Flow Directions and Paleomagnetic Study of Rocks from the Azufre Volcano, Argentina

Abstract

Determination of the stable direction of magnetization was made on eight lava flows from the Azufre volcano, Southern Volcanic Zone of the Andes. From these eight paleomagnetic sites, only six independent samples of the geomagnetic field were identified. Combination of these with results of a work made by CREER and VALENCIO (1969) allowed a better determination of a geomagnetic pole for the Bruhnes chron in this region of the Andes than that previously calculated. The coordinates of the new pole are 87°N, 236°E, and have an α₉₅ region of confidence of 12°. Statistical comparison of directions of magnetization of groups of flows was used 1) to test the hypothesis of rapid extrusion of flows, and 2) to constrain the age of the lavas sampled in this work to more than 0.4 my. Finally, the utility of the anisotropy of magnetic susceptibility measurements on the determination of flow direction of lava flows was established despite the great scatter on the observations of multiple samples from the same unit. Criteria to determine the size of the region of confidence around the mean maximum susceptibility in order to accept or reject results were developed in analogy with those used in paleomagnetic studies.