Geochemistry, Geophysics, Geosystems

Structural and petrophysical characterization of the upper basement crustal section at ODP/IODP Site 1256 (East Pacific Ocean)



[1] New ocean crust is constantly being formed from mid-ocean ridge axis. Voluminous flows of lava are emplaced also away from the ridge axis, adding off-axis crustal layers to the crustal pile. Research on deep sea is of great importance to better understand the mechanisms and the nature of the crust forming and evolution. In this work, we decipher the first stages of the postmagmatic evolution of an intact volcanic section from the upper oceanic crust at ocean drilling program/integrated ocean drilling program (ODP/IODP) Site 1256 (Eastern Pacific Ocean). Using for the first time an innovative core-log integration technique to match direct (core-related) and indirect (borehole-related) data by depth shifting and reorienting individual core pieces recovered by drilling, we are able to identify the clusterization of structures and physical properties within distinct downdeep “strong” and “weak” lava zones, reflecting the cooling and tectonic evolution of lavas rather than lithological variations. We define the evolution of the structural zones that typically affect lava flows: colonnades and entablature zones, studying an off-axis lava flow encountered in present-day upper ocean crust. For the same off-axis flow, we are also able to suggest the lava flow direction (NW-SE) and its relationships with the paleoridge axis. Despite the environmental difficulties in the study of the subseafloor under deep water and using only one-dimensional data deriving from ocean drilling, this work shows how an array of diverse data can be integrated into a coherent interpretation of lava flow history obtaining detailed information on the mechanism of submarine lava emplacement and flow.