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12. Zircons to the front: accretionary history of the Rheno-Hercynian active margin (Variscides, Germany)

Author

Franke, Wolfgang, Huckriede, Hermann, O'Sullivan, Paul, and Wemmer, Klaus

Subjects
Exxon Mobil Corp., Petroleum industry -- Analysis, Tectonics (Geology) -- Analysis, Sedimentary basins -- Analysis, Zirconium -- Analysis, Sediments (Geology) -- Analysis, Earth sciences
Abstract

Our paper reports the detrital zircon record from Late Devonian to late Carboniferous foreland basin deposits in the Rheno-Hercynian (RH) Variscides of Germany. Together with a review of petrography and detrital mineral ages from the literature, the data permit to reconstruct accretion and exhumation along the RH active margin. From Frasnian to latest Carboniferous, the main source (now eroded) was a north-Armorican microcontinent (Franconia) with magmatic rocks representing late Neoproterozoic arc or back-arc, Cambro-Ordovician rift and Silurian--Early Devonian subduction of the Rheic ocean and (or) RH rifting. At ca. 380 Ma, detrital magmatic zircons combined with high- to medium-pressure mica and detrital glaucophane suggest the existence of a paired metamorphic belt at the RH tectonic front. From the Visean onwards, zircons reveal younging of granitoid debris from ca. 380-360 Ma in Late Devonian sediments to ca. 320-300 Ma in the Westphalian C-D and Stephanian. Greywackes of the Namurian A record a change from dominant magmatic clasts toward meta-arenites associated with Baltoscandian zircons, which document accretion to and exhumation from the base of the orogenic wedge. Their source must be sought in metamorphosed Devonian sandstones of the type presently encountered in parts of the active margin crystallines (Mid-German Crystalline High), but in eroded higher units. Basal accretion implies heating of the lower plate beyond the brittle--ductile boundary and supports the model of a high-temperature regime before and during Variscan collision. Palinspastic restoration of the estimated volume of recycled material yields >100 km of distal shelf deposits lost in the process, which adds to the known shortening of the RH basin. The Variscan geology of southwestern England and southern Portugal and provenance studies in those areas are compatible with a geodynamic evolution similar to that in Germany. Key words: detrital zircon, U--Pb laser ICP-MS, foreland basin deposits, Rheno-Hercynian belt, Variscides. Nous rendons compte du registre des zircons detritiques de depots de bassin d'avant-pays d'ages devonien tardif a carbonifere tardif dans la zone rheno-hercynienne (RH) de la chame varisque d'Allemagne. Combinees a un examen de la petrographie et des ages de mineraux detritiques publies, les donnees permettent de reconstituer l'accretion et l'exhumation le long de la marge RH active. Du Frasnien a la fin du Carbonifere, la source principale (aujourd'hui erodee) etait un microcontinent nord-armoricain (la Franconie) avec des roches magmatiques representant un arc ou arriere-arc d'age neoproterozoique tardif, un rift cambro-ordovicien et la subduction du Silurien au Devonien precoce de l'ocean Rheique ou un rifting RH. Vers 380 Ma, des zircons magmatiques detritiques combines a des micas de haute a moyenne pression et du glaucophane detritique indiquer-aient l'existence d'une ceinture metamorphique jumelee au front tectonique RH vers 380 Ma. A partir du Viseen, les zircons revelent un rajeunissement des debris de granitoide a partir d'environ 380-360 Ma dans des sediments d'age devonien tardif a environ 320-300 Ma dans le Westphalien C-D et le Stephanien. Des grauwackes du Namurien A enregistrent le passage de clastes principalement magmatiques a des meta-arenites associees a des zircons baltoscandiens, qui documentent l'accretion a la base du biseau orogenique et l'exhumation subsequente. Leur source doit se trouver dans des gres devoniens metamorphises semblables a ceux qui se trouvent actuellement dans les roches cristallines de la marge active (ride cristalline medio-allemande), mais dans des unites plus hautes erodees. L'accretion basale signifie que la plaque inferieure a ete chauffee au-dela de la limite cassant--ductile et appuie le modele d'un regime de haute temperature avant et durant la collision varisque. La reconstitution palinspatique du volume estime de materiau recycle donne >100 km de depots de plateforme distale evacues durant le processus, ce qui vient s'ajouter au raccourcissement connu du bassin RH. La geologie varisque du sud-ouest de l'Angleterre et du sud du Portugal et des etudes de provenance dans ces regions sont compatibles avec une evolution geodynamique semblable a celle observee en AUemagne. Mots-cles : zircon detritique, analyse U--Pb par ICP-MS avec ablation au laser, depots de bassin d'avant-pays, ceinture rhenohercynienne, chame varisque., Introduction Rationale The Rheno-Hercynian (RH) Variscides (Portugal, southwestern England, Germany, Poland, Turkey) were formed from the infill of the narrow RH ocean. Closure of that ocean is documented, especially in [...]

