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Disintegrated mudstone due to slaking, subjected to hydraulic pressure, could lead to internal erosion. To examine the combined effects of slaking and internal erosion on gravelly mudstone in one dimensional deformation under a constant vertical load, a series of modified oedometer tests and laboratory penetration tests were conducted with drying-wetting and hydraulic pressure cycles. Some loading conditions showed severe erosion along the drying-wetting cycle. Susceptibility to internal erosion was evaluated in terms of nonfilter and filter factor coefficients. Key words: vertical strain, slaking, internal erosion, particle breakage. La desintegration du mudstone due a l'eboulement, soumise a une pression hydraulique, pourrait entrainer une erosion interne. Pour examiner les effets combines de l'ebranlement et de l'erosion interne du mudstone graveleux dans une deformation unidimensionnelle sous une charge verticale constante, une serie d'essais oedometriques modifies et d'essais de penetration en laboratoire ont ete realises avec des cycles de sechage-mouillage et de pression hydraulique. Certaines conditions de chargement ont montre une erosion severe le long du cycle de sechage-mouillage. La susceptibilite a l'erosion interne a ete evaluee en termes de coefficients de facteur non filtrant et filtrant. [Traduit par la Redaction] Mots-cles: deformation verticale, agitation, erosion interne, rupture de particules., Introduction Environmental and economic concerns suggest the possible use of soft sedimentary rocks, with moderate slaking nature, which could be disintegrated by drying-wetting cycles and consequently be influenced by physical [...]

Microwave energy is a promising application in future rock breakage operations in the civil, mining, processing, and space industries. Rock engineering projects frequently experience mechanical vibration and blasting impacts. Thus, understanding the dynamic fracturing behavior of microwave-treated rock is essential for its future application in microwave-assisted mechanical rock breakage. A customized industrial microwave system with a multimode resonant cavity was used to heat red sandstone at different microwave power levels (up to 4 kW) for a constant exposure time (4 min). The rock surface temperature distribution after microwave treatment was measured by an infrared camera. Dynamic splitting tests were conducted using a split Hopkinson pressure bar (SHPB) system in combination with a high-speed camera. Experimental results indicate that the rock dynamic splitting strength is negatively related to the microwave power, and the maximum reduction is 47.8%. Microwave treatment induced an obvious nonuniform temperature distribution and C-shaped surface cracks on disc specimens. During the dynamic splitting test, the crack induced by dynamic loading always initiates from the crack tip induced by microwave irradiation and then propagates along the loading diameter. The distribution of the inner high-temperature zone in the disc specimen is symmetric along the horizontal centerline of the disc specimen. Key words: microwave treatment, dynamic splitting behavior, infrared temperature, rock fracturing, dynamic nominal tensile strength. Le recours a l'energie micro-ondes represente un potentiel prometteur dans les futures operations de bris de roche dans les industries civiles, minieres, de transformation et spatiales. La vibration mecanique et les impacts des explosions sont frequents dans les projets d'ingenierie des roches. Il est donc essentiel de comprendre le comportement dynamique de fracturation de la roche traitee par micro-ondes pour son application future dans les operations de rupture mecanique de la roche assistee par micro-ondes. On a utilise un systeme micro-ondes industriel personnalise equipe d'une cavite resonnante multimode afin de chauffer du gres rouge a differents niveaux de puissance micro-ondes (jusqu'a 4 kW) durant un temps d'exposition constant (4 min). La distribution de la temperature de la surface de la roche apres le traitement par micro-ondes a ete mesuree par une camera infrarouge. Des essais de fendage dynamique ont ete realises a l'aide d'un systeme de barre de pression Hopkinson fendue (SHPB) associe a une camera a grande vitesse. Selon les resultats experimentaux, la limite de fendage dynamique de la roche est negativement liee a la puissance des micro-ondes, et la reduction maximale est de 47,8 %. Le processus de traitement par micro-ondes a provoque une distribution non uniforme de la temperature et des fissures superficielles en forme de C sur les specimens de disques. Pendant l'essai de fendage dynamique, la fissure induite par le chargement dynamique commence toujours a partir de la pointe de la fissure induite par l'irradiation par micro-ondes, puis se propage le long du diametre de chargement. La distribution de la zone interne a haute temperature du specimen de disque est symetrique le long de la ligne centrale horizontale du specimen de disque. [Traduit par la Redaction] Mots-cles: traitement par micro-ondes, comportement dynamique de fendage, temperature infrarouge, fracturation de la roche, resistance nominale dynamique a la traction., 1. Introduction Safe and efficient continuous rock breakage significantly affects the progress of rock engineering projects. As the most commonly used rock breakage technique, drilling and blasting have been widely [...]

