Long-term activity of shear zones in the Dom Feliciano Belt and associated terranes (South America)

The Dom Feliciano Belt in southern Brazil and Uruguay records the superposed tectonic events that led to the assembly of southwestern Gondwana during the Neoproterozoic Brasiliano-Pan-African orogenic cycle. During the course of the orogeny, the belt and associated Precambrian domains were affected by widespread crustal deformation, leading to a complex set of shear zones. This thesis investigates the tectono-thermal history of the main shear zones in the Dom Feliciano Belt and associated terranes. Deformation conditions and the evolution of the shear zones are characterized using structural and microstructural observations, combined with quartz CPO textural analyses. New K-Ar data and a review of the literature are used to constrain this evolution in the geochronological timescale. In addition, the Phanerozoic thermal history of the study area is investigated combining (U-Th)/He analyses on zircon and apatite, thermal modelling, and K-Ar dating of fault gouges. In this way, it is possible to examine the impact of the main Neoproterozoic structures as preferential sites for reactivation. The oldest terrane boundary in the region is the Ibaré Shear Zone, which records the accretion of the Tonian juvenile São Gabriel Terrane to the Archean-Paleoproterozoic Nico Pérez Terrane as a dextral lateral ramp during SW-verging thrusting. New-K-Ar analyses suggest that it was established at ca. 760 to 740 Ma, and reactivated in the Cryogenian-Ediacaran in narrow sinistral shear zones at cooler conditions, during the formation of the Dom Feliciano Belt. The belt was formed during oblique collision between the Congo and Río de la Plata cratons, together with the Nico Pérez and Luís Alves Terranes, resulting in widespread transpression. This process was probably diachronic, with onset of transcurrent structures being recorded between ca. 650 and 620 Ma in different sectors of the belt, and led to the formation of its main terrane boundary, the Major Gercino-Dorsal do Canguçu-Sierra Ballena lineament. This shear zone system records an intense amount of pure shear and contrasting kinematics along its extension, suggesting local variations to the main horizontal compression and partitioning into different transcurrent vectors. After 600 Ma there is a decrease in wide-scale regional compression, transitioning to localized strike-slip deformation along the main shear zones, suggesting a post-collisional stage. Late ductile reactivations were active until ca. 540-530 Ma. With the cessation of the orogenic processes, the study area stabilized and achieved an intracratonic position inside Gondwana, experiencing a protracted evolution during the Phanerozoic. Exhumation during the early Paleozoic probably exposed much of the present-day crystalline basement to near-surface conditions, and was followed by regional subsidence during the sedimentation of the Paraná Basin. For most of the belt’s extension, final exhumation was achieved at the latest during the rift stage of the South Atlantic in the Lower Cretaceous, but its northernmost portion records up to 2 km of post-rift exhumation. While recurrent brittle reactivation of Neoproterozoic structures is recorded by the dating of fault gouges, this process is not reflected in the study area’s thermal history. Instead, the main structural control is by transecting fault systems, oriented perpendicular to the South Atlantic coastline. Along the south-southeastern South American passive margin, major reactivation of the inherited structures is predominantly recorded in strongly uplifted regions

The Precambrian to Paleozoic crustal growth of South America: From collisional to accretionary tectonics

Southern 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

Zircon U-Pb geochronology and Hf isotopes of the Luís Alves Terrane: Archean to Paleoproterozoic evolution and Neoproterozoic overprint

International audienceThe Luís Alves Terrane in southern Brazil is one of the largest expositions of the Archean to Paleoproterozoic units that acted as basement for the development of the Neoproterozoic Pan-African/Brasiliano orogenic belts in the Mantiqueira Province, in South America. Combined field observations, petrography, Hf and U-Pb LA-ICP-MS zircon and titanite isotopic data are presented for the basement of this terrane. The zircon U-Pb dataset spans a large time range with concordant ages from 3.2-1.8 Ga. Several magmatic and metamorphic events are recorded by the U-Pb concordant ages reflecting the complex evolution of this crustal block. The oldest inherited zircon grains have Mesoarchean ages (3.2–3.1 Ga), while two other magmatic populations yield ages of 2683 ± 70 Ma and 2498 ± 11 Ma. Most zircon grains crystallized during two high-grade metamorphic events at 2352 ± 23 Ma and 2183 ± 17 Ma. Titanite from two samples crystallized at 2.02–1.99 Ga, probably during a retrograde metamorphic trajectory that re-equilibrated the studied samples in amphibolite-facies conditions. A late pegmatite dyke was emplaced between ca. 1.96 and 1.79 Ga. Cathodoluminescence images show that the analyzed zircon samples, including those in the pegmatite, had their internal structure modified by hydrothermal processes. The localization of the outcrop close to the rim of the Campo Alegre Basin affected by an important Neoproterozoic hydrothermal event as well as normal and reverse discordant U-Pb ages in our dataset indicate that this event took place during the Brasiliano orogenic cycle at the end of the Neoproterozoic. The Hf isotope data show predominantly crustal signatures with εHf(t) values ranging from 1.3 to −16.8. Hf TDM model ages cluster in two groups (4.32–3.48 and 3.38–2.27 Ga) indicating two pulses of magma differentiation from the mantle with subsequent mixing of the material during the Paleoproterozoic high grade metamorphic events

Evolution of the Major Gercino Shear Zone in the Dom Feliciano Belt, South Brazil, and implications for the assembly of southwestern Gondwana

The 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

The 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

Investigating the Shallow to Mid-Depth (>100–300 °C) Continental Crust Evolution with (U-Th)/He Thermochronology: A Review

