U-Pb zircon age of 548 Ma for the leptynites (high-grade felsic rocks) of the central part of the Maures Massif. Geodynamic significance of the so-called leptyno-amphibolitic complexes of the Variscan belt of western Europe

2003 ◽  
Vol 174 (6) ◽  
pp. 585-594 ◽  
Author(s):  
Christophe Innocent ◽  
Annie Michard ◽  
Catherine Guerrot ◽  
Bruno Hamelin
Keyword(s):  
Western Europe ◽  
Alkali Basalts ◽  
Massif Central ◽  
Zircon Age ◽  
Clear Cut ◽  
Lower Ordovician ◽  
Isotopic Studies ◽  
Crustal Contribution ◽  
Maures Massif ◽  
End Members

Abstract U-Pb zircon and Rb-Sr geochronological, and Sm-Nd isotopic studies have been carried out on the so-called leptyno-amphibolitic complex of the central part of the Maures Massif. The emplacement of the protolith of the felsic end-member (« leptynites ») has been dated at 548 Ma, an age much older than those (lower Ordovician) previously obtained on other leptyno-amphibolitic complexes. Rb-Sr data obtained on whole rocks and on mineral separates give an age of 348 Ma for the amphibolite-facies metamorphism. Nd isotopes indicate that the amphibolites display clear-cut mantle-derived signatures, whereas a significant crustal contribution is recorded in the three analyzed felsic facies. One of these acidic terms can be interpreted in terms of a simple mixing between two components, respectively similar to the amphibolites and to the two other felsic samples. These latter involve another mantle source, distinct from that of the amphibolites, and comparable to that of continental alkali basalts. These data indicate that the central part of the Maures Massif and the southern Massif Central were possibly part of the same pre-Variscan structural unit. The lack of evidence for a clear genetic relationship between the respective protoliths of the two end-members of the leptyno-amphibolitic complex raises once again the problem of the geodynamic significance of these formations.

Oxygen, hydrogen, and strontium isotope constraints on the origin of granites

1988 ◽  
Vol 79 (2-3) ◽  
pp. 317-338 ◽  
Author(s):  
Hugh P. Taylor
Keyword(s):  
Large Scale ◽  
Wide Spectrum ◽  
Volcanic Field ◽  
Parent Material ◽  
Rock Interaction ◽  
Metasedimentary Rocks ◽  
Clear Cut ◽  
End Members ◽  
Type 3

