Zircon U-Pb geochronology and Nd isotope systematics of the Abas terrane, Yemen : Implications for Neoproterozoic crust reworking events

High-spatial-resolution secondary-ion mass spectrometry (SIMS) U-Pb zircon ages, whole-rock Nd isotopic and geochemical data are reported for granites and granitic gneisses from a traverse across the Abas terrane, Yemen, a part of the Precambrian basement of southern Arabian Peninsula. SIMS U-Pb dating identifies two magmatic episodes, the first at c. 790-725 Ma represented by granitic gneisses, the second clearly post-tectonic at c. 625-590 Ma. The oldest sample in the post-tectonic group is slightly deformed while younger samples are undeformed indicating that penetrative deformation ceased at c. 625 Ma in the Abas region. Whole-rock(Nd)(t) values between -11 and +0.8, Nd model ages of 1.70-1.13 Ga indicate a significant contribution of evolved continental material in the genesis of the Abas granitoids, unlike most of the juvenile Arabian-Nubian Shield (ANS), although there are few inherited zircons. Secular variation in epsilon(Nd)(t)reflects a change in magma source with increasing juvenile magma and diminishing crustal input during post-tectonic (625-590 Ma) magmatism. The combination of subduction zone chemistry, absence of older rocks, paucity of inherited zircons, evolved Nd isotopic signatures and the I-type characteristics of the samples suggest that assimilation occurred at depth.