Structural constraints on the evolution of the Central Asian Orogenic Belt in SW Mongolia

Abstract

International audienceWe provide a detailed description of the structures along a 300 km long and 50 km wide transect across the Central Asian Orogenic Belt (CAOB) in southwestern Mongolia, covering the Precambrian Dzabkhan continental domain with overthrust Neoproterozoic ophiolites in the north (Lake Zone), a Silurian-Devonian passive margin association (Gobi-Altai Zone) and oceanic domain (Trans-Altai Zone) in the center, and a continental area (South Gobi Zone) in the south. Structural analysis suggests late Cambrian collapse of the thickened Lake Zone continental crust, leading to stretching of the lithosphere and followed by Silurian-Devonian formation of oceanic crust in the Trans-Altai domain. Subsequent emplacement of Devonian-Carboniferous and late Carboniferous magmatic arcs occurred on the Gobi-Altai and South Gobi Zone crusts, respectively, during E-W shortening. Finally, the entire system was affected by N-S convergence from the Permian to Jurassic, leading to heterogeneous shortening of the orogenic domain. The model best fitting these observations is one of generalized westward drift of the Tuva-Mongol-Dzabkhan-Baydrag ribbon continents during the Silurian-Devonian, associated with westward-subduction of the Mongol-Okhotsk Ocean and sequential growth of syn-convergent magmatic arcs. Back-arc basins opened during this period in the area of the western Paleoasian Ocean. The present-day shape of the CAOB in southern Mongolia was probably formed during Permian to Mesozoic anticlockwise rotation and folding of the Tuva-Mongol-Dzabkhan-Baydrag continental ribbons, combined with a strike-slip (transpressional) reactivation of ancient transform boundaries in the Paleoasian oceanic domain. All continental and oceanic crustal domains were reactivated and intensely deformed during this convergence in a style controlled by crustal rheology and a heterogeneous Permian magmatic-thermal input. The sequence of tectonic events is tested against published paleomagnetic data, paleogeographic reconstructions and tectonic models, leading to a revised model for the accretion of juvenile crust to a continental margin in the CAOB of southern Mongolia

Folded Basinal Compartments of the Southern Mongolian Borderland: A Structural Archive of the Final Consolidation of the Central Asian Orogenic Belt

“…Terrane maps of Mongolia with accompanying stratigraphic columns and geochronological data provide a regional lithotectonic framework for understanding the region's crustal evolution [4,21]. More recently, new maps, structural and geochronological data, and gravity and magnetic models from different areas in southern Mongolia further refine the polyphase metamorphic, deformational, and magmatic evolution of the different terranes and call into question the locations of some previously mapped terrane boundaries [8,20,22].…”

“…Permian sediments from the Tien Shan through the Beishan to southern and eastern Mongolia and adjacent regions of China record the marine-terrestrial transition [23,24] and were affected by crustal shortening due to terminal closure of the final Paleo-Asian ocean seaway [5,7,18,25]. Collision-related crustal shortening likely persisted into the Triassic [5,8,18]. It is proposed that CAOB terrane amalgamation in southern Mongolia throughout the Paleozoic occurred along a north-south oriented active margin and that the accreted terrane assemblage was subsequently oroclinally bent in a counterclockwise sense during the Permo-Triassic into an east-west orientation and cut by sinistral strike-slip faults in the Triassic-mid Jurassic [8,9,24,26,27].…”

“…Collision-related crustal shortening likely persisted into the Triassic [5,8,18]. It is proposed that CAOB terrane amalgamation in southern Mongolia throughout the Paleozoic occurred along a north-south oriented active margin and that the accreted terrane assemblage was subsequently oroclinally bent in a counterclockwise sense during the Permo-Triassic into an east-west orientation and cut by sinistral strike-slip faults in the Triassic-mid Jurassic [8,9,24,26,27]. The terrane amalgamation history of southern Mongolia and the Beishan region imparted a dominant east-west structural grain throughout the region (modern coordinates) consisting of terrane boundaries (including suture belts), other faults, metamorphic foliation and sedimentary strike belt trends, and magmatic arc trends [4,8,9,28].…”

Geology of the Gobi Altai and Tseel terranes in the central part of the Sagsai River Watershed, SE Mongolian Altai

“…This area is located south of the Main Mongolian Lineament (Figure 1), which represents the main tectonic boundary separating the Neoproterozoic domain in the north, affected by early Palaeozoic orogenic event, from the early Palaeozoic domain to the south (e.g. Badarch, Cunningham, & Windley, 2002;Kröner et al, 2010;Ruzhentsev & Pospelov, 1992) affected by late Devonian to late Palaeozoic deformation and metamorphism (Edel, Schulmann, Hanžl, & Lexa, 2014;Lehmann et al, 2010;Xiao et al, 2009).…”

Foreword to the special volume 'Magmatic evolution of Mongolian part of the Central Asian Orogenic Belt and its geodynamic significance'

“…This orogen was formed by accretion of Cambrian, Ordovician and Devono-Carboniferous arcs, back-arcs and accretionary wedges (Badarch et al 2002;Windley et al 2007) and Grenville-age microcontinents (RojasAgramonte et al 2011) of both Siberian and Gondwanan affinities (Cocks and Torsvik 2007;Wilhem et al 2012). The most puzzling is its mixed character, starting from purely Pacific-type accretionary system that developed progressively into collisional orogen of Tethysian type (Lehmann et al 2010;Xiao and Santosh 2014). Magmatic evolution of such a transient geodynamic setting may provide pivotal insight into understanding of differences between Circum-Pacific accretionary and collisional processes and can be used as a proxy of purely juvenile crustal growth or subsequent recycling of assembled crust.…”