Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q04003, doi:10.1029/2005GC001038.
Description:
The geology and structure of the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR) have been
examined using high-resolution mapping systems, observations by remotely operated vehicle (ROV),
ROV-mounted magnetometer, and the geochemical analysis of recovered lavas. Bathymetric mapping
using multibeam (EM300) coupled with in situ observations that focused on near-axis and flank regions
provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the JdFR. A total
of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that
included sixteen ROV dives. Our observations of the seafloor during these dives suggest that many of the
unfaulted and extensive lava flows that comprise and/or cap the prominent ridges that flank the axial valley
emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the
walls of the axial valley. The geochemically evolved and heterogeneous nature of these near-axis and flank
eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush
zone. In contrast, the most recent axial eruptions are more primitive (higher MgO), chemically
homogeneous lobate, sheet, and massive flows that generate a distinct magnetic high over the axial valley.
We suggest that the syntectonic capping volcanics observed off-axis were erupted from near-axis and flank
fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data. This model
suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the Cleft
Segment were erupted during the collapse of a magmatic cycle not during the robust phase that established
a new magmatic cycle.
Description:
This research has been partially supported by a NSF grant
to M. Perfit (OCE-0221541). M. Tivey acknowledges support
from WHOI’s Mellon grant for Independent Study. Support for D. Stakes, T. Ramirez, D. Caress, and
N. Maher and for the entire field program was provided by funds
to MBARI from the Lucille and David Packard Foundation.
Keywords:
Basalt
;
Ridge
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
27662490 bytes
Format:
application/pdf
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