New Mexico Geological Society Annual Spring Meeting — Abstracts

The NSF MARGINS Program has four initiatives focused on continental margins: Source to Sink (sedimentary processes), SEIZE (subduction zone seismicity), SubFac (arc magmatism) and RCL (rifting). Each has two focus sites, in which various, complementary new data sets will synergistically advance the science. RCL targets the complete rifting process (initial extension to sea floor spreading), with focus sites in the Gulf of California and Red Sea (presently "on hold"). The MARGINS Program is in its seventh year of ten with a ten-year renewal anticipated.

The Gulf of California is a strongly oblique, active-margin rift, significantly different from "typical" mid-continent orthogonal rifts. Our study combines geology and marine seismology. Offshore-onshore wide-angle reflection transects used ocean-bottom seismometers about every 10 km and PASCAL RefTec seismometers similarly spaced onshore for ~100 km. Vertical-incidence reflection data were collected on transects and in transit between transects. We aimed to characterize the overall crustal rift architecture, offshore sedimentary sequences, and use onshore geology to constrain upper crustal strain, timing, and correlative sedimentary sequences. Three main transform-parallel transects connect originally conjugate margins. One "composite" transect crosses the peninsula, is offset about 300 km to the SE, and continues onto mainland Mexico. Moho was well imaged to ~30 km inland of the coasts and locally has significant relief. Both wide-rift and narrow-rift styles occur in different spreading segments, but without a progressive north-to-south change. Preliminary total extension estimates (continental plus sea floor spreading) are ~450 km. Significant Moho topography exists in places, and continent-ocean transitions are abrupt.