Paleomagnetism and rock magnetism of the Jurassic La Negra Formation, Northern Chile: Implications for tectonics and volcanic stratigraphy
Por:
Goguitchaichvili A., Alva-Valdivia L.M., Urrutia-Fucugauchi J.
Publicada:
1 ene 2003
Resumen:
A detailed paleomagnetic investigation was carried out on the Jurassic La Negra Formation. A total of 32 consecutive lava flows (about 280 standard paleomagnetic cores) were collected. Several rock-magnetic experiments were carried out in order to identify the magnetic carriers and to obtain information about their paleomagnetic stability. Continuous susceptibility measurements with temperature yield in most cases reasonably reversible curves with Curie points close to that of Ti-poor titanomagnetite. Titanomaghemites seem to be the main magnetic carrier in a few cases. Judging from the ratios of hysteresis parameters. it seems that all samples fall in the pseudo-single domain grain-size region, probably indicating a mixture of multidomain and a significant amount of single-domain grains. Twenty-five flows yielded reliable paleomagnetic results. The mean paleodirection obtained in this study is l = -30.7, D = 11.3°. k = 18, ?95 = 6.8°, N = 25. Combining all currently available data, including those obtained in previous studies for the La Negra volcanic sequence, we obtained a well-defined mean paleomagnetic direction with I = -33.9°. D = 10.5°, k = 15, ?95 = 6.1°. N = 40. These directions are in good agreement with the expected paleodirections at about 180 Ma, which indicates that studied units do not show evidence for significant tectonic rotation. Fifteen sites yield reverse polarity magnetization and 11 flows are normally magnetized. The tentative direct magnetostratigraphic correlation suggests that La Negra volcanics have been emplaced during a relatively large time span of about 5 m.y.
Filiaciones:
Goguitchaichvili A.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Laboratorio de Paleomagnetismo y Geofisica Nuclear, Ciudad Universitaria, DF, 04510, Mexico
Alva-Valdivia L.M.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Laboratorio de Paleomagnetismo y Geofisica Nuclear, Ciudad Universitaria, DF, 04510, Mexico
Urrutia-Fucugauchi J.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Laboratorio de Paleomagnetismo y Geofisica Nuclear, Ciudad Universitaria, DF, 04510, Mexico
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