Detachment folding of partially molten crust in accretionary orogens: A new magma-enhanced vertical mass and heat transfer mechanism

Abstract

International audienc

Structural and Geochronological Constraints on Devonian Suprasubduction Tectonic Switching and Permian Collisional Dynamics in the Chinese Altai, Central Asia

“…Although we have no specific age constraints for these leucosomes in the current area, we propose that the upright F2 folding follows rapidly the 400‐ to 380‐Ma extension in the deep crust, probably in the early Late Devonian. Magmatism during F2 folding has also been inferred by Jiang et al () in an area 100 km to the west and by Broussolle et al () and Lehmann et al () for the Mongolian Altai. Based on the ingress of magma into the cores of F2 antiforms, the age of F2 folds growth has been estimated to be between 400 and 380 Ma in the Chinese Altai (Jiang et al, ) and between 360 and 350 Ma in the Mongolian Altai (Broussolle et al, ; Lehmann et al, ).…”

“…These data are compatible with recumbent isoclinal flow in the orogenic lower crustal rocks 100 km to the west interpreted as a result of horizontal flow of partially molten crust (Zhang et al, ). Formation of subhorizontal Middle Devonian sheeted granites was also reported from the lower crustal section of the neighboring Mongolian Altai (Hanžl et al, ; Lehmann et al, ). This event is associated with formation of sedimentary and volcanic Devonian basins displaying horizontal bedding and layering in rhyolite lavas in both the Chinese and Mongolian Altai (Figure a).…”

“…These authors argued that such process might cause crustal differentiation that can transform the accretionary wedge sediments into a vertically stratified and stable continental crust (Jiang et al, ). The extended and partially molten crust is ideally suited to develop crustal‐scale doming and upright folding when submitted to horizontal compression as modeled in Lehmann et al (). Using their model as a basis, we suggest that the NE‐SW trending F2 folding of the crust and exhumation of partially molten rocks in the core of large antiforms (Figure b) were driven by a NW‐SE directed shortening.…”

“…This systematic change in fold intensity favors a northward progressive model of folding, probably resulting from the Junggar‐Chinese Altai collision (Li et al, , and references therein). This folding process can be compared to indentation‐driven fold detachment model of Lehmann et al (), who applied partially molten wax‐sand experiments to simulate the deformation of a crust characterized by a partially molten and thermally weak layer at depth overlain by competent material. The model shows progressive locking of detachment folds as the deformation progress, with new folds developing progressively away from the indenter (see also Blay et al, ).…”

“…The early Paleozoic accretionary history of the Mongolian collage was considered to be initially related to a general nearly E‐W convergence forming nearly N‐S trending orogenic zones and structures (Lehmann et al, ). In their model, the final WNW‐ESE orientation of CAOB belt was related to Late Carboniferous to Triassic NNE‐SSW shortening associated with the formation of the Mongolian orocline (Edel et al, ; Guy et al, ; Lehmann et al, ) which can be attributed to the northward movement of the Tarim‐North China Collage (Edel et al, ; Lehmann et al, , ; Xiao et al, ). This shortening is coeval with the development of South Tianshan‐Solonker suture and/or the collision zone along the contact of the Mongolian Collage and the Tarim‐North China Collage in the south (see summary in Xiao et al, ).…”