Unravelling the interaction between tectonic and sedimentary processes during lithospheric thinning in the Alpine Tethys margins

The discovery of exhumed continental mantle and hyper-extended crust in present-day magma-poor rifted margins is at the origin of a paradigm shift within the research field of deep-water rifted margins. It opened new questions about the strain history of rifted margins and the nature and composition of sedimentary, crustal and mantle rocks in rifted margins. Thanks to the benefit of more than one century of work in the Alps and access to world-class outcrops preserving the primary relationships between sediments and crustal and mantle rocks from the fossil Alpine Tethys margins, it is possible to link the subsidence history and syn-rift sedimentary evolution with the strain distribution observed in the crust and mantle rocks exposed in the distal rifted margins. In this paper, we will focus on the transition from early to late rifting that is associated with considerable crustal thinning and a reorganization of the rift system. Crustal thinning is at the origin of a major change in the style of deformation from high-angle to low-angle normal faulting which controls basin-architecture, sedimentary sources and processes and the nature of basement rocks exhumed along the detachment faults in the distal margin. Stratigraphic and isotopic ages indicate that this major change occurred in late Sinemurian time, involving a shift of the syn-rift sedimentation toward the distal domain associated with a major reorganization of the crustal structure with exhumation of lower and middle crust. These changes may be triggered by mantle processes, as indicated by the infiltration of MOR-type magmas in the lithospheric mantle, and the uplift of the Brianconnais domain. Thinning and exhumation of the crust and lithosphere also resulted in the creation of new paleogeographic domains, the Proto Valais and Liguria-Piemonte domains. These basins show a complex, 3D temporal and spatial evolution that might have evolved, at least in the case of the Liguria-Piemonte basin, in the formation of an embryonic oceanic crust. The re-interpretation of the rift evolution and the architecture of the distal rifted margins in the Alps have important implications for the understanding of rifted margins worldwide, but also for the paleogeographic reconstruction of the Alpine domain and its subsequent Alpine compressional overprint.

Inverse metamorphic zonation in very low-grade Tibetan zone series of SE Zanskar and its tectonic consequences (NW India, Himalaya)

The metamorphism of the carbonate rocks of the SE Zanskar Tibetan zone has been studied by `'illite crystallinity'' and calcite-dolomite thermometry. The epizonal Zangla unit overlies the anchizonal Chumik unit. This discontinuous inverse zonation demonstrates a late to post-metamorphic thrust of the first unit over the second. The studied area underwent a complex tectonic history: - The tectonic units were stacked from the NE to the SW, generating recumbent folds, NE dipping thrusts and the regional metamorphism. The compressive movements were active under lower temperature conditions, resulting in late thrusts that disturbed the metamorphic zonation. The discontinuous inverse metamorphic zonation dates from this phase. - A NE vergent backfolding phase occurred at lower temperature conditions. It caused the uplift of more metamorphic levels. - A late extensional phase is revealed by the presence of NE dipping low angle normal faults, and a major high angle fault, the Sarchu fault. The low angle normal faults locally run along earlier thrusts (composite tectonic contacts). Their throw has been sufficient to reset a normal stratigraphic superposition (young layers overlying old ones), but insufficient to erase the inverse metamorphic relationship. However, the combined action of backfolding and normal faulting can locally lessen, or even cancel, the inverse metamorphic superposition. After deduction of the normal fault translation, the vertical component of the original thrust displacement through stratigraphy is 400 m, which is a value far too low to explain the temperature difference between the two units. The horizontal component of displacement is therefore far more important than the vertical one. The regional distribution of metamorphism within the Zangla unit points out to an anchizonal front and an epizonal inner part. This fact is in agreement with nappe tectonics.

Use of Longitudinal Subdrains in the 3R Program, HR-509, Progress Report #2, 1981

The main consideration for base construction under the pavement, in the design of Iowa's interstate, was structural capacity. The material was dense graded with the aim of supporting the pavement and distributing the load as it is transferred to the underlying grade. The drainage characteristics of the base was apparently not given adequate consideration. On jointed portland cement concrete pavement, the water that is trapped immediately beneath the pavement causes severe problems. The traffic causes rapid movement of the water resulting in the hydraulic pressures or "pumping" (movement and redeposit of base fine material), further resulting in faulting between individual slabs. The objective of this evaluation is to determine if longitudinal subdrains are effective in preventing or reducing pumping, faulting and related deterioration. Results suggest that, based upon the flow from the outlets observed during periodic checks and evidence of water flow at the outlets, it appears that to date the subdrains are effective in draining the subbase and subgrade. Because of the limited data available at this time, however, the pavement condition and faulting results are inconclusive.

