Architecture of the Oman-UAE ophiolite : evidence for a multi-phase magmatic history

The Oman–United Arab Emirates ophiolite is the
world’s largest ophiolite. It is divided into 12 separate faultbounded
blocks, of which the northern three lie wholly or
partly in the United Arab Emirates. Extensive mapping has
shown that the United Arab Emirates blocks contain mantle
and crustal sections which correspond to the classic
‘Penrose conference’ ophiolite definition but which are
cut by a voluminous later magmatic sequence including
ultramafic, mafic and felsic components. Samples from the
later magmatic sequence are dated at 96.4±0.3, 95.74±0.3
and 95.2±0.3 Ma; the early crustal section, which has not
been dated directly, is thus constrained to be older than c.
96.4 Ma. Petrological evidence shows that the early crustal
section formed at a spreading ridge, but the later magmatic
sequence was formed from hydrous magmas that produced
different mineral crystallisation sequences to normal midocean
ridge basalt (MORB). Mineral and whole-rock
geochemical analyses show that the early crustal rocks are
chemically similar to MORB, but the later magmatic
sequence has chemical features typically found in suprasubduction
zone (SSZ) settings. The ophiolite in the United
Arab Emirates thus preserves clear evidence for two stages
of magmatism, an early episode formed at a spreading
centre and a later episode associated with the onset of
subduction. Similar two-stage magmatism has been recognised
in the Oman sector, but the United Arab Emirates
contains the most voluminous SSZ magmatism yet described
from this ophiolite.