1,720,981 research outputs found
The Precambrian to Paleozoic crustal growth of South America: From collisional to accretionary tectonics
No full textSouthern South America hosts a vast geologic record of Precambrian to Paleozoic geodynamic and tectonic processes, particularly related to the assembly and crustal growth of Western Gondwana. This special volume comprises 24 novel contributions focused on the Precambrian to Paleozoic tectonic evolution of southern South America, focused on different tectonostratigraphic domains of southeastern Brazil, Uruguay, Argentina and Chile (Figs. 2, 3). Papers also cover a wide temporal frame, including Archean to Tonian processes of pre-Brasiliano basement inliers; the tectonometamorphic, magmatic and sedimentary record of the late Neoproterozoic Brasiliano Orogeny, particularly related to the Dom Feliciano Belt; and Paleozoic accretionary systems of the proto-Pacific margin (Fig. 4).Fil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Hueck, Mathias. Universidade de Sao Paulo; BrasilFil: Oyhantcabal, Pedro. Universidad de la República; UruguayFil: Siegesmund, Siegfried. Universität Göttingen; Alemani
Evolution of the Major Gercino Shear Zone in the Dom Feliciano Belt, South Brazil, and implications for the assembly of southwestern Gondwana
No full textThe Dom Feliciano Belt developed during the Brasiliano–Pan-African orogenic cycle due to the tectonic interaction between the Rio de la Plata, Congo and Kalahari cratons, along with the amalgamation of smaller continental fragments. Together with its prolongations to the south, the Major Gercino Shear Zone constitutes one of the main lineaments of the orogenic system, establishing a more than 1000 km long NE-trending tectonic boundary between a granitic batholith and a metavolcano-sedimentary association. Based on combined field, structural, microstructural and textural data, together with new and published geochronological data, a refined model for the geological evolution of the Major Gercino Shear Zone is presented. Regional NW-verging, low-dipping structures were generated between 650 and 615 Ma, preceding the formation of the shear zone. This was followed by the main deformation phase, corresponding to pure-shear dominated dextral strike-slip, interpreted do be controlled by regional transpression during oblique convergence of the continental terranes. This stage lasted until ca. 585 Ma and was coeval with the continuous emplacement of granitic magmatism along the structure. Strain partitioning and localization led to the development of mylonitic belts along the intrusion borders mostly under greenschist facies metamorphic conditions. Late-stage ductile deformation along the structure was active during the cooling of the intrusions until ca. 550 Ma, while the deformation front of the orogenic system migrated to counterpart orogenic belts in the African continent. After tectonic stabilization, the Major Gercino Shear Zone recorded episodic brittle reactivation, possibly related to the Phanerozoic evolution of the active margins and intracratonic basins in Gondwana.Fil: Hueck, Mathias. Universität Göttingen; AlemaniaFil: Stipp Basei, Miguel Angelo. Universidade de Sao Paulo; BrasilFil: Wemmer, Klaus. Universität Göttingen; AlemaniaFil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Heidelbach, Florian. University Of Bayreuth; AlemaniaFil: Siegesmund, Siegfried. Universität Göttingen; Alemani
Comparing contiguous high- and low-elevation continental margins: New (U-Th)/He constraints from South Brazil and an integration of the thermochronological record of the southeastern passive margin of South America
No full textThe southeastern coast of South America is an example of the complexity of passive continental margins, as it displays both high- and low-elevation segments despite sharing a similar pre-rift geological history and structural configuration. As such, it is a prime candidate for investigating debated questions concerning the evolution of passive margins, such as the tectonic mechanisms driving uplift, their relationship to rifting and continental break-up, and why some margins are elevated when others are not. In this contribution, we present new (U-Th)/He data from a low-altitude portion of the South American passive margin in South Brazil, the Sul-rio-grandense Shield, and interpret it in the context of the regional thermochronological record. New results produce widespread apparent ages and reveal a complex exhumation history from the early Paleozoic onwards, including