Low-pressure regional amphibolite-facies to granulite-facies metamorphism of the Paleoproterozoic Thompson Nickel Belt, Manitoba

2012 ◽  
Vol 49 (10) ◽  
pp. 1117-1153 ◽  
Author(s):  
Chris G. Couëslan ◽  
David R.M. Pattison
Keyword(s):  
Regional Scale ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Iron Formation ◽  
The West ◽  
Mafic Rocks ◽  
Temperature Conditions ◽  
Mineral Assemblages ◽  
Facies Zone ◽  
Superior Craton

The Thompson Nickel Belt is a ca. 35 km × 400 km northeast-trending segment of the northwest margin of the Archean Superior craton in Manitoba, bounded to the west by the Paleoproterozoic Reindeer Zone. The belt was metamorphosed and deformed during the Trans-Hudson orogeny (ca. 1.9–1.7 Ga). Mineral assemblages in metamorphosed pelite, aluminous greywacke, mafic igneous rock, iron formation, and ferruginous wacke define regional metamorphic domains, separated by mineral isograds, that are subparallel to the strike of the belt and to regional-scale D3 structures. An elongate, ca. 5 km × 73 km, central zone of middle amphibolite-facies rocks is characterized by the following: muscovite-bearing mineral assemblages in pelites containing combinations of staurolite, andalusite, and sillimanite; muscovite-free, staurolite + cordierite + garnet-bearing mineral assemblages in greywackes; hornblende-bearing mineral assemblages in mafic metaigneous rocks; and grunerite-bearing mineral assemblages in iron formation. Pressure–temperature (P–T) conditions of the middle amphibolite-facies zone are ca. 550–620 °C and 3.0–5.0 kbar (1 kbar = 100 MPa), with pressure increasing to the northeast. The middle amphibolite-facies zone is bordered to the east and west by an upper amphibolite-facies zone, ca. 5 km wide on the east and ca. 3–5 km on the west. The upper amphibolite-facies zone is characterized by variably migmatitic K-feldspar + sillimanite-bearing mineral assemblages in pelites; migmatitic, garnet + cordierite + sillimanite-bearing mineral assemblages in greywackes; orthopyroxene-free, hornblende-bearing mineral assemblages in mafic rocks; and orthopyroxene-bearing mineral assemblages in iron formations. Pressure–temperature conditions of the upper amphibolite-facies zone are ca. 640–710 °C and 3.0–5.5 kbar in the southeast, and 675–755 °C and 4.5–6.0 kbar in the northwest. The outermost metamorphic zone is of the granulite facies, characterized by migmatitic garnet + cordierite + K-feldspar-bearing assemblages in pelites and greywackes, orthopyroxene + clinopyroxene ± garnet-bearing mineral assemblages in mafic rocks, and orthopyroxene + K-feldspar-bearing mineral assemblages in iron formation in which biotite is unstable. Pressure–temperature conditions of the granulite-facies zone are ca. 775–830 °C and 5.0–7.0 kbar. The P–T paths in the Thompson Nickel Belt appear to be broadly clockwise, except for some domains where they are close to isobaric. The peak P–T conditions, combined with local but widespread development of andalusite, imply relatively steep geothermal gradients of ca. 33–51 °C/km during metamorphism. Regional bathozones (domains of uniform peak-metamorphic pressure) correspond in general but not in detail with the metamorphic-facies zones. They reveal an increase in pressure towards the northeast, suggesting greater degrees of postmetamorphic exhumation in that region. Microstructural analysis suggests that peak metamorphism coincided with, and possibly outlasted, the D2 deformation event. Metamorphic isograds were deformed by D3–D4 structures. These features are consistent with a tectonic model in which the Superior craton moved in a northwest or west-northwest direction relative to the Reindeer Zone, with greatest convergence and tectonic burial occurring at the Thompson promontory.

