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Geochronology; thermochronology; nothern andes; pangea; Caribbean Plateau; exhumation; tectonics; Colombia; Ecuador

English title	Thermochronology and tectonics of the Northern Andes (Colombia and Ecuador)
Applicant	Spikings Richard A.
Number	119871
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	01.04.2008 - 31.03.2011
Approved amount	204'230.00

Lead

Lay summary
Triassic to Early Cretaceous rocks exposed in the central and eastern cordilleras of the Northern Andean Segment (NAS; north of 5°S) record the local disassembly of Pangea, and the subsequent initiation and evolution of an active continental margin. Late Cretaceous mafic rocks, which crop-out in the western cordilleras, are a juxtaposition of allochthonous 90-75 Ma island arc and oceanic plateau rocks that collided with the northwestern South American (SOAM) Plate at ~75-73 Ma. This proposal requests funds to i) constrain the geological history of the NW SOAM Plate margin during Pangean disassembly and subsequent active margin evolution, prior to the collision of the Caribbean Plateau (project A), and ii) constrain the timing and duration of Late Cretaceous accretionary events in Colombia, and quantify cooling and exhumation rates during periods of Andean orogenesis (project B). A wide disparity exists in the documented evolution of the Mesozoic and Cenozoic rocks within Ecuador. These differences render it difficult to compare geochronological and stratigraphic information from different regions and hence coherent models for the evolution of the NAS during the Triassic - Recent have not been proposed. Significant problems include: 1. The British Geological Survey divided the Palaeozoic - Mesozoic rocks of Ecuador (Eastern Cordillera) into four terranes (Litherland et al., 1994). However, Pratt et al. (2005) proposed an autochthonous geological model for the rocks of the Eastern Cordillera of Ecuador. These contrasting models form the core of Project A. 2. Late Cretaceous island arc and oceanic plateau rocks in the western NAS accreted against the NW SOAM Plate (Hughes and Pilatasig, 2002). The timing of accretion (75-73 Ma) and subsequent reactivation of faulted blocks in Ecuador has been tightly constrained (Litherland et al., 1994; Spikings et al., 2000, 2001a, 2005; Vallejo et al. 2006; Luzieux et al. 2006). However, similar detailed information has not been obtained from Colombia. This paucity of data is addressed in Project B. Our interpretations will be used to develop models for the Mesozoic - Cenozoic geological evolution of the NW SOAM plate margin. The models should constrain the i) timing of break-up of western Pangea, ii) timing of arc volcanism within the far western Tethyan realm, iii) origin and timing of accretion of suspect terranes onto the NW SOAM Plate margin, prior to the collision of the Caribbean Plateau, iv) late Cretaceous accretionary history of the Caribbean Plateau, and v) the response of the margin of the NW SOAM Plate to the subduction of heterogeneities in the oceanic crust (e.g. the Carnegie Ridge).