Abstract
AbstractNew paleomagnetic data isolated in Upper Triassic to Aptian rocks exposed in the Colombian Andes and west of the Guyana craton, in conjunction with paleomagnetic data from the Andes of Venezuela and the South American craton, permit the interpretation of along-margin northward translations of Andean Colombian terranes during the Early-Middle Jurassic. Field tests and comparison with reference paleopoles for South America indicate that characteristic components uncovered in red-siliciclastic and igneous rocks are primary, or near-depositional, and they are carried dominantly by hematite, magnetite and Ti-magnetite. Difference in declination values of characteristic components isolated in fault-bounded blocks document counter-clockwise rotations previous to syn-extensional deposition. The Jurassic tectonic scheme proposed here for the northwestern corner of South America shows an Early Jurassic, linear subduction-related magmatic arc evolving to Late Jurassic rift-related setting associated to the opening of the Proto-Caribbean Ocean and westward retreat of the subduction zone. A similar tectonic evolution for the Jurassic has been proposed for southwestern USA and the Nazas arc in Mexico.
Highlights
Triassic and Jurassic units exposed in the Andes of Ecuador, Colombia and Venezuela (Fig. 1) encompass a complex association of limestone, red siliciclastic, volcaniclastic and plutonic rocks (Mojica et al, 1996)
Previous paleomagnetic results from Middle Jurassic and younger rocks exposed in the Merida Andes (Castillo et al, 1991) and Santa Marta massif (MacDonald and Opdyke, 1984) in the northern Andes indicate no paleolatitudinal translations of allochthonous terranes since the Mid-Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB
Low-temperature/coercivity magnetic components and moderate to high-temperature/coercivity characteristic magnetic components were successfully uncovered in Upper Triassic to Lower Cretaceous rocks exposed in the Upper Magdalena Valley, Floresta massif and Bucaramanga area (Fig. 1A)
Summary
Triassic and Jurassic units exposed in the Andes of Ecuador, Colombia and Venezuela (Fig. 1) encompass a complex association of limestone, red siliciclastic, volcaniclastic and plutonic rocks (Mojica et al, 1996). The western compartment (eastern flank of the CC, UMV, SL, SMM in Fig. 1A) includes Upper Triassic-Lower Jurassic shallow-marine strata covered with a 1-km-thick volcanic-related succession, and Aptian-Albian rocks unconformably overlie this succession (Fig. 1B). In Bucaramanga (BA) red-siliciclastic beds with minor volcanic interbeds of the Jordan (LowerMiddle Jurassic), Giron and Los Santos Fms (Upper Jurassic-Berriasian) were collected in two structural domains, named the northern and southern blocks (Fig. 2A). Two areas were selected in the northern Upper Magdalena Valley (UMV, Fig. 2C), where the Aptian Yavı Fm rests in an angular unconformity upon Upper TriassicLower Jurassic Saldana Fm. In Olaya Herrera area (OH), located close the Jurassic magmatic belt exposed in the Central Cordillera, samples were collected from lavas and red-volcaniclastic beds of the Saldana Fm at the southeastern and northwestern flank of an anticline structure along the Chipalo river, as well as in the Macule river (Fig. 2D). Details of stratigraphic columns and statistics of Saldana and Yavı sites are in Bayona et al (2005)
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