Conservation and redistribution of crust during the Indo-Asian collision

Abstract

We evaluate the mass balance of the Indo-Asian orogen by reconstructing the Indian and Asian margins prior to collision using recently published paleomagnetic and surface shortening constraints, and subtracting modern crustal volumes derived from gravity inversions and deep seismic soundings. Results show a~30% deficit between original and modern orogen volumes if the average global crustal thickness of 41 km is assumed prior to collision, even once eastward extrusion and crustal flow are considered. Such a large discrepancy requires crustal recycling of a magnitude that is greater than one half of the modern orogenic mass, as others have previously suggested. Proposals for extensive high elevations prior to or soon after the collision further exacerbate this mismatch and dramatically increase the volume of material necessary to be placed into the mantle. However, we show that this discrepancy can be eliminated with a 23-29 km thick crust within the orogen prior to collision along with a thick southern Tibet margin (the Lhasa and Qiangtang terranes). Because of the relatively low magnitude of surface shortening in Asia, an initially thin crust would require underplating of Indian crust in southern Tibet and displacement of a highly mobile lower crust to the north and east in order to explain modern crustal thicknesses. The contrast between a proposed thinner Asian interior and older and thicker lithosphere of the North China block may have defined the distal extent of deformation at the time of collision and since.

Crustal rheology controls on the Tibetan plateau formation during India-Asia convergence

“…2b). Moho depth estimates in this area indicate a wide area with thicknesses in excess of 80 km beneath the southernmost portion of the Tibetan plateau, whereas similar thicknesses are found in a narrow belt beneath the western Tibet2. The crustal thicknesses and distribution beneath these two domains are compatible with the outcomes of the model where the two crustal rheologies are embedded (Fig.…”

Rates and style of Cenozoic deformation around the Gonghe Basin, northeastern Tibetan Plateau

“…Lease et al (2012b) determined that this relatively modest shortening is suffi cient to account for modern crustal thicknesses of 56 ± 4 km without invoking thickening by channel fl ow in the lower crust, given a preCenozoic crustal thickness of 45 ± 5 km (which is similar to stable cratonal regions adjacent to the Tibetan Plateau; see Lease et al, 2012b, and references therein). However, the assumption of 45 km pre-Cenozoic crustal thickness requires crustal recycling in an amount nearly equal to the modern orogenic volume in order to accommodate Indo-Asian crustal convergence since 40 Ma (Yakovlev and Clark, 2014). Modest Cenozoic shortening is similar to the fi ndings of other studies focused on northern Qaidam (e.g., Yin et al, 2008a) and along the Haiyuan fault (Gao et al, 2013).…”

Relict basin closure and crustal shortening budgets during continental collision: An example from Caucasus sediment provenance

“…Active collisional orogens are particularly significant because they provide unique opportunities to relate the response of continents to the plate motions driving deformation [e.g., Clark , ]. However, crustal shortening measured in most active orogens is typically hundreds to thousands of kilometers less than postcollisional plate convergence [ Lippert et al ., ; McQuarrie et al ., ; van Hinsbergen et al ., ; Yakovlev and Clark , ]. For example, in the India‐Eurasia collision zone (Figure ), total plate convergence (2400 to 3200 km) since the onset of collision at ~50 Ma exceeds the sum of known or inferred crustal shortening in Eurasia (1050 to 600 km) and India (675 ± 225 km) by at least 450 to 1700 km [ van Hinsbergen et al ., ; Yakovlev and Clark , ], although lithospheric‐scale balancing has been reported [e.g., Guillot et al ., ; Replumaz et al ., ; Replumaz et al ., ].…”

“…However, crustal shortening measured in most active orogens is typically hundreds to thousands of kilometers less than postcollisional plate convergence [ Lippert et al ., ; McQuarrie et al ., ; van Hinsbergen et al ., ; Yakovlev and Clark , ]. For example, in the India‐Eurasia collision zone (Figure ), total plate convergence (2400 to 3200 km) since the onset of collision at ~50 Ma exceeds the sum of known or inferred crustal shortening in Eurasia (1050 to 600 km) and India (675 ± 225 km) by at least 450 to 1700 km [ van Hinsbergen et al ., ; Yakovlev and Clark , ], although lithospheric‐scale balancing has been reported [e.g., Guillot et al ., ; Replumaz et al ., ; Replumaz et al ., ]. Likewise, the deficit of crustal shortening in the Arabia‐Eurasia collision zone east of 48°E (Figure ) is at least 220 to 420 km since 35 Ma, based on the difference between 750 to 950 km of post‐35 Ma plate convergence and ~530 km of documented shortening (i.e., ~175 km in Eurasia, ~175 km in the Zagros, and ~180 km from Arabian underthrusting) [ McQuarrie and van Hinsbergen , ] (Figure ).…”