This paper presents the characteristics of the high resolution secondary ion mass spectrometer coupled with an Ion Microprobe (SHRIMP IIe/MC), installed at the Institute of Geosciences of the University of São Paulo (IGc-USP), as well as the respective analytical procedures and the first results obtained with standard samples, making possible to conduct routine analysis of zircon samples. The standard of the Temora 2 zircon, with age of 416.78 Ma, was analyzed by the SHRIMP IIe/ MC at the Institute of Geosciences of the University of São Paulo and yielded the age of 416.8 ± 3.8 Ma. Samples of the Archean zircon OG1 and the Neoproterozoic zircon Z6266, which yielded U-Pb ages of 3465.4 ± 0.6 Ma and of 559 ± 0.2 Ma, respectively, using Thermal Ionization Mass Spectrometry (TIMS), were analyzed by SHRIMP IIe/MC at the IG-USP and yielded U-Pb ages of 3462.6 ± 5.1 Ma and 561.0 ± 0.92 Ma, respectively, in Concordia diagrams. Therefore, these values and the literature values are very close. Both OG1 and Z6266 samples, due to the homogeneity in their composition and isotopic relationship, can be used as SHRIMP standard. These results indicate that data obtained using SHRIMP IIe at the IGc-USP are reliable and compatible with international standards. Dating of samples with ages ranging from Cenozoic to Archean, obtained using SHRIMP IIe/MC U-Pb geochronology on zircon crystals, is presented here to illustrate this point.

Palavras-chave: Araçaíba, Formação Água Clara, metabásica, Mesoproterozóico, U-Pb. RESUMOO objetivo deste trabalho fundamenta-se no estudo isotópico dos corpos metabasíticos associados à Formação Água Clara e as suas relações com as encaixantes. A Formação Água Clara é constituída predominantemente por uma seqüência de rochas carbonáticas (mármores puros a impuros). Rochas cálcio-silicáticas, cálcio xistos, mica xistos, anfibólio xistos, quartzitos, granada-clorita-biotita xistos, metacherts, metatufos básicos e intermediários, metabasitos, anfibolitos e cornubianitos. As rochas metabásicas estudadas normalmente têm dimensões longitudinais expressivas chegando a quilométricas, com dimensões transversais de até centenas de metros. São de coloração cinza -esverdeada, apresentam granulometria fina a média e textura normalmente nematoblástica. Ocorrem termos mais isótropos que exibem textura granoblástica. São compostos por piroxênios (diopsídio ou augita), anfibólios (actinolita e hornblenda) e plagioclásios (andesina/oligoclásio). Os acessórios mais comuns são apatita, magnetita, epidoto, titanita e raramente zircão. Em lâmina observa-se texturas ofíticas e subofíticas preservadas o que indica uma provável origem ígnea para esses corpos. Os dados geoquímicos sugerem composições semelhantes a basaltos enriquecidos de cadeias mesoceânicas (E-MORB) com tendências a basaltos de ilhas oceânicas (OIB). As características de basaltos toleíticos, subalcalinos semelhantes a basaltos enriquecidos de cadeias mesoceânicas com tendência a basaltos de ilhas oceânicas (OIB), permitem sugerir como ambiente geotectônico gerador deste magmatismo básico, ambientes distensivos ou em bacias de retroarco. Os dados analíticos U-Pb (convencional, EMF e SHRIMP) obtidos para os litotipos metabásicos indicam épocas de cristalização dos zircões e conseqüente formação dessas rochas durante o mesoproterozóico, com idades do intervalo 1590 -1470 Ma. Os valores neoproterozóicos obtidos (~600 Ma) provavelmente referem-se a processos de recristalização e neoformação de zircões nas rochas metabásicas, colocação de rochas de natureza granítica e resfriamento regional da Formação Água Clara.Keywords: Água Clara Formations, Araçaíba, metabasic rocks, Mesoproterozoic, U-Pb. ABSTRACTThe main objective of this work is to present U-Pb isotopic data obtained from zircons of metabasic rocks and subordinate acid and associated rocks of the Água Clara Formation in the Araçaíba region -São Paulo. The Água Clara Formation is predominantly constituted by a sequence of carbonate rocks (pure to impure marbles), calc-silicate rocks, calc schists, mica schists, amphibole schists, quartzites, garnet-chlorite-biotite schists, metacherts, basic and intermediate metatuffs, metabasites, amphibolites and cornubianites. The metabasic bodies are usually a few km long with widths of hundreds of m. They are greenish gray, fine-to medium-grained, and usually present nematoblastic texture. More isotropic terms also occur, showing granoblastic texture. They are composed of pyrox...

