Publication
Jackson,
M. P. A., Cramez, C., and Fonck, J. -M., 2000, Role of subaerial
volcanic rocks and mantle plumes in creation of South Atlantic margins:
implications for salt tectonics and source rocks: Marine and Petroleum
Geology, v. 17, p. 477-498
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Role of Subaerial
Volcanic Rocks and Mantle Plumes in Creation of South Atlantic Margins:
Implications for Salt Tectonics and Source Rocks
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Abstract
Seaward-dipping reflectors (SDRs) represent flood basalts rapidly
extruded during either rifting or initially subaerial sea-floor
spreading. Evaporites can form on this basaltic proto-oceanic crust,
as in the Afar Triangle today. Evidence for SDRs in South Atlantic
deep-water regions comes from proximity to the uniquely large Paraná-Etendeka
volcanic province onshore, the Tristan and Gough hot spots, drilled
volcanic rocks, and seismic profiles showing SDR provinces more
than 100 km wide, as much as 7 km thick, and thousands of kilometers
long. SDRs are clearest adjoining the Aptian salt basins. However,
we speculate that SDRs are also present but seismically obscured
below the salt basins. We argue that the conjugate Aptian salt basins
are post-breakup, not pre-breakup; they were separated from the
start by a mid-oceanic ridge; distal salt accumulated on proto-oceanic
crust, not rift basins. This hypothesis is supported by: seismic
stratigraphy and structure; magnetic anomalies; plate reconstructions;
and hydrothermal potash evaporites. An important implication for
exploration is that thick basalts, rather than rift-age source rocks,
may underlie distal parts of the salt basins.
Jean-Michel
Fonck and Carlos Cramez: TotalFina Exploration and Production, 24
Cours Michelet, La Defense 10, 92069 Paris La Defense Cedex, France
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