Resetting of Nd and Sr whole-rock isochrons from polymetamorphic granulites, northeastern Alberta

1985 ◽  
Vol 22 (7) ◽  
pp. 992-1000 ◽  
Author(s):  
R. A. Burwash ◽  
J. Krupicka ◽  
A. R. Basu ◽  
P. A. Wagner
Keyword(s):  
Regional Scale ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Lower Pressure ◽  
Mafic Rocks ◽  
Isotopic System ◽  
Mineral Assemblages ◽  
The Times ◽  
Northeastern Alberta

At Mountain Rapids on the Slave River, mafic xenoliths are enclosed by a granodiorite host, which is, in turn, surrounded by a granitic migmatite complex. The mafic and granodioritic rocks are both metamorphosed to the hornblende granulite facies, and the migmatite has been metamorphosed to the upper amphibolite facies. The banding of the mafic granulites is truncated by sharply defined boundaries with the felsic granulites. The felsic granulites contain K-feldspar, the mafic rocks almost none. The mineral assemblages are otherwise identical: plagioclase–hypersthene–quartz–biotite–magnetite.A whole-rock Sm–Nd isochron of one felsic and six mafic granulites gives 2436 ± 44 Ma [Formula: see text]. This time is significantly younger than the Sm–Nd model ages. The same mafic samples give a Rb–Sr age of 1898 ± 5 Ma. These are interpreted as the times of reequilibration and closure of the Rb–Sr isotopic systems within the Mountain Rapids Granulite enclave. From cordierite–garnet barometry the indicated pressure of the younger event is 5.5 ± 0.7 kbar (550 ± 70 MPa). By analogy with hornblende granulite assemblages elsewhere, the older event probably occurred in the intermediate crust (~25–30 km depth). This event apparently effectively reset the Sm–Nd isotopic system; subsequent cooling closed it. Once established this system withstood the later, lower pressure event that reset the Rb–Sr geochronometer on a regional scale.

Metamorphic pressure-temperature conditions of the Lützow-Holm Complex of East Antarctica deduced from Zr-in-rutile geothermometer and Al2SiO5 minerals enclosed in garnet

2021 ◽  
Author(s):  
Kota Suzuki ◽  
Tetsuo Kawakami
Keyword(s):  
Granulite Facies ◽  
Transitional Zone ◽  
East Antarctica ◽  
High Grade ◽  
Temperature Conditions ◽  
Mineral Assemblages ◽  
Facies Zone ◽  
Metamorphic Zone ◽  
Reliable Temperature ◽  
Zr In Rutile

<p>The Zr content of rutile coexisting with zircon and quartz is mainly a function of the temperature condition and is calibrated as Zr-in-rutile geothermometers. Because of their robustness under high-temperature conditions, they have been applied to granulite facies rocks instead of the conventional Fe-Mg exchange type geothermometers to estimate more reliable temperature conditions. However, it is recently pointed out that in order for rutile to retain the primary Zr content, rutile must be chemically isolated from zircon and quartz during cooling. In this context, inclusion rutile separately enclosed in garnet can be considered to retain the primary Zr content at the time of entrapment, only if rutile, zircon, and quartz are all enclosed in a contemporaneous domain of the garnet.</p><p>In this study, we re-examined the pressure-temperature (<em>P-T</em>) conditions of high-grade pelitic gneisses from selected regions (Akarui Point, Skarvsnes, Skallen, and Rundvågshetta) of the Lützow-Holm Complex (LHC), East Antarctica. The LHC has been divided into the upper-amphibolite facies zone, the transitional zone, and the granulite facies zone, based on matrix mineral assemblages of mafic- to intermediate gneisses. Akarui Point is located in the transitional zone and others in the granulite facies zone.</p><p>While previous studies commonly applied the conventional Fe-Mg exchange type geothermometers, we applied the Zr-in-rutile geothermometer of Tomkins et al. (2007) to rutile grains enclosed in garnet that also encloses zircon, quartz, and Al<sub>2</sub>SiO<sub>5</sub> minerals. By utilizing the phosphorus zoning in garnet, we defined contemporaneous domains of the garnet and identified coexisting inclusion minerals in each domain. In this way, coexisting Al<sub>2</sub>SiO<sub>5</sub> minerals and rutile grains were utilized to constrain the <em>P-T</em> condition of each domain of the garnet.</p><p>As a result, samples from Akarui Point, Skarvsnes, and Skallen were shown to have experienced almost the same <em>P-T</em> conditions around the kyanite/sillimanite transition boundary (~ 830-850 °C/~ 11 kbar). This is significantly higher than the previously estimated peak condition of 770-790 °C/7.7-9.8 kbar based on the conventional garnet-biotite geothermometer in the case of Akarui Point. From Rundvågshetta, where ultrahigh-<em>T</em> metamorphism is reported by previous studies, higher-<em>T</em> condition (850 ± 15 °C/0.1 kbar to 927 ± 16 °C/12.5 kbar) than those of other three regions was confirmed from inclusion rutile in garnet enclosing sillimanite. Therefore, the traditional metamorphic zone mapping, which classified Akarui Point as belonging to the transitional zone, does not reflect the highest metamorphic grade attained. It should be noted that the regional <em>P-T</em> conditions estimated from inclusion minerals in this study is that of earlier higher-<em>P</em> metamorphic stage than the regional <em>P-T</em> conditions determined by the metamorphic zone mapping utilizing matrix mineral assemblages. This result indicates that the Zr-in-rutile geothermometer is a powerful tool to reveal the <em>P-T</em> evolution of high-grade metamorphic terrains, when combined with detailed microstructural observations focusing on the relationship between rutile, zircon, and quartz.</p>

