Relations between basalts and adakitic–felsic intrusive bodies in a soft-substrate environment: the South Ouessant Visean basin in the Variscan belt, Armorican Massif, France

The metasedimentary and magmatic terranes in the southern part of the Ouessant Island (Western Brittany, France) are the offshore prolongation of the Léon Variscan metamorphic domain. They mainly consist of micaschists and subordinate amphibolitic lenses (meta-pillow lavas and volcaniclastic successions) cut by a swarm of trondhjemite sills, together with a large porphyritic monzogranite body, newly dated at 336 Ma, and later syeno-leucogranitic intrusions. A large spectrum of fluidal peperites, including spectacular “fiamme”-bearing breccias, is observable at the contact between metasediments and most of the intrusives. The coexistence of amphibolitized basalts, adakitic trondhjemites, and peraluminous granites in the inferred South Ouessant basin is assigned to a variety of deep subcontemporaneous processes, including asthenospheric partial melting, high-pressure fractionation in lithospheric reservoirs (or partial remelting of deep crystallized mafic intrusions), and continental crust melting. Implications of these new results are discussed in the Visean basinal framework of the Armorican Massif, formed at an early stage of the Variscan orogeny.

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Age and depositional environment of the Sainte-Anne Formation (Armorican Massif, France): the oldest (Emsian) evidence for mountain erosion in the Variscan belt

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.180.6.529 ◽

2009 ◽

Vol 180 (6) ◽

pp. 529-544 ◽

Cited By ~ 9

Author(s):

Céline Ducassou ◽

Christine Strullu-Derrien ◽

Michel Ballevre ◽

Marie-Pierre Dabard ◽

Philippe Gerrienne ◽

...

Keyword(s):

Depositional Environment ◽

Source Area ◽

Variscan Orogeny ◽

Variscan Belt ◽

Delta Front ◽

Volcanic Origin ◽

Sedimentary Sequences ◽

Erosion Level ◽

Continental Area ◽

Armorican Massif

Abstract The palaeogeography of the internal zones of the Variscan belt during the early stages of the convergence remains unclear. Sedimentary sequences that recorded the denudation of an early relief have generally been removed by erosion. In the Chalonnes area (southeast of the Armorican Massif), the reefal carbonates of the Chalonnes Formation (Fm) are overlain by the immature, poorly-sorted sandstones of the Sainte-Anne Fm. This formation is characterised by the occurrence of gravity flow deposits and contains immature and poorly sorted sandstones with a large amount of plant debris and lithic fragments, suggesting a depositional environment in a delta front dominated by floods. A revision of the palaeoflora content allows to assign an Emsian age to the Sainte-Anne Fm. Lithic fragments are mainly of sedimentary and volcanic origin, suggesting moderate erosion level of the source area. Palaeocurrent data indicate a southern origin for the sediments. These features collectively demonstrate that the Sainte-Anne Fm is the record of the erosion of a continental area located farther south, and experiencing incipient tectonic uplift during the Emsian. The Sainte-Anne Fm could represent therefore the earliest record in France of the very first stages of the Variscan orogeny.

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From Burial to Exhumation: Emplacement and Metamorphism of Mafic Eclogitic Terranes Constrained Through Multimethod Petrochronology, Case Study from the Lévézou Massif (French Massif Central, Variscan Belt)

Journal of Petrology ◽

10.1093/petrology/egaa046 ◽

2020 ◽

Vol 61 (4) ◽

Cited By ~ 1

Author(s):

C Lotout ◽

M Poujol ◽

P Pitra ◽

R Anczkiewicz ◽

J Van Den Driessche

Keyword(s):

