The dynamics of oceanic transform faults : constraints from geophysical, geochemical, and geodynamical modeling

Abstract

Abstract : Segmentation and crustal accretion at oceanic transform fault systems are investigated through a combination of geophysical data analysis and geodynamical and geochemical modeling. In Chapter 1, results of thermal modeling suggest that fault segmentation by intra-transform spreading centers (ITSC) drastically reduces the available brittle area of a transform fault and thus limits the available earthquake rupture area. Coulomb stress models illustrate that long ITSCs will prohibit static stress interaction between segments of a transform system and further limit the maximum possible magnitude of a given transform fault earthquake. In Chapter 2, residual mantle Bouguer gravity anomalies are investigated from a global set of oceanic transform fault systems. Negative anomalies are found within fast-slipping transform fault domains suggesting a mass deficit in these sellings, which may be due to crustal thickness excesses in these locations. Finally, in Chapter 3, mantle thermal models for a viscoplastic rheology are developed to investigate the process of mantle melting and crustal accretion at ITSCs within segmented transform faults, and applied to the Siqueiros transform fault. Models in which melt migrates into the transform fault domain from a large region of the mantle best explain the gravity-derived crustal thickness variations observed at the Siqueiros transform.