scholarly journals The evolution of the Massif Central Rift; spatio-temporal distribution of the volcanism

2001 ◽  
Vol 172 (2) ◽  
pp. 201-211 ◽  
Author(s):  
Laurent Michon ◽  
Olivier Merle
Keyword(s):  
Central Area ◽  
Temporal Distribution ◽  
Rift System ◽  
The South ◽  
Volcanic Event ◽  
Quaternary Volcanism ◽  
Massif Central ◽  
Lithospheric Thinning ◽  
The North ◽  
Magmatic Event

Abstract The Massif Central area is the largest magmatic province of the West-European Rift system. The spatial-temporal distribution of Tertiary-Quaternary volcanism in the Massif Central, France, shows that three magmatic phases can be defined, each of them characterized by different volumes and different locations. The first event, termed the pre-rift magmatic event, is very scarce and restricted to the north of the Massif Central. It is suggested that this could result from lithospheric bending of the European lithosphere ahead of the incipient Alpine chain during the Paleocene. The second event, termed the rift-related magmatic event, is located in the north of the Massif Central only and is spatially connected with zones of high crustal thinning (i.e. the Limagne graben). It immediately follows Oligocene graben formation and associated sedimentation, and is represented by more than 200 scattered monogenic edifices. This second event can be attributed to partial melting as a consequence of lithospheric thinning that affected the north of the Massif Central during the rifting event. The lack of volcanism in the south during the same period of time is probably related to the very slight lithospheric thinning during the Oligocene. The third event, termed the major magmatic event, started first in the south in the upper Miocene at about 15 Ma, well after the end of the sedimentation. It is unrelated to any extensional event. This major magmatic event reached the north of the Massif Central at about 3.5 Ma, following a pause in volcanism of about 6 Ma after the rift-related magmatic event. These two episodes of the major magmatic event are spatially and temporally associated with the two main periods of uplift, suggesting a common origin for volcanism and uplift processes. The major magmatic event can be attributed to late thermal erosion of the base of the lithosphere above a mantle diapir, as suggested by seismic tomography data. This general magmatic evolution drawn from data at the Massif Central scale may apply to the Eger graben as well, as the three magmatic events described in this study (pre-rift magmatic event, rifting event and post-Miocene volcanic event) are also reported in the literature. This suggests that a single cause should explain the formation of the entire western European rift surrounding the Alpine mountain belt.

scholarly journals The formation of the West European Rift; a new model as exemplified by the Massif Central area

2001 ◽  
Vol 172 (2) ◽  
pp. 213-221 ◽  
Author(s):  
Olivier Merle ◽  
Laurent Michon
Keyword(s):  
Sea Level ◽  
Central Area ◽  
Rift System ◽  
The South ◽  
The West ◽  
Massif Central ◽  
New Model ◽  
The North ◽  
Crustal Thinning ◽  
West European

Abstract In this paper, we use mainly field data from the Massif Central area, which have been presented in a companion paper [Michon and Merle, 2001], to discuss the origin and the evolution of the West European Rift system. It is shown that the tectonic event in the Tertiary is two-stage. The overall geological evolution reveal a tectonic paradox as the first stage strongly suggests passive rifting, whereas the second stage displays the first stage of active rifting. In the north, crustal thinning, graben formation and sedimentation at sea level without volcanism during the Lower Oligocene, followed by scattered volcanism in a thinned area during Upper Oligocene and Lower Miocene, represent the classical evolution of a rift resulting from extensional stresses within the lithosphere (i.e. passive rifting). In the south, thinning of the lithospheric mantle associated with doming and volcanism in the Upper Miocene, together with the lack of crustal thinning, may be easily interpreted in terms of the first stage of active rifting due to the ascent of a mantle plume. This active rifting process would have been inhibited before stretching of the crust, as asthenospheric rise associated with uplift and volcanism are the only tectonic events observed. The diachronism of these two events is emphasized by two clearly distinct orientations of crustal thinning in the north and mantle lithospheric thinning in the south. To understand this tectonic paradox, a new model is discussed taking into account the Tertiary evolution of the Alpine chain. It is shown that the formation of a deep lithospheric root may have important mechanical consequences on the adjacent lithosphere. The downward gravitational force acting on the descending slab may induce coeval extension in the surrounding lithosphere. This could trigger graben formation and laguno-marine sedimentation at sea level followed by volcanism as expected for passive rifting. Concurrently, the descending lithospheric flow induces a flow pattern in the asthenosphere which can bring up hot mantle to the base of the adjacent lithosphere. Slow thermal erosion of the base of the lithosphere may lead to a late-stage volcanism and uplift as expected for active rifting.