Fluid-rock interaction during late stages of the Alpine exhumation

Résumé de la thèseLa fracturation des roches au cours de phases compressives ou extensives est un souvent évoquée pour expliquer la circulation de fluide au sein des roches cristallines. Dans le cadre de cette thèse, la circulation des fluides lors de l'exhumation tardive des Alpes a été étudiée en utilisant deux approches différentes: analyses structurales de la déformation fragile d'une part et analyses géochimiques des roches et des minéraux (isotopes stables, datations U/Pb, thermochronologie (U-Th)/He) d'autre part. Cette approche combinée a permis de mieux comprendre l'interaction existante entre les fluides métamorphiques et les fluides météoriques, ainsi que leur interaction avec les roches encaissantes. Le travail a été effectué dans la zone Pennique du Valais suisse.La première partie était focalisée sur la déformation fragile, le but étant de définir les différents types de déformations existantes et de déterminer l'âge relatif des différentes familles de failles. Dans la région d'étude, quatre domaines ont été distingués. Chacun d'eux comportent deux types de structures fragiles, certaines sont minéralisées alors que d'autre non. Au sein de chaque domaine, la direction principale des structures minéralisées correspond à l'orientation des accidents tectoniques majeurs de la région (Aosta- Ranzola Line au Sud, Rhône Line au Nord et Simplon Fault Zone à l'Est), alors que les structures non- minéralisées montrent des orientations plus variables. Ainsi, le premier type de structure est interprété comme résultant d'une dislocation tectonique alors que le deuxième type de structure résulterait d'une dislocation gravitaire locale. Il n'est néanmoins pas possible de classer chronologiquement la formation de ces deux types de structure ni d'attribuer un âge relatif aux changements d'orientation des contraintes majeures.La deuxième étude a été effectuée dans la région de la zone de faille du Simplon. Dans cette zone, la composition isotopique des minéraux ayant cristallisé à l'intérieur des fractures tardives permet de distinguer différents types de circulation de fluide. Les valeurs δ180 du quartz de la roche encaissante ainsi que ceux des veines tardives du bloque inférieur de la faille sont comparables. Ces valeurs indiquent un rééquilibrage et un tamponnage isotopique des fluides tardifs au contact de la roche encaissante lors de la fracturation de cette dernière et de la cristallisation des veines tardives. La même situation est observée dans la partie nord du bloque supérieur ainsi que dans sa partie sud. Ceci n'est néanmoins pas le cas pour la partie centrale du bloque supérieur où les valeurs isotopiques des minéraux dans les veines tardives sont approximativement 3 %o plus basses (avec des valeurs extrêmes négatifs), indiquant une contribution d'eau météorique aux fluides circulant dans les veines. Ces données suggèrent qu'une infiltration d'eau météorique a pu avoir lieu dans le bloque supérieur, où la fracturation des roches est plus intensive car le déplacement relatif le long de la faille y fut plus important, et la température maximale du métamorphisme plus basse. La troisième contribution traite de la géo-thermochronologie de la zone de contact entre la klippe de la Dent Blanche et la nappe de Tsaté. De petits zircons euhédraux ont été trouvés dans un plan de faille minéralisé (parallèle à la Faille du Rhône, voir première partie de l'étude), riche en hématite et quartz, de la zone d'étude. Les analyses U/Pb donnent des âges radiométriques autour de 270 - 280 Ma aux zircons extraits de la minéralisation ainsi que ceux extraits de la roche encaissante, ce qui correspond à l'âge de la nappe de la Dent Blanche et non celui de la nappe du Tsaté qui est elle-même classiquement interprétée comme une ophiolite Jurassique de l'Océan Liguro-Piémontais. Ces données suggèrent que les zircons contenus dans la veine ont été hérités de la roche encaissante. Les résultats (U-Th)/He indiquent un âge de refroidissement différent pour la roche encaissante (25.5 ± 2.0 Ma) que celui de la minéralisation (17.7 ±1.4 Ma). Le thermomètre isotopique quartz-hématite indique une température d'équilibre, et donc de mise en place de la minéralisation, d'environ 170 °C, température très proche de la température de -180 °C de fermeture du zircon pour le système (U-Th)/He. Ceci suggère que l'âge de refroidissement des zircons de la minéralisation correspond aussi à l'âge de formation de la faille.Thesis abstractFluid circulation in fractured rocks is a common process in geology, and it is generally the consequence of faulting and fracturing during both tectonic compression and extension. This thesis is focused on fluid circulation during late stages of the Alpine exhumation. After a structural analysis of the late brittle deformation of the studied samples, several analytical methods (stable isotope investigations, U/Pb radiometric dating, (U-Th)/He thermochronology) have been applied to understand the interaction of metamorphic and meteoric fluids with one another as well as with the host rock. This thesis is articulated around three study directions. All studies were conducted in the Penninic Zone of the Valais, Switzerland. The first study deals with late, brittle deformation and focuses on the different deformation styles and on the relative age of the different families of fractures. In order to do this, late brittle structures observed in four different domains have been subdivided as a function of the existence (or not) and type of mineralization. Comparisons between mineralized and non-mineralized strike directions for all four domains show that mineralized structures follow the strike orientation of major tectonic movements indicated in the Penninic Zone of the Valais (Aosta-Ranzola Line to the S, Rhône Line to the Ν and Simplon Fault Zone to the E), whereas non-mineralized fractures have a more variable strike orientation. This difference could be interpreted as indicative of tectonic-related faulting (mineralized structures) vs. local, collapse-related faulting (non-mineralized fractures), but it is not strong enough to indicate a relative age of the late brittle structures, and/or a change in the orientation of the strain field in post-Miocene times. The second studied area is focused on the Simplon Fault Zone (SFZ). Stable isotope analyses of minerals filling these late fractures indicate that there are two different fluid circulation systems in the footwall and hanging wall of the SFZ. In the footwall, δ180 values of quartz from both the host rock and the late veins range from +10 %o to +12 %o. This is consistent with buffering of circulating fluids by the host rock during fracturing and vein precipitation. In the hanging