Seismic evidence for large-scale compositional heterogeneity of oceanic core complexes
Canales, J. Pablo
Tucholke, Brian E.
Collins, John A.
DuBois, David L.
MetadataShow full item record
KeywordOceanic core complex; Detachment fault; Mid-Atlantic Ridge; Seismic structure; Gabbro; Serpentinized peridotite
Long-lived detachment faults at mid-ocean ridges exhume deep-seated rocks to form oceanic core complexes (OCCs). Using large-offset (6 km) multichannel seismic data, we have derived two-dimensional seismic tomography models for three of the best developed OCCs on the Mid-Atlantic Ridge. Our results show that large lateral variations in P wave velocity occur within the upper ~0.5–1.7 km of the lithosphere. We observe good correlations between velocity structure and lithology as documented by in situ geological samples and seafloor morphology, and we use these correlations to show that gabbros are heterogeneously distributed as large (tens to >100 km2) bodies within serpentinized peridotites. Neither the gabbros nor the serpentinites show any systematic distribution with respect to along-isochron position within the enclosing spreading segment, indicating that melt extraction from the mantle is not necessarily focused at segment centers, as has been commonly inferred. In the spreading direction, gabbros are consistently present toward the terminations of the detachment faults. This suggests enhanced magmatism during the late stage of OCC formation due either to natural variability in the magmatic cycle or to decompression melting during footwall exhumation. Heat introduced into the rift valley by flow and crystallization of this melt could weaken the axial lithosphere and result in formation of new faults, and it therefore may explain eventual abandonment of detachments that form OCCs. Detailed seismic studies of the kind described here, when constrained by seafloor morphology and geological samples, can distinguish between major lithological units such as volcanics, gabbros, and serpentinized peridotites at lateral scales of a few kilometers. Thus such studies have tremendous potential to elucidate the internal structure of the shallow lithosphere and to help us understand the tectonic and magmatic processes by which they were emplaced.
Author Posting. © American Geophysical Union, 2008. 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 9 (2008): Q08002, doi:10.1029/2008GC002009.
Suggested CitationGeochemistry Geophysics Geosystems 9 (2008): Q08002
Showing items related by title, author, creator and subject.
Heterogeneous seismic velocity structure of the upper lithosphere at Kane oceanic core complex, Mid-Atlantic Ridge Xu, Min; Canales, J. Pablo; Tucholke, Brian E.; DuBois, David L. (American Geophysical Union, 2009-10-10)The Kane oceanic core complex (OCC) is a large, corrugated megamullion that was formed by a long-lived detachment fault at the axis of the Mid-Atlantic Ridge adjacent to Kane Fracture Zone between 2.1 and 3.3 Ma. We use ...
Downward continued multichannel seismic refraction analysis of Atlantis Massif oceanic core complex, 30°N, Mid-Atlantic Ridge Henig, A. S.; Blackman, Donna K.; Harding, Alistair J.; Canales, J. Pablo; Kent, Graham M. (American Geophysical Union, 2012-05-19)Detailed seismic refraction results show striking lateral and vertical variability of velocity structure within the Atlantis Massif oceanic core complex (OCC), contrasting notably with its conjugate ridge flank. Multichannel ...
Small-scale structure of the Kane oceanic core complex, Mid-Atlantic Ridge 23°30′N, from waveform tomography of multichannel seismic data Canales, J. Pablo (American Geophysical Union, 2010-11-03)Frequency-domain waveform tomography applied to deep-sea multichannel seismic data collected across the Kane oceanic core complex (OCC) reveals the small-scale structure of this section of oceanic lithosphere formed at the ...