Palaeomagnetic and rock magnetic results from serpentinized peridotites beneath the Iberia abyssal plain

Author(s): Zhao, Xixi
Author Affiliation(s): Primary:
University of California at Santa Cruz, Institute of Geophysics and Planetary Physics, Santa Cruz, CA, United States
Other:
Southampton Oceanography Center, United Kingdom
University of Hawaii, United States
University of Bonn, Federal Republic of Germany
Volume Title: Non-volcanic rifting of continental margins; a comparison of evidence from land and sea
Volume Author(s): Wilson, R. C. L., editor; Whitmarsh, R. B.; Taylor, B.; Froitzheim, N.
Source: Non-volcanic rifting of continental margins; a comparison of evidence from land and sea, edited by R. C. L. Wilson, R. B. Whitmarsh, B. Taylor and N. Froitzheim. Geological Society Special Publications, Vol.187, p.209-234. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719. ISBN: 1-86239-091-6
Note: In English. 71 refs.; illus., incl. 2 tables, sketch map
Summary: A palaeomagnetic and rock magnetic study has been performed on serpentinized peridotite rocks recovered at Ocean Drilling Program (ODP) Leg 149 and 173 sites, off the west coast of Portugal (Sites 897, 899 and 1070). Stable components of magnetization are revealed after detailed thermal and alternating field demagnetization. Results from a series of rock magnetic measurements with advanced instrumentation all corroborate the demagnetization behaviour and show that (titano)magnetites and maghemite are present in the peridotites. At Leg 149 and 173 sites, the inclinations of characteristic magnetization in the "fresher" lower part of the serpentinized peridotite section show a pre-dominantly reversed polarity in a depth zone of c. 25 m, which is compatible with a reversed event (probably correlated with marine Anomaly M0 at c. 121 Ma) before the Cretaceous Long Normal Superchron (83-120 Ma) and is incompatible with a Holocene field direction. In contrast, the inclinations of samples from the more "altered" upper part are predominantly normal. In view of the polarity of magnetization identified from the overlying Cretaceous and Tertiary sediments and the newest interpretation of the drilling results for the Iberia margin, our results suggest that the Iberian peridotites were emplaced during Aptian-Barremian time and recorded the middle Cretaceous geomagnetic field during Anomaly M0 time (c. 121 Ma). Our data are consistent with new radiometric dates for the Iberian peridotites at Leg 173 drill sites.
Year of Publication: 2001
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Aptian; Atlantic Ocean; Barremian; Continental crust; Continental margin; Cretaceous; Crust; Demagnetization; East Atlantic; Europe; Iberian Peninsula; Iberian abyssal plain; Igneous rocks; Leg 149; Leg 173; Lower Cretaceous; Mesozoic; North Atlantic; Northeast Atlantic; ODP Site 1070; ODP Site 897; ODP Site 899; Ocean Drilling Program; Oceanic crust; Paleomagnetism; Peridotites; Plutonic rocks; Portugal; Southern Europe; Spain; Ultramafics
Coordinates: N405019 N405019 W0122847 W0122847
N404622 N404622 W0121604 W0121604
N404747 N404747 W0124326 W0124326
Record ID: 2003063774
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