ABSTRACTOxygen isotope data are very useful in determining the source rocks of granitic magmas, particularly when used in combination with Sr, Pb, and Nd isotope studies. For example, unusually high δ18O values in magmas (δ18O> +8) require the involvement of some precursor parent material that at some time in the past resided on or near the Earth's surface, either as sedimentary rocks or as weathered or hydrothermally altered rocks. The isotopic systematics which are preserved in the Mesozoic and Cenozoic batholiths of western North America can be explained by grand-scale mixing of three broadly defined end-members: (1) oceanic island-arc magmas derived from a “depleted” (MORB-type?) source in the upper mantle (δ18O c. +6 and 87Sr/86Sr c. 0·703); (2) a high-18O (c. +13 to +17) source with a very uniform 87Sr/86Sr (c. 0·708 to 0·712), derived mainly from eugeosynclinal volcanogenic sediments and (or) hydrothermally altered basalts; and (3) a much more heterogeneous source (87Sr/86Sr c. 0·706 to 0·750, or higher) with a high δ18O (c. +9 to +15) where derived from supracrustal metasedimentary rocks and a much lower δ18O (c. +7 to +9) where derived from the lower continental crust of the craton. These end-members were successively dominant from W to E, respectively, within three elongate N–S geographic zones that can be mapped from Mexico all the way N to Idaho.18O/16O studies (together with D/H analyses) can, however, play a more important and certainly a unique role in determining the origins of the aqueous fluids involved in the formation of granitic and rhyolitic magmas. Fluid-rock interaction effects are most clear-cut when low-18O, low-D meteoric waters are involved in the isotopic exchange and melting processes, but the effects of other waters such as seawater (with a relatively high δD c. 0) can also be recognised. Because of these hydrothermal processes, rocks that ultimately undergo partial melting may exhibit isotopic signatures considerably different from those that they started with. We discuss three broad classes of potential source materials of such “hydrothermal-anatectic” granitic magmas, based mainly on water/rock (w/r), temperature (T), and the length of time (t) that fluid-rock interaction proceeds: (Type 1) epizonal systems with a wide variation in whole-rock δ18O and extreme 18O/16O disequilibrium among coexisting minerals (e.g. quartz and feldspar); (Type 2) deeper-seated and (or) longer-lived systems, also with a wide spectrum of whole-rock δ18O, but with equilibrated 18O/16O ratios among coexisting minerals; (Type 3) thoroughly homogenised and equilibrated systems with relatively uniform δ18O in all lithologies. Low-18O magmas formed by melting of rocks altered in a Type 2 or a Type 3 meteoric-hydrothermal system are the only kinds of “hydrothermal-anatectic” granitic magmas that are readily recognisable in the geological record. Analogous effects produced by other kinds of aqueous fluids may, however, be quite common, particularly in areas of extensional tectonics and large-scale rifting. The greatly enhanced permeabilities in such fractured terranes make possible the deep convective circulation of ground waters and sedimentary pore fluids. The nature and origin of low-18O magmas in the Yellowstone volcanic field and the Seychelles Islands are briefly reviewed in light of these concepts, as is the development of high-D, peraluminous magmas in the Hercynian of the Pyrenees.

Geoconservation

2005 ◽  
Author(s):  
Gerard Gonggrijp
Keyword(s):  
The Netherlands ◽  
Western Europe ◽  
Physical Geography ◽  
Policy And Practice ◽  
Human Welfare ◽  
Massif Central ◽  
Landscape Preservation ◽  
Visual Landscape ◽  
The Rich ◽  
North Western

The detailed descriptions of the physical geography in the previous chapters show the rich geodiversity of north-western Europe, reflected in its many geological landscapes (landscapes without the biological and cultural ‘furnishing’). The various geological forces, acting in time and space have created the foundation for this richness. The landscape’s framework has mainly been designed by such endogenic processes as tectonics, orogenesis, and volcanism, while its details have been sculptured by such exogenic processes as weathering, gravity, and glacial-, fluvial-, aeolian-, and marine activities. These modelling processes resulted in a very diverse geology, geomorphology, and pedology. The long scientific tradition and the rich geodiversity made north-western Europe one of the classical areas for geological research. It therefore includes many of the international case studies in earth sciences and became the cradle of numerous international reference localities such as Emsian (Rheinland-Pfalz, Germany), Dinantian (Ardennes, Belgium), Aptian (Provence, France), Danian—Dane is Latin for Denmark (Stevens Klint), Tiglian (Middle Limburg, The Netherlands), Eemian (river in western Netherlands), etc. The chronological division of glacial and fluvioglacial features is primarily based on type localities (villages, rivers, etc.) in Denmark, northern and southern Germany, and The Netherlands. Moreover, a multitude of Tertiary and Pre-Tertiary stages of the standard geological timetable have been named after type localities of geological and prehistoric sites in France. Geological landscapes such as the Maare system of the Eifel, the volcanoes on the Massif Central (France), the Saalian and Weichselian ice-pushed ridges of Germany, The Netherlands, and Denmark as well as the impressive dunes along the coast from France to the northernmost tip of Denmark have been subjects of detailed research. These geological landscapes form a unique geological patchwork. The activities of humans, especially in the last century, have damaged or destroyed many of these landscapes and sites of geological interest. However, selected sites and areas representing the geogenesis of the earth should be preserved for the benefit of science, education, and human welfare. In all European countries attention is given to landscape preservation; however, policy and practice have mainly been based on specific biological, historical-cultural, and visual landscape qualities.

