Crustal deformation and exhumation within the India-Eurasia oblique convergence zone: New insights from the Ailao Shan-Red River shear zone

Abstract

During the collision of India and Eurasia, regional-scale strike-slip shear zones played a key role in accommodating lateral extrusion of blocks, block rotation, and vertical exhumation of metamorphic rocks as presented by deformation on the Ailao Shan-Red River shear zone (ARSZ) in the Eastern Himalayan Syntaxis region and western Yunnan, China. We report structural, mica Ar/Ar, apatite fission-track (AFT), and apatite (U-Th)/He (AHe) data from the Diancangshan massif in the middle segment of the ARSZ. These structural data reveal that the massif forms a region-scale antiform, bordered by two branches of the ARSZ along its eastern and western margins. Structural evidence for partial melting in the horizontal mylonites in the gneiss core document that the gneiss experienced a horizontal shear deformation in the middle crust. Muscovite Ar/Ar ages of 36−29 Ma from the core represent cooling ages. Muscovite Ar/Ar ages of 25 and 17 Ma from greenschist-facies mylonites along the western and southern shear zones, respectively, are interpreted as recording deformation in the ARSZ. The AFT ages, ranging from 15 to 5 Ma, represent a quiescent gap with a slow cooling/exhumation in the massif. AHe results suggest that a rapid cooling and final exhumation episode of the massif could have started before 3.2 Ma, or likely ca. 5 Ma, and continue to the present. The high-temperature horizontal shearing layers of the core were first formed across the Indochina Block, locally antiformed along the tectonic boundaries, and then cooled through the mica Ar-Ar closure temperature during Eocene or early Oligocene, subsequently reworked and further exhumed by sinistral strike-slip movement along the ARSZ during the early Oligocene (ca. 29 Ma), lasting until ca. 17 Ma, then final exhumation of the massif occurred by dextral normal faulting on the Weixi-Qiaohou and Red River faults along the limbs of the ARSZ since ca. 5 Ma. The formation of the antiform could indicate local crustal thickening in an early transpressional setting corresponding to India-Asia convergence. Large-scale sinistral ductile shear along the ARSZ in the shallow crust accommodated lateral extrusion of the Indochina Block, and further contributed to the vertical exhumation of the metamorphic massif from the late Oligocene to the middle Miocene. Furthermore, the change of kinematic reversal and associated cooling episodes along the ARSZ since the middle Miocene or early Pliocene imply a tectonic transfer from strain localization along the major tectonic boundaries to continuous deformation corresponding to plateau growth and expansion.

Thermal and Physical Properties of Barrovian Metamorphic Sequence Rocks in the Ailao Shan‐Red River Shear Zone, and Implications for Crustal Channel Flow

“…Four discrete metamorphic massifs are exposed within the 1000‐km‐long ARSZ, which share a common geodynamic history, but unique tectonic characteristic (Leloup et al., 2001). For example, regional antiforms with gneissose cores and micaschist limbs occur in the Xuelong Shan (Zhang et al., 2017a), DCS (Zhang et al., 2021) and DNCV massif (Anczkiewicz et al., 2007; Leloup et al., 2001). Nevertheless, the spatial distribution and structural features of metamorphic supracrustal rocks in the largest massif—the ALS—show significant differences.…”

“…In situ leucosomes that formed by partial melting of preexisting mafic, sedimentary, and granitic rocks are present as both discontinuous and concordant layers and lenses within the migmatites and adjacent rocks (Liu, Wang, et al, 2015;Searle, 2006). Previous work within the ARSZ has mainly focused on the timing and nature of strike-slip displacement, as constrained from field structures, microstructures, and petrofabric studies (Cao et al, 2017;Liu et al, 2012;Wu et al, 2017;Zhang et al, 2012Zhang et al, , 2017aZhang et al, , 2021. It is generally accepted that significant left-lateral strike-slip shear initiated after the Eocene-Oligocene (Cao et al, 2009;Liu et al, 2007Liu et al, , 2012Tang et al, 2013;Yang et al, 2019) and accompanied clockwise rotation of the Indochina Block (Briais et al, 1993;Li et al, 2017).…”

Middle–Late Cenozoic Stepwise Deformation Propagation in Eastern Tibet

“…Owing to the blocking of stable basement of the Sichuan Basin, a subsequent southeastward propagation of deformation occurred across eastern Tibet during the Late Oligocene and Early Miocene (Figure 4b). Later, the motion along the Ailao Shan–Red River shear zone shifted to right‐lateral slip (Leloup et al., 1993, 2001; Schoenbohm, Burchfiel, Chen, & Yin, 2006; B. Zhang et al., 2021). Following the southeastward deformation propagation across the Yalong thrust belt, the Anninghe fault (H. Wang et al., 2020; Y.…”

Slab Tear of Subducted Indian Lithosphere Beneath the Eastern Himalayan Syntaxis Region

“…White mica and biotite 40 Ar/ 39 Ar ages serve as valuable indicators for unraveling the thermotectonic evolution of metamorphic rocks during deformation and cooling processes (McDougall & Harrison, 1999;B. Zhang et al, 2021;L.…”

“…A prominent outcome of Indian indentation into Asia is the development and progressive evolution of regionalscale V-shaped conjugate strike-slip shear zones/faults in the Tibetan Plateau and Southeastern Asia (Figures 1a-1c; Leloup et al, , 2001Tapponnier et al, 2001;Taylor & Yin, 2009;Yin et al, 2006;B. Zhang et al, 2021).…”