The Tectonic and Geological Environment of Coastal South America
11
Seismic sections across the southern margin of the Caribbean reveal
structures related to the oblique right-lateral convergence of the Caribbean plate and the northern margin of South America (Lu and McMillen
1982; Ladd et al. 1984). Undeformed Caribbean acoustic basement dips
landward beneath folded sediments of the Panama and Colombia deformed belts with the youngest sediments involved in the folding.
Global Positioning System (GPS) measurements suggest the existence of
a rigid Panama-Costa Rica microplate that is moving northward relative to
the stable Caribbean plate (Kellogg and Vega 1995). Northward motion of
Panama and Costa Rica relative to the Caribbean plate is independently
suggested by the April 1991 Costa Rica earthquake, active folding in the
North Panama deformed belt, and a south-dipping Wadati-Benioff zone
beneath Panama. The 1991 earthquake produced up to 20-30cm of uplift
along the coast, measured by uplift of coral reefs and other shoreline
features and by repeated geodetic leveling. Panama is also continuing to
collide eastward with the northern Andes. The Panama-Colombia border
area is one of the most seismically active areas in northwestern South
America.
Rapid subduction of the Cocos and Nazca oceanic plates is occurring at
the Middle America (76 mm year- 1 ), Ecuador (71 mm year- 1 ), and Colombia (54mm year- 1 ) trenches. The subduction of the buoyant Cocos Ridge,
the mirror image of the Carnegie Ridge on the Nazca Plate, is raising the
coastline, and may be slowing down subduction at the southern end of the
Middle America Trench (Pennington 1981) and detaching the Panama
microplate from the Caribbean plate. The oblique subduction of the Nazca
Plate and the Carnegie Ridge has resulted in about 8 mm year- 1 of northeastward "escape" of the northern Andes relative to stable South America.
GPS results and seismic imaging also reveal Caribbean-North Andean slow
(about 17mm year- 1 ) oblique amagmatic subduction.
4.2 Tectonic History
We propose a simplified sequence of events for the accretionary development of southern Central America, the northern Andes, and the southern
Caribbean margin. Until the middle of the Middle Jurassic, the northern
margin of South America was joined with North America on the north.
By the end of the Middle Jurassic, South America began to rift apart from
North America. Paleomagnetic reconstruction of the Pacific plate and the
Pacific-Farallon spreading ridge suggests that an oceanic plateau may
have formed the core of the present Caribbean plate (Duncan and Hargraves 1984). The plateau was postulated to have been erupted onto late
11
Seismic sections across the southern margin of the Caribbean reveal
structures related to the oblique right-lateral convergence of the Caribbean plate and the northern margin of South America (Lu and McMillen
1982; Ladd et al. 1984). Undeformed Caribbean acoustic basement dips
landward beneath folded sediments of the Panama and Colombia deformed belts with the youngest sediments involved in the folding.
Global Positioning System (GPS) measurements suggest the existence of
a rigid Panama-Costa Rica microplate that is moving northward relative to
the stable Caribbean plate (Kellogg and Vega 1995). Northward motion of
Panama and Costa Rica relative to the Caribbean plate is independently
suggested by the April 1991 Costa Rica earthquake, active folding in the
North Panama deformed belt, and a south-dipping Wadati-Benioff zone
beneath Panama. The 1991 earthquake produced up to 20-30cm of uplift
along the coast, measured by uplift of coral reefs and other shoreline
features and by repeated geodetic leveling. Panama is also continuing to
collide eastward with the northern Andes. The Panama-Colombia border
area is one of the most seismically active areas in northwestern South
America.
Rapid subduction of the Cocos and Nazca oceanic plates is occurring at
the Middle America (76 mm year- 1 ), Ecuador (71 mm year- 1 ), and Colombia (54mm year- 1 ) trenches. The subduction of the buoyant Cocos Ridge,
the mirror image of the Carnegie Ridge on the Nazca Plate, is raising the
coastline, and may be slowing down subduction at the southern end of the
Middle America Trench (Pennington 1981) and detaching the Panama
microplate from the Caribbean plate. The oblique subduction of the Nazca
Plate and the Carnegie Ridge has resulted in about 8 mm year- 1 of northeastward "escape" of the northern Andes relative to stable South America.
GPS results and seismic imaging also reveal Caribbean-North Andean slow
(about 17mm year- 1 ) oblique amagmatic subduction.
4.2 Tectonic History
We propose a simplified sequence of events for the accretionary development of southern Central America, the northern Andes, and the southern
Caribbean margin. Until the middle of the Middle Jurassic, the northern
margin of South America was joined with North America on the north.
By the end of the Middle Jurassic, South America began to rift apart from
North America. Paleomagnetic reconstruction of the Pacific plate and the
Pacific-Farallon spreading ridge suggests that an oceanic plateau may
have formed the core of the present Caribbean plate (Duncan and Hargraves 1984). The plateau was postulated to have been erupted onto late