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Regionally recognized dextral strike-slip faulting is present in the Monashee complex of the southern Canadian Cordillera but is overprinted and partially obscured by subsequent extension. Eocene brittle faults and fractures within the Thor–Odin culmination of the Monashee complex are divisible into three distinct sets. Initial 340°–010° trending strike-slip faults (set 1) were locally overprinted and reactivated by normal faults with a 325°–020° trend (set 2). A third set of 255°–275° trending fractures (set 3) are interpreted as conjugates to set 1, reactivated as transfer faults to the set 2 normal faults. Large regional faults weather recessively, forming topographic lineaments that transect the Monashee complex. The Victor Creek Fault defines one such lineament. Detailed mapping within the northern Thor–Odin culmination reveals piercement points (fold hinges) on the east side of the fault that are not readily matched on the west side. The minimum displacement required on the Victor Creek Fault to down-drop the fold hinge below the level of exposure on the west side is 1370 m, assuming normal down-to-the-west displacement. The geometry of the fault is consistent with a set 1 dextral strike-slip fault, however. Matching the piercement points in the study area with possible equivalents to the north indicates 55–60 km of dextral strike-slip displacement.

The newly named Three Valley Suite (TVS) kersantite lamprophyre to shoshonitic mafic dykes of the Monashee Complex are inferred to be hypabyssal feeder dykes to an alkaline to calc-alkaline volcanic suite related to the Kamloops Group. These dykes were emplaced in a subvertical north-trending orientation coincident with inferred Eocene crustal extension (~50.0 Ma), based on the flat 40Ar/39Ar step-heating plateau of contact-metamorphic muscovite on the margin of a TVS dyke. These weakly altered mafic dykes are fine grained with phenocrysts (0.5–2.0 mm) of phlogopite, augite, amphibole, and olivine (pseudomorphed by clays), rare labradorite, and both primary and secondary carbonates set in a fine-grained groundmass of similar mineralogy consistent with their classification as plagioclase-bearing potassic diorite to kersantite lamprophyre. The dykes are weakly silica-undersaturated and alkalic (2.8 wt.% K2O, 7.7 wt.% MgO), with high large ion lithophile element contents (~300 times primitive mantle) and elevated high-field-strength element contents, with a prominent negative Nb (Ta) anomaly, and have radiogenic Nd and Sr isotopic signatures; these geochemical attributes are consistent with a calc-alkaline shoshonitic affinity. Therefore, it is inferred that the subducting oceanic plate influenced subcrustal mantle wedge metasomatism in the region. Decompression partial melting of this metasomatised lithospheric mantle was initiated by coupled rapid unroofing, regional trans pression, slab rollback, and slab window development to the south. The TVS is similar to the mafic volcanic rocks within the nearby Eocene volcanic rocks, suggesting that these dykes represent the feeder system to a volcanic field that is now eroded, i.e., a broad-terrane association.

The Snow Lake Allochthon is a zone of tectonic interleaving of sedimentary rocks of an inverted marginal basin (Kisseynew Domain) with island-arc and oceanic rocks. It is located in the southeastern part of the exposed internal zone of the Paleoproterozoic Trans-Hudson Orogen in Manitoba, Canada, near the external zone (Superior collision zone or Thompson Belt), which constitutes the local boundary between the Trans-Hudson Orogen and the Archean Superior Craton. The Snow Lake Allochthon formed, was deformed, and was metamorphosed up to high grade at low to medium pressure during the Hudsonian orogeny as a result of the collision of Archean cratons ~1.84-1.77 Ga. Four generations of folds (F1-F4) that formed in at least three successive kinematic frames over a period of more than 30 Ma are described. Isoclinal to transposed southerly verging F1-2 structures are refolded by large, open to tight F3 folds and, locally, by open to tight F4 folds. The axes of the F1-2 folds are parallel or near parallel to the axes of F3 folds, owing to progressive reorientation of the F1-2 axes during south- to southwest-directed tectonic transport, followed by F3 refolding around the previous linear anisotropy. A tectonic model is presented that reconciles the distinct tectono-metamorphic developments in the Snow Lake Allochthon and the adjacent part of the Kisseynew Domain on the one hand, and in the Thompson Belt on the other, during final collision of the Trans-Hudson Orogen with the Superior Craton.

