Continental arc magmatism dwindled after ~430 Ma and terminated at ~415 Ma, coevally with most of the western margin of Gondwana. Subsequent retrogression resulted from localised back-arc or intra-arc extension at ~ 453 Ma, when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement. Peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at ~477 Ma and the intrusion of synkinematic granitoids until ~472 Ma. The oldest Palaeozoic arc magmatism is recorded at ~500 Ma, and was followed shortly by Barrovian metamorphism. These data show that the basement rocks of these massifs are autochthonous to Gondwana and share a similar tectono-magmatic history with the Gondwanan margin of Peru, Chile and Argentina, which evolved during the subduction of oceanic lithosphere of the Iapetus Ocean. We present new zircon U–Pb (ICP-MS) data from 52 igneous and metamorphic rocks, which we combine with whole rock geochemical and Pb isotopic data to constrain the tectonic history of the Precambrian to Mesozoic basement of the Mérida Andes and the Santander Massif. A general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of Gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the Mérida Andes and the Santander Massif. However, terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains. Keywords: Geochronology Colombia Merida Andes Santander Massif Iapetus Ocean Palaeozoic The Palaeozoic to Mesozoic igneous and metamorphic basement rocks exposed in the Mérida Andes of Venezuela and the Santander Massif of Colombia are generally considered to define allochthonous terranes that accreted to the margin of Gondwana during the Ordovician and the Carboniferous.
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