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Oceanic core complexes and crustal accretion at slow-spreading ridges

B. Ildefonse^*,1, D.K. Blackman², B.E. John³, Y. Ohara⁴, D.J. Miller⁵, C.J. MacLeod⁶ and Integrated Ocean Drilling Program Expeditions 304/305 Science Party^,1

¹ Géosciences Montpellier, CNRS, Université Montpellier 2, CC 60, 34095 Montpellier cedex 05, France
² Scripps Institution of Oceanography, La Jolla, California 92093, USA
³ Department of Geology and Geophysics, University of Wyoming, 1000 East University Avenue, Department 3006, Laramie, Wyoming 82071, USA
⁴ Ocean Research Laboratory, Hydrographic and Oceanographic Department of Japan, 5-3-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan
⁵ Integrated Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845-9547, USA
⁶ School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, UK

Oceanic core complexes expose gabbroic rocks on the seafloor via detachment faulting, often associated with serpentinized peridotite. The thickness of these serpentinite units is unknown. Assuming that the steep slopes that typically surround these core complexes provide a cross section through the structure, it has been inferred that serpentinites compose much of the section to depths of at least several hundred meters. However, deep drilling at oceanic core complexes has recovered gabbroic sequences with virtually no serpentinized peridotite. We propose a revised model for oceanic core complex development based on consideration of the rheological differences between gabbro and serpentinized peridotite: emplacement of a large intrusive gabbro body into a predominantly peridotite host is followed by localization of strain around the margins of the pluton, eventually resulting in an uplifted gabbroic core surrounded by deformed serpentinite. Oceanic core complexes may therefore reflect processes associated with relatively enhanced periods of mafic intrusion within overall magma-poor regions of slow- and ultra-slow-spreading ridges.

Key Words: Integrated Ocean Drilling Program • Ocean Drilling Program • oceanic lithosphere • mid-ocean ridges • Mid-Atlantic Ridge • oceanic core complex • gabbro • serpentinite

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