Intra-continental transpression and gneiss doming in an obliquely convergent regime in SE Asia

Abstract

The Tengchong terrane comprises a sequence of linear dome-like zones, cored by granite and migmatitic layers. These cores are mantled by predominantly gneiss and subordinate schist sequences, decreasing in deformation intensity outward from extensive mylonitization to weak mylonitization. The pre-doming deformation was characterized by the formation of large-scale top-to-the-east shearing (D1) in the gneiss terrane, locally preserved flat-lying foliation (S1), weak folding (F1) and emplacement of the Mangbang granite during the Cretaceous (114-104 Ma). The second stage of deformation (D2) consisted of map-scale east-verging folds (F2, dome amplification) and minor lateral strike-slip shear zones between the anticlines in the gneiss and migmatitic sequences. Extensive partial melting and emplacement of 67-30 Ma synkinematic granitoid bodies/veins occurred, leading to the emplacement of wedges of granite into the easterly directed F2 fold cores. These wedges formed kilometer-scale granitoid domes. The post-doming D3 deformation with transpression recorded strain partitioning with simple shear-dominated high-strain zones along the Gaoligong and Nabang dextral lateral strike-slip shear zones (active during 30-11 Ma). Late transtensional deformation (D4) during cooling of the entire terrane involved the localized low-temperature Gaoligong west and east detachment faults that controlled the late exhumation of the Gaoligong metamorphic zone (since 10 Ma). Our structural observations, combined with previous studies, suggest that this style of doming is a representative type of intra-continental deformation in the Cenozoic during the oblique India-Asia collision. The actual dome shapes reflect formation of antiforms during compression-dominated transpression, prior to localized strike-slip shearing, in the accommodation belt around the Eastern Himalayan Syntaxis. Vertical exhumation of crustal material by contractional doming played an important role in absorbing the vast majority of the internal deformation of crustal fragments during oblique collision.

The Anatomy and Origin of a Synconvergent Grenvillian-Age Metamorphic Core Complex, Chottanagpur Gneiss Complex, Eastern India

“…The formation of Metamorphic Core Complexes (MCCs) is conventionally related to extensional tectonic processes ( [1] and references therein), although proposed models vary in the details [2][3][4][5][6][7][8][9]. In addition to regions dominated by extension, such as the Basin and Range province, MCCs have been reported from accretionary margins [10] and in convergent regimes [1,11,12]. Despite the convergent nature of these tectonic settings, MCC development is associated with extension-related processes such as slab rollback, intrusion driven extension [13], or orogenic collapse under fixed boundary conditions or slow plate convergence [14].…”

Strain localized deformation variation of a small-scale ductile shear zone

“…As mentioned above, the GLG-SZ exposed widespread granitic intrusions of various ages (Fig. 1B) (Zhang et al, 2017;Zhu et al, 2017;Chiu et al, 2018; Tang et al, 2020;Dong et al, 2021). Most granitic intrusions underwent strong mylonitization within the GLG-SZ.…”

“…Around 24-23 Ma, the later stage was defined by amphibolite-greenschist facies conditions in connection with shearing deformation (Ji et al, 2000b;Song et al, 2010). The analysis of geochronological data from the Tengchong area suggests that the dome uplift and deep crustal material was exhumed during 32-10 Ma in the south of the GLG-SZ (Xu et al, 2015;Zhang et al, 2017;Dong et al, 2019).…”

The atypical Gaoligong orocline: Its geodynamic origin and evolution

“…The existence of the Gaoligong orocline has long been recognized, and its structural evolution has been debated for an equally long period (Y.G. Wang et al, 2006a;Song et al, 2010;Eroglu et al, 2013;Xu et al, 2015;Zhang et al, 2017;Chiu et al, 2018). Previous studies mostly focus on reconstructing the detailed evolution of either the northern or the southern section of the Gaoligong orogen, but not the Gaoligong orocline.…”