Signatures of Residual Melts, Magmatic and Seawater-Derived Fluids in Oceanic Lower-Crust Gabbro from the Vema Lithospheric Section, Central Atlantic

Crystallographic and shape orientations of magnetite micro-inclusions in plagioclase

“…The Fe-Ti oxides are present as large interstitial grains of magnetite and as micron-and sub-micron-sized inclusions in plagioclase and pyroxene. Detailed descriptions of the mineralogy and petrography of the gabbros with complex petrogenetic history (Samples L32-101-1, L2612-41, L2612-47) can be found in Pertsev et al (2015), Aranovich et al (2015) and Ageeva et al (2017).…”

Fe-Ti oxide micro-inclusions in clinopyroxene of oceanic gabbro: Phase content, orientation relations and petrogenetic implication

“…In this communication we focus on the evolution of clinopyroxene-hosted Fe-Ti oxide micro-inclusions in oceanic gabbro that was dredged from the Mid Atlantic ridge at 10°42.95ʹN, 41°34.60ʹW. An earlier study (Pertsev et al, 2015) suggests that the petrogenetic history of the gabbro includes late magmatic crystallization of Fe-Ti oxides, interaction between a crystal aggregate and residual liquid, and multistage hydrothermal alteration. We report on the shape and crystallographic orientation relationships between Fe-Ti oxide micro-inclusions, associated amphibole lamellae and a clinopyroxene host.…”

“…The gabbro sample -L2612-41 (gabbro-41) -was collected together with more abundant mantle-derived peridotites from the Vema lithospheric section, Central Atlantic (Auzende et al, 1989;Bonatti et al, 2003Bonatti et al, , 2005) by dredging at 10°42.95ʹN, 41°34.60ʹW, 5195-4620 mbsl (Cipriani et al, 2009). This gabbro-peridotite assemblage was formed close to or within the crust-mantle transition zone near the end of a slow-spreading segment, where thin igneous crust and underlying mantle were affected by intense fracturing and hydrothermal alteration during interaction with seawater (Pertsev et al, 2015).…”

“…A detailed mineralogical and petrographic description, including fluid inclusion data of gabbro-41 is available in Pertsev et al (2015). The main petrogenetic stages reconstructed by the latter authors include: (i) early magmatic crystallization of plagioclase + augite ± enstatite; (ii) late magmatic formation of Ti-bearing hornblende, Fe-Ti oxides and local recrystallization of plagioclase and augite related to reaction with residual melt at 800-900°C;…”

“…The gabbro-41 sample is mainly composed of coarse-grained (3-7 mm sized) primary magmatic plagioclase Pl 1 (44)(45) (Pertsev et al, 2015). The late magmatic hornblende (titanian pargasite) is brown and often occurs as blebs in a clinopyroxene host.…”