Crystallization depth beneath an oceanic detachment fault (ODP Hole 923A, Mid-Atlantic Ridge)
Lissenberg, C. Johan
MacLeod, Christopher J.
Bowring, Samuel A.
MetadataShow full item record
Oceanic detachment faults are increasingly recognized as playing an integral role in the seafloor spreading process at slow and ultraslow spreading mid-ocean ridges, with significant consequences for the architecture of the oceanic lithosphere. Although melt supply is considered to play a critical control on the formation and evolution of oceanic detachments, much less well understood is how melts and faults interact and influence each other. Few direct constraints on the locus and depth of melt emplacement in the vicinity of detachments are available. Gabbros drilled in ODP Hole 923A near the intersection of the Mid-Atlantic Ridge and the Kane transform fault (23°N; the MARK area) represent magmas emplaced into the footwall of such a detachment fault and unroofed by it. We here present U-Pb zircon dates for these gabbros and associated diorite veins which, when combined with a tectonic reconstruction of the area, allow us to calculate the depths at which the melts crystallized. Th-corrected single zircon U-Pb dates from three samples range from 1.138 ± 0.062 to 1.213 ± 0.021 Ma. We find a crystallization depth of 6.4 +1.7/−1.3 km, and estimate that the melts parental to the gabbros were initially emplaced up to 1.5 km deeper, at <8 km below the seafloor. The tectonic reconstruction implies that the detachment fault responsible for the exposure of the sampled sequence likely crossed the ridge axis at depth, suggesting that melt emplacement into the footwall of oceanic detachment faults is an important process. The deep emplacement depth we find associated with “detachment mode” spreading at ∼1.2 Ma appears to be significantly greater than the depth of magma reservoirs during the current “magmatic mode” of spreading in the area, suggesting that the northern MARK segment preserves a recent switch between two temporally distinct modes of spreading with fundamentally different lithospheric architecture.
© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 162–180, doi:10.1002/2015GC006027.
The following license files are associated with this item:
Showing items related by title, author, creator and subject.
Karson, Jeffrey A.; Fruh-Green, Gretchen L.; Kelley, Deborah S.; Williams, E. A.; Yoerger, Dana R.; Jakuba, Michael V. (American Geophysical Union, 2006-06-21)Near-bottom investigations of the cross section of the Atlantis Massif exposed in a major tectonic escarpment provide an unprecedented view of the internal structure of the footwall domain of this oceanic core complex. ...
Crustal structure of the Trans-Atlantic Geotraverse (TAG) segment (Mid-Atlantic Ridge, 26°10′N) : implications for the nature of hydrothermal circulation and detachment faulting at slow spreading ridges Canales, J. Pablo; Sohn, Robert A.; deMartin, Brian J. (American Geophysical Union, 2007-08-09)New seismic refraction data reveal that hydrothermal circulation at the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge at 26°10′N is not driven by energy extracted from shallow or mid-crustal ...
Three-dimensional seismic structure of a Mid-Atlantic Ridge segment characterized by active detachment faulting (Trans-Atlantic Geotraverse, 25°55′N-26°20′N) Zhao, Minghui; Canales, J. Pablo; Sohn, Robert A. (American Geophysical Union, 2012-11-02)We use air gun shots recorded by ocean bottom seismometers (OBSs) to generate a three-dimensional (3D) P-wave tomographic velocity model of the Trans-Atlantic Geotraverse (TAG) segment of the Mid-Atlantic Ridge, and to ...