The Teslin zone in south-central Yukon has previously been described as a discrete zone with a steep foliation unique to the zone. It includes the Anvil assemblage and the narrowest portion of the Yukon-Tanana terrane (the Nisutlin assemblage), and is defined by post-accretionary faults: the Big Salmon fault to the west and the d'Abbadie fault system to the east. The zone was interpreted as a lithospheric suture or a crustal-scale transpression zone, and as the root zone of klippen lying on the North American craton to the east. We demonstrate that deformation and metamorphism are the same inside and outside the zone. The steep transposition foliation in the zone, in contrast to adjacent rocks to the east, coincides with the steep limb of a regional F3 structure. This fold has a shallow limb in the easternmost part of the zone and immediately east of the zone. Thus we reject earlier interpretations. If a suture exists between the obducted Anvil and Yukon-Tanana Nisutlin assemblages and North America, it is a shear zone that occurs at the base of the obducted rocks, which has been folded by the F3 fold. However, evidence that this thrust boundary is a lithospheric suture is lacking. A consequence of our interpretation is that North American rocks pass under the eastern Teslin zone and outcrop to the west of the Nisutlin and Anvil assemblages. This geometry precludes the possibility of the Teslin zone being the root zone of the klippen.

The Humber Zone of the western Newfoundland Appalachians represents the early Paleozoic Laurentian margin established by Neoproterozoic rifting. After a period of passive margin thermal subsidence, Taconian deformation began in the Early Ordovician with westward thrusting. Subsequently, an extensive foreland basin developed beneath the Gulf of St. Lawrence. It records rapid Late Ordovician to Early Silurian subsidence; mid-Silurian erosion; and renewed Late Silurian to Devonian subsidence. The Humber Zone was traversed by Lithoprobe seismic reflection profiles. Within the external part of the orogen, seismic reflections in the upper crustal section appear more coherent where seismic lines are parallel to fold hinges. Some subhorizontal reflectors are interpreted as thrust sheets of shelf limestone, but others probably represent intrabasement structures. A group of moderately northwest-dipping reflections probably represents late extensional shear zones. On the Baie Verte Peninsula, low-angle reflections passing beneath the Baie Verte Line are probably also late extensional shears, possibly reactivating earlier thrusts. Tectonism in the Humber Zone probably began with attempted eastward subduction of the Laurentian margin. Deep burial of the margin, accompanied by eclogite-facies metamorphism, probably coincided with rapid subsidence in the foreland basin. Later Barrovian metamorphism was associated with cleavage development and east-directed shear, and with dextral oblique slip, in Baie Verte Peninsula. Later Silurian sinistral transpression with thrusting east of the Baie Verte Line was followed by dextral transpression to transtension. "Acadian" thrusting dominated the western margin of the orogen in the Devonian and possibly earliest Carboniferous.

In southern New Brunswick the Kennebecasis Fault follows the northern boundary of a crystalline portion of the late Precambrian – Cambrian Avalon terrane. This low-grade crystalline complex forms the basement to a series of Carboniferous through Triassic basins. This complex also contains a major shear zone relic that is largely flat lying but upturned adjacent to the fault, and that with it defines the Pocologan–Kennebecasis fault zone. The orientation of the main composite foliation (S1) and the included mineral (stretching) lineation (L1) indicate that this geometry is a primary feature of the shear zone, representing a linked pair of horizontal and vertical detachments bounding an allochthonous unit. Kinematic indicators show that this allochthon moved parallel to the strike of the north Appalachian orogen, with top towards the west or west-southwest. The bounding shear zone is not uniform, but consists of a mylonite–phyllonite adjacent to the detachment. The upturned segment of the shear zone has been the site of later, brittle reactivation, one episode of which is represented by the Kennebecasis Fault. The main shear zone relic relates to more fundamental events, such as the accretion of the Avalon terrane.

