Wagner da Silva Amaral

Provenance and tectonic setting of neoproterozoic supracrustal rocks from the Ceará Central Domain, Borborema Province (NE Brazil): constraints from geochemistry and detrital zircon ages

Major- and trace-element and U–Pb analyses of detrital zircons were performed on metavolcano sedimentary sequences and igneous rocks from the Ceará Central Domain (CCD) in the Borborema Province of northeastern Brazil. No significant geochemical differences were found between these rocks, which were possibly initially deposited as parts of a very large metavolcano-sedimentary sequence. Weathering in the source area was moderate, and the sediments were deposited as both sands and clays. The sources of the sediments were likely mixtures of felsic and intermediate rocks deposited predominantly in an active-margin setting with minor contributions of both continental arc and passive margin components. Three main source ages were identified: Palaeoproterozoic (~2.2 Ga), for which potential sources include the Palaeoproterozoic Madalena-Algodões Suite; early Neoproterozoic (~850 Ma), related to felsic volcanic magmatism due to continental rifting, initial phases of the Santa Quitéria Magmatic Arc, or magmatic arc systems on the margins of the Palaeoproterozoic crust; and late Neoproterozoic (~650 Ma), associated with extensive granite generation and migmatization events accompanying Santa Quitéria Arc activity. Deposition of the CCD volcanosedimentary rocks occurred shortly before regional, collision-type metamorphism accompanying the amalgamation of the São Francisco-Congo Cratons (~ 620–630 Ma).Major- and trace-element and U–Pb analyses of detrital zircons were performed on metavolcano sedimentary sequences and igneous rocks from the Ceara Central Domain (CCD) in the Borborema Province of northeastern Brazil. No significant geochemical differences were found between these rocks, which were possibly initially deposited as parts of a very large metavolcano-sedimentary sequence. Weathering in the source area was moderate, and the sediments were deposited as both sands and clays. The sources of the sediments were likely mixtures of felsic and intermediate rocks deposited predominantly in an active-margin setting with minor contributions of both continental arc and passive margin components. Three main source ages were identified: Palaeoproterozoic (~2.2 Ga), for which potential sources include the Palaeoproterozoic Madalena-Algodoes Suite; early Neoproterozoic (~850 Ma), related to felsic volcanic magmatism due to continental rifting, initial phases of the Santa Quiteria Magmatic Arc, or magmatic ar...

Airborne geophysical and tectonics of the Ceará central domain, eastern region of the Santa Quitéria magmatic ARC, Borborema Province, NE Brazil

The airborne geophysical data gamma-spectrometric and magnetic from Itatira Project (1977) was carried out, in the central region of the State of the Ceara, Brazil. Their processing produced products useful to indirectly identify regional geologic features. The verification and applicability of this approach was tested in a pilot-area whose limits are within the Umirim and Caninde topographic sheets, at 1:100,000 scale. The integration between the airborne geophysical and the geologic field data supported to the geologic mapping at the same cited scale. Two main units were recognized: the Santa Quiteria magmatic arc and the supracrustal sequences that surround the arc. The rocks fram Santa Quiteria magmatic arc are characterized by high counting on the K-channel in its almost entire region and intermediate and low counting of eTh and eU. Generally, the supracrustal sequences are characterized by high values on the eU-and-eTh-channels and low on K-channel. The subunit metaultramafics and, mafics granulites, are remarkable by the occurrence retrograde eclogites bands and mafic granulites as lenses within gneisses and migmatites. These subunits present strong negative anomalies, with low counting on the three K, eTh and eU channels. That area also has positive magnetic anomalies, and may reflect high values of magnetic susceptibility.

Geoquímica do Plúton Serra das Melancias, Suíte Serra da Aldeia: um clássico granito pós-colisional de alto Ba-Sr na Faixa Riacho do Pontal, NE Brasil