The Snow Lake gold camp is located within amphibolite facies volcanic rocks of the ca. 1.88-1.87 Ga Flin Flon--Glennie Complex (FFGC) in the Trans-Hudson Orogen, Manitoba. During thrusting and collision with the Archean Sask craton, volcanic rocks were interleaved with turbidites of the ca. 1.855-1.84 Ga Burntwood Group and sandstone and conglomerate of the ca. 1.845-1.835 Ga Missi Group. The main cleavage in the turbidites was previously attributed to thrusting and used as a marker for correlating structures across the camp. A re-examination of this cleavage suggests that it overprints the thrust faults and formed during later collision between the FFGC and the Archean Superior craton. This has important implications as it further suggests that (1) previously unrecognized, early brittle thrust faults repeat volcanic stratigraphy and may have created the boundary conditions that enabled the formation of ductile thrust faults, fold nappes, and mega sheath folds; (2) shear sense indicators along ductile thrust faults formed during their reactivation as sinistral shear zones rather than during thrusting; and (3) peak metamorphic conditions were caused by thrusting and stacking during collision with the Sask craton but were attained later during collision with the Superior craton due to the time lag between orogenesis and the re-equilibration of regional isotherms. Results from this study may be applicable to other complexly deformed terranes where the dominant regional cleavage differs in expression in mixed volcanic and sedimentary successions and has been used as a marker for correlating structures. Key words: Trans-Hudson Orogen, Snow Lake, New Britannia Mine, Flin Flon Belt, Snow Lake arc assemblage, brittle thrust faults. Le camp aurifère de Snow Lake se trouve dans des roches volcaniques au faciès des amphibolites du complexe de Flin Flon--Glennie (CFFG), d'environ 1,88-1,87 Ga, de l'orogène transhudsonnien, au Manitoba. Durant le chevauchement et la collision avec le craton archéen de Sask, des roches volcaniques ont été intercalées avec des turbidites du Groupe de Burntwood, d'environ 1,855-1,84 Ga, et des grès et conglomérats du Groupe de Missi, d'environ 1,845-1,835 Ga. Le clivage principal dans les turbidites était auparavant attribué au chevauchement et utilisé comme marqueur pour corréler des structures à l'échelle du camp. Le réexamen de ce clivage donne à penser qu'il est superposé sur les failles de chevauchement et s'est formé durant la collision ultérieure du CFFG et du craton archéen du Supérieur. Cette nouvelle interprétation a d'importantes conséquences, puisqu'elle indiquerait que (1) des failles de chevauchement cassantes précoces non reconnues auparavant produisent une répétition de la stratigraphie volcanique et pourraient avoir créer les conditions limites qui ont permis la formation de failles de chevauchement ductiles, de nappes de recouvrement et de plis en fourreau mégascopiques, (2) des indicateurs de sens de cisaillement le long de failles de chevauchement ductiles se sont formés durant la réactivation de ces dernières en tant que zones de cisaillement senestres plutôt que durant le chevauchement et (3) les conditions du pic du métamorphisme ont été causées par le chevauchement et l'empilement durant la collision avec le craton de Sask, mais ont été atteintes plus tard durant la collision avec le craton du Supérieur en raison du décalage entre l'orogenèse et le rééquilibrage des isothermes régionaux. Les résultats de l'étude pourraient être appliqués à d'autres terranes de déformation complexe dans lesquels le clivage régional dominant s'exprime différemment dans des séquences volcaniques et sédimentaires mixtes et a été utilisé comme marqueur pour la corrélation de structures. [Traduit par la Rédaction] Mots-clés : orogène transhudsonnien, Snow Lake, mine New Britannia, ceinture de Flin Flon, assemblage d'arc de Snow Lake, failles de chevauchement cassantes., Introduction The Snow Lake gold camp contains one of the largest gold mines in the Paleoproterozoic Trans-Hudson Orogen. The New Britannia Mine in the town of Snow Lake, Manitoba, produced [...]

