Tectonic uplift of the Xichang Basin (SETibetan Plateau) revealed by structural geology and thermochronology data

Abstract

The Xichang Basin in southeastern Tibet provides crucial information about formation and tectonic processes affecting the eastern Tibetan Plateau. To determine when and how the uplift developed, we conducted detailed studies of structures and obtained thermochronology data from the Xichang Basin and its periphery. The Xichang Basin is characterized by gentle deformation of the strata, segmented by an E-vergent boundary thrust fault. Two stages of deformation, strike-slip followed by an E-W oriented shortening resulted in oblique shortening between the southeastern Tibetan Plateau and the Sichuan Basin. New apatite fission-track data interpreted together with (U-Th)/He data confirm a simple burial/heating and exhumation/cooling history across the Xichang Basin and its periphery. Subsidence and burial of the Xichang Basin peaked between 80-30 Ma, followed by mountain building with a protracted cooling starting at around 40-20 Ma, with rates of ca. 2.0-8.0°C Myr À1 (i.e. 0.1-0.3 mm year À1 ). Our data indicate that the Xichang Basin has experienced ca. 2.5-5 km of exhumation, much more intensive than the ca. 1-2 km of exhumation inferred for the southwestern Sichuan Basin. Restored balanced cross-sections of post-Late-Triassic strata along a ca. 250 km traverse indicate ca. 10-20% east-west shortening strain (i.e. ca. 20-30 km) at the southeastern Tibetan Plateau during Cenozoic time. Study of crustal thickening and erosion supports a tectonic shortening mechanism to account for the uplift of the Xichang Basin on the southeastern Tibetan Plateau.

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

“…In this case, upper crustal shortening and thickening probably affected a large area from the Longmen Shan to the Laojun Shan in the Oligocene‐Early Miocene (Figure a) and would be responsible for the generation of similar topographic relief above major thrust faults along the margins of southeastern Tibet. However, Oligocene‐Miocene sediments are pervasively absent in the footwalls of the Yalong‐Yulong and Longmen Shan thrust belts (BGMRY, ; Deng et al, ). This is also the case for some large basins in southeastern Tibet, as for instance the Sichuan, Xichang, and Chuxiong basins (Deng et al, , Figure a).…”

“…However, Oligocene‐Miocene sediments are pervasively absent in the footwalls of the Yalong‐Yulong and Longmen Shan thrust belts (BGMRY, ; Deng et al, ). This is also the case for some large basins in southeastern Tibet, as for instance the Sichuan, Xichang, and Chuxiong basins (Deng et al, , Figure a). One possible explanation is that southeastern Tibet was not a closed system for water and sediments (Richardson et al, ); large amounts of eroded sediments may have been transferred by large rivers and eventually deposited into the peripheral seas.…”

Present‐Day Activity of the Anninghe Fault and Zemuhe Fault, Southeastern Tibetan Plateau, Derived From Soil Gas CO2Emissions and Locking Degree

“…This area is characterized by a wider fault system (e.g., curved fault plane, irregular fractures and fault-related folds) with complex geometry which has a wide fracture zone surrounding the main fault (Deng et al, 2017). Site C is characterized by the lowest locking degree, but the strongest CO2 release, which could suggest the presence of greater numbers of crustal channels conducive to CO2 migration.…”

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

“…CD: Chuandian terrane, CN‐ML suture: Changning‐Menglian suture, JS‐SM suture: Jinshajiang‐Song Ma suture, EHS: Eastern Himalaya Syntaxis, JCF: Jianchuan fault, CHF: Chenghai fault, CXF: Chuxiong fault, YYF: Yulong‐Yunlong fault, JJF: Jinhe‐Jianhe fault, LMST: Longmenshan thrust fault, XSH‐XJF: Xianhuihe‐Xiaojiang fault, LvF: Lvzhijiang fault, YMF: Yimenhe fault, PF: Puduhe fault, WXF: Western Xiaojiang fault, EXF: Eastern Xiaojiang fault, QJF: Qujiang fault, JSF: Jianshui fault. Reference: 1—Yang et al, 2017, 2—Wang, Kirby, et al, 2012, 3—Arne et al, 1997, 4—Wilson & Fowler, 2011, 5—Enkelmann et al, 2006, 7—Cook et al, 2013, 8—Tian et al, 2015; 9—Clark et al, 2005, 10—Ouimet et al, 2010, 11—Godard et al, 2009, 12—Xu & Kamp, 2000, 13—Wang, Jiang, et al, 2012, 14—Deng et al, 2017, 15—H. Zhang et al, 2016, 16—Tian et al, 2014, 17—Shen et al, 2016, 18—Lacassin et al, 1996, 19—Leloup et al, 2001, 20—K.…”