scholarly journals Early Holocene Thermal Maximum recorded by branched tetraethers and pollen in Western Europe (Massif Central, France)

2020 ◽  
Vol 228 ◽  
pp. 106109 ◽  
Author(s):  
Céline Martin ◽  
Guillemette Ménot ◽  
Nicolas Thouveny ◽  
Odile Peyron ◽  
Valérie Andrieu-Ponel ◽  
...  
Keyword(s):  
Western Europe ◽  
Early Holocene ◽  
Massif Central ◽  
Holocene Thermal Maximum ◽  
Thermal Maximum

scholarly journals Thermochemical study of sodium and sodium-calcium amphibols

2019 ◽  
Vol 64 (5) ◽  
pp. 520-528
Author(s):  
L. P. Ogorodova ◽  
I. A. Kiseleva ◽  
M. F. Vigasina ◽  
Yu. D. Gritsenko ◽  
I. A. Bryzgalov ◽  
...  
Keyword(s):  
Kola Peninsula ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Thermochemical Study ◽  
Massif Central ◽  
Calvet Microcalorimeter ◽  
Gibbs Energies ◽  
Sodium Calcium ◽  
Isomorphic Series ◽  
End Members

A thermochemical study of six natural sodium and sodium-calcium amphiboles was carried out using the high-temperature melt solution calorimetry on a Tian-Calvet microcalorimeter. The enthalpies of formation from the elements have been obtained for arfvedsonites: K0.5(Na1.5Ca0.5)(Mg4.0Fe0.93+Al0.1)[Si8.0O22](OH)2 (Inaglinsky Massif, Central Aldan, Russia) (-11626.6 ± 8.9 kJ/mol), (Na0.5K0.1)(Na1.6Ca0.4)(Mg3.6Fe0.42+Fe0.83+Al0.2)[Si8.0O22](OH)2 (Khibiny Massif, Kola Peninsula, Russia) (-11520.8 ± 14.6 kJ/mol) and (Na0.7K0.3)Na2.0(Fe4.02+Fe0.63+Mn0.1Ti0.1Al0.2)[Si8.0O22](OH)2 (Katuginskoe deposit, Transbaikalia, Russia) (-11384.7 ± 17.1 kJ/mol); for riebeckites: Na2.0(Mg2.5Fe0.52+Fe1.53+Al0.5)Si8O22(OH)2 (Kumula deposit, Central Kazakhstan) (-10791.0 ± 10.1 kJ/mol) and Na2.0(Mg0.9Fe2.12+Fe1.93+Al0.1)[Si8O22](OH)2 (Krivoy Rog, Ukraine) (-10260.8 ± 10.9 kJ/mol) and richterite (Na0.7K0.3)(Ca1.2Na0.8)(Mg4.6Fe0.42+)[Si7.8Al0.2O22](OH)2 (Kovdorsky Massif, Kola Peninsula, Russia) (-12154.2 ± 9.7 kJ/mol). The values of the standard entropies, enthalpies, and Gibbs energies of formation are estimated for the end members of isomorphic series: arfvedsonite – magnesioarfvedsonite, riebeckite – magnesioriebeckite and richterite – ferrochichthite.

scholarly journals Tectonic-thermal constraints on the Pb-Zn ore deposits from southeastern French Central Massif by K-Ar and Pb-Pb dating of illite

2020 ◽  
Vol 28 (2) ◽  
pp. 307-321
Author(s):  
Theofilos Toulkeridis ◽  
Nicole Liewig
Keyword(s):  
Western Europe ◽  
Regional Scale ◽  
Isotopic Signature ◽  
Ore Deposits ◽  
Massif Central ◽  
Sedimentary Sequences ◽  
New Information ◽  
Heat Transfers ◽  
Thermal Pulses ◽  
Hydrothermal Activities

