Petrologic characteristics of the ultramafic rocks from the ocean/continent transition in the Iberia abyssal plain

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doi: 10.2973/odp.proc.sr.149.215.1996
Author(s): Cornen, Guy; Beslier, Marie-Odile; Girardeau, Jacques
Author Affiliation(s): Primary:
Université de Nantes, Laboratoire de Pétrologie Structurale, Nantes, France
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
Géosciences Azur, 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.377-395. Publisher: Texas A&M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 0884-5891
Note: In English. 38 refs.; illus., incl. 6 tables, geol. sketch map
Summary: Ultramafic rocks were recovered at Sites 897 and 899, drilled during Ocean Drilling Program (ODP) Leg 149 to the ocean/continent transition in the Iberia Abyssal Plain. Such recoveries, in particular that at Site 897, attest to the southward extension of a peridotite ridge previously studied along the Galician Margin. The ultramafic rocks are coarse-grained websterites and depleted peridotites with some minor plagioclase-rich lherzolites. The variations in modal compositions and primary-phase chemistry show that many of the peridotites were subjected to significant partial melting. These rocks also underwent some impregnation by undersaturated alkali magmas that, in many samples, have given rise to local resorption of orthopyroxene, cryptic enrichment in Fe and Ti of most phases, and plagioclase crystallization. Such magmas have left discrete traces composed of clinopyroxene, kaersutite, phlogopite, ilmenite, and rutile. This impregnation occurred during the last stages of the high-temperature deformation event that produced the porphyroclastic foliation in the peridotites. It stopped under static conditions, at a temperature around 965°-880°C and at a pressure below 1 GPa. Subsequently, the websterites underwent a subsolidus reequilibration event, well defined by textural features, which implies that some spinel and plagioclase formed after Al-pyroxenes and Al-spinel, and also defined by some local Ti enrichment of both spinels and pyroxenes. This reequilibration event occurred after the main high-temperature deformation, at a temperature of about 78O°C and a pressure below 1 GPa, but before a mylonitic stage well displayed in a few rocks, which ceased at a temperature close to 735°C. The magmatic signature of the Leg 149 ultramafic rocks, their petrological and tectonometamorphic evolution, and their similarities with the peridotites recovered at the western edge of Galicia Bank support the hypothesis that they originated as a piece of asthenospheric mantle that has been accreted to the lithosphere in a rift system during stretching of the continental lithosphere.
Year of Publication: 1996
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; Atlantic Ocean; Chemical composition; Continental crust; Crust; Enrichment; Europe; Galicia Bank; Galicia Spain; Iberian Peninsula; Iberian abyssal plain; Igneous rocks; Leg 149; Lherzolite; Mantle; North Atlantic; Northeast Atlantic; ODP Site 897; ODP Site 899; Ocean Drilling Program; Oceanic crust; P-T conditions; Peridotites; Petrology; Plate tectonics; Plutonic rocks; Rifting; Southern Europe; Spain; Ultramafics
Coordinates: N404622 N404622 W0121604 W0121604
N405019 N405019 W0122847 W0122847
Record ID: 2007088102
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