Temporal variations in the orientation of Cenozoic range growth in northeastern Tibet defi ne two modes by which India-Asia convergence was accommodated. Thermochronological age-elevation transects from the hanging walls of two major thrust-fault systems reveal diachronous Miocene exhumation of the Laji-Jishi Shan in northeastern Tibet. Whereas accelerated growth of the WNW-trending eastern Laji Shan began ca. 22 Ma, rapid growth of the adjacent, north-trending Jishi Shan did not commence until ca. 13 Ma. This change in thrust-fault orientation refl ects a Middle Miocene change in the kinematic style of plateau growth, from long-standing NNE-SSW contraction that mimicked the plate convergence direction to the inclusion of new structures accommodating east-west motion. This kinematic shift in northeastern Tibet coincides with expansion of the plateau margin in southeastern Tibet, the onset of normal faulting in central Tibet, and accelerated shortening in northern Tibet. Together these phenomena suggest a plateau-wide reorganization of deformation.

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We used airborne light detection and ranging (LiDAR) data to reevaluate the singleevent offsets of the 1920 Haiyuan Ms 8.5 earthquake and the cumulative offsets along the western and middle segments of the coseismic surface rupture zone. Our LiDAR data indicate that the offset observations along both the western and middle segments fall into groups. The group with the minimum slip amount is associated with the 1920 Haiyuan Ms 8.5 earthquake, which ruptured both the western and middle segments. Our research highlights two new interpretations: First, the previously reported maximum displacement of the 1920 earthquake was likely due to at least two earthquakes; second, our results reveal that the cumulative offset probability density (COPD) peaks of the same offset amounts on the western and middle segments do not correspond to one another one-to-one. We suggest that any discussion of the rupture pattern of a certain fault based on the offset data should also consider fault segmentation and paleoseismological data. Therefore, the COPD peaks should be computed and analyzed on fault subsections and not entire fault zones to study the number of paleoearthquakes and their rupture patterns.

The time-space patterns of deformation throughout the Indo-Asian collision zone can place constraints on the processes responsible for the development of high topography. Although most agree that high topography associated with the Tibetan Plateau expanded throughout the Cenozoic, it is increasingly being recognized that portions of the present-day plateau experienced a protracted history of deformation starting before or shortly after collision. Deciphering the history of deformation in these regions is central to understanding the dynamics of plateau formation. Here, we report new constraints on the timing of shortening along the southern margin of the Gonghe Basin complex, a broad Tertiary-Quaternary depocenter within the interior region of the northeastern Tibetan Plateau. Deformation of basin strata, lithostratigraphic patterns, and changes in paleocurrents record the growth of structures along the southern margin of the basin. A novel combination of magnetostratigraphy and cosmogenic burial ages from fl uvial deposits provides a chronology that suggests that sediment accumulation initiated at ca. 20 Ma and that indicates the basin-bounding structures became active during the late Miocene, between ca. 10 and 7 Ma. The probable onset of basin development in the early Miocene is similar to other regions of the northeastern Tibetan Plateau, and it appears to herald the onset of widespread contractional deformation in the region. Moreover, late Miocene activity on thrusts bounding the southern margin of Gonghe Basin was broadly synchronous with the rise of mountain ranges elsewhere along the periphery of the plateau, suggesting a coordinated pulse of growth of high topography during this time.

Rivaling the Himalaya in relief, the Longmen Shan is probably one of the most enigmatic mountain ranges in the world: high mountains reach more than 4000 m relief but without adjacent foreland subsidence and with only slow active convergence. What are geological and geodynamic processes that built the Longmen Shan? Coseismic deformation associated with the 2008 Wenchuan earthquake could hold clues to answer these questions. The primary features associated with the 2008 Wenchuan earthquake rupture have been narrowly distributed coseismic deformation and predominantly vertical displacements that could be interpreted as the result of slips on high‐angle listric seismogenic faults. Deep sounding seismic reflection profiling across the seismogenic faults indeed reveals high‐angle listric reverse faulting in the brittle upper crust and east‐dipping reflectors that we interpret as ductile shearing, in the viscous lower crust. In conjunction with a visco‐elastic finite element modeling of coseismic displacements associated with the Wenchuan earthquake, we show that the high‐angle listric nature of earthquake faults produces insignificant horizontal shortening across the fault and facilitates upward slips along the fault that both explain the localized coseismic deformation and vertical displacement, as well as the presence of high mountains without adjacent foreland flexure. We suggest that the formation of the Longmen Shan may be better understood in terms of partitioned lithospheric pure‐shear thickening in which upward high‐angle listric faulting of brittle upper crust is linked to thickening of the more viscous lithospheric mantle through downward ductile shearing of rheologically deformable lower crust.

The growth of the Tibetan Plateau is related to the Cenozoic India-Eurasia plate collision; however, its growth and evolution to its present margins remain matters of debate. The Qilian Shan, which is located along the northeastern margin of the Tibetan Plateau, plays a central role in understanding the outward growth of the plateau. In this paper, we present new low-temperature thermochronologic data from the hanging wall of the Huangcheng-Shuangta fault (HSF) and the Lenglongling west region in the eastern part of the Qilian Shan. Cooling ages and thermal history modeling show increased exhumation rates at~15 Ma along the HSF and~5 Ma in the Lenglongling west region. We suggest that the middle Miocene beginning of rapid exhumation reflects the expansion of the larger Qilian Shan driven by thrust fault systems. The fast Pliocene exhumation may have been related to left-lateral motion on the Haiyuan fault during the late stage of orogenic development. Post-Miocene episodes of rapid exhumation in the eastern Qilian Shan are similar to those in other regions on the northeastern margin of the Tibetan Plateau, suggesting that middle to late Miocene initiation or acceleration of crustal shortening occurred along this margin.

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