The S reflector and rifting processes: Iberia Abyssal Plain/Galicia Bank
Funded by NSF Marine Geology and Geophysics Program for 1997
Abstract
We propose a joint USA-German multichannel and wide-angle seismic experiment to
study the apparently non-volcanic Galicia Interior Basin/Galicia Bank rifted continental
margin and the transform boundary with the Iberia Abyssal Plain margin segment to the
south. A focus of the study will be improving our understanding of the S reflector under the
outer Galicia Bank. S is a prominent reflector that forms the base of a set of faulted and
tilted basement blocks. S appears to have played an important, but not yet understood, role
in the structural evolution of the rifted margin.
The objectives of the proposed study are to determine:
- the seismic velocity of the rocks that bound the S reflector where it is best expressed in
the crust of the Galicia Bank.
- using structure and seismic velocity, the character of the eastward termination of S
where it appears to split into three or more, lower amplitude reflectors.
- using structure and seismic velocity, the character of S where it terminates westward
and identify its relationship, if any, with the Peridotite Ridge.
- the seismic character of the Moho, if it is distinct from S, beneath the Galicia Bank.
- the velocity depth function above S and compare it to that obtained by migration focusing
analysis and use the result to determine the three dimensional shape of S.
- the structure and thickness of the crust under the Galicia Interior Basin.
- how the structure and thickness of the crust changes along the Iberia margin from the
Galicia Bank into the Iberia Abyssal Plain and how those changes relate to the location
and nature of a transform segment boundary.
- the nature and thickness of the unrifted continental crust landward of the Galicia
Interior Basin.
These objectives may be achieved by acquiring three densely instrumented MCS/OBS
wide-angle seismic profiles (a total of 56 OBS deployments) and twelve complementary
deep-penetration MCS profiles. The wide-angle profiles will be located across 1) the Galicia
Interior Basin, 2) the Galicia Bank, and 3) the transform boundary between the Galicia Bank
and the Iberia Abyssal Plain.
The Iberia Margin is a good place to study rifted continental margins because 1) the
margin from which it rifted, its conjugate, is well constrained, 2) the Iberia Margin and its
conjugate margin are relatively sediment starved so basement, intracrustal reflectors, and
Moho can be easily imaged, 3) because there has been no postrift volcanism or salt tectonics
to disrupt the basement or the overlying sediments, or prevent their imaging, and 4) because
we can build upon the results of ODP Legs 103 and 149, which provide "ground-truth"
regarding the character of basement at several key points in the proposed survey area.
Cooperating Institutions:
Rice University
Dept. of
Geology and Geophysics,
GEOMAR in Kiel Germany,
The University of Texas at Austin,
Institute
of Earth Sciences in Barcelona Spain,
The University of Madrid Spain,
and the
Lamont Doherty Earth Observatory
R/V Maurice Ewing.
Cooperating Scientists:
Dale Sawyer
Dale S. Sawyer,
Tim Reston,
James A. Austin, Jr.,
Colin Zelt
Colin Zelt,
Ernst Flueh,
Yosio Nakamura,
Montse Torne,
Juanjo Danobeitia,
and
Diego Cordoba.
Department of Geology and Geophysics / Rice University / dale@geophysics.rice.edu
Last change: 08 Nov 1995