Gold in the ALPS: A View from the South

AbstractWe investigate the geodynamics of the Southeast Basin with the help of maps of the basement and of major sedimentary horizons based on available seismic reflection profiles and drill holes. We also present a study of the seismicity along the Middle Durance fault. The present seismic activity of the SE Basin cannot be attributed to the Africa/Eurasia shortening since spatial geodesy demonstrates that there is no significant motion of Corsica-Sardinia with respect to Eurasia and since gravitational collapse of the Alps has characterized the last few millions years. Our study demonstrates that the basement of this 140 by 200 km Triassic basin has been essentially undeformed since its formation, most probably because of the hardening of the cooling lithosphere after its 50% thinning during the Triassic distension. The regional geodynamics are thus dominated by the interaction of this rigid unit with the surrounding zones of active deformation. The 12 km thick Mesozoic sediment cover includes at its base an up to 4 km thick mostly evaporitic Triassic layer that is hot and consequently highly fluid. The sedimentary cover is thus decoupled from the basement. As a result, the sedimentary cover does not have enough strength to produce reliefs exceeding about 500 to 750 m. That the deformation and seismicity affecting the basin are the results of cover tectonics is confirmed by the fact that seismic activity in the basin only affects the sedimentary cover. Based on our mapping of the structure of the basin, we propose a simple mechanism accounting for the Neogene deformation of the sedimentary cover. The formation of the higher Alps has first resulted to the north in the shortening of the Diois-Baronnies sedimentary cover that elevated the top of Jurassic horizons by about 4 km with respect to surrounding areas to the south and west. There was thus passage from a brittle-ductile basement decollement within the higher Alps to an evaporitic decollement within the Diois-Baronnies. This shortening and consequent elevation finally induced the southward motion of the basin cover south of the Lure mountain during and after the Middle Miocene. This southward motion was absorbed by the formation of the Luberon and Trévaresse mountains to the south. To the east of the Durance fault, there is no large sediment cover. The seismicity there, is related to the absorption of the Alps collapse within the basement itself. To the west of the Salon-Cavaillon fault, on the other hand, gravity induces a NNE motion of the sedimentary cover with extension to the south and shortening to the north near Mont Ventoux. When considering the seismicity of this area, it is thus important to distinguish between the western Basin panel, west of the Salon-Cavaillon fault affected by very slow NNE gliding of the sedimentary cover, with extension to the south and shortening to the north; the central Basin panel west of the Durance fault with S gliding of the sedimentary cover and increasing shortening to the south; and finally the basement panel east of the Durance fault with intrabasement absorption of the Alps collapse through strike-slip and thrust faults.

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The arc of the Western Alps : understanding its kinematics and formation mechanisms based on new structural and paleomagnetic datas, and thermo-mechanical modelling.

10.5194/egusphere-egu21-16529 ◽

2021 ◽

Author(s):

Quentin Brunsmann ◽

Claudio Rosenberg ◽

Nicolas Bellahsen ◽

Laetitia Le Pourhiet

Keyword(s):

