Geochronological and isotopic evidence for Paleoproterozoic and Archean crust in the eastern Arabian Shield of Saudi Arabia: The Khida terrane
|Location||International Geological Congress,oslo 2008|
|Author||Whitehouse, Martin۱; Stoeser, Douglas۲; Stacey, John۲|
|Holding Date||29 September 2008|
Pb isotope data from Neoproterozoic granitoids has long indicated that the Khida terrane of the eastern Arabian Shield of Saudi Arabia is underlain by Paleoproterozoic to Archean continental crust (Stoeser and Stacey, 1988). We present here results from field observations in the Muhayil area combined with ion-microprobe U-Pb zircon geochronology, Nd whole-rock, and feldspar Pb isotope data that further elucidate the pre-Neoproterozoic evolution of the Khida terrane.
The Muhayil area comprises three Paleoproterozoic units, the Libab complex, the Muhayil anorthosite, and the Muhayil granite. The Libab complex consists of quartzitic metasediments intercalated with leucogranite gneisses. On the basis of in situ zircon analysis of thick rims, the probable magmatic protolith age of the gneisses that intrude the metasediments is ca. 1.85 Ga, with an older component(s) evidenced by >2.4 Ga zircon cores and a Sm-Nd depleted mantle model age (tDM) of ca. 3.0 Ga. Samples from the more than 50 km long Muhayil anorthosite are barren of zircon but Nd (tDM of ca. 2.3-2.6 Ga) and feldspar Pb isotopic systematics indicate an early Paleoproterozoic component. The adjacent Muhayil granite yields a zircon age of 1660 ± 10 Ma. Its Sm-Nd depleted mantle model age (tDM) of ca. 2.5 Ga, together with modelling of feldspar Pb-isotopic data, requires a late-Archean or early Paleoproterozoic source region. The similar old crustal source for the Muhayil granite and anorthosite suggests a genetic relationship, however, the contact between them cannot be observed and the presence of a suite of dykes in the anorthosite that are apparently absent in the granite indicates an older age for the anorthosite.
The Khida terrane contains the only documented exposures of Paleoproterozoic rocks within the Arabian basement. Their occurrence in only one outcrop area, however, complicates regional correlations. Late Archean detrital zircons and required source region for the plutonic rocks suggest a relationship to the gneisses of the Al-Mahfid terrane of eastern Yemen, that have been dated at ca. 2.55 Ga (U-Pb zircon, Whitehouse et al., 1998).