U-Pb SHRIMP and Sm-Nd geochronology of the Silvânia Volcanics and Jurubatuba Granite: juvenile Paleoproterozoic crust in the basement of the Neoproterozoic Brasília Belt, Goiás, central Brazil

U-Pb SHRIMP and Sm-Nd isotopic ages were determined for felsic metavolcanic rocks from the Silvânia Sequence and Jurubatuba Granite in the central part of the Brasília Belt. Zircon grains from a metavolcanic sample yielded 2115 ± 23 Ma and from the granite yielded 2089 ± 14 Ma, interpreted as crystallization ages of these rocks. Six metavolcanic samples of the Silvânia Sequence yielded a six-point whole-rock Sm-Nd isochron indicating a crystallization age of 2262 ± 110 Ma and positive epsilonNd(T) = +3.0 interpreted as a juvenile magmatic event. Nd isotopic analyses on samples from the Jurubatuba Granite have Paleoproterozoic T DM model ages between 2.30 and 2.42 Ga and epsilonNd(T) values vary between -0.22 and -0.58. The oldest T DM value refers to a sedimentary xenolith in the granite. These results suggest crystallization ages of Silvânia volcanics and Jurubatuba Granite are the first evidence of a ca. 2.14-2.08 juvenile magmatic event in the basement of the central part of the Brasília Belt that implies the presence of arc/suture hidden in reworked basement of the Brasília Belt.Idades isótopicas U-Pb SHRIMP e Sm-Nd foram determinadas em rochas metavulcânicas félsicas da Seqüência de Silvânia e Granito Jurubatuba na porção central da Faixa Brasília. Grãos de zircão da rocha metavulcânica da Seqüência de Silvânia e do granito forneceram, respectivamente, as idades de 2115 ± 23 Ma e 2089 ± 14 Ma, interpretadas como idades de cristalização destas rochas. Amostras da Seqüência de Silvânia resultaram em isócrona Sm-Nd em rocha total, indicando idade de cristalização de 2262 ± 110 Ma e épsilonNd(T) = +3.0 interpretada como representativa de evento magmático juvenil para estas rochas. Análises isótopicas de Nd em amostras do Granito Jurubatuba resultaram em idades modelo T DM entre 2.30 e 2.42 Ga e valores de épsilonNd(T) variando entre -0.22 e -0.58. O valor mais antigo de idade modelo T DM refere-se a xenólito de rocha metassedimentar no granito. As idades de cristalização paleoproterozóicas da Seqüência de Silvânia e do Granito Jurubatuba são a primeira evidência de evento magmático juvenil ocorrido entre 2.14-2.08 Ga no embasamento da porção central da Faixa Brasília

Vp/Vs ratios in the Parnaíba Basin from joint active-passive seismic analysis – Implications for continental amalgamation and basin formation

Acknowledgements The authors thank Jordi Julià and two anonymous reviewers for valuable comments on an earlier version of the manuscript. Thanks to the PBAP program for the availability of WARR, DSR and teleseismic three-component data (Project 5547: BP ENERGY/FUB/FINATEC— PARNAÍBA BASIN REFRACTION EXPERIMENT). RAF thanks CNPq and INCT Estudos Tectônicos (CNPq, CAPES, FAP-DF) for research fellowship and funds. *The data that support the findings of this study may be available from the authors upon reasonable request.Peer reviewedPublisher PD

Neoarchean crustal growth and Paleoproterozoic reworking in the Borborema Province, NE Brazil : insights from geochemical and isotopic data of TTG and metagranitic rocks of the Alto Moxotó Terrane

ELD and RAF acknowledge CNPq financial support through INCT Estudos Tectônicos and research fellowships. PAC was supported by Australian Research Council grant FL160100168.Pre-Brasiliano rocks in the Borborema Province (NE Brazil) are concentrated in basement blocks, such as the Alto Moxotó Terrane. Petrographic, geochemical, and U-Pb and Sm-Nd isotopic data from two basement metagranitic suites within the terrane provide evidence for Neoarchean (2.6 Ga) and Paleoproterozoic (2.1 Ga) subduction-related events. The Riacho das Lajes Suite is made of medium to coarse-grained hornblende and biotite-bearing metatonalites and metamonzogranites. Whole-rock geochemical data indicate that these rocks represent calcic, magnesian and meta-to peraluminous magmas, and have unequivocal affinities with high-Al low-REE tonalite-trondhjemite-granodiorites (TTG). Zircon U-Pb data from two samples of this suite indicate that they were emplaced at 2.6 Ga, which is the first discovered Archean crust in the central portion of the province. The suite has Neoarchean depleted mantle model ages (TDM) and slightly negative to positive εNd(t), indicating slight crustal contamination. The overall geochemical and isotopic data indicate a Neoarchean intraoceanic setting for genesis of the Riacho das Lajes magma via melting of basaltic oceanic crust submitted to high-pressure eclogite facies conditions. On the other hand, the Floresta Suite comprise metaigneous rocks, which are mostly tonalitic and granodioritic in composition. Geochemical data indicate that this suite shares similarities with calcic to calc-alkalic magmas with magnesian and metaluminous to slightly peraluminous characteristics. Other geochemical features include anomolous Ni, V and Cr contents, as well as high large-ion litophile elements (LILE) values. The suite yields U-Pb zircon ages of approximately 2.1 Ga, Archean to Paleoproterozoic TDM ages, and negative to positive εNd(t) values, suggesting both new crust formation and reworking of Archean crust, in addition to mantle metasomatism, reflecting mixed sources. The most likely tectonic setting for the Floresta Suite magmas involved crustal thickening by terrane accretion, coeval to slab break off. Our results provide new insights on proto-Western Gondwana crustal evolution.PostprintPeer reviewe

