In his pioneering work, Irving (1971) recognized that most of the western Northern Andes were formed by oceanic rocks west of the Dolores-Romeral fault system (presently known as the Romeral-Peltetec fault; Fig. 13). This work was complemented by the proposal of obduction of this oceanic crust (Restrepo and Toussaint, 1974), which led to the present interpretation of a collisional orogen. This concept was developed by Barrero (1979) and Restrepo and Toussaint (1988) in Colombia, and by Feininger (1987) in Ecuador and northern Perú. Geochemical, petrological, isotopic, and geochronological data, together with evidence for intense deformation, associated in part with blue- schist metamorphism, constrain the evolution into three major stages following the proposals of Aspden and McCourt (1986), Mégard (1987, 1989), Duque Caro (1990), Aleman and Ramos (2000), Cediel et al. (2003), López Ramos and Barrero (2003), and Vallejo (2007), among others. These three stages are: initial collision of a series of island arcs during the Early Cretaceous (Aspden et al., 1987); collision of the Caribbean oceanic plateau along the margin in the Late Cretaceous–Paleocene (Dewey and Pindell, 1986; Burke, 1988); and fi nal collision of an island arc of Caribbean affi nities in Miocene times (Dengo, 1983; Duque Caro, 1990).
Island Arc Collisions
Fragments of oceanic rocks associated with blueschist meta- morphic facies along the Romeral fault system are interpreted as the suture between these rocks and the early Mesozoic margin of South America (Fig. 13). These greatly deformed and altered oceanic fragments have received several names since the terrane proposal of Etayo Serna and Barrero (1983). One of the more detailed studies was done in the Amaime area, where high-pres- sure lawsonite-glaucophane schists and, locally, eclogites were
tectonically emplaced into the Paleozoic metamorphic rocks dur- ing the Mesozoic (Aspden and McCourt, 1984). Associated with accretion, there was a major period of dynamic metamorphism throughout the Central Cordillera of Colombia and the Cordillera Real of Ecuador. This episode, known in southern Ecuador as the Peltetec event, occurred around 125–132 Ma, based on the age of the high-pressure metamorphic rocks considered to rep- resent the emplacement age of the blueschists (Feininger, 1982; Aspden et al., 1992b; Litherland et al., 1994). This event refl ects the accretion of an Early Cretaceous island arc along the west- ern margin of the Cordillera Real, as recognized by Aspden and Litherland (1992) and Litherland et al. (1994). They recognized the Early Cretaceous suture further south, as well as the emplace- ment of the Raspas ophiolitic complex and associated blueschists at 132 Ma (Apsden et al., 1995; Reynaud et al., 1999). The study by Bosch et al. (2002) concluded that the latest Jurassic–Early Cretaceous suture observed along the Romeral-Peltetec fault sys- tem exhibits high-pressure assemblages and low-grade metamor- phic rocks, suggesting that this suture was involved in at least two distinct episodes related to the accretion of an island arc and subsequent collision of an oceanic plateau.
Other authors have interpreted part of these collisions as the closure of a backarc basin that recorded Early Cretaceous sedi- mentation (Bourgois et al., 1987; Nivia et al., 2006). The main assumption is related to the nature of the metamorphic basement of the western margin of the backarc basin known as the Arquía terrane in Colombia, which for some authors could be older than Paleozoic (Nivia et al., 2006). Due to the intense deformation and the strike-slip displacements of the Romeral fault, it cannot be overlooked that part of the protolith of this Arquía terrane could have been derived from the Paleozoic basement of the Central Cordillera. Similar problems exist in southern Ecuador, where the Chaucha terrane of Feininger (1986) has been interpreted as nonoceanic or different from the Piñón terrane based on the exis- tence of quartzitic sandstones.
All of the oceanic exposures along the Romeral-Peltetec fault system are grouped as a single episode here (Fig. 13) and related to the early accretion of some oceanic island terranes such as the Amaime, Peltetec, Raspas, and Chaucha, among others. This accretion occurred prior to the Late Cretaceous collision of the plateau as proposed by Pindell and Tabbutt (1995), Ale- man and Ramos (2000), and Bosch et al. (2002). During Middle Jurassic to Early Cretaceous time, a magmatic arc also devel- oped on continental basement as the island arc was approaching the Central Cordillera, as recognized by Toussaint and Restrepo (1994) and Aleman and Ramos (2000) (see Fig. 14).