The Serra da Aldeia Suite is composed by circular or oval-shaped plutons, intrusive in meta-sedimentary and meta-volcanosedimentary rocks in the Riacho do Pontal Fold Belt, NE Brazil. The Serra das Melancias Pluton, belonging to Serra da Aldeia Suite, is located southeastern of Piaui state, near Paulistana city. These plutons represent a major magmatic expression in this area and contain important information about the late magmatic/collisional geologic evolution of the Brasiliano Orogeny. Based on petrographic and geochemical data, three facies were defined in the Serra das Melancias Pluton: granites, syenites and quartz monzonites. The rocks display high-K and alkaline to shoshonitic affinities, are metaluminous and show ferrous character. They are enriched in Light Rare Earth Elements and Large Ion Lithophile Elements, with negative anomalies in Nb, Ta and Ti. Their high Ba, Sr, K/Rb, low Rb, relatively low U, Th, Nb to very low Heavy Rare Earth Elements and Y resemble those of typical high Ba-Sr granitoids. The geochemical data suggest the emplacement of Serra das Melancias Pluton in a transitional, late to post-orogenic setting in the Riacho do Pontal Fold Belt during the late Brasiliano-Pan African Orogeny.Manuscript ID: 20160002. Received in: 01/06/2016. Approved in: 04/28/2016. ABSTRACT: The Serra da Aldeia Suite is composed by circular or oval-shaped plutons, intrusive in meta-sedimentary and meta-volcanosedimentary rocks in the Riacho do Pontal Fold Belt, NE Brazil. The Serra das Melancias Pluton, belonging to Serra da Aldeia Suite, is located southeastern of Piaui state, near Paulistana city. These plutons represent a major magmatic expression in this area and contain important information about the late magmatic/collisional geologic evolution of the Brasiliano Orogeny. Based on petrographic and geochemical data, three facies were defined in the Serra das Melancias Pluton: granites, syenites and quartz monzonites. The rocks display high-K and alkaline to shoshonitic affinities, are metaluminous and show ferrous character. They are enriched in Light Rare Earth Elements and Large Ion Lithophile Elements, with negative anomalies in Nb, Ta and Ti. Their high Ba, Sr, K/Rb, low Rb, relatively low U, Th, Nb to very low Heavy Rare Earth Elements and Y resemble those of typical high Ba-Sr granitoids. The geochemical data suggest the emplacement of Serra das Melancias Pluton in a transitional, late to post-orogenic setting in the Riacho do Pontal Fold Belt during the late Brasiliano-Pan African Orogeny.

Detrital zircon U–Pb ages and whole-rock geochemistry of the Neoproterozoic Paulistana and Santa Filomena complexes, Borborema Province, northeastern Brazil: implications for source area composition, provenance, and tectonic setting

ABSTRACT The Paulistana and Santa Filomena Complexes are situated in the southern part of the Borborema Province (northeastern Brazil), in the Riacho do Pontal Orogen, and represent meta-volcano-sedimentary sequences. We present compositional variations in the metasedimentary rocks and new U–Pb detrital zircon data. Major and trace elements indicate that the metasedimentary rocks from the Paulistana and Santa Filomena Complexes are composed mostly of immature to mature sediments derived from felsic-intermediate sources with moderate to slightly high chemical weathering. The geochemical signatures of the sediment protoliths for both complexes are characteristic of continental magmatic arc settings with minor contribution from recycled sediment sources. The source area for the Paulistana Complex rocks follow the compositional trend between calc-alkaline granites and granodiorites, whereas the Santa Filomena Complex rocks have a more restricted composition trending to more granodioritic sources. For the Paulistana Complex, two main source ages were identified: (1) Tonian (ca. 950 Ma – sample RPE-58) and Tonian–Stenian (ca. 1.0 Ga – sample RPE-103). These data coupled with geochemical information suggest that the Cariris Velhos arc system was the main source area for the Paulistana Complex. Regarding the Santa Filomena metasedimentary rocks, potential source-areas include: (1) Neoarchaean rocks (~2.6 Ga) represented by the adjacent basement rocks of the Riacho do Pontal Orogen; (2) Rhyacian–Orosirian rocks (2.2–2.0 Ga) of the Riacho do Pontal Orogen and the Pernambuco–Alagoas terrain, which include an augen-gneiss with arc-related geochemical signature; (3) Statherian granites (1.7–1.6 Ga); and (4) Cariris Velhos crust (1000–920 Ma). The metasedimentary rocks of the Paulistana Complex were deposited in a rift stage (ca. 900 Ma), which is related to the break-up of the Rodinia supercontinent. The metasedimentary rocks of the Santa Filomena Complex most probably were deposited in another rift stage (ca. 750–700 Ma) and could be correlatives of the rift formation of the Canindé Domain (Sergipano Orogen).

Levantamento de feições estruturais lineares a partir de sensoriamento remoto - uma contribuição para o mapeamento geotécnico na Serra de Baturité, Ceará

The use of techniques of digital image processing remote sensing allows applications of great importance for the geosciences. One of the possible fields of application of these resources is the geotechnical mapping. Filtering techniques for radar and optical images emphasize natural linear structures that can be interpreted as fractures, drainages, ridges, valley bottoms and foliation. With the lifting of these data, combined with field work, the geotechnical mapping gains in precision and agility. The high incidence of slope instability events recently occurred in some parts of Brazil, especially in the Southeast, has attracted the interest of researchers in engineering and geoscience areas in the preparation of monographs, dissertations, theses and academic articles that address this issue. For subsequent generation of a diagram rosettes and visualization of regional trend of the structures and preparation of lineament density map, the vectors corresponding to the guidelines direction were measured in azimuth, and the length was measured in meters. The importance of applying frequency spectrum filters is therefore to quantify and qualify these geological and geomorphological structures, which are among the main components of conditions of mass movements and erosion.