Estudio paleomagnético de lavas y flujos piroclásticos de edad Plioceno-Holoceno de los complejos volcánicos del centrooccidente y sur-occidente de Colombia
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Cincuenta y dos lavas del Pleistoceno a la actualidad del complejo volcánico del centrooccidente de Colombia y cuarenta lavas del Plioceno a la actualidad pertenecientes a los complejos volcánicos del sur-occidente de Colombia han sido muestreados para realizar estudios de campo geomagnético promediado en el tiempo (TAF) y variaciones paleoseculares. Un total de 10 núcleos fueron extraídos por lava (sitio), siendo sometidos a desmagnetización progresiva AF y térmica. Posteriormente se realizaron análisis de componentes principales y cálculos de la dirección media por sitio, 40 sitios del complejo volcánico del centro-occidente de Colombia (37 y 3 con polaridad normal e inversa, respectivamente) y 28 sitios pertenecientes a los volcanes andinos del sur-occidente (16 y 12 con polaridad normal e inversa, respectivamente), con 95 5.5o fueron seleccionados para cálculos posteriores. La dirección media para todos los sitios del complejo volcánico del centro-occidente de Colombia ( D = 3.7o ; I = 6.4o ; 95 = 4.6o ) ajusta bien (a un nivel de confianza del 95%) con la dirección paleomagnética esperada (en el área de estudio) de un campo geomagnético compuesto principalmente por un dipolo axial geocéntrico con un 5% de componente cuadrupolar ( I = 5.59o ), pero no coincide con modelo simple de GAD ( I = 9.8o ) . La dispersión de los VGP's (12.5°) es similar a la predicha por el Modelo G (12.0°). Para los complejos volcánicos del sur-occidente de Colombia la dirección media para todos los sitios ( D = 357.7o ; I = 7.0o ; 95 = 7.3o ) ajusta bien (a un nivel de confianza del 95%) con la dirección paleomagnética esperada (en el área de estudio) de un simple campo geomagnético GAD ( I = 3.25o ) , pero no coincide con un campo geomagnético compuesto principalmente por un dipolo axial geocéntrico con un 5% de componente cuadrupolar ( I =−1.03o ) . La dispersión de los VGP's (14.1°) es
Abstract. Fifty two Pleistocene to recent lava flows from the west-central volcanic complex of Colombia and fourty Pliocene to recent lava flows that belong to the southwestern volcanic complex of Colombia have been sampled for geomagnetic time average field (TAF) and paleosecular variation studies. A total of 10 cores were drilled per lava (site), stepwise AF and thermal demagnetization has been carried out. After principal component analysis and mean-site direction calculations, 40 sites from the west-central volcanic complex (37 and 3 with normal and reverse polarity, respectively) and 28 sites from the southwestern volcanic complex (16 and 12 with normal and reverse polarity, respectively), with 95 5.5o were selected for further calculations. The overall mean direction among the sites from the west-central volcanic complex of Colombia ( D = 3.7o ; I = 6.4o ; 95 = 4.6o ) closely fits (at the 95% confidence level) the expected paleomagnetic direction (at the area of study) of a geomagnetic field composed primarily by a geocentric axial dipole with 5% axial quadrupole component ( I = 5.59o ), but do not coincides with a simple GAD model ( I = 9.8o ) . VGP's scatter (12.5°) is similar to that expected from Model G (12.0°). For the southwestern volcanic complex of Colombia the overall mean direction among the sites ( D = 357.7o ; I = 7.0o ; 95 = 7.3o ) fits (at the 95% confidence level) the expected paleomagnetic direction (at the area of study) of a geomagnetic field of a simple GAD ( I = 3.25o ) , but do not coincides with a geomagnetic field composed primarily by a geocentric axial dipole with 5% axial quadrupole component ( I =−1.03o ). VGP scatter (14.1°) is slightly highe
Abstract. Fifty two Pleistocene to recent lava flows from the west-central volcanic complex of Colombia and fourty Pliocene to recent lava flows that belong to the southwestern volcanic complex of Colombia have been sampled for geomagnetic time average field (TAF) and paleosecular variation studies. A total of 10 cores were drilled per lava (site), stepwise AF and thermal demagnetization has been carried out. After principal component analysis and mean-site direction calculations, 40 sites from the west-central volcanic complex (37 and 3 with normal and reverse polarity, respectively) and 28 sites from the southwestern volcanic complex (16 and 12 with normal and reverse polarity, respectively), with 95 5.5o were selected for further calculations. The overall mean direction among the sites from the west-central volcanic complex of Colombia ( D = 3.7o ; I = 6.4o ; 95 = 4.6o ) closely fits (at the 95% confidence level) the expected paleomagnetic direction (at the area of study) of a geomagnetic field composed primarily by a geocentric axial dipole with 5% axial quadrupole component ( I = 5.59o ), but do not coincides with a simple GAD model ( I = 9.8o ) . VGP's scatter (12.5°) is similar to that expected from Model G (12.0°). For the southwestern volcanic complex of Colombia the overall mean direction among the sites ( D = 357.7o ; I = 7.0o ; 95 = 7.3o ) fits (at the 95% confidence level) the expected paleomagnetic direction (at the area of study) of a geomagnetic field of a simple GAD ( I = 3.25o ) , but do not coincides with a geomagnetic field composed primarily by a geocentric axial dipole with 5% axial quadrupole component ( I =−1.03o ). VGP scatter (14.1°) is slightly highe