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In the central part of the internal Western Alps, widespread multidirectional normal faulting resulted in an orogen-scale radial extension during the Neogene. We revisit the frontal Piémont units, between Doire and Ubaye, where contrasting lithologies allow analysing the interference with the N–S trending Oligocene compressive structures. A major extensional structure is the orogen-perpendicular Chenaillet graben, whose development was guided by an E–W trending transfer fault zone between the Chaberton backfold to the north and the Rochebrune backthrust to the south. The Chaberton hinge zone was passively crosscut by planar normal faults, resulting in a E–W trending step-type structure. Within the Rochebrune nappe, E–W trending listric normal faults bound tilted blocks that slipped northward along the basal backthrust surface reactivated as an extensional detachment. Gravity-driven gliding is suggested by the general northward tilting of the structure in relation with the collapse of the Chenaillet graben. The stress tensors computed from brittle deformation analysis confirm the predominance of orogen-parallel extension in the entire frontal Piémont zone. This can be compared with the nearby Briançonnnais nappe stack where the extensional reactivation of thrust surfaces locally resulted in prominent orogen-perpendicular extension. Such a contrasting situation illustrates how the main direction of the late-Alpine extension may be regionally governed by the nature and orientation of the pre-existing structures inherited from the main collision stage. 相似文献
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Pierre Lanari Yann Rolland Stéphane Schwartz Olivier Vidal Stéphane Guillot Pierre Tricart Thierry Dumont 《地学学报》2014,26(2):130-138
Pressure–Temperature–time (P–T–t) estimates of the syn‐kinematic strain at the peak‐pressure conditions reached during shallow underthrusting of the Briançonnais Zone in the Alpine subduction zone was made by thermodynamic modelling and 40Ar/39Ar dating in the Plan‐de‐Phasy unit (SE of the Pelvoux Massif, Western Alps). The dated phengite minerals crystallized syn‐kinematically in a shear zone indicating top‐to‐the‐N motion. By combining X‐ray mapping with multi‐equilibrium calculations, we estimate the phengite crystallization conditions at 270 ± 50 °C and 8.1 ± 2 kbar at an age of 45.9 ± 1.1 Ma. Combining this P–T–t estimate with data from the literature allows us to constrain the timing and geometry of Alpine continental subduction. We propose that the Briançonnais units were scalped on top of the slab during ongoing continental subduction and exhumed continuously until collision. 相似文献
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William C. Mahaney Michael W. Milner Rana Sodhi Ronald I. Dorn Sal Boccia Roelf P. Beukens Pierre Tricart Stphane Schwartz Eva Chamorro‐Perrez Ren W. Barendregt Volli Kalm Randy W. Dirszowsky 《Geoarchaeology》2007,22(7):797-816
Identification of the exact route followed by Hannibal during his invasion of Italia in the Second Punic War is one of the major questions of antiquity and one that historians/archaeologists have long studied. One of the many clues in the ancient literature that can help answer this question is the mention of fired rock, the result of a conflagration Hannibal is reputed to have employed to reduce the size of boulders in a blocking rockslide some distance down from the high col on the Italian side. The only route with evidence of fired rock along the roadway leading into Italia follows the Col du Clapier, one of the possible northern routes discussed by historians. Radiocarbon dating of calcined rocks is not possible, but whereas Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS), Field Emission Scanning Electron Microscope (FESEM‐EDS), backscatter electron scanning microscopy (BSE), High Resolution Transmission Electron Microscope (HRTEM), and Raman Spectroscopic data do not provide an age for the burnt rock, compositional evidence of the conflagration derived from these analyses may shed light on Hannibal's actual route. © 2007 Wiley Periodicals, Inc. 相似文献
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Olivier Le Roux Stéphane Schwartz Jean François Gamond Denis Jongmans Pierre Tricart Michel Sebrier 《International Journal of Earth Sciences》2010,99(2):427-441
In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides,
from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into
a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary
fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic
and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone
(SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the
bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin
and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited
structures, the BMF and the SFZ. 相似文献
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Fabrice Cordey Pierre Tricart Stéphane Guillot Stéphane Schwartz 《Swiss Journal of Geoscience》2012,105(1):39-48
For the first time in the Western Alps, radiolarite pebbles collected from Tertiary foreland molasse conglomerates are treated for microfossil extraction and dated. Among forty pebbles collected in the field, seven of them released diagnostic radiolarian assemblages ranging in age from Late Bajocian?CEarly Callovian to Middle Oxfordian?CEarly Tithonian. These ages overlap previous biochronological data obtained from in situ localities of the Schistes Lustrés Piemont zone of the French-Italian Alps and triple the number of diagnostic radiolarite samples known so far in this segment of the chain. The diagnostic pebbles are characterized by low grade metamorphism, showing that some eroded thrust-sheets from the oldest parts of the ocean escaped any tectonic burial during the Alpine convergence. Mixing of low and high-grade radiolarites, mafics and ultramafics pebbles implies that various ocean-derived units were exposed. This tectonic scenario involves tight refolding and severe uplift of the Eocene subduction wedge in the Early Oligocene. 相似文献
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The succession recovered in ODP hole 107–651 in the young oceanic Vavilov basin (Tyrrhenian Sea) comprises, beneath a thick Pleistocene to Upper Pliocene sedimentary cover (chiefly volcanoclastics), four basement units: (1) MORB-type basaltic pillows and breccias; (2) a complex succession made of dolerites, albitites, basaltic breccias, metadolerite pebbles (including an intercalated sandy layer with periodotite clasts); (3) MORB-type basaltic pillows and breccias; (4) highly serpentinized peridotite. Between units 3 and 4, granitoid pebbles occur.This sequence is surprisingly similar to successions known in the Western Alps' Tethyan ophiolites. There, the sediments (Callovian-Oxfordian radiolarian cherts) lie stratigraphically upon breccias mostly derived from underlying serpentinite, and sometimes gabbroic basement. At some places, thin basaltic (tholeiitic) pillows and breccias occur between the radiolarian cherts and the breccias.From the comparison between a present day setting (the central Tyrrhenian Sea) and a formerly emplaced basement succession (the Western Alps), we stress the following (a) both the here-discussed ophiolites and oceanic basement are different from classical ophiolite sequences; (b) both occurrences imply unroofing of mantle rocks that therefore were directly outcropping on the seafloor; (c) such a comparison may indicate a very slow spreading rate for the Alpine Tethyan ocean. 相似文献
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J. Tricart 《International Journal of Earth Sciences》1955,43(2):384-397
Sans résuméLa présente étude est fondée sur les résultats de missions effectuées pour le compte de la Mission d'Aménagement du Sénégal et notamment sur une carte géomorphologique au 1/50.000 du delta levée pour cet organisme par le Laboratoire de Géographie de l'Université de Strasbourg (L. I. G. U. S.). Cette carte doit être publiée dans le Bulletin du Service Géologique de l'A. O. F. (Dakar). Que tous ceux qui ont facilité nos recherches, et principalement Mr. G.Nesterenko, Directeur de la M. A. S., trouvent ici l'expression de nos plus sincères remerciements. 相似文献
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Eric Barrier Samir Bouaziz Jacques Angelier Gilles Creuzot Jamel Ouali Pierre Tricart 《Geodinamica Acta》2013,26(1):39-57
AbstractA detailed analysis of brittle deformations in the Saharian platform of southern Tunisia is based on studies of fault-slip data sets and joint sets. It allows reconstruction of the Mesozoic paleostress evolution. During the Permo-Triassic, N-S extensions occurred with high late Permian subsidence rates. During the Norian, strike-slip movements reactivated former normal faults. During the Jurassic and the Cretaceous a succession of extensional events was characterized by : (1) a N-S extension which dominated from late Triassic to early Aptian. We relate this extension to the Africa-Eurasia divergence; (2) a ENE-WSW extension during the Cenomanian. We relate this extension to the opening of «he African basins ; (3) a NE-SW Senonian extension that continued during the Cenozoic in the Jeffara and in the Gabes Gulf, during the further evolution of the northern African margin. The various compressional trends recorded in the platform are attributed to Cenozoic events. 相似文献