Geologia e controle estrutural do enxame de diques Rio Ceará-Mirim na porção Leste do Rio Grande do Norte

Abstract

The Rio Ceará-Mirim Dikes Swarm (EDCM) is composed of E-W oriented tabular bodies of basalts/diabases, mainly exposed in Rio Grande do Norte, Brazil. The EDCM extends to southern Ceará showing progressively less frequent occurrences. The western termination of EDCM follows the NE-SW Cariri-Potiguar trend, which control some sedimentary basins. Expressive rifting systems involving South America and Africa is responsible for generation of the EDCM during Lower Cretaceous. The present paper aims a better comprehension of the structural control related to accommodation and propagation of EDCM. The methodology comprised remote sensors image analysis, visits to outcrops and microscopic description. It is possible to divide the dikes sampled into two groups according to mineralogical and petrographic characteristics. The first comprises diabases and basalts containing augite, plagioclase, crypto / microcrystalline groundmass, opaque, apatite and vesicular zeolite. The second group has olivine, titanoaugite, plagioclase, biotite, opaque and apatite as mineral assemblage. Integrated analysis of maximum distension plane associated to the dikes indicates crustal distension approximately NS with slight transcurrent dextral component (sigma3 = 005 Az). Crosscutting relationships show three magmatic pulses with the E-W dikes as the first one, later affected by NE-SW dike of second pulse. Finally, a third pulse cuts with WNW-ESE direction the previous structures. This relationship is related to NW-SE alignment of distension axis in Rio Salgado River dikes (Lajes/RN), according to Potiguar Rift orientation. Morphological features suggest a predominant crustal stretching for dikes accommodation and propagation. However, some structures denote a participative hydraulic fracturing.