Oligocene‐Early Miocene Topographic Relief Generation of Southeastern Tibet Triggered by Thrusting

Abstract

The timing and mechanisms of uplift in southeastern Tibet remain disputed. To address this debate, we conducted structural and morphological analyses of the Yulong thrust belt; we also reconstruct the cooling and exhumation history of the Jianchuan basin in the hanging wall of the thrust system using inverse thermal modeling of apatite fission-track and (U-Th)/He thermochronology data. Our results provide evidence for 2.3-3.2 km of rapid exhumation in the Jianchuan basin between~28 and~20 Ma, followed by limited exhumation of less than 0.2 km since then. The magnitude of basin exhumation is consistent with the present-day topographic step of 1.8-2.4 km across the Yulong and Chenghai thrust belts, as shown by morphometric analysis. We thus infer that the present-day morphology of the southeastern margin of Tibet results partly from thrusting along the Yulong thrust belt during the Late Oligocene-Early Miocene. This structure may be the southwest continuation of the Longmen Shan thrust belt, offset by the Xianshuihe fault in the Late Miocene. On a regional scale, the approximate synchronicity of exhumation in the hanging walls of the Yalong-Yulong and Longmen Shan thrust systems indicates that widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene. Plain Language SummaryThe timing and mechanisms for the high-elevation, low-relief landscape in southeastern Tibet remain at the center of debate. Using apatite fission track and apatite (U-Th)/He thermochronology and thermal modeling, this study sheds new lights on this issue by reconstructing the cooling and exhumation history of the Jianchuan basin, western Yunnan. One major finding is that the Jianchuan basin experienced rapid exhumation during~28-20 Ma at a rate of 0.57-0.80 km/Myr, coinciding with the absence of coeval sedimentation within the basin. Furthermore, morphometric and structural analyses point out a reasonable causal link between production of the topographic relief in the SE Tibet, exhumation of the Jianchuan basin, and thrusting of the Yalong thrust belt. These results allow us to propose a regional-scale tectonic scenario of widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene.

Evolution of the Yangtze River network, southeastern Tibet: Insights from thermochronology and sedimentology

“…However, in the same area, Yang et al (2016) reported a late Eocene AHe age. Based on AHe ages ranging from 30 to 20 Ma, Shen et al (2016) proposed that incision occurred during the Miocene-early Oligocene, which was confirmed by new AHe and fission-track data by Cao et al (2019), who showed a rapid exhumation phase from 28 to 20 Ma. Downstream of the Yangtze first bend, in the Tiger Leap Gorge (TLG in Fig.…”

“…3) a few kilometers north. Last, Cao et al (2019) collected two samples in the same area that yielded mean AHe ages of ca. 38 and 30 Ma.…”

“…38 and 30 Ma. By modeling these ages along with fission-track data from an altitudinal profile, Cao et al (2019) showed that a rapid cooling episode occurred from 28 to 20 Ma, leading to a total exhumation of 2.3-3.2 km. According to Cao et al (2019), there has been less than 0.2 km of exhumation in the Jianchuan Basin since 20 Ma.…”

“…By modeling these ages along with fission-track data from an altitudinal profile, Cao et al (2019) showed that a rapid cooling episode occurred from 28 to 20 Ma, leading to a total exhumation of 2.3-3.2 km. According to Cao et al (2019), there has been less than 0.2 km of exhumation in the Jianchuan Basin since 20 Ma. If during the Miocene, incision was less than ~2 km (as proposed by McPhillips et al, 2016), then it would have limited effects on the AHe system, which in turn would not record this late incision phase.…”

Genetic structure and phylogeographic relationships of the Bellamya complex: A nascent aquacultural snail in the Pearl River basin, China

“…This timescale correlated with the conclusion of the initial uplift of the QTP during the early Miocene (25 ~ 17 mya; Shi et al, ). The extensive uplift of the Himalayas and subsequent uplift of the Southeastern Tibet and Yunnan Plateau (Figure S2) during the early Miocene to Pliocene (Cao et al, ; Favre et al, ; Harrison, Copeland, Kidd, & Yin, ; Ruddiman, ; Shi et al, ) would have completely divided the Bellamya lineage in the Pearl River basin from that in India and Thailand. Many studies have associated the divergence of organisms, such as in lizards, birds, frogs and fish, with the Miocene uplift of the QTP and simultaneous climate changes (Che et al, ; Guo & Wang, ; Johansson et al, ; Wang, Gan, Li, Chen, & He, ).…”