Analysis of the Aeromagnetic Anomalies of the Auca Mahuida Volcano, Patagonia, Argentina

Abstract

We present the analysis of the subsurface structure of the Auca Mahuida volcano based on high-resolution aeromagnetic data integrated with the available geological information. Most of the detected magnetic anomalies have a dipolar structure opposite to that of the present geomagnetic field. According to the available geochronological data and paleomagnetic measurements, the source bodies of Auca Mahuida mainly emplaced in the Matuyama reverse polarity chron. The Reduction-to-the-Pole map confirms that the magnetization direction is mainly reverse with only few anomalies normally magnetized. Two opposite, coexisting polarities do not allow to fully remove the dipolar character of the field in the Reduction-to-the-Pole transformation. Therefore, we model the measured anomaly field by applying analytical techniques that are independent of the magnetization direction. The obtained anomaly strikes and source geometries indicate an emplacement of intrusive bodies controlled by the regional faults affecting the Auca Mahuida basement and the sedimentary successions of the Neuquen basin. Magma upraised along these faults and fractures feeding the volcanic activity and subsequently crystallized. The averaged power spectrum and Euler Deconvolution indicate source depths consistent with those of the intrusions recognized in wells. Borehole data highlight the widespread presence of intrusive bodies below the Auca Mahuida central crater and the peripheral sectors at depth of 2 km below sea level. These bodies have played a major role in the thermal maturation of hydrocarbons and in the subsequent accumulation of oil below the volcano. The obtained results shed light on the Auca Mahuida feeding system and on the intrusions geometry, also pointing out the effectiveness of the magnetic prospecting in the oil industry even in presence of strong remanent magnetization.