Late-stage foreland growth of China’s largest orogens (Qinling, Tibet): Evidence from the Hannan-Micang crystalline massifs and the northern Sichuan Basin, central China

Abstract

This paper addresses the timing of fi nal foreland growth of China's largest orogens: the Mesozoic Qin Mountains (Qinling) and the Cenozoic Tibetan Plateau. In particular, we ask when the front of the Qinling orogen fold-thrust belt was emplaced, and when the northern Sichuan Basin was affected by the eastward growth of the Tibetan Plateau. We employ zircon and apatite fi ssion-track and (U-Th)/He dating in the Proterozoic crystalline rocks of the Hannan-Micang massifs and the sedimentary rocks of the northern Sichuan Basin. The Hannan-Micang rocks remained in the zircon fi ssion-track partial annealing zone (240 ± 30 °C) throughout the Paleozoic-Middle Triassic (481-246 Ma). From the late Middle Jurassic (ca. 165 Ma) to the early Late Cretaceous (ca. 95 Ma), enhanced cooling and exhumation, with rates of 1.2-2.5 °C/m.y. and 0.04-0.10 mm/yr, respectively, record propagation of the Qinling orogen into its leading foreland; the timing of foreland growth is supported by sedimentologic evidence, i.e., regional variation in sediment thickness and depocenter migration. Negligible cooling and exhumation since the Late Cretaceous (ca. 95 Ma) likely mark the end of the foreland fold-thrust belt formation and the subsequent persistence of a low-relief landscape that occupied extensive parts of central China; cooling and exhumation rates of 0.38-0.70 °C/m.y. and <0.02 mm/yr characterize this tectonic stagnation period. Accelerated cooling (4-5 °C/m.y.) since the Late Miocene (13-8 Ma), derived from apatite fi ssion-track temperature-time path models, signifi es involvement of the Hannan-Micang massifs and the northern Sichuan Basin into the eastward-growing Tibetan Plateau. Their inclusion into the plateau growth initiated faulting and stripped off 1.4-2.0 km of rock from the Hannan-Micang massifs and northern Sichuan Basin.

Apatite fission-track thermochronological constraints on the pattern of late Mesozoic–Cenozoic uplift and exhumation of the Qinling Orogen, central China

“…2; Chen et al, 2010;Dong et al, 2011a;Hu et al, 2012;Meng et al, 2007;Meng and Zhang, 2000;Li et al, 2007;Ratschbacher et al, 2003;Shi et al, 2012Shi et al, , 2013Wang et al, 2011a;Yin andNie, 1993, 1996;Zhang et al, 2001Zhang et al, , 2010. For the intracontinental deformation, various fission-track and U-Th/He thermochronological investigations of the apatite and zircon have indicated that the Qinling Orogen experienced an intricate pattern of postorogenic uplift and exhumation during the Mesozoic-Cenozoic (Enkelmann et al, 2006;Hu et al, 2006aHu et al, , 2012Li et al, 2010a;Liu et al, 2009Liu et al, , 2013Shen et al, 2007;Tian et al, 2010;Wan et al, 2000Wan et al, , 2005Wang et al, 2011b;Xu et al, 2005Xu et al, , 2010Yang et al, 2013;Yin et al, 2001). The southern Qinling orogen has been uplifted since the Triassic-Jurassic Shen et al, 2007;Xu et al, 2010;Yang et al, 2013), but the northern Qinling Orogen uplifted only since the Cenozoic (Enkelmann et al, 2006;Hu et al, 2006a;Liu et al, 2013), and the rapid cooling documented in the southwestern Qinling Orogen started during the late Miocene (Enkelmann et al, 2006).…”

“…For the intracontinental deformation, various fission-track and U-Th/He thermochronological investigations of the apatite and zircon have indicated that the Qinling Orogen experienced an intricate pattern of postorogenic uplift and exhumation during the Mesozoic-Cenozoic (Enkelmann et al, 2006;Hu et al, 2006aHu et al, , 2012Li et al, 2010a;Liu et al, 2009Liu et al, , 2013Shen et al, 2007;Tian et al, 2010;Wan et al, 2000Wan et al, , 2005Wang et al, 2011b;Xu et al, 2005Xu et al, , 2010Yang et al, 2013;Yin et al, 2001). The southern Qinling orogen has been uplifted since the Triassic-Jurassic Shen et al, 2007;Xu et al, 2010;Yang et al, 2013), but the northern Qinling Orogen uplifted only since the Cenozoic (Enkelmann et al, 2006;Hu et al, 2006a;Liu et al, 2013), and the rapid cooling documented in the southwestern Qinling Orogen started during the late Miocene (Enkelmann et al, 2006). The variable timings of uplift and exhumation at different locations in the Qinling Orogen represent differences in the pattern and timing of tectonism not only from south to north (Hu et al, 2006a;Liu et al, 2013) but also from east to west (Enkelmann et al, 2006).…”

“…Recently, there are some studies on the regional evolution of Qinling Orogen based on the north-south transects (Hu et al, 2006a), east-west different , individual micro-block of S-NCB and NQB or N-SCB (Yang et al, 2013), and have also discussed the tectonic context of different uplift and exhumation stages (Enkelmann et al, 2006;Hu et al, 2006a;Liu et al, 2013;Yang et al, 2013). Previous studies were dominantly on the individual pluton, and the spatial coverage is limited to reveal the uplift and exhumation for the entire Qinling Orogen (Fig.…”

Mesozoic intracontinental orogeny in the Qinling Mountains, central China

“…The orogenic collapse resulted in relatively minor and continuous exhumation and erosion of the orogen although major transtensional and strike-slip faults were activated. This is also proved by some low-temperature geothermal ages (Hu et al, , 2006Dong et al, 2008;Liu et al, 2013;Yang et al, 2013;Heberer et al, 2014).…”

“…Meanwhile, within the orogen, the Lower Jurassic strata were overthrusted, and the foreland fold-thrust belt formed in front of the MBXF. Rapid exhumation of some sectors of the Qinling orogen and adjacent areas is also elucidated by thermochronological studies (Zheng et al, 2004;Hu et al, 2005;Shen et al, 2007;Chang et al, 2010;Yang et al, 2013).…”