wall, δΙ80 values for quartz crystals from the host rock and the late veins are similar in both the northern and southern parts of the detachment that are both affected by the same degree of metamorphism (greenschist to the Ν and amphibolite to the S). This is not the case in the central part of the SFZ, where there is a jump from amphibolite facies in the footwall to greenschist facies in the hanging wall. δ,80 values for quartz from the hanging wall late veins are approximately 3.0 %o lower (down to negative values in some cases) than the values observed in the footwall These data suggest that infiltration of meteoric water may have occurred in the most fractured parts of the hanging wall, where relative displacement on the SFZ was the greatest and the peak temperature lower. In the less fractured footwall the δ180 values reflect a host rock-buffered system.The third study is focused on geo-thermochronology at the contact between the Dent Blanche nappe and the Tsaté nappe where small, euhedral zircons were found in a hematite- and quartz-rich mineralization on a late normal fault plane parallel to the Rhône Line (see first part of the study). U/Pb analysis indicates that the zircons - both in the late mineralization and in the host rock - have absolute radiometric ages clustering around 270 - 280 Ma, which is the accepted age for intrusive rocks from the Austroalpine Dent Blanche units but not for the Tsaté nappe. The latter is classically interpreted as an ophiolitic remnant of the Jurassic Liguro-Piemontais Ocean. U/Pb analyses suggest that zircons in late mineralization are all inherited from the host rock; however, results of (U-Th)/He analyses indicate that cooling ages for the host rocks are different to the cooling ages for the zircons in late mineralization. Indeed, the calculated cooling age for the Arolla gneiss is 25.5 ± 2.0 Ma, whilst the cooling age for the associated mineralized fault plane is 17.7 ±1.4 Ma. Oxygen stable isotope fractionation between quartz and hematite in the same late mineralization corresponds to temperatures of about 170 °C. The proximity of the calculated emplacement temperature for the mineralization and the lower accepted closure temperature for zircon in the (U-Th)/He system (-180 °C) imply that the age of 17.7 ± 1.4 Ma can also be interpreted as the formation age of this late brittle fault.Résumé grand publicLa circulation des fluides dans les roches fracturées est typique de nombreux processus géologiques, et très souvent est la conséquence de la fracturation des roches. Cette thèse aborde la question de la circulation des fluides pendant les dernières phases du soulèvement des Alpes. Après une analyse structurale de la fracturation directement sur le terrain, plusieurs méthodes géochimiques ont été appliquées pour comprendre l'interaction entre les différents fluides circulants, et avec leur propre roche mère. L'étude, concentrée sur trois directions principales, a été conduite dans la zone Pennique du Valais suisse. La première partie traite de la déformation cassante dans le secteur cité. L'analyse détaillée des fractures a permis de les subdiviser en structures minéralisées et non-minéralisées, sur quatre domaines différents. La comparaison entre les directions des structures minéralisées et non-minéralisées a permis de montrer que les premières suivent l'orientation des accidents tectoniques majeurs de la région, alors que les structures non- minéralisées ont une orientation plus variable. Cette différence pourrait être interprétée comme indication d'une dislocation tectonique (structures minéralisées) contre une dislocation gravitaire locale (structures non-minéralisées), mais elle n'est pas assez forte pour indiquer un âge relatif des structures tardives et/ou un changement de l'orientation des contraintes après -20 Ma vers le présent.A partir de ces observations, la deuxième étude est concentrée dans la région de la faille du Simplon. Les analyses géochimiques sur les minéraux remplissant les structures tardives indiquent qu'il y a deux différents systèmes de circulation des fluides dans les deux parties (toit et mur) de la faille. Dans le mur, les valeurs isotopiques des minéraux cristallisés à partir d'un fluide tardif sont les mêmes de ceux de la roche mère, donc il y a eu rééquilibration chimique entre fluide et roche pendant la fracturation de cette dernière et la précipitation des minéraux. Dans le toit, les valeurs isotopiques dans la roche mère et dans les minéraux des veines tardives sont comparables dans les parties Ν et S de la faille, où les roches du toit et du mur ont atteint une température maximale - pendant phase prograde de la formation des Alpes - comparable. Au contraire, dans la partie centrale, où le mur a atteint des températures maximales plus élevées par rapport au toit, les valeurs géochimiques des minéralisations tardives du toit sont parfois plus basses que les valeurs observées dans le mur. Ces données suggèrent que l'infiltration de l'eau de surface aurait pu se produire dans la partie plus fracturée du toit, où le déplacement relatif le long de la faille était majeur et les températures maximales mineures. Au contraire, les données géochimiques du mur de la partie centrale indiquent un système isotopique équilibré par la roche mère.La troisième partie de ce travail se base sur l'étude géochimique intégrée des isotopes stables d'Oxygène et radioactifs du Plomb, Uranium, Thorium et Hélium, auprès d'une faille normale minéralisée et des roches de la région à cheval entre deux nappes, la nappe de la Dent Blanche et la nappe de Tsaté. Ici, des petits zircons ont été trouvés dans la minéralisation citée, riche en hématite et quartz. L'analyse radiométrique Uranium/Plomb a montré que les zircons dans la minéralisation et dans les roches autour ont des âges comparables (autour 280 Ma). Cela signifie que les zircons dans la minéralisation tardive ont été hérités de la roche mère pendant la fracturation et la circulation des fluides tardives. De l'autre coté, les résultats des analyses Uranium-Thorium/Hélium indiquent que les âges de refroidissement pour les roches mères sont différents comparés aux âges de refroidissement pour les zircons dans la minéralisation tardive: ces derniers sont plus jeunes d'environ 8 Ma (autour 25 Ma et autour 17 Ma respectivement). Les analyses des isotopes de l'oxygène sur quartz et hématite dans la même minéralisation donnent une température de mise en place de cette dernière d'environ 170° C. La température de fermeture du système chimique des zircons dans le système (Uranium-Thorium)/Hélium est d'environ 180 °C: la proximité de ces deux températures implique que l'âge de refroidissement de la minéralisation tardive peut également être interprété comme âge de formation de la faille.

