Mapeamento geológico-estrutural de uma porção da unidade independência do complexo Ceará localizada no distrito de São José dos Guerra, no município de Lagoa do Mato - CE

Abstract

The present report corresponds to a geological map on a scale of 1: 20,000, in an area of approximately 60 km2, located in the district of São José dos Guerra in the municipality of Lagoa do Mato, in the central portion of the state of Ceará, and it has the goal of making up a geological map, a macro and microscopic detail of the region, the definition of a tectonic environment and the description of the geological evolution. The characterization of the studied area was concluded from the bibliographical survey, geological mapping made in the field, evaluation of structural data and laboratory analyzes of petrography. It was observed that 2 foliation patterns Sn, Sn + 1, with Sn being the main one, marked by a strong migmatitic banding with NNW / SSE trend, low angle variable dives, approximately 20 ° for W, and some inflections for E / W caused by Movement of blocks or local shear portions, plus some extra median points, with high dips of up to 75 °. The low angle values clearly suggest a thrust tectonics, generating nappes in the central portion of the mapped area and the high angle values, not associated with milonites, suggest a transtrative shear tectonics in the local ductile shear zones. The region is interpreted as a continental shelf, formed by the intercalation of quartzous, clayey and carbonate sandstone rocks, where the metamorphism of the quartz portions generated quartiles, from the clayey portions generated shale and metatexts the biotite and the carbonate portions generating marbles. Despite the lack of geochronological data, the absence of deformation in the leucosomes of the migmatites suggests a neoproterozoic age for the metamorphism of these rocks. The rocks described in this report comprise a classic metamorphic sequence, type QPC, inserted in the Guia and São José dos Guerra subunits, which are part of the Unidade Independencia, located in the Complexo Ceará, undoubtedly metamorphic, with migmatitic features. Owing to a chronological order the lithologies identified in the field are: shales, marbles, quartizites, paleoprotoerozoic, paraderivados metatexts, calcissilictic rocks and, to a lesser extent, pegmatites, basic dikes, albithic dykes, and neoproterozoic silexes. There is also a late-Brazilian intrusion of a sienogranite, in the NE portion of the mapped area breached by late fluids that host amethyst mineralizations. In general, the units recognized in the area are parifed and were metamorphosed in amphibolite facies during the Brasilian orogeny. The parsed metatexito is the most abundant lithologic type and varies according to a composition some times arcoseana some times gradevaqueana, suggesting the alternation of the types of sediments that generated it. Shales, marbles and quartzites, in turn, occur in the form of lenses or bands with varying extensions and widths. The calcissilictic rocks are in the form of small blocks and small lenses or bands bordering, preferably, the shales and marbles. The magma bodies identified in the area, such as the sienogranite, appear intruding the paraderivadas rocks and exhibit characteristics that suggest a generation without the tardi-orogenic. Shear zones were recognized in the area and may have been facilitators for the intrusive processes that generated the albite bodies, the small pegmatites and aplitos, as well as the mineralization in amethyst.