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To help understand the relationship between global cooling and Tibetan uplift in the middle to late Miocene, multiple proxy data including carbonate stable isotope records, magnetic susceptibility, and sediment color references were obtained from a magnetostratigraphic section (14.5-6.0 Ma) of the Wushan Basin along the northeastern margin of the Tibetan Plateau. New proxies identify two phase changes that may have been controlled by global cooling and tectonic deformation at this time. During 14.5-13.2 Ma, positive shifts of ~2.0? in &#94818O and δ13C, an increase in lightness (L*), and a decrease in redness (a*) suggest gradually increasing aridity. Relatively high δ18O and δ13C values and low a*/L* and magnetic susceptibility values continue until ca. 10 Ma, when δ18O and δ13C significantly decrease and redness as well as magnetic susceptibility significantly increase. The negative shifts in δ18O and δ13C and increases in redness and magnetic susceptibility at 10 Ma are consistent with coeval basin environment and provenance changes. Combining these data with basin analysis, we suggest that global cooling was the dominant factor and Tibetan uplift was the subordinate factor for the middle Miocene aridification of the Wushan Basin. In contrast, the contribution of Tibetan uplift was dominant and global climate change was subordinate in the late Miocene basin paleogeographic reorganization. [ABSTRACT FROM AUTHOR]

The Cenozoic Asian climate system experienced a transformation from a zonal pattern to a monsoon-dominant pattern around the Paleogene-Neogene boundary. A series of dynamic mechanisms, such as uplift of the Tibetan Plateau, retreat of the Paratethys Sea, expansion of the South China Sea, and decreasing atmospheric CO2 content, has been suggested to be responsible for the transformation of the Asian climate pattern. However, the role of topographic growth in eastern China has been rarely considered. As the natural divides of geography, climate, and biology, the two most distinct sets of topographic relief in eastern China, the Qinling and Taihang Mountains, play an important role in shaping the Asian climate pattern. We report low-temperature thermochronology data from the Qinling and Taihang Mountains and use age-elevation relationships and thermal history modeling to show that both mountain ranges experienced a phase of rapid exhumation during the late Oligocene and early Miocene. The building of the Qinling and Taihang Mountains around the Oligocene-Miocene boundary temporally and spatially coincided with the reorganization of the Cenozoic Asian climate regime, suggesting that the mountain building in eastern China acted as a possible driving mechanism for the alleged reorganization of the Cenozoic Asian climate regime. [ABSTRACT FROM AUTHOR]

New apatite (U-Th)/He from the northeastern margin of the Tibetan Plateau (north Qilian Shan) indicate rapid cooling began at ~10 Ma, which is attributed to the onset of faulting and topographic growth. Preservation of the paleo-PRZ in the hanging wall and growth strata in the footwall allow us to calculate vertical and horizontal fault slip rates averaged over the last 10 Myr of ~0.5 mm/yr and ~1 mm/yr respectively, which are within a factor of two consistent with Holocene slip rates and geodetic data. Low fault slip rates since the initiation of the northern Qilian Shan fault suggest that total horizontal offset did not exceed 10 km. Further, emergence of the northern Qilian Shan occurs during a period of increased aridity in northern Tibet but is associated with only a minor expansion of the northern plateau perimeter, which is well established near collision time. Outgrowth of the northern Qilian Shan at ~10 Ma could be simple propagation of the larger Qilian Shan system, occurring in response to decreased slip rates on the Altyn Tagh fault or as a result of the change in GPE of the central plateau. [ABSTRACT FROM AUTHOR]

High-resolution topographic or imagery data effectively reveal geomorphic offsets along faults that can be used to deduce slip-per-event of recurrent rupture events. Documentation of patterns of geomorphic offsets is scarce on faults that undergo both creep and coseismic rupture. In this paper, we used newly acquired high-resolution light detection and ranging (LiDAR) data to compile geomorphic offsets along the Laohu Shan section of the Haiyuan fault, in the northern Tibetan Plateau, where interferometric synthetic aperture radar (InSAR) data suggest creep presently occurs over a 35-km-long stretch at a rate comparable to the long-term geological slip rate, despite evidence for past coseismic fault rupture. Numerous offset gullies identified using the LiDAR data yield a range of offsets from less than 2 m up to 50 m. These offsets have well-separated probability density peaks at 2-3 m, ~7 m, and ~14 m, with increments of 2-3 m, 4-6 m, and 5-7 m. The sequence of paleoseismic events along the Laohu Shan section indicates that the gullies with offsets of 2-3 m are likely related to surface rupture of the historical 1888 Jingtai earthquake, plus subsequent creep. Offset increments of 4-6 m and 5-7 m may represent coseismic slip in past paleoseismic events plus creep during the interseismic period. The creeping Laohu Shan section preserves numerous discrete cumulative offsets, with an offset clustering pattern indistinguishable from that on a locked fault with recurrent earthquake ruptures. Association of offset increments with known paleoseismic events yields a slip rate of 3-5 mm/yr during the past 200 years, roughly similar to the ~5 mm/yr creep rate. If the ratio of surface creep rate to the total fault slip rate has been continuous, then seismic moment release by brittle ruptures, and thus seismic hazard, would be much reduced on the Laohu Shan section of the Haiyuan fault. Alternatively, the current high creep rate may be a transient phenomenon, perhaps after slip following the 2000 Jingtai Mw 5.6 earthquake or in response to the adjacent 1920 M ***8 Haiyuan earthquake rupture that terminated immediately to the east. [ABSTRACT FROM AUTHOR]