Ana Cláudia Dantas da Costa

Magmatismo cálcio-alcalino Calimiano no embasamento do Terreno Jauru (Província Rondoniana - San Ignácio), Cráton Amazônico: geoquímica e geocronologia Sm-Nd E U/Pb

The Taquarussu Orthogneiss and the Guadalupe Granodiorite, part of the Rondonian-San Ignacio Province basement, southwest of the Amazonian Craton, correspond to oriented bodies with a NW trend. The rocks show granodiorite composition with minor occurrences of coarse grained monzogranites consisting essentially of plagioclase, quartz, microcline, orthoclase and biotite. The accessory minerals are amphibole, titanite, garnet, apatite, epidote, zircon and opaque. The geochemical data indicate that the rocks are classified as granodiorites and monzogranites, with an intermediate to acid magmatism, sub-alkaline character, from the calc-alkaline to the high-K calc-alkaline series, with alumina ratios ranging from metaluminous to lightly peraluminous. The rocks were classified as generated in volcanic islands arc environment and the U-Pb data (SHRIMP zircon) show a concord age 1575 ± 6 Ma. The Sm-Nd model age (T DM) is 1.63 Ga with eNd (t = 1.57 Ga) ranging from -1.52 to +0.78. These data indicate that these rocks are probably a juvenile crust with a possible contamination of crustal rocks.

Geologia e petrografia do Grupo Alto Jauru na região da Fazenda Retiro Novo, SW do Cráton Amazônico: evidências de um prisma acrescionário estateriano

The Alto Jauru Group, located in southwestern Amazonian Craton, region of Retiro Novo Farm, comprises biotite-muscovite-quartz schists, chlorite-biotite-muscovite schists, garnet-cordierite-biotite schist and staurolite-andalusite-biotite schist, associated with garnet-sillimanite-biotite gneiss, biotite gneiss, amphibolite and muscovite granite. The group shows evidence of being an accretionary prism dominated by sediments. Petrography and structural relationships indicate that it was affected by two deformational events, Dn and Dn+1, associated with Sn foliation (schistosity and gneissic banding) and Sn+1 (crenulation cleavage), and three metamorphic events (M1, M2 and M3): the first is contemporary with Sn in lower greenschist facies; M2 is associated with the second phase of Sn+1 under greenschist to amphibolite facies; the third thermal event of amphibolite facies resulted from intrusion of the Cabacal tonalite. Determination obtained by U-Pb (SHRIMP) on zircon provided the age of 1819 ± 6.7 Ma for the crystallization biotite gneiss igneous protolith. From the tectonic point of view, the Alto Jauru Group corresponds to an accretionary prism formed in the Statherian.

Caracterização estrutural do domínio interno da Faixa Paraguai na região de cangas, porção centro-sul do Estado de Mato Grosso

The structural study of rocks in the district of Cangas showed the identification of three phases of deformation for the Cuiaba Group in this region. The main structure oriented 120/27 is related to the first phase of deformation defined by a slate cleavage, parallel to the bedding and to the axial plane of recumbent folds. In the early stages of this phase a family of quartz veins (V1) was generated, arranged parallel to the structures of this phase of deformation, being all almost deformed. The second phase of deformation formed a crenulation cleavage (Sn+1), axial plane of opened to gentle and asymmetric normal folds, with preferential orientation 110/68. The third phase of deformation is represented by a set of centimetric to decametric scale fractures and faults with metric slip that cut all previous structures, with orientations 35/82. Related to this phase of deformation occurs a second family of quartz veins (V2), which fills the fractures related to Dn+2 and may or may not be carrying gold mineralization.