Papers by Pedro Oyhantcabal
Supplementary electonic material 1. Petrography description of some granitic plutons and stocks c... more Supplementary electonic material 1. Petrography description of some granitic plutons and stocks cropping out at both sides of the Sierra Ballena Shear Zone in the south-eastern section of the Dom Feliciano Belt in Uruguay. Supplementary electronic material 2. Processing and analytical methods implemented during the laboratory processing of the samples described in this manuscript.
Journal of South American Earth Sciences, Apr 1, 2021
Abstract The Sierra de Aguirre Fm. in southern Uruguay constitutes one of several post-collisiona... more Abstract The Sierra de Aguirre Fm. in southern Uruguay constitutes one of several post-collisional basins of the Dom Feliciano Belt, preserving an important volcanic record associated with this protracted stage of the orogenic system. This study combines new stratigraphic, structural, geochronological and isotopic geochemical results, together with a reassessment of the available geochemical data, to present new insights in the evolution and sources of the basin, as well as a contextualization of it within the post-collisional development of the belt. The opening of the basin was related to a major discontinuity within the belt, with geometrical features suggesting an inverted half-graben structure. Stratigraphic and petrographic studies indicate that the Sierra de Aguirre Fm. preserves the original unconformity with its basement, and represent distal volcanic deposits. U–Pb SHRIMP-IIe zircon ages establish an interval of ca. 10 m.y. for the filling of the basin, between 581.7 ± 5.1 Ma and 571 ± 8 Ma. After the end of deposition, the basin underwent folding associated with the development of axial plane cleavage under lower greenschist facies conditions. This event is interpreted to represent regional transpression recorded also in nearby shear zones between 570 and 560 Ma, as constrained by new K–Ar ages in muscovite and white mica fine fractions. Geochemical and isotopic signature indicate dominant crustal sources for the volcanism, compatible with the basement of the eastern domain of the Dom Feliciano Belt, supporting a trend also observed in the coeval plutonic magmatism.
Journal of South American Earth Sciences, Jun 1, 2021
New isotopic and geochemical data for the Paleo-Meso-and Neoproterozoic metasedimentary cover of ... more New isotopic and geochemical data for the Paleo-Meso-and Neoproterozoic metasedimentary cover of the southern Dom Feliciano Belt (Brasiliano/Pan-African) are presented and evaluated combined with published information. Whole-rock major and trace element geochemistry indicates that the dominant source for all the units had a composition similar to average upper continental crust. The geochemistry is similar even for late Ediacaran successions with a source component from slightly older Ediacaran granites, due to the crustal origin of these granites. Age constraints based on detrital zircon, fossil content, interbedded volcanic rocks and isotope geochemistry confirm Paleo-, Meso-, and Neoproterozoic successions, despite uncertainties remain in some cases. Detrital zircon data show the dominance of Archean (3.3-2.8 Ga) to Paleoproterozoic (2.2-1.9 Ga), and subordinated Mesoproterozoic (1.5-1.3 and 1.1 Ga) and Neoproterozoic (0.5-0.6 Ga) ages. Lu-Hf zircon and Sm-Nd whole-rock model ages confirm that the Archean and the Paleoproterozoic were the major crustal growth periods for the source areas. U-Pb detrital zircon age distributions and model ages demonstrate that the Nico Pérez Terrane and not the Río de la Plata Craton was the source for most metasedimentary rocks of the western Dom Feliciano Belt. Likewise, comparison of Archean, Paleo-, Meso-and Neoproterozoic events supports that the Nico Pérez Terrane could represent a fragment of the Congo Craton.