The high-grade sylvinite orebody (28% K2O) mined by the Potacan Mining Company (formerly the Denison Potacan Potash Company) near Sussex, New Brunswick, Canada, has undergone intense internal folding. The folds vary in size from centimetres to hundreds of metres, are mostly tight to isoclinal, recumbent and asymmetrically overfolded towards the southeast, and belong to a single varied style group suggesting one deformation event. Folds are noncylindrical to sheath-like locally and have highly variable cross-sectional morphologies. Slickensides are locally common and penetrative. Slickenline trends in all parts of the mine are northwest–southeast. All the evidence is consistent with a southeast-directed movement across the top of the evaporite body having caused extensive ductile drag folding within both the sylvinite and halite lithologies. The evaporites, in fact, have all the characteristics of a near-horizontal mylonite zone. Variscan deformation during the Late Carboniferous is generally cited as being the most recent tectonic activity immediately north of the Caledonia Highlands, and the evaporite deformation has, in the past, been attributed to these events. This viewpoint is here reexamined, since reverse faults that are locally associated with the Variscan orogeny do not adequately explain the evaporite deformation. With increasing evidence for significant Mesozoic extensional faulting and the need for low-angle detachments, it is more likely that the evaporite deformation is linked to these later events than to earlier Palaeozoic deformation.

Eastern Notre Dame Bay, Newfoundland, is divided into five fault-bounded terranes. They are, from north to south, the Twillingate Terrane, the Chanceport Terrane, the New World Island Terrane, the Dildo Run Terrane, and the Port Albert Terrane. The New World Island Terrane is characterized by fault-repeated sequences of Middle Ordovician to Early Silurian turbiditic sandstones (Sansom Formation) and conglomerates (Goldson Formation). The Chanceport Terrane has a lower volcanic unit and an upper sedimentary unit consisting of red and green siltstones–shales overlain by turdiditic sandstones. This sequence is structurally overlain by a mafic and felsic volcanic unit.The clastic sedimentary rocks of the Chanceport, New World Island, and Port Albert terranes best record the Silurian deformation in the area. Silurian deformation is divided into two deformation events: an Early Silurian D1 thrusting event and a Late Silurian D2 dextral ductile faulting event. The Early Silurian Joey's Cove Mélange constrains the age of D1 thrusting. Few small-scale fault ramps and intrafolial F1 folds are associated with D1 thrusting. Most penetrative deformation structures in eastern Notre Dame Bay formed during D2. Three fold generations (F2, F3, F4), the regional cleavage (S3), and tectonic mélanges are associated with D2 dextral ductile faulting. D2 structures overprint Early Silurian Goldson conglomerates, and are overprinted by Late Silurian to Early Devonian Loon Bay Suite intrusions. Devonian to Mesozoic brittle D3 faults cut across the ductile regional structures.Silurian deformation in eastern Notre Dame Bay began during the closure of the Iapetus Ocean when the Chanceport, New World Island, and Port Albert terranes, and possibly the Twillingate and Dildo Run terranes, were thrust towards the south over the Gander Zone. D2 dextral ductile faults formed to accommodate the nonorthogonal final closure of the Iapetus Ocean. The closure of the Iapetus Ocean in eastern Notre Dame Bay was oblique with a dextral horizontal component.

