U-Pb laser ablation inductively coupled plasma mass spectrometry ages and Hf isotopes in zircons were used to constrain the nature of two geological units representative of the basement of the Central Cordillera of Colombia. Graphite-quartz-muscovite schists from the Cajamarca Complex show inherited detrital zircons supplied mostly from Late Jurassic (ca. 167 Ma), Ediacaran (ca. 638 Ma), and Tonian (Grenvillian; ca. 1000 Ma) sources. These marine volcanosedimentary deposits form an N-trending metamorphic belt in fault contact to the east with orthogneisses and amphibolites of the Tierradentro unit. Zircon U-Pb determinations of the Tierradentro rocks-previously interpreted as Grenvillian basement slices-yielded crystallization ages between 271 and 234 Ma. Initial Hf data reveal that the Tierradentro unit shares isotopic characteristics similar to other Permo-Triassic rocks of the Central Cordillera. In contrast, inherited detrital zircons from the Jurassic metasedimentary rocks suggest that their sources are distinct from the plutonic rocks that crop out in the Central Cordillera with Jurassic crystallization ages. Large xenoliths of the Tierradentro unit within the Ibagué batholith indicate that the granodioritic magma mostly intruded a Permo-Triassic basement possibly by exploiting the Otú-Pericos fault. The Jurassic metasedimentary belt is correlated further south with a similar sequence in the Ecuadorian Andes named Salado terrane.

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A Late Palaeozoic accretionary prism, formed at the southwestern margin of Gondwana from Early Carboniferous to Late Triassic, comprises the Coastal Accretionary Complex of central . This fossil accretionary system is made up of two parallel contemporaneous metamorphic belts: a high-pressure/low temperature belt (HP/LT -Western Series) and a low pressure/high temperature belt (LP/HT -Eastern Series). However, the timing of deformation events associated with the growth of the accretionary prism (successive frontal accretion and basal underplating) and the development of the LP/HT metamorphism in the shallower levels of the wedge are not continuously observed along this paired metamorphic belt, suggesting the former existence of local perturbations in the subduction regime. In the Pichilemu region, a well-preserved segment of the paired metamorphic belt allows a first order correlation between the metamorphic and deformational evolution of the deep accreted slices of oceanic crust (blueschists and HP greenschists from the Western Series) and deformation at the shallower levels of the wedge (the Eastern Series). LP/HT mineral assemblages grew in response to arc-related granitic intrusions, and porphyroblasts constitute time markers recording the evolution of deformation within shallow wedge material. Integrated P-T-t-d analysis reveals that the LP/HT belt is formed between the stages of frontal accretion (D 1 ) and basal underplating of basic rocks (D 2 ) forming blueschists at c. 300 Ma. A timeline evolution relating the formation of blueschists and the formation and deformation of LP/HT mineral assemblages at shallower levels, combined with published geochronological/thermobarometric/geochemistry data suggests a cause-effect relation between the basal accretion of basic rocks and the deformation of the shallower LP/HT belt. The S 2 foliation that formed during basal accretion initiated near the base of the accretionary wedge at~30 km depth at c. 308 Ma. Later, the S 2 foliation developed at c. 300 Ma and 15 km depth shortly after the emplacement of the granitoids and formation of the (LP/HT) peak metamorphic mineral assemblages. This shallow deformation may reflect a perturbation in the longterm subduction dynamics (e.g. entrance of a seamount), which would in turn have contributed to the coeval exhumation of the nearby blueschists at c. 300 Ma. Finally, 40 Ar-39 Ar cooling ages reveal that foliated LP/HT rocks were already at~350°C at c. 292 Ma, indicating a rapid cooling for this metamorphic system. Key words: accretionary prism; central Chile; paired metamorphic belt; P-T-t-d path. INTRODUC TIONThe temporal and spatial relationships of thermal and mechanical processes in orogens have been a topic of debate for the past 40 years. Our understanding of accretionary wedge dynamics remains incomplete. More specifically the relation between the two main geodynamic processes, namely (i) the formation of thermally-contrasted (pene-) contemporaneous metamorphic belts (sensu Miyashiro, 1961;Maruyama, 1997; and...