Western Alps ◽

Strike Slip ◽

Rheological Parameters ◽

The South ◽

Adriatic Plate ◽

The North ◽

Field Evidence ◽

Internal Zone ◽

The Alps ◽

East West

The Alps have an overall East-West orientation, which changes radically in their western termination, where they rotate southward into a N-S strike, and then eastward into an E-W strike, forming the arc of the Western Alps. This arc is commonly inferred to have formed during collision, due to indentation of the Adriatic plate into the European continental margin. Several models attempted to provide a kinematic explanation for the formation of this arched, lateral end of the Alps. Indeed, the radial nature of the transport directions observed along the arc of the Western Alps cannot be explained by a classic convergence model. For more than 50 years the formation of this arc was been associated to westward-directed indentation of Adria, accommodated along East-West oriented strike-slip faults, a sinistral one in the South of the arc and a dextral one in the North. The dextral one correspond to the Insubric Fault. The sinistral strike-slip zone, inferred to be localized along the &#171;Stura corridor&#187; (Piedmont, Italy) would correspond to a displacement of 100 to 150 km according to palaeogeographical, and geometric analyses. However, field evidence is scarce and barely documented in the literature. Vertical axis rotations of the Adriatic indenter also inferred to be syn-collisional could have influenced the acquisition of the morphology of the arc. Paleomagnetic analyses carried out in the Internal Zone and in the Po plain suggest a southward increading amount of counter-clockwise rotation of the Adriatic plate and the Internal Zone, varying from 20&#176;-25&#176; in the North to nearly 120&#176; in the South. Dextral shear zones possibly accommodating this rotation in some conceptual models is observed in several places below the Penninic Front and affect the Argentera massif to the south. However, the measured displacement quantities do not appear to be equivalent to those induced by such rotations. The present study aims to constrain the kinematic evolution of the arc of the Western Alps through a multidisciplinary approach. The first aspect of this project is the structural analysis of the area (Stura corridor) inferred to accommodate large sinistral displacements allowing for the westward indentation of the Adriatic indenter. We discuss the general lack of field evidence supporting sinistral strike-slip movements, in contrast to large-scale compilation of structures suggesting the possible occurrence of such displacement. The second part consists of a palaeomagnetic study, in which new data are integred with a compilation of already existing data. This compilation shows that several parts of the arc in the External Zone did not suffer any Cenozoic rotations, hence suggesting that a proto-arc already axisted at the onset collision, as suggested by independent evidence of some paleogeographic reconstruction. Finally, 2D and 3D thermo-mechanical modeling in using the pTatin3D code is used to test which structural (geometrical), and rheological parameters affected the first-order morphology of the Western Alpin arc and its kinematics. The synthesis of these different approaches allows us to propose a new model explaining the kinematics and the mechanisms of formation of the Western Alps arc.

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Tectonophysique comparee des chaines telliennes et rifaines

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.s6-ii.7-9.619 ◽

1952 ◽

Vol S6-II (7-9) ◽

pp. 619-639

Author(s):

Louis Glangeaud

Keyword(s):

Fourth Order ◽

Coastal Region ◽

Second Order ◽

North African ◽

The South ◽

Structural Interpretation ◽

The North ◽

The Alps

Abstract Correlates the structure and evolution of the Atlas ranges of the Tell and Rif regions and presents a general structural interpretation of the north African coastal region. The Miocene thrusts in the south are local regional adjustments (of the fourth order) to second-order processes occurring farther to the north--compression of the Alps in upper Nummulitic time (Tertiary).

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I.—Coral in the “Dolomites” of South Tyrol

Geological Magazine ◽

10.1017/s0016756800140464 ◽

1894 ◽

Vol 1 (2) ◽

pp. 49-60 ◽

Cited By ~ 3

Author(s):

Maria M. Ogilvie

Keyword(s):