The structural geometry of the eastern Notre Dame Bay area is that of an allochthonous sequence (related to F1 thrusting and folding), folded by F2 asymmetrical folds, and offset by F3-related high-angle faults. F1 folds are isoclinal and commonly intrafolial. F2 folds are asymmetrical (generally tight) with axial surfaces that dip 30–85° southeast. The prominent northeast-striking, penetrative cleavage (S2) is axial planar to F2 folds. F3 structures include chevron folds, box folds, kink bands, and local S3 crenulation cleavage.F1 folds are overprinted by F2 folds producing coaxial and mushroom interference patterns. This and the subhorizontal enveloping surface of F2 indicate that F1 folds were recumbent prior to F2. A zone of F1 folds separating Silurian turbidites from subaerial volcanics on the Port Albert Peninsula suggests F1 was related to macroscopic thrusting, as does the association of F1 with mesoscopic thrust faults.F2 folds are the most obvious structures in the area. Macroscopic examples include an anticline–syncline pair on Milleners Peninsula; an anticlinorium cored by the Dunnage mélange, and a synclinorium cored by subaerial sandstones on the Port Albert Peninsula. These folds repeat the stratigraphy across areas that have been incorrectly interpreted in terms of fault-bounded, north-younging homoclines. A shallow enveloping surface for F2 is supported by the uniformly low metamorphic grade in the area and detailed structural profiles. In view of the shallow dip of the enveloping surface, it is possible to correlate the Dunnage mélange, the Carman ville mélange, and other mélanges in the area.Contrary to prevailing interpretations of a structural setting involving fault-bounded tectonostratigraphic zones, we demonstrate a similar deformational history and a general continuity of macroscopic F2 folds throughout our area. Rectilinear faults on geologic maps, used by previous workers as the boundaries between tectonostratigraphic zones, are post-F2 features. They cross-cut F2 folds and are at a high angle to the F2 enveloping surface. These include the Chanceport, Lukes Arm, Dildo, and Reach Faults.All three fold generations affect rocks ranging in age from Ordovician to Middle Silurian. Thus, irrespective of when the earliest deformation began, it continued into Silurian times.

Enigmatic and heterogeneously deformed burrows are described from the Cambrian?–Early Ordovician Meguma Group of Nova Scotia. Because of their morphological variability and the absence of previously defined morphotypes, the burrows are unnamed yet do provide a cautionary note to the naming of trace fossils, even at the ichnogeneric level, by ichnologists. The traces record the activity of unknown and mobile deposit-feeding organisms that inhabited interchannel or levee areas immediately adjacent to and up to 5 m laterally from a 2 m deep channel developed on a deep-sea, mid–outer submarine-fan complex. Many of the vertically to subvertically oriented systems penetrate up to 40 cm, suggesting that existing models on the depth of early Palaeozoic benthic boundary layers obtained from shelf environments must be utilized with caution.

Stockmal et al. recently presented a simple, three-dimensional, plate tectonic model by which they attempted to explain the pre-Carboniferous evolution of the northern Appalachians. This model, which in part follows the basic principles of the two-stage collision model of Colman-Sadd (1982), is mainiy based on the results of a marine seismic profile across northem Newfoundland and on large-scale geometrical considerations. Such models are useful because they provide geologists with a framework that can be tested against field data. However, in this case the existing geological data base, in Our opinion, is incompatible with the model. We will discuss the inconsistencies and present an altemative model. The main thesis of the Stockmal et al. model is that the Taconian and Acadian orogenies are explained in terms of continuous southeastward subduction of Iapetus oceanic lithosphere. During the collision between the Taconic magmatic arc and the irregular margin of North America the Benioff zone "clogged," first in Newfoundland and then in mainland Canada. The continuing convergence between the Taconic arc and North America in Newfoundland was then achieved by delamination of lithospheric mantle while B subduction continued between the Taconic arc and North America in mainland Canada. Evidence in support of this model includes the 300-400 km right-hand offset of equivalent tectono-stratigraphic zones between Newfoundland and mainland Canada and a difference in style and vergence of the Acadian structures in Newfoundland and New Brunswick. The idea of a diachronous collision is not a new one, but the sense of diachronism remains unresolved (see e. g . , Dallmey er 1977; Clague et al. 1981). Lux (1986) considered the allochthonous ophiolites in the Humber Zone and argued in favour of a north to south diachronism. His conclusion is consistent with the fact that the oldest fossil-dated, autochthonous flysch is younger in Quebec than in Newfoundland. Since there is no overstepping autochthonous cover in Quebec, Stockmal et al. argue that the timing of the final emplacement of the allochthons and the closure of Iapetus is not well constrained there, and they explain the Acadian orogeny in mainiand Canada as