reheating during Paleo-Mesozoic sedimentation. For most of the study area, however, final exhumation was achieved at the latest during the rifting and early opening of the South Atlantic Ocean (135 Ma to 100 Ma). In spite of the presence of major Neoproterozoic shear zones, the inherited NE-SW structural framework seems not to have strongly influenced the thermochronological record. The new data were integrated into a large compilation of apatite fission track and (U-Th)/He results from southeast South America, in order to compare regional trends and investigate possible tectonic controls in the exhumation history. Low-elevation areas of the passive margin consistently record complex pre-rift cooling histories, while high-elevation areas experienced significant Upper Cretaceous/Paleogene uplift associated with the reactivation of Neoproterozoic shear zones. Because the inherited structural features of both segments are similar, plate dynamics alone cannot be responsible for the variating response. Hence, mantellic processes associated with post-rift alkaline magmatism may have affected the contrasting exhumation histories. This process was probably controlled by important South Atlantic fracture zones.Fil: Hueck, Mathias. Universidade de Sao Paulo; Brasil. Universität Göttingen; AlemaniaFil: Dunkl, István. Universität Göttingen; AlemaniaFil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Wemmer, Klaus. Universität Göttingen; AlemaniaFil: Stipp Basei, Miguel Angelo. Universidade de Sao Paulo; BrasilFil: Siegesmund, Siegfried. Universität Göttingen; Alemani
Dating recurrent shear zone activity and the transition from ductile to brittle deformation: white mica geochronology applied to the neoproterozoic Don Feliciano Belt in South Brazil
No full textArgon geochronology of white mica has a good potential of recording recurrent dynamic recrystallization in shear zones in the transition from ductile to brittle deformation, as temperature ranges for mineral crystallization and isotopic closure of different grain-size fractions overlap between ca. 275–425 ◦C. This study presents over 40 K-Ar ages of coarse-grained muscovite and multiple clay-sized white mica fractions extracted from mylonites and fault gouges in southernmost Brazil, complemented by detailed structural and XRD characterization. The widespread obtained ages are best explained in the context of recurrent deformation under retrograde conditions during progressive strain localization and transition from low-grade ductile deformation into brittle faulting. The onset of the Ibar´e Shear Zone is constrained in the Tonian, followed by reactivation during the Ediacaran evolution of the adjacent Dom Feliciano Belt, which records a remarkable long-term history of recurrent deformation for over 100 Myr. New data extends the geochronological constraints of the Dorsal do Canguçu Shear Zone into low-temperature conditions, estimating the onset of brittle activity at 525-470 Ma by dating early fault gouges formed shortly after final syn-kinematic white mica crystallization in the hosting mylonites. Dating of recurrent faulting events during the Paleo-Mesozoic complement the regional sedimentary and thermochronological record.Fil: Hueck, Mathias. Universität Göttingen; Alemania. Universidade de Sao Paulo; BrasilFil: Wemmer, Klaus. Universität Göttingen; AlemaniaFil: Basei, Miguel A. S.. Universidade de Sao Paulo; BrasilFil: Philipp, Ruy P.. Universidade Federal do Rio Grande do Sul; BrasilFil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Heidelbach, Florian. University of Bayreuth; AlemaniaFil: Oyhantcabal, Pedro. Universidad de la República; UruguayFil: Siegesmund, Siegfried. Universität Göttingen; Alemani
Cadomian to Cenerian accretionary orogenic processes in the Alpine basement: the detrital zircon archive
No full textNew whole-rock geochemical and detrital zircon U–Pb and Lu–Hf data of metasedimentary sequences of the Silvretta Nappe, Orobic Alps, Strona-Ceneri Zone, Gotthard Massif and Venediger Nappe are presented. These units seem to share a common early to middle Paleozoic geological record, which has alternatively been interpreted as the result of intraplate or orogenic processes. Detrital zircon data mainly indicate late Ediacaran to early Ordovician maximum sedimentation ages for the studied sequences, suggesting that they were intimately related to Cadomian and Cenerian orogenic processes along the northwestern Gondwana margin. The common presence of late Ediacaran to Cambrian Cadomian ages associated