtang oil and gas-bearing basin. Based on stratigraphic correlation, sandstone
petrography analysis and detrital zircon U-Pb dating, this paper reconstructs provenance changes in the Dongqiao-Beila
area and reveals multi-stage subduction processes and microblock amalgamations in the central Bangong Lake-Nujiang
Ocean (BNO). The BNO branch (Amdo Ocean) at Dongqiao-Beila area began to subduct in the Early Jurassic, resulting
in amalgamation of the Amdo block to the southern Qiangtang terrane and rifting the Dongkaco microblock away from the
northern Lhasa terrane and formed two new BNO branches of the Dongqiao Ocean to the north and Beila Ocean to the
south. The lower Xihu Group close to the Beila suture in the south of the Dongkaco micoblock shows recycle deposits
from the underlying Upper Triassic Quehala Group, while the upper Xihu Group close to the Dongqiao suture in the north
of the Dongkaco microblock began to receive detritus from the southern Qiangtang terrane, indicating the Dongqiao
Ocean demised and the Dongkaco microblock has amalgamated on the southern margin of the Qiangtang terrane with a
peripheral foreland basin developed during the Middle Jurassic. Subsequent subduction of the Beila Ocean droved the
Dongkaco microblock continuing to converge with south Qiangtang terrane in the Middle Jurassic and promote abundant
materials from the south Qiangtang terrane transporting into the Middle-Upper Jurassic Jienu Group in the foreland basin
on the Dongkacuo microblock. Wide collision between the Qiangtang and Lhasa terrane occurred during the latest Jurassic
and Early Cretaceous (147-141 Ma) and continued during Aptian (ca. 120 Ma) until the Beila Ocean finally dimed at
Dongqiao-Beila Area.
In response to multi-stage northward subductions of the BNO, the south Qiangtang Basin changed from passive
continental margin to active continental margin during earliest Jurassic and developed arc-related basin system of eastwest
extending back-arc basin, volcanic arc and fore arc basin from north to south. The Lower Jurassic Quse black shale
and overlying Buqu bioclastic limestone deposited in the back-arc basin. Continuous convergence and microblock
collision contributed to rapid regression and uplift of the south Qiangtang basin,resulting in the deposition of tidal Xiali
Formation with gypsum and mudstone during the Middle Jurassic. As the result of collision between the Lhasa and
Qiangtang terrane in the Early Cretaceous, the south Qiangtang Basin evolved in fold thrust belt of the peripheral foreland
basin and resulted in differential burial and denudation of the Jurassic successions. During the Late Jurassic-Early
Cretaceous, the Quse black shale and Buqu bioclastic limestone were correspondingly buried rapidly due to the tectonic
compression and entered the stage of oil generation and dolomitization, making it become the most important
accumulation period in the south Qiangtang Basin. |
| Keywords: Bangong Lake-Nujiang suture zone; zircon U-Pb dating; the process of subduction and closure; provenance
change; southern Qiangtang Basin |
|
投稿时间：
2024-04-07 |
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