Earth and Planetary Sciences Events

Events Calendar

Unless noted, all listed events are open to the general public.

Wednesday Seminar in Geology: GEL 190/290
Seminars are scheduled for Wednesday afternoon at 4:00 PM. Additional optional seminars that may be included as part of the Geology 190 series may be scheduled at other times.

Friday Lunch Talk"A Geology tradition since the Phanerozoic!"
Fridays at noon. Students and faculty give informal lectures on research, travel, or other interests.

submit an event to the department calendar (restricted access)

Thursday, March 23rd, 2023, Special Seminar

1:00 PM, 1348 Earth and Physical Sciences
Masters exit talk

“Insights into the nature of deep mantle material from noble gas analyses of basalts from the Easter and Salas y Gomez Seamount Chain”

      – by Nathalie Niepagen, Zoom link:

The Easter and Salas y Gomez seamount chain (ESC) consists of two sub-parallel chains on the southwest corner of the Nazca plate and were formed by the deep mantle Salas y Gomez (SyG) plume. The SyG plume has been previously characterized as a compositionally striped plume after geochemical data revealed an isotopically enriched northern chain and an isotopically depleted southern chain. The enriched chain is hypothesized to originate from the Pacific large low shear velocity province (LLSVP) while the depleted material is hypothesized to be entrained ambient deep Pacific mantle and shallow asthenospheric mantle. To test this hypothesis, we measured He and Ne isotopes on samples with existing Sr, Nd and Pb isotopic ratios.

Our noble gas data from the ESC samples show good co-variations with Sr, Nd and Pb isotopic composition and reveal the presence of primitive material in both the northern and southern chain but the southern chain appears to have a greater proportion of the primitive material. Our observations rule out shallow asthenospheric mantle as the reason for the depleted compositions observed in the southern chain and further suggests that the material erupted in the southern chain might be derived from the LLSVPs rather than the deep ambient Pacific mantle. We also find that the juvenile water content of the more primitive component is ~180 ppm, which is much drier compared to previous suggestions of ~750 ppm. Our results show that higher water content of 750 ppm is due to recycled water. The combined deuterium (dD) and He isotopic relationship suggests that the juvenile water in the deep mantle is likely derived from a chondritic source, contrary to the suggestions of a nebular source inferred from a study in basalts from Baffin Island.

Friday, March 24th, 2023, CIG Fault Mechanics Webinar

1:00 PM, zoom

“Hydrothermal friction experiments on simulated basaltic fault gouge and implications for megathrust earthquakes”

      – by Hanaya Okuda, University of Tokyo

Nucleation of earthquake slip at the plate boundary fault (décollement) in subduction zones has been widely linked to the frictional properties of subducting sedimentary facies. However, recent seismological and geological observations suggest that the décollement develops in the subducting oceanic crust in the depth range of the seismogenic zone, at least in some cases. To understand the frictional properties of oceanic crustal material and their influence on seismogenesis, we performed hydrothermal friction experiments on simulated fault gouges of altered basalt, at temperatures of 100–550°C. The friction coefficient (μ) lies around 0.6 at most temperature conditions but a low μ down to 0.3 was observed at the highest temperature and lowest velocity condition. The velocity dependence of μ, (a−b), changes with increasing temperature from positive to negative at ∼100°C and from negative to positive at ∼450°C. Compared to gouges derived from sedimentary facies, the altered basalt gouge showed potentially unstable velocity weakening over a wider temperature range. Microstructural observations and microphysical interpretation infer that competition between dilatant granular flow and viscous compaction through pressure-solution creep of albite contributed to the observed transition in (a−b). Alteration of oceanic crust during subduction produces fine grains of albite and chlorite through interactions with interstitial water, leading to reduction in its frictional strength and an increase in its seismogenic potential. Therefore, shear deformation possibly localizes within the altered oceanic crust leading to a larger potential for the nucleation of a megathrust earthquake in the depth range of the seismogenic zone.