Late Cenozoic evolution of the eastern margin of the Tibetan Plateau: Inferences from ⁴⁰Ar/³⁹Ar and (U‐Th)/He thermochronology

Abstract

[1] High topography in central Asia is perhaps the most fundamental expression of the Cenozoic Indo-Asian collision, yet an understanding of the timing and rates of development of the Tibetan Plateau remains elusive. Here we investigate the Cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the Sichuan Basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed. Temperaturetime paths inferred from 40 Ar/ 39 Ar thermochronology of biotite, multiple diffusion domain modeling of alkali feldspar 40 Ar release spectra, and (U-Th)/He thermochronology of zircon and apatite imply that rocks at the present-day topographic front of the plateau underwent slow cooling (<1°C/m.y.) from Jurassic times until the late Miocene or early Pliocene. The regional extent and consistency of thermal histories during this time period suggest the presence of a stable thermal structure and imply that regional denudation rates were low (<0.1 mm/yr for nominal continental geotherms). Beginning in the late Miocene or early Pliocene, these samples experienced a pronounced cooling event (>30°-50°C/m.y.) coincident with exhumation from inferred depths of $8 -10 km, at denudation rates of 1 -2 mm/yr. Samples from the interior of the plateau continued to cool relatively slowly during the same time period ($3°C/m.y.), suggesting limited exhumation (1 -2 km). However, these samples record a slight increase in cooling rate (from <1 to $3°C/m.y.) at some time during the middle Tertiary; the tectonic significance of this change remains uncertain. Regardless, late Cenozoic denudation in this region appears to have been markedly heterogeneous, with the highest rates of exhumation focused at the topographic front of the plateau margin. We infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable Sichuan Basin and thus marks the onset of deformation related to the development of the Tibetan Plateau in this region. The present margin of the plateau adjacent to and north of the Sichuan Basin is apparently no older than the late Miocene or early Pliocene ($5 -12 Ma).

Late Miocene provenance change on the eastern margin of the Yinggehai-Song Hong Basin, South China Sea: Evidence from U–Pb dating and Hf isotope analyses of detrital zircons

“…For example, Clift and Sun (2006) suggested that the sedimentation rates in the Y-SH Basin increased sharply at the end of the Miocene. Clark et al (2005) used an initiation of the major river incisions to identify the timing of the initial uplift at 13e9 Ma and the high erosion rates between 0.23 and 0.47 mm/yr, and the result does coincide with the thermochronology data published by Xu and Kamp (2000) and Kirby et al (2002). Gong and Li (2004) found that the uplift of the Tibetan Plateau since 10 Ma has had an important influence on the climate and sedimentary environment of the South China Sea, and the thick infill of the Y-SH Basin has been supplied by paleo-Red River delta during the Late Miocene.…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…The eastern margin of the Tibetan Plateau along the Long Men Shan is almost as abrupt as the southern margin along the Himalaya, but the two show very different geology (Kirby et al 2002). The eastern part of Tibet shows no evidence of major Late Cenozoic crustal shortening, no evidence of post-collisional metamorphism or middle-lower crustal flow as seen along the Himalaya, and no flexural foreland basin to the east.…”

“…Maggi et al (2000), Jackson (2002), Priestley & McKenzie (2006) and Priestley et al (2008) found no convincing evidence for substantial seismicity in the continental upper mantle, and proposed instead that the deep earthquakes in the eastern Himalaya occurred along the crust-mantle boundary or within the lowermost crust fig. 1 (Kirby et al 2002).…”

Analysis of longitudinal profiles along the eastern margin of the Qinghai-Tibetan Plateau

“…Current estimates for when the QTP reached its current elevation are based on inferences regarding the initiation age of east-west extension in central and southern Tibet (Coleman and Hodges 1995;Harrison et al 1992) or potassic volcanism in north central Tibet (Hacker et al 2000) sometime during the early Miocene (~23 Ma BP). Regardless of the conceptually compelling nature of these geodynamic models, a temporal and genetic link between structural extension, volcanism and uplift is yet to be thoroughly demonstrated (Kirby et al 2002).…”

“…Previous work on erosion rates inferred from 10 Be analysis indicate erosion rates of 1-4 mm yr -1 in the Namche Barwa region and 0.14-0.58 mm yr -1 for incised regions east of the TRR (see Figure 2; Booth et al 2004;Burg et al 1997;Ding et al 2001;Finnegan et al 2008;Malloy 2004;Ouimet et al 2009;Reid et al 2005;Seward and Burg 2008;Stewart et al 2008). Exhumation rates indicate that parts the eastern margin of the QTP have been as high as 10 mm yr -1 for at least the last 1 to 10 Ma (Arne et al 1997;Clark et al 2005b;Enkelmann et al 2006;Godard et al 2009;Kamp 2000;Kirby et al 2002). Towards the east of the TRR, exhumation rates derived from biotite 40 Ar/ 39 Ar, apatite and zircon U-Th/He, and apatite fission track thermochronometry for incised regions indicate rates of 0.25 and 0.65 mm yr -1 since 9-13 Ma (Henck et al 2011).…”