Multi-stage metamorphism of the South Altyn ultrahigh-pressure metamorphic belt, West China: insights into tectonic evolution from continental subduction to arc–backarc extension

2021 ◽  
Author(s):  
Jie Dong ◽  
Chunjing Wei
Keyword(s):  
Late Stage ◽  
Tectonic Evolution ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Ultrahigh Pressure ◽  
Garnet Amphibolite ◽  
The South ◽  
Metamorphic Belt ◽  
Mineral Assemblages ◽  
Eclogite Facies

Abstract The South Altyn ultrahigh-pressure (UHP) metamorphic belt is claimed to host the deepest subducted continental crust based on the discovery of former stishovite, and thus can provide unique insights into the tectonic evolution from deep continental subduction and exhumation to arc–backarc extension. In this paper, we present detailed studies of petrography, mineral chemistry, phase equilibria modelling and zircon U-Pb dating for three representative samples involving garnet amphibolite (A1531 & A1533) and associated garnet-biotite gneiss (A1534) from the UHP belt. Three phases of metamorphism are inferred for the rocks. The first phase high pressure (HP)–UHP-type eclogite facies is represented by the mineral assemblages of garnet and phengite inclusions in zircon and garnet cores with the high grossular (XGrs = 0.33–0.34). The Si contents of 3.40–3.53 and 3.24–3.25 p.f.u. in phengite inclusions yield pressure conditions of >1.7–2.3 GPa for A1533 and 2.5–2.55 GPa for A1534 at a fixed temperature of 770 °C. The second phase medium-pressure (MP)-type overprinting of garnet amphibolite facies shows P–T conditions of 0.8–1.2 GPa/750–785 °C based on the stability fields of corresponding mineral assemblages, the measured isopleths of Ti contents in biotite and amphibole cores, and XGrs in garnet. The third phase low-pressure (LP) type overprinting includes early-stage heating to peak granulite facies followed by cooling towards a late-stage amphibolite facies. The peak granulite facies is represented by the high Ti amphibole mantle, high Zr titanite and the intergrowths of clinopyroxene + ilmenite in A1533 & A1531, with P–T conditions of 800–875 °C/0.80–0.95 GPa. The late-stage is defined by the solidus assemblages, giving P–T conditions of 0.5–0.7 GPa/720–805 °C. U-Pb geochronology on metamorphic zircons from A1533 and A1534 gives three ages of c. 500 Ma, c. 482 Ma and c. 460 Ma. They are interpreted to represent the HP–UHP, MP and LP types of metamorphism respectively, based on cathodoluminescence images, mineral inclusions and trace element patterns. Combining the regional geology and metamorphic evolution from the Altyn Orogen, a tectonic model is inferred, including the following tectonic scenarios. The small Altyn Microcontinent was subducted to great mantle depths with dragging of the surrounding vast oceanic lithosphere to undergo the HP–UHP eclogite facies metamorphism during the early subduction stage (c. 500 Ma) of the Proto-Tethys Ocean. Then, the subducted slabs were exhumed to a thickened crust region to be overprinted by the MP-type assemblages at c. 482 Ma. Finally, an arc–backarc extension was operated within the thickened crust region due to the retreat of subduction zones. It caused evident heating and the LP-type metamorphic overprinting at c. 460 Ma, with a fairly long interval of 30–40 Myr after the HP–UHP metamorphism, distinct from the short interval of <5–10 Myr in the Bohemian Massif.

