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Les terrains cristallins des Monts du Lyonnais (Massif Central Français)

Abstract : This work comprises a geological map at the 1:125,000 scale of the region (50 km x 50 km), located immediately to the West of Lyons, bordered by the Rhône-Saône rivers valley to the E, the Loire river valley to the W, the Gier river valley to the S and the Azergues river valley to the N. The interpretation of the metamorphisms was based on the mono-dimensional Zoneographic model proposed by Jung & Roques (1952, Bull. Serv. Carte géol. France, n° 235, tome 50). The pre-Coal Measures metamorphic units were subdivided into the Monts du Lyonnais Series (MLS: gneiss, micaschists, embrechites, leptynites, anatectites, migmatites) to the SE and the Brévenne Series (BS: sedimentary and volcanic rocks) to the NW. The BS, probably of Upper Devonian to Early Visean age, would have endured only a weak Hercynian metamorphic imprint, not stronger than the base of the Upper Micaschists Zone. The BS would rest, along a locally high angle unconformity, upon the MLS, that was metamorphosed previously at a much stronger degree (the so-called Normal Metamorphism from the Fundamental Gneisses and Migmatites Zone, plus a strata-bound metsasomatic metamorphism), and is thus seen as of Precambrian age. Various granites were also emplaced across this pile. 54 whole-rock major elements analyses of the various metamorphic rock-types and granites help investigating their volcanic or magmatic protoliths. Four radiochronological attempts, using the lead-alpha-zircon method (Larsen, Keevil & Harrison, 1952, Bulletin of the Geological Society of America 63: 1045-1052), yielded apparent ages at 620, 660, 460 et 440 million years for one gneiss and three anatexites of the MLS.
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Submitted on : Monday, December 12, 2016 - 3:32:21 PM
Last modification on : Wednesday, December 14, 2016 - 1:08:31 AM
Long-term archiving on: : Tuesday, March 28, 2017 - 12:20:23 AM

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  • HAL Id : tel-01414782, version 1

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Jean-Marc Peterlongo. Les terrains cristallins des Monts du Lyonnais (Massif Central Français). Pétrographie. Faculté des Sciences de l'Université de Clermont-Ferrand, 1958. Français. ⟨tel-01414782⟩

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