Maria Zélia Aguiar de Sousa

Batólito Guaporeí: uma extensão do Complexo Granitoide Pensamiento em Mato Grosso, SW do Cráton Amazônico

O Batolito Guaporei e um corpo de aproximadamente 240 km 2 alongado segundo a direcao NW, localizado na regiao de Vila Bela da Santissima Trindade, estado de Mato Grosso. Situa-se nos domi- nios da Provincia Rondoniana-San Ignacio, no Terreno Paragua, na por- cao meridional do Craton Amazonico. E formado por monzogranitos e, subordinadamente, granodioritos, quartzo-monzonitos e sienogranitos, caracterizados por granulacao grossa e textura, em geral, porfiritica a porfi- roclastica. Possui biotita como mineral mafico primario, por vezes, associa- da a anfibolio, e encontra-se metamorfizado na facies xisto verde, exibindo estrutura milonitica, em estreitas zonas de cisalhamento. Evidencias geo- quimicas indicam que essas rochas derivam de um magma calcio-alcalino de alto potassio a shoshonitico, metaluminoso a levemente peraluminoso evoluido por cristalizacao fracionada associada a assimilacao crustal, possi- velmente gerado em ambiente de arco continental. Duas fases de deforma- cao relacionadas a Orogenia San Ignacio, caracterizadas pelo estiramento e alinhamento mineral evidenciadas pelas foliacoes S 1 e S 2 , foram identifica- das nestas rochas. Foi obtida pelo metodo de evaporacao de Pb em zircao uma idade de 1.314 ± 3 Ma, interpretada como idade de cristalizacao do corpo granitico. Dados Sm-Nd em rocha total indicam idade modelo T DM em torno de 1,7 Ga e valor negativo para e Nd (t = 1,3) (-14), corroborando a hipotese de envolvimento crustal na genese do magma. Os resultados ob- tidos apontam semelhancas entre essas rochas e aquelas de regiao adjacente em territorio boliviano, sugerindo que o Granito Guaporei representa uma extensao do Complexo Granitoide Pensamiento.

Geologia e Geoquímica do Batólito Rapakivi Rio Branco, SW do Craton Amazônico - MT

The Rio Branco Rapakivi Batholith belongs to the Cachoeirinha Tectonic Domain, part of the Rio Negro-Juruena Geochronological Province located on the southwestern portion of the Amazonian Craton in Mato Grosso, Central Brasil. A systematic geological mapping on a 1:100.000 scale, coupled with petrographic and geochemical studies allowed to redefine this batholithic unit, to recognize faciological variations and to characterize the geochemical features of this rapakivi magmatism. The batholith is constituted by two major plutonic suites, the first forming a basic suite of fine-grained, equigranular, meso- to melanocratic gray to black lithotypes, with usually discontinuous porphyritic varieties located near the margins of the intrusion. The second one is characterized by acid to intermediate rocks constituted by porphyritic granites, in part granophyric, with rapakivi textures. They have K-feldspar phenocrysts of up to 4cm. Three distinct petrographic facies are recognized in this suite: 1. equigranular to pegmatitic monzogranites; 2. red rapakivi leuco-monzogranites; 3. dark red rapakivi monzogranites to quartz-monzonites. Rocks present SiO 2 contents from 67% to 73%, show peraluminous to metaluminous compositions and define a high-K calc-alkaline to shoshonitic magmatism in an I- and A-type, post-orogenic to anorogenic intraplate environment. The magmatic processes are associated with the end of the collisional event that consolidated and stabilized the SW part of the Amazonian Craton.

Geology, petrology and geochronology (Pb-Pb) of the Serra da Bocaina Formation: evidence of an Orosirian Amoguijá Magmatic Arc in the Rio Apa Terrane, south of the Amazonian Craton

This work presents the results of the geological mapping and the petrological characterization of the Serra da Bocaina Formation belonging to the Amoguija Magmatic Arc of the Rio Apa Terrain. In the Bocaina hills, the Serra da Bocaina Formation consists of intermediately to predominately acidic volcanic rocks, classified as andesites and rhyolites and subdivid- ed into five petrographic facies, which include four volcanoclas- tics and one effusive. In the studied rocks, tectonic structures are generated in two compressive ductile to ductile-brittle deforma- tional phases. The first phase, which is more intense, presents along the entire studied area and is responsible for the Santa Rosa Shear Belt, whereas the second phase is more localized. The geochemical study indicates a calc-alkaline magmatism of medium to high K, peraluminous, and generated in a volcanic arc environment. These volcanic rocks formed in an explosive environment related to the Amoguija Magmatic Arc, as indicat- ed by their Pb-Pb zircon age of 1877.3 ± 3.9 Ma.