scholarly journals GEOLOGIA DA REGIÃO DE JEQUERI-VIÇOSA (MG), ORÓGENO ARAÇUAÍ MERIDIONAL

2013 ◽  
Author(s):  
Daniel Tavares Gradim ◽  
Gláucia Nascimento Queiroga ◽  
Tiago Amâncio Novo ◽  
Carlos Maurício Noce ◽  
Antônio Carlos Pedrosa-Soares ◽  
...  
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Granulite Facies ◽  
Minas Gerais ◽  
Amphibolite Facies ◽  
Ultramafic Rocks ◽  
Metamorphic Rocks ◽  
The West ◽  
Minas Gerais State ◽  
Araçuaí Orogen

RESUMO: A característica fundamental da região de Jequeri-Viçosa, situada no extremo sul do Orógeno Araçuaí, é a abundância de rochas metamórficas, ortoderivadas e paraderivadas, de fácies anfibolito alto e granulito. O embasamento paleoproterozóico é representado, a oeste, por ortognaisses tonalíticos a graníticos do Complexo Mantiqueira e, a leste, por ortognaisses charno-enderbíticos do Complexo Juiz de Fora. Ambos os complexos incluem anfibolitos e exibem intensidades variáveis de migmatização. O contato entre eles é marcado pela zona de cisalhamento transpressiva destral de Abre Campo, interpretada como uma sutura paleoproterozóica reativada no Neoproterozóico. O Anfibolito Santo Antônio do Grama e rochas meta-ultramáficas associadas (Córrego do Pimenta) representam restos ofiolíticos ediacaranos, colocados ao longo da Zona de Cisalhamento de Abre Campo. Assentada sobre o embasamento, na parte oeste da área, ocorre uma associação metavulcano-sedimentar neoproterozóica do Grupo Dom Silvério, composta por xistos diversos e quartzito. Na porção leste da área mapeada, a cobertura metassedimentar neoproterozóica é atribuída ao Grupo Andrelândia que inclui paragnaisse migmatítico e raro quartzito. Corpos de hidrotermalito quartzoso, indiscriminadamente associados às unidades do embasamento e da cobertura neoproterozóica, ocorrem ao longo de zonas de cisalhamento. Hidrotermalitos ferruginosos associam-se ao Complexo Mantiqueira na Zona de Cisalhamento de Ponte Nova. O granito foliado a milonitizado da Serra dos Vieiras parece ser um produto de fusão parcial do paragnaisse Andrelândia. Completam o quadro geológico os pegmatitos da Suíte Paula Cândico e diques de diabásio mesozóicos.Palavras-chave: Paleoproterozóico, Neoproterozóico, Orógeno AraçuaíABSTRACT: GEOLOGY OF THE JEQUERI-VIÇOSA REGION, MINAS GERAIS STATE, SOUTHERN ARAÇUAÍ OROGEN. This paper focuses on the southwestern sector of the Araçuaí orogen in a region located close to the boundary with the northern Ribeira orogen. This region is rich in ortho- and para-derived metamorphic rocks of the high amphibolite and granulite facies. The Paleoproterozoic basement includes, to the west, tonalitic to granitic orthogneisses of the Mantiqueira Complex and, to the east, enderbitic to charnockitic orthogneisses of the Juiz de Fora Complex. Both complexes also include amphibolite enclaves and show several rates of partial melting. The contact between them is marked by the dextral transpressional Abre Campo shear zone, considered to be a Paleoproterozoic suture reactivated during the Neoproterozoic Era. The Santo Antônio do Grama Amphibolite and associated meta-ultramafic rocks (Córrego do Pimenta) are Ediacaran ophiolite slivers emplaced along the Abre Campo shear zone. In the western part of the region, the Paleoproterozoic basement is locally covered by a metavolcano-sedimentary assemblage composed of amphibolite facies schist and quartzite of the Neoproterozoic Dom Silvério Group. To the east, the Neoproterozoic cover comprises the migmatized paragneiss and rare quartzite of the Andrelândia Group. The Serra dos Vieiras foliated to mylonitic granite seems to be formed from the partial melting of the Andrelândia paragneiss. Pegmatites of the Paula Cândido Suite and Mesosozic diabase dikes complete the geologic framework of the mapped area.Keywords: Paleoproterozoic, Neoproterozoic, Araçuaí Orogen

