4 research outputs found
The Caldas Novas dome, central Brazil : structural evolution and implications for the evolution of the Neoproterozoic Brasilia belt
The Caldas Novas dome (Goiaas state, central Brazil) lies in the southern segment of the Neoproterozoic Brasilia belt (center of the Tocantins Province) between the Goias magmatic arc and the margin of the ancient Sao Francisco plate. The core of the dome comprises rocks of the Meso-Neoproterozoic
Paranoa group (passive margin psamitic-pelitic sediments and subgreenschist
facies) covered by a nappe of the Neoproterozoic Araxa group (backarc basin
pelitic-psamitic sediments and volcanics of greenschist facies, bitotite zone).
Hot underground waters that emerge along fractures in the Paranoa quartzite
and wells in the Araxa schist have made the Caldas Novas dome an international tourist attraction. A recent detailed structural analysis demonstrates that the dome area was affected by a DâDâ Brasiliano cycle
progressive deformation in the â 750-600 Ma interval (published U-Pb and Sm-Nd data). During event Dâ, a pervasive layer- parallel foliation developed coeval the regional metamorphism. Event Dâ (intense Fâ isoclinal folding) was responsible for the emplacement of the nappe. Dâ and Dâ record a regime of
simple shear (top-to-SE relative regional movement) due to a WNW-ESE subhorizontal compression (a1). Event Dâ records a WSW-ENE compression, during which the dome rose as a large-scale Fâ fold, possibly associated with a duplex structure at depth. During the domeâs uplift, the layers slid back and
down in all directions, giving way to gravity-slide folds and an extensional
crenulation cleavage. A set of brittle fractures and quartz veins constitutes the
record of a late-stage Dâ event important for understanding the thermal water reservoir
GeoquĂmica de rocha total, geocronologia de u-pb e geologia isotĂłpica de sm-nd das rochas ortognĂĄissicas e unidades litolĂłgicas associadas da regiĂŁo ipameri - CatalĂŁo (GoiĂĄs)
Tese (doutorado)âUniversidade de BrasĂlia, Instituto de GeociĂȘncias, 2008.A parte sul da Faixa BrasĂlia, ProvĂncia Tocantins, localizada na regiĂŁo central
do Brasil, Ă© constituĂda por metassedimentos, seqĂŒĂȘncias vulcano-sedimentares, granitos intrusivos e um significativo cinturĂŁo de ortognaisses. Estas unidades estĂŁo sobrepostas tectonicamente e o metamorfismo varia do fĂĄcies xisto verde atĂ© anfibolito, caracterizado pelos eventos extensionais ocorridos em 720 e 800 Ma e colisional em 660 Ma. Os anfibolitos da ĂĄrea indicam a presença de protĂłlitos gabrĂłicos e basĂĄlticos de afinidade toleiĂtica com enriquecimento de Fe, baixo teor de Ti, baixa razĂŁo La/Yb, fraca anomalia negativa de Eu e ΔNd(T) prĂłximos Ă zero, associado a fonte magmĂĄtica primitiva, variando de basaltos de cordilheiras meso-oceĂąnicas transicionais a basaltos enriquecidos (T-MORB a E-MORB). Um dos anfibolitos Ă© alcalino, com alto teor de TiO2 e razĂŁo La/Yb, fraca anomalia de Eu, genericamente relacionado Ă ambientes tectĂŽnicos de rift.
Os dados geoquĂmicos das metavulcĂąnicas intermediĂĄrias a ĂĄcidas do Grupo AraxĂĄ e SeqĂŒĂȘncia MaratĂĄ da RegiĂŁo Ipameri-CatalĂŁo, caracterizam eventos extensionais em 720 e 800 Ma. Idade modelo (TDM) entre 1,91 e 2,08 Ga e valores de Nd(T) entre -7,95 e -9,30 indicam que os magmas parentais sĂŁo derivados da fusĂŁo crustal de protĂłlitos variados. Idade modelo (TDM) entre 1,77 e 1,97 e ΔNd(T) negativos (-7,26 to â9,48) dos
metapelitos da ĂĄrea mostram fonte associada Ă crosta continental paleoproterozĂłica.
