40Ar/39Ar ages from blueschists of the Jambaló region, Central Cordillera of Colombia: implications on the styles of accretion in the Northern Andes

A. BUSTAMANTE, C. JULIANI, C.M. HALL, E.J. ESSENE

Abstract


This paper presents the first argon dating of blueschists from the Jambaló area (Cauca Department) in the Central Cordillera of the Colombian Andes. Step-heating 40Ar/39Ar spectra were obtained for mica from several lenses of blueschists including greenschist facies rocks. The blueschists are mainly constituted of preserved lenticular cores in strongly mylonitic rocks, which resulted from retrometamorphic processes that affected the high pressure rocks during their exhumation. The majority of 40Ar/39Ar data points to metamorphic ages close to 63±3Ma, but some ages are older than 71Ma. These Maastritchtian–Danian ages correspond to the timing of exhumation of the blueschists near metamorphic peak conditions, because the dated paragonite and phengite crystallized during development of the mylonitic foliation. The continuous exhumation of this blueschist belt between 71–63Ma reflects the flow on an accretionary system/subduction channel environment that was interrupted by the collision of an intra-oceanic arc with the continental margin. Regional geological correlations suggest that this arc–continent collision also took place in Ecuador. This collisional event, although synchronous with other arc–continent collisions in the Northern Andes, was apparently not related to the formation of the great Caribbean arc, but to an arc built in the southeastern margin of the Caribbean plate

Keywords


Blueschists; Colombian Andes; Jambaló area; 40Ar/39Ar geochronology

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DOI: http://dx.doi.org/10.1344/105.000001697

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Geologica Acta (ISSN-1695-6133)
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