 2002 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. Geology; March 2002; v. 30; no. 3; p. 235–238; 3 figures; Data Repository item 2002019. 235 African provenance for the metasediments and metaigneous rocks of the Cyclades, Aegean Sea, Greece Sue Keay* Department of Earth Sciences, University of Queensland, St. Lucia, QLD 4072, Australia Gordon Lister Australian Crustal Research Centre, Monash University, Clayton, VIC 3128, Australia ABSTRACT U-Pb geochronology on detrital and inherited zircons from metasediments as well as gneissic and metaigneous basement rocks of the Cyclades, Aegean Sea, Greece, defines several periods of crustal growth prior to the Carboniferous. These ages are consistent with Cycladic rocks being derived from the northern margin of Gondwana. There is a distinct Mesoproterozoic age gap evident in zircons from the 25 samples considered. This is characteristic of the West African craton, and we suggest it will also prove characteristic of the Aegean region. This Mesoproterozoic age gap may be used as a tool in terrane reconstruction to distinguish crustal material derived from different parts of Gondwana. Keywords: zircon, geochronology, provenance, Cyclades, tectonic models. Figure 1. Generalized tectonic map of Aegean region (modified from Du ¨ rr et al., 1978; Robertson and Dixon, 1984). Inset shows location of Cycladic islands be- tween Greece and Turkey, part of Attic-Cycladic massif, possible extension of Menderes Massif, and Pelagonian zone. Seven islands from which analyzed sam- ples were obtained are highlighted. INTRODUCTION Dating detrital minerals in sediments is a common method used to determine sedimen- tary provenance (Hurley et al., 1961), to de- fine periods of crustal growth (Tatsumoto and Patterson, 1964), or to trace the origin of al- lochthonous terranes (Krogh and Keppie, 1990). Attempts to trace crustal evolution have also been made by dating inherited zir- con grains in granites (Pidgeon and Aftalion, 1978) and orthogneisses (Compston and Kro ¨- ner, 1988). In this paper the crustal evolution of rocks from the Cyclades, Aegean Sea, Greece, is determined by dating detrital and inherited zircons from gneissic basement and overlying tectonic slices of metasediments and metavolcanic units. This is the first study to define the early geological evolution of Cy- cladic continental crust. In pre-Mesozoic time, the continental blocks of the Hellenides (including the Cyc- lades) (Fig. 1) are thought to have formed part of the northern margin of Africa (see Robert- son and Dixon, 1984). Tracing the dispersal of microcontinental blocks derived from the northern margin of Gondwana is difficult due to their complex geological histories. Pre- Mesozoic plate reconstructions are particular- ly difficult (Dercourt et al., 1986), given that the outcrop patterns have been disrupted by the Variscan and Alpine orogenic events, and paleontological and paleomagnetic controls in many areas such as the Cyclades are absent (Du ¨rr et al., 1978; Morris and Anderson, 1996). However, the general location of the major continental blocks is well defined, and the Precambrian geological evolution of the Cyclades is expected to be broadly similar to that of the sparsely dated North African crust. *Corresponding author’s e-mail: sue@earth.uq. edu.au. GEOLOGIC SETTING Metamorphic core complexes in the Cyc- lades form the central part of the Attic- Cycladic Massif, which extends through the central Aegean from Attica in southeastern Greece to Turkey (Fig. 1). Correlations be- tween the Pelagonian zone, the Menderes Massif, and the Cyclades have been suggested due to the geological similarities between these terranes (Fig. 1) (Papanikolaou and De- mirtasli, 1987; Candan et al., 1997). While complicated structures make it difficult to cor- relate between islands, three main lithological groups have been distinguished (Fig. 2) (Du ¨rr et al., 1978). An upper unit at the highest structural levels usually occupies the lowest topography as scattered outcrops of fault- juxtaposed unmetamorphosed sedimentary and ophiolitic rocks. At structurally interme- diate levels the Mesozoic series consist of a sequence of intensely deformed platform sed- iments, including neritic carbonates, psammi- tic to pelitic sediments, and volcanics meta- morphosed to eclogite-blueschist facies. The above units structurally overlie an inferred pre-Alpidic basement consisting of complex schists, gneisses, and amphibolites (Andries- sen et al., 1987; Henjes-Kunst and Kreuzer, 1982) (Fig. 1). These different tectonic slices have been juxtaposed along low-angle normal faults forming metamorphic core complexes (Lister et al., 1984). Basement and series rocks have undergone at least two sequences of regional metamorphic events. A sequence of high-pres- sure blueschist to eclogite facies metamorphic episodes (M 1A –M 1D ) occurred from ca. 65 to 32 Ma, followed (ca. 32–15 Ma) by a se-