Tuesday, February 25, 2014

Evidence of a Silurian to Triassic Gondwana Origin Superfan Formation in the Eastern Mediterranean

The dispersal of the Gondwana Super-fan System in the eastern Mediterranean: New insights from detrital zircon geochronology


Kydonakis et al


We report here new LA-ICPMS detrital zircon U–Pb ages of a quartzite from the autochthon of Peloponnesus (Feneos locality), southern Greece. The rock classifies as a mature quartz arenite and belongs to an original shale–sandstone succession now metamorphosed into a phyllite–quartzite unit. Zircon age clusters at 0.52–0.75, 0.85, 0.95–1.1, 1.75–2 and 2.4–3 Ga point at the Saharan Metacraton and the Transgondwanan Supermountain as contributing sources; the youngest concordant grain is 522 Ma old. Our data collectively suggest deposition during the Cambro-Ordovician in a collisional setting and are in excellent agreement with those of the virtually intact Cambro-Ordovician sandstone–shale sequences of Libya (Murzuq and Kufrah basins) and the Middle East (Israel and Jordan), interpreted to have been deposited in the Gondwana Super-fan System which draped the northern Gondwanan periphery from ~ 525 to 460 Ma. By contrast, re-evaluating the available zircon age-distribution pattern and depositional setting of an analogous sequence forming the autochthon of north-central Crete (Galinos beds) we demonstrate that it was originally deposited in a completely different setting, i.e. in an accretionary/fore-arc complex outboard of the south Laurussian active margin (Pelagonia) during the Late Carboniferous. Comparing similar Cambro-Ordovician metasiliciclastic rocks from north-eastern Crete (Sfaka paragneiss), north-central continental Greece (Vertiskos terrane), north-western Turkey (central Sakarya terrane) and the Romanian Carpathians we show that their detrital zircon distribution patterns testify to an original depositional setting similar to that of Peloponnesus (Feneos), Libya and the Middle East. Using key time-frames from previously published palaeogeographic reconstruction models we are able to trace in space and time the Palaeozoic–Early Mesozoic wondering paths of the aforementioned sequences. Thus, time- and facies-equivalent rocks presently cropping out in the eastern Mediterranean share a common provenance from the Gondwana Super-fan System which was diachronously dispersed between Early Silurian and Early Triassic.

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