Continental hyperextension, mantle exhumation, and thin oceanic crust at the continent‐ocean transition, West Iberia: New insights from wide‐angle seismic. Issue 5 (17th May 2016)

• Record Type: Journal Article
• Authors: Davy, R. G.; Minshull, T. A.; Bayrakci, G.; Bull, J. M.; Klaeschen, D.; Papenberg, C.; Reston, T. J.; Sawyer, D. S.; Zelt, C. A.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 5(2016:May)
• Page Start: 3177
• Page End: 3199
• Publication Date: 2016-05-17
• Subjects: COT -- Galicia -- rifting -- serpentinization -- hyperextension -- wide‐angle seismic; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB012825
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Hyperextension of continental crust at the Deep Galicia rifted margin in the North Atlantic has been accommodated by the rotation of continental fault blocks, which are underlain by the S reflector, an interpreted detachment fault, along which exhumed and serpentinized mantle peridotite is observed. West of these features, the enigmatic Peridotite Ridge has been inferred to delimit the western extent of the continent‐ocean transition. An outstanding question at this margin is where oceanic crust begins, with little existing data to constrain this boundary and a lack of clear seafloor spreading magnetic anomalies. Here we present results from a 160 km long wide‐angle seismic profile (Western Extension 1). Travel time tomography models of the crustal compressional velocity structure reveal highly thinned and rotated crustal blocks separated from the underlying mantle by the S reflector. The S reflector correlates with the 6.0–7.0 km s −1 velocity contours, corresponding to peridotite serpentinization of 60–30%, respectively. West of the Peridotite Ridge, shallow and sparse Moho reflections indicate the earliest formation of an anomalously thin oceanic crustal layer, which increases in thickness from ~0.5 km at ~20 km west of the Peridotite Ridge to ~1.5 km, 35 km further west. P wave velocities increase smoothly and rapidly below top basement, to a depth of 2.8–3.5 km, with an average velocity gradient of 1.0 s −1 . Below this, velocities slowly increase toward typical mantle velocities. Such a downward increase into mantle velocities is interpreted as decreasing serpentinization of mantle rock with depth. Key Points: West of PR, exhumed mantle is present over a short distance before the onset of thin oceanic crust Upper age of thin oceanic crust is 122 Ma, consistent with south‐north continental breakup Pattern of high and low velocities below S is the result of preferential mantle hydration along faulting