scholarly journals Eclogite resembling metamorphic disequilibrium assemblage formed through fluid-induced metasomatic reactions

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Sanghoon Kwon ◽  
Vinod O. Samuel ◽  
Yungoo Song ◽  
Sung Won Kim ◽  
Seung-Ik Park ◽  
...  
Keyword(s):  
Local Equilibrium ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Length Scale ◽  
Important Criterion ◽  
Garnet Amphibolite ◽  
Mafic Rocks ◽  
Facies Metamorphism ◽  
Crustal Reworking ◽  
Eclogite Facies

AbstractEquilibrium omphacite-garnet-bearing mafic rocks have been classified as eclogites, either pristine or retrogressed, that were formed at great depths in the lithosphere. Here we report a unique natural example of eclogite resembling assemblage in disequilibrium formed through fluid-induced metasomatic reactions under the amphibolite to granulite facies. Primarily, the amphibolized protolith experienced a garnet-amphibolite facies metamorphism at ~ 500–700 °C and ~ 0.8–1 GPa. Subsequently, CO2 fluid induced fracturing and dissolution-reprecipitation reactions occurred at peak metamorphic conditions of ~ 700 °C and ~ 1 GPa. Occasional omphacite-albite assemblage, which gradually replace diopside-oligoclase symplectite adjacent to albite veins along fractures, indicates fluid-induced coupled dissolution-reprecipitation disequilibrium reactions. Here the albite-omphacite assemblage is in local equilibrium at least on 1 mm length scale, during cooling, below ~ 600 ºC and ~ 1 GPa, within the amphibolite facies conditions. The results from this study clearly suggest that disequilibrium garnet-omphacite assemblage in mafic rocks could be formed by crustal reworking processes below granulite facies conditions, and their textural equilibrium is an important criterion while defining eclogite facies.

Pressure–temperature conditions of Early Proterozoic metamorphism during the Trans-Hudson Orogen as determined from rocks straddling the Flin Flon – Kisseynew boundary at Niblock and File lakes, Manitoba

1992 ◽  
Vol 29 (11) ◽  
pp. 2497-2507 ◽  
Author(s):  
William Briggs ◽  
C. T. Foster
Keyword(s):  
Amphibolite Facies ◽  
Lake Area ◽  
Relative Timing ◽  
Early Proterozoic ◽  
Temperature Conditions ◽  
Mineral Assemblages ◽  
Flin Flon ◽  
The Town

The Niblock Lake and File Lake areas straddle the boundary between the Kisseynew gneiss belt and the Flin Flon belt, near the town of Snow Lake, Manitoba. The region contains pelitic schists metamorphosed to lower to middle almandine–amphibolite facies. Metamorphic conditions were studied by examining relative timing of growth of metamorphic minerals by geothermobarometry of selected samples. Calculated temperatures and pressures are compared with those estimated from mineral assemblages and reactions on a petrogenetic grid.Two metamorphic (M1 and M2) and deformation (D1 and D2) phases have been recognized in the Niblock Lake and File Lake areas. M1 (contemporaneous with D1 folding) was characterized by growth of micas but no higher grade minerals. Temperatures and pressures of M1, therefore, were probably less than about 475 °C and 3.5 kbar (1 kbar = 100 MPa). Peak conditions, reached during M2 (late- to post-D2 folding), resulted in growth of garnet, staurolite, sillimanite, and (in the Niblock Lake area) andalusite. In the Niblock Lake area, M2 temperatures range from 525 to 625 °C, with most samples between 550 and 600 °C; pressures range from 2.5 to 5 kbar, with most samples between 2.5 and 4 kbar. In the File Lake area, M2 temperatures range from approximately 560 to 625 °C; pressures range from 3.3 to 4.6 kbar.

