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[1] Tertiary convergence, high-pressureÀlow-temperature (HP-LT) metamorphism and subsequent exhumation in the internal Western Alps were concurrent with detrital deposition in foreland basins at the external periphery of the orogen. In the present work we have probed the geochronology and chemistry of white mica grains and metamorphic pebbles from the foreland basins of SE France in order to gain additional perspective on exhumation rates and mountain building processes in the internal domain of the Tertiary orogen. Our data indicate that throughout the Tertiary these basins were mainly fed from a relatively low pressure source, dominated by Si-poor micas yielding pre-Alpine 40 Ar/ 39 Ar ages. Small amounts of detritus composed of high-pressure minerals and pebbles are first detected in early Oligocene ($30À32 Ma) strata of the Barrême basin. The 40 Ar/ 39 Ar geochronology of phengites from garnet-blueschist pebbles from these strata yielded 34 ± 3 Ma ages indicating rapid ascent and exposure of HP-LT rocks in the internal part of the orogen shortly after metamorphism. To explain the preponderance of pre-Alpine micas alongside the rare presence of Alpine HP-LT detritus we suggest that the general architecture of the Western Alps, whereby inner HP-LT metamorphic units are cut off from the SE France basins by a low-grade lid of Brianconnais back thrusts, was rapidly built in the early Oligocene and did not change significantly since then.

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The timing and mode of uplift of the Troodos ophiolite are constrained by low-temperature thermochronology combined with geomorphic analysis. Zircon (U-Th)/He and apatite fission track cooling ages in the Troodos plutonic sequence are all Cretaceous (83-106 Ma) and within error of published zircon U-Pb crystallization ages. This indicates early cooling of the oceanic crust and termination of spreading axis magmatism at~90 Ma. Apatite (U-Th)/He ages decrease with reconstructed crustal depths from~40 Ma near the top of the sheeted-dike complex to~4 Ma within the mantle sequence. A prominent inflection point in the age versus depth curve defines the bottom of the exhumed helium partial retention zone and records the onset of rapid exhumation of the main Troodos massif at 6 ± 2 Ma. Inverse thermal modeling supports this conclusion, indicating that the timing of uplift is earlier than previously estimated. The boundaries of the mantle sequence exposed in the core of the Troodos structure closely overlap the boundaries of a concentric zone delineated by high local relief and higher channel steepness indices, indicating differential exhumation and uplift of this area relative to its surroundings. This zone also overlaps with a prominent negative Bouguer gravity anomaly. The timing and pattern of the Troodos ophiolite uplift suggest that it is driven by serpentinite diapirism, possibly triggered by Miocene reactivation of subduction along the Cyprean Arc. The worldwide ubiquity of suprasubduction zone ophiolites may thus reflect the importance of extensive serpentinization at the overthrusting mantle wedge in obduction processes.