PadrĂ”es heterogĂȘneos dos ETR destas rochas sugerem diferente proveniĂȘncia dos protĂłlitos sedimentares do Grupo AraxĂĄ â DomĂnio Oeste. ΔNd(T) e dados geoquĂmicos permitiram separar dois grupos de granitĂłides. Um, constituĂdo pelos granitos Pires Belo e DavinĂłpolis com deformação incipiente, fracamente peraluminosos a metaluminosos do tipo A, com idades de 798 ± 2 Ma e 775 ± 5 Ma. As idade modelo destes corpos sĂŁo 1,29 e 1,52 Ga e ΔNd(T) igual a â1,31 e â0,77, respectivamente, sugerindo contribuição de fontes juvenis e mais primitivas. O outro Ă© formado por granitos do Tipo S, gnaissificados com idade modelo entre 1,79 e 2,41 Ga e idade de cristalização de c. 663 Ma, ΔNd(T) por volta de â9.68, refletindo fonte crustal retrabalhada e ambiente tectĂŽnico colisional.
Os ortognaisses meso-neoproterozĂłicos da regiĂŁo de Ipameri - Nova Aurora localizam-se na parte central da ĂĄrea estudada. Dados geolĂłgicos, geoquĂmicos, isotĂłpicos de Sm-Nd e idades U-Pb em zircĂŁo permitiram discriminar trĂȘs domĂnios: (1) Ortognaisses Nova Aurora de 1.2 Ga; (2) Ortognaisses Goiandira de 640 Ma; e (3) Ortognaisses Ipameri de 790 Ma. A petrografia e geoquĂmica de rocha total em amostras selecionadas indicam que os protĂłlitos destes ortognaisses sĂŁo de composição tonalĂtica a granĂtica, com afinidade peraluminosa e cĂĄlcio-alcalina. Estas rochas sĂŁo cĂĄlcicas a alcali-cĂĄlcicas, com ΔNd(T)
entre +2,52 to -11,69, provavelmente associado Ă margem de arco continental.
O domĂnio mais a oeste, em torno de Nova Aurora, Ă© formado por ortognaisses
mesoproterozĂłicos datados em 1219±13 Ma, ΔNd(T) = -4,89 e 1259 ± 7 Ma, ΔNd(T) = - 4,57. Idade modelo deste grupo variam entre 1413 e 2624 Ma e ΔNd(T) entre -6,52 e +2,52, mostrando mistura de fontes heterogĂȘneas mais antigas com fontes juvenis. Isto permite sugerir que este domĂnio pode ser a fonte potencial de parte das populaçÔes de zircĂŁo detrĂtico mesoproterozĂłicos do segmento sul da Faixa BrasĂlia. Os ortognaisses do entorno de Goiandira possuem idades entre 634±9 e 717±39 Ma. As idades TDM variam entre 1371 e 2541 Ma e valores calculados de ΔNd(T) estĂŁo entre -4,15 e -11,69. O terceiro domĂnio ortognĂĄissico ocorre na ĂĄrea de Ipameri. Idades U-Pb em
zircão de duas amostras possuem idades de 796 ± 64 Ma e 771 ± 13 Ma, idade modelo
(TDM) entre 1913 e 2057 Ma e ΔNd(T) entre -3,65 e -9,83, sendo que uma das amostras
idade por volta de 1284 Ma. Alguns ortognaisses diorĂticos, tonalĂticos e granĂticos da regiĂŁo de Ipameri - Nova Aurora sĂŁo provavelmente de natureza alcalina com muito alto a alto K e peraluminosos. Os domĂnios Goiandira 640 Ma e Ipameri 790 Ma estĂŁo relacionados com arco
magmĂĄtico continental, construĂdo Ă s margens do Craton do SĂŁo Francisco. Sua extensĂŁo para norte constitui os terrenos granulĂticos do Complexo AnĂĄpolis-Itauçu.
