RAPID EXTENSION RECORDED BY COOLING-AGE PATTERNS AND BRITTLE DEFORMATION, NAXOS, GREECE

The metamorphic core complex exposed as the island of Naxos in the Aeg ean Sea records an unusually complete sequence of structures developed as a result of continental extension. The structures formed during Mi ocene rise and cooling from ductile, upper amphibolite facies and anat ectic conditions to brittle neat-surface conditions beneath the Naxos detachment fault. Top-to-the-north ductile fabrics in the footwall, wh ich initially developed during amphibolite facies prograde metamorphis m, were overprinted by a succession of north directed, normal sense lo wer-temperature brittle structures as the footwall was tectonically un loaded and unroofed. Pseudotachylite and cataclasite formation, brittl e faulting, alteration, and erosion of the footwall occurred during co ntinued slip and tectonic denudation. Neogene conglomerate and megabre ccia, in part derived from exhumation of this footwall, lie structural ly above the peripheral Naxos fault. Published K-Ar and Ar-40/Ar-39 ag es for hornblende, white mica, and biotite in the footwall decrease no rthwestward; apparent ages 17-50 Ma in the southeast correspond to are as of low metamorphic grade where preextension argon was partially ret ained. Published ages 16-10 Ma in higher-grade rocks of the domal core in the north are cooling ages that for each of the three minerals sho w a component of younging in the NNE direction of extension. Assuming this is the direction of unroofing, we interpret the rate of this youn ging as the fault slip rate as the footwall rocks moved >20 km SSW rel ative to their hanging wall along the base of the Naxos detachment fau lt. The calculated rates of slip average 5-8 mm/yr, comparable to maxi mum rates reported in the Basin and Range province.