The Mesozoic-Tertiary evolution of the Aquitaine Basin

1982 ◽  
Vol 305 (1489) ◽  
pp. 63-84 ◽  
Keyword(s):  
Upper Cretaceous ◽  
Oil Fields ◽  
Upper Eocene ◽  
The South ◽  
Gas Field ◽  
Massif Central ◽  
Tectonic Plates ◽  
The North ◽  
Basic Magmatism ◽  
Aquitaine Basin

The Aquitaine Basin, situated in southwest France, with an area of about 60 000 km 2 , has the form of a triangle which opens towards the Atlantic (Bay of Biscay) and is limited to the north by the Hercynian basement of Brittany and the Massif Central, and to the south by the Pyrenean Tertiary orogenic belt. Beneath the Tertiary sequence (2 km thick, and which outcrops over much of the basin) a Mesozoic series, up to 10 km thick, rests generally on a tectonized Hercynian basement but locally it covers narrow (NW-SE-trending) post-orogenic trenches of Stephano-Permian age. The Mesozoic history can be subdivided into four major structural-sedimentary episodes: (1) during a Triassic taphrogenic phase a continental-evaporitic complex developed with associated basic magmatism; (2) throughout the Jurassic, a vast lagoonal platform developed, initially (Lower Lias) as a thick evaporitic sequence followed by a uniform shale-carbonate unit, indicating a relative structural stability; (3) the end of the Jurassic and the Lower Cretaceous saw a fragmentation of this platform, due to an interplay between the Iberian and European tectonic plates, resulting in an ensemble of strongly subsident sub-basins; (4) during the Upper Cretaceous and until the end of the Neogene, the evolution of the Aquitaine Basin was influenced by the Pyrenean orogenic phase, with the development, towards the south, of a trench infilled by flysch which, from the Upper Eocene, is succeeded by a thick post-orogenic molasse complex. The main hydrocarbon objectives in the basin are situated in the Jurassic platform (e.g. the Lacq giant gas field) and the Cretaceous sub-basins (e.g. the Cazaux and Parentis oil fields). To date, production has been about 4 x 10 7 m 3 of oil, and about 15 x 10 10 m 3 of gas since the first gas discovery (St Marcet) in 1939.

scholarly journals The Geology of the Perches - Terrier Rouge Area, A Potential Copper and Gold Mineralized Belt in Northern Haïti.

2019 ◽  
Author(s):  
Ricardo A. Valls
Keyword(s):  
Volcanic Belt ◽  
The South ◽  
Magmatic Complex ◽  
Volcanic Event ◽  
The North ◽  
Two Samples ◽  
Volcanic Formation ◽  
Lead Zinc ◽  
Geological Observation ◽  
Ore Potential

A geological reconnaissance at an approximated scale of 1:100000 was done over 112 km2, between the townships of Roche Platte to the West, Jasquezyl to the North, Grand Basin to the East, and Perches to the South. A total of 56 points were described for an average of one geological observation per two square kilometers.Also, 18 grab samples were taken from mineralized showings, as well as three heavy mineral concentrates and two samples for whole rock analysis.All the collected information was kept in a database created on MS Access by the author of this report. The database, including the results of the analysis, can be consulted on Mendeley at doi:10.17632/b35fmjntnr.1.A model for the regional geological evolution of the area is presented, as well as a proposal for the denomination of the three basic geological structures found in the area, The Douvray Volcanic Group, the Grand Basin Magmatic Complex, and the Bercera Volcanic Formation, which the author interpreted as the last volcanic event of the Douvray Volcanic Group.This study revealed several new prospective zones for copper to the North, and gold-copper-lead-zinc mineralization to the South, along the volcanic belt and its orogenic intrusives, chiefly related to the occurrences of iron hats.The author recommends more detailed prospecting work, including ground geophysics and trenching, to better evaluate the ore potential of these new areas.

Tectonics of the Northern Red Sea, insights from multibeam bathymetric mapping of Mabahiss Deep.

