Root zone of the sheeted dike complex in the Oman ophiolite

Abstract

[1] In the Oman ophiolite crustal section, a contact zone between the gabbro unit and the volcanics and diabase sheeted dikes, called the root zone of the sheeted dike complex, has been recently mapped at a fine scale in a selected area. The Oman ophiolite is derived from a fast spreading ridge which had a melt lens located between the main gabbro unit and the root zone of the sheeted dike complex. With a few exceptions accounted for, this horizon has a fairly constant thickness, $100 m, and a crude internal pseudo-stratigraphy. At the base of the root zone are isotropic ophitic gabbros interpreted as a thermal boundary layer. This layer is transitional between the magmatic system of the melt lens, convecting at 1200°C, and a high-temperature (<1100°C) hydrothermal system, convecting within the root zone. Above this level, the isotropic gabbros have been, locally, largely molten due to an influx of seawater, at $1100°C, thus generating varitextured ophitic and pegmatitic gabbros. These latter gabbros constitute the upper part of the root zone and are associated with trondjhemitic intrusions as screens in the lower sheeted dikes. Diorites and trondjhemites were also generated by hydrous melting, at temperatures below 1000°C. The whole root zone is a domain of very sharp average thermal gradient ($7°C/m). At the top of the root zone, a new thermal boundary layer, with diabase dikes hydrated in amphibolite facies conditions, separates the preceding high-temperature convective system from the well-known greenschist facies (<450°C) hydrothermal system operating throughout the sheeted dike complex, up to the seafloor. The isotropic gabbros near the base of the root zone are intruded by protodikes with distinctive microgranular margins and an ophitic center. Protodike swarms are exceptional because, intruding a medium at $1100°C, they are largely destroyed by dike-in-dike intrusions and by hydrous melting. However, they demonstrate that this zone was generated by melt conduits issued from the underlying melt lens. Each dike of the sheeted dike complex is thus fed by one protodike. As this zone has been recently drilled by IODP in the eastern Pacific Ocean, a brief comparison is proposed.

Linking process, dimension, texture, and geochemistry in dolomite geobodies: A case study from Wadi Mistal (northern Oman)

“…Magmatic fluids are typically characterized by a 18 O of +6 to +8‰ VSMOW (Hoefs, 2009). There is obducted ophiolite in the study area (Nicolas et al, 2008), but no magmatic intrusions that could explain the stable oxygen isotopic signature of the dolomite studied. As mentioned above, the high 87 Sr/ 86 Sr ratios in D2 dolomites are inconsistent with an ophiolite-derived fluid source (Bosch et al, 2004).…”

Rare earth element evolution and migration in plagiogranites: a record preserved in epidote and allanite of the Troodos ophiolite

“…Epidote growth is in fact an opportunistic form of autometasomatism, whereby the plagiogranite is epidotised by the means of its own exsolved fluids. Growth of epidote from magmatic fluids has been suggested before based on fluid inclusion studies from Troodos (Kelley and Robinson 1990;Kelley et al 1992;Nehlig 1991;Hayes 1996;Petko 1997), Tonga (Banerjee et al 2000;Banerjee and Gillis 2001), and Oman (Stakes and Taylor 2003;Nicolas et al 2008).…”

Root zone of a continental rift: the Neoproterozoic Kebnekaise Intrusive Complex, northern Swedish Caledonides

“…Such gabbro -sheeted dyke transitions have been identified in ophiolites worldwide (e.g. Allen, 1975;Rothery, 1983;Nicolas et al, 2008;Grimes et al, 2013), as well as in present-day oceanic crust (e.g. Teagle et al, 2012).…”