The Palaeozoic Variscan oceans revisited

Franke, Wolfgang; Cocks, L. Robin M.; Torsvik, Trond H.

doi:10.1016/j.gr.2017.03.005

Cited by 241 publications

(197 citation statements)

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“…This dynamic is attributed to a large-scale clockwise rotation of Gondwana related to the opening of the Paleotethys Ocean associate to a largescale mantle anomaly (Edel et al, 2018;Frizon de Lamotte et al, 2013). In fact, high heat flow, magmatism, and HT-LP metamorphism event at approximately 340 Ma, caused by mantle heat advection and related to Paleotethys rifting, affected different areas across the entire Variscan belt as shown by Franke (2014) and Franke et al (2017).…”

Section: 1029/2018tc005002mentioning

confidence: 99%

The Geological Evolution of the Variscan Jebilet Massif, Morocco, Inferred From New Structural and Geochronological Analyses

et al. 2018

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The present work aims at understanding the tectonic evolution of the Jebilet massif, Morocco, during the Late Paleozoic as constrained by structural, metamorphic, and geochronological studies. From Late Devonian to Early Carboniferous, bordering faults controlled the opening of the Jebilet intracontinental basin (D0 stage) as shown by sedimentary infill. This episode was accompanied by a magmatic activity, newly dated between 358 ± 7 Ma and 336 ± 4 Ma. The first record of the Variscan event affected the Jebilet by the Late Visean‐Namurian and is represented by allochthonous superficial nappes emplaced at shallow depth in a moderately lithified sedimentary succession. D1 also developed regional‐scale recumbent folds trending E‐W that may suggest N‐S crustal shortening not generating crustal thickening nor contributing to metamorphism. The main Variscan D2 episode consists of a progressive evolution from bulk coaxial deformation to noncoaxial dextral transpression consistent with NW‐SE horizontal shortening, resulting in a moderate thickening. This episode was accompanied by HT‐LP metamorphism and syntectonic intrusions controlled by an inherited thermal anomaly in relation with the intracontinental rifting stage (D0). Based on previous age determinations from syntectonic leucogranite and metamorphic rocks, D2 is dated between 310 and 280 Ma. The tectono‐metamorphic evolution of the Jebilet massif can be correlated with a plate‐tectonic scenario evolving from, first a Late Devonian‐Early Carboniferous basin formation during stretching of the north‐Gondwana margin and initiation of the Paleotethys Ocean, and, second, to a Late Carboniferous‐Early Permian ocean closure (Rheic or Paleotethys Oceans depending of scenarios) that resulted in the final Variscan‐Alleghanian tectonics.

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Section: 1029/2018tc005002mentioning

confidence: 99%

The Geological Evolution of the Variscan Jebilet Massif, Morocco, Inferred From New Structural and Geochronological Analyses

et al. 2018

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“…The Variscan belt is generally thought to be the result of the collision between Laurussia to the north and Gondwana to the south, and this collision was preceded by the subduction of one or several oceans (e.g. Pin, 1990;Matte, 2001;Lardeaux, 2014;Franke et al, 2017), the largest one being the Rheic Ocean, separating Avalonia to the North from Armorica and other Gondwana-derived terranes to the South. The geological history of Southern Brittany in Western France records the rift-drift history of Armorica away from Gondwana and its late shearing during the oblique convergence between Laurussia (incorporating Avalonia) and…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…Dismembered ophiolite complexes are recognized throughout the belt, from Iberia to Bohemia (e.g. Dubuisson et al, 1989;Pin, 1990;Girardeau et al, 1994;Sánchez Martínez, 2009;Kryza and Pin, 2010;Arenas and Sánchez Martínez, 2015;Franke et al, 2017). In the absence of fossiliferous sedimentary sequences deposited on top of these ophiolite sequences, geochronology is the only tool available for assessing their age.…”

Section: Geological Setting and Studied Samplesmentioning

confidence: 99%

“…The second group includes However, despite these progress in geochronological characterization of the ophiolitic complexes, the identification and correlation of oceanic sutures in the Variscan belt remain largely elusive, as shown by an array of contrasting proposals recently published (e.g. Díez Fernández and von Raumer et al, 2015;Arenas et al, 2016;Murphy et al, 2016;Simancas et al, 2016;Franke et al, 2017). We favour a model where the ophiolitic complexes from southern Brittany derive from a Cambro-Ordovician ocean (the Galicia-Southern Brittany Ocean of Matte (2001), equivalent to the Galicia-Moldanubian Ocean of Franke et al (2017) (Fig.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