Lithos, Apr 1, 2017
Post-collisional, granitic magmatism with high-barium-strontium (HiBaSr) content and shoshonitic ... more Post-collisional, granitic magmatism with high-barium-strontium (HiBaSr) content and shoshonitic affinity has been recently recognised both in the southern section of the Dom Feliciano Belt of Uruguay and its cratonic foreland. This group of granitic rocks has a distinctive age, mineralogy, chemistry and field characteristics. New zircon U-Pb LA-ICP-MS data for three of the plutons confirm their Late Neoproterozoic age; 634 ± 7.3 (Sierra de los Caracoles), 604 ± 3.0 Ma (Cortez Blanco) and 597 ± 3.6 Ma (Guayabo). Similar ages were published previously for the Solis de Mataojo Granitic Complex (584 ± 13 Ma) as well as Las Flores (586 ± 2.7 Ma) and Sobresaliente plutons (585 ± 2.5 Ma). Mineral assemblages of the studied quartz-monzonites, granodiorites and monzogranites comprise quartz, orthoclase and microcline, plagioclase (Ab 10-30 ), hornblende, green biotite, apatite, titanite and allanite. They plot predominantly in the high-K calc-alkaline field with the exception of a few that plot in the shoshonitic field; characteristically they are relatively high Na 2 O (normally > 4.5%) in acid varieties (SiO 2 >65%) decreasing to between 3 and 4% for more basic types; K 2 O normally exceeds 3.5% but can be as low as <2% in the basic varieties. The Uruguayan HiBaSr granitoids show high abundances of Ba (>700 ppm), Sr (>500 ppm) and light REEs alongside low Nb, Ta and heavy REEs. The Eu anomalies are negligible to slightly positive. Intermediate initial 87Sr/86Sr values (0.7077 to 0.7090) and very low initial epsilon Nd values (-15.8 to -19.3) at 600 Ma with high Nd TDM (2.2-2.8 Ga) suggest a recycling of ancient Paleoproterozoic to Late Archaean sources. Late Neoproterozoic granitoids of Uruguay have been emplaced within a post-collisional tectonic setting controlled by major shear zones and strike-slip fault zones. Current field and analytical data suggest that these granitoids could have been mostly generated through the partial melting of an intermediate to lower mafic continental crust and/or "enriched" crustal sources (in the
International Journal of Earth Sciences, Dec 26, 2017
Early Neoproterozoic metaigneous rocks occur in the central part of the Kaoko-Dom Feliciano-Garie... more Early Neoproterozoic metaigneous rocks occur in the central part of the Kaoko-Dom Feliciano-Gariep orogenic system along the coasts of the southern Atlantic Ocean. In the Coastal Terrane (Kaoko Belt, Namibia), the bimodal character of the ca. 820-785 Ma magmatic suite and associated sedimentation sourced in the neighbouring pre-Neoproterozoic crust are taken as evidence that the Coastal Terrane formed as the shallow part of a developing back arc/rift. The arc-like chemistry of the bimodal magmas is interpreted as inherited from crustal and/or lithospheric mantle sources that have retained geochemical signature acquired during an older (Mesoproterozoic) subduction-related episode. In contrast, the mantle contribution was small in ca. 800-770 Ma plutonic suites in the Punta del Este Terrane (Dom Feliciano Belt, Uruguay) and in southern Brazil; still, the arc-like geochemistry of the prevalent felsic rocks seems inherited from their crustal sources. The withinplate geochemistry of a subsequent, ca. 740-710 Ma syn-sedimentary volcanism reflects the ongoing crustal stretching and sedimentation on top of the Congo and Kalahari cratons. The Punta del Este-Coastal Terrane is interpreted as an axial part of a Neoproterozoic "Adamastor Rift". Its opening started in a back-arc position of a long-lasting subduction system at the edge of a continent that fragmented into the Nico Pérez-Luís Alves Terrane and the Congo and Kalahari cratons. The continent had to be facing an open ocean and consequently could not be located in the interior of the Rodinia. Nevertheless, the early opening of the Adamastor Rift coincided with the lifetime of the circum-Rodinia subduction system.
Journal of South American Earth Sciences, Dec 1, 2021
Precambrian Research, Jun 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Regional geology reviews, 2018
The Nico Perez Terrane of Uruguay and southeastern Brazil is characterized by an important compon... more The Nico Perez Terrane of Uruguay and southeastern Brazil is characterized by an important component of Archean crustal growth and extensive post-Archean crustal reworking recorded in Paleoproterozoic zircon magmatic crystallization ages in widely distributed granitic orthogneisses. Supracrustal blocks of an older Neoarchean to Siderian sedimentary cover including BIFs, quartzites and marbles are preserved only as minor relics. Additionally, an intraplate Mesoproterozoic record includes anorthosite complexes, metagabbros, amphibolites, felsic volcanic rocks and sediments assumed to correspond to a stable platform cover. Rocks with similar isotopic features occur also as basement inliers and roof pendants in the batholiths of the Dom Feliciano Belt. Two different subterranes are recognized in the Nico Perez Terrane, separated by the north-northeast-trending Cacapava–Sierra de Sosa Shear Zone. The granulite-facies Valentines Rivera and Santa Maria Chico granulitic complexes crop out in the western side of the shear zone and were less reworked during the Neoproterozoic, while the Pavas Block of Uruguay and several basement inliers in the Tijucas Terrane and Pelotas Batholith of Brazil were strongly reworked. Cooling ages, extensive shear zones and granite intrusions document this reworking that was probably facilitated by a thin lithosphere. The Nico Perez Terrane represents a fragment of the Congo Craton separated during the Neoproterozoic.
