Aeromagnetic expression of faults that offset basin fill, Albuquerque basin, New Mexico

Abstract

High‐resolution aeromagnetic data acquired over the Albuquerque basin show widespread expression of faults that offset basin fill and demonstrate that the aeromagnetic method can be an important hydrogeologic and surficial mapping tool in sediment‐filled basins. Aeromagnetic expression of faults is recognized by the common correspondence of linear anomalies to surficial evidence of faulting across the area. In map view, linear anomalies show patterns typical of extensional faulting, such as anastomosing and en echelon segments. Depths to the tops of faulted magnetic layers showing the most prominent aeromagnetic expression range from 0 to 100 m. Sources related to subtler fault expressions range in depths from 200 to 500 m. We estimate that sources of the magnetic expressions of the near‐surface faults likely reside within the upper 500–600 m of the subsurface. The linear anomalies in profile form show a range of shapes, but all of them can be explained by the juxtaposition of layers having different magnetic properties. One typical anomaly differs from the expected symmetric fault anomaly by exhibiting an apparent low over the fault zone and more than one inflection point. Although the apparent low could easily be misinterpreted as representing multiple faults or an anomalous fault zone, geophysical analysis, magnetic‐property measurements, and geologic considerations lead instead to a “thin‐thick model” in which magnetic layers of different thickness are juxtaposed. The general geometry of this model is a thin magnetic layer on the upthrown block and a thick magnetic layer on the downthrown block. The thin‐thick model can be represented geologically by growth faulting and syntectonic sedimentation, where relatively coarse‐grained sediment (which is more magnetic than fine‐grained material) has accumulated in the hanging wall. This implies that the aeromagnetic data have potential for mapping growth faults and locating concentrations of coarse‐grained material that may have high hydraulic transmissivity. Although cementation along fault zones is common in portions of the area, we found no evidence that this secondary process results in measurable aeromagnetic anomalies. This observation differs from the findings in other sedimentary basins suggesting that magnetic anomalies arise from secondary magnetization along fault planes.

High-resolution aeromagnetic survey of Calabria (Southern Italy)

“…Aeromagnetic surveys are largely applied in subsurface exploration (ore and oil exploration), environmental and ground-water investigation, and geological mapping. Moreover, recent works from the western US, Australia, Antarctica and Southern Italy show that high-resolution magnetic surveys can provide new insights on the crustal setting, highlighting previously unrecognized upper crust fault geometry (Aitken & Betts, 2009;Blakely et al, 2000;Chiappini, Ferraccioli, Bozzo, & Damaske, 2002;Dentith, Clark, & Featherstone, 2009;Grauch, Hudson, & Minor, 2001;Grauch & Hudson, 2007;Hudson, Grauch, & Minor, 2008;Minelli et al, 2016). Calabria (Southern Italy) is one of the most seismically active regions of Italy as witnessed by the occurrence of several destructive earthquakes (M 6-7) in recent centuries (Galli, Scionti, & Spina, 2007).…”

Structural mapping of Chikotra River basin in the Deccan Volcanic Province of Maharashtra, India from ground magnetic data

“…Keeping the two objectives, i.e., structural mapping and delineating the presence of Proterozoic Kaladgi sediments, if any, below the trap cover, a ground magnetic survey was conducted over the Chikotra basin. Magnetic surveys can be used primarily to delineate buried igneous rocks and to locate faults within the basin fill (Grauch et al 2001) as well as map the basement. It also helps construct the geometry of the subsurface as lithology controls magnetic properties through mineralogy and hence sharp variation in rock properties generally coincides with lithological contacts.…”

Geologic interpretation of the aeromagnetic survey in the Agourai area (Central Morocco)

“…The horizontal-gradient method (Fig. 7) (Blakely 1995;Grauch et al 2006) is based on a principle from gravity methods according to which steep gradients occur over near vertical contacts between units with differing physical properties (Grauch et al 2001).…”

“…However, the interpretation of magnetic anomalies in terms of geologic features requires great care (Henkel 1991;Clark 1997;Naba 2007;Naba et al 2004;Randrianasolo 2009); it is not always a straightforward matter to assign magnetic signatures to rocks. Aeromagnetic surveys are widely used throughout the world in regional geologic studies (Galdeano 1980;Blakely 1995;Grauch et al 2001;Aspler et al 2003;Naba et al 2004;Randrianasolo 2009;Groune et al 2009;Aryamanesh 2009). However in Morocco, aeromagnetic surveys have only concerned regions with mining potential (Hercynian Central Massif, Anti Atlas, Tazekka Massif, Akil et al 2008;El Gout et al 2010;Bouya et al 2012;Amar et al 2012).…”