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Hydrothermal circulation and the dike-gabbro transition in the detachment mode of slow seafloor spreading

Andrew M. McCaig and Michelle Harris
Hydrothermal circulation and the dike-gabbro transition in the detachment mode of slow seafloor spreading
Geology (Boulder) (March 2012) 40 (4): 367-370

Abstract

One of the most ubiquitous boundaries within our planet is between sheeted dikes and gabbros in fast-spreading ocean crust. This boundary marks the brittle-ductile transition at the ridge crest, and is localized by a decametric conductive boundary layer between hydrothermal circulation in the sheeted dike layer and a shallow quasi-steady-state melt lens. In contrast, at slow-spreading ridges, the crustal structure appears chaotic, with no consistent sheeted dike layer and widespread occurrences of gabbro and serpentinized peridotite on the seafloor. Recent work suggests that as much as 50% of the Atlantic Ocean crust formed by a detachment mode of seafloor spreading, including the formation of oceanic core complexes capped by long-lived, convex-upward detachment faults. These detachment faults are often associated with large hydrothermal systems in which the location of any magmatic heat source is uncertain. Here we show that detachment faults can act as thermal boundaries between gabbroic melt in the fault footwall and hydrothermal circulation in the fault zone and hanging wall, thus explaining the link between faulting and black smoker systems. We suggest that interaction between magmatism and hydrothermal circulation means that detachment faults can act as the dike-gabbro transition in the detachment mode of spreading, inevitably leading to exposure of gabbros on the seafloor through continued faulting. This concept provides a means of unifying apparently contrasting processes and crustal structures at different spreading rates.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 40
Serial Issue: 4
Title: Hydrothermal circulation and the dike-gabbro transition in the detachment mode of slow seafloor spreading
Affiliation: University of Leeds, Institute of Geophysics and Tectonics, Leeds, United Kingdom
Pages: 367-370
Published: 20120302
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 34
Accession Number: 2012-035904
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2012100; accessed on March 22, 2012
Illustration Description: illus. incl. sect.
Source Medium: WWW
N30°10'00" - N30°10'60", W42°07'00" - W42°06'00"
N26°07'60" - N26°07'60", W44°49'00" - W44°49'00"
Secondary Affiliation: University of Southampton, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201219
Program Name: IODPIntegrated Ocean Drilling Program
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