Crustal deformation along the present-day northern margin of the Tibetan Plateau has occurred since mid to late Eocene time, soon after India collided with Eurasia. Assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet, we show that far-field lithospheric deformation caused by an indenting boundary is expected to start shortly after collision begins. When a strong region analogous to cratonic lithosphere like that of the Tarim Basin is included in the calculations, shear and vertical strain rates concentrate along the southern edge of the strong region, resulting in enhanced deformation there. In calculations scaled to the dimensions of India and the Tibetan Plateau, shear and vertical strain rates on the northern edge of the plateau increase soon after collision begins. Crustal thickening accelerates later in the calculations. We propose that the apparent increased exhumation (and perhaps surface uplift) around 10 Ma may signal the arrival of the thickening front. Citation: Dayem, K. E., P. Molnar, M. K. Clark, and G. A. Houseman (2009), Far-field lithospheric deformation in Tibet during continental collision, Tectonics, 28, TC6005, doi: 10.1029/2008TC002344.

The origin of the Porma Melange, a unit up to 1 kilometer thick underlying the Forcada Nappe in the Iberian Peninsula, is discussed and the shape, attitude, internal structure of the blocks, and the block-matrix relationships are described. The arrangement of major submarine nappe fragments does not agree with the geometric rules of thrusting, and are reinterpreted as megablocks resulting from gravitational sliding during denudation of advancing nappes.

Neogene nonmarine strata in the southernmost part of the Precordillera thrust belt of the Andes of Argentina accumulated during the Miocene and Pliocene in response to eastward advance of thrust sheets located to the west. To link the sequence of deformational events with the sedimentary record, five stratigraphic sections in the Mendoza Province were dated using magnetic polarity stratigraphy calibrated with (super 40)Ar-(super 39) dates from interbedded tephras. These data establish age control on tectonic activity, volcanism, and deposition. The existence of a backarc foreland basin that developed prior to or ca. 16 Ma is recorded by the oldest strata, the ca. 15.7-12.2 Ma (Baksi time scale) Marino Formation. Deposition of this unit is linked to a major phase of thrust activity in the central part of the Aconcagua fold-and-thrust belt, in the Principal Cordillera. Initiation of deposition coincides with an eastward shift of the subduction-related magmatic foci to the Argentine Principal Cordillera. The overlying ca. 11.7-9.0 Ma La Pilona Formation is thought to record the initiation of exhumation of the Frontal Cordillera to the northwest of the study region. An extensive ash-rich unit, the 8.9 (locally 9.5?) to 8.7 Ma Tobas Angostura Formation, is correlated with the latest and probably the largest extrusive episode in the Principal Cordillera. Chronologic data constrain the timing of oil generation in the Cuyo basin and development of prospective closures. The new data also require that land mammalian fossils found in the Rio de los Pozos Formation are late Miocene, rather than Pliocene, as previously believed. Keywords: Andes, Ar/Ar, Argentina, magnetostratigraphy, Miocene, Precordillera.

Gravitational body forces (i.e., buoyancy forces) have come to be seen as critical to the evolution of orogens. Nevertheless, constraining the role of body forces in specific geologic scenarios is made difficult by the substantial number of poorly constrained physical parameters needed to fully relate forces to deformation. By separating the calculation of buoyancy forces from the calculation of the resulting deformation, models based on relatively simple descriptions of the lithosphere can yield geologically useful constraints. Among these are the importance of paleoelevation in driving syn- and postcontractional extension and in localizing contractional strain. Although such phenomena have been considered in more complex models of continental deformation, the simpler analysis presented here clearly establishes first-order limits on lithospheric structures and paleoelevations consistent with buoyancy-driven deformation. In the early Cenozoic Great Basin of the western United States, we show that the low elevations inferred in much of the geologic literature are inconsistent with a body-force origin for observed extensional tectonism. East of the Colorado Plateau, localization of Laramide deformation coincides with pre-Laramide subsidence of the Western Interior seaway. This subsidence prestressed the lithosphere, making the Southern Rocky Mountains the weak link in responding to regional compressional stress.

Results of experimental and theoretical studies of the micromechanical behavior of marble under compression are presented. A cylindrical marble specimen was submerged in a molten metal alloy under compression and the alloy was driven into voids and fractures by pore pressure. The alloy was solidified at a certain stage of the experiment in order to preserve the geometry of microcracks as they existed under load and to distinguish these cracks from those generated during sample polishing. With a surface tension of 400 mN/m, the alloy could penetrate into flat cracks with apertures as fine as 0.08 [[micro]meter] under a pore pressure of 10.3 MPa (1,500 psi). This technique also facilitated observation of the microcracks in three dimensions. A comprehensive image analysis was performed on the cracking pattern developed in the marble samples. The propagation of the cracking process was modeled using nonlinear discontinuous deformation analysis (DDA) with a finite-element meshed block system.