Batólito Cerro Porã: granito tipo-A pós-orogênico do arco magmático Amoguijá - terreno Rio Apa - sul do Cráton Amazônico

The Cerro Pora Batholith has an approximately area of 30 km by 4 km, situated at the region of Porto Murtinho, Mato Grosso do Sul. It is located in Rio Apa Terrane, at the southern portion of the Amazonian Craton. It consists of Pink Syenogranitic Facies and Gray Monzogranitic Facies. The first facies is characterized by xenomorphic equigranular texture to essentially inequigranular texture with graphic and granophiric intergrowths. Both facies are composed of alkali feldspar, quartz, and plagioclase with biotite as the only primary mafic mineral. The Gray Monzogranitic Facies has porphyritic texture with graphic to granophiric fine-grained groundmass. It consists of quartz, plagioclase, alkali feldspar, and mafic aggregates (biotite and amphibole). Both facies were metamorphosed at greenschist facies and the Pink Syenogranitic Facies, which is milonytic in nature when it is in shear zones. One event of ductile-brittle deformation was identified, originated in a compressive system. It was responsible for the schistosity and mineral-stretching lineation. The development of the Esperanca shear zone is related to this deformational phase and reflects the cinematic history of the reverse convergent system with top transport to NWW. Chemically, these rock types are classified as A2-type granitoids of range alkaline potassium saturated on silica. Geochronological data obtained by U-Pb (Sensitive High Resolution Ion Microprobe) method in zircon resulted in an age of 1749 ± 45 Ma, interpreted as crystallization age of the batholith. From the geotectonic point, the Cerro Pora Granite is considered to be the product of a magmatism associated with a magmatic arc developed in Statherian and emplaced in late-orogenic to post-orogenic stage.

Geology, Geochemistry, and Geochronology (U-Pb) of the Rio Fortuna Gneiss - Serra do Baú Intrusive Suite - Paraguá Terrane - SW Amazonian Craton

O Gnaisse Rio Fortuna aflora na regiao da serra Santa Barbara, nas imediacoes do Destacamento Militar Fortuna, na fronteira Brasil-Bolivia. Do ponto de vista geologico-tectonico, estes gnaisses estao inseridos no Terreno Paragua, em um setor afetado pela Orogenia Sunsas (1.0 a 0.9 Ga). Os dados geologicos e petrograficos obtidos mostram que estas rochas sao ortognaisses de composicao monzo a granodioritica, com registros de tres fases de deformacao. Idade U-Pb em zircao de 1711 ± 13 Ma obtida por MC-ICP-MS com ablacao a laser, deve corresponder aidade de cristalizacao do protolito igneo. Geoquimicamente, essas rochas constituem uma sequencia acida formada por um magmatismo subalcalino, do tipo calcio-alcalino de alto potassio, metaluminoso a peraluminoso. No contexto tectonico do Terreno Paragua, os dados obtidos indicam que o Gnaisse Rio Fortuna foi formado durante a Orogenia LomasManechis. Os resultados obtidos apontam semelhancas entre esta rocha e a que se prolonga na contraparte boliviana.

Geology and petrology of the Salto do Céu Suite: tectonic and stratigraphic implications on the SW Amazonian Craton

The basic rocks of the Salto do Ceu Suite outcrop as sills and flows in the southwestern Amazon Craton, Rondonian-San Ignacio Province, with an age of about 1.44 Ga. Sills are 2 to 30 m thick being hosted by pelites of the Aguapei Group. The flows are up to 5 m thick and cover this unit. Typical textures of magma mingling are observed near the contact with granites of Rio Branco Suite. The Rio Branco Intrusive Suite is composed of basic and acid rocks, as well as hybrid rocks that indicate mixing processes between basic and acids magmas. U-Pb (TIMS zircon) results indicate ages around 1.4 Ga for both terms. The Salto do Ceu Suite rocks have tholeiites affinity classified as subalkaline and iron-rich tholeiitic basalts, with mg# values between 0.30 and 0.51. They can be separated into two groups, based on La N ; one is richer in ETR with La N greater than 100, while the other one has La N less than 100. Rocks of the Salto do Ceu Suite and Rio Branco Suite are interpreted as a bimodal suites showing magma mingling features such as those developed in continental intraplate settings, extensional regime associated to the Columbia/Nuna breakup.