Detrital zircon age patterns from turbidites of the Balagne and Piedmont nappes of Alpine Corsica (France): Evidence for an European margin source (original) (raw)
Related papers
2016
In the internal zone of the European Alps, late Carboniferous to Permian sediments have been detached from their basement (e.g. the Zone Houillère in the Briançonnais Zone). The Pinerolo Unit (Dora-Maira Massif) is the deepest unit exposed in the stack of the Western Alps and is considered to be Carboniferous in age based on lithological considerations. Detrital zircon grains from the Pinerolo Unit and the Zone Houillère display similar age patterns, with the youngest and largest population being Carboniferous (340–330 Ma). The distribution of Carboniferous magmatism in the Alps and surrounding areas suggests that the detritus was transported from Maures-Corsica and Accepted Article This article is protected by copyright. All rights reserved. possibly from the Helvetic Zone into the Zone Houillère and the Pinerolo basin. Our results highlight the potential of detrital zircon geochronology for deciphering the sources of detrital material in metasediments, even if they have been affected by metamorphic overprints.
Comptes Rendus de l'Académie des Sciences, 2007
Zircons from a metagranite sample from the Lower Gneiss Unit in Limousin (French Massif Central) were dated by the U-Pb ion probe method. Apart from inherited Palaeoproterozoic ages (1.8 to 2.1 Ga), all analyses are concordant to sub-concordant and fall into three age groups: 617 AE 17, 526 AE 14, and 457 AE 23 Ma. Distinct oscillating banding domains within the zircons analysed suggest that the ages correspond to at least two consecutive episodes of protolith reworking. The ages obtained are similar to other found in the French Massif Central, but the fact that here they are seen in a single zircon grain or in a single grain population points out to the cyclic evolution of the protolith in a succession of tectonic events also affecting the microplates between Laurussia and Gondwana. To cite this article: P. Alexandre, C. R. Geoscience 339 . # 2007 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved. Résumé Â ges U-Pb sur zircon (SIMS) dans le Massif central français et implications pour l'évolution pré-Varisque de l'Europe occidentale. Les zircons extraits d'un métagranite de l'unité inférieure des gneiss dans le Limousin (Massif central) ont été datés par la méthode U-Pb à la sonde ionique. Mis à part les âges paléoprotérozoïques (de 1,8 à 2,1 Ga), toutes les analyses sont concordantes ou subconcordantes, et forment trois groupes d'âges : 617 AE 17, 526 AE 14, et 457 AE 23 Ma. Des zones de croissance oscillatoires observées dans les zircons datés suggèrent que ces âges correspondent à au moins deux épisodes consécutifs de recyclage du protolithe. Des âges similaires ont été obtenus ailleurs dans le Massif central, mais le fait qu'ils soient observés ici dans une seule population de grains révèle le caractère cyclique de l'évolution du protolithe, dans le cadre d'une suite d'événements tectoniques qui affectent les microplaques entre l'Eurasie et le Gondwana. Pour citer cet article : P. Alexandre, C. R. Geoscience 339 (2007).
