[S-IT41_28PM2] 海洋プレートの一生：誕生から解体，そして復活

[SIT41-20] オマーンオフィオライト地殻セクション中に分布する超苦鉄質岩体の多様性

*金子 龍¹、足立 佳子²、宮下 純夫² (1.新潟大学大学院自然科学研究科、2.新潟大学)

キーワード：オマーンオフィオライト, 超苦鉄質岩体, 海嶺火成活動, 島弧火成活動

Although all the wehrlitic intrusions in the Oman Ophiolite are regarded as a single group (e.g. Koepke et al. 2009), there are two different types of wehrlitic intrusions. The first are ordinary wehrlitic intrusions that have similar features to the crustal sequence of V1 (MOR basalt). The second are a depleted type characterized by the appearance of true wehrlite and depleted mineral compositions (Adachi & Miyashita 2003; Yamasaki et al. 2006; Goodenough et al. 2010). The former and latter groups are linked to V1 and V2 magmatism, respectively. We report the discovery of a new occurrence of the ultramafic rock in the oceanic crustal sequence from the Oman ophiolite, which does not intrude into the crustal sequence. This ultramafic rock is referred to as the Lasail-South complex, and the oldest rock in the study area because of being intruded by sheeted dyke complex. TiO2 and Na2O contents of clinopyroxene from the complex range 0.06-0.59 and 0.09-0.42 wt%, respectively, and are similar to the fractional crystallization trend of oceanic gabbro. Co-variation of Mg values of clinopyroxene and An contents of plagioclase show that most of samples plot in the Oman layered gabbro field. Although mineral compositions of the Lasail-South complex show characteristic of mid-ocean ridge magmatism, the complex mainly comprises plagioclase?hornblende lherzolite, olivine clinopyroxenite and clinopyroxenite. Such rock assemblage of is different from the assemblage of the oceanic crust of the Oman ophiolite. The Lasail-South complex shows intermediate characteristic of mid-ocean ridge and island arc magmatisms, and we attempt to discuss the origin of the complex.ReferencesAdachi and Miyashita, 2003. Geochemistry Geophysics Geosystems, 4(9), doi.org/10.1029/2001GC000272.Goodenough et al., 2010. Arabian Journal of Geosciences, 3, 439-458, doi.org/10. 1007/s12517-010-0177-3.Koepke et al., 2009.Geochemistry Geophysics Geosystems, 10, 10002, doi.org/10.1029/ 2009GC002488.Yamasaki et al., 2006. Earth and Planetary Science Letters, 251, 52-65, doi.org/10.1016/j.epsl.2006.08.027.