High-temperature metasomatism during magmatic-hydrothermal transition observed in lower crustal gabbros, IODP Hole U1309D, Mid-Atlantic Ridge: Implication of native Ni

Abstract

Incipient stage of interaction between gabbros and fluids in mid-ocean ridge environments has not been fully described. We found high-temperature metasomatic veins in lower crustal gabbros recovered from 1400-m-long IODP Hole U1309D on the Mid-Atlantic Ridge. Furthermore, we found a tiny grain of native Ni within the metasomatic vein. It is most likely that the metasomatism in the incipient stage of gabbro-fluid interaction was related to CH4-bearing reducing fluids separated from evolved intercumulus or interstitial melts.