EAPSI: Quantifying Tectonic Controls on Changing Segmentation of Oceanic Transform Faults

Morrow Thomas A, Brighton MA

Investigators

Abstract

Oceanic transform faults (TFs) are tectonic plate boundaries that are fundamental to accommodating tectonic plate motions along mid-ocean ridges (MORs). Although classically defined as a single boundary offsetting two segments of a MOR, TFs can split into several fault strands and subsequently re-unify to a single trace. Formation of segmented TFs is likely due to extensional tectonic motions across the TF. Conversely, unification of segmented TFs may be associated with compressional tectonic motions, however, the processes governing this evolution are poorly known. Structural features on the ocean floor, such as fracture zones (FZs), faults, and topography produced by lithospheric deformation, record tectonic responses to plate motions oblique to the original TF. In collaboration with Dr. Seung-Sep Kim of Chungnam National University, an expert in marine geology, flexure, and tectonics, the PI will quantify the processes that govern unification of the previously segmented Clarion FZ in the central Pacific Ocean. Segmentation and unification of TFs can alter the location of plate boundaries over time. Quantifying segmentation processes will enhance our understanding of evolving plate boundaries as well as their magmatic and seismic expressions. The research has 3 primary goals: 1) Using recently acquired high-resolution bathymetry over the Clarion FZ provided by the host researcher, Dr. Kim, we will identify styles and distributions of deformation; 2) We will analyze flexural evolution of a segmented FZ using 2D numerical models; 3) We will assess the tectonic conditions of the Clarion FZ through time by comparing model-predicted gravity anomalies (a proxy for flexural evolution of a FZ) to shipboard measurements. To quantify the hypothesized effect of compression on TF unification, our models will compare various rates and magnitudes of compressional strain, age offsets across the FZ, as well as the number, age, and geometry of intra-transform spreading segments to predicted flexural profiles. Finally, using these results we plan to develop predictive scaling laws that relate tectonic compression to the location and timing of TF unification. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the National Research Foundation of Korea.