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The evolution of amphibolites from Site 1067, ODP Leg 173 (Iberia Abyssal Plain): Jurassic rifting to the Pyrenean compression

By
V. Gardien
V. Gardien
UMR 5570, CNRS and UCB-Lyonl, 43 Bd 11 Novembre 1918, 69622 Villeurbanne Cedex, France
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G. Poupeau
G. Poupeau
UPRES-A 5025, CNRS-University Joseph Fourrier, Institut Dolomieu, 15 rue Maurice Gignoux, 38031 Grenoble, France
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B. Muceku
B. Muceku
UPRES-A 5025, CNRS-University Joseph Fourrier, Institut Dolomieu, 15 rue Maurice Gignoux, 38031 Grenoble, France
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R. Hébert
R. Hébert
Département de Géologie et de Génie géologique, Pavillon Adrien-Pouliot, Université Laval, Ste-Foy, Québec G1K 7P4, Canada
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G. Beaudoin
G. Beaudoin
Département de Géologie et de Génie géologique, Pavillon Adrien-Pouliot, Université Laval, Ste-Foy, Québec G1K 7P4, Canada
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E. Labrin
E. Labrin
UPRES-A 5025, CNRS-University Joseph Fourrier, Institut Dolomieu, 15 rue Maurice Gignoux, 38031 Grenoble, France
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Published:
January 01, 2001

Abstract

During ODP Leg 173 (April-May 1997) five new sites (1065, 1067-1070) were drilled at the ocean-continent transition (OCT) zone off the West Iberia margin in the Iberia Abyssal Plain. At Site 1067 the 92 m of cored amphibolites were subdivided into three units based on textural criteria. Unit 1 consists of highly foliated and folded amphibolites and acidic gneiss concordant to and folded along with the foliation of the amphibolite. Unit 2, in the middle part of the section, consists of brecciated amphibolites. Unit 3, at the bottom of the hole, is a weakly deformed zone where magmatic textures are observed in the amphibolites and in associated anorthosites. The amphibolites contain tschermakitic to magnesio-hornblende amphibole, plagioclase, zircon, apatite ± titanite ± Fe-oxide ± quartz. The acidic gneiss consists of garnet, plagioclase, alkali-feldspar, quartz, biotite and zircon. Chlorite, sericite and ilmenite occur as secondary phases. The metamorphic evolution of the amphibolite and acidic gneiss started under amphibolite- facies conditions (Stage I: 670 ± 40 °C and 7 ± l kbar). Further exhumation took place through low-grade amphibolite-facies (Stage II: 550 ± 50°C and 5.5 ± l kbar) to greenschist-facies (Stage III: 500 °C and 3 kbar) conditions contemporaneous with the development of ductile structures. The late metamorphic evolution of the amphibolite ended under ocean-floor conditions. Oxygen isotope ratios and studies of fluid inclusion indicate that a magmatic waterrich fluid in equilibrium with the igneous protolith predominated during Stage I. During Stages II and IIII low-temperature waterrich fluids of metamorphic origin predominated, with a probable contribution of sea water. Apatite fission-track dating indicates that the amphibolites record two thermal excursions below 120°C. The first took place at c. 113 – 100Ma and could be related to Cretaceous rifting. The second was brief, and so did not anneal older tracks; it occurred between 75 and 55 Ma and could be related to the Pyrenean orogeny.

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Contents

Geological Society, London, Special Publications

Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea

R. C. L. Wilson
R. C. L. Wilson
The Open University, UK
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R. B. Whitmarsh
R. B. Whitmarsh
Southampton Oceanography Centre, UK
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B. Taylor
B. Taylor
University of Hawaii, Hawaii
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N. Froitzheim
N. Froitzheim
University of Bonn, Germany
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Geological Society of London
Volume
187
ISBN electronic:
9781862394353
Publication date:
January 01, 2001

GeoRef

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