The leading edge of the North American plate along the Cascadia subduction zone is deforming and rotating clockwise as a consequence of both underthrusting of the Gorda-Juan de Fuca plate and collision of the North American plate with the Pacific plate. The details of late Quaternary ([less than or equal to]125 ka) upper-plate deformation resulting from these plate interactions are largely obscured because the most recent deformation overprints earlier deformation in the Tertiary rocks of the Coast Range. However, by mapping uplifted wave-cut platforms formed during times of high sea level in the past [approximately equal to]500 000 yr, we identify faults and folds active in the late Quaternary in central coastal Oregon. Through along-coast correlation of these platforms using elevation and soil development, we infer that several major faults have vertically offset platforms at rates as high as 0.6 m/k.y. for the past 125 k.y. We regionally extend our analysis by incorporating all known faults and folds in southern and central coastal Oregon that deform wave-cut platforms. Most platforms along the southern and central Oregon coast have been uplifted at rates of 0.1-0.3 m/k.y. since the late Pleistocene; however, platform uplift rates approach 1 m/k.y. in the vicinity of faults. The trend and distribution of these upper-plate coastal faults are consistent with their interpreted role as left-lateral, strike-slip, block-bounding structures accommodating clockwise rotation. We speculate that these upper-plate faults have a component of dip slip because of their association, in many instances, with localized uplift. If these faults bound rotating blocks, the dip-slip component of displacement may be either contractional or extensional, depending on the orientation of the fault relative to the north-south trend of the plate margin.

Combined sedimentological, structural, and geochemical studies of a lower Paleozoic succession within the Pensacola Mountains, Antarctica, suggest that it probably formed in a foreland basin setting during the Ross-Delamerian orogen, a complex early Paleozoic convergent margin of Antarctica and Australia. The lower Paleozoic succession lies unconformably on a deformed(?) Neoproterozoic sequence (referred to here as Sequence 1) and is divided into three unconformity-bounded sequences (Sequences 2-4). The oldest sequence, Sequence 2, comprises Middle-Upper Cambrian platformal limestone (Nelson Limestone) and overlying Lower Ordovician silicic volcanic rocks of the Gambacorta Formation (U-Pb zircon age of 501 [+ or -] 3 Ma). The volcanic rocks crystallized from a high-temperature anhydrous magma derived from a lower crustal igneous source and may represent magmatism on the inboard side of a magmatic arc now largely absent from this part of the margin. Sequence 3 (Wiens Formation), in part conformable with Sequence 2, represents deposition by unconfined ephemeral streams followed by a marine transgressive unit. The base of Sequence 4 (Neptune Group) is a major erosion surface marked by karstification of the exposed Nelson Limestone and by calcrete pedogenesis. The Neptune Group is an alluvial fan complex typical of many syn- and post-orogenic red beds. The predominance of nonmarine and shallow marine sequences, and the facies and paleocurrent directions within the basin, suggest that it may be more typical of a 'piggyback' basin than of a foredeep basin, with the alluvial fan complexes derived from advancing thrust sheets. Growth folds, progressive unconformities, and deformed clasts of underlying strata within basal conglomerates are consistent with active deformation during sedimentation and the proposed tectonic setting. The presence of variably plunging folds, some of which are transected by a slaty cleavage, suggests that deformation was in an oblique-slip setting perhaps due to oblique convergence along this part of the Antarctic margin during the Ross-Delamerian orogeny.

The deformations in the Alleghanian roof sequence of the central Appalachians in Maryland, Virginia, and West Virginia are due to micro- and outcrop- scale structures rather than macroscale thrusts. Macroscale thrusts are not widespread in the roof sequence. The hangingwall ramp of the North Mountain thrust sheet may have moved up the North Mountain thrust rather than into the foreland beneath the roof sequence.

Deformation patterns in the Victoria Land and the Ross Sea are different from the large-magnitude crustal stretching within the West Antarctic rift system during the Cenozoic, and the patterns can be explained by a transtensional model. The crustal thinning probably took place in the Mesozoic during the block motions of major crusts of West Antarctic. The Cenozoic deformation can be explained with plate interaction due to global Eocene plate reorganization before the separation of Antarctica and southern Australia.

