April 7 @ 12:00 pm - 12:50 pm CDT
Who: Gary Linkevich & Proteek Chowdhury
When: Noon, Friday, April 7, 2017
Where: Room 100, KWGL
Linkevich “3D Seismic Observations of the Peridotite Ridge in the Deep Galicia Margin”
The west coast of the Iberian Peninsula is a classic magma-poor rifted margin, where slow crustal hyperextension allowed the mantle rising beneath to cool and harden, instead of melting. The boundary between the last crustal blocks and this transitional zone of exhumed mantle is marked by a long, margin-parallel peridotite ridge (PR). Over the past few decades, this PR was dredged, cored, and imaged in several 2D seismic surveys. These efforts documented its regional extent and thorough serpentinization, but offered limited insight into its internal structure. And while several hypotheses have evolved regarding the PR’s origin, there is no consensus, and almost no discussion of its post-emplacement evolution. Finally, there are major uncertainties not just within the PR, but in the jumbled-up material surrounding it.
The recently-acquired Galicia3D seismic dataset reveals several internal structures within the PR, including a large landward-dipping normal fault cleaving off its eastern flank, and a continuous internal boundary separating a reflective, chaotic upper layer from a more homogeneous core. The eastern fault dives to at least 10 s TWT, and is hypothesized to restore in some way to the S detachment fault in the east. It also appears to continue into the post-rift sediments overlying the PR, offsetting material up to 100 myr younger than the PR itself. The reflective upper layer of the PR may represent the extent of its serpentinization, but could also include a variety of prerift or synrift material.
On the surface of the PR, the western flank contains several arcuate, scoop-like scarps that correspond to substantial mass wasting events. A similar feature on the eastern flank has been mapped in 3D, and display deformational structures usually observed in mass transport deposits on land. However the PR achieved its distinctive shape, the processes involved have broad implications on the timing and evolution of the margin as a whole.
Chowdhury: “Effect of sulfate on the liquidus and Sulfur Concentration at Anhydrite Saturation (SCAS) of hydrous basalt at Subduction Zones”
“Sulfur as sulfide and sulfate plays an important role in various processes at subduction zones including element partitioning, redox evolution of magma, degassing of magma and volcanic eruptions. Experiments were designed and carried out to investigate the effect of sulfate on the liquidus of a hydrous basalt. Both sulfate undersaturated and saturated conditions were used to understand the effect of small amounts of sulfate at 2 GPa. The S content varied from around 0.2-2 wt % determined by electron microprobe. Along with this to understand the solubility of sulfate in a hydrous basaltic melt SCAS experiments were carried out on the hydrous arc basalt at 1-3 GPa and 1250-1325 ᵒC. A new parameterization is developed based on our experiments and from previous experiments. Our parameterization was then used to calculate the saturation value at various arcs and those values are then used to compare with sulfur contents from the arcs throughout the world to see whether arcs reach sulfate saturation or not. Furthermore, the maximum global SO2 flux is calculated to compare with the modern global SO2 flux using data from our experiments.”