Journal of the Geological Society, Mar 7, 2017
The crystalline basement of Uruguay was assembled during the Brasiliano Orogeny in the Neoprotero... more 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.
Earth-Science Reviews, Oct 1, 2018
Shear zones play a major role in the deformation of the crust at a variety of scales, as expressi... more Shear zones play a major role in the deformation of the crust at a variety of scales, as expressions of strain localization during orogeny and rifting, and also as reactivated structures. They influence the geometry and evolution of orogenic belts and rifts, crustal rheology, magma ascent and emplacement, and fluid flow. Consequently, assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere. The interpretation of thermochronologic data from shear zones is, however, not straightforward. In the first place, closure temperatures depend on a number of factors (grain size, cooling rate, mineral composition and pressure, among others). On the other hand, deformation-related processes such as dynamic recrystallization, neocrystallization and fluid circulation seem to be crucial for isotopic systems and, thus, the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks. For this reason, geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo-or recrystallization, fluid-assisted deformation and inheritance of the protolith age(s). In order to robustly reconstruct P-T-ε-t paths of long-term crustal-scale shear zones, structural, microstructural and petrologic data from mylonites need to be integrated with ages from different thermochronometric systems. In addition, geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications. One of the most challenging aspects that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored aspects of isotopic diffusion, particularly the coupling with deformation processes, based on natural, theoretical and experimental data. Future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks.
Journal of the Geological Society, Oct 28, 2009
... Scientific Editing By Quentin Crowley. Next Section. Abstract: New UPb sensitive high ... 57... more ... Scientific Editing By Quentin Crowley. Next Section. Abstract: New UPb sensitive high ... 571 ± 8 Ma). Transpression and coeval high-K calc-alkaline magmatism is recorded in the Maldonado granite dated at 564 ± 7 Ma. The following ...
Regional geology reviews, 2018
Crustal-scale shear zones are ubiquitous in most Brasiliano–Pan-African belts of southwestern Gon... more Crustal-scale shear zones are ubiquitous in most Brasiliano–Pan-African belts of southwestern Gondwana and they resulted from the assembly of the Rio de la Plata, Congo and Kalahari cratons. In the Dom Feliciano Belt, the Sierra Ballena-Dorsal do Cangucu-Major Gercino shear zone system and Sarandi del Yi Shear Zone are the most prominent structures, and they share a common history with shear zones of the Kaoko Belt, such as the Purros and Three Palms Mylonite Zones. The Purros Mylonite Zone, in turn, can be traced further south in the Damara Belt, where it is correlated with the Ogden Mylonite Zone. All these orogen-parallel shear zones underwent ductile deformation mostly at c. 630–580 Ma. However, further shearing is recorded in both the Kaoko and Dom Feliciano Belts at c. 550 Ma, thus being coeval with shearing along the Colenso Fault of the Saldania Belt. Though the Brasiliano–Pan-African Orogeny led to a relative stabilization of the South American and African continental crust by the early Paleozoic, shear zones were subsequently reactivated under brittle conditions during the Phanerozoic. These fault zones were particularly active during the opening of the South Atlantic Ocean in the Cretaceous, controlling magmatism emplacement, basin development and crustal exhumation. Shear zones thus played a major role not only during the Neoproterozoic assembly but also during the subsequent break-up of Gondwana.
Regional geology reviews, 2018
The Dom Feliciano Belt is an orogenic association that extends from southern Brazil to Uruguay pa... more The Dom Feliciano Belt is an orogenic association that extends from southern Brazil to Uruguay parallel to the Atlantic coastline for over 1100 km. It was assembled in the Neoproterozoic, during the Brasiliano orogenic cycle, and is the result of interaction between the Rio de la Plata, Congo and Kalahari cratons, together with several microplates, juxtaposed along major shear zones. Along its extension, the Dom Feliciano Belt is exposed in three sectors: in the Brazilian states of Santa Catarina and Rio Grande do Sul, and in Uruguay. The blocks that acted as direct forelands to the belt in South America are smaller fragments to the main cratons: Luis Alves and Nico Perez. Three main lithotectonic domains are recognized in the belt, from east to west: a granitic batholith, a metasedimentary sequence and an association of foreland basins. Basement inliers are common, and evidence intense reworking and magmatism during the Neoproterozoic. Cryogenian to Ediacaran granitogenesis is widespread and voluminous, and usually displays an evolutionary tendency from medium- to high-K calc-alkaline, finishing with alkaline magmatism. The early evolution of the Dom Feliciano Belt is recorded in the Sao Gabriel Terrane, in which convergent tectonics is associated with intense juvenile magmatism, ophiolite complexes and accretion between 870 and 680 Ma. This is followed by two more deformational phases, identified in all three sectors. A convergent phase is associated with the deformation of the metavolcano-sedimentary complexes, shear zone nucleation and granitic magmatism associated with high-grade collisional metamorphism. This stage is constrained between c. 650–620 Ma in Santa Catarina and Rio Grande do Sul, and between c. 630–600 Ma in Uruguay. The last stage marks a transition to strike-slip deformation, with common shear zone reactivation associated with refolding in the metamorphic associations and widespread post-collisional granitic and volcanic magmatism. This phase is predominant from 610 to 550 Ma. The opening of the foreland basins was initiated during this period, probably associated with transtension along the main structures. Late-stage deformation and magmatism is common until 550–540 Ma. Abundant geochronological data have been added to the Dom Feliciano Belt in the last decades, leading to more precise time constraints for most of the geologic processes in the orogen. Details of its tectonic model, however, are still matters of debate, in terms of both the setting of its main units and its position into the assembly of southwestern Gondwana.