Structural analysis using argon isotopes on shear zones in the Flin Flon area in Canada indicate five stages of development. The collision between the Archean Rae-Hearne and Archean Superior plates during the Trans-Hudson Orogeny resulted in deformations. The geodynamic evolution involved a transformation from island arc supracrustal development to tectonic mountain building under brittle-ductile conditions, and the metamorphosis took place in three stages.

A study of the North West Mayo Inlier in Ireland, with elongation along the east to northeast direction, through structural mapping indicates pre-Caledonian folds and deformations directed west to northwest. The mafic dykes are deformed due to the disturbance of existing structures to shear zones. A major portion of the inlier constitutes flat-lying zones, which are D2 in age. A crustal scale ramp zone contains the D2 folding, the deformation of the ramp leading to F1 folds.

Palaeomagnetic studies of the rotations in Late Ordovician dolerites of the northern Welsh Basin and of Lower Palaezoic inliers of Eastern Avalonia indicate that the Breidden Hills Inlier has the maximum rotation. Local rotations about a bend in the Severn Valley Fault System cause fractures between the Breidden Hills Inlier and the neighboring Shelve Inlier and rotation of Late Ordovician fold axes. There is a rapid movement of the Avalonian Plate toward southern palaeolatitudes, as revealed by studies on Upper Ordovician.

U-Pb dating of zircons from the Croghan Kinshelagh alkali granite in southeast Ireland suggests a mid-Caradoc emplacement age of 454 plus or minus 1 Ma. Age and geochemical data of granite and volcanic rocks indicate that they are the products of major Ordovician magnetic episode which generated the Avoca Volcanic Belt and other Ordovician volcanoes in eastern Ireland. The closure of the Iapetus Ocean or events of local origin are responsible for the intra-Ordovician deformation in the volcanic rocks and sediments.

Numerical and geological measurements support a model explaining the deformation arrangement of lithospheric plates, which follow the collision of India and Asia and the submergence of Asian lithospheric mantle within the Tibetan plateau. The collision does not lead to deformation of lithospheric mantle along with the crust, but results in mantle subduction, expressed through lithospheric union. The continental collision zones are similar to oceanic subduction zones.

U/Pb and Ar/Ar isotopic age data from the Corner Brook Lake region of the eastern Appalachian Humber zone in western Newfoundland indicate that regional deformation and peak amphibolite-facies metamorphism are Early Silurian. A lower limit on deformation is provided by a U/Pb zircon age of 434 +2/-3 Ma for a pegmatite that is affected by the regional foliation and is interpreted to be syntectonic. Monazite and rutile from a garnet-kyanite-staurolite schist, which records peak-metamorphic conditions and in which porphyroblasts have overgrown the regional foliation, gave U/Pb ages of 430 + or - 2 Ma and 437 + or - 6 Ma, respectively. Ar/Ar cooling ages for hornblende from amphibolites and muscovite from psammitic and pelitic schists range from 430 to 420 Ma. A Silurian age for deformation and metamorphism of the Laurentian margin is coincident with the timing of similar events along the Newfoundland Gondwana margin and suggests that the Silurian was a period of major continent-continent collision.

Abstract: The LeMay Group of Alexander Island, Antarctica, is a Mesozoic accretionary prism that contains slivers of ocean floor and ocean island material, accreted underka range of conditions and depths. It provides a rare opportunity to compare the deformation mechanism paths between oceanic andktrench-fill lithologies duriol subduction and accretion by offscrapiol or underplatiol. Ocean floor slivers consist of a bedded basalt--volcaniclastite--chert rock association, overlain by trench-fill sedimentary rocks. The oceanic lithologies initially deformed by cataclasis, combined with particulat, flow in the volcaniclastic rocks. At shallow levels the clastic trench-fill sedimentary rocks deformed by independent particulat, flow, which changed to cataclastic flow at depth. Atkthos, depths crystal plasticity affected the cherts and jaspers. Atkthe deepest levels achieved in ts, subduction zooe, crystal plasticity was the domioant deformation mechanism in ts, clastic sedimentary rocks, whilst cataclasis continued in ts, lavas. Deformation was synchronous with metamorphism up to transitional greenschist--blueschist faci,s. All lithologies w,re affected by pressureksolution after accretion, with tse formation of a bedding-parallel or sub-parallel cleavage. Ts, deformation mechanism paths indicate thatk(1)kthere is a crystal plastic deformation field atkdeep levels in tse subduction zone, and (2) thatkthe base of the pressureksolution field is concordant with tse decollement. A frontally accreted ocean island is exposed in ts, Lully Foothills, and consists of a basalt--volcaniclastite--tuff rock association. Deformation is represented only by a patchily distributed bedding-sub-parallel pressureksolution cleavage in the tuffs and volcaniclastites, and is probably related to loadiol. Metamorphism doesknot exceed prehnite--pumpellyite faci,s. Ts, accreted ocean island indicates tsatksuch features can be incorporated into accretionary prisms atkshallow levels withoutksignificant segmentation.