Longitudinal Grinding and Transverse Grooving to Improve Frictional and Profile Properties, HR-1035, 1983

There are many miles of portland cement concrete pavement in Iowa that due to normal wear, and in some cases accelerated wear from studded tires, the surface has become polished resulting in less than desirable friction values. Retexturing the surface may be an economical way to re-establish desirable friction values. Retexturing by grinding with diamond blades and transverse grooving with diamond blades are two methods of rehabilitating p.c.c. surfaces. MU Inc. of Lebanan, Tennessee proposed to provide without charge to the Iowa Department of Transportation, one 1500 ft x 12 ft section each of three methods of texturing. They are longitudinal grinding, transverse grooving and longitudinal grinding followed by transverse grooving. A section of 1500 feet is needed to properly evaluate a texturing method. It was decided by Iowa DOT personnel that due to possible differential friction it would be undesirable to texture only one lane. The decision was made to do test sections of 1500 ft x 24 ft with the cost of the additional texturing paid by the Iowa DOT. Iowa also has areas where the p.c.c. pavement has faulted at the joints and cracks which results in poor riding quality. Methods of correcting the faulting are to underseal the pavement where needed and/or grinding the surface to eliminate the faulted areas. It was decided to include in this research project a section for profiling by grinding.

Use of Longitudinal Subdrains in the 3R Program, Progress Report 1, HR-509, 1980

The main consideration for base construction under the pavement, in the design of Iowa's interstate, was structural capacity. The material was dense graded with the aim of supporting the pavement and distributing the load as it is transferred to the underlying grade. The drainage characteristics of the base was apparently not given adequate consideration. On jointed portland cement concrete pavement, the water that is trapped immediately beneath the pavement causes severe problems. The traffic causes rapid movement of the water resulting in the hydraulic pressures or "pumping" (movement and redeposit of base fine material), further resulting in faulting between individual slabs. The objective of this evaluation is to determine if longitudinal subdrains are effective in preventing or reducing pumping, faulting and related deterioration. Results suggest that, based upon the flow from the outlets observed during periodic checks and evidence of water flow at the outlets, it appears that to date the subdrains are effective in draining the subbase and subgrade. Because of the limited data available at this time, however, the pavement condition and faulting results are inconclusive.

Use of Longitudinal Subdrains in the 3R Program, Final Report, HR-509, 1981

Construction of the interstate highway system began in 1956. This U.S. network of highway consists of more than 41,000 miles with 790 miles in Iowa. There have been many benefits of the controlled access roadway, but probably the most significant is the improved safety for the motorist. In Iowa, we have always endeavored to utilize quality locally available materials in our construction using the most economical or cost effective methods. Obviously when the effort is to build a cost effective system, there will be some portions of the network that will not perform as well as expected. In the design of our interstate, the main consideration for base construction under the pavement was structural capacity. The material was dense graded with the aim of supporting the pavement and distributing the load as it is transferred to the underlying grade. The drainage characteristic of the base was apparently not given adequate consideration. On jointed portland cement concrete (pcc) pavement, the water that is trapped immediately beneath the pavement causes severe problems. The traffic causes rapid movement of the water resulting in the hydraulic pressures or "pumping" (movement and redeposit of base fine material) resulting in faulting between individual slabs. Recognizing the need for maintaining this large national highway network, the Federal Highway Administration has initiated a funding program for resurfacing, restoration and rehabilitation (3R). Many miles of the system are more than 20 years old and in need of major maintenance. This new 3R Program necessitated a complete inventory of the Iowa interstate system to establish priorities and to identify those sections in need of immediate remedial treatments.

Pavement Management Performance Modeling: Evaluating the Existing PCI Equations, RB14-013 2014

The work described in this report documents the activities performed for the evaluation, development, and enhancement of the Iowa Department of Transportation (DOT) pavement condition information as part of their pavement management system operation. The study covers all of the Iowa DOT’s interstate and primary National Highway System (NHS) and non-NHS system. A new pavement condition rating system that provides a consistent, unified approach in rating pavements in Iowa is being proposed. The proposed 100-scale system is based on five individual indices derived from specific distress data and pavement properties, and an overall pavement condition index, PCI-2, that combines individual indices using weighting factors. The different indices cover cracking, ride, rutting, faulting, and friction. The Cracking Index is formed by combining cracking data (transverse, longitudinal, wheel-path, and alligator cracking indices). Ride, rutting, and faulting indices utilize the International Roughness Index (IRI), rut depth, and fault height, respectively.

Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials, HR-1069, 2003

Transverse joints are placed in portland cement concrete pavements to control the development of random cracking due to stresses induced by moisture and thermal gradients and restrained slab movement. These joints are strengthened through the use of load transfer devices, typically dowel bars, designed to transfer load across the joint from one pavement slab to the next. Epoxy coated steel bars are the materials of choice at the present time, but have experienced some difficulties with resistance to corrosion from deicing salts. The research project investigated the use of alternative materials, dowel size and spacing to determine the benefits and limitations of each material. In this project two types of fiber composite materials, stainless steel solid dowels and epoxy coated dowels were tested for five years in side by side installation in a portion of U.S. 65 near Des Moines, Iowa, between 1997 and 2002. The work was directed at analyzing the load transfer characteristics of 8-in. vs. 12-in. spacing of the dowels and the alternative dowel materials, fiber composite (1.5- and 1.88-in. diameter) and stainless steel (1.5-in. diameter), compared to typical 1.5-in. diameter epoxy-coated steel dowels placed on 12-in. spacing. Data were collected biannually within each series of joints and variables in terms of load transfer in each lane (outer wheel path), visual distress, joint openings, and faulting in each wheel path. After five years of performance the following observations were made from the data collected. Each of the dowel materials is performing equally in terms of load transfer, joint movement and faulting. Stainless steel dowels are providing load transfer performance equal to or greater than epoxy-coated steel dowels at the end of five years. Fiber reinforced polymer (FRP) dowels of the sizes and materials tested should be spaced no greater than 8 in. apart to achieve comparable performance to epoxy coated dowels. No evidence of deterioration due to road salts was identified on any of the products tested. The relatively high cost of stainless steel solid and FRP dowels was a limitation at the time of this study conclusion. Work is continuing with the subject materials in laboratory studies to determine the proper shape, spacing, chemical composition and testing specification to make the FRP and stainless (clad or solid) dowels a viable alternative joint load transfer material for long lasting portland cement concrete pavements.

