SNSF | P3 Research Database

Northern Andes; terrane accretion; thermochronology; geochronology; geochemistry; Caribbean Plateau; exhumation; accretion; Nortern Andes

English title	Accretionary and post-accretionary cooling, exhumation and tectonic history of the central and western Andes of Colombia
Applicant	Spikings Richard A.
Number	107596
Funding scheme	Project funding
Research institution	Département des sciences de la Terre Université de Genève
Institution of higher education	University of Geneva - GE
Main discipline	Geochemistry
Start/End	01.04.2005 - 31.03.2008
Approved amount	175'550.00

Lead

Lay summary
The cordilleras of the Northern Andean Segment (NAS) are a juxtaposition of ocean island arcs, an oceanic plateau and rocks of the paleo-continental margin. This project aims to determine the pre-, syn- and post-accretionary history of individual terranes in Colombia, with an emphasis on determining the timing and duration of accretionary events, and quantifying cooling and exhumation rates prior to and during periods of Andean orogenesis. A major, N-S trending, regional scale, topographic depression (Interandean Valley) exists along a suture between oceanic and continental provinces throughout the NAS, although the nature of its basement is unknown. Published hypotheses propose that the valley is composed of microplates and can be considered as a separate terrane(s), (Toussaint & Restrepo, 1994). However, we suggest that this interpretation is incorrect because it is based on inaccurate radiometric data and limited geochemical analyses. Spikings et al. (2005) proposed that the valley is floored by a regional scale, tectonised zone defined by a mélange, which has captured rocks from both the continental and oceanic provinces. The project applicants, and a single PhD student have completed a sampling survey along several traverses across the Central and Western cordilleras and the Interandean Valley in Colombia. A thermochronological (40Ar/39Ar, fission-track and (U-Th)/He)) study of various mineral phases extracted from crystalline rocks is being combined with petrological studies to constrain the thermal, faulting and exhumation history of fault blocks within the cordilleras. This work is being combined with geochemical and geochronological analyses of crystalline rocks that are exposed within the Interandean Valley in Colombia and Ecuador to assess their origin, timing of crystallisation, and cooling and exhumation histories. The acquired data and interpretations are being used to develop hypotheses for the accretionary and post-accretionary history of oceanic terranes, the ocean-continent suture and the Central Cordillera of Colombia. These hypotheses will be compared with published models of the geological history of the Ecuadorian Andes and their interaction with the Caribbean Plate. The hypotheses will be tested against the kinematics of the present day and relic subducting and approaching oceanic plate to check if significant upper-plate tectonic episodes such as sudden increases in exhumation rate, correspond to tectonic rearrangements or subducted heterogeneities in the Nazca and Farallon plates. The final aim is to propose a coherent geological model for the NAS and to further assess the influence of the Caribbean Plate on this region.