Local Variation ◽

Point Of View ◽

The South ◽

South Tyrol ◽

The Alps ◽

As If

The Raibl period was the natural sequel of the variable and unequal movements which prevailed over Alpine areasinPermian and pre-Raibl Triassic time. Many basins formerly open were then enclosed; rauchwackes and beds of dolomite and gypsum were interbedded with fossiliferous deposits. Whereas,insome places, the dolomitic nature of the deposit is confined to special horizons, in the South Tyrol “Dolomites” it may almost be said to reign throughout. This makes it all but impossible to say when Schlern dolomite ends and Raibl beds begin. in the present incomplete state of our knowledge with regard to the heteropism of the Raibl series throughout the whole Alps, I have judged it best to begin the Raibl horizon at any particular place with the first appearance of a distinctly Raibl fauna, even although that fauna may not have been proved to correspond to the acknowledged lowest fauna of Raibl age in distant parts of the Alps.To return for a moment to the succession of Schlern dolomite upon the Cassian beds of Enneberg, I found that, where Schlern dolomite rests on Cipit limestones, it has at its base a conglomeratic appearance, as if Cipit blocks had been imbedded in a beautifully fine white or reddish dolomitic mud, instead of the dingy brown and black tufaceous sediments. This is the case in several places, e.g. upon Pordoi and Sella Jochs, where there is no evidence of unconformity. Again, where the dolomite succeeds the thin-bedded marls and limestones of Cassian age, it does so conformably; but one and the same bed is at some parts calcareous and fossiliferous, at other parts dolomitic and unfossiliferous. Seeing that this holds good at various horizons in Lower as well as Middle Trias over the whole area of South Tyrol, we need f in d nothing remarkable in it from the point of view of the stratigraphical succession. Indeed, I have only mentioned these observations as an indication of the particular mode of transition from conditions of deposition favourable for the Cassian fauna to those in which the Raibl fauna was enabled to make an occasional appearance in the South Tyrol dolomites. At a very little distance above the base of Schlern dolomite all signs of Coral life disappear, and the deposit looks a homogeneous rock, although always retaining local variation in the degree of its dolomitism. At this stage the rock often shows typical Oolite structure. As regards the presence or want of stratification, it has as little to do with the question of the Coral Keef origin of the dolomite as the amount of magnesic salts in the rock—stratification is present and absent in one and the same “Keef.”

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Retrospective analysis of a nonforecasted rain-on-snow flood in the Alps – a matter of model limitations or unpredictable nature?

Hydrology and Earth System Sciences ◽

10.5194/hess-18-2265-2014 ◽

2014 ◽

Vol 18 (6) ◽

pp. 2265-2285 ◽

Cited By ~ 52

Author(s):

O. Rössler ◽

P. Froidevaux ◽

U. Börst ◽

R. Rickli ◽

O. Martius ◽

...

Keyword(s):

Snow Cover ◽

Temperature Increase ◽

Hydrological Model ◽

Small Scale ◽

The South ◽

Flood Peak ◽

Forecast Data ◽

The Alps ◽

Model Setup ◽

Local Rainfall

Abstract. A rain-on-snow flood occurred in the Bernese Alps, Switzerland, on 10 October 2011, and caused significant damage. As the flood peak was unpredicted by the flood forecast system, questions were raised concerning the causes and the predictability of the event. Here, we aimed to reconstruct the anatomy of this rain-on-snow flood in the Lötschen Valley (160 km2) by analyzing meteorological data from the synoptic to the local scale and by reproducing the flood peak with the hydrological model WaSiM-ETH (Water Flow and Balance Simulation Model). This in order to gain process understanding and to evaluate the predictability. The atmospheric drivers of this rain-on-snow flood were (i) sustained snowfall followed by (ii) the passage of an atmospheric river bringing warm and moist air towards the Alps. As a result, intensive rainfall (average of 100 mm day-1) was accompanied by a temperature increase that shifted the 0° line from 1500 to 3200 m a.s.l. (meters above sea level) in 24 h with a maximum increase of 9 K in 9 h. The south-facing slope of the valley received significantly more precipitation than the north-facing slope, leading to flooding only in tributaries along the south-facing slope. We hypothesized that the reason for this very local rainfall distribution was a cavity circulation combined with a seeder-feeder-cloud system enhancing local rainfall and snowmelt along the south-facing slope. By applying and considerably recalibrating the standard hydrological model setup, we proved that both latent and sensible heat fluxes were needed to reconstruct the snow cover dynamic, and that locally high-precipitation sums (160 mm in 12 h) were required to produce the estimated flood peak. However, to reproduce the rapid runoff responses during the event, we conceptually represent likely lateral flow dynamics within the snow cover causing the model to react "oversensitively" to meltwater. Driving the optimized model with COSMO (Consortium for Small-scale Modeling)-2 forecast data, we still failed to simulate the flood because COSMO-2 forecast data underestimated both the local precipitation peak and the temperature increase. Thus we conclude that this rain-on-snow flood was, in general, predictable, but requires a special hydrological model setup and extensive and locally precise meteorological input data. Although, this data quality may not be achieved with forecast data, an additional model with a specific rain-on-snow configuration can provide useful information when rain-on-snow events are likely to occur.

