Study Tour
The field study tour for this seminar series is to Costa Rica, which is one of the MARGINS Subduction Factory focus sites. The list of potential speakers is weighted toward scientists that are working in Costa Rica, so that the field trip and the seminar series are tightly integrated.
Student Projects
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Geodynamics supervisors and potential projects
1) Laura Robinson (lrobinson@whoi.edu)Lithology and climate controls on uranium isotopes in river waters of central and southern Chile.
This project will produce uranium isotopic measurements on river and lake samples using clean-lab chemistry and mass spectrometry. The sample set covers Chilean rivers that are sourced in, and flow through diverse climate and lithologic regimes, including high to low rainfall zones, glaciated and lacustrine terrain and a range of rock types. The results will be used to determine the major controls on U-series isotopes in Chile, and to interpret isotopic records in cold water corals that live in the nearby fjords.
Robinson, L. F., Henderson, G. M., Hall, L., and Matthews, I., 2004. Climatic control of riverine and Seawater uranium-isotope ratios. Science 305, 851-854.
2) Pablo Canales (jpcanales@whoi.edu)
I have three multichannel seismic profiles across the Juan de Fuca Plate towards the Cascadia subduction zone. The profiles do not reach the trench, but preliminary imaging shows faulting of the sediments related to bending of the incoming plate. The topic is
pretty much similar to what Cesar talked about last week. The project would consist on processing the seismic data to image faulting in the sediments and crust, and then quantify how far from the trench does bending-related faulting initiate, quantify the
number of faults and test if they increase in number towards the trench, and relate faults in the sediments with basement topography to test if bending-related faulting is focused on pre-existing abyssal hill fabric.
The student would get training in basic seismic reflection processing and interpretation/quantification of seismic images.
3) Brian Tucholke (btucholke@whoi.edu)
Morphology and sedimentary processes in Hydrographer submarine canyon, New England continental slope (multibeam bathymetry and backscatter-amplitude data).
4) Adam Soule (ssoule@whoi.edu)
Vesicle size distribution in Deccan Flood Basalt lava flows (65.5 Ma): mechanisms of flow emplacement
Patterns in the size, number density, and deformation state of vesicles can provide insight into the mechanisms of lava flow emplacement. The aim of this project is to evaluate the vesicle size distribution in a suite of samples from the Deccan Flood Basalts, and through comparison to modern lava flows, evaluate whether flow inflation is a valid mechanism for their emplacement as has been suggested for other well-studied flood basalt provinces (e.g., Columbia River Flood Basalts). Stratigraphic logs of an ~250 m thick section of flood basalts have been constructed and sampled at 10-50 cm resolution. Thin sections of fresh to highly altered basalts are available for vesicularity analysis by microscopy (standard petrographic and scanning electron microscope) and image analysis.
5) Hans Shouten (hschouten@whoi.edu) and Debbie Smith
FLEXURAL ROTATION OF NORMAL FAULTS AN THE FORMATION OF SEA FLOOR TOPOGRAPHY
Goal: to test the hypothesis that most outward-facing slopes in slow- spreading environments like the mid-Atlantic Ridge (MAR) are due to flexural rotation of normal faults rather than to outward-facing faults cutting volcanic topography. Oceanic core complexes, which expose deep-seated rocks, are found along the MAR and other slow-spreading mid-ocean ridges and demonstrate how flexural rotation of normal faults can be playing an important role in the formation of the morphology of the sea
floor. Steep inward-facing normal faults originating at the edge of the rift valley floor rapidly rotate outward upon extension, the top of the fault reaching maximum rotations of 30-40 degrees after only 5 km horizontal extension, resulting in symmetrical narrow linear ridges with roughly 30 degree inward- and outward facing slopes. Upon further extension, the newly exhumed deeper part of the fault develops into a characteristic subhorizontal surface, or, low- angle detachment surface, that caps a dome and is often striated parallel to the exhumation direction.
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In a recent paper entitled "Fault rotation and core complex formation: Significant processes in seafloor formation at slow- spreading mid-ocean ridges (Mid-Atlantic Ridge, 13ºN)" (G-cubed, in press) Debbie Smith et al. estimated fault rotation vs distance from the axis in three MAR spreading segments south of the Fifteen Twenty FZ, which indicated that the lithosphere in the rift valley has an elastic plate thickness of Te = 0.5-1 km.
This Geodynamics project will consist of documenting and compiling additional fault rotations (by measuring outward facing slopes of sea floor using Fledermaus) in available multi beam bathymetry of the MAR rift valley between 25ºN and 15ºN and use the slope of the rotation vs distance plot to estimate elastic thickness and use this thickness to constrain models of flexural fault rotation.
The documentation of large fault rotations near the spreading axis will make a strong case for the flexural rotation of all normal faults in the slow-spreading MAR, no matter what the extension or the magmatic budget of the ridge segment, and might explain most of
the topography observed on the flanks of the ridge. It will make an important argument for a cruise proposal to observe the rotations in situ, because, at the present time there are still very few of such in-situ observations.
6) Alison Shaw (ashaw@whoi.edu)
Degassing trends in magmas from the Large Fissure Tolbachik Eruption (Kamchatka, Russia)
This project would focus on looking at the changes in lavas chemistry during the course of the eruption of Tolbachik volcano. The student would be involved in all aspect of the project, preparing rock samples, separating minerals, mounting grains, analyzing volatiles and major elements on the melt inclusions.
7) Rob Reves-Sohn (rsohn@whoi.edu) and Jeff McGuire (jmcguire@whoi.edu)
Rate-State Parameterization of Stable Seismic Slip on an Active Oceanic Detachment Fault.
Stable seismic slip is an intriguing characteristic of earthquakes in a variety of geologic settings, including subduction zones, transforms, and, as it has recently been shown, detachment faults on mid-ocean ridges. The Rate-State model of seismicity provides a means to quantify stable sliding in a statistically rigorous fashion, and also provides insight into the physical processes that govern seismogenesis. In this project a student would fit rate-state parameters to the seismicity catalog generated for the active oceanic detachment fault at the TAG segment of the Mid-Atlantic Ridge (26N). The parameter estimates would then be compared to those from other stable sliding environments, Including subduction zones, to try and gain insight into the factors that produce this unique seismic behavior.