Geological and geophysical implications of deep-tow magnetometer observations near sites 897, 898, 899, 900, and 901 on the west Iberia continental margin

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doi: 10.2973/odp.proc.sr.149.241.1996
Author(s): Whitmarsh, Robert B.; Miles, Peter R.; Sibuet, Jean-Claude; Louvel, Véronique
Author Affiliation(s): Primary:
Institute of Oceanographic Sciences Deacon Laboratory, Wormley, United Kingdom
Other:
Rice University, United States
Ocean Drilling Program, United States
Université Pierre et Marie Curie, France
Dalhousie University, Canada
Universidad de Granada, Spain
Université de Nantes, France
Florida State University, United States
Universidade de Aveiro, Portugal
INTERGEOS, Netherlands
University of Waterloo, Canada
Lamont-Doherty Earth Observatory, United States
University of Tokyo, Japan
GEOMAR, Federal Republic of Germany
University of Leicester, United Kingdom
University of Texas at El Paso, United States
University of Michigan, United States
Universität Kiel, Federal Republic of Germany
Cornell University, United States
California State University, United States
Iowa State University, United States
University of Maryland System, United States
Open University, United Kingdom
University of California, United States
Ifremer, Centre de Brest, France
EOPGS, France
Volume Title: Proceedings of the Ocean Drilling Program; scientific results, Iberia abyssal plain; covering Leg 149 of the cruises of the Drilling Vessel JOIDES Resolution; Balboa Harbor, Panama, to Lisbon, Portugal; sites 897-901, 10 March-25 May 1993
Volume Author(s): Whitmarsh, Robert B.; Sawyer, Dale S.; Klaus, Adam; Beslier, Marie-Odile; Collins, Eric S.; Comas, María Carmen; Cornen, Guy; de Kaenel, Eric; Pinheiro, Luis de Menezes; Gervais, Elisabeth; Gibson, Ian L.; Harry, Dennis L.; Hobart, Michael A.; Kanamatsu, Toshiya; Krawcyzk, Charlotte M.; Liu, Li; Lofts, Jeremy C.; Marsaglia, Kathleen M.; Meyers, Philip A.; Milkert, Doris; Milliken, Kitty L.; Morgan, Julia K.; Ramirez, Pedro; Seifert, Karl E.; Shaw, Timothy J.; Wilson, Chris; Yin, Chuan; Zhao, Xixi
Source: Proceedings of the Ocean Drilling Program; scientific results, Iberia abyssal plain; covering Leg 149 of the cruises of the Drilling Vessel JOIDES Resolution; Balboa Harbor, Panama, to Lisbon, Portugal; sites 897-901, 10 March-25 May 1993, Robert B. Whitmarsh, Dale S. Sawyer, Adam Klaus, Marie-Odile Beslier, Eric S. Collins, María Carmen Comas, Guy Cornen, Eric de Kaenel, Luis de Menezes Pinheiro, Elisabeth Gervais, Ian L. Gibson, Dennis L. Harry, Michael A. Hobart, Toshiya Kanamatsu, Charlotte M. Krawcyzk, Li Liu, Jeremy C. Lofts, Kathleen M. Marsaglia, Philip A. Meyers, Doris Milkert, Kitty L. Milliken, Julia K. Morgan, Pedro Ramirez, Karl E. Seifert, Timothy J. Shaw, Chris Wilson, Chuan Yin and Xixi Zhao. Proceedings of the Ocean Drilling Program, Scientific Results, Vol.149, p.665-674. Publisher: Texas A&M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 0884-5891
Note: In English. 25 refs.; illus., incl. geol. sketch maps, 1 table, sects.
Summary: We present new magnetic measurements from deep-towed magnetometers, operated within a few hundred meters of the seabed of the Iberia Abyssal Plain, over oceanic crust and within the ocean-continent transition itself. In December 1991, the Charles Darwin towed a three-component fluxgate magnetometer, mounted on the Institute of Oceanographic Sciences' towed ocean-bottom instrument (TOBI), along 40°40'N in the Iberia Abyssal Plain. In July 1993, Le Suroit towed a similar magnetometer fitted to Ifremer's Systeme Acoustique Remorque (SAR) deep-tow vehicle over Ocean Drilling Program (ODP) Sites 897, 898, and 899. The observed TOBI profile shows not only a steep gradient on the east flank of the J anomaly, but also anomalies of hundreds of nT over the oceanic crust. Immediately east of the peridotite ridge sampled at Site 897 there are two strong peaks, but further east the anomalies become more subdued. The SAR profile similarly shows a large broad anomaly of hundreds of nT over the oceanic crust and a very strong peak over Site 899 within the ocean-continent transition. Both profiles exhibit the broad trough identified on surface anomalies immediately west of the peridotite ridge. We present two-dimensional models constrained by seismic refraction and reflection profiles and loosely constrained by the magnetic properties of the ODP cores. The common mismatch in amplitude and phase, between the observations and the anomalies resulting from basement relief alone, indicates that magnetization contrasts must exist within the ocean-continent transition crust itself. The results presented here do not at present help us to distinguish definitively between a number of alternative hypotheses for the formation of the ocean-continent transition. However, the unexpectedly low amplitude of some of the relatively short (a few kilometers) wavelength anomalies in the observations may indicate that no significant magnetization contrasts exist on scales of less than 10 km along the profiles near the top of basement. Nevertheless, such contrasts may still exist a few kilometers below the top of basement.
Year of Publication: 1996
Research Program: ODP Ocean Drilling Program
Key Words: 16 Structural Geology; 20 Geophysics, Applied; Atlantic Ocean; Block structures; Continental crust; Continental margin; Crust; Deep-tow methods; Europe; Faults; Geophysical methods; Geophysical surveys; Iberian Peninsula; Iberian abyssal plain; Leg 149; Magnetic anomalies; Magnetic methods; Marine methods; North Atlantic; Northeast Atlantic; ODP Site 897; ODP Site 898; ODP Site 899; ODP Site 900; ODP Site 901; Ocean Drilling Program; Oceanic crust; Southern Europe; Surveys; Systems; Transition zones
Coordinates: N404029 N404029 W0110335 W0110335
N404059 N404059 W0113616 W0113616
N404622 N404622 W0121604 W0121604
Record ID: 2007088124
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