HR: 10:55h
AN: V22A-03 INVITED     [Abstracts]
TI: An ocean floor prospecting: Implications from the petrological insights of the abyssal chromitites from ODP Leg 209, MAR 15 20 N FZ
AU: * Abe, N
EM: abenatsu@jamstec.go.jp
AF: Program for Deep Sea Research, IFREE, JAMSTEC, 2-15 Natsushima-cho,, Yokosuka, 237-0061 Japan
AB: ODP Leg 209 performed to drill mantle peridotites and associated gabbroic rocks (at 8 Sites, 19 holes) along the Mid- Atlantic Ridge (MAR) from 14 to 16 N, both sides of 15 20 N FZ. Several podiform chromitites were recovered at Site 1271, both Hole 1271A and B, south of 15 20 N FZ during the cruise. These chromitites are the first sampled from the Mid-Atlantic Ridge. The primary chromites in the chromitites have moderately high-Cr# (0.52 and 0.48 for Hole 1271A and 1272B, respectively) and chromian spinels in the surrounding chromitites have similar composition. It is considered that podiform chromitite is formed by two kind of melt (melt-mantle interaction, therefore there should be plenty volume of melt in the mantle beneath this area. Abundant of gabbro and dunite were recovered from this area suggest that main volume of melt body were consumed in the upper mantle by melt-wallrock interaction. On the other hand, chromite grains have thick rims of Cr-magnetite or completely replaced by magnetite without chromite core. Cr content elevation in the Cr-magnetite rim occurred with Fe-enrichment. These chemical modifications suggest that the chromitite from Site 1271 were metamorphosed at amphibolite facies because significant Al-missing from chromite cores is taken place above 550 degree Celsius.
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 3660 Metamorphic petrology
DE: 3665 Mineral occurrences and deposits
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting