5th Swiss Geoscience Meeting, Geneva 2007
Tectonic evolution of the Northern Andes: constrains
from thermochronology and geochronology
Villagomez Diego*, Spikings Richard*, Seward Diane**, Magna Tomas*** &
Winkler Wilfried**
* Départment de Minéralogie, Rue des Maraîchers 13, CH-1205 Genève-Suisse
(Diego.Villagomez@terre.unige.ch)
** Geologisches Institut, ETH, 8092 – Zürich.
*** Institute de Minéralogie et géochemie, l’Anthropole-CH-1015. Lausanne.
The Northern Andean Zone (NAZ) comprises Ecuador, Colombia and
Venezuela and is characterized by three sublinear topographic ridges, referred
to as the Western, Central and Eastern Cordillera, respectively. The basement
of the Western Cordillera of Colombia is formed by multiple oceanic terranes
mainly accreted during the Mesozoic; the terranes are juxtaposed against the
paleo-continental margin (Central Cordillera) across the Romeral-Peltetec Fault
Zone (Fig. 1). This project seeks to determine the crystallization age of
continental and oceanic basement units (using zircon U-Pb LA ICP-MS) and the
response of the continent to the accretion of the allochthonous terranes (apatite
& zircon fission track analysis, AFT-ZFT).
Within Colombia, the continental province crops out in the Central Cordillera
and is partly composed of a supracrustal sequence of Paleozoic – Early
Cretaceous metamorphic rocks intruded by Permo-Triassic granitic gneisses
and Early Jurassic-Late Cretaceous granites (Fig. 1). Medium- to low-pressure
Paleozoic metamorphic rocks (detrital U-Pb zircon ages ranging from 270-380
Ma) are intruded by poorly isotopically characterized granitic gneisses with UPb zircon ages ranging between 200-300 Ma, and Jurassic calc-alkaline
granites of the Ibague Batholith (160 ± 3Ma, U-Pb).
The oceanic basement is exposed immediately to the west of the RomeralPeltetec Fault Zone and consists of basalts, gabbros and ultramafic cumulates
of mantle plume-derived material (oceanic plateau-like characteristics with flat
REE patterns, no negative Nb-Ta anomalies; Kerr et al 1997, this project) which
may represent a portion of the large Late Cretaceous Caribbean oceanic
plateau (Kerr et al., 1997). Some granitoids intrude these mafic sequences and
thus constrain a minimum age for the accreted oceanic terranes of the Western
Cordillera: i) the Buga Batholith (90.6 ± 1.2 Ma, U-Pb), and ii) the Cordoba
Batholith, (79.3 ± 1.5 Ma, U-Pb).
Our on-going study has shown that Jurassic granitoids emplaced along the
eastern border of the Central Cordillera in Colombia cooled rapidly through the
≥250˚C to ~ 60˚C interval at ~ 80-70 Ma (AFT inverse modeling and ZFT age at
250 ˚C; Fig. 2). This time period slightly predates the accretion of the Caribbean
Plateau in Ecuador (75-65 Ma, Vallejo et al., 2006) suggesting that plateau
accretion did not proceed in northward direction. Alternatively, the exhumation
of the buttressing rocks produced in response to the accretion in Ecuador did
not occur as immediate as in Colombia.
5th Swiss Geoscience Meeting, Geneva 2007
REFERENCES
Kerr, A.C., Marriner, G.F., Tarney, J., Nivia, A., Saunders, A.D., Thirlwall, M.F.&
Sinton, C.W., 1997. Cretaceous Basaltic Terranes in Western Colombia:
Elemental, Chronological and Sr-Nd Isotopic Constraints on Petrogenesis.
Journal of Petrology, 38, 677 – 702.
Vallejo, C., Spikings R., Luzieux L., Winkler W., Chew D., & Page L., 2006. The
early interaction between the Caribbean Plateau and the NW South American
Plate. Terranova 18; 264-269.