Geologically calculated convergence rates in the Ventura basin are high by a factor of two when compared to the geodetic convergence rate measurements done using the global positioning system. Two theories for convergence rates state that the difference is either due to incorrect geologic dates or due to a stable fault dip angle into the lower crust instead of flattening. Rotation and strain components cause crustal deformation in the Ventura basin.

Dome-stage or backfold-deformation resulted in the formation of several structural features of the small-scale Acadian. Two stages of shearing existed in the Bronson Hill anticlinorium and the eastern side of the Monson Gneiss. Peak metamorphism preceded late-stage deformation during Acadian orogeny. There was a shift into orogen-parallel extension during this deformation. There may be a variation in the orientation of the direction of maximum extension at the backfold-stage uplift, from near vertical to near parallel and horizontal to the orogen at the stage of dome-formation.

The Irian Jaya Mobile Belt (IJMB), Indonesia, experienced a structural evolution initiated by Late Oligocene Collision between Australia and the Sepik ArC, over a duration of 30 m.y. The edge of the Australian continent harbors allochthonous metamorphic rocks, distal passive margins and ophiolites since the collision extended till the middle Miocene times. Deformation in IJMB is due to the combined effect of basement-involved thrusting and East-West sinistral wrenching. Northern IJ is being underthrust by the Pacific Plate, as revealed by seismicity and geological analysis.

The Sierra Espuna in the Betic Cordillera in southern Spain was compressively deformed, and this continued till the Miocene times. The deformation reveals kinematics that correspond with those that were observed between the Eocene and the initial period of Miocene. The Sierra Espuna's kinematics reveal that it was the center point of oblique convergence between early and middle Miocene periods. There was late Eocene thrusting from the Southeast to the South in the Sierra Espuna, as revealed by paleomagnetic data.

The structures of two areas, one in the Northern Belt and one in the Central Belt of the Southern Uplands are described and compared. The main structural histories are the same, both show a main deformation phase related to SE-directed thrusting with associated fold and cleavage formation. Both areas exhibit late, minor NW-directed thrusting with related refolding and crenulation cleavage development in the case of the Central Belt. Both areas also show evidence of sinistral strike-slip or transpressive deformation which reactivates steepened thrust faults. When these deformation histories are reviewed in the context of geophysical, radiometric and biostratigraphical data from the region a forearc accretionary setting for the whole of the Southern Uplands appears the most likely. The strike-slip deformation has internally disrupted an accretionary prism but has not juxtaposed originally unrelated terranes. The effects of the late Silurian closure of Iapetus and subsequent events are also represented in the Southern Uplands.

Fracture patterns in some of the clasts of the Gowganda Formation, Ontario, are inconsistent with aqueous deposition and suggest that locally the diamictites are tillites. Similar fracture patterns have been found in the clasts of modern tills in the Cascade Mountains. Rare examples were also seen on the Garvellachs, Scotland. Laboratory experiments indicate that such patterns can be developed by the impaction of one clast against another while surrounded by a compliant matrix. The stresses which induced cracking were of the same order of magnitude as those which can be expected to occur in a sub-glacial environment.

The Kurusuno formation in Western Shikoku, Southwest Japan, is part of the late Eocene to early Oligocene Shimanto Belt. Structural analysis shows that the formation was developed by transverse currents which generated trench fan deposition. The duplex nature of the formation was created by underthrust and underplate thick trench sedimentation. Younger trench fill sediments which underplated below previously accreted material conditioned uplift formation.