Sugerimos que o domĂnio dos ortognaisses Nova Aurora, de idades 1230-1260 Ma, associa-se a um fragmento alĂłctone de arco mesoproterozĂłico. Estas evidĂȘncias demonstram que o magmatismo bimodal das rochas da regiĂŁo de Ipameri - CatalĂŁo correspondem a um evento de rift continental entre 720 e 800 Ma, associado Ă crosta oceĂąnica T-MORB a E-MORB. Em 660 Ma ocorreu magmatismo originado pela colisĂŁo do Bloco Paranapanema com a regiĂŁo sudoeste do CrĂĄton do SĂŁo Francisco. ______________________________________________________________________________ ABSTRACTThe part of the southern BrasĂlia Belt, Tocantins Province, exposed in central Brazil, comprises metasedimentary rocks, metavolcano-sedimentary sequences, amphibolites and intrusive granites, and a large orthogneiss belt. These units are
tectonically imbricated, and vary in metamorphic grade from lower greenschist to
amphibolite facies, characterized by a 720 and 800 Ma extensional, and 660 Ma collisional events. The amphibolites indicate gabbroic and basaltic protoliths, typically of tholeiitic affinity, showing Fe enrichment, low Ti content, low La/Yb ratios, small negative Eu anomalies and ΔNd(T) close to zero, associated to primitive magma sources varying from transitional to enriched mid-ocean ridge (T-MORB to E-MORB) basalts. One amphibolite is alkaline, with high TiO2 and La/Yb ratio, small negative Eu anomaly and general rift-related characteristics. Geochemical data of the intermediate to acid metavolcanic rocks of the AraxĂĄ Group and MaratĂĄ Sequence suggest formation in 720 and 800 Ma extensional events. TDM model ages varying from 1.91 to 2.08 Ga and ΔNd(T) values between -7.95 and -9.30 indicate that the parental magmas derived from crustal melting of varied protoliths. Model ages between 1.77 and 1.97 and negative ΔNd (-7.26 to â9.48) of
metapelitic rocks show a continental crust source indicating provenance of paleoproterozoic rocks. The REE from these rocks indicates heterogeneous patterns, suggesting a different provenance for sedimentary protoliths of the western domain of the AraxĂĄ Group in the area.
ΔNd(T) and geochemical data allow the distinction of two groups of granitoids.
One comprises the less deformed, slightly peraluminous to metaluminous, A-type, Pires
Belo and DavinĂłpolis granites, dated at 798 ± 2 Ma and 775 ± 5 Ma. Their model ages are 1.29 and 1.52 Ga, ΔNd(T) â1.31 and â0.77, respectively, suggesting important contribution of more primitive and juvenile sources. The second group is formed by
more deformed, gneissified peraluminous S type granites with model ages between 1.79
and 2.41 Ga with one crystallization age of c. 663 Ma, with ΔNd(T) of â9.68, reflecting a
reworked crustal source. The meso- neoproterozoic orthogneisses from Ipameri-Nova Aurora occur within the central part of the studied area. From west to east, geological, geochemical and Sm- Nd isotopic data and U-Pb zircon age determinations allow to discriminate three
domains: (1) Nova Aurora 1.2 Ga orthogneiss; (2) Goiandira 640 Ma orthogneiss; and (3) Ipameri 790 Ma orthogneiss. Petrography and whole rock geochemistry of selected samples characterize their protoliths as tonalite to granite in composition, with calc-alkaline and peraluminous affinity. They vary from calcic to alkaline-calcic, with variated ΔNd(T) range (+2.52 to - 11.69), probably formed in a continental margin arc environment. The westernmost domain, around Nova Aurora, comprises mesoproterozoic orthogneisses, dated at 1219±13 Ma, ΔNd(T) = -4.89 and 1259 ± 7 Ma, ΔNd(T) = -4.57. Model ages of this group vary between 1413 and 2624 Ma and ΔNd(T) between -6.52 and
+2.52, suggesting mixed juvenile and older heterogeneous sources. This leads to the
suggestion that this domain could have been a potential source for part of the mesoproterozoic detrital zircon population reported from the southern BrasĂlia Belt.
The orthogneiss domain around Goiandira yielded neoproterozoic ages between 634±9 and 717±39 Ma. Model ages range between 1371 and 2541 Ma and calculated ΔNd(T) values between -4.15 and -11.69. The third orthogneiss domain is exposed in the Ipameri area. U-Pb zircon ages of two samples yielded 796 ± 64 Ma and 771 ± 13 Ma, ΔNd(T) between -3.65 and -9.83 and TDM model ages between 1913 and 2057 Ma, with one lower value of 1284 Ma. Some dioritic, tonalitic and granitic orthogneiss in the Ipameri-Nova Aurora region have a different behavior. They have very high- to high-K character and peraluminous affinity with probably alkaline nature. The Goiandira 640 Ma and Ipameri 790 Ma domains are related to a continental magmatic arc, built-up at the margin of the plate that includes the São Francisco Craton.
Their northward continuity constitutes the Anåpolis-Itauçu granulite terrain. As for the
1230-1260 Ma orthogneiss domain in Nova Aurora, we suggest that it is an exotic
fragment of a mesoproterozoic arc built elsewhere. The overall evidence demonstrates that the bimodal magmatism presented in the
rocks outcropping in the Ipameri-CatalĂŁo region, are related to an extensional
continental rift event occurred between 720 and 800 Ma, evolving to an oceanic crust
with T-MORB to E-MORB affinity. At 660 Ma there is evidence of continental collision magmatism related to compressional movement between the southwestern portion of SĂŁo Francisco Craton and Paranapanema Block