Illite-rich size-fractions (<0.2, <0.4, 0.4-1, 0.4-2 and <2 µm) of Cambrian, Permian, Triassic and Jurassic calcschists, shales and dolostones from Pb-Zn ore-district of the southeastern French Massif Central were dated by the K-Ar method, and some by the Pb-Pb method after removal of the Pb external to the illite particles. The combined mineralogical and isotopic determinations show that illitization occurred successively at 285 ± 5, 240 ± 20, 185 ± 15, 140 ± 10 and 105 ± 5 Ma in the district. These tectonic-thermal pulses, which were also reported at a larger regional scale, did not systematically release Pb-mineralizing fluids. The mineralizing episodes seem to have only contributed to contemporaneous illitization and Pb precipitation at 191 ± 41 Ma, by Pb-Pb dating of illite, and at 105 ± 5 Ma in a reactivated fault containing illite mixed with Pb precipitates. The scatter of the Pb-Pb data suggests an incompletely equilibrated Pb isotopic signature when incorporated into the illite structure during crystallization. Pb-isotopic determinations of barren illite-type minerals provide new information about the circulation timing of the mineralizing hydrothermal fluids. The fluid migrations related to recurrent hydrothermal activities occurred within a segment of a continental margin that was located away from main rift zones and far (more than 500 km) from major orogenic zones of Western Europe. The lack of major geodynamic activities near metal deposits needs to hypothesize periodic migrations of hot -fluids in the underneath continental crust. Metals were concentrated at specific places, but not necessarily during each tectonic-thermal pulse recorded by illite. These tectonic-thermal activities confirm local geodynamic re-activations of previously occurring events with effects on local mass and heat transfers in the plutonic basements, as well as in the sedimentary sequences.

scholarly journals Erosional response to land abandonment in rural areas of Western Europe during the Anthropocene: A case study in the Massif-Central, France

2019 ◽  
Vol 284 ◽  
pp. 106582 ◽  
Author(s):  
Anthony Foucher ◽  
Olivier Evrard ◽  
Clément Chabert ◽  
Olivier Cerdan ◽  
Irène Lefèvre ◽  
...  
Keyword(s):  
Rural Areas ◽  
Western Europe ◽  
Land Abandonment ◽  
Massif Central

scholarly journals Geochemistry of Gold Ores Mined During Celtic Times from the North-Western French Massif Central

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sandrine Baron ◽  
Călin G. Tămaș ◽  
Marion Rivoal ◽  
Béatrice Cauuet ◽  
Philippe Télouk ◽  
...  
Keyword(s):  
Western Europe ◽  
Gold Mining ◽  
Isotope Geochemistry ◽  
Ore Deposits ◽  
Mining District ◽  
French Massif Central ◽  
Massif Central ◽  
Gold Ores ◽  
The North ◽  
Field Evidence

AbstractThe Celtic culture of Western Europe left magnificent gold objects, such as jewellery and weapons from nobility graves and hoarded coins, as well as field evidence of pre-Roman gold mining and metallurgical workshops that attest to the mining of local ores. This is the case of Central France where many precious metallic ores have been mined throughout the ages from the Prehistoric times onwards. One of the lingering problems in assessing the provenance of gold artefacts and coins is the lack of relevant data on the isotope geochemistry and mineralogy of ore sources. Forty gold ores samples were collected and studied from Limousin (French Massif Central), a very significant gold mining district from the Celtic times. Their Pb isotope compositions clearly show a local dichotomy i.e. two distinct groups of ores, one of Late Proterozoic to Early Paleozoic Pb model age and another associated to Variscan ages and consistent with field relationships, mineralogy and elemental analyses. The use of Cu and Ag isotopes, and their coupling with Pb isotopes, will refine the tracing of future metal provenance studies, but also highlight some metallurgical practices like deliberate metal additions to gold artefact or debasement of gold coins. The newly acquired Pb, Ag, and Cu isotopic data on gold ores improves our understanding of ore deposits geology and provide clarifications on the provenance of Celtic gold from this area and its economic importance.

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