A fossil melt lens in the Oman ophiolite: Implications for magma chamber processes at fast spreading ridges

摘要: From seismic evidence we know that a small body of magma is present at mid-crustal levels beneath most fast spreading ridges, and this sill or melt lens overlies much broader area hot but largely solid material (a ‘crystal mush’) constitutes the lower ocean crust. Beyond this, however, have little direct knowledge physical chemical processes operate in below lens, nor role plays storage aggregation mid-ocean ridge basalts (MORB). We here offer constraints on transport, modification residence ridges from coupled structural geochemical study through crustal section Oman ophiolite, concentrating uppermost plutonic rocks transition into sheeted dykes. find almost entire suite - layered gabbro, ‘high-level gabbro’ dominated by cumulate containing very low proportions trapped interstitial melt. The exception to part section, within ∼150 metres base dyke complex, which level gabbros instead display marked heterogeneity structure, texture composition, generally basaltic composition occur for first time. Associated pegmatitic ferrogabbros formed situ fractionation these liquids. This horizon passes up more homogeneous microgabbroic facies, also isolated asymmetric doleritic chilled margins are found, thence argue thin heterogeneous gabbro fossilised pooled liquids net (Mg# ∼65) expelled crystal mush beneath. Existing models suggested steep fabrics observed subsidence originally horizontal cumulus layers not supported field relationships. Instead propose record buoyant ascent pile (probably porous flow) reflect crystallisation essentially situ, without significant vertical transport mush. Low residual porosities sub-melt region imply efficient extraction liquid least episodically high permeabilities upper