Paquette

Ballèvre

Peucat

et al. 2017

Lithos

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International audienceIn the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples.Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism

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“…It is onshore in a seismically active (e.g., Reference [79]) Eurasian intraplate location, proximal to the uplifting North Alpine Foreland Basin and Alps orogenic belt (Figure 8). The region formed by the amalgamation of supra-subduction zone micro-plates during the Devonian-Carboniferous Variscan Orogeny [80]. The mineral system is located in and around the Southern URG basin (Figures 8 and 9).…”

Section: Case Study: the Southwest Germany Tentative Variscan-miocementioning

confidence: 99%

A Workflow to Define, Map and Name A Carbonatite- or Alkaline Igneous-Associated REE-HFSE Mineral System: A Case Study from SW Germany

et al. 2019

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Security of supply of "hi-tech" raw materials (including the rare earth elements (REE) and some high-field-strength elements (HFSEs)) is a concern for the European Union. Exploration and research projects mostly focus on deposit-to outcrop-scale description of carbonatite-and alkaline igneous-associated REE-HFSE mineralization. The REE-HFSE mineral system concept and approach are at a nascent stage, so developed further here. However, before applying the mineral system approach to a chosen REE-HFSE metallogenic province its mineral system extent first needs defining and mapping. This shifts a mineral system project's foundation from the mineral system concept to a province's mineral system extent. The mapped extent is required to investigate systematically the pathways and potential trap locations along which the REE-HFSE mass may be distributed. A workflow is presented to standardize the 4-D definition of a REE-HFSE mineral system at province-scale: (a) Identify and hierarchically organize a mineral system's genetically related sub-divisions and deposits, (b) map its known and possible maximum extents, (c) name it, (d) discern its size (known mineral endowment), and (e) assess the favorability of the critical components to prioritize further investigations. The workflow is designed to generate process-based perspective and improve predictive targeting effectiveness along under-evaluated plays of any mineral system, for the future risking, comparing and ranking of REE-HFSE provinces and plays.or geophysical pathfinder signatures [7]; or serendipitously, e.g., during uranium prospecting [7]. Knowledge of the location controls of these metals remains limited compared to knowledge about base and precious metal deposits [5]. Many of the >500 known carbonatite occurrences [8] remain under evaluated. The result is recent REE mining from only a few deposits related to carbonatite and alkaline igneous bodies [1,9], e.g., the Bayan Obo Fe-REE deposit in China [10,11]; the Mountain Pass carbonatite-hosted REE deposit in the USA [12]; the Mount Weld carbonatite-associated lateritic REE and Nb-Ta deposits in Australia (e.g., Reference [13]) and the Araxa carbonatite-associated, lateritic Nb deposit in Brazil [14]. Other REE mines are of ion-adsorption clay deposits and monazitexenotime-bearing placer deposits (e.g., Reference [9]). For details of REE and carbonatite-related data, uses, occurrences, and mines refer to References [1,5,[15][16][17][18][19]. Aims and AudienceAs most REE-HFSE-centric exploration and research projects tend to focus efforts on the depositto outcrop-scale they neglect to place occurrences within their wider context, where significant undiscovered potential may exist. To help address this knowledge gap we present a method and workflow for defining, mapping and naming any REE-HFSE mineral system associated with carbonatite and alkaline igneous rocks. The objective is to 4-D summarise the current knowledge status of the selected mineral system. It is designed so that geoscientists, economists, and stra...

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The Palaeozoic Variscan oceans revisited

Cited by 241 publications

References 132 publications

The Geological Evolution of the Variscan Jebilet Massif, Morocco, Inferred From New Structural and Geochronological Analyses

The Geological Evolution of the Variscan Jebilet Massif, Morocco, Inferred From New Structural and Geochronological Analyses

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

A Workflow to Define, Map and Name A Carbonatite- or Alkaline Igneous-Associated REE-HFSE Mineral System: A Case Study from SW Germany

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