High Pressure ◽

Trace Element ◽

Metamorphic Rocks ◽

Variscan Orogeny ◽

Continental Margins ◽

Variscan Belt ◽

French Massif Central ◽

Massif Central ◽

Mineral Growth ◽

Exhumation Rates

Abstract Linking mineral growth and time is required to unravel the evolution of metamorphic rocks. However, dating early metamorphic stages is a challenge due to subsequent retrograde overprinting. A fresh eclogite and a former eclogite retrogressed under amphibolite facies from the southern French Massif Central (Lévézou massif, Variscan belt) were investigated with a large panel of geochronometers (U–Pb in zircon, rutile and apatite, Lu–Hf and Sm–Nd in garnet) in a petrological context tightly constrained by petrographic observations, trace element analyses and phase equilibrium modelling. Both samples recorded similar HP conditions at 18–23 kbar and 680–800°C, whereas the retrogressed eclogite later equilibrated at 8–9·5 kbar and c.600°C. In the retrogressed sample, most of the zircon grains are characterized by negative Eu anomalies and HREE enrichment, and yield an Ordovician U–Pb date of 472·3 ± 1·7 Ma, interpreted as the emplacement age of the mafic protolith. In agreement with other data available for the Variscan belt, and based on zircon trace element record and whole-rock geochemistry, this age is considered to represent the magmatism associated with the extreme thinning of the continental margins during the Ordovician. In the same sample, a few zircon rims show a weaker HREE enrichment and yield a date of 378 ± 5·7 Ma, interpreted as a prograde pre-eclogitic age. Lu–Hf garnet dating from both samples yields identical dates of 357 ± 13 Ma and 358·0 ± 1·5 Ma inferred to approximate the age of the high-pressure metamorphic peak. Fresh and retrogressed samples yield respectively 350·4 ± 7·7 Ma and 352 ± 20 Ma dates for Sm–Nd garnet dating, and 367·8 ± 9·1 Ma and 354·9 ± 9·5 Ma for U–Pb rutile dating. Apatite grains from the retrogressed sample give a mean age of 351·8 ± 2·8 Ma. The similarity between all recorded ages from distinct chronometers and radiometric methods (U–Pb, rutile, apatite; Lu–Hf, garnet; Sm–Nd, garnet) combined with P–T estimations from high-pressure metamorphic rocks equilibrated under different conditions testifies to very fast processes that occurred during the Variscan orogeny, highlighting a major decompression of 15–8·5 kbar in less than 7 Myr, and suggesting mean exhumation rates in excess of 6·3 mm/yr.

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Visean sinistral wrench faulting along the Sillon Houiller in the French Massif Central: Late Variscan tectonic implications

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.180.6.513 ◽

2009 ◽

Vol 180 (6) ◽

pp. 513-528 ◽

Cited By ~ 6

Author(s):

Vincent Thiery ◽

Patrick Rolin ◽

Didier Marquer ◽

Alain Cocherie ◽

C. Mark Fanning ◽

...

Keyword(s):

Western Europe ◽

Variscan Orogeny ◽

French Massif Central ◽

Massif Central ◽

Mafic Intrusions ◽

Crustal Block ◽

History Of ◽

Armorican Massif ◽

Brittle Faulting ◽

Granitoid Intrusions

AbstractThe Sillon Houiller is one of the main crustal discontinuities of the Variscan domain of the French Massif Central. Paradoxically, its kinematics and its tectonic significance are still a matter of debate.Since Grolier and Letourneur [1968]’s works, a Stephanian sinistral offset, inferred from the emplacement of numerous coal basins along the fault, is widely accepted.The earlier history of this accident is still debated and subject to controversies. The finite offset of the Sillon Houiller results from the superposition of 3 distinct events. The first one is a brittle/ductile accident that is probably at the origin of the main left-lateral motion. Dated granitoid intrusions and Visean tuff basins seal this accident. The later Stephanian motion is revealed by brittle faulting related to coal basin opening. Finally, a vertical offset of the fault is suggested by a few strong-dipping striations.The Visean offset of the Sillon Houiller has first order implications for the understanding of the western Europe Variscan orogeny. We suggest that the Sillon Houiller and the Paris Basin Magnetic anomaly belong to a single crustal discontinuity interpreted as the eastern boundary of the Armorican/Massif Central block. The 15° clockwise rotation affecting this crustal block and inferred from the structural study of this domain occurred along this accident. The magnetic and gravimetric anomaly may be the result of Visean mafic intrusions, such as quartz diorites that are exposed in the northern part of the Massif Central close to the southern end of the anomaly.