Published
2019
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13. Shear Zones in Brasiliano-Pan-African Belts and Their Role in the Amalgamation and Break-Up of Southwest Gondwana

Author

Oriolo, Sebastián, Hueck, Mathias, Oyhantçabal, Pedro, Goscombe, Ben, Wemmer, Klaus, Siegesmund, Siegfried, Oberhänsli, Roland, Series editor, de Wit, Maarten J., Series editor, Roure, François M., Series editor, Siegesmund, Siegfried, editor, Basei, Miguel A. S., editor, Oyhantçabal, Pedro, editor, and Oriolo, Sebastian, editor

Published
2018
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14. Untangling the Neoproterozoic-Early Paleozoic Tectonic Evolution of the Eastern Sierras Pampeanas Hidden in the Isotopical Record

Author

López de Luchi, Mónica G., Martínez Dopico, Carmen I., Wemmer, Klaus, Siegesmund, Siegfried, Oberhänsli, Roland, Series editor, de Wit, Maarten J., Series editor, Roure, François M., Series editor, Siegesmund, Siegfried, editor, Basei, Miguel A. S., editor, Oyhantçabal, Pedro, editor, and Oriolo, Sebastian, editor

Published
2018
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15. The Nico Pérez Terrane of Uruguay and Southeastern Brazil

Author

Oyhantçabal, Pedro, Oriolo, Sebastián, Philipp, Ruy Paulo, Wemmer, Klaus, Siegesmund, Siegfried, Oberhänsli, Roland, Series editor, de Wit, Maarten J., Series editor, Roure, François M., Series editor, Siegesmund, Siegfried, editor, Basei, Miguel A. S., editor, Oyhantçabal, Pedro, editor, and Oriolo, Sebastian, editor

Published
2018
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16. The Río de la Plata Craton of Argentina and Uruguay

Author

Oyhantçabal, Pedro, Cingolani, Carlos A., Wemmer, Klaus, Siegesmund, Siegfried, Oberhänsli, Roland, Series editor, de Wit, Maarten J., Series editor, Roure, François M., Series editor, Siegesmund, Siegfried, editor, Basei, Miguel A. S., editor, Oyhantçabal, Pedro, editor, and Oriolo, Sebastian, editor

Published
2018
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34. PAIRED RESIDUAL DEFORMATION AND POST-OROGENIC EXHUMATION OF THE KAOKO AND DOM FELICIANO BELTS: impacts of the migrating orogenic front during the assembly of western Gondwana

Author

HUECK, MATHIAS, BASEI, MIGUEL A.S., WEMMER, KLAUS, DUNKL, ISTVÁN, TESSER, LUCAS, CAMPOS NETO, MARIO C., FRIMMEL, HARTWIG, and SIEGESMUND, SIEGFRIED

Subjects
shear zone reactivation, ductile-brittle transition, structural inheritance, low-T thermochronology, Brasiliano/Pan-African orogenic cycle
Abstract

The reactivation of shear zones under brittle conditions during exhumation due to extensional collapse of the thickened continental crust is a common feature of post-collisional settings. New illite K-Ar analyses and (U-Th)/He data help establish the timing of exhumation and residual deformation during the final stages of orogenic activity in the Kaoko Belt, NW Namibia. Dating of clay-sized white mica from fractionated samples can be used to estimate late-stage deformation in shear zones and constrain the transition from the ductile to the brittle regime. XRD characterization of the dated material indicates crystallization under epizonal conditions (>300°C), which, together with the lack of correlations with age in fractionated samples are suggestive of protracted mineral growth. This supports the interpretation that K-Ar ages at 510-480 Ma in the analyzed samples set a maximum age for the end of ductile activity in the Kaoko Belt, after which brittle faulting is interpreted to have been the predominant style of deformation. This is in accordance with zircon thermochronological data, which predominantly record fast cooling towards temperatures below 200°C shortly thereafter. When compared with equivalent data in South America, the new results reveal that, while the peak orogenic stage of the Dom Feliciano Belt (650-570) took place many tens of Myr earlier than in the Kaoko Belt (580-550 Ma), the transition from ductile to brittle deformation (535-465 Ma and 510-480 Ma, respectively) and rapid exhumation into upper crust conditions (550-400 Ma and 500-350 Ma, respectively) has much more significant overlaps. This observation suggests that, with the progression of the main deformation front from present- day South America to Africa at the time of the collisional process in the Kaoko Belt, the late-stage deformation and eventual post-orogenic exhumation of the Dom Feliciano Belt may have been controlled by the far-field tectonic influence of the continuing orogenic activity to the West. The late stages of the Kaoko Belt, on its turn, are also influenced by a continuation of the progressive migration of the orogenic front towards the Damara Belt, thus highlighting the interconnected character of deformation and exhumation within the entire orogenic system., 4° Encontro dos Pesquisadores de Pós-Doutorado do IGc/USP, Instituto de Geociências da Universidade de São Paulo, São Paulo, SP, Brasil, 29 e 30 de novembro de 2022.

