Geophysical reassessment of the Azimuth 125° Lineament: emplacement model and propagation of its dikes

Abstract

This study analyzes the area along the Azimuth 125° Lineament (Az 125°) supposed to occur from Rondônia to Rio de Janeiro, in Brazil. The lineament is an important structural feature in association with great carbonatite and kimberlite complexes in Brazil (e.g., Goiás and Alto Paranaíba Alkaline Provinces), consisting of extensive NW-SE oriented faults. The origin of the Az 125° Lineament and its dikes emplacement are widely discussed. The main intention of this work is to propose a model of emplacement of the Az 125° dikes. Also, some important magnetic characteristics of the lineament are presented. The magnetic data clearly define the features of the Az 125° in the southern portion of the study area, but we found no magnetic geophysical evidence that this lineament occurs from the Mato Grosso state to the Rondônia state. The dikes that compose the great Az 125° feature have dis-tinct magnetic attributes, as their polarities (normal and reversed). It is suggested that the alternating polarity is due to local re-magnetization sometime after their intrusion. It is proposed that the dikes were positioned along a zone of lithospheric weakness and their propagation was facilitated due to the occurrence of mid-crustal axial feeder chambers.