Two types of bedding-parallel faults are common in the Dunnage Zone of eastern Notre Dame Bay. They are (i) early thrusts, which together with bedding were rotated by later folding into steep attitudes; and (ii) postfolding transcurrent faults. Both types of faults occur at all scales and give rise to repetitions in the stratigraphic sequence.A compilation of the ages of various rock types based on fossil evidence indicates a relatively simple stratigraphy for the Dunnage Zone. This interpretation appears to be at variance with many reported stratigraphic successions, until repetitions by bedding-parallel faulting are taken into account.Examples are given of sequences in which the repetition of various rock types, dated by means of fossils, is due to bedding-parallel faulting. We believe that the simple lithostratigraphy is a reliable aid for structural interpretations in areas where fossils are scarce or absent.

The identification of fossils from 16 new localities on southwestern New World Island has resulted in the refinement and simplification of local stratigraphy and in the correlation of rock units across an intensely deformed area. Complex stratigraphic classifications of earlier workers are replaced by a simpler scheme consisting of four formations: the Summerford Formation (oldest), Rogers Cove Formation, Sansom Formation, and Goldson Formation. Mélange units are fault related and cannot be included in the stratigraphy. Fossil and lithological data provided here confirm previous indications that the rocks of the Summerford Formation are the remains of a long-lived volcanic-island complex. This complex is overlain by a markedly diachronous coarsening-upwards sequence of marine clastic sediments, now represented by the Rogers Cove, Sansom, and Goldson formations.The new stratigraphic data, combined with structural evidence, indicate that the stratigraphy is repeated across several bedding-parallel faults. Significant diachroneity of formation boundaries and the absence of syndepositional high-angle faults suggest deposition in one large mid-Paleozoic basin rather than in a number of small dynamic basins.

"Rocks, Minerals, and Materials Science," a special session of the Geological Association of Canada and Mineralogical Association of Canada joint annual meeting, was convened in Fredericton, May 16, 1985, under the auspices of the Geological Association of Canada. The special session was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) conference grant. The intention of the session was to foster a multidisciplinary approach to geological and mineralogical studies by bringing together researchers from classically divergent disciplines who nonetheless follow similar experimental approaches based on consideration of the physical and chemical processes responsible for the phenomena they study. Authors of contributed papers included mineralogists, petrologists, field and experimental structural geologists, material scientists, and physicists. Several of the papers follow.Although such unifying approaches are not new, it was appreciated by the organizers of the special session that there still exists in the geological sciences a tendency to fall back into established niches and to de-emphasize the usefulness of "cross-pollenating" ideas and methods. As indicated by the title, this approach is well recognized in nongeological studies, such as materials science, the principles of which are fundamental to everything from petrology (by way of ceramic phase chemistry) to modern structural geology (by way of the physics of polycrystalline deformation). Because of the relative simplicity of many nongeological materials systems, concepts and methods often have been developed for such systems first and then applied to more complex geological problems. This is well illustrated by the adaptation of electron microscopy to various geological studies to characterize atomistic and grain-scale processes and associated features. As emphasized in several of the included papers, the application of the materials-science approach is ultimately constrained by the unique geological problem of long and complicated chemical and physical histories, developed over an extreme range of temperatures, pressures, and chemical environments. The necessity for integrated field observations remains as always vital.