U-Pb data for granulites of the Anápolis-Itauçu complex: evidence for two high-grade events in the Brasília belt

Em processament

Neoproterozoic evolution of the basement of the South-American\ud platform

Neoproterozoic geologic and geotectonic processes were of utmost importance in forming and structuring\ud the basement framework of the South-American platform. Two large domains with distinct\ud evolutionary histories are identified with respect to the Neoproterozoic era: the northwest-west\ud (Amazonian craton and surroundings) and the central-southeast (the extra-Amazonian domain).\ud In the first domain, Neoproterozoic events occurred only locally and were of secondary significance, and\ud the geologic events, processes, and structures of the pre-Neoproterozoic (and syn-Brasiliano) cratonic\ud block were much more influential. In the second, the extra-Amazonian domain, the final evolution,\ud structures and forms are assigned to events related to the development of a complex net of Neoproterozoic\ud mobile belts. These in turn resulted in strong reworking of the older pre-Neoproterozoic basement. In this\ud domain, four distinct structural provinces circumscribe or are separated by relatively small pre-\ud Neoproterozoic cratonic nuclei, namely the Pampean, Tocantins, Borborema and Mantiqueira provinces.\ud These extra-Amazonian provinces were formed by a complex framework of orogenic branching systems\ud following a diversified post-Mesoproterozoic paleogeographic scenario. This scenario included many types\ud of basement inliers as well as a diversified organization of accretionary and collisional orogens. The\ud basement inliers date from the Archean toMesoproterozoic periods and are different in nature. The escape\ud tectonics that operated during the final consolidation stages of the provinces were important to and\ud responsible for the final forms currently observed. These latest events, which occurred from the Late\ud Ediacaran to the Early Ordovician, present serious obstacles to paleogeographic reconstructions.\ud Two groups of orogenic collage systems are identified. The older system from the Tonian (>850 Ma)\ud period is of restricted occurrence and is not fully understood due to strong reworking subsequent to\ud Tonian times. The second group of orogenies is more extensive and more important. Its development\ud began with diachronic taphrogenic processes in the Early Cryogenian period (ca. 850e750 Ma) and\ud preceded a complex scenario of continental, transitional and oceanic basins. Subsequent orogenies (post\ud 800 Ma) were also created by diachronic processes that ended in the Early Ordovician. More than one\ud orogeny (plate interaction) can be identified either in space or in time in every province. The orogenic\ud processes were not necessarily synchronous in different parts of the orogenic system, even within the\ud same province. This particular group of orogenic collage events is known as the “Brasiliano”.\ud All of the structural provinces of the extra-Amazonian domain exhibit final events that are marked by\ud extrusion processes, are represented by long lineaments, and are fundamental to unraveling the structural\ud history of the Phanerozoic sedimentary basins

U-Pb SHRIMP and Sm-Nd geochronology of the Silvânia Volcanics and Jurubatuba Granite: juvenile Paleoproterozoic crust in the basement of the Neoproterozoic Brasília Belt, Goiás, central Brazil

U-Pb SHRIMP and Sm-Nd isotopic ages were determined for felsic metavolcanic rocks from the Silvânia Sequence and Jurubatuba Granite in the central part of the Brasília Belt. Zircon grains from a metavolcanic sample yielded 2115 ± 23 Ma and from the granite yielded 2089 ± 14 Ma, interpreted as crystallization ages of these rocks. Six metavolcanic samples of the Silvânia Sequence yielded a six-point whole-rock Sm-Nd isochron indicating a crystallization age of 2262 ± 110 Ma and positive epsilonNd(T) = +3.0 interpreted as a juvenile magmatic event. Nd isotopic analyses on samples from the Jurubatuba Granite have Paleoproterozoic T DM model ages between 2.30 and 2.42 Ga and epsilonNd(T) values vary between -0.22 and -0.58. The oldest T DM value refers to a sedimentary xenolith in the granite. These results suggest crystallization ages of Silvânia volcanics and Jurubatuba Granite are the first evidence of a ca. 2.14-2.08 juvenile magmatic event in the basement of the central part of the Brasília Belt that implies the presence of arc/suture hidden in reworked basement of the Brasília Belt