Gravity structure of segmented oceanic transform faults

Posted on 08.25.2015
Conceptual diagram to illustrate the processes, which may contribute to the gravity anomalies observed at intermediate and fast-slipping transform faults. Some processes include: intra-transform volcanism, propagation of dikes from nearby ridge axis, hydrothermal alteration, and variations in porosity.

Analysis of gravity from transform faults across the globe indicates that there may be a spreading rate dependence on the crustal structure of transform faults. Using a combination of three-dimensional mantle flow and thermal models and satellite gravity analyses, we found that as spreading rate increases to intermediate spreading rates, transform faults appear to have thickened crust. As this was a very strange finding, I also ran a variety of 2D forward gravity models to try to figure out what processes were impacting the gravity signal we observed. We explored a variety of possibilities including porosity variations, serpentinization, variations in thermal expansion, variations in thermal structure, etc, and found that the easiest way to produce the anomalies we observed is by overall thickening of the crust. 

This, of course, is a very contentious result and will require additional investigations and observations to help us track down the mechanics of what is occurring. If the crust within intermediate and fast slipping transform faults is indeed thicker than the nearby ridge axis, this as implications for how crustal accretion is occurring at these systems and requires a paradigm shift in our thinking. Furthermore, it has implications for fault dynamics and how melt migrates both within the mantle and in the crust.

COLLABORATORS: Jian Lin (WHOI), Mark Behn (WHOI), Laurent Montesi (Univ. of Maryland)

FUNDING: This work was funded by a National Science Foundation Graduate Research Fellowship (Gregg).