Published
2022
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36. Provenance of the Bosnian Flysch

Author

Mikes, Tamás, Christ, Dominik, Petri, Rüdiger, Dunkl, István, Frei, Dirk, Báldi-Beke, Mária, Reitner, Joachim, Wemmer, Klaus, Hrvatović, Hazim, von Eynatten, Hilmar, Froitzheim, Nikolaus, editor, and Schmid, Stefan M., editor

Published
2009
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40. The Cuesta de Rahue Basement Inlier (Southern Neuquén Precordillera, Argentina): a Devonian to Triassic polyphase orogenic record in northern Patagonia.

Author

Oriolo, Sebastián, González, Pablo D., Alegre, Pablo, Wemmer, Klaus, Varela, Ricardo, and Basei, Miguel A. S.

Subjects
BASEMENTS, DEVONIAN Period, X-ray diffraction, MESOZOIC Era, BIOTITE, PALEOZOIC Era
Abstract

We present new geological, structural and microstructural data, together with K–Ar biotite and illite geochronological data, for the igneous–metamorphic rocks exposed in the Cuesta de Rahue Basement Inlier in the Southern Neuquén Precordillera, Argentina. We use these data to reconstruct the Late Paleozoic to Mesozoic tectonometamorphic and magmatic history of northwestern Patagonia. This block consists of a medium-grade metasedimentary sequence (the Cuesta de Rahue Metamorphic Complex), Late Carboniferous granitoids and a low-grade metavolcano-sedimentary unit (the Arroyo Coloco Metamorphic Complex). The Cuesta de Rahue Metamorphic Complex was deposited during the mid-Paleozoic and underwent Devonian low-pressure regional metamorphism, followed by the intrusion of granitoids at c. 300 Ma. By contrast, the Arroyo Coloco Metamorphic Complex records deformation and metamorphism under epizonal conditions (>300°C), constrained at c. 232–199 Ma by K–Ar and X-ray diffraction illite data. The Cuesta de Rahue Basement Inlier thus records a protracted orogenic evolution, recording Devonian metamorphism, Late Carboniferous–Permian Gondwanide tectonomagmatic processes, and Late Triassic deformation and metamorphism. This block was later affected by Mesozoic normal faulting and Miocene–Pliocene Andean deformation. The Andean deformation was intimately related to the reactivation of inherited basement fabrics, favouring a transpressional deformation regime. Supplementary material: Supplementary Material 1 – Analytical procedures is available at https://doi.org/10.6084/m9.figshare.c.6484467 [ABSTRACT FROM AUTHOR]

Published
2023
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44. Posteruptive Thermal History of the Proterozoic Basaltic North Shore Volcanic Group of the Midcontinent Rift: Evidence from K/Ar Data of Celadonite

Author

Schmidt, Susanne Theodora, Suessenberger, Annette, and Wemmer, Klaus

Subjects
ddc:550
Abstract

This study reports three K/Ar ages on celadonite, a dioctahedral K-Fe mica, in the Proterozoic North Shore Volcanic Group (NSVG) of the Midcontinent Rift in northeastern Minnesota. Celadonite formed during beginning posteruptive, lowtemperature conditions at temperatures < 100°C and with input of meteoric water. K/Ar ages between 1062 ± 16 Ma and 955:0 ± 12 Ma document a remarkably long posteruptive thermal history of >100 myrs in a thick continental basaltic sequence. In the stratigraphically lower part of the NSVG, celadonite formation occurred at 1062 ± 16Ma in an amygdule or a vesicle filled with celadonite, while another celadonite amygdule in a stratigraphically higher flow was dated at 1039:4 ± 14Ma. Both flows are overprinted by a later multistage lower zeolite-phyllosilicate facies assemblage (laumontite-albite-corrensite±chlorite±smectite ±prehnite±pumpellyite). In the stratigraphically higher part of the sequence, celadonite crystallization at an amygdule rim is followed by upper zeolite facies conditions (stilbite-heulandite-smectite assemblage) and was dated at 955:0 ± 12:4 Ma. The constrained time frame of 107 myrs indicates a long-lived, probably not continuous and locally occurring, posteruptive thermal alteration process. The data suggest that alteration was depth-controlled and temporally and spatially inhomogeneous and implies the progression of the sequence from a close-to-the-surface alteration mode with input of meteoric water to a burial metamorphic mode and with locally occurring hydrothermal activity due to continuous magmatic activity. Volcanism in the Midcontinent Rift system is supposed to have lasted between 1109 Ma and 1083 Ma based on U/Pb zircon ages. The first crystallization of celadonite is recorded in the lower part of the NSVG and occurred ca. 30 myrs after the emplacement of the Silver Bay aplite intrusion in the upper part of the NSVG. Burial rates are determined to be 0.04 km·Ma-1and 0.10 km·Ma-1. The hydrothermal alteration under low-temperature burial conditions clearly postdates the rift-related alkaline and tholeiitic magmatism of the Midcontinent Rift and overlaps with the depositional window of the sedimentary rocks that overlie the Midcontinent Rift volcanics, as well as crustal-scale fault systems that were active during Grenvillian tectonic uplift after the cessation of magmatic activity.

Published
2021

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