Na porção sul do Cinturão Ribeira, especificamente região sul-oriental do Estado de São Paulo, quatro domínios tectônicos distintos foram definidos, delimitados por importantes zonas de cisalhamento neoproterozóicas. O Domínio Embu, situado a norte da Zona de Cisalhamento Cubatão (ZCC), compreende metassedimentos parcialmente fundidos e granitos peraluminosos intrusivos, que são balizados por zonas de cisalhamento ENE e apresentam idades U-Pb em torno de 600 Ma, e idade TDM de 2,0 Ga. Rochas gnáissico-migmatíticas (612 Ma) e graníticas associadas (580 Ma) predominam no Domínio Mongaguá, limitadas a NW pela ZCC, e a sul pela Zona de Cisalhamento Itariri (ZCI), com idades TDM variadas, entre 1,7 e 2,2 Ga. O Domínio Registro é limitado a norte pelo Sistema de Cisalhamento Cubatão Itariri (SCCI) e a sul pela Zona de Cisalhamento Serrinha (ZCS), composto por rochas metassedimentares de alto grau e rochas graníticas com feições migmatíticas. Representa um terreno paleoproterozóico (1,9 -2,2 Ga) fortemente afetado durante o Neoproterozóico (750 -580 Ma). O Domínio Iguape é limitado a norte pela ZCS e compreende rochas graníticas, com cerca de 600 Ma, intrudidas em metassedimentos de baixo grau. Granitos semelhantes aos da Suíte intrusiva Serra do Mar ocorrem nos Domínios Registro e Iguape, com idades em torno de 580 Ma. Possivelmente, a justaposição destes domínios tectônicos ocorreu em épocas neoproterozóicas próximas: 1) a justaposição do Domínio Registro ao Embu, através de zona de cisalhamento EW, teve como época máxima 596 Ma; 2) granitos intrusivos no Domínio Embu, com cerca de 598 Ma, controlados pelo SCCI podem estar associados à justaposição do Domínio Mongaguá, aos Domínios Registro e Embu; 3) a época mais provável da colagem Domínio Iguape / Registro de 575 Ma é sugerida através de datações U-Pb (monazita) em protomilonito granítico da ZCS.Keywords: Neoproterozoic, tectonic domains, shear zones, gneiss-migmatite rocks. ABSTRACTIn the southeastern region of São Paulo State four major tectonic domains were defined. The Embu Domain, north of the Cubatão Shear Zone (CSZ), is composed of metasedimentary rocks, and peraluminous granites (ca. 600 Ma), whose intrusion was controlled by E-NE shear zones, and which have model Nd TDM age around 2.0 Ga. Gneiss-migmatite rocks (612 Ma) and related granites (580 Ma) predominate in the Mongaguá Domain, which is limited by the Cubatão and Itariri shear zones. These rocks have different model Nd TDM ages between 1.7 and 2.2 Ga. The Registro Domain, between Cubatão -Itariri Shear System (CISS) and the Serrinha Shear Zone (SSZ), is formed by metasediments and granitic rocks with migmatitic features, and represents a paleoproterozoic domain (1.9 -2.2 Ga) intensely affected in Neoproterozoic times . Rocks of the Iguape Domain, limited to the north by the SSZ, include granites (ca. 600 Ma) and low grade metasediments. It is probable that all these tectonic blocks were juxtaposed during a short time interval at the end of Neoproterozoic. The joining of the Registro to the Embu Dom...