Evaluation of Dowel Bar Retrofits for Local Road Pavements, TR-520, 2008

As truck traffic on Iowa secondary roads has increased, engineers have moved to concrete pavements of greater depths. Early designs included thickened edge pavements and depths of seven inches or greater. The designs typically did not have load transfer devices installed in the transverse joints and relied on aggregate interlock for this purpose. In some cases, aggregate interlock was not adequate to deal with the soils and traffic conditions and faulting of the joints has begun to appear. Engineers are now faced with the need to install or retrofit load transfer in the joints to preserve the pavements. Questions associated with this decision range from the type of dowel material to dowel diameter, spacing, number of bars, placement method, and construction techniques to be used to assure reduction or elimination of faulting. Buena Vista County constructed a dowel bar retrofit project on one mile of road. The plan called for addition of the dowels (2, 3, or 4) in the outer wheel path only and surface grinding in lieu of asphalt overlay. The project included the application of elliptical- and round-shaped dowels in a rehabilitation project. Dowel material types included conventional epoxy-coated steel and fiber-reinforced polymer (FRP). This work involved the determination of relative costs in materials to be used in this type of work and performance of FRP and elliptical-shaped steel dowels in the retrofit work. The results indicate good performance from each of the bar configurations and use the results of ride and deflection testing over the research period to project the benefits that can be gained from each configuration vs. the anticipated construction costs. The reader is cautioned that this project could not relate the number of dowels required to the level of anticipated truck traffic for other roads that might be considered.

Field Evaluation of Alternative Load Transfer Device Locations in Low Traffic Volume Pavements, TR-420, 2003

In jointed portland cement concrete pavements, dowel bars are typically used to transfer loads between adjacent slabs. A common practice is for designers to place dowel bars at a certain, consistent spacing such that a sufficient number of dowels are available to effectively transfer anticipated loads. In many cases, however, the standards developed today for new highway construction simply do not reflect the design needs of low traffic volume, rural roads. The objective of this research was to evaluate the impact of the number of dowel bars and dowel location on joint performance and ultimately on pavement performance. For this research, test sections were designed, constructed, and tested in actual field service pavement. Test sections were developed to include areas with load transfer assemblies having three and four dowels in the outer wheel path only, areas with no joint reinforcement whatsoever, and full lane dowel basket assemblies as the control. Two adjacent paving projects provided both rural and urban settings and differing base materials. This report documents the approach to implementing the study and provides discussion and suggestions based on the results of the research. The research results indicate that the use of single three or four dowel basket assemblies in the outer wheel path is acceptable for use in low truck volume roads. In the case of roadways with relatively stiff bases such as asphalt treated or stabilized bases, the use of the three dowel bar pattern in the outside wheel path is expected to provide adequate performance over the design life of the pavement. In the case of untreated or granular bases, the results indicate that the use of the three or four dowel bar basket in both wheel paths provides the best long-term solution to load transfer and faulting measurements.

Événements et déformations tardi-métamorphiques dans le segment Ossola-Ticino (Val Vigezzo-Centovalli, Italie-Suisse)

