2.1. Geological Setting
 The Oman ophiolite is the best-exposed piece of oceanic lithosphere at the surface of the Earth and also, one of the best-documented ophiolite, after the systematic work of several research groups (see for instance Boudier and Nicolas , Coleman and Hopson , Glennie et al. , Lippard et al. , Peters et al. , and, more recently, Boudier and Juteau ). It represents part of the Neo-Tethys ocean obducted onto the Arabian plate at the end of the Cretaceous (∼78 Myr [Hacker et al., 1996]).
 The ophiolite is made up of several large (up to 4500 km2) massifs aligned along the Oman coast (Figure 1b). Each massif exposes a more or less complete ophiolitic sequence, comprising a thick mantle section, gabbros and sheeted dykes topped by a 0.5–2 km thick extrusive sequence and interbedded oceanic sediments. Three magmatic sequences within the lavas constituting the extrusive section can be distinguished using petrographic and geochemical studies.
 The lower sequence, V1 [Beurrier, 1987; Ernewein et al., 1988] also called Geotimes by Pearce and co-workers [Alabaster et al., 1982; Lippard et al., 1986; Pearce et al., 1981] represents most of the exposed extrusives (>60% [Nicolas et al., 2000]). It consists mainly of poorly vesicular brownish pillow basalts with scarce massive lava flows. Its composition is close to mid-ocean-ridge basalts -MORB- [Alabaster et al., 1982; Einaudi et al., 2000; Ernewein et al., 1988]. The eruption of V1 lavas is associated with the accretion of the Oman paleo-ridge, dated at 94–95 Ma [Hacker et al., 1996].
 The middle sequence outcrops mainly in the northern part of the ophiolite and represents most of the remaining lavas (>35%). It is separated from the V1 sequence by a more or less continuous layer of pelagic sediments. Three units, Lasail, Alley and clinopyroxene-phyric, were recognized by Pearce and co-workers [Alabaster et al., 1982; Lippard et al., 1986; Pearce et al., 1981] and later merged together under the same name, V2, by Beurrier  and Ernewein et al. . V2 lavas are of tholeiitic affinity and are distinguished from V1 by low-Ti and low incompatible trace element contents [Beurrier et al., 1989; Ernewein et al., 1988; Lippard et al., 1986]. V2 lavas were emplaced shortly after the V1 lavas (<2 Ma [Hacker et al., 1996]). They are thought to represent either the first stages of island arc volcanism in an immature arc environment [Beurrier et al., 1989; Pearce et al., 1981], either the product of the hydrous melting of the over-ridden lithosphere during intraoceanic thrusting at the Oman paleo-ridge [Boudier et al., 1988; Ernewein et al., 1988].
 The uppermost sequence, Salahi [Alabaster et al., 1982], later defined as V3 [Beurrier, 1987; Ernewein et al., 1988], is volumetrically the least significant. It has been observed only in the Salahi area in the Hilti massif, where it is separated from the lower sequences by a layer of pelagic sediments. It comprises alkaline to transitional within-plate basalts and they are thought to result from intraplate seamount volcanism, produced after the beginning of oceanic thrusting but preceding the end of the obduction of the ophiolite onto the Arabian continental margin [Ernewein et al., 1988; Lippard et al., 1986].
 Hydrothermal circulations, contemporaneous with the various phases of volcanic activity, induced secondary recrystallization in the lava and interbedded sediments [Alabaster and Pearce, 1985; Pflumio, 1991].
Table 1. Location of Sampled Areas
|Site Name||Massif||Lava Type||Location|
 Distinction between V1 and V2 units was made according to the 1:50 000 geological maps published by the Bureau de Recherches Geologiques et Minieres  and on the basis of the field criteria (sample color, flow jointing, and erosion resistance) defined by Alabaster et al. . However, the V1 and V2 volcanic units are often hardly distinguishable in the field and to find irrefutable discrimination criteria is one of the challenges of the study of the Oman ophiolite extrusive section. Even petrologic criteria, such as texture and clinopyroxene composition, are inefficient because both V1 and V2 basalts are hyalopilitic and contain identical low Ti and Na endiopside. Furthermore their groundmasses cannot be used because alteration has obliterated their original texture: both are altered to chlorite, quartz, hematite, Fe hydroxide, epidote, prehnite and zeolite. The best approach to discriminate the two series is geochemical analysis [Alabaster et al., 1982; Ernewein et al., 1988; Lippard et al., 1986; Pearce et al., 1981].