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II.—The Dolomite Reefs of the South Tyrol and Venetia. Contribution to the History of the Formation of the Alps. (Die Dolomit - Riffe von Süd-Tyrol und Venetia. Beiträge zur Bildungsgeschichte der Alpen. Von Edmond Mojsisovics von Mojsvár.) With a Map, in 6 Sheets, of the Tyrolese Venetian Alps, 30 Photographs, and 110 Woodcuts; pp. 552.

Geological Magazine ◽

10.1017/s0016756800165677 ◽

1879 ◽

Vol 6 (09) ◽

pp. 428

Author(s):

Keyword(s):

The South ◽

South Tyrol ◽

History Of ◽

The Alps

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The Paragenesis of Kyanite-amphibolites (With Plate XX.)

Mineralogical Magazine and Journal of the Mineralogical Society ◽

10.1180/minmag.1937.024.158.02 ◽

1937 ◽

Vol 24 (158) ◽

pp. 555-568 ◽

Cited By ~ 6

Author(s):

C. E. Tilley ◽

H. C. G. Vincent

Keyword(s):

The Other ◽

Retrograde Metamorphism ◽

Present Communication ◽

The South ◽

South Side ◽

The Alps ◽

The One

In an earlier paper the writer has discussed the paragenesis - kyanite-omphacite as observed in certain ec|ogites. The fate of this association under conditions of retrograde metamorphism has led to a consideration of rocks showing the paragenesis amphibole-kyanite, a point which is briefly taken up in the present communication. Rocks containing this latter assemblage include two groups, the one better known, of sedimentary origin, the other essentially igneous in origin.Here are included members of the para-amphibolites, biotite-hornblende- schists, and hornblende-Garbenschiefer derived from sediments of the character of calcareous and dolomitic shales. The best-known examples come from the Alps—particularly the Triassic and pre- Triassic sediments on the south side of the St. Gotthard massif.

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The structural evolution of the Albula Pass region, Graubünden, eastern Switzerland: the origin of the various vergences in the structure of the Alps

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2016-0020 ◽

2016 ◽

Vol 53 (11) ◽

pp. 1279-1311 ◽

Cited By ~ 3

Author(s):

A.M. Celâl Şengör

Keyword(s):

Early Cretaceous ◽

Sedimentary Rocks ◽

Structural Evolution ◽

Normal Faults ◽

Thrust Faults ◽

The South ◽

The Future ◽

Structural Fabric ◽

The Alps ◽

Entire Ensemble

The Albula Pass region lies between the Lower Austroalpine Err Nappe and the Middle Austroalpine Silvretta Nappe. They will be treated here as the frame of the non- to gently metamorphic sedimentary units between the two during the Alpide times. Sedimentation started on a metamorphic Hercynian basement during the latest Carboniferous(?) and continued into the Permian. Then a sequence from the Alpine Buntsandstein to the medial Jurassic to early Cretaceous Aptychenkalk (=Maiolica) and radiolarites were deposited in an environment of rifting and subsidence. The succeeding Palombini clastics were laid down after the Aptychenkalk and mark the onset of shortening in the Alpine realm. The initial structures that formed were at least two north-dipping normal faults which formed before the deposition of the Jurassic sedimentary rocks. When shortening set in, the first structure that came into being was the south-vergent Elalbula Nappe, bending the normal faults into close antiforms. It became further dismembered into two pieces creating parts of the future Ela and Albula nappes in the Albula region. This motion was later reversed, when the entire ensemble became bulldozed by the immense body of the Silvretta Nappe along numerous, closely spaced thrust faults, some of which only very locally followed horizontal bits of the old normal faults, but in principle they determined their own course. No evidence for westerly motion could be identified, although microstructures in the structural fabric were not studied. The reason for this may be the pre-orogenic fabric in the bounding tectonic units.

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