Well productivity in the Ponta Grossa Dike Swarm, Brazil: An integrated study with magnetic data inversion and clustering analysis of model solutions.

Dike swarms are igneous structures of continental expression accounting for major episodes of magmatism in igneous provinces, mantle plume heads, and continental breakup. In regional magnetic maps, dike swarms are recognized by high-amplitude lineaments indicative of lengthy and juxtaposed magnetized bodies. High-anomaly amplitudes from such tabular (2D) bodies tend to obscure lower amplitude contributions from localized 3D sources, representative of magmatic structures that once served as magma plumbing and storage. The recognition of such subtle signals with conventional filtering techniques is prevented due to spectral overlapping of individual contributions. We have developed a processing scheme to remove contributions from elongated, homogeneous sources to make clear contributions from 3D sources located below, in the middle of, or above a framework of elongated homogeneous sources. The canceling of 2D fields is accomplished by evaluating the horizontal component of the magnetic anomaly along the lineament strike, which for true elongated and homogeneous sources gives a null response. The gradient intensity of the transformed field is then evaluated to enhance residual fields over 3D sources. Lineaments thus removed identify tabular bodies with homogeneous magnetization, interpreted as being indicative of the uniform distribution (mineral type, concentration, and grain-size distribution) of magnetic carrier content in the rock. We evaluated our technique with synthetic data from multiple 2D-3D interfering sources and then applied it to interpret airborne data from the Ponta Grossa Dike Swarm of the Paraná-Etendeka Magmatic Province in Southeastern Brazil.

No abstract

Seu conteúdo foi revisado pelo ComitêTécnico do VI SimBGf, mas não necessariamente representa a opinião da SBGf ou de seus associados. É proibida a reprodução total ou parcial deste material para propósitos comerciais sem prévia autorização da SBGf.

Dike swarms are mega-structures observed in different geological contexts. However, it is very difficult to obtain quantitative information about the units that make up these structures from magnetometric data. This work uses a method that performs the inversion of magnetic data profiles and cluster analysis of obtained solutions. The results are used to interpret the effects of a dike swarm on water-well's productivity. The method is applied to a region in the Ponta Grossa Dike Swarm. The results show that wells located in zones of influence of dikes, which intrude crystalline rocks of high metamorphic grade, are 14.5 times more productive than those located in the host rocks outside these zones. For crystalline rocks of low metamorphic degree, wells in the zones of influence of dikes are 4.3 times more productive than when allocated in the host rocks not affected by the presence of dikes.