Abe, Natsue (2011): Petrology of podiform chromitite from the ocean floor at the 15 degrees 20' FZ in the MAR, Site 1271, ODP Leg 209

Leg/Site/Hole:
ODP 209
ODP 209 1271
Identifier:
2012-020606
georefid

10.2465/jmps.101022
doi

Creator:
Abe, Natsue
Japan Agency for Marine-Earth Science and Technology, Institute for Research on Earth Evolution, Yokosuka, Japan
author

Identification:
Petrology of podiform chromitite from the ocean floor at the 15 degrees 20' FZ in the MAR, Site 1271, ODP Leg 209
2011
Journal of Mineralogical and Petrological Sciences
Mineralogical Society of Japan and the Japanese Association of Mineralogists, Petrologists and Economic Geologists, Sendai, Japan
106
2
97-102
Several podiform chromitite samples from abyssal peridotite have been recovered from Site 1271 at the 15 degrees 20' N fracture zone (FZ) in the Mid-Atlantic Ridge (MAR) during an Ocean Drilling Program cruise, ODP Leg 209. It is observed that only chromian spinel is preserved as the primary mantle mineral and that all other primary minerals in the chromitite samples are completely altered. The primary chromian spinel has moderately high Cr#=Cr, (Cr-Al) atomic ratio; approximate value=0.5, which is comparable with Cr# value of the chromitite "minipod" sampled from Hess Deep (Arai and Matsukage, 1996). Samples associated with chromitites consist of mainly dunite, some amphibole-bearing gabbros and troctolite, and a very small amount of harzburgite. Therefore, the chromitites from this site are categorized under the rock series that composes the Moho transition zone, similar to those in ophiolites This implies that a mass of melt existed, but was consumed by melt-rock interactions in the uppermost mantle beneath this area. This in turn means that the area is not magma-starved, although it is unclear when and where the interactions occurred. The formation of the chromitites at Site 1271 is probably occurs through the series of hybridization processes which suggested by Takazawa et al. (2007). Some grains of the chromian spinel in the samples have thick rims of Cr magnetite or of magnetites. Increase in the Cr content in the Cr-magnetite rim is accompanied by Fe enrichment. The chemical modification of the chromian spinel suggests that the chromitite from Site 1271 was metamorphosed at a high temperature up to the upper greenschist facies because the depletion of Al in the region extending from spinel cores to the rim takes place at high temperature as a result of equilibration of fluids in equilibrium with chlorite.
English
Serial
Coverage:Geographic coordinates:
North:15.0200
West:-44.5700East: -44.5700
South:15.0200

Igneous and metamorphic petrology; Atlantic Ocean; chrome spinel; chromitite; chromium; dunite; East Pacific; enrichment; facies; greenschist facies; Hess Deep; high temperature; hybridization; igneous rocks; Leg 209; magmas; magnetite; mantle; metals; metamorphism; Mid-Atlantic Ridge; Mohorovicic discontinuity; North Atlantic; North Pacific; Northeast Pacific; Ocean Drilling Program; ocean floors; ODP Site 1271; ophiolite; oxides; Pacific Ocean; peridotites; petrography; plutonic rocks; podiform deposits; temperature; ultramafics; upper mantle;

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