Late Miocene Hinterland Crustal Shortening in the Longmen Shan Thrust Belt, the Eastern Margin of the Tibetan Plateau

Abstract

Long-term (million year time scale) fault-slip history is crucial for understanding the processes and mechanisms of mountain building in active orogens. Such information remains elusive in the Longmen Shan, the eastern Tibetan Plateau margin affected by the devastating 2008 Wenchuan earthquake. While this event drew attention to fault deformation on the foreland side (the Yingxiu-Beichuan fault), little is known about the deformation history of the hinterland Wenchuan-Maoxian fault. To address this gap, thermochronological data were obtained from two vertical transects from the Xuelongbao massif, located in the hanging wall of the Wenchuan-Maoxian fault. The data record late Miocene rapid cooling and rock exhumation at a rate of 0.9-1.2 km/m.y. from~13 Ma to present. The exhumation rate is significantly higher than that in the footwall (~0.3-0.5 km/m.y.), indicating a differential exhumation of~0.6 km/m.y. across the fault. This differential exhumation provides the first and minimum constraint on the long-term throw rate (~0.6 km/m.y) of the Wenchuan-Maoxian fault since the late Miocene. This new result implies continuous crustal shortening along the hinterland fault of Longmen Shan, even though it has not been ruptured by major historic earthquakes. Our study lends support to geodynamic models that highlight crustal shortening as dominating deformation along the eastern Tibetan Plateau.

Exploiting Thermochronology to Quantify Exhumation Histories and Patterns of Uplift Along the Margins of Tibet

“…The exhumation of rocks within the Longmen Shan, as recorded by thermochronology, plays a central role in the understanding of the timing and rates of growth of high topography (Arne et al, 1997;Xu and Kamp, 2000;Kirby et al, 2002;Wang et al, 2012) and places constraints on the total amount of Cenozoic slip along fault systems in the thrust belt (e.g., Godard et al, 2009;Wang et al, 2012;Tan et al, 2017;Ansberque et al, 2018;Shen et al, 2019). In addition, recent studies of the Mesozoic metamorphic conditions experienced during Indosinian crustal thickening (Airaghi et al, 2017;Airaghi et al, 2018a;Airaghi et al, 2018b) provide important constraints on depth and temperature of the rocks prior to the Cenozoic.…”

“…140 Ma; Airaghi et al, 2018a). Young cooling ages for thermochronologic systems west of the Wenchuan-Maowen fault (Arne et al, 1997;Godard et al, 2009;Kirby et al, 2013;Creason et al, 2016;Tan et al, 2017;Shen et al, 2019) imply significant differential exhumation during the Late Cenozoic across this fault.…”

Late Cenozoic Denudation and Topographic Evolution History of the Lhasa River Drainage in Southern Tibetan Plateau: Insights From Inverse Thermal History Modeling

“…Moreover, we also compared the denudation rate with climate change (Figure 7B) and found that the rapid denudation in this stage also corresponds to the intensification of the Asian monsoon. Recent studies have shown that climatic change (precipitation or glacier development) determines the denudation of a large-scale area (Montgomery et al, 2001;Clift et al, 2008), but the orogenic tectonics could only trigger the erosion of the relatively local region (Beaumont et al, 2001;Luszczak et al, 2018;Yang et al, 2019;Shen et al, 2019). Based on this hypothesis, we have summarized the cooling history of five large rivers in the southeastern Tibetan Plateau from ∼40 Ma to the present to identify the possible effect of climate on the denudation (Figure 8).…”

“…The Tibetan Plateau, created by the India-Asia collision since the Cenozoic (Molnar et al, 2010), is a natural laboratory for examining the coupling of tectonics, climate, and erosion in shaping the landscape. Previous studies have important findings in the Himalayas (Beaumont et al, 2001;Bookhagen et al, 2005;Clift et al, 2008;Zhang et al, 2012) and the southern and southeastern Tibetan Plateau (Lang and Huntington, 2014;Liu-Zeng et al, 2018;Nie et al, 2018;Shen et al, 2019). However, these studies have not reached a consensus about the mechanism of the landscape evolution in some regions, such as the Gangdese region, a low-relief and high-elevation landscape in the southern Tibetan Plateau (Figure 1).…”

“…A numerical simulation method for inverse thermal history modeling, three-dimensional (3D) thermal kinematic model Pecube (Braun, 2002(Braun, , 2003Braun et al, 2012) coupled with the neighborhood algorithm (Sambridge, 2010a,b), has considered these limiting factors of one-dimension cooling. This method has been successfully applied to the inversion of denudation and topographic evolution in orogenic regions (Braun et al, 2012;Wang et al, 2016;McDannell et al, 2018;Shen et al, 2019;Yang et al, 2019). Here, we used this 3D thermokinematic modeling approach to invert both denudation and topographic evolution history in the Lhasa River drainage using low-temperature thermochronologic data from the Lhasa River Valley.…”