2020 ◽  
Author(s):  
Daniele Trippanera ◽  
Margherita Fittipaldi ◽  
Nico Augustin ◽  
Froukje M. van der Zwan ◽  
Sigurjón Jónsson
Keyword(s):  
Oceanic Crust ◽  
Red Sea ◽  
Spreading Rate ◽  
Ocean Floor ◽  
Tectonic Activity ◽  
Rift System ◽  
Central Volcano ◽  
The South ◽  
The North ◽  
Northern Red Sea

<p>The Red Sea is a unique place to study the birth of an oceanic rift basin and the interplay between magma and tectonics at a young divergent plate boundary. The Red Sea is a NNW-SSE oriented and 2000 km long rift system with a spreading rate decreasing from ~16 mm/yr in the south to ~7 mm/yr in the north. The morphology also changes along the rift axis: the south portion is a continuous and well-developed rift, clearly exposing oceanic crust, the central portion is characterized by deeps made by oceanic crust separated by shallower inter-trough zones, and the northern part contains more widely spaced and less obvious deeps with the transition to the continental crust not well defined. While the central Red Sea morphology has been extensively studied, the structure of the northern Red Sea and its link to the central Red Sea are still unclear. Indeed, the northern Red Sea rift is offset by 100 km to the central Red Sea axis by the still poorly understood Zabargad fracture zone.</p><p>Here we aim at improving the understanding of the volcano-tectonic structure of the axial part of the southern tip of the northern Red Sea that corresponds to the Mabahiss Deep. To this aim, we carried out multiple multibeam surveys with R/V Thuwal and R/V Kobi Ruegg to map the sea bottom to add to what had been done in earlier surveys. In addition, we obtained several sub-bottom profiling lines across and along the deep to better constrain the shallow sedimentary structure.</p><p>Our results show that the 15 km long, 9 km wide and 2250 m deep Mabahiss Deep along with the 800 m high and 5 km wide central volcano are the key prominent structures of the area. The deep is bordered by a series of Red Sea parallel normal faults on two sides forming a graben-like structure and thus suggesting a rift-like morphology. The central volcano is well preserved and has a 2 km wide summit caldera containing several volcanic cones and thus suggesting a permanent magmatic source underneath of a relatively young age. The ocean floor outside the deep and the volcanic edifice is mostly covered by salt flows, limiting structural analysis of the surrounding areas.</p><p>A comparison between the northern and central Red Sea suggests, although in both areas thick salt covers most of the ocean floor, that the axes have similar rift-like structures with stable axial volcanism. However, in the central Red Sea larger portions of the oceanic crust are free of salt and the deformation seems larger with more prominent faults that also affect the floor of the deeps and split apart volcanic edifices, enhancing the occurrence of diffused monogenic volcanic cones. Therefore, this might suggest, despite the central and northern Red Sea sharing the same structure and evolution, that the less volcanic and tectonic activity in the north probably reflects the decreasing spreading rate from south to north along the Red Sea.</p>

Des images du systeme lithosphere-asthenosphere sous la France et leurs implications geodynamiques; l'apport de la tomographie telesismique et de l'anisotropie sismique

2000 ◽  
Vol 171 (2) ◽  
pp. 149-167 ◽  
Author(s):  
Michel Granet ◽  
Sebastien Judenherc ◽  
Annie Souriau
Keyword(s):  
Seismic Anisotropy ◽  
Thermal Anomaly ◽  
Rift System ◽  
Low Velocity ◽  
Geological Structures ◽  
Tectonic Event ◽  
Lithospheric Deformation ◽  
Massif Central ◽  
The North ◽  
Armorican Massif

Abstract From seismic tomography and seismic anisotropy, images of the lithosphere-asthenosphere system beneath France for some remarkable tectonic areas have been computed : a continental rift system (the Upper Rhinegraben), an Hercynian structure reactivated by Neogene volcanism (Massif central), a region of a recent continental collision (Pyrenees) and finally a region of an ancient orogeny (Armorican Massif). These images have a horizontal spatial resolution of the order of 10 km and show not only the geometry of the deep geological structures but will also illustrate the link between surface observations and structures detected at depth. The images demonstrate the passive character of the Rhinegraben mainly because no low-velocity was found below the Moho, show the presence of a thermal anomaly beneath the Massif central interpreted as caused by a mantle plume in the decaying phase of its evolution and prove the lithospheric scale of the North Pyrenean fault and of the South-Armorican shear zone. The anisotropic measurements suggest a lithospheric deformation related to the most recent tectonic event. In the Pyrenees, the Armorican Massif or the Rhinegraben areas, the directions of the fast-polarisation azimuth (the polarisation direction of the fast shear wave) are parallel to the tectonic texture of the last events, but suggest also a reactivation of inherited Hercynian discontinuities. In the Massif central, the splitting parameters distinguish between two lithospheric units regions marked by a distinct fast-polarisation azimuth on each side of the Sillon Houiller fault zone.