RESUME: Une zone tectonique large et complexe, connue sous le nom de ligne des Centovalli, traverse le secteur des Alpes Centrales compris entre Domodossola et Locarno. Cette région, formée par le Val Vigezzo et la vallée des Centovalli, constitue la terminaison méridionale du dôme Lepontin et représente une portion de la zone des racines des nappes alpines. Elle fait partie d’une grande et complexe zone de cisaillement, en partie associée à des phénomènes hydrothermaux d’âge alpin (<20 Ma), qui comprend le système tectonique Insubrien et celui du Simplon. Le Val Vigezzo et les Centovalli constituent un vrai carrefour entre les principaux accidents tectoniques des Alpes ainsi qu'une zone de juxtaposition du socle Sudalpin avec la zone des racines de l’Austroalpin et du Pennique. Les phases de déformation et les structures géologiques qui peuvent être étudiées s'étalent sur une période comprise entre environ 35 Ma et l'actuel. L’étude détaillée de terrain a mis en évidence la présence de nombreuses roches et structures de déformation de type ductile et cassant tels que des mylonites, des cataclasites, des pseudotachylites, des kakirites, des failles minéralisées, des gouges de faille et des plis. Sur le terrain on a pu distinguer au moins quatre générations de plis liés aux différentes phases de déformation. Le nombre et la complexité de ces structures indiquent une histoire très compliquée, selon plusieurs étapes distinctes, parfois liées, voire même superposées. Une partie de ces structures de déformation affectent aussi les dépôts sédimentaires d’âge quaternaire, notamment des limons et des sables lacustres. Ces sédiments constituent les restes d'un bassin lacustre attribué à l'époque interglaciaire Riss/Würm (éemien, 67.000-120.000 ans) et ils affleurent dans la partie centrale de la zone étudiée, à l'Est de la plaine de Santa Maria Maggiore. Ces sédiments montrent en leur sein toute une série de structures de déformation tels que des plans de faille inverses, des structures conjuguées de raccourcissement et des véritables plis. Ces failles et ces plis représenteraient les évidences de surface d’une déformation probablement active en époque quaternaire. Une autre formation rocheuse a retenu tout notre attention; il s'agit d'un corps de brèches péridotitiques monogéniques qui affleure en discontinuité le long du versant méridional et le long du fond de la vallée Vigezzo sur environ 20 km. Ces brèches se posent indifféremment sur le socle (unités Finero, Orselina) ou sur les sédiments lacustres. Elles sont traversées par des plans de failles qui développent des véritables stries de faille et des gouges de faille; l’orientation de ces plans est la même que celle affectant les failles à gouges du socle. La genèse de cette brèche est liée à l'altération et au modelage glacier (rock-glaciers) d'une brèche tectonique originelle qui borde la partie externe du Corps de Finero. Les structures de déformation de cette brèche, pareillement à celles des sédiments lacustres, ont été considérées comme les évidences de surface d'une tectonique quaternaire active dans la région. La dernière phase de déformation cassante qui affecte cette région peut donc être considérée comme active en époque quaternaire. Une vue d’ensemble de la région étudiée nous permet de reconnaître à l’échelle régionale une zone de cisaillement complexe orientée E-W, parallèlement à l’axe de la vallée Centovalli-Val Vigezzo. Les données de terrain, indiquent que cette zone de cisaillement débute sous conditions ductiles et évolue en plusieurs étapes jusqu’à des conditions de failles cassantes de surface. La reconstruction de l'évolution géodynamique de la région a permis de définir trois étapes distinctes qui marquent le passage, de ce secteur de socle cristallin, de conditions P-T profondes à des conditions de surface. Dans ce contexte, on a reconnu trois phases principales de déformation à l’échelle régionale qui caractérisent ces trois étapes. La phase la plus ancienne est constituée par des mylonites en faciès amphibolite, associées à des mouvements de cisaillement dextre, qui sont ensuite remplacés par des mylonites en faciès schistes verts et des plis rétrovergentes liés au rétrocharriage des nappes alpines. Une deuxième étape est identifiée par le développement d’une phase hydrothermale liée à un système de failles extensives et décrochantes dextres à direction principale E-W, NE-SW et NW-SE. Leur caractérisation minéralogique a permis la mise en évidence des phases cristallines de néoformation liées à cet événement constituées par : K-feldspath (microcline), chlorites (Fe+Mg), épidotes, prehnite, zéolites (laumontite), sphène, calcite. Dans ce contexte, pour obtenir une meilleure caractérisation de cet événement hydrothermal on a utilisé des géothermomètres sur chlorites, sensible aussi à la pression et a la a(H2O), qui ont donné des valeurs descendantes comprises entre 450-200°C. Les derniers mouvements sont mis en évidence par le développement d’une série de plans majeurs de failles à gouge, qui forment une structure en sigmoïdes d’épaisseur kilométrique reconnaissable à l’échelle de la vallée et caractérisée par des mouvements transpressifs avec une composante décrochante dextre toujours importante. Cette phase de déformation forme un système conjugué de failles avec direction moyenne E-W qui coupent la zone des racines des nappes alpines, la zone du Canavese et le corps ultramafique de Finero. Ce système se déroule de manière subparallèle à l'axe de la vallée le long de plusieurs dizaines de kilomètres. Une analyse complète et détaillée des gouges de faille par XRD a montré que la fraction argileuse (<2 µm) de ces gouges contient une partie de néoformation très importante constituée par, des illites, des chlorites et des interstratifiés de type illite/smectite ou chlorite/smectite. Des datations avec méthode K-Ar sur ces illites ont donné des valeurs comprises entre 12 et 4 Ma qui représentent l'âge de cette dernière déformation cassante. L'application de la méthode de la cristallinité de l'illite (C.I.) a permis d'évaluer les conditions thermiques qui caractérisent le déroulement de cette dernière phase tectonique qui se produit sous conditions de température caractéristiques de l'anchizone et de la diagenèse. L'ensemble des structures de déformation qu'on vient de décrire s'insère parfaitement dans le contexte de convergence oblique entre la plaque adriatique et celle européenne qui à produit l'orogène alpin. On peut considérer les structures tectoniques du Val Vigezzo-Centovalli comme l'expression d'une zone majeure de cisaillement "Simplo-Insubrienne". L'empilement structural et les structures tectoniques affleurantes dans la région sont le résultat de l'interaction entre un régime tectonique transpressif et un régime transtensif. Ces deux champs de tension sont antagonistes entre eux mais sont reliés, de toute façon, à une seule phase décrochante dextre principale, due à une convergence oblique entre deux plaques. À l'échelle de l'évolution géodynamique on peut distinguer différentes étapes au cours desquelles les structures de ces deux régimes tectoniques interagissent en manière différente. En accord avec les données géophysiques et les reconstructions paléodynamiques prises dans la littérature on considère que la ligne Rhône-Simplon-Centovalli représente l'évidence de surface de la suture majeure profonde entre la plaque Adriatique et celle Européenne. Les vitesses de soulèvement qui ont été calculées dans