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ANALYSIS OF HIGH-PRESSURE DIESEL SPRAY FORMATION IN THE EARLY STAGE OF INJECTION

Atomization and Sprays ◽

10.1615/atomizspr.v7.i1.20 ◽

1997 ◽

Vol 7 (1) ◽

pp. 33-42 ◽

Cited By ~ 6

Author(s):

Hideo Takahashi ◽

Hiroki Yanagisawa ◽

Siichi Shiga ◽

Takao Karasawa ◽

Hisao Nakamura

Keyword(s):

High Pressure ◽

Early Stage ◽

Diesel Spray ◽

Spray Formation

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Parametric diagnostics of the condition of a dual-flow turbojet engine using neural network simulation of the operating process

MATEC Web of Conferences ◽

10.1051/matecconf/201822402057 ◽

2018 ◽

Vol 224 ◽

pp. 02057

Author(s):

Anas S. Gishvarov ◽

Julien Celestin Raherinjatovo

Keyword(s):

Neural Network ◽

High Pressure ◽

Combustion Chamber ◽

Early Stage ◽

Low Pressure ◽

Similarity Criteria ◽

Ann Model ◽

Turbojet Engine ◽

Operating Process ◽

Pressure Compressor

The article presents a method of parametric diagnostics of the condition of a dual-flow turbojet engine (DFTE). The method is based on the identification (determination) of the condition of the DFTE components (the compressor, combustion chamber, turbine) with application of a mathematical model of the operating process which is presented as an artificial neural network (ANN) model. This model describes the relation between the monitored parameters of the DFTE (the air temperatures (Tlpc*, Thpc*) beyond the low pressure compressor (LPC) and the high pressure compressor (HPC), the pressure beyond the LPC (Plpc), the fuel consumption rate (Gf), the gas temperatures (Thpt*, Tlpt*) beyond the high pressure turbine (HPT) and the low pressure turbine (LPT)) and the parameters of the condition of its components (the efficiencies of the LPC and the HPC (ηlpc*, ηhpc*), the stagnation pressure recovery factor in the combustion chamber (σcc), the efficiencies of the HPT and the LPT (ηhpt*, ηlpt*)). The parameters of the condition of the engine components (ηlpc*, ηhpc*, σcc, ηhpt*, ηlpt*) are the similarity criteria (integral criteria) which enable to identify the condition of the DFTE components to a high degree of reliability. Such analysis enables to detect defects at an early stage, even if the values of the monitored parameters (Тlpc*, Тhpc*, Plpc, Gf, Тhpt*, Тlpt*) are within the permissible limits. We provide the sequence for development of the ANN model and the results of its performance study during the parametric diagnostics of the condition of the DFTE.

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A revised age (Emsian-Eifelian) for the Sainte-Anne Formation (Armorican Massif, France): implications for the onset of mountain building in the Variscan belt

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen ◽

10.1127/0077-7749/2009/0046 ◽

2010 ◽

Vol 255 (3) ◽

pp. 237-254 ◽

Cited By ~ 6

Author(s):

Michel Ballèvre ◽

Céline Ducassou ◽

Hubert Lardeux ◽

Serge Régnault

Keyword(s):

Variscan Belt ◽

Mountain Building ◽

Armorican Massif

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Sur les rhyolites et les granites prevarisques en Normandie et en Vendee

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.s5-xiii.4-6.139 ◽

1943 ◽

Vol S5-XIII (4-6) ◽

pp. 139-151

Author(s):

Gilbert Mathieu

Keyword(s):

Variscan Orogeny ◽

The South ◽

The North ◽

Rigid Mass ◽

Armorican Massif

Abstract An account of the pre-Carboniferous rhyolites and granites of Normandy and Vendee, France. Precambrian granite masses and Precambrian and Cambrian conglomerates containing ancient granite and rhyolite pebbles occur in both regions, and indicate that the Carboniferous granites of the Armorican massif were emplaced during the Variscan orogeny in a zone of subsidence between the rigid mass of Normandy to the north and Vendee to the south.

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