Submarine lava flow direction revealed by neutron diffraction analysis in mineral lattice orientation

The ocean crust is formed by the rising of magma from mid-ocean ridges and voluminous (1-30 km3) flows of lava away from ridge axes. However, our understanding of the emplacement kinematics of submarine lava is often limited to plan view geometries of near-axis lava. Drilled cores provide in situ access to the intact internal structure of submarine lavas. We used neutron diffraction to study off-axis lava flows drilled into the uppermost crust of ODP/IODP-Site 1256 (Cocos Plate). We provide quantitative insights into submarine lava microstructures and strong evidence for a secondary lava injection into the interior of a solidifying flow of lava along the NW-SE direction parallel to the paleo-ridge axis of the East Pacific Rise. The dynamics of lava inflow are controlled by crystal abundance and the temperature of the lava-crystal mixture rather than by local seafloor topography. We provide a description of an in situ shear within submarine lavas revealed by composite shape and lattice preferred orientations, accounting for a dominant laminar nonuniform-type flow. Key Points Method to define the direction of subaqueous lava flow First LPO and SPO analysis conducted on subaqueous basalt Evidence for inflated lava flows at ODP Site 1256 Laminar flow and evidence of vertical shear supporting inflation of the lava flow by a second episode.