HR: 0800h
AN: GP41B-0871    [Abstracts]
TI: Broadband Marine Magnetotelluric Exploration of the East Pacific Rise at 9 N
AU: * Myer, D G
EM: dmyer@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, MC 0225, La Jolla, CA 92093-0225
AU: Key, K
EM: kkey@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, MC 0225, La Jolla, CA 92093-0225
AU: Constable, S
EM: sconstable@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Drive, MC 0225, La Jolla, CA 92093-0225
AB: In February 2004, we conducted the world's largest academic broadband marine magnetotelluric (MT) experiment at the RIDGE2000 integrated study site (ISS) on the East Pacific Rise (EPR). Forty broadband EM receivers were deployed a total of 72 times to yield 69 sites of data. Twenty instruments were deployed in a small aperture (30 km) transect of densely spaced MT sites across the ridge at the ISS ``bull's eye'' focus area at 9°50' N. Further south, 40 sites were collected along a 200 km aperture transect at 9°30'} N. This larger aperture transect was positioned to avoid 3D structure associated with the Lamont seamounts and the Clipperton transform. The site density in the middle 30 km of the longer transect matches the density of the smaller transect, providing two separate data sets for shallow imaging. Twelve additional MT sites were collected in a grid along the ridge axis just north of the longer transect. Robust multi-station MT processing has provided good quality MT impedance responses for most of the data. Eigenvalue analysis of the robustly estimated spectral density matrix for arrays of 3 to 4 MT sites show high signal-to-noise ratios for periods between about 20 s to 5000 s. Based on our earlier pilot MT experiment of 4 sites (Key and Constable, 2000), this bandwidth of data is sensitive to structures from the near surface to about 300 km depth. We will present pseudo-sections of both MT transects as well as 2D conductivity models computed using a new adaptive finite-element modeling technique. Key issues of the ridge magmatic and hydrothemal systems to be addressed by this experiment are: 1. The distribution, vertical extent and volume fraction of melt present in the mid to lower crust. 2. The extent that hydrothermal circulation plays a role in heat removal from the crust as well as the linkages between hydrothermal activity and crustal magma. 3. The extent of melt accumulation at the base of the crust. Does a relatively thin layer of concentrated melt pond at the base of the crust, or does melt accumulate from a broader region of the mantle? 4. What, if any, connection exists between the crustal melt accumulations and the region of decompression melting deeper in the mantle?
DE: 0600 ELECTROMAGNETICS
DE: 0925 Magnetic and electrical methods (5109)
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 3006 Marine electromagnetics
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005