(Press-News.org) Boulder, Colo., USA: Several articles were published online ahead of print
for GSA Bulletin in February. Topics include earthquake cycles in
southern Cascadia, fault dynamics in the Gulf of Mexico, debris flow after
wildfires, the assembly of Rodinia, and the case for no ring fracture in
Mono basin.
Jurassic evolution of the Qaidam Basin in western China: Constrained by
stratigraphic
succession, detrital zircon U-Pb geochronology and Hf isotope analysis
Tao Qian; Zongxiu Wang; Yu Wang; Shaofeng Liu; Wanli Gao ...
Abstract:
The formation and evolution of an intracontinental basin triggered via the
subduction or collision of plates at continental margins can record
intracontinental tectonic processes. As a typical intracontinental basin
during the Jurassic, the Qaidam Basin in western China records how this
extensional basin formed and evolved in response to distant subduction or
collisional processes and tectonism caused by stresses transmitted from
distant convergent plate margins. The Jurassic evolution of the Qaidam
Basin, in terms of basin-filling architecture, sediment dispersal pattern
and basin properties, remains speculative; hence, these uncertainties need
to be revisited. An integrated study of the stratigraphic succession,
conglomerates, U-Pb geochronology, and Hf isotopes of detrital zircons was
adopted to elucidate the Jurassic evolutionary process of the Qaidam Basin.
The results show that a discrete Jurassic terrestrial succession
characterized by alluvial fan, braided stream, braided river delta, and
lacustrine deposits developed on the western and northern margins of the
Qaidam Basin. The stratigraphic succession, U-Pb age dating, and Hf isotope
analysis, along with the reconstructed provenance results, suggest
small-scale distribution of Lower Jurassic sediments deposited via
autochthonous sedimentation on the western margin of the basin, with
material mainly originating from the Altyn Tagh Range. Lower Jurassic
sediments in the western segment of the northern basin were shed from the
Qilian Range (especially the South Qilian) and Eastern Kunlun Range. And
coeval sediments in the eastern segment of the northern basin were
originated from the Quanji massif. During the Middle-Late Jurassic, the
primary source areas were the Qilian Range and Eastern Kunlun Range, which
fed material to the whole basin. The Jurassic sedimentary environment in
the Qaidam Basin evolved from a series of small-scale, scattered, and
rift-related depressions distributed on the western and northern margins
during the Early Jurassic to a larger, extensive, and unified depression
occupying the whole basin in the Middle Jurassic. The Altyn Tagh Range rose
to a certain extent during the Early Jurassic but lacked large-scale
strike-slip tectonism throughout the Jurassic. At that time, the North
Qaidam tectonic belt had not yet been uplifted and did not shed material
into the basin during the Jurassic. The Qaidam Basin experienced
intracontinental extensional tectonism with a northeast-southwest trend
throughout the Jurassic in response to far-field effects driven by the
sequential northward or northeastward amalgamation of blocks to the
southern margin of the Qaidam Block and successive accretion of the
Qiangtang Block and Lhasa Block onto the southern Eurasian margin during
the Late Triassic−Early Jurassic and Late Jurassic−Early Cretaceous,
respectively.
View article: END
New GSA bulletin articles published ahead of print in February
2021-03-02
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