Latest Triassic to Early Jurassic Thrusting and Exhumation in the Southern Ordos Basin, North China: Evidence from LA-ICP-MS-based Apatite Fission Track Thermochronology

The contractional structures in the southern Ordos Basin recorded critical evidence for the interaction between Ordos Basin and Qinling Orogenic Collage. In this study, we performed apatite fission track （AFT） thermochronology to unravel the timing of thrusting and exhumation for the Laolongshan-Shengrenqiao Fault （LSF） in the southern Ordos Basin. The AFT ages from opposite sides of the LSF reveal a significant latest Triassic to Early Jurassic time-temperature discontinuity across this structure. Thermal modeling reveals at the latest Triassic to Early Jurassic, a ~50~C difference in temperature between opposite sides of the LSF currently exposed at the surface. This discontinuity is best interpreted by an episode of thrusting and exhumation of the LSF with -1.7 km of net vertical displacement during the latest Triassic to Early Jurassic. These results, when combined with earlier thermochronological studies, stratigraphic contact relationship and tectono-sedimentary evolution, suggest that the southern Ordos Basin experienced coeval intense tectonic contraction and developed a north-vergent fold-and-thrust belt. Moreover, the southern Ordos Basin experienced a multi-stage differential exhumation during Mesozoic, including the latest Triassic to Early Jurassic and Late Jurassic to earliest Cretaceous thrust-driven exhumation as well as the Late Cretaceous overall exhumation. Specifically, the two thrust-driven exhumation events were related to tectonic stress propagation derived from the latest Triassic to Early Jurassic continued compression from Qinling Orogenic Collage and the Late Jurassic to earliest Cretaceous intracontinental orogeny of QinUng Orogenic Collage, respectively. By contrast, the Late Cretaceous overall exhumation event was related to the collision of an exotic terrain with the eastern margin of continental China at -100 Ma.

Cenozoic low temperature cooling history of the eastern Lhasa terrane:Implications for high-relief topography of external drainage area in the southern Tibetan Plateau

The Tibetan Plateau geographically contains internal and external drainage areas based on the distributions of river flows and catchments.The internal and external drainage areas display similar highelevations,while their topographic reliefs are not comparable;the former shows a large low-relief surface,whereas the latter is characterized by relatively high relief.The eastern Lhasa terrane is a key tectonic component of the Tibetan Plateau.It is characterized by high topography and relief,but the thermal history of its basement remains relatively poorly constrained.In this study we report new apatite fission track data from the eastern part of the central Lhasa terrane to constrain the thermo-tectonic evolution of the external drainage area in the southern Tibetan Plateau.Twenty-one new AFT ages and associated thermal history models reveal that the basement underlying the external drainage area in southern Tibet experienced three main phases of rapid cooling in the Cenozoic.The Paleocene-early Eocene(-60–48 Ma)cooling was likely induced by crustal shortening and associated rock exhumation,due to accelerated northward subduction of the NeoTethys oceanic lithosphere.A subsequent cooling pulse lasted from the late Eocene to early Oligocene(-40–28 Ma),possibly due to the thickening and consequential erosion of the Lhasa lithosphere resulted from the continuous northward indentation of the India plate into Eurasia.The most recent rapid cooling event occurred in the middle Miocene-early Pliocene(-16–4 Ma),likely induced by accelerated incision of the Lhasa River and local thrust faulting.Our AFT ages and published low-temperature thermochronological data reveal that the external drainage area experienced younger cooling events compared with the internal drainage area,and that the associated differentiated topographic evolution initiated at ca.30 Ma.The contributing factors for the formation of the high-relief topography mainly contain active surface uplift,fault activity,and the enhanced incision of the Yarlung River.

The uplifting and denudation of main Huangshan Mountains,Anhui Province,China

The Huangshan Mountain Geopark is an important geological landmark and tourist attraction.In this paper,we apply fission track dating to examine the uplift and exhumation processes that created the Huangshan Mountains and provide a timeline for their development.In addition to being an important scientific contribution,this information can be used on guided tours and to promote tourism.The results of eight apatite fission-track analyses suggest three age groups:56,45-30,and 15 Ma.These age groups are related to the uplifting-erosion processes involved in forming ancient multilevel denudation planes at 85-50,45-30,and 24-5 Ma,respectively.The scenic area has experienced three stages of thermal evolution.The first stage occurred before 80 Ma and the third stage after 13 Ma.The three stages had varying cooling rates:2.69,0.62,and 4.23°C/Ma,respectively.Uplifting rates also varied:0.08,0.02,and 0.12 mm/a.The uplifting ranges were also variable:1.14,1.57,and 4.00 km,respectively.Significant uplifting differences between diverse areas are obvious and there were four magnitudes of cumulative uplifting range:4060-3950,3760-3490,3190-3070,and 2650 m.The surface uplifting range varied from 450 to 2230 m.Denudation and uplifting amount averaged 2340 and 3400 m,respectively.The 1060 m difference between them is the average elevation at present.