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Concordia diagram, together with the frequency and probability density distribution plot, show different populations of zircons with ages ranging between c . 538–622 (Figures 10c and 10d). A coherent group of 16 crystals represents the highest frequency and is consid- ered to reflect the crystallization age of the metatonalite. These 16 crystals provide a Concordia age of 565 ± 2.1 Ma (Figure 10 e) and a weighted average of 206 Pb/ 238 U ages of 566 ± 2.9 Ma (Figure 10f). Zircons older than this group of 16 orthomagmatic crystals are interpreted to be inherited. But their ages are not greatly higher, ruling out a tectonic setting in which much older igneous rocks existed. Such a setting is compatible with an active magmatic arc. The few zircons with ages of c . 540 Ma are considered metamorphic, having formed at the end of the episodes of deformation and metamorph- ism that affected the Mérida Ophiolite (see below). 5.3. Hf isotope data results The analysed zircon crystals show generally positive values of Ɛ Hf (t), but these values are different in the OM-2 metagabbro relative to the OM-1 metatonalite. Ɛ Hf (t) values in the most consistent metagabbro zircon Figure 9. Backscattered images of zircons analyzed in metagabbro OM-2 and metatonalite OM-1 (a and b, respectively). 206 Pb/ 238 U ages (red circles; numbers reflect age in Ma) and ɛ Hf (t) values (green circles) are shown. 16 R. ARENAS ET AL. &KDSWHU