Morphological Variability in Illex Coindetii (Cephalopoda: Ommastrephidae) Along the North-West Coast of Africa

1998 ◽  
Vol 78 (4) ◽  
pp. 1259-1268 ◽  
Author(s):  
V. Hernández-García ◽  
J.J. Castro
Keyword(s):  
Sexual Dimorphism ◽  
Morphological Variability ◽  
Central Area ◽  
Gulf Of Guinea ◽  
The South ◽  
Differential Growth ◽  
North West ◽  
The North ◽  
Starting Point ◽  
Males And Females

This paper gives morphometric variations and dorsal mantle length–total weight (DML-TW) relationships for Illex coindetii in the eastern Central Atlantic area. Positive allometry was observed in males and negative in females of the species. The most variable body measurements between males and females were width and perimeter of the head. In the study area, divergence of morphometric measurement starts at 95 mm. The point of divergence, however, varies with latitude; fluctuating from 104 mm in the north (Morocco and Sahara) to 76 mm in the central area (Mauritania and north of Senegal) and 73 mm in the south (Gulf of Guinea).The relationships between DML and TW showed that sexual dimorphism due to differential growth between males and females starts to occur at 56 mm ML. The starting point of sexual dimorphism (56 mm) varies according to the zone; the higher the latitude, the later it occurs. Thus, sexual dimorphism occurs at 49 mm in the south (Gulf of Guinea), at 54 mm in the central area (Mauritania and north of Senegal) and at 74 mm in the north (Morocco and Sahara). Females grow larger than males, but males were heavier at any given length. As latitude decreased, a slow down in the increase in weight-at-length was observed in both sexes.

scholarly journals SPATIAL AND TEMPORAL DISTRIBUTION OF THE CLOUD HEIGHT AND CLOUD THICKNESS OVER CHINA AND THE ADJACENT AREAS BASED ON CALIOP

2019 ◽  
Vol XLII-3/W9 ◽  
pp. 15-22
Author(s):  
X. Feng ◽  
H. K. Cai ◽  
B. W. Wang ◽  
X. M. Li ◽  
L. Zhang
Keyword(s):  
Regional Differences ◽  
Temporal Distribution ◽  
The Tibetan Plateau ◽  
Spatial And Temporal Distribution ◽  
The South ◽  
The North ◽  
Cloud Height ◽  
The Mean ◽  
Cloud Thickness ◽  
The Western Pacific

Abstract. Based on CALIOP data, spatial and temporal distribution of cloud height and thickness over China as well as the adjacent areas have been analysed in this paper. The results show significant regional differences. The heights of clouds that lie to the south of 27.6°N are greater than those to the north of 27.6°N. The highest and thickest clouds are located above the Bay of Bengal and the Western Pacific, while the lowest values distribute in the northwest of the Tibetan Plateau and Sichuan Basin. The clouds ranging from 0.3 km to 0.6 km thickness account for a large proportion of total clouds. And the probability of occurrence of clouds decreases as cloud thickness increases. Overall, within the area under study, the thick clouds are higher than the thin clouds. Besides, low and thin clouds occur more frequently than high and thick clouds. As for their seasonal variation, the height of clouds peaks in summer. In addition, the mean of cloud thickness to the south of 27.6°N is 2.4 km thicker in summer than in any other season.

scholarly journals Influence of discharge variability on denudation rates and relief : example from the south-eastern margin of the Massif Central, France

2021 ◽  
Author(s):  
Clement Desormeaux ◽  
Vincent Godard ◽  
Dimitri Lague ◽  
Lucilla Benedetti ◽  
Jules Fleury ◽  
...  
Keyword(s):  
Extreme Events ◽  
River Sediments ◽  
Central Area ◽  
Complex Model ◽  
The South ◽  
Massif Central ◽  
Eastern Margin ◽  
South Eastern ◽  
Denudation Rates ◽  
River Incision