Precambrian Research, Feb 1, 2022
EGUGA, Apr 1, 2012
ABSTRACT Different building stones of the Cologne Cathedral show a large variation of weathering ... more ABSTRACT Different building stones of the Cologne Cathedral show a large variation of weathering phenomena. The Drachenfels trachyte, which was the construction material for the medieval part of the cathedral, shows significant surface deterioration, back-weathering coexisting with flaking, crumbling or the massive formation of gypsum crusts. Wolff (1992) first mentioned the negative interferences between the Schlaitdorfer sandstone and the Londorfer basalt lava or the Drachenfels trachyte and the Krensheimer muschelkalk. Crust formation on limestone, sandstone, and volcanic rock from the Cologne Cathedral as well as from the Xanten and Altenberg Cathedral are investigated. These three buildings are located in different areas and exposed to varying industrial, urban, and rural environmental situations. The material investigated range from dark grey to black framboidal crusts. This 3 to 10 mm thick cauliflower-like form of gypsum crust incorporates particles from the pollution fluxes. It covers the stone surface and mainly occurs at sites protected from wind and direct rain. Secondly, thin laminar black crusts trace the stone surface and may cover complete sections of the building&#39;s structure not necessarily preferring protected sites. This kind of crust seems to have very strong bonds between the thin black crust and the stone surface. Major and trace element distribution show an enrichment of sulfur, indicating the presence of gypsum, lead and other typical pollutants (arsenic, antimony, bismuth, tin etc.), which generally can be linked to traffic and industry. This indicates that even though the SO2 emission has decreased due to i.e. stronger regulations of waste incineration plants and the ban of leaded petrol, the pollutants are still present in the crusts on the building stones. From systematic SEM observations it becomes evident that the total amount of pollution is less pronounced in the Altenberg and Xanten Cathedrals as compared with the Cologne Cathedral. The formation of gypsum occurs at lower amounts in Altenberg, which correlates well with the measured SO2 content. On the other hand, the increasing H2O content in the trachyte and the crusts correlates well with an increasing phyllosilicate formation. Through the combination of different analytical techniques it was possible to clearly distinguish samples from the industrial or rural environment. If the data is compared to actual pollutant emissions, the analyzed samples imply present but also past pollution fluxes. Thus, the soiled zones of the built environment can function as environmental indicators.
Journal of Metamorphic Geology
The Dom Feliciano Belt of southern Brazil and Uruguay represents part of a larger Neoproterozoic ... more The Dom Feliciano Belt of southern Brazil and Uruguay represents part of a larger Neoproterozoic orogenic system formed during the amalgamation of Western Gondwana. The hinterland and foreland domains in parts of the belt preserve deformation structures and metamorphic assemblages that developed during early crustal thickening from c. 650 Ma. However, the metamorphic history of the southern foreland, in Uruguay, and its relationship with the hinterland, is not so well understood. We show that metamorphism in the southern hinterland is characterized by near‐isothermal decompression from ~10 kbar (~770°C) down to ~6 kbar, reflecting exhumation from depths of ~40 km during convergent thrusting and crustal thickening. This metamorphic event and associated magmatism is constrained by garnet Lu–Hf and zircon U–Pb dating to c. 655–640 Ma, supporting age and P–T constraints from previous studies. In contrast, prograde metamorphism in the foreland supracrustal rocks reached maximum lower‐amp...
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Papers by Pedro Oyhantcabal