Role of strain localization and melt flow on exhumation of deeply subducted continental crust

0494976 - GFÚ 2019 RIV US eng J - Journal Article
Závada, Prokop - Schulmann, K. - Racek, M. - Hasalová, P. - Jeřábek, P. - Weinberg, R. F. - Štípská, P. - Roberts, A.
Role of strain localization and melt flow on exhumation of deeply subducted continental crust.
Lithosphere. Roč. 10, č. 2 (2018), s. 217-238. ISSN 1941-8264. E-ISSN 1947-4253
R&D Projects: GA ČR GA14-15632S
Institutional support: RVO:67985530
Keywords : Central European Variscides * Bohemian massif * partially molten rocks
OECD category: Geology
Impact factor: 2.486, year: 2018

A section of anatectic felsic rocks from a high-pressure (>13 kbar) continental crust (Variscan Bohemian Massif) preserves unique evidence for coupled melt flow and heterogeneous deformation during continental subduction. The section reveals layers of migmatitic granofels interlayered with anatectic banded orthogneiss and other rock types within a single deformation fabric related to the prograde metamorphism. Granofels layers represent high strain zones and have traces of localized porous melt flow that infiltrated the host banded orthogneiss and crystallized granitic melt in the grain interstices. This process is inferred from: (1) gradational contacts between orthogneiss and granofels layers, (2) grain size decrease and crystallographic preferred orientation of major phases, compatible with oriented growth of crystals from interstitial melt during granular flow, accommodated by melt-assisted grain boundary diffusion creep mechanisms, and (3) pressure-temperature equilibria modeling showing that the melts were not generated in situ. We further argue that this porous melt flow, focused along the deformation layering, significantly decreases the strength of the crustal section of the subducting continental lithosphere. As a result, detachment folds develop that decouple the shallower parts of the layered anatectic sequence from the underlying and continuously subducting continental plate, which triggers exhumation of this anatectic sequence.
Permanent Link: http://hdl.handle.net/11104/0288024