Constructing the Longmen Shan eastern Tibetan Plateau margin: Insights from low‐temperature thermochronology

Abstract

[1] Contrasting models of upper crustal shortening versus lower crustal flow have been proposed to explain the formation of thickened crust in the Longmen Shan (LMS), eastern Tibetan Plateau (TP) margin. These models require different structural kinematics along the LMS, whose structural geometry is defined by three parallel NW-dipping fault zones. From foreland (southeast) to hinterland (northwest), they are the Guanxian-Anxian Fault, Yingxiu-Beichuan Fault (YBF), and Wenchuan-Maowen Fault (WMF). Newly derived and previously published low-temperature thermochronology data from the LMS were synthesized to constrain the spatial exhumation and test previous models. The results show that (1) exhumation increases abruptly across the range-bounding YBF, suggesting the fault being the main thrust boundary between the LMS and the Sichuan Basin to the east; (2) Younger Late Cenozoic cooling ages are found on the hinterland WMF, where a dichotomy of ages on the hanging wall versus footwall suggests Late Cenozoic thrust activity; and (3) toward the hinterland to the west, exhumation rates decrease twofold over a distance of~30-40 km. This exhumation pattern indicates a westward decrease of tectonic uplift, providing the regional topography approached a steady state, whereby exhumation is in balance with tectonic uplift. The observed exhumation estimates support an upper crustal configuration where thrusts in the LMS merge gradually into a gentle detachment seated at a depth of~20-30 km. Results of this study support a revised upper crustal thrusting model.

Late Permian–Triassic siliciclastic provenance, palaeogeography, and crustal growth of the Songpan terrane, eastern Tibetan Plateau: evidence from U–Pb ages, trace elements, and Hf isotopes of detrital zircons

“…Chen et al 2011). It probably indicates that the Longmenshan orogen was elevated from the middle Late Triassic period (Figure 12c-d; Arne et al 1997;Li et al 2012;Tian et al 2013). The Longmenshan orogen 16…”

Oligocene-Early Miocene river incision near the first bend of the Yangze River: Insights from apatite (U-Th-Sm)/He thermochronology

“…Besides the Laojunshan area, Oligocene to Early Miocene phase of river incision has only been identified in the Longmen Shan Guenthner et al, 2014). In other adjacent areas, previous low-temperature thermochronological studies suggest that river incision occurred later in the Miocene (Kirby et al, 2002;Clark et al, 2005b;Enkelmann et al, 2006;Godard et al, 2009;Ouimet et al, 2010;Tian et al, 2013Tian et al, , 2015. Further, the amount of post ~20 Ma cooling (< 80 o C) and erosion (< 2.5 km) in the study area is significantly lower than in other areas, where those previous studies suggested an average post ~12 Ma erosion rate of 0.3-1.0 mm/yr.…”

Denudation pattern across the Longriba fault system and implications for the geomorphological evolution of the eastern Tibetan margin

“…Thrusting results from positive tectonic inversion of Paleozoic to early Mesozoic passive margin normal faults, affecting the western edge of the Yangtze craton (Mattauer et al, 1992;Roger et al, 2010;de Sigoyer et al, 2014). The Beichuan fault, which is the main active structure of the Longmen Shan, contributed to the exhumation of the Yangtze crystalline basement during early Cenozoic times (Arne et al, 1997;Kirby et al, 2002;Li et al, 2012;Wang et al, 2012;Cook et al, 2013;Tian et al, 2013).…”

“…1) has been a key research area over the last two decades for the study of crustal deformation mechanisms (Royden et al, 1997(Royden et al, , 2008Clark and Royden, 2000;Tapponnier et al, 2001;Clark et al, 2005;Hubbard and Shaw, 2009;Qi et al, 2011;Tian et al, 2013;Zhang, 2013) and their links with surface processes (Kirby et al, 2000(Kirby et al, , 2003Kirby and Ouimet, 2011;Zhang et al, 2011). Indeed, the apparently peculiar setting of this plateau margin attracted much attention as its elevation rise is about 3500 m over only 50 km (Fig.…”