Inferences about the geometry and distribution of magma supply to oceanic crust at slow and intermediate spreading rates from AMS studies in the Troodos Ophiolite, Cyprus.

HR: 1340h
AN: T13B-1365 [Abstracts]
TI: Inferences about the geometry and distribution of magma supply to oceanic crust at slow and intermediate spreading rates from AMS studies in the Troodos Ophiolite, Cyprus.
AU: * Morton, V
EM: vmorton@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UC San Diego, SIO/IGPP 225 UC San Diego, La Jolla, CA 92093 United States
AU: Fialko, Y
EM: fialko@radar.ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UC San Diego, SIO/IGPP 225 UC San Diego, La Jolla, CA 92093 United States
AU: Staudigel, H
EM: hstaudig@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UC San Diego, SIO/IGPP 225 UC San Diego, La Jolla, CA 92093 United States
AB: We investigate magma flow directions in the sheeted dike complex of the Troodos Ophiolite, Cyprus, using anisotropy of magnetic susceptibility (AMS) data. Suites of oriented cores collected from the dike chilled margins were analyzed to determine the AMS orientations, and infer the magma flow directions. With newly collected data from the Kionia Peak area, our dataset includes 115 dikes sampled over an area of about 8 km along the ridge axis, and 2 km across the ridge axis. The inferred magma flow vectors are corrected for tectonic rotation and tilting, and present day elevation variations serve as estimators of individual site depths in the pseudostratigraphy along the paleo ridge axis. Analysis of flow directions as a function of depth indicates more vertical flow directions in the shallow section of the sheeted dike complex. Also, the horizontal component of magma velocity is found to correlate with the along-axis distance from the presumed segment center. The flow vectors rotate from more vertical directions by about 30 degrees toward horizontal over a distance of 8 km from the presumed magma source toward the bounding transform fault. Chemical analysis shows horizontal flow directions in the shallow section also correlate with low Ti magma chemistry. We use the observed magma flow orientations in the sheeted dike complex to constrain the along-axis distribution of magma supply from the mantle source to the crust. The two end-member models are: a predominantly vertical magma supply to the crust from the underlying mantle, and a highly focused supply to the center of the segment with subsequent lateral redistribution via blade-like dike injections in the shallow magma plumbing system. We show that the flow directions inferred from AMS are not a direct proxy for the mode of magma supply to the crust, as some vertical flow directions may be imprinted at the leading edge of a horizontally propagating dike, while horizontal flow directions may result from magma flowing along the level of neutral buoyancy in dikes that travel vertically from an underlying mantle source. A fraction of up to 1/3 of magma flow directions toward the presumed segment center indicate that not all dikes are emplaced laterally, and at least some melt is generated in the mantle underlying the segment ends.
DE: 8145 Physics of magma and magma bodies
DE: 3035 Midocean ridge processes
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting