Lau Basin Mantle Dynamics Using Geodynamic Modeling in Conjunction with Seismic Observations

J.A. Conder

Corresponding author: conder@geo.siu.edu
Southern Illinois University, Department of Geology, Carbondale, MO, 62901

Abstract:
My R2K related research focuses on mantle and crustal dynamics using geodynamic modeling and seismic observations. In particular, the Lau basin has been a focus of my research and looking at how arc proximity affects melting, melt structure, and other active processes at mid-ocean ridges. Data collection is still in process for the Lau 3D passive tomography experiment with deployment of the OBSs to occur in the next few months (Doug Wiens, project, PI). The aim of this work is to integrate seismic observations with models of mantle flow and melt production to explore dynamics of arc affected spreading centers. The active portion of this experiment occurred ealier this year aboard the R/V Langseth. Continuing analysis of the data will provide constraints on crustal production and structure along the Eastern Lau Spreading Center and will inform the forthcoming tomography experiment. Donna Blackman and others, including myself will explore implications of the seismic results, both tomographic and anisotropic, through numerical modeing patterned after the dynamics of the Lau basin.

Recent modeling of mantle flow at mid-ocean ridges demonstrates that the asthenosphere may flow more rapidly than plate tectonic rates. While the asthenosphere is likely moving across-axis at the southern EPR (Conder, 2007, GRL). the asthenosphere is likely flowing closer to axis-parallel in the Lau basin (Conder & Wiens, 2007). If this hypothesis is correct in the Lau, with the forthcoming OBS deployment, we may expect to see variations in the anisotropy structure - possibly both in fast axis azimuth and splitting magnitude - along the ELSC relative to the prior anisotropy work across the Central Lau Spreading Center (Smith et al., 2001) resulting from decreasing spreading rate and changes in wedge geometry.

Other ongoing work entails a currently deployed hydrophone array in the Lau Basin (Del Bohnenstiehl, project PI). One of our aims is to use T-waves to extend our understanding of microseismic patterns in the southern Lau Basin. Work from an earlier 2D OBS experiment near the Central Lau spreading center details microseismicity in the northern Lau basin (Conder and Wiens, in prep.). Although the microseimic activity in the northern Lau seems dominated by tectonic activity, it is possible that extending the aperture further south will capture possible hydrothermal activity, in addition to uncovering tectonic events defining lithospheric rupture.

Contributions to Integration and Synthesis:
Most of the work outlined above aims to further our understanding of the underlying mantle dynamics governing ridge behavior, anchoring the holistic vision of ridge dynamics to the mantle as the primary source of energy, chemistry, and material for ocean floor construction. In addition to contributing to our understanding of ridge behavior from a mantle and source perspective, this work will help provide the context for other aspects of geophysical investigations of ridge processes. For example, detailing patterns and process of how the spreading center is fed melt can inform experiments and data synthesis of hydrothermal work. Likewise, examination of microseismicity patterns in space and time will both further out tectonic understanding of lithospheric deformation and potentially illuminate hydrothermal venting processes, which in turn could potentially inform models of crustal structure and deformation to be considered in seismic interpretation and geodynamic modeling.