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Gneiss domes are ubiquitous structures in all exhumed orogens, and their formation represents a fi rst order thermal-tectonic process that has operated from the Archean to the present. The vertical fl ow of crust to create domal structures is a signifi cant factor in the redistribution of heat and material in orogens and therefore in the evolution of continents. Worldwide, gneiss domes display many similarities in geometry (aspect ratio), petrology, and structure, and these similarities transcend differences in tectonic setting. Gneiss domes are cored by high-grade metamorphic rocks (including migmatite) ± granitoids, and the core rocks commonly record a component of isothermal decompression, in contrast to mantling schists, and may exhibit a late, low-pressure-high-temperature metamorphic assemblage. Rapid cooling typically follows isothermal decompression, as hot rocks are rapidly emplaced at higher structural levels. Most gneiss domes are elongate parallel to the strike of the orogen. Domes with long dimension ≤90 km have a ratio of long to short axes of ~2:1-3:1. The elliptical shape of gneiss domes worldwide suggests that their morphology, and therefore genesis, is controlled by crustal fl ow dynamics, including the magnitude of vertical versus lateral crustal fl ow. The conditions and mechanisms involved in dome formation inform the relative rates of vertical and lateral crustal fl ow during orogeny.

Migmatite domes are common in metamorphic core complexes. 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. We use field observations and magnetic fabrics in the Naxos dome (Greece) to quantify the complex flow of anatectic crust beneath an extensional detachment system. The internal structure of the Naxos dome is characterized by second‐order domes (subdomes), pinched synforms, and curved lineation trajectories, which suggest that buoyancy‐driven flow participated in dome evolution. Subdomes broadly occur within two 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 models of isostasy‐dominated flow. The preferred model involves a combination of buoyancy‐ and isostasy‐driven processes: 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 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. Dome formation therefore occurred by a combination of coeval and coupled processes: 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.

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This paper presents new structural data on the Naxos migmatite dome, exhumed in the central part of the Aegean Sea in Greece. The dome is cored by anatectic granites and migmatites that have preserved magmatic textures, and it is mantled by a dominantly metasedimentary sequence grading outward from amphibolite to greenschist facies. The elliptical shape of the dome is outlined by a composite transposition foliation in the mantling metasedimentary sequence. The lineation trends NNE-SSW and is associated with top-to-the-NNE shearing. Within the fi rst order dome, kilometer-scale second order domes are evidenced by the orientation of the magmatic fabric, of the syn-migmatitic foliation trends, and by a concentration of enclaves along their margins. A network of granitic veins, structurally rooted in the migmatites, intrudes the mantling metasedimentary sequence. Subvertical granitic dikes, discordant to the foliation, are dominantly oriented parallel or perpendicular to the lineation. These dikes have preserved a magmatic texture and cross-cut partially to totally transposed veins. Kinematic analysis indicates that transposition is consistent with top-to-the-NNE shearing combined with outward rotation of the veins in the mantling metasedimentary sequence during upward migration of the migmatites in the core of the dome. Accordingly, the Naxos migmatite dome is interpreted as a diapir formed in response to a gravitational instability developed in the buoyant, partially molten rocks in a context of regional NNE-SSW extension during gravitational collapse of the Ae gean orogenic wedge.

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