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G-Cubed: Geochemistry, Geophysics, Geosystems

 

Index Terms

  • Mineralogy and Petrology: Igneous petrology
  • Marine Geology and Geophysics: Midocean ridge processes
  • Geochemistry: Composition of the mantle
Abstract
Cited By (9)
 

Abstract

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 4, 8611, 22 PP., 2003
doi:10.1029/2002GC000469 [Citation]

Peridotites and gabbros from the Parece Vela backarc basin: Unique tectonic window in an extinct backarc spreading ridge

Yasuhiko Ohara

Hydrographic and Oceanographic Department of Japan, Tokyo 104-0045, Japan

Kantaro Fujioka

Japan Marine Science and Technology Center, Yokosuka 237-0061, Japan

Teruaki Ishii

Ocean Research Institute, University of Tokyo, Tokyo 164-8639, Japan

Hisayoshi Yurimoto

Department of Earth Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan

Peridotite samples from a backarc basin setting will help better understand global mid-oceanic ridge processes. Here we report detailed petrological data of serpentinized peridotite and gabbro from the extinct Parece Vela Basin in the Philippine Sea. Despite its relatively fast spreading rate (8.8–7.0 cm/y full-rate), the Parece Vela Basin spreading ridge (the Parece Vela Rift) has the distinct morpho-tectonic characteristics that indicate a small degree of mantle melting, including the presence of a huge mullion structure (the Godzilla Mullion). Peridotites in the Parece Vela Rift are exposed on the Godzilla Mullion as well as at a segment midpoint. The most notable characteristic of Parece Vela Rift peridotites is small-scale juxtaposition (i.e., a single-dredge-haul scale) of fertile peridotite and depleted peridotite (dunite and plagioclase-bearing peridotite). We interpret that the fertile peridotite (F-type) is the residue of a small degree of mantle melting (∼4% near-fractional melting of a MORB-type mantle), whereas dunite (D-type) and plagioclase-bearing peridotite (P-type) are products of melt-mantle interaction. The associated evolved gabbros may represent the shallow level fractionated melt intruded into P-type. The distinct morpho-tectonic characteristics, peridotite exposure at a segment midpoint, and the presence of fertile peridotite may result from an extreme transform fault effect caused by the ridge-transform geometry of short first-order segments sandwiched by closely spaced fracture zones (“transform sandwich effect”).

Received 1 November 2002; accepted 13 May 2003; published 12 July 2003.

Citation: Ohara, Y., K. Fujioka, T. Ishii, and H. Yurimoto (2003), Peridotites and gabbros from the Parece Vela backarc basin: Unique tectonic window in an extinct backarc spreading ridge, Geochem. Geophys. Geosyst., 4(7), 8611, doi:10.1029/2002GC000469.

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