Virtual Pole from Magnetic Anomaly (VPMA): A procedure to estimate the age of a
rock from its magnetic anomaly only
, Wladimir Shukowsky
Reconsult Geofísica, Brazil
Received 14 February 2008
Accepted 6 July 2009
Paleomagnetic virtual poles
South American tectonic plate
Virtual Pole from Magnetic Anomaly (VPMA) is a new multi-disciplinary methodology that estimates the age of a
source rock from its magnetic anomaly, taken directly from available aeromagnetic data. The idea is to use those
anomalies in which a strong remanent magnetic component is likely to occur. Once the total magnetization of the
anomaly is computed through any of the currently available methods, the line that connects all virtual
paleogeographic poles is related with the position, on a paleogeographic projection, of the appropriate age fragment
of the APWP curve. We applied this procedure to ﬁve (5) well-known magnetic anomalies of the South American
plate in SE Brazil, all of them associated to alkaline complexes of Mesozoic age. The apparent ages obtained from
VPMA on three of the anomalies where the radiometric age of the source rock is known – Tapira, Araxá and Juquiá –
were inside the error interval of the published ages. The VPMA apparent ages of the other two, where the age of the
source rock is not known (Registro and Pariqueraçu magnetic anomalies) were geologically coherent. We expect that
the application of the VPMA methodology as a reconnaissance geochronological tool may contribute to geological
knowledge over continental areas, especially when the source rocks of the magnetic anomalies are unknown or
buried below superﬁcial sediments.
© 2009 Elsevier B.V. All rights reserved.
The determination of magnetic paleopoles from seamount magnetic
anomalies constitutes the major data source for the Paciﬁc Apparent
Polar Wander Path (APWP); Emilia & Massey (1974); Hilderbrand &
Parker (1987); Gee et al. (1989); Sager & Koppers (2000); Lee et al.
(2003); Kubota & Uchiyama (2005). In these cases the bathymetry
provides an immediate constrain for the geometry of the magnetic
sources, i.e., the submarine volcanic cones.
This article was motivated by the great success in using seamount
magnetic anomalies for APWP mapping. However, the main difﬁculty is
that in this case we are dealing with continental magnetic anomalies
difﬁcult to characterize.
One of the traditional applications of paleomagnetism consists in
isolating the primary natural remanent magnetization (NRM) of a given
rock, and then determining the correspondent paleogeographic pole at
the time of the rock emplacement. This result is then compared to
the APWP. As it will be described later, the Virtual Pole from Magnetic
Anomaly (VPMA) technique proposed here is based on the assumption
that the remanent component
Jr determined from the anomaly, would
be approximately correspondent to the primary NRM of the source
Therefore, this methodology produces an age estimation of the rocks
without need of sampling them. Here we apply this methodology to ﬁve
Mesozoic alkaline intrusions in Southeast Brazil, and compare the VPMA
age results to the known radiometric ages obtained from geochronological
All the magnetic data used in this work came from CPRM (Brazilian
Geological Survey) regional aeromagnetic database. Line spacing
varied from 1000 to 2000 m. Application of the VPMA methodology to
high-resolution magnetic datasets should yield better results.
2. VPMA methodology description
The main concept of VPMA methodology is to isolate the remanent
Jr of the magnetic anomaly and use it in paleomagnetic
studies. Therefore, ﬁrst we calculate the total magnetization of the
magnetic source using one of the existing methods, and then we
remove the induced component using the following vectorial equa-
i + J
Journal of Applied Geophysics 69 (2009) 96–102
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