Tectonic core of a sedimentary drift: a potential ridge propagation feature beneath the Blake Outer Ridge
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ORIGINAL PAPER
Tectonic core of a sedimentary drift: a potential ridge propagation feature beneath the Blake Outer Ridge Dayton Dove Æ Steven C. Jaume Æ Erin Beutel
Received: 20 December 2005 / Accepted: 21 September 2006 / Published online: 23 November 2006 Springer Science+Business Media B.V. 2006
Abstract The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period of midocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene.
D. Dove S. C. Jaume (&) E. Beutel Department of Geology and Environmental Geosciences, College of Charleston, 66 George Street, Charleston, SC 29424, USA e-mail: [email protected] Present Address: D. Dove Department of Geology and Geophysics, University of Alaska Fairbanks, Natural Sciences Building, 900 Yukon Drive, P.O. Box 755780, Fairbanks, AK 99775-5780, USA
Keywords Blake Outer Ridge Crustal density model Gravity anomalies Magnetic anomalies Ridge propagation Sedimentary drift
Introduction The Blake Outer Ridge is a very linear and actively accreting submarine sedimentary ridge located beyond the continental shelf offshore of the southeastern United States (Fig. 1). It strikes N40W, roughly perpendicular to the Atlantic coastline and parallel to the onshore Cape Fear Arch. The Blake Outer Ridge extends ~480 km in length, and rises ~2 km above the surrounding abyssal plain. Deep Sea Drilling Program and Ocean Drilling Program boreholes into the Blake Outer Ridge have penetrated up to 750 m of middle Miocene through Holocene nannofossil-rich clay and claystones (Jansa et al. 1979; Paull et al. 2000). Tucholke et al. (1982) used seismic reflection and refraction profiles to estimate total sediment thickness in excess of 4 km beneath the axis of the Blake Outer Ridge. Early seismic refraction work found evidence of faulting beneath the Blake Outer Ridge that suggested a tectonic origin (Hersey et al. 1959). However, more recent explanations of the origin of the Blake Outer Ridge describe it
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