Age of Alpine Corsica ophiolites revisited: Insights from in situ zircon U–Pb age and O–Hf isotopes
Lithos, 2015
Knowledge of the age and timing of ophiolite sequences is essential for understanding the mechanisms of plate tectonics. The ophiolites in the Schistes Lustrés and the Upper nappes of Alpine Corsica represent remnants of the Liguria-Piemonte ocean basin that formed as a branch of the Central Atlantic basin during the opening of the Mesozoic Western Alpine Tethys. Despite numerous isotopic and paleontological studies, the age and timing of the ophiolites in the Schistes Lustrés nappe are still controversial. This study presents integrated in situ analyses of zircon U-Pb age and O-Hf isotopic data for ophiolitic gabbros and plagiogranites from three localities in the Schistes Lustrés nappe of Eastern Corsica. Our new results demonstrate that these rocks crystallized synchronously at~159 Ma, approximately 10 m.y. younger than the ophiolites in the Balagne Upper nappe. Zircons from the gabbros and plagiogranites are characterized by highly positive εHf(t) (+15.0 to +15.9) and mantlelike δ 18 O(5.2-5.4‰) values. Thus, these ophiolitic rocks were cogenetic, and crystallized from magmas produced by partial melting of a depleted, N-MORB type mantle. By contrast, in the Balagne Upper nappe, the~169 Ma ophiolites contain numerous xenocrystic zircons inherited from a continental crust. Our current knowledge of isotopic geochronology and geochemistry supports a paleogeographic reconstruction, in which the earliest ophiolites in the Balagne nappe were emplaced close to a continental margin at~169 Ma, while the N-MORB type ophiolites in the Schistes Lustrés nappe were likely formed approximately 10 m.y. later in the central part of the Liguria-Piemonte oceanic basin. The relative location of the Schistes Lustrés and Balagne Upper nappes with respect to continental margins is discussed.
The first LA-ICP-MS U–Pb detrital zircon ages from quartzites located below (three samples) and above (one sample) the Upper Ordovician unconformity in the Central Pyrenees (the Rabassa Dome, Andorra) were investigated. The maximum depositional age for the Jújols Group, below the unconformity, based on the youngest detrital zircon population, is around 475 Ma (Early Ordovician), whereas for the Bar Quartzite Fm., above the unconformity, the presence of only two zircons of 442 and 443 Ma precludes obtaining a precise maximum sed-imentation age. A time gap of ~20 million years for the Upper Ordovician unconformity in the Pyrenees can be proposed, similar to that of the Sardic unconformity in Sardinia. The similar age patterns obtained on both sides of the Upper Ordovician unconformity suggest that there was no change in the source area of these series, while the absence of a Middle Ordovician age population may be due to a lack of sedimentation at that time. The four study samples present very similar U–Pb age patterns: the main age populations correspond to Neoproterozoic (Ediacarian–Cryogenian, ca. 550–750 Ma); Grenvillian (Tonian–Stenian, ca. 850–1100 Ma); Paleoproterozoic (Orosirian, ca.1900–2100 Ma) and Neoarchean (ca. 2500–2650 Ma). The similarity with the Sardinian age distribution suggests that these two terranes could share the same source area and that they were paleogeographically close in Ordovician times in front of the Arabian–Nubian Shield.
International Journal of Earth Sciences, 2019
Constraining the source terranes of Alpine siliciclastic flysch sequences is crucial for building a clearer picture of the palaeogeography and geodynamic evolution of the Western Tethys in the framework of impending continental collision. This paper presents an integrated study that involves palaeocurrent dispersal analysis, sandstone petrography and detrital zircon geochronology of the Upper Cretaceous-Paleocene Monte Bignone Sandstones, a siliciclastic turbidite system deposited during the precollisional evolution of the Ligurian Alps. Palaeocurrent analysis illustrates an overall eastward transport of the proximal sediments in the present configuration. Considering the ca. 45-50° counterclockwise rotation of the Tertiary Piedmont Basin and of the Corsica-Sardinia block in the late Paleogene, this indicates the derivation of the sediments from the northern margin of the Piedmont-Ligurian Ocean. Sandstone petrography records a stratigraphic evolution from quartzose sandstones towards lithic and then to lithic sub-arkosic composition. This trend is interpreted to reflect the gradual unroofing of the provenance terrane. The lithotypes of the recycled sedimentary rock fragments and the up-section increase in dolostone and carbonate clast proportions suggest the erosion of the sedimentary cover of the southern European palaeo-margin. New geochronological data (U-Pb detrital zircon ages) correspond to the pre-Alpine stages of crustal growth recorded in the Variscan Maures-Tanneron Massif, and therewith confirm the derivation of the sediments from the passive palaeo-European margin. This conclusion highlights the importance of the lower plate in providing the source of coarse-clastic deep-water successions during pre-collisional convergent steps. Results from this multi-proxy provenance analysis contribute to better defining the detrital signatures associated to the continental micro-fragments that constituted the palaeo-European plate as it supplied deep-sea siliciclastic sediments into the Piedmont-Ligurian ocean prior to continental collision.