cette étude pour cette région des Alpes donnent une valeur moyenne de 0.8 mm/a qui est tout à fait comparable avec les données proposées par la littérature sur cette zone. La zone Val Vigezzo-Centovalli peut être donc considérée comme un carrefour géologique où se croisent différentes phases tectoniques qui représentent les évidences de surface d'une suture profonde majeure entre deux plaques dans un contexte de collision continentale. ABSTRACT: A wide and complex tectonic zone known as Centovalli line, crosses the Central Alps sector between Domodossola and Locarno. This area, formed by the Vigezzo Valley and Centovalli valley, constitutes the southernmost termination of the Lepontin dome and represents a portion of the alpine nappes root zone. It belongs to a large and complex shear-zone, partly associated with hydrothermal phenomena of alpine age (<20 My), which includes the Insubric Line and the Simplon fault zone. Vigezzo Valley and Centovalli constitute a real crossroads between the mains alpines tectonics lines as well as a zone of juxtaposition of the Southalpine basement with the Austroalpin and Pennique root zone. The deformation phases and the geological structures that can be studied between approximately 35 My and the present. The detailed field study showed the presence of many brittle and ductile deformation structures and fault rocks such as mylonites, cataclasites, pseudotachylites, kakirites, mineralized faults, fault gouges and folds. In the field we could distinguish at least four folds generations related to the various deformation phases. The number and the complexity of these structures indicate a very complicated history, comprising several different stages, that sometimes are related and even superimposed. Part of these deformation structures affect also the sedimentary deposits of quaternary age, in particular the silts and sands lake deposit. These sediments constitute the remainders of a lake basin ascribed to the interglacial Riss/Würm (Eemien, 67.000-120.000 years) and outcroping in the central part of the studied area, in the Eastern part of Santa Maria Maggiore plain. These sediments show a whole series of deformation structures such as inverse fault planes, combined shortening structures and true folds. These faults and folds would represent the surface evidence of a probably active tectonic deformation in quaternary time. Another rock formation attracted all our attention. It is a body of monogenic peridotite breccia which outcrops in discontinuity along the southernmost slope and the bottom of the Vigezzo valley on approximately 20 km. This breccia lies indifferently on the basement (Finero and Orselina units) or on the lake sediments. They are crossed by fault planes which developed slikenside and fault gouges whose orientation is the same of the faults gouges in the alpine basement. This breccia results from the weathering and the surface modelling of an original tectonic breccia which borders the external part of Finero peridotite body. This breccia deformation structures, like those of the lake sediments, were regarded as the surface interaction of active quaternary tectonics in the area. So the last brittle deformation phases which affects this area seems to be actives in quaternary time. Theoverall picture of the studied area on a regional scale enables us to point out a complex shear-zone directed E-W, parallel to the axis of the Centovalli and Vigezzo Valley. The field analysis indicates that this shear-zone began under ductile conditions and evolved in several stages to brittle faulting under surface conditions. The analysis of the geodynamic evolution of the area allows to define three different stages which mark the transition of this alpine basement root zone, from deep P-T conditions to P-T surface conditions. In this context on regional scale three principal deformation phases, which characterize these three stages can be distinguished. The oldest phase consisted of the amphibolitie facies mylonites, associated to dextral strikeslip movements. They are then replaced by green-schists facies mylonites and backfolds related to the backthrusting of the alpines nappes. A second episode is caracterized by the development of an hydrothermal phase bound to an extensive fault and dextral strike-slip fault system, with E-W, NW-SE and SE-NW principal directionsThe principal neoformed mineral phases related to this event are: K-feldspar (microcline), chlorites (Fe+Mg), epidotes prehnite, zéolites (laumontite), sphene and calcite. In this context, to obtain a better characterization of this hydrothermal event, we have used an chlorite geothermometer, sensitive also to the pressure and has the a(H2O), which gave downward values ranging between 450-200°C. The last movements are caracterized by the development of important gouge fault plans, which form a sigmoid structure of kilometric thickness which is recognizable at the valley scale, and is characterized by transpressive movements always with a significant dextral strike-slip component. This deformation phase forms a combined faults system with an average E-W direction, which cuts trough the alpine root zone, the Canavese zone and the Finero ultramafic body. This fault system takes place subparallel to the axis of the valley over several tens of kilometers. A complete and detailed XRD analysis of the gouges fault showed that the clay fraction (<2µm) contains a very significant neo-formation of illite, chlorites and mixed layered clays such as illite/smectite or chlorite/smectite. The K-Ar datings of the illite fraction <2µm gave values ranging between 12 and 4 My and the illite fraction <0.2µm gave more recents values until to 2,4-0 My.This values represent the age of this last brittle deformation. The application of the illite crystallinity method (C.I.) allowed evaluating the thermal conditions which characterize this tectonic phase that occured under temperature conditions of the anchizone and diagenesis. The whole set of deformation structures which we just described, perfectly fit the context of oblique convergence between the Adriatic and the European plate that produced the alpine orogen. We can regard the Vigezzo valley and Centovalli tectonic structures as the expression of a major "Simplo-Insubric" shear-zone. Structural stacking and tectonic structures that outcrop in the studied area, are the result of the interaction between a transpressive and a transtensve tectonic phases. These two tension fields are antagonistic but they are also connected, in any event, with only one principal dextral strike-slip movement, caused by an oblique convergence between two plates. On the geodynamic evolution scale we can distinguish various stages during which these two tectonic structures fields interact in various ways. In agreement with the geophysical data and the paleodynamic recostructions taken in the literature we considers that the Rhone-Simplon-Centovalli line are the surface feature of the major collision between the Adriatique and the European plate at depth. The uplift speeds we calculated in this study for this Alpine area give an average value of 0.8 mm/a, which is in good agreement with the data suggested by the literature on this zone. TheVigezzo Valley and Centovalli zone can therefore be regarded as a geological crossroad where various tectonic phases are superimposed. They represent the evidences of a major and deeper suture between two plates in a continental collision context.