Map-, outcrop-, and microstructural-scale examination of the footwall of the Willard thrust sheet in the Sevier fold-and-thrust belt, northern Utah, reveals deformation of footwall rocks before or during emplacement of the Willard thrust sheet. The Willard thrust sheet contains Proterozoic metasedimentary rocks in its hanging wall and has a footwall lateral ramp that cuts up section southward. In the northern part of the study area, Cambrian Maxfield and Ophir Formations were pervasively ductilely deformed at all scales. There, east-and northeast-vergent recumbent isoclinal folds with well-developed axial-planar cleavage, kink folds, small shear zones, and solution cleavage are developed in a 100- to 200-m-thick zone of footwall deformation. Calcite deformed by dynamic recrystallization and diffusive mass transfer; rare twinned dolomite crystals deformed by intracrystalline glide. In the central part of the study area, the Cambrian Maxfield, Ophir, and Nounan Formations are complexly folded and faulted below the Willard thrust. Plastic deformation is largely restricted to a 5- to 10-m-thick limestone mylonite in the Maxfield Formation, with cataclastic deformation predominant below the mylonite. Axes of map-scale folds are nearly parallel with the Willard thrust, and a small thrust appears to be cut by the Willard thrust. Southward, the thrust climbs section in its footwall to Devonian and Mississippian strata, and deformation in the footwall is predominantly brittle, superimposed on locally developed ductile structures. The change from pervasive plastic to brittle deformation and accompanying change in structural style of footwall rocks occurs in the Cambrian Ophir and Maxfield Formations. The lateral changes of footwall deformation may be due to (1) lateral variations of footwall rock rheology and thus a variation in bulk strain of the rocks; (2) different temperature or confining or fluid pressure conditions along strike, perhaps due to a pre-existing footwall high; or (3) lateral variations in stress and strain conditions in the footwall. Whatever the cause, the data show that significant amounts of deformation occurred in the footwall of the Willard thrust before and(or) during motion along the thrust.

Byline: C.E. Anastasiadis, I.D. Stavrakas, D.A. Triantis, A.D. Kyriazopoulos, K.D. Ninos In addition to existing non-destructive testing methods a novel technique is presented here. It is based on Dielectric Spectroscopy (DS) methodology for the verification of mechanical damages in geomaterial structures. Such techniques do not influence the material structure or properties, thus it can be re-examined with various methods. In this work damages are introduced in a geomaterial by uniaxial stress isothermally. The damage caused to marble samples and its influences on the dielectric loss angle were examined relative to stress. Results indicate that when stress produces microcracks then tan I[acute accent] increases and a loss peak appears in the studied frequency range.

To investigate neotectonism in the Mississippi Embayment east of the New Madrid seismic zone, we identified geomorphic domains that show evidence of ground tilting during Quaternary time. Transverse basin profiles were converted to two-dimensional vectors that denote channel position with respect to basin divides. These basin-asymmetry vectors record the net direction and degree of lateral migration of trunk streams. More than 2500 vectors were measured and spatially averaged within 400 [km.sup.2] bins. This field of 300 mean vectors delineates several domains that show preferred directions of stream migrations possibly driven by ground tilting. The timing of stream migration was interpreted using across-valley distributions of Quaternary alluvial terraces. Comparison of our mean vector field with subsurface structures suggests that some domain boundaries may be related to reactivated faults. Late Quaternary activity is suggested for two northeast-striking faults of the southeastern Reelfoot Rift margin. We acquired two seismic profiles showing near-surface faulting beneath scarps that follow the domain boundary associated with one of these northeast-striking faults (Big Creek fault zone). Reelfoot thrust seismicity ends on the south against this fault, suggesting that the rift margin has dextral slip accommodating northeastward movement of the thrust hanging wall. Our vector field also suggests late Quaternary movement on the Reelfoot thrust and on two other northwest-striking faults, here termed the Hatchie River fault and the Wolf River fault. Several other weak domains may imply minor elements of neotectonism. Our results demonstrate that morphometric analysis of drainage-basin asymmetry can be an effective reconnaissance tool within neotectonic settings. Keywords: drainage basins, geomorphology, Mississippi Embayment, neotectonics, Quaternary.

The Rocky Mountains, Colorado Plateau, and Midcontinent, regions of the North American cratonic platform, display similar styles and patterns of Phanerozoic deformation. In these regions, movement on basement-penetrating faults during the late Paleozoic Ancestral Rockies event and/or during the Mesozoic-Cenozoic Laramide event generated flat-topped uplifts bordered by outward-verging, monoclinal forced folds. We suggest that these structures, divided into two sets on the basis of orientation (west to northwest and north to northeast), formed by inversion of Proterozoic extensional-fault systems. In this model, Proterozoic rifting events formed weak faults in the cratonic platform crust, and these faults were reactivated by stress transmitted during Phanerozoic compressional orogenies. If this model is correct, the pattern of Ancestral Rockies and Laramide contractional structures reflects the trends of Proterozoic extensional faults, and regional variation in forced-fold vergence reflects the control of antecedent fault dips on fault-propagation fold geometry during inversion. Late Proterozoic rifts formed throughout Rodinia, so inversion tectonics likely occurred in cratonic platforms worldwide. Keywords: Laramide, Ancestral Rockies, inversion tectonics, Colorado Plateau, Proterozoic rifting, Rocky Mountains, intracratonic deformation, Midcontinent, fault-propagation folding.

