October 13 @ 12:00 pm - 1:00 pm CDT
Departmental Research in Earth, Environmental and Planetary Sciences
Graduate Interdisciplinary Earth Science Symposia (GIESS)
“Plate Tectonics” by Nur Schuba and Chengzu Wang
Lunch begins at 11:30 am
3-D structure and morphology of the S-reflector detachment fault, offshore Galicia, Spain
The crustal architecture of continental margins provides valuable clues for understanding rift initiation and evolution. The Galicia margin is an archetypal magma-poor margin displaying exhumed serpentinized mantle, and is an optimal setting in which to examine rift-related processes. The S-reflector detachment fault, one of the most prominent structural features associated with the Galicia margin, is imaged as a continuous interface for over an area of 600 km2 with a new 3-D seismic survey. The high impedance contrast of the reflection of this fault interface enables seismic attribute and morphologic analyses of this fault. The seismic reflection amplitudes and residual time structure map show coherent lineations with an average azimuth of 107o. These features are interpreted as fault kinematic indicators such as slickensides, grooves, and corrugations observed in other fault zones. The striations are shown to be perpendicular to the known paleo extension orientation and appear to be evidence for low-angle (<20o) fault slip. Another reflection above the S-reflector is identified as the upper boundary of the fault gouge associated with the S-reflector, here labelled as the S-interval. This gouge layer has variable thickness averaging 57 m and a hyperextensional displacement which, though larger than those studied before, follows previously determined predictive fault zone thickness to displacement relationships for deformation zones.
Bounds on geologically current rates of motion of groups of hotspots
It is widely believed that groups of hotspots in different regions of the world are in relative motion at rates of 10 to 30 mm a–1 or more. Here we present a new method for analyzing geologically current motion between groups of hotspots beneath different plates. In an inversion of 56 globally distributed, equally weighted trends of hotspot tracks, the dispersion is dominated by differences in trend between different plates rather than differences within plates. Nonetheless the rate of hotspot motion perpendicular to the direction of absolute plate motion, vperp, differs significantly from zero for only three of ten plates and then by merely 0.3 to 1.4 mm a–1. The global mean upper bound on |vperp| is 3.2 ±2.7 mm a–1. Therefore, groups of hotspots move slowly and can be used to define a global reference frame for plate motions. Further implications for uncertainties in hotspot trends and current plate motion relative to hotspots will be discussed.