Influencia de la tectónica en la sedimentación continental de la cuenca del Vallés-Penedés (Prov.Barcelona, España) durante el Mioceno inferior.

A very important alluvial fan clastic sedimentation, took place in the NNESSW trending Valles-Penedes graben (northeastem Spain) during Miocene time. Shallow lacustrine and paludine areas developed in distal zones of these alluvial fan complexes during Burdigalian (Early Miocene). At that time both facies development and their distribution were closely controlled by tectonic activity. Fault scarp retreat and back-faulting processes in the southeastem edge of the basin (observed in westem Valles afea), originated an expansive advance of distal alluvial-fan facies in that direction. The decreasing or cessation of the activity of the southeastern margin fault ca~sedi,n Late Burdigalian time (while faults in the northwestern margin were still active) facies redistribution, and gave way to the assymetry of the basin. Finally lacustrine, marine and transitional deposits of late burdigalian and langhian age, were laid down overlapping the southeastem inactive margins.

Structural studies in the Southern Province, South of Sudbury, Ontario

Rocks correlated with the Hough Lake and Quirke Lake Groups of the Huronian Supergroup form part of a northeasterly trending corridor that separates 1750 Ma granitic intrusive rocks of the Chief Lake batholith from the 1850 Ma mafic intrusive rocks of the Sudbury Igneous Complex. This corridor is dissected by two major structural features; the Murray Fault Zone (MFZ) and the Long Lake Fault (LLF). Detailed structural mapping and microstructural analysis indicates that the LLF, which has juxtaposed Huronian rocks of different deformation style and metamorphism grade, was a more significant plane of dislocation than the MFZ. The sense of displacement along the LLF is high angle reverse in which rocks to the southeast have been raised relative to those in the northwest. South of the LLF Huronian rocks underwent ductile defonnation at amphibolite facies conditions. The strain was constrictional, defined by a triaxial strain ellipsoid in which X > Y > z. Calculations of a regional k value were approximately 1.3. Penetrative ductile defonnation resulted in the development of a preferred crystallographic orientation in quartz as well as the elongation of quartz grains to fonn a regional southeast-northwest trending, subvertical lineation. Similar lithologies north of the LLF underwent dominantly brittle deformation under greenschist facies conditions. Deformation north of the LLF is characterized by the thrusting of structural blocks to form angular discordances in bedding orientation which were previously interpreted as folds. Ductile deformation occurred between 1750 and 1238 Ma and is correlated with a regional period of south over north reverse faulting that effected much of the southern Sudbury region. Post dating the reverse faulting event was a period of sedimentation as a conglomerate unit was deposited on vertically bedded Huronian rocks. Rocks in the study area were intruded by both mafic and felsic dykes. The 1238 Ma mafic dykes appear to have been offset during a period of dextral strike slip displacement along the major fault'). Indirect evidence indicates that this event occurred after the thrusting at 950 to 1100 Ma associated with the Grenvillian Orogeny.

Evolution of an Archean greenstone belt in the Stormy Lake - Kawashegamuk Lake area (stratigraphy, structure and geochemistry) - Western Wabigoon Subprovince, Northwest Ontario /

330 km 2 of the easter-n part of the Archean Manitou Lakes - Stormy Lake metavolcanic - metasedimentary belt have been mapped and sampled. A large number of rocks ~.vere analyzed for the major and trace constituents including the rare-earth elements (REE). The Stormy Lake - Kawashegamuk Lake area may be subdivided into four major lithological groups of supracrustal rocks 1) A north-facing mafic assemblage, consisting of pillowed tholeiitic basalts and gabbro sills characterized by flat REE profiles, is exposed in the south part of the map area and belongs to a 8000 m thick homoclinal assemblage outside the map area. Felsic pyroclastic rocks believed to have been issued from a large central vent conformably overlie the tholeiites. 2) A dominantly epiclastic group facing to the north consists of terrestrial deposits interpreted to be an alluvial fan deposit ; a submarine facies is represented by turbiditic sediments. 3) The northeastern part of the study area consists of volcanic rocks belonging to two mafic - felsic cycles facing to the southuest ; andesitic flows with fractionated REE patterns make up a large part of the upper cycle, whereas the lower cycle has a stronger chemical polarity being represented by tholeiitic flows, with flat REE, which a r e succeeded by dacitic and rhyolitic pyroclasti cs. iii 4) A thick monotonous succession of tholeiitic pillmled basalt f lows and gabbro sills with flat REE represent the youngest supracrustal rocks. TIle entire belt underwent folding, faulting and granitic plutonism during a tectono-thermal event around 2700 Ma ago. Rocks exposed in the map area were subjected to regional greenschist facies metamorphism, but higher metamorphic grades are present near late granitic intrusions. Geochemical studies have been useful in 1) distinguishing the various rock units ; 2) relating volcanic and intrusive rocks 3) studying the significance of chemical changes due to post magmatic processes 4) determining the petrogenesis of the major volcanic rock types. In doing so, two major volcanic suites have been recognized : a) a tholeiitic suite, mostly represented by mafic rocks, was derived from partial melting of upper mantle material depleted in Ti, K and the light REE ; b) a calc-alkalic suite which evolved from partial melting of amphibolite in the lower crust. The more differentiated magma types have been produced by a multistage process involving partial melting and fractional crystallization to yield a continuum of compos i t i ons ranging from basaltic andesite to rhyolite. A model for the development of the eastern part of the Manitou Lakes - Stormy Lake belt has been proposed.