The Paranaguá Terrane is composed of precambrian geological units distributed in a NE-SW elongated swath, about 250 km long and 30 km wide, in south-southeastern Brazil, within the States of São Paulo (Nothern Paranaguá Terrane), Paraná and Santa Catarina (Southern Paranaguá Terrane). This terrane is constituted mainly by an igneous complex, represented by the Morro Inglês, Rio do Poço and Canavieiras-Estrela suites. The country rocks of these l.s. granites are gnaissic and gnaissic-migmatitic rocks of the São Francisco do Sul Complex and metassedimentary rocks of the Rio das Cobras Sequence. Lithochemical signatures of the Morro Inglês Suite are compatible with arc magmatic-generated granitic rocks, with high-K to shoshonitic calc-alkaline character and relatively high contents of Ba, Nb, Zr, Rb, Sr, Th and K 2 O. This pattern resembles the one observed in sin-to late-collisional environments related to mature magmatic arcs, with sources modified by crustal contamination. The Canavieiras-Estrela Suite is composed of quartz-monzodiorites, leucogranites and monzogranites, with porphyritic and inequigranular rocks, with mafics represented by biotite ± anfibole. Comparativily, the Morro Inglês Suite rocks present higher values of K 2 O and smaller values of Na 2 O than the rocks of the Canavieiras-Estrela Suite. Both suites show important variations of Ba and Sr, high values of Rb and Zr, and medium-to-high values of Nb and Y. Two distinct rock units can be individualized in the Rio do Poço Suite, based on petrographical and lithogeochemical differences. The rapakivi sienogranites characteristics are compatible with metaluminous to marginally peraluminous type A granites. Such interpretation does not seem adequate for the two-mica leucogranites in this suite, which present a marginally peraluminous character, with HREE-depleted rocks, without an Eu negative anomaly. Petrographic and, mostly, structural data suggest that the Morro Inglês, Canavieiras-Estrela and Rio do Poço suites emplacement occurred during a late stage of the collisional event. U-Pb ages (zircon) of these suites are very close and does not allow a clear separation of them. A high concentration of ages between 600-580 Ma represent the main magmatic period of the Paranaguá Terrane. Although less frequent, older ages between 620-610 Ma were obtained in the three suites, suggesting the presence of a relatively early magmatism in this terrane's evolution. U-Pb ages (zircon) obtained in crystals borders, as well as in late leucogranitic veins, are distributed between 560-480 Ma. These ages must be related with important thermotectonic events of the Cambro-Ordovician Rio Doce Orogeny. The metassedimentary rocks of the Rio das Cobras Sequence occur as elongated strips, with little areal expression. In the southern portion of the Paranaguá Terrane, green schist (biotite zone) paragenesis are present (Serra da Prata -PR), while in the central and northern portions there are afibolite facies paragenesis up to granulite facies in association with kyanite-garne...

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Os estudos rt:aIizados nos terrenos localiudo$ entre 05 Cinturoes Ribeira (N) e Dom feliciano (S)pennitiram caracterizar a existência dc lIis dominios geotectônicos com evoluçlles próprias c distintas: Dom.iniosLuisAlves, Curitiba e PBI'8IlagUá. O Complexo AlUba se insere no imbito do Domínio Curitiba, que se limita a Il(Il'OCSIe com as seq~as metasscdlmmtare dos Grupos AÇWlgUi e Setuva, c a 5Udeste com os gnaisses granuiíticos do Domínio Luis Alves, contatos = que se fazem por Unportanle3 zonas de ci$alhamento. PmIominarn. no Domínio Cwitiba rodlas gnáissicas bandadas, migmatiticas, do fácics anfibolito. representadas principalmen!e por biotita-anfibólio-gnaisses contendo leuoossomas de composiçõe5 tooalitogranodioriticas albll de granítiC8$, que compilem O aqui denominado Compkx:o Aruba. CaJ1Icteriu-se por migmatitosfonnadosooPalcopMerozóico(2.000±200Ml),remigoWiz;ldosnoNcoproterozóico(6OQ± 20 MI), período esse em que as isotmnas atingiram temperaturas superiores a 500 oCo O padrão esautunJ obsenoado é indicativo de uma tectônica controLada em grande pane por cisaLhamento, com importante componente lateral, e transpOrte relativo em direçlo a sul-sudeste. As rochas pertencentes ao CompLexo Atuba repre$CIWIIIl terrenos rdativamente profundos, do fides anfibolito, migrru.tizados, granitiudos &ere$cidos oi borda do Domínio Luis Alves (MicropLaca Luis Alvcs) dunlnte o Ncoproterozóico. Este quadro tectônico ddinido no finaL do Ncoprote-rozóicocomcontinuidadeatéoCambro-Ordoviciano,pareceserorcsultadode proccssosmaiores,envol_ vendo aglutinações de massas continentais, que cuIminarnrn com a formaçJo do Gond\wna Ocidental.

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The production of juvenile continental crust was larger in the Proterozoic than Archean. During Proterozoic the production was about 64%, while during Archean was around 34% of the total volume. The great accretion from mantle to crust happened between 2,2 to 1,9Ga corresponding 35% of the total volume of the actual continental crust. During Archean an intense recycling between mantle and continental crust took place, while in Paleoproterozoic the rate of mantle accretion to continental crust was larger than the assimilation. During MesoNeoproterozoic little accretion of juvenile material occurred, predominating crustal reworking. Consequently the chemical depletion rate (fractionation) of the upper mantle was smaller in Archean than Proterozoic. The isotopic data show a certain increase of the depletion degree of Sm-Nd and Rb-Sr in the upper mantle that began at 2.2 Ga as a reflex of the strong differentiation of the upper mantle to continental crust.