Rb-Sr and Ar-40/Ar-39 mineral ages of granitoid intrusives in the Mabujinaunit, central Cuba: Thermal exhumation history of the Escambray Massif

We present new and critical isotopic data for late- to postkinematic granit oid intrusions and their epidote-amphibolite-facies country rocks (Mabujina unit) in central Cuba. The Mabujina unit tectonically overlies a nappe seq uence of high-pressure (HP) metamorphic rocks in the Escambray Massif. Thes e granitoid rocks have a variable granodioritic to granitic composition, ar e generally rich in large ion lithophile elements, and resemble normal mido cean ridge basalts in their high field strength element concentrations. On the basis of low initial Sr-87/Sr-86 ratios, it is inferred that Sr is very likely to be mantle derived. Primary coarse-grained muscovite from pegmati tic intrusions yields Rb-Sr crystallization ages of similar to 86-88 Ma (Ri o Jicaya region) and similar to 80-82 Ma (Yayabo region). Laser Ar-40/Ar-39 ages for coarse- and fine-grained white mica (72-74 Ma) and Rb-Sr ages for biotite (73 Ma) outline the cooling history of these granitoids and their country rock. Dating of pegmatites within the Mabujina unit places minimum age limits on the epidote-amphibolite-facies metamorphism, on the end of th e magmatic activity and initial collision of the Cretaceous island arc, and on the HP metamorphism and juxtaposition of tectonometamorphic units in th e Escambray Massif. The combination of the new thermochronological data wit h constraints from the geological record indicates thermal relaxation durin g the initial stages of the arc-continent collision.