THÈME 3. DYNAMIQUE INTERNE des Sciences de la Terre 24 e Réunion 27-31 octobre 2014 Résumés de la RST2014 the Ceret gabbro, both located in the Roc the Frausa massif (eastern Pyrenees). Zircons from both samples display core-rim features, with more contrasting cathodoluminescence textures in the gabbro sample (nonluminescent cores and luminescent rims. Ages in cores and rims are also different in both rock types. In the tonalite, cores yield a mean age of 314± 2 Ma, and rims yield a mean age of 311± 1 Ma. Compositionally, the tonalite zircons show rough differences between cores and rims, suggesting that both areas were originated in magmas with different chemical characteristics. The chemical composition differences are more pronounced between core and rim from the gabbro. The nonluminescent cores correspond to an early magmatic pulse that occurred at 312± 2 Ma. They grew from a more evolved magma where most of the plagioclase had already crystallized, in accordance with the lower values for Eu anomalies. The luminescent rims correspond to a second pulse that took place at 307± 4 Ma. They originated from a less evolved magma where plagioclase had not completely crystallized, as suggested by the lower Hf content and the shallower Eu anomaly. The absence of meso-and microscopic evidence of physical mixing (mingling) suggests that the mixture was complete ; therefore, the existence of these two magmatic pulses is recorded only in zircon. In summary, zircon geochemistry suggests a complex magmatic history for the Sant Llorenc-La Jonquera suite and the gabbro Ceret stock. This history includes several pulses of magma and mixing of magmas with different geochemical characteristics. Moreover, the chemistry of zircon supports the previous models stating that these two igneous bodies are geochemically diverse and they belong to genetically distinct igneous suites produced in different levels of the lithosphere.
Alpine provenance studies based on conventional methods such as sandstone framework grain and heavy mineral analyses are now enhanced by improved techniques in laser ablation inductively coupled plasma mass spectrometry detrital zircon analysis. Although the conventional methods appear to have reached their limits of resolution in palaeogeographic problems, laser ablation inductively coupled plasma mass spectrometry U-Pb dating of detrital zircons adds the time dimension to the provenance analysis. Hafnium-isotope ratios measured on dated zircons give further information on the origin of the magmas in which the detrital zircons have grown. This study reports detrital zircon U-Pb dating and Hf-isotope results from sandstone formations related to rifting, drifting and subduction settings at different stages of the Alpine Tethys development. This study is a first evaluation of the correlation between U-Pb age and isotopic features of detrital zircons aimed at describing source terranes in different palaeogeographic domains in the Alpine Tethys area. Pan-African/Cadomian (Ediacaran-Ordovician), Variscan (Middle Devonian-Carboniferous) and Post-Variscan (Permian) detrital zircon populations are present in nearly all palaeogeographic settings, but in varying amounts. Single Mesoproterozoic and Palaeoproterozoic detrital zircons are found as minor populations. When comparing the northern and southern margins of the Alpine Tethys, the southern margin detrital sources are characterized mostly by a decreased occurrence or by the absence of Silurian-Devonian zircons. A major distinction between northern (Helvetic, North and Middle Penninic domains) and southern (Austro-Alpine and South Alpine domains) detrital sources is the occurrence of Triassic zircons at the southern Alpine Tethys margin during rifting and subduction stage sedimentation. Hafnium-isotope ratios measured on uppermost Permian-Triassic zircons from the South Alpine domain suggest a continental crust derivation of the hosting magmas, as expected in a continental rift environment. In the late stage of Alpine convergence (Late Cretaceous-Palaeogene), the Permian-Triassic zircons are reworked into basins situated on the northern Alpine Tethys margin.