Oceanic Plateau Collision
The Western Cordilleras of Colombia and Ecuador con- tain Upper Cretaceous turbidites with small but signifi cant fault-bounded slivers of basalts and ultramafi c rocks that were formerly interpreted as a mid-ocean-ridge basalt (MORB) rock assemblage (Lebras et al., 1987) but later recognized as an oce-
anic plateau sequence (Cosma et al., 1998; Reynaud et al., 1999; Lapierre et al., 2000) and a tectonic mélange.
There have been various interpretations for the characteris- tic and genesis of this oceanic plateau. The original proposal of Feininger (1986), that pieces of oceanic rocks grouped in a single Piñón terrane were accreted to the continental margin, was chal- lenged by subsequent workers (Kerr et al., 2002; Hughes and Pilatasig, 2002, among others), who proposed a series of colli- sions between Late Cretaceous and Eocene times. However, recent work based on petrological, geochronologic, and paleomagnetic
grounds, has demonstrated that multiple plateaus (or terranes) can be precluded. For example, the paleomagnetic data indicate a sin- gle oceanic plateau that fragmented during collision with the South American plate, giving rise to distinct structural blocks (Luzieux et al., 2006). Likewise, new U-Pb SHRIMP zircon data show a lim- ited time span between 87.10 ± 1.66 Ma and 85.5 ± 1.4 Ma for the formation of the oceanic plateau (Vallejo et al., 2006, this volume).
The oceanic plateau continues into Colombia as a part of the Dagua terrane (Etayo Serna and Barrero, 1983; Alemán and Ramos, 2000), although other authors such as Cediel et al.
78-73 Ma 92-76 Ma 160-130 Ma 98-86 Ma 123 Ma 84.7±1.1 Ma 132 Ma 85.8±0.7 Ma 92-76 Ma 75°W 80°W 10°N 5°N 0° La Guajira Córdoba San Jacinto Acandi Caribbean Sea Serranía de Baudó VENEZUELA COLOMBIA ECUADOR PERÚ Pacific Ocean Gorgona Island Barragán Bogotá Quito Cuenca Pijao Jambaló El Tambo Peltetec Pallatanga Pujilí Saloya Los Azules Mesozoic proto-margin Gondwana proto-margin Accreted Paleozoic T erranes Amaime Choco T errane Dagua T errane Piñón T errane Raspas Cenozoic cover
Chocó terrane accreted during late Tertiary
Late Cretaceous oceanic plateau of the Piñón-Dagua terrane
Early Cretaceous high pressure metamorphic and volcanic rocks
Ophiolite and blueschists
Paleozoic accreted terranes Early Cretaceous Amaime and related terranes
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0 300 km
Cauca FaultRomeral Fault
Peltetec Fault Pujilí Fault Garra pata s F au lt C añ as G o rd a s F a u lt ECUADOR COLOMBIA
Figure 13. Different oceanic rocks west of the Romeral-Peltetec fault system in west- ern Colombia and Ecuador based on Mc- Court et al. (1984), Aspden et al. (1992a, 1992b), Reynaud et al. (1999), Aleman and Ramos (2000), Kerr et al. (2003), Cediel et al. (2003), and Vallejo et al. (2006, this volume). Note the accretion in three succes- sive stages: the Amaime terrane and related rocks (Early Cretaceous); the Dagua-Piñón oceanic plateau (latest Cretaceous); and the Chocó terrane (middle Miocene). The col- lision of the Chocó terrane in the middle Miocene thrusted part of the Dagua terrane to the east along the Cañas Gordas fault, north of Garrapatas fault.
