CRUSTAL EVOLUTION AND TERRANE CORRELATION IN THE EASTERN ARABIAN SHIELD, YEMEN - GEOCHRONOLOGICAL CONSTRAINTS

Ion-microprobe U-Pb zircon and Ar-40-Ar-39 geochronology is presented for two gneiss terranes and an island are terrane in the Arabian Shiel d of Yemen. These data confirm the presence of late Archaean (c. 2.95- 2.55 Ga) crust in the Al-Mahfid (eastern) terrane, previously inferred from Nd model age determinations; a minor late Archaean component in the Abas (western) terrane is revealed by a single c. 2.6 Ga zircon co re. No ages have been obtained corresponding to documented c. 1.8-1.4 Ga events in neighbouring Somalia and Saudi Arabia, but both gneiss te rranes are strongly affected by c. 760 Ma Pan-African reworking which is recorded by Pb loss in zircons of the Al-Mahfid terrane and zircon crystallization ages of granitic gneisses and sheets in both the Al-Ma hfid and Abas gneiss terranes. Ar-40-Ar-39 ages obtained from intrusiv e rocks in the intervening Al-Bayda are terrane provide a lower age li mit of 615 Ma upon terrane assembly. Correlation of pre-Pan-African ev ents within the Arabian-Nubian Shield remains problematic because of t he still limited sampling and available geochronology.