Publications

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2015
Greene, JA, Tominaga M, Blackman DK.  2015.  Geologic implications of seafloor character and carbonate lithification imaged on the domal core of Atlantis Massif. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 121:246-255.   10.1016/j.dsr2.2015.06.020   AbstractWebsite

We document the seafloor character on Atlantis Massif, an ocean core complex located at 30 degrees N on the Mid-Atlantic Ridge, with an emphasis on the distribution of carbonate features. Seafloor imagery, near-bottom backscatter, and bathymetry were analyzed on the Central Dome and the Western Shoulder of the exposed footwall to the detachment, and on the Eastern Block, a hanging wall to the fault. We merged Argo II still images to produce photo-mosaics and evaluated these together with video imagery, acoustic reflectivity, and basic rock composition. The seafloor was classified as unconsolidated sediment, lithified carbonate crust, consolidated carbonate cap, exposed basement, or rubble, and the spatial distribution of each type was assessed. Unconsolidated sediment, exposed basement, and rubble were documented in all three regions studied. Lithified carbonate crust was also present on the Western Shoulder and eastern Central Dome. Consolidated carbonate cap was found on the Eastern Block. The formation of the carbonate rock is interpreted to reflect precipitation and/or sediment cementation via fluids derived from serpentinization. Both processes occur at the nearby Lost City Hydrothermal Field. The newly documented locations of seafloor carbonate lithification therefore mark pathways of past, possibly recent, fluid flux from subsurface water-rock reaction zones and represent an additional constituent of the carbon cycling hosted by oceanic lithosphere. (C) 2015 Elsevier Ltd. All rights reserved.

2001
Klingelhofer, F, Minshull TA, Blackman DK, Harben P, Childers V.  2001.  Crustal structure of Ascension Island from wide-angle seismic data: implications for the formation of near-ridge volcanic islands. Earth and Planetary Science Letters. 190:41-56.   10.1016/s0012-821x(01)00362-4   AbstractWebsite

The study of the internal structure of volcanic islands is important for understanding how such islands form and how the lithosphere deforms beneath them. Studies to date have focused on very large volcanic edifices (e.g., Hawaiian Islands, Marquesas), but less attention has been paid to smaller islands, which are more common. Ascension Island, a 4-km high volcanic edifice with a basal diameter of 60 kin, is located in the equatorial Atlantic (8 degreesS), 90 km west of the Mid-Atlantic Ridge on 7 Ma oceanic lithosphere. We present results of a wide-angle seismic profile crossing the island revealing a crustal thickness of 12-13 kin, an overthickened layer 3 (7 kin thick) and little evidence of lithospheric flexure. Together these results suggest Ascension Island may be older than previously assumed and may have begun forming at an on-axis position around 6-7 Ma. This hypothesis is further supported by the presence of a young 1.4-km high edifice directly adjacent to the Mid-Atlantic Ridge with a volume about 1/7 that of Ascension Island, possibly representing the earliest stages of seamount formation. Excess magmatism appears to be related to the tectonic setting at the ridge-fracture zone intersection. (C) 2001 Elsevier Science B.V. All rights reserved.