Gabbroic pegmatite intrusions, Iberia Abyssal Plain, ODP Leg 173, Site 1070; magmatism during a transition from non-volcanic rifting to sea-floor spreading

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doi: 10.1093/petrology/43.5.885
Author(s): Beard, James S.; Fullagar, Paul D.; Sinha, A. Krisha
Author Affiliation(s): Primary:
Virginia Museum of Natural History, Martinsville, VA, United States
Other:
University of North Carolina, United States
Virginia Polytechnic Institute and State University, United States
Volume Title: Journal of Petrology
Source: Journal of Petrology, 43(5), p.885-905. Publisher: Oxford University Press, Oxford, United Kingdom. ISSN: 0022-3530 CODEN: JPTGAD
Note: In English. 84 refs.; illus., incl. 6 tables, sketch map
Summary: On the Iberia Abyssal Plain, gabbroic pegmatites and related rocks (127 ± 4 m.y.) intrude upper mantle that was subsequently exposed and serpentinized during early Cretaceous non-volcanic rifting. The pegmatites include a 3-4 m dyke or sill (the 'main' pegmatite), numerous dyklets 1-5 cm thick and clasts within the overlying ophicalcite breccia. Exclusive of rodingitization, the main pegmatite has 40-70% calcic andesine, 25-35% kaersutitic amphibole (mg 60-70, TiO2 4.6 wt.%), 5-25% augite (mg 70-80) and 1-2% ilmenite; the dykelets are slightly more magnesian. Isotopic and elemental chemistry indicate that the pegmatite-forming melt was enriched in incompatible elements relative to MORB, but not as enriched as Azores basalts. The amphibole-bearing plagioclase peridotites of the Iberia Abyssal Plain are an appropriate source for the pegmatite melts. A combination of decompression accompanying unroofing and heating from the upwelling asthenosphere beneath the developing rift caused P-T conditions in the amphibole-bearing lithosphere to exceed the dehydration-melting solidus (∼ 1050°C), producing small-volume, enriched hydrous melts. Pegmatite intrusion pre-dates unroofing and post-dates syn-rift sedimentation and faulting of serpentinite seen inboard of the Iberia Abyssal Plain.
Year of Publication: 2002
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; 18 Geophysics, Solid-Earth; Atlantic Ocean; Gabbroic composition; Granites; Iberian abyssal plain; Igneous rocks; Intrusions; Leg 173; Magmatism; Metaigneous rocks; Metamorphic rocks; Metasomatic rocks; North Atlantic; Northeast Atlantic; ODP Site 1070; Ocean Drilling Program; Pegmatite; Peridotites; Plate tectonics; Plutonic rocks; Rifting; Sea-floor spreading; Serpentinite; Ultramafics
Coordinates: N390000 N410000 W0102000 W0153000
Record ID: 2003010460
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom