THREE-DIMENSIONAL MANTLE MELT GENERATION, MIGRATION AND EXTRACTION AT THE QUEBRADA-DISCOVERY-GOFAR FRACTURE ZONES ON THE SOUTHERN EAST PACIFIC RISE

Transform fault systems are fundamental to accommodating the geometry and crustal accretion processes along the global mid-ocean ridge system. The presence of large transform fault offsets influences mantle melting and impacts how melts focus as they migrate through the mantle back to narrow mid-ocean ridge spreading centers. We focus our investigation of three-dimensional mantle melting processes at the Quebrada/Discovery/GoFar (QDG) fracture zone system located between 3°S and 5°S along the Southern East Pacific Rise. QDG is a fast slipping left-lateral, transform fault system, with a slip rate of 140 mm/yr, characterized by 9 strike-slip transform fault segments and 8 intra-transform spreading centers (ITSCs). Using the observed ridge segmentation, the three-dimensional mantle flow and thermal structure are modeled using a three-dimensional temperature-dependent finite element model, with a viscoplastic approximation for the brittle deformation of the lithosphere. Melt generation is calculated using the near-fractional, polybaric melting model of Kinzler and Grove (1992). Melt migration and extraction is assumed to occur as a three-step process: 1) melting begins where the mantle reaches its pressure-dependent solidus temperature, 2) the melts ascend vertically through the mantle and are transported along an inclined low permeability barrier toward the ridge axis, 3) melts are extracted in a pre-defined extraction zone. Models are constrained using gravity derived crustal thickness variations as well as major element melt composition of lavas erupted along the QDG transform faults and at their ITSCs to investigate regional variations in mantle source and melting processes such as how melts focus in the mantle.