International audienceQuantifying geological processes has greatly benefited from the development and use of thermochronometric methods over the last fifty years. Among them is the (U-Th)/He dating method, which is based on the production and retention, within a crystal structure, of radiogenic 4He atoms associated with the alpha decay of U, Th and Sm nuclei. While apatite has been the main target of (U-Th)/He studies focusing on exhumation and burial processes in the upper levels of the continental crust (~50–120 °C), the development of (U-Th)/He methods for typical phases of igneous and metamorphic rocks (e.g., zircon and titanite) or mafic and ultramafic rocks (e.g., magnetite) over the last two decades has opened up a myriad of geological applications at higher temperatures (>100–300 °C). Thanks to the understanding of the role of radiation damage in He diffusion and retention for U-Th-poor and rich mineral phases, the application of (U-Th)/He thermochronometry to exhumation processes and continental evolution through deep time is now mainstream. This contribution reviews the (U-Th)/He thermochronometer principle and the influence of radiation damage in modifying the diffusion behavior. It presents applications of (U-Th)/He dating to problems in tectonic and surface processes at shallow to middle crustal depths (>100–300 °C). New and promising applications using a combination of methods will stimulate a research avenue in the future

Archean to early Neoproterozoic crustal growth of the southern South American Platform and its wide-reaching “African” origins

The amalgamation of southwestern Gondwana during the late Neoproterozoic Brasiliano/Pan-African orogenic cycle involved the tectonic interaction of the Congo, Kalahari and Rio de la Plata cratons, together with numerous smaller basement fragments scattered throughout South America. A comprehensive review of U-Pb and Lu-Hf spot analyses in zircon provides new insights on the pre-Brasiliano crustal growth of the main tectonic domains of the southern South American Platform from the Archean to the early Neoproterozoic. The results highlight similarities between five basement fragments, from south to north: the Nico Pérez Terrane, Tijucas Terrane, Camboriú Complex, Luis Alves Terrane and Curitiba Terrane. Whereas these units have variable characteristics, especially concerning differing degrees of tectonic reworking in the late Neoproterozoic, they share similarities in their geological evolution. They were all originally accreted in the Archean, as evidenced by Hf TDM model ages and zircon inheritance, and later experienced intense orogenic reworking during the Rhyacian and Orosirian. The Paleoproterozoic record is diverse and indicates a complex episodic evolution instead of a single orogenic event. Conspicuous diachronic magmatic events took place locally in the Late Paleoproterozoic and Mesoproterozoic, interrupting an otherwise relatively stable tectonic setting until the Neoproterozoic. The Archean origin and strong crustal signatures of the main Paleoproterozoic units distinguish these terranes from the Rio de la Plata Craton, evidencing instead stronger affinities with African crustal blocks such as the Congo and Kalahari cratons. This relationship has implications for the geodynamic reconstruction of southwest Gondwana that extend into the early Neoproterozoic, as it contextualizes the genetic link between the main Tonian events in the region, namely the formation of the São Gabriel Terrane and the emplacement of the magmatic protoliths of the basement of the Punta del Este Terrane. They can be understood as marginal and within-plate manifestations of an accretionary orogen, respectively. The basement of the Punta del Este Terrane has signatures compatible with the recycling of ancient crust through the mixture of mantellic magmatic input with the partial melting of Archean or Archean-derived Proterozoic lithosphere, a process that likely took place multiple times from the Paleoproterozoic onwards in the region.Fil: Hueck, Mathias. Universidade de Sao Paulo; 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: Basei, Miguel A. S.. Universidade de Sao Paulo; BrasilFil: Oyhantcabal, Pedro. Universidad de la Republica; UruguayFil: Heller, Beatrix M.. Universite Paris-Saclay; FranciaFil: Wemmer, Klaus. Universität Göttingen; AlemaniaFil: Siegesmund, Siegfried. Universität Göttingen; Alemani

Phanerozoic low-temperature evolution of the Uruguayan Shield along the South American passive margin

The crystalline basement of Uruguay was assembled during the Brasiliano Orogeny in the Neoproterozoic Era and was later affected by discrete tectonic activity. A new multi-method low-temperature dataset including (U-Th)/He ages from both zircon and apatite, T-t modelling and K-Ar dating of fine sericite fractions and fault gouge reveal a detailed post-orogenic geological history spanning the Phanerozoic Eon. The juxtaposition of the terranes that compose the area was achieved in the Ediacaran Period, and post-collision was marked by intense exhumation, in which the crystalline basement reached near-surface conditions by the early to mid-Palaeozoic. Regional subsidence promoted sedimentation in the Paraná Basin until the Permian, covering and reheating much of the basement that is at present exposed. Afterwards, deposition and volcanism were mostly confined to its current limits. Regional exhumation of the shield during the Permo-Triassic exposed much of the northern portion of the basement, and the south was further affected by the opening of the South Atlantic Ocean during the Mesozoic. Little exhumation affected the Uruguayan Shield during the Cenozoic, as reflected in its modest topography. The reactivation of inherited Neoproterozoic structures influenced the development of Mesozoic basins and the present-day landscape.Fil: Hueck, Mathias. Universität Göttingen; AlemaniaFil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universität Göttingen; AlemaniaFil: Dunkl, István. Universität Göttingen; AlemaniaFil: Wemmer, Klaus. Universität Göttingen; AlemaniaFil: Oyhantçabal, Pedro. Universidad de la Republica. Instituto de Ciencias Geológicas; UruguayFil: Schanofski, Max. 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

Argon 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