<p>The evolution of continental relief results from the combined action of tectonic and climatic forcings. These processes do not act continuously but often through punctual events (earthquakes, major floods, landslides) whose integrated action over time (100 Kyr to Myr) leads to the formation of landscapes. The distribution of these extreme events is often described by statistical functions involving power-law relationships between frequency and magnitude, which, coupled with the non-linearity of the geomorphological response and threshold effects for the activation of erosion agents, leads to a complex and often poorly understood relief dynamics.</p><p>Studying the influence of discharge variability helps to better constrain river incision and long-term relief evolution. The south-eastern margin of the Massif Central (France) is a very interesting target for such investigations because it presents episodes of very intense precipitation focused on the relief resulting in marked differences in the statistical discharges distributions across the landscape. Some theoretical river incision models incorporate such variability (Lague et al., 2005) but they have been confronted with real data only in a limited number of cases (DiBiase et al., 2011; Scherler et al., 2017; Campfort et al., 2020). Here we test these models  in the Massif Central area and in particular on Cévennes, Ardèche and Margeride mountains by quantifying denudation rates using cosmogenic nuclides (10Be), characterizing discharges variability and performing morphological analysis on longitudinal rivers profiles.</p><p>The analysis of 326 river gauging stations allow us to observe a strong gradient in discharge variability from the external SE border to the interior of the Massif Central. The <sup>10</sup>Be concentrations measured from river sediments in 36 catchments imply a large variation of denudation rates between 29 mm/kyr and 126 mm/kyr. We compare these denudation rates with the spatial distribution of mean annual precipitations, local relief, slope and concavity index, and also integrate all the observations in the frame of a stochastic threshold incision model. Our results confirm the complex model predictions of non-linear relationships between mean denudation rates and the channel steepness index and their dependence on hydrological variability and run-off.</p><p>key-words : extreme events, stochastic threshold incision model, denudation rates, discharge variability, morphometric parameters, Massif Central</p>

The Mesolithic in the South of France: a critical analysis

1953 ◽  
Vol 18 (1) ◽  
pp. 103-120 ◽  
Author(s):  
M. A. Smith
Keyword(s):  
Mediterranean Climate ◽  
High Mountains ◽  
The South ◽  
Massif Central ◽  
The North ◽  
South West ◽  
Mediterranean Countries ◽  
The Mediterranean ◽  
To Come ◽  
River Valleys

At the time when the type-sites of the Dordogne were being explored French archaeologists were equally active further south in their country. From caves and surface sites in the Mediterranean provinces local landowners, doctors and clergy were collecting material which not only matched most of the palaeolithic tool forms being distinguished in the south-west of France, but was later to provide Déchelette with many of his illustrations for the neolithic and metal ages. It was not uncommon for flints, pottery and metal all to come from the same cave.These old collections, or such of them as can be traced, are the basis of what is known about the prehistory of the south of France. Unfortunately, much of the material has come down to us with very little information, apart from provenance, and although some details of excavation were carefully recorded it seems generally to have been considered that plans of caves were more informative than sections through them.Topographically the south of France consists largely of a narrow alluvial plain, stretching right round the Gulf of Lions between the Italian and Spanish frontiers and broadening out in the delta of the Rhône. Today the region is distinguished from the rest of France by its Mediterranean climate. East of the Rhône, in Provence, this coastal climate is soon modified to the north by the high mountains, but in the old province of Languedoc between the Rhône and the Pyrenees the typical Mediterranean vegetation is carried up onto the rocky limestone plateau, or Garrigue, until it reaches the barren Causses of the Massif Central. In France, the western limit of this climatic zone falls between Carcassonne and Toulouse, but eastward and to the south the Mediterranean conditions continue, so that the south French plain forms a climatic unit with the coastlands of Italy and Spain.This plain, shut in to the north by high land, is most easily accessible from the sea or coastwise from adjacent Mediterranean countries. Easy communication with the rest of France is confined to the great river valleys of the Rhône and Aude which cut through the mountains to the north and west.

Esquisse geologique du prolongement nord du granite de Saint-Maurice-Chateauneuf (Saone-et-Loire, Massif central francais)

1966 ◽  
Vol S7-VIII (1) ◽  
pp. 118-124 ◽  
Author(s):  
Paul Tempier
Keyword(s):  
Coarse Grained ◽  
The South ◽  
Massif Central ◽  
Modes Of Occurrence ◽  
Northeastern Part ◽  
The North ◽  
The Difference

Abstract In the Charolais ridge in the northeastern part of the Central Massif (France) two granites can be distinguished. The Vauzelles granite to the south, is subalkaline, medium-grained, slightly porphyritic, and poor in inclusions. The Mary granite to the north is a coarse-grained monzonitic porphyry, containing green hornblende, and rich in inclusions. Identical granophyres are associated with both granites, but in differing modes of occurrence. This is ascribed to the difference in depth of the granites, the Vauzelles being deeper. The age of the granites is Visean (Carboniferous).

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