Thermal History of Rocks in the Shiwandashan Basin, Southern China: Evidence from Apatite Fission Track Analysis

Based on interpretations of the apatite fission track analysis data for 10 outcrop samples and forward modeling of confined fission track length distributions, the thermal history of rocks in the Shiwandashan basin and its adjacent area, southern China, has been qualitatively and semi quantitatively studied. The results reflect several features of the thermal history. Firstly, all the samples have experienced temperatures higher than 60-70 ℃. Secondly, the time that the basement strata (T 1 b ) on the northwestern side of the Shiwandashan basin were uplifted and exhumed to the unannealed upper crust (with a paleogeotemperature of below 60-70 ℃) is much earlier than the basement rocks ( γ 1 5) on the southeastern side of the basin. Thirdly, the thermal history of samples from the basin can be divided into six stages, i.e., the fast burial and heating stage (220-145 Ma), the transient cooling stage (145-135 Ma), the burial and heating stage (135-70 Ma), the rapid cooling stage (70-50 Ma), the relatively stable stage (50-20 Ma) and another rapid cooling stage (20 Ma to present).

Apatite Fission Track Evidence of Uplift Cooling in the Qiangtang Basin and Constraints on the Tibetan Plateau Uplift

The Qiangtang basin is located in the central Tibetan Plateau. This basin has an important structural position, and further study of its tectonic and thermal histories has great significance for understanding the evolution of the Tibetan Plateau and the hydrocarbon potential of marine carbonates in the basin. This study focuses on low temperature thermochronology and in particular conducted apatite fission track analysis. Under constraints provided by the geological background, the thermal history in different tectonic units is characterized by the degree of annealing of samples, and the timing of major （uplift-erosion related） cooling episodes is inferred. The cooling history in the Qiangtang basin can be divided into two distinct episodes. The first stage is mainly from the late Early Cretaceous to the Late Cretaceous （69.8 Ma to 108.7 Ma）, while the second is mainly from the Middle- Late Eocene to the late Miocene （10.3 Ma to 44.4 Ma）. The first cooling episode records the uplift of strata in the central Qiangtang basin caused by continued convergent extrusion after the Bangong- Nujiang ocean closed. The second episode can be further divided into three periods, which are respectively 10.3 Ma, 22.6-26.1 Ma and 30.8-44.4 Ma. The late Oligocene-early Miocene （22.6-26.1 Ma） is the main cooling period. The distribution and times of the earlier uplift-related cooling show that the effect of extrusion after the collision between Eurasian plate and India plate obviously influenced the Qiangtang basin at 44.4 Ma. The Qiangtang basin underwent compression and started to be uplifted from the middle-late Eocene to the early Oligocene （45.0-30.8 Ma）. Subsequently, a large-scale and intensive uplift process occurred during the late Oligocene to early Miocene （26.1-22.6 Ma） and the basin continued to undergo compression and uplift up to the late Miocene （10.3 Ma）. Thus, uplift-erosion in the Qiangtang basin was intensive from 44.5 Ma to about 10 Ma. The timing of cooling in the second episode shows that the uplift of the Qiangtang basin was caused by the strong compression after the collision of the Indian plate and Eurasian plate. On the whole, the new apatite fission-track data from the Qiangtang basin show that the Tibetan Plateau started to extrude and uplift during 45-30.8 Ma. The main period of uplift and formation of the Tibetan Plateau took place about 22.6-26.1 Ma, and uplift and extrusion continued until the late Miocene （10.3 Ma）.

Timing of uplift and evolution of the Lüliang Mountains,North China Craton

This study analyses evidence for reformed basin development and basin-mountain coupling associated with devel- opment of the Ordos Basin and the Laliang Mountains, China. Gaining an improved understanding of the timing and nature of uplift and evolution of the Ltiliang Mountains is important for the reconstruction of the eastern sedimentary boundary of the Ordos Basin （a major petroliferous basin） as well as for providing insight into the evolution and breakup of the North China Craton （NCC）. Based on systematic sampling for fission track analysis, it is suggested that the main phase of uplift of the Laliang Mountains occurred since later part of the Early Cretaceous. Three evolutionary stages of uplift and development are identified： slow initial uplift （120-65 Ma）, accelerated uplift （65-23 Ma）, and intensive uplift （23 Ma to present）, with the ma- jority of the uplift activity having occurred during the Cenozoic. The history of uplift is non-equilibrium and exhibits complex- ity in temporal and spatial aspects. The middle and northern parts of the Ltiliang Mountains were uplifted earlier than the southern part. The most intensive episode of uplift activity commenced in the Miocene and was associated with a genetic cou- pling relationship with the eastern neighboring Cenozoic Shanxi Grabens. The uplifting and evolutionary processes of the Ltiliang Mountains area since later part of the Early Cretaceous share a unified regional geodynamic setting, which was ac- companied by uplift of the Mesozoic Ordos Basin and development of the neighboring Cenozoic Shanxi Grabens. Collectively, this regional orogenic activity is related principally to the far-field effects of both the compression sourced from the south- western Tibet Plateau and westward subduction of the Pacific Plate in Cenozoic.