Nonvolcanic seafloor spreading and corner‐flow rotation accommodated by extensional faulting at 15°N on the Mid‐Atlantic Ridge: A structural synthesis of ODP Leg 209

Abstract

[1] Drilling during ODP Leg 209, dredging, and submersible dives have delineated an anomalous stretch of the Mid-Atlantic Ridge north and south of the 15°20 0 N Fracture Zone. The seafloor here consists dominantly of mantle peridotite with gabbroic intrusions that in places is covered by a thin, discontinuous extrusive volcanic layer. Thick lithosphere (10-20 km) in this region inhibits magma from reaching shallow levels beneath the ridge axis, thereby causing plate accretion to be accommodated by extensional faulting rather than magmatism. The bathymetry and complex fault relations in the drill-core suggest that mantle denudation and spreading are accommodated by a combination of high-displacement, rolling-hinge normal faults and secondary lower-displacement normal faults. These extensional faults must also accommodate corner flow rotation (up to 90°) of the upwelling mantle within the shallow lithosphere, consistent with remnant magnetic inclinations in denuded peridotite and gabbro from Leg 209 core that indicate up to 90°of sub-Curie-temperature rotation.

Catabolic and anabolic energy for chemolithoautotrophs in deep-sea hydrothermal systems hosted in different rock types

“…Rainbow and Logatchev are high-temperature (350-365°C) black smoker deposits with high concentrations of metals (e.g., 2-24 mM Fe), H 2 (12-19 mM), and CH 4 (>2 mM) Schmidt et al, 2007). Rainbow is located near a nontrans- (Battley, 1991). form discontinuity and bound to normal faults; Logatchev is situated 7 km east of the rift valley floor on the slope of a detachment fault (German and Parson, 1998;Schroeder et al, 2007). At both locations, mantle peridotite is the principle host lithology, but gabbroic rocks and sparse basalt are also observed in the vicinity of the vent sites (Marques et al, 2006;Petersen et al, 2009).…”

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

“…Reston & Ranero 2011). In some segments, detachment faults can dominate crustal accretion for many millions of years, producing large areas of seafloor covered by extinct detachment faults and exhumed deep-seated rocks (Dick et al 2003;Schroeder et al 2007;MacLeod et al 2008;Smith et al 2008). Escartín et al (2008) estimated that active detachment faults occur along nearly 50% of the MAR axis between 12.…”

Oceanic Core Complex Development in Modern and Ancient Oceanic Lithosphere: Gabbro‐Localized versus Peridotite‐Localized Detachment Models

“…These fault systems are distinctive domeshaped massifs that typically exhibit ∼1000 m of relief above the surrounding sea floor (Tucholke et al 1998), and they form along mid-ocean ridge segments at locations ranging from ridge segment centers to ridge-transform intersections (Cann et al 1997;Smith et al 2006Smith et al , 2008. Denudation of footwall rocks beneath moderate-angle, inward-dipping (toward the axis), large-offset detachment faults results in the development of domes through either passive rotation or flexure of the detachment-fault surface to low-angle orientations (e.g., Dick et al 1981Dick et al , 1992Tucholke and Lin 1994;Lavier et al 1999;Smith et al 2006;Schroeder et al 2007). Oceanic core complexes commonly expose lower-crustal and upper-mantle Manuscript received May 19, 2008;accepted September 11, 2009.…”