Jurassic–Early Cretaceous (185–130 Ma) Late Cretaceous (90–80 Ma) Latest Cretaceous– Paleogene (45–35 Ma) North of Garrapatas Miocene to Present (15–0 Ma) South of Garrapatas Miocene to Present (15–0 Ma) Amaimé arc 140–124 Ma 185–142 Ma
AMAIME TERRANERomeral faultGranitoid stocks
SOUTH AMERICA
SOUTH AMERICA Blueschists
125–120 Ma
AMAIME TERRANE
Baudó arc DAGUA
TERRANE
Mandé arc Antoquía BatholithMagdalena V alley
CENTRAL CORDILLERA
Serranía de BaudóAtrato Basin Cañas Gordas faultRomeral fault Magdalena V alley Frente Llanero DAGUA TERRANE CENTRAL CORDILLERA EASTERN CORDILLERA WESTERN CORDILLERA FARALLON AMAIME TERRANE CHOCÓ TERRANE
Romeral fault Magdalena
Valley DAGUA TERRANE NAZCA PLATE CENTRAL CORDILLERA 3.6–0 Ma EASTERN CORDILLERA WESTERN CORDILLERA 11–8.5 Ma
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CHIBCHA TERRANE
Cauca fault
Early Cretaceous arc Jurassic arc
Granitoid stocks Oceanic plateau
AMAIME TERRANE
Figure 14. Schematic tectonic evolution of the Northern Andes at the latitude of Colombia show- ing the polarity of the subduction and subsequent collisions based on Lebras et al. (1987), Mégard (1987), and Aleman and Ramos (2000). Note the different vergence of the Dagua terrane north and south of the Garrapatas fault (based on López Ra- mos and Barrero, 2003).
(2003) and López Ramos and Barrero (2003) favor multiepi- sodic collisions. Available geochemical data show the uniform composition of the oceanic rocks, which is also interpreted as the leading edge of the Caribbean plateau (Kerr et al., 1998) that collided with the South American plate at 75–65 Ma (Ramos and Alemán, 2000; Cediel et al., 2003).
Subduction occurred above the oceanic plateau on the Pacifi c side, as has been demonstrated by volcanic arc assemblages that have been described overlying the plateau (Lebras et al., 1987; Toussaint and Restrepo, 1994; Reynaud et al., 1999; Alemán and Ramos, 2000). At the same time, the approaching plateau gener- ated a magmatic arc on the Central Cordillera of Colombia and the Cordillera Real of Ecuador until the Late Cretaceous. The Paleocene granites of the large Antioquia batholith (59–57 Ma), which partially postdate the collision of the Dagua Plateau, may represent a slab break-off episode that developed in the northern Central Cordillera east of Medellín.
Chocó Collision
The Serranía de Baudó along the Pacifi c margin of Colom- bia has been described as an allochthonous oceanic terrane accreted to South America during Cenozoic times (Dengo, 1983; Case et al., 1984; Restrepo and Toussaint, 1988). This area has been interpreted as part of a larger block that includes the Darien of Panamá, the Acandí arc (Fig. 13), and a sliver of the Western Cordillera, named the Chocó terrane by Duque Caro (1990), after Dengo (1983). Based on precise biostratigraphic dating, Duque Caro (1990) constrained the docking of the Chocó terrane at ca. 13 Ma. The basement of this terrane has been interpreted as a different part of the Caribbean plateau based on geochemical and isotopic data (Kerr and Tarney, 2005), although it has an age similar to the Dagua oceanic plateau.
An important sector of the Western Cordillera at the lat- itudes of the Chocó terrane, north of the Garrapatas fault, is considered to be an independent terrane (Cediel et al., 2003) named the Cañas Gordas terrane following Etayo Serna and Barrero (1983). Based on the same isotopic and geochemical characteristics to the north and south of this fault, Aleman and Ramos (2000) considered the Cañas Gordas block to be part of the Dagua terrane. The unusual tectonic eastward vergence of the Cañas Gordas terrane (Bourgois et al., 1987; López Ramos and Barrero, 2003), when compared with the southern part of the Dagua terrane, can be explained by a transposition of the structure related to the Miocene deformation associated with the docking of the Chocó terrane (Fig. 14).
Isotopic and paleomagnetic data led Kerr and Tarney (2005) to consider the mafi c and ultramafi c rocks of the Gorgona Island to be part of the Chocó terrane and, at the same time, independent of the Western Cordillera oceanic plateau.
The general tectonic evolution of the oceanic rocks of the western sector of the Northern Andes that formed as part of the Caribbean plateau and formed above the Galápagos hot spot is summarized in Figure 14.