Lithological heterogeneity controls high-temperature ductile deformation and late melt infiltration in moderately-magmatic OCCs

Oceanic core complexes (OCCs) are a fundamental component of slow-to-ultraslow spreading mid-ocean ridges, yet the processes that control OCC formation and evolution are poorly understood especially with respect to their high-temperature lithospheric roots. We present detailed analyses of high-temperature ductile deformation preserved in drill-core from IODP Hole U1601C, on the Atlantis Massif OCC (30°N, MAR). We show that gabbroic intrusions within peridotite accommodated significant high-temperature deformation, especially within Fe-Ti oxide-bearing assemblages. This deformation spatially localizes in zones of high lithological heterogeneity created by meter-to-submeter-scale gabbroic intrusions within peridotite. High-temperature ductile deformation often localizes close to, and/or along, intrusive contacts, accompanied by localized, evolved, melt-reactive porous flow (crystallizing Fe-Ti oxides), and followed by fluid-rock reaction that enhanced and sustained further ductile deformation. These spatially controlling relationships between magmatism, deformation, and late melt ± fluid infiltration are a direct consequence of the lithological heterogeneity within moderately-magmatic OCCs, which are the dominant style of OCC along the Mid-Atlantic Ridge and other slow-spreading ridges.