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

0483167 - GFÚ 2018 RIV US eng J - Journal Article
Lehmann, J. - Schulmann, K. - Lexa, O. - Závada, Prokop - Štípská, P. - Hasalová, Pavlína - Belyanin, G. - Corsini, M.
Detachment folding of partially molten crust in accretionary orogens: A new magma-enhanced vertical mass and heat transfer mechanism.
Lithosphere. Roč. 9, č. 6 (2017), s. 889-909. ISSN 1941-8264. E-ISSN 1947-4253
Institutional support: RVO:67985530
Keywords : continental crust * shear-zone * gneiss domes
OECD category: Geology
Impact factor: 2.766, year: 2017

We use structural, petrographic, and geochronological data to examine processes of exhumation of partially molten crust in the Late Devonian-early Carboniferous Chandman dome in the Mongolian tract of the Central Asian Orogenic Belt. The dome is composed of a magmatite-migmatite core and a low-grade metamorphic envelope of early Paleozoic metasediments and Carboniferous clastics. Its tectonic evolution can be divided into three main stages. The oldest fabric is a subhorizontal foliation, S-1, in migmatites that is subparallel to the magmatic foliation in granitoids and to the greenschist facies schistosity in the enveloping metasediments. This event is interpreted as a result of horizontal deep crustal flow at depths of 20-25 km. The S-1 layering was subsequently transposed into a new foliation, S-2, or affected by open to close upright F-2 folds that are locally truncated by steep walls of diatexites, suggesting influx of partially molten crust into fold cores. The shallow-dipping magmatic foliation in granitoids is locally reworked by vertical magmatic to gneissic S-2 fabrics. Syn-S-2 metamorphic assemblages and synkinematic to postkinematic cordierite point to exhumation of the migmatites and granitoids from 20-25 km to similar to 10 km, and concomitant isobaric heating of the surrounding upper crust. New Ar-40/Ar-39 ages of 350-340 Ma from both the high-grade core and the metamorphic mantle overlap with previously published crystallization ages of 360-340 Ma, suggesting that magmatism and cooling in the upper crust are partly synchronous. Late syn-D-2, S-2-parallel leucogranite sheets crosscutting both the magmatic core and the mantling migmatites either exploit S-2 or crosscut horizontal S-1 fabrics. They are interpreted as brittle expulsion of magma during ongoing syn-D-2 exhumation.
Permanent Link: http://hdl.handle.net/11104/0278564