Three multichannel seismic profiles imaged a normal fault to at least 10 km depth in the North Aegean Trough and Thermaikos basin. The fault is active and recent, forming a scarp at sea bottom and crossing the Quaternary deltaic front on the northern slope of the trough controlled to the south by the North Anatolian fault. Prestack depth migration imaged the fault as a seismic reflector cutting steeply across the sedimentary rocks and flattening in the basement. From the seismic image, the N100 [degrees] E strike of the fault scarp, and the orientations of the three profiles, the true fault dip is constrained to an average 20 [degrees] in the basement, a low-angle dip. The throw and age estimated from the geometry in the sedimentary rocks document recent onset of the motion that must have occurred at a high rate. Both the direction and the rate of slip are consistent with the instantaneous motion as measured by space-based geodesy, which shows the fault to be forming by pure normal slip. Large earthquakes that have occurred in the basin may relate to such normal faults, whereas the North Anatolian fault with its current strike-slip earthquakes appears to slip here under low resolved shear stress. Keywords: North Aegean basin, reflection seismic imaging, normal fault, active crustal extension, earthquakes.

Reports of shock-deformed phenocrysts from the Toba ignimbrite deposits, Sumatra, have prompted considerable debate over whether shock-deformation products are clear evidence of a meteorite impact origin for the Cretaceous/Tertiary (K/T) boundary deposits as well as terrestrial 'cryptoexplosion' structures. Evidence presented in favor of volcanically induced shock at Toba includes kinked biotites and rare occurrences of single sets of lamellae in quartz grains but rests most heavily upon occurrences of mosaic extinction patterns in plagioclase phenocrysts. Our analysis of several of the same Toba samples reveals that these mosaic patterns are related to distinct compositional zoning and cannot be attributed to deformation of the crystal lattice that shock would produce. Additionally, in more than 200 quartz grains examined, we detected no occurrences of microdeformation features or mosaic textures similar to those associated with known impact structures and the K/T boundary. We conclude that evidence of shock deformation in the Toba deposits has not been demonstrated.

Vitrinite in coal is optically anisotropic in reflected light, owing to a preferred orientation of its component molecular structure. Such reflectance fabrics can, under some circumstances, provide a record of stress and strain events occurring during coal metamorphism. Based upon observed differences in the orientation and shape of vitrinite reflectance indicatrices (VRIs), differing tectonic histories are suggested for three regions within the bituminous and anthracite coal fields of the northern Appalachian (coal) basin, Pennsylvania. VRIs of coals from the North-Central fields on the Allegheny Plateau have oblate geometries similar to those of most coals worldwide, indicative of only mild tectonic deformation. Maximum reflectance orientations for North-Central field coals are polymodal and aligned with polymodal Alleghanian fold axes. Low-volatile bituminous coals from the Broad Top field, south-central Pennsylvania, exhibit much stronger tectonic reflectance fabrics and bear evidence that low-volatile bituminous rank was attained only after folding was completed in this part of the fold-and-thrust belt. VRIs of coals from the Western Middle anthracite field reflect a more complex tectonic history and indicate that most coalification here preceded the final phase of Alleghanian folding. VRIs of coals from an underground mine in the Western Middle anthracite field provide additional details on strain directions and timing of coalification. Coal rank increases very slightly down section, but [R.sub.min] decreases down section, opposite to the expected trend. These coals probably attained anthracite rank prior to the principal phase of Alleghanian folding, but at least some coalification continued after folding, as suggested by reconstructed coalification pathways on the axial ratio diagram. During this final coalification phase, the stratigraphically upper beds 'caught up' in rank with the stratigraphically lower beds through elongation of [R.sub.max] parallel to the fold axes and elongation of [R.sub.min] in a subvertical direction. VRIs of the stratigraphically upper beds were transformed to a prolate geometry, whereas those of the lower beds retained their original oblate form.