Inverse modelling of the reversely magnetized, shallow plumbing system hosting oil reservoirs of the Auca Mahuida volcano (Payeina retroarc, Neuquén Basin, Argentina)

The Auca Mahuida volcano (2.03–0.88 Ma) located east of the Andean thrust front in the
Neuqu´en basin (Argentina) hosts an oil system of thermogenic origin and is affected by the
NW–SE striking-faults. Intrusive bodies and the underlying Jurassic sediments constitute the
reservoir rocks. Aeromagnetic data collected in the Auca Mahuida area detected multiple
dipolar magnetic anomalies, many of which have reverse polarity. Palaeomagnetic measurements
on rock samples collected in the field together with available age determinations indicate
that the reversely magnetized sources were mainly emplaced during the Matuyama reverse
polarity chron while the normal polarity sources were emplaced during the Olduvai and/or
Jaramillo subchrons. The location and geometry of the intrusive bodies is poorly known and
the customary magnetic inversion is rendered difficult because of multiple natural remanent
magnetization directions. To address these difficulties, a voxel inversion was applied to model
the vector residual magnetic intensity (VRMI) transformation of the observed total magnetic
intensity data. The modelling showed a 1.5 km deep, subcircular ring-shaped intrusion below
the summit of the volcano and a series of NW–SE elongated, fault-controlled intrusive bodies
to depths up to 3–4 km. Our results show that magnetic data and VRMI modelling help resolve
the geometry of the shallow plumbing system of volcanoes with remanently magnetized
sources, and estimate the depth and geometry of potential oil reservoirs in volcanic areas.