A hidden Tonian basement in the eastern Mediterranean: Age constraints from U–Pb data of magmatic and detrital zircons of the External Hellenides (Crete and Peloponnesus)

Abstract

A newly discovered Precambrian basement of the External Hellenides (Peloponnesus) is composed of mica schist, quartzite and meta-greywackes intruded by Cambrian granitoids (524+6/−5Ma). As such Cambrian intrusions are frequent in the eastern Mediterranean, but are lacking in northern Africa, they are interpreted to result from a Cadomian magmatic arc that was situated along the northern margin of East Gondwana. This arc was rifted off from Gondwana in Early Paleozoic times. The sedimentation age of the meta-greywackes is bracketed between the age of their youngest detrital zircons (541±7Ma, Crete; 546±7Ma, Peloponnesus) and the intrusion of the Cambrian granitoids. The detrital zircon age spectra are dominated by two significant age peaks at ca. 600Ma and ca. 1Ga, which are characteristic for Cambrian platform sediments of Jordan, Israel and Lybia and for the Minoan-type terranes with an East Gondwana provenance. The high amount of 1Ga old zircons points to a Tonian basement as provenance, which is situated at the northern margin of the Arabian Nubian Shield (N'Sinai) and the Sahara Metacraton, today hidden under Mesozoic cover. There is a good correlation between the detrital age spectra of the Late Ediacaran/Cambrian basement of the External Hellenides and of the eastern Mediterranean realm. Apart from the Hellenides and Turkey (Menderes, Sakarya), the Minoan-type terranes have also been found in Sicily, Sardinia, and NW Iberia. Our review of detrital zircon ages obtained from Europe and northern Africa revealed four different domains during Early Cambrian times, which have affinities to (1) Baltica, (2) South-America (Avalonian-type terranes), (3) W Africa (Armorican-type terranes), and (4) E Gondwana (Minoan-type terranes and the platform sandstones of E Africa).