MOBILIZATION OF PARTIALLY MOLTEN CRUST DURING EXTENSION AND THE INTERNAL DYNAMICS OF THE NAXOS MIGMATITE DOME, GREECE

Migmatite domes are common in metamorphic core complexes and form in response to contemporaneous upper crustal extension and mobilization of the deep crust. Dome migmatites deform in the partially molten or magmatic state and commonly record complex form surfaces, folds, and fabrics while units mantling the dome display a simpler geometry, typically formed by transposition during crustal extension. Using field observations and magnetic fabric studies from migmatites in the core of the Naxos dome (Greece), together with insights from two-dimensional thermal-mechanical models, we quantify the complex flow of anatectic crust beneath an extensional detachment system during dome formation.

The migmatitic infrastructure of the Naxos dome is characterized by kilometer-scale, second-order domes (i.e. subdomes), pinched synforms, and variable fabric and strain patterns not present in the mantling metasedimentary units, suggesting that buoyancy-driven flow participated in dome evolution. Subdomes broadly occur within two structural compartments that are separated by a steep, N-S oriented, high-strain zone. This pattern has been recognized in domes formed by polydiapirism and in numerical models of isostasy-dominated flow; in the latter, localized extension in the upper crust triggers deep crustal flow, contraction, and the upwelling of oppositely verging flows into the extending region forming subdomes.

The Naxos dome may have been generated by regional N-S extension that triggered convergent flow of partially molten crust at depth and the upwelling of anatectic migmatites within the dome. This pattern is complicated by the formation of gravitational instabilities and/or overturning of the high melt fraction crust leading to the growth of subdomes. As the migmatites within the Naxos dome reached a higher structural level, they were affected by regional top-to-the-NNE kinematics of the detachment system. Our combined results therefore suggest that dome formation occurred by a combination of coeval and coupled processes, including: upper crustal extension, deep crust contraction during convergent flow of anatectic crust, diapirism and/or density-driven crustal convection forming subdomes, and north-directed detachment kinematics.