Palaeozoic oolitic ironstone of the French Armorican Massif: a chemical and structural trap for orogenic base metal–As–Sb–Au mineralisation during Hercynian strike-slip deformation

AbstractAn intimate lithostratigraphic and lithodemic connection between syn-orogenic rock masses inside the different lithotectonic units of the 2.0–1.8 Ga (Svecokarelian) orogen, Sweden, is proposed. A repetitive cyclic tectonic evolution occurred during the time period c. 1.91–1.75 Ga, each cycle lasting about 50–55 million years. Volcanic rocks (c. 1.91–1.88 Ga) belonging to the earliest cycle are host to most of the base metal sulphide and Fe oxide deposits inside the orogen. Preservation of relict trails of continental magmatic arcs and intra-arc basins is inferred, with differences in the depth of basin deposition controlling, for example, contrasting types of base metal sulphide deposits along different trails. The segmented geometry of these continental magmatic arcs and intra-arc basins is related to strike-slip movement along ductile shear zones during transpressive events around and after 1.88 Ga; late orogenic folding also disturbed their orientation on a regional scale. A linear northwesterly orogenic trend is suggested prior to this structural overprint, the strike-slip movement being mainly parallel to the orogen. A solely accretionary orogenic model along an active margin to the continent Fennoscandia, without any trace of a terminal continent–continent collision, is preferred. Alternating retreating and advancing subduction modes that migrated progressively outboard and southwestwards in time account for the tectonic cycles.

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The La Bellière gold and antimony district (French Armorican Massif): A two-stage evolution model controlled by Variscan strike-slip tectonic

Ore Geology Reviews ◽

10.1016/j.oregeorev.2020.103681 ◽

2020 ◽

Vol 125 ◽

pp. 103681

Author(s):

Florent Cheval-Garabédian ◽

Michel Faure ◽

Eric Marcoux ◽

Jérome Gouin ◽

Maxime Picault

Keyword(s):

Strike Slip ◽

Evolution Model ◽

Two Stage ◽

Armorican Massif

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Cenozoic Sedimentation Along the Piedmonts of Thrust Related Basement Ranges and Strike-Slip Deformation Belts of the Iberian Variscan Massif

The Geology of Iberia: A Geodynamic Approach - Regional Geology Reviews ◽

10.1007/978-3-030-11190-8_5 ◽

2019 ◽

pp. 131-165 ◽

Cited By ~ 3

Author(s):

Pedro P. Cunha ◽

G. de Vicente ◽

F. Martín-González

Keyword(s):

Strike Slip ◽

Slip Deformation

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Polygenic chamosite from a hydrothermalized oolitic ironstone (Saint-Aubin-des-Châteaux, Armorican Massif, France): crystal chemistry, visible–near-infrared spectroscopy (red variety) and geochemical significance

Clay Minerals ◽

10.1180/clm.2020.13 ◽

2020 ◽

Vol 55 (1) ◽

pp. 83-95 ◽

Cited By ~ 1

Author(s):

Yves Moëlo ◽

Emmanuel Fritsch ◽

Eric Gloaguen ◽

Olivier Rouer

Keyword(s):

Near Infrared ◽

Vanadium Content ◽

Published Data ◽

Octahedral Sheet ◽

New Variety ◽

Intervalence Charge Transfer ◽

Geochemical Significance ◽

Red Variety ◽

Armorican Massif ◽

Oolitic Ironstone

AbstractSeveral generations of chamosite, including a red variety, occur in the Ordovician hydrothermalized oolitic ironstone from Saint-Aubin-des-Châteaux (Armorican Massif, France). Their chemical re-examination indicates a low Mg content (0.925 < Fe/(Fe + Mg) < 0.954), but a significant variation in IVAl. Minor vanadium is present at up to 1.1 wt.% oxide. Variations in IVAl, the vanadium content and the colour of chamosite are related to the hydrothermal reworking of the ironstone. Taking into account other published data, the ideal composition of chamosite is (Fe5–xAl1+x)(Si3–xAl1+x)O10(OH)8, with 0.2 < x < 0.8 (0.2: equilibrium with quartz; 0.8: SiO2 deficit). The red chamosite (IIb polytype) has a mean composition of (Fe3.87Mg0.23Mn0.01□0.07Al1.74V0.07)(Si2.33Al1.67)O10(OH)8. This chamosite is strongly pleochroic, from pale yellow (E || (001)) to deep orange red (E ⊥ (001)). Visible–near-infrared absorbance spectra show a specific absorption band centred at ~550 nm for E ⊥ (001), due to a proposed new variety of Fe/V intervalence charge-transfer mechanism in the octahedral sheet, possibly Fe2+ – V4+ → Fe3+ – V3+. While the formation of green chamosite varieties is controlled by reducing conditions due to the presence of organic matter as a buffer, that of red chamosite would indicate locally a weak increase of fO2 related to oxidizing hydrothermal solutions.

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Shallow Seismic Reflection Survey of the Bootheel Lineament Area, Southeastern Missouri

Seismological Research Letters ◽

10.1785/gssrl.63.3.285 ◽

1992 ◽

Vol 63 (3) ◽

pp. 285-295 ◽

Cited By ~ 17

Author(s):

Eugene S. Schweig ◽

Fan Shen ◽

Lisa R. Kanter ◽

Eugene A. Luzietti ◽

Roy B. VanArsdale ◽

...

Keyword(s):

Seismic Reflection ◽

Strike Slip ◽

Seismic Reflection Data ◽

Reflection Data ◽

Shallow Seismic ◽

Slip Deformation ◽

Flower Structures

Abstract During 1990 we collected eight lines (11.5 km) of shallow seismic reflection data across the Bootheel lineament, a discontinuous feature that extends about 135 km in a north-northeast direction through northeastern Arkansas and southeastern Missouri. The profiles image reflectors at depths between about 55 m to 800 m. Gentle folding with wavelengths of about 800 m and amplitudes of 10 m to 25 m is evident on nearly every profile, generally coinciding with the surface traces of the lineament. We interpret our lines to show a complex zone of strike-slip deformation consisting of multiple flower structures, with deformation at least as young as the Eocene/Quaternary unconformity.

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