with variable subchondritic to suprachondritic Lu–Hf compositions points to recycling processes of Cadomian sequences, further supported by geochemical data indicating a relatively low to moderate maturity of sedimentary protoliths. The occurrence of Cenerian arc-related intrusions in Austroalpine and South Alpine basement unit points to an arc/back-arc position in the early Paleozoic Cenerian orogen, except for the Strona-Ceneri Zone, which was likely located closer to the forearc region, as indicated by the presence of high-pressure metamorphism. Younger sequences, such as the Landeck Quartz-phyllite, document post-Cenerian sedimentation, whereas those of the Venediger Nappe more likely record the early stages of Variscan subduction, as indicated by Devonian maximum deposition ages.Fil: Siegesmund, Siegfried. Universität Göttingen; AlemaniaFil: Oriolo, Sebastián. Universität Göttingen; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Broge, Alena. Universität Göttingen; AlemaniaFil: Hueck, Mathias. Universidade de Sao Paulo; BrasilFil: Lammerer, Bernd. Ludwig Maximilians Universitat; AlemaniaFil: Basei, Miguel A. S.. Universidade de Sao Paulo; BrasilFil: Schulz, Bernhard. No especifíca
Origin and evolution of the granitic intrusions in the Brusque Group of the Dom Feliciano Belt, south Brazil: Petrostructural analysis and whole-rock/isotope geochemistry
No full textIn the southern Brazilian state of Santa Catarina the Dom Feliciano Belt, formed by the tectonic juxtaposition of different crustal blocks during the Brasiliano-Pan African Orogenic cycle, can be divided into three domains. In the central domain, three granitic suites intrude the metavolcanosedimentary sequence of the Brusque Group: Sao Joao Batista (SJBS), Valsungana (VS) and Nova Trento (NTS), from the oldest to the youngest. This extensive magmatism, here referred to as granitic intrusions in the Brusqe Group (GIBG), is coeval with the thermal peak in the host metamorphic successions, but postdates its main foliation. A progressive deformation starting from the magmatic stage throughout the cooling history points to the influence of the late stages of deformation recorded in the Brusque Group. The SJBS consists of gray to white leucocratic, equigranular granites, with aluminous minerals such as muscovite, garnet and tourmaline. The porphyritic VS is the largest of the suites and is characterized by its cm-sized K-feldspar megacrysts in a coarse-grained biotite-rich matrix. The granites from the NTS are equigranular, light gray to pink in color and have biotite as the main mafic mineral, but magmatic muscovite, tourmaline and hornblende can occur as well. Geochemically, the GIBG are mildly peraluminous and show a calc-alkaline affinity. Most intrusions have a high REE fractionation, but some SJBS granites show a characteristic pattern with no fractionation and strong negative Eu anomalies ("seagull pattern"). Elevated Sr(i) values, between 0.707 and 0.735, and negative epsilon(Nd) values as low as -24 points to the melting of old evolved crust. The Nd (T-DM) ages are scattered between 1.54 and 2.76 Ga, with a predominance of values around 2.0 Ga. The GIBG have a strong crustal signature that most closely connects, within the regional units, to that of the metasedimentary rocks of the Brusque Group and its crystalline basement, the Cambodia Complex. All three suites seem to have been produced during a same regional melting event, but at different crustal levels and reflecting heterogeneities within the same source rocks. Most evidences imply that sedimentary source rocks were especially important to the SJBS, which probably originated in a shallower environment, whilst the VS and NTS represent the melting of deeper crystalline crust, probably sharing some magmatic interaction. (C) 2016 Elsevier Ltd. All rights reserved.FAPESP [2005/58688-1, 2006/06957-1]; CNP
Tracking the sources and the evolution of the late Neoproterozoic granitic intrusions in the Brusque Group, Dom Feliciano Belt, South Brazil: LA-ICP-MS and SHRIMP geochronology coupled to Hf isotopic analysis
No full textShear zones in Brasiliano–Pan-African Belts and their role in the amalgamation and break-up of southwestern Gondwana
No full textThe Sierra de Aguirre Formation, Uruguay: Post-collisional Ediacaran volcanism in the southernmost Dom Feliciano Belt
No full textShear zones in Brasiliano–Pan-African Belts and their role in the amalgamation and break-up of southwestern Gondwana
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