Ground magnetic survey and 3D geophysical model of ultrabasic rocks from the Martín García Complex (Buenos Aires, Argentina)

BENÍTEZ, MANUELA; PREZZI, CLAUDIA BEATRIZ; BALLIVIÁN JUSTINIANO, CARLOS; VERDECCHIA, SEBASTIÁN; DE MARTINO, FACUNDO; CARLINI, MERCEDES; LANFRANCHINI, MABEL

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2023 vol. 121

0895-9811

The Martín García Complex, which crops out at the homonymous island of the Río de la Plata Estuary, is composed of intermediate to silicic orthogneisses and granitoids, hornblende and olivine gabbros, and felsic dykes of Paleoproterozoic and Mesoproterozoic ages, as well as serpentinized ultrabasic rocks of unknown age. A major part of this igneous-metamorphic basement is covered by sediments and vegetation, hiding the relationships between the different rock units and hindering their study. Therefore, a ground magnetic survey and the consequent 3D geophysical modeling were conducted in order to elucidate the geometry of the ultrabasic bodies in the subsurface. Normal and reverse dipolar sub-circular and elongated (~ ENE-WSW) magnetic anomalies were identified. It is proposed that Fe-chromite 28 and/or Cr-magnetite would be responsible for some of the detected magnetic anomalies. Our results suggest the existence of three magnetic units with a dyke-type geometry, all of them with ~ ENE-WSW trend and steep dip. The magnetic survey and 3D modeling allowed us to confirm the continuity and extension in the subsurface of the ultrabasic bodies cropping out discontinuously on the surface. Magnetic patterns identified in Isla Martín García are similar to those observed in Western Uruguay, suggesting that the Martín García Complex would be part of the Piedra Alta Terrane (Río de la Plata Craton).