Nd, Pb, Hf isotope characteristics and provenance of glacial granitic pebbles from Late Ordovician diamictites in the Taurides, S Turkey

Abstract

Outcrops of the Late Ordovician glacio-marine deposits in Tauride Anatolide Platform contain rare rounded/sub-rounded glacially transported granitic pebbles. Recently determined crystallization ages of the granitic fragments by LA-ICP-MS U-Pb zircon dating fall in two groups, 575 to 600Ma and 700 to 965Ma. Crystallization ages are in the range of juvenile magmatic rocks in the Arabian Nubian Shield except one sample implying pre-0.87Ga magmatic activity. All dated granitic pebbles geochemically show arc-related compositions and juvenile isotopic systematics (whole rock ƐNd(T), Pb-Pb and zircon ƐHf(T) isotopic data). Marginal arc type sources fit well with the geochemical and isotopic data of the granitic pebbles of 700 and 800Ma that have juvenile Hf-TDM and older Nd-TCR modal ages. However, A-type affinity of three samples, ranging from 575 to 600Ma show that they might have been derived from mixing of juvenile mantle and older crustal sources having older Hf-TDM and Nd-TCR modal ages. A 965Ma granitic fragment has the oldest Hf-TDM and Nd-TCR model age(s) implying involvement of pre-Neoproterozoic crustal source(s) in its genesis. These results collectively suggest that the glacio-marine successions in the Tauride Anatolide Platform were eroded from Neoproterozoic granitic/meta-granitic/meta-granodioritic rocks in the northern Nubian Shield (Egypt) and were then transported to the Tauride-Anatolide Platform by the glacial sheets during Late Ordovician time.