Two‐Phase Exhumation Along Major Shear Zones in the SE Tibetan Plateau in the Late Cenozoic

Abstract

Three continent-scale shear zones are arguably the most outstanding structural features in the southeastern Tibetan Plateau, and therefore, their tectonic and landscape evolution have significant implications for understanding the history and mechanisms of intracontinental mountain building and plateau growth. This study presents low-temperature thermochronology from the Gaoligong and Chongshan shear zones (GLSZ and CSSZ) and quantitative analyses of fluvial longitudinal profiles of tributaries in the Salween drainage, which lies between the shear zones. Apatite and zircon (U-Th)/He data reveal a two-stage exhumation history for both shear zones: rapid and prominent cooling in the middle Miocene followed by a second, lower magnitude cooling event in the late Miocene to early Pliocene. Ductile transpressional shearing is inferred to have caused the first cooling, continuing until~11 Ma. The northward migration of the tectonic events along the Mogok metamorphic belt and GLSZ and synchronous dextral displacement along the Jiali fault indicate the dominant role of the north advancing eastern Himalayan syntaxis on the surrounding structures. Increased river incision is identified in the middle Salween drainage, leading to two-segment river profiles and further exhumation along the GLSZ and CSSZ. The tributary transient response could result from temporal changes in uplift or adjustments of the trunk channel to climatic change. Furthermore, glaciers play an important role in shaping the landscape of the upper reaches of catchments in the northern segment of the shear zones. Different drivers for the two exhumation events may reflect distinct stages of plateau growth characterized by different crustal deformation patterns.

Oligocene Deformation of the Chuandian Terrane in the SE Margin of the Tibetan Plateau Related to the Extrusion of Indochina

“…Since it remains unclear whether or not the paleo‐Red River existed (e.g., Wei et al, 2016; Wissink et al, 2016; P. Zhang et al, 2019), the timing of uplift derived from river captures will not be considered here. Earlier low‐temperature thermochronology studies suggested a middle‐late Miocene (13–9 Ma, Serravallian‐Tortonian) rapid rock uplift of the eastern and SE margin of the Tibetan Plateau (Clark et al, 2005; Kirby et al, 2002; Ouimet et al, 2010; Figure 1), but later studies revealed episodic rock uplift of the area prior to the late Miocene, especially in the Oligocene (K. Cao et al, 2019; Liu‐Zeng et al, 2018; Tian et al, 2014; Wang, Kirby, et al, 2012; Y. Wang et al, 2018).…”

“…Recent paleomagnetic reconstruction, however, showed that the displacement along the Ailao Shan‐Red River fault is ~600 km in the northwest, but only 250 km in the southeast, which suggests that the Indochina Block did not behave as a rigid entity during the extrusion (Li et al, 2017). The motion on the Ailao Shan‐Red River fault has reversed to act as a right‐lateral fault since at least ~10 Ma with ~40 km displacement (Leloup et al, 1995; Li et al, 2013; Y. Wang et al, 2018), which was inferred to mark the onset of either the second stage of Tibet extrusion (Tapponnier et al, 1982) or lower crustal flow (Y. Wang et al, 2018).…”

“…However, the timing of possible river captures, and subsequent drainage reorganization determined by provenance shifts, ranges from pre‐Eocene to middle Miocene (e.g., Cao et al, 2018; Clift et al, 2006; Wissink et al, 2016; Yan et al, 2012). Recently, multiphased rapid uplift of the SE margin of the Tibetan Plateau, starting as early as the late Cretaceous, has been recognized by a growing number of low‐temperature thermochronological studies (K. Cao et al, 2019; Liu‐Zeng et al, 2018; Tian et al, 2014; Wang, Kirby, et al, 2012; Y. Wang et al, 2018) (Figure 1a).…”

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story

“…The Hengduan Mountains lie in an area on the south-eastern margin of the modern Tibetan Plateau, accommodating the eastward extrusion of parts of the Qiangtang Terrane and the Indo-China and Chuandian blocks ( Li et al., 2020b , c ; Searle et al., 2011 ; Tapponnier et al., 1982 , 2001 ; Tong et al., 2017 ). This area has experienced strong episodic deformation since the late Cretaceous ( Cao et al., 2019 ; Liu-Zheng et al., 2018 ; Tian et al., 2014 ; Wang et al., 2012 , 2018 ), resulting in several major strike-slips fault systems, tightly folded synclines and anticlines ( YBGMR, 1990 ; Burchfiel and Chen, 2012 ), and a complex of regional high elevation but low-relief relictual landscapes that have become deeply dissected by large rivers draining from the plateau ( Clark et al., 2006 ; Liu-Zheng et al., 2008 ).…”

Contrasting exhumation histories and relief development within the Three Rivers Region (Southeast Tibet)

“…1b), subsequently inverted along the right-lateral Red River fault since ~5-10 Ma (Leloup et al, 1995(Leloup et al, , 2001Replumaz et al, 2001;Fyhn and Phach, 2015). High-temperature thermochronologic data from SE Tibet shear zones show ages mainly between ~34 and ~17 Ma, along the Red, the Salween and the Mekong rivers, which have been linked to this extrusion process (Leloup et al, 2001;Wang et al, 2016Wang et al, , 2018. In contrast, no clear estimation for the age of plateau uplift in the Three Rivers Region has been obtained.…”