Geophysical signatures of past and present hydration within a young oceanic core complex

TitleGeophysical signatures of past and present hydration within a young oceanic core complex
Publication TypeJournal Article
Year of Publication2014
AuthorsBlackman D.K, Slagle A., Guerin G., Harding A.
JournalGeophysical Research Letters
Volume41
Pagination1179-1186
Date Published2014/02
Type of ArticleArticle
ISBN Number0094-8276
Accession NumberWOS:000333022700015
Keywords30-degrees-n; accretion; atlantis massif; borehole geophysics; crust; field; hydrothermal circulation; IODP; massif; mid-atlantic ridge; oceanic core complex; zone
Abstract

Borehole logging at the Atlantis Massif oceanic core complex provides new information on the relationship between the physical properties and the lithospheric hydration of a slow-spread intrusive crustal section. Integrated Ocean Drilling Program Hole U1309D penetrates 1.4km into the footwall to an exposed detachment fault on the 1.2Ma flank of the mid-Atlantic Ridge, 30 degrees N. Downhole variations in seismic velocity and resistivity show a strong correspondence to the degree of alteration, a recorder of past seawater circulation. Average velocity and resistivity are lower, and alteration is more pervasive above a fault around 750m. Deeper, these properties have higher values except in heavily altered ultramafic zones that are several tens of meters thick. Present circulation inferred from temperature mimics this pattern: advective cooling persists above 750m, but below, conductive cooling dominates except for small excursions within the ultramafic zones. These alteration-related physical property signatures are probably a characteristic of gabbroic cores at oceanic core complexes. Key Points Borehole T indicates shallow present circulation, conductive regime > 750 mbsf Narrow fault zones have seismic, T, resistivity signal indicating localized flow Hydration of gabbroic oceanic core complexes is limited below fault damage zone

DOI10.1002/2013gl058111
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