Retrograde contact meta-morphism in the granulite facies terrain of Mont Tremblant Park, Quebec, Canada

1968 ◽  
Vol 105 (5) ◽  
pp. 487-492 ◽  
Author(s):  
Michael B. Katz
Keyword(s):  
Late Stage ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Grenville Province ◽  
South West ◽  
Mineral Assemblages ◽  
Park Area

SUMMARYThe Pre-Cambrian rocks of the Grenville province of south-west Quebec in the Mont Tremblant Park area consists of granulites and associated gneisses formed under granulite facies conditions which are intruded by members of an anorthosite suite. At the contacts of these intrusives especially the late-stage members, the granulites and gneisses were found to be retrograded into rocks with mineral assemblages typical of the amphibolite facies. The transformation of the granulite facies rocks into rocks of lower amphibolite grade can be attributed to local introduction of water which was supplied during the emplacement and crystallization of this late-stage, volatile-enriched magma of the anorthosite suite.

Opening of the West Paleo-Tethys Ocean: New insights from earliest Devonian meta-mafic rocks in the Saualpe crystalline basement, Eastern Alps

2021 ◽  
Author(s):  
Qingbin Guan ◽  
Yongjiang Liu ◽  
Franz Neubauer ◽  
Sanzhong Li ◽  
Johann Genser ◽  
...  
Keyword(s):  
Eastern Alps ◽  
Crystalline Basement ◽  
The West ◽  
Mafic Rocks ◽  
Tethys Ocean

Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands

1993 ◽  
Vol 5 (2) ◽  
pp. 193-206 ◽  
Author(s):  
P. D. Kinny ◽  
L. P. Black ◽  
J. W. Sheraton
Keyword(s):  
Granulite Facies ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
High Grade ◽  
Ion Microprobe ◽  
Rock Interaction ◽  
Mafic Rocks ◽  
Grade Fluid ◽  
Vestfold Hills ◽  
Intrusive Suite

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

scholarly journals A synthetic view of rainfall intensification in the West African Sahel

2022 ◽  
Author(s):  
Guillaume Chagnaud ◽  
Geremy Panthou ◽  
Theo Vischel ◽  
Thierry Lebel
Keyword(s):  
Decadal Variability ◽  
Regional Scale ◽  
Daily Rainfall ◽  
Extreme Value Distribution ◽  
Extreme Rainfall ◽  
West African ◽  
Rainfall Regime ◽  
The West ◽  
West African Sahel ◽  
African Sahel

Abstract The West African Sahel has been facing for more than 30 years an increase in extreme rainfalls with strong socio-economic impacts. This situation challenges decision-makers to define adaptation strategies in a rapidly changing climate. The present study proposes (i) a quantitative characterization of the trends in extreme rainfalls at the regional scale, (ii) the translation of the trends into metrics that can be used by hydrological risk managers, (iii) elements for understanding the link between the climatology of extreme and mean rainfall. Based on a regional non-stationary statistical model applied to in-situ daily rainfall data over the period 1983-2015, we show that the region-wide increasing trend in extreme rainfalls is highly significant. The change in extreme value distribution reflects an increase in both the mean and variability, producing a 5%/decade increase in extreme rainfall intensity whatever the return period. The statistical framework provides operational elements for revising the design methods of hydraulic structures which most often assume a stationary climate. Finally, the study shows that the increase in extreme rainfall is more attributable to an increase in the intensity of storms (80%) than to their occurrence (20%), reflecting a major disruption from the decadal variability of the rainfall regime documented in the region since 1950.

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