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 Požarevac loess–paleosol sequence: a record of increased aridity in the south‐eastern margin of the Carpathian Basin during the last 350 ka

2021 ◽  
Author(s):  
Slobodan B. Marković ◽  
Eric A. Oches ◽  
Zoran M. Perić ◽  
Tivadar Gaudenyi ◽  
Mlađen Jovanović ◽  
...  
Keyword(s):  
Carpathian Basin ◽  
The South ◽  
Eastern Margin ◽  
South Eastern

The composition and paragenesis of the hornblendes of the Glen Tilt complex, Perthshire

1938 ◽  
Vol 25 (161) ◽  
pp. 56-74 ◽  
Author(s):  
W. A. Deer
Keyword(s):  
Chemical Investigation ◽  
Optical Investigation ◽  
The South ◽  
Eastern Margin ◽  
South Eastern ◽  
Single Complex

The south-eastern margin of the Glen Tilt complex consists of a long strip of diorites with a number of small associated patches of rocks of appinitic type. Xenoliths, both of hornblendite and hornblendeschist, the latter belonging to the Perthshire series of the Dalradian, are found enclosed within the dioritic rocks, which range petrographically from diorite to quartz-mica-diorite. In all these rocks hornblende is the most important fcrromagnesian constituent always predominating over pyroxene in the basic members and frequently persisting to the exclusion of biotite in the intermediate rocks of the intrusion. The hornblendes were examined chemically because of the difficulty of estimating their composition even from a thorough optical investigation. As they play such an important role in the complex it is considered that they may give some indication of the history and mode of formation of the rocks in which they occur. Such a chemical investigation of a series of related hornblendes will also indicate the possible range of composition of common amphiboles within the diorites and related rocks of a single complex.

Proposed chronostratigraphic units for the Carboniferous and Early Permian of the southwestern Gondwana margin

2020 ◽  
pp. SP512-2020-48
Author(s):  
Carlos R. González ◽  
Pamela Díaz Saravia
Keyword(s):  
Ice Age ◽  
South American ◽  
Early Permian ◽  
The South ◽  
Eastern Margin ◽  
South Eastern ◽  
Gondwana Margin ◽  
Central Western Argentina ◽  
Southwestern Margin ◽  
Regional Reference

AbstractThe western Andean belt of Argentina displays a comprehensive record of the Carboniferous and earliest Permian rocks so extensive that it allows an exceptional reconstruction of the Late Palaeozoic Ice Age of the southwestern margin of the South American Gondwana area. Severe endemism of the Gondwana biota during this period makes it difficult to achieve a precise correlation of these glacially influenced deposits with the coeval sequences of the Palaeoequatorial belt, where the subdivisions of the International Chronostratigraphic Chart are currently defined. The abundant paleontological record available from the Upper Palaeozoic deposits of central-western Argentina, central Patagonia, and eastern Argentina, makes it possible to recognize five successive faunal stages that allow a proper ordering of the sequences of this period. The proposed regional stages, and their assumed chronologic position regarding the standards of the current International Chronostratigraphic Chart, are: the Malimanian (late Tournaisian), Barrealian (Mid-Carboniferous or Serpukhovian-Bashkirian), Aguanegrian (Upper Pennsylvanian), Uspallatian (Asselian-Tastubian?) and Bonetian (Sakmarian). This paper aims to reiterate former recommendations about the convenience of having regional reference units and suggests the consideration of the available faunal stages as possible chronostratigraphic subdivisions for the Carboniferous-early Permian of the south-eastern margin of Gondwana.

Mesoproterozoic island arc magmatism along the south-eastern margin of the Indian Plate: Evidence from geochemistry and zircon U-Pb ages of mafic plutonic complexes

2016 ◽  
Vol 130 ◽  
pp. 116-138 ◽  
Author(s):  
K.S.V. Subramanyam ◽  
M. Santosh ◽  
Qiong-Yan Yang ◽  
Ze-ming Zhang ◽  
V. Balaram ◽  
...  
Keyword(s):  
Island Arc ◽  
Indian Plate ◽  
Arc Magmatism ◽  
The South ◽  
Eastern Margin ◽  
South Eastern

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 Compound flood potential from storm surge and heavy precipitation in coastal China

2020 ◽  
Author(s):  
Jiayi Fang ◽  
Thomas Wahl ◽  
Jian Fang ◽  
Xun Sun ◽  
Feng Kong ◽  
...  
Keyword(s):  
Storm Surge ◽  
Extreme Events ◽  
Heavy Precipitation ◽  
Tide Gauges ◽  
The South ◽  
South Eastern ◽  
Significant Dependence ◽  
Coastal China

Abstract. The interaction between storm surge and concurrent precipitation can cause greater flooding impacts than either in isolation. This paper investigates the potential compound effects from these two flooding drivers along the coast of China. Statistically significant dependence between them exists at the majority of locations that are analysed, but the strength of the correlation varies spatially and depending on how extreme events are defined. In general, we find higher dependence at the south-eastern tide gauges (TGs) (latitude 

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.

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