Gravimetric characterization of Ponte Nova mafic-ultramafic massif (SP-MG)

Abstract

The Ponte Nova massif is located in Serra do Mar Alkaline Province in the southeast part of Brazil. The massif is mainly composed of alkaline gabbro association, with 2 outcrops of 5km2 and 1 km2 areas. A detail gravimetric survey was made, resulting 98 stations, to model the subsurface mass distribution and to understand the geodynamic context of the massif. The data processing shows high gravimetric anomaly (33.3 mGal) in accordance with the Ponte Nova outcrop after removal of a first order polynomial trend line. The gravity high suggests one body with an area not much larger than the intrusion. Based on these results, a 2D preliminary mass distribution model was made. It resulted a body that extends to 5 km in depth. Introduction Parana Basin, at the SE of Brazil, is surrounded by some alkaline provinces with outcrops and covered intrusions, with mafic ultramafic lithologies, some with carbonatite rocks. One of these provinces is Serra do Mar Alkaline Province (SMAP), located at the eastern border, with age between 750-450 Ma. Some of regions around Parana Basin have been geophysically studied (Marangoni and Mantovani, 2013) to understand geological and geodynamic context about their preferential location bordering the basin and the viability of mineral prospecting. The SMAP presents alkaline occurrences in the coastal region of the states of Sao Paulo and Rio de Janeiro and it extends into the country up to Serra da Mantiqueira. These alkaline are embedded in igneous and metamorphic rocks mainly granitic composition from Ribeira Belt. The gravity method has been used as a tool to model alkaline intrusions in subsurface. It has been applied, for instance, at the study of Morro do Engenho Alkaline Complex by Dutra and Marangoni (2009), which shows 3D models of subsurface mass distribution. Marangoni and Mantovani (2013) present a compilation of geophysical studies of three alkaline provinces in the Parana Basin's edge. Due to the good results obtained with the provinces around the Parana Basin, it was made a detail gravimetric acquisition to characterize the Ponte Nova Massif (PNM). This massif is one of the intrusions of SAMP, located 100 km from the coast. The Bouguer anomaly map of the area shows the presence of a gravimetric high in accordance with the Ponte Nova outcrop. Figure 1 presents the location of Bouguer anomaly map. In this study we intend to discuss the results and preliminary model. Figure 1 – Bouguer map of area. SC – Santa Catarina State. PR – Parana State. SP – Sao Paulo State. MG – Minas Gerais State. RJ – Rio de Janeiro State.