Multiple episodes of fast exhumation since Cretaceous in southeast Tibet, revealed by low-temperature thermochronology

Abstract

Multiple episodes of fast exhumation since Cretaceous in southeast Tibet, revealed by low-temperature thermochronology, Earth and Planetary Science Letters, pp 62-76, https://doi. Abstract 33The southeast margin of the Tibetan plateau is characterized by deeply incised river 34 valleys separated by a perched low relief landscape that gently descends from the high 35 Tibetan plateau towards the southeast. When and how this unique landscape formed is 36 debated. The onset of increased river incision is often interpreted as a proxy for the timing of 37 surface uplift. Here, apatite and zircon (U-Th)/He and apatite fission track 38 thermochronometries are employed to map the spatial and temporal pattern of exhumation in 39 the region. Vertical profiles of granitic rocks were collected near Deqin (~28.5°N) and Weixi 40 (~27.5°N). The two transects share a similar exhumation history, with two episodes of 41 relatively fast exhumation (~100-300 m/Myr) in the Cenozoic: during the Paleocene to 42 Eocene (60-40 Ma) and Miocene to present (20-0 Ma), separated by an intervening period of 43 slow exhumation. A pulse of moderate to high exhumation (70-300 m/Myr) during the mid-44 to late-Cretaceous (120-80 Ma) is also present in the data. However, the rate and total amount 45 of exhumation near Deqin is larger than at Weixi and is especially pronounced in the interval 46 between 20 Ma to present. We interpret this difference as possibly related to differences in 47 erosion rates between the Lancang (Deqin) and the Jinsha (Weixi) rivers. The Paleocene to 48 Eocene episode of fast exhumation is likely in response to early Cenozoic deformation along 49 tectonic boundary structures, related to the transpressional collision of the Indian plate with 50 this region. Pre-Miocene episodes of fast exhumation corroborate recent paleoaltimetric 51 studies, which show that the southeast margin of the Tibetan plateau was elevated prior to the 52 Oligocene.53 54

Thermochronological Constraints on the Late Cenozoic Morphotectonic Evolution of the Min Shan, the Eastern Margin of the Tibetan Plateau

“…Previous studies reported an Oligocene‐early Miocene phase of enhanced exhumation in the central segment of the Longmen Shan (Wang et al, ), Jiulong Shan (Zhang et al, ), and sites further to the south (Liu‐Zeng et al, ; Shen et al, ). But this phase of exhumation is not found in the Min Shan area, even though we have used a similar combination of thermochronology methods as those previous studies.…”

“…First, many studies used exhumation history determined from thermochronology data as an index for surface uplift and suggested that growth of the high‐relief topography initiated at the late Miocene (5–12 Ma) in the eastern Tibetan Plateau (Clark, Bush, et al, ; Jolivet et al, ; Kirby et al, ; Ouimet et al, ; Tan et al, ), mid‐Miocene (15–22 Ma) in southeastern Tibetan Plateau (Tian, Kohn, Hu, et al, ), or at variable times in different sectors (Shen et al, ; Tian, Kohn, Hu, et al, ; Yang et al, ; Wang et al, ). It is worth noting that the multimethod thermochronology data from vertical profiles in the central Longen Shan (Wang et al, ), Jiulong Shan (Zhang et al, ), the First Bend of the Yangtze River (Shen et al, ), and Three River region (Liu‐Zeng et al, ) suggested an Oligocene‐early Miocene (~35–15 Ma) phase of exhumation, prior to the late Miocene phase. However, it remains unknown whether this earlier phase of exhumation was a regional or local event.…”

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

“…West of the first topographic step, in the hanging wall of the YTB, an area with a mean elevation of ~3.5 km encompasses most of the Jianchuan basin. The present‐day landscape is characterized by relict low‐relief surfaces as defined by Clark et al () and Liu‐Zeng et al () but is locally controlled by a set of normal faults bounding the Pliocene‐Quaternary Dianwei and Heqing basins (Figures , , and g–i). Between the YTB and the CHT‐JQTB, the mean elevation is ~2.7 km and the landscape is shaped by incision of the Jinsha River and normal faults bounding the Chenghai Lake.…”

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

“…2). In the Mekong area, Liu- Zeng et al (2018) and Yang et al (2016) combined AHe, ZHe, and apatite fission-track dating that indicate two exhumation phases ca. 60-40 Ma and ca.…”

“…1). Several studies based on different techniques have constrained erosion in several locations along these rivers at the million-year time scale (Clark et al, 2005;Ouimet et al, 2010;Wilson and Fowler, 2011;Duvall et al, 2012;Tian et al, 2014;Ping et al, 2015;Zhang et al, 2015;Shen et al, 2016;Yang et al, 2016;McPhillips et al, 2016;Liu-Zeng et al, 2018;Nie et al, 2018) and at the 1-100 k.y. time scale (Henck et al, 2011;Zhang et al, 2018).…”