Accretion of Oman and United Arab Emirates ophiolite – Discussion of a new structural map


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Abstract

This study is altogether an extended legend forthe folded maps incorporated in this volume, a review of the current knowledge on the Oman-United Arab Emirates ophiolite belt, and a new synthesis at the scale of the entire belt. Following a brief description of the petrological and structural units composing the ophiolite, the content of the three structural maps (planar structures, linear structures and dikes) is presented. Next, we discuss the various constraints introduced by these data in view of a synthesis of the ophiolite belt in terms of an ocean floor spreading system. Because they are the link between the factual results summarised in the maps, and the ridge models, these constraints are critical (and are central to the structural analysis of ophiolites). They introduce severe limits to possible ridge models such as those proposed in the conclusion. After being reassembled in a best geometrical and structural fit, the belt is parted into three domains (Figure 1). The south-eastern and central domains (from Wadi Tayin to Haylayn and possibly Sarami massifs) incorporate a 40–50 km-wide and possibly over 200 km long new ridge segment, oriented NW–SE, which is opening into a 1–2 My older lithosphere oriented NE–SW. The northern domain (from Khawr Fakkan to Hilti massifs) is well explained by a model of propagating (Aswad) and failing (Fizh) ridge segments of nearly parallel NNW-SSE orientation which are separated by a 10–20 km-wide transform zone covering the north of Fizh massif. This new synthesis integrates and updates the local syntheses published so far. It illustrates again the contrast between locally simple ridge segments organised around mantle diapirs and the tectonic complexity of the two larger domains, with, as an example, sheared mantle, vertical Moho and dismembered lower crust with hydrous contamination, near the tip of ridge propagators. The relation between the northern and central-southern domains is obscure because the paleomagnetic results suggest that, with respect to the central-southern domain, the northern domain should have rotated 130° clockwise. Such a large rotation of a 200 km long domain is difficult to explain, inasmuch as the age constraints seem to restrict the possible duration of the rotation to a couple of Myr. The preferred model consists in a progressive clockwise rotation during tectonic accretion of increasingly larger blocks. This is initiated in the northern massifs, progressing over 1–2 Myr, southward to finally integrate the entire ophiolite.

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