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Background: This article examines the subjective impact of medical cannabis on the use of both licit and illicit substances via self-report from 404 medical cannabis patients recruited from four di...

The arcuate Outer Carpathian accretionary wedge formed in front of the East Alpine-Carpathian-Pannonian (ALCAPA) megablock during the Eocene-Sarmatian. The wedge accreted sediments of the subducting remnants of the Carpathian Flysch Basin, a large oceanic tract left in front of the Alpine orogen. The palaeostress data for the orogenic hinterland (particularly the data related to the Early Miocene extension that was expanding towards the NE), combined with coeval subduction-related volcanism that was expanding towards the NE, indicate that the uneven roll-back of the subduction zone was the main mechanism controlling the development of the northern West Carpathian arc. The palaeostress data for the Tertiary accretionary wedge from the same time period are characterized by outward-fanning σ 1 trajectories that changed gradually during the wedge development. In contrast, the palaeostress data for the hinterland are characterized by preferred-directional stress events that changed abruptly during the wedge development. These palaeostress results are in accordance with the behaviour of the wedge and the hinterland, as the wedge behaved as a weak continuum and the hinterland behaved as a block mosaic with weak boundaries. The fault traces of the northern West Carpathian arc converge to both ends of the arc and suggest that the pre-existing basin was the factor that controlled the arc location. These fault trace patterns are asymmetric, indicating a slightly oblique overall convergence in a NE-SW direction. In accordance with this convergence, the palaeostress data for the accretionary wedge indicate that the western part of the wedge, which is characterized by NW-SE-oriented maximum principal compressional stress σ 1 , was undergoing sinistral transpression. Meanwhile, the eastern part, which is characterized by NE-SW-oriented σ 1 , was undergoing compression. Apparently, the dynamics of the accretionary wedge was further influenced by the shape of an elongated NE-SW-trending ALCAPA megablock, which was located behind the wedge and advanced in the direction of the general Early Miocene convergence during the most pronounced stages of the wedge development. This megablock served as the local indenter, as its strength surpassed that of the accretionary wedge located to its front. Further dynamic complexities were added because of the complex shape of the Magura Unit, which was located in the most proximal portion of the wedge and was stronger than the units in front of it. Wedge outcrops indicate that the large-scale shortening, which is characterized by the development of detachments and ramps, was preceded by an initial layer-parallel shortening. This is indicated by scaly fabrics and minor reverse faults that rotated into locked positions during the later accretion. Several outcrops with a wedge detachment fault indicate that there was a relatively low amount of friction during its development. The decollement zone is several hundred metres thick and shows evidence of transient fluid flow that was driven by pressure gradients. This is documented by frequent hydrofracturing, sandstone dykes and fibrous veins that opened against the weight of the whole wedge, all of which indicate cycles of higher pore fluid pressures that lowered the basal friction.

In this study, surface geological data resulting from a detailed field survey, including structural and biostratigraphic analysis, have been integrated with subsurface (seismic lines and well logs) data in order to reconstruct the tectonic evolution of the external zones of the northern Italian Apennines in the Romagna-Marche foothills and Adriatic Sea areas. This integrated analysis shows: (1) a late Messinian to lower Pleistocene progression of structural development from the hinterland to the foreland of the studied sector of the thrust belt; (2) relatively limited (≤20%), southward increasing, amounts of shortening (obtained by the construction of line-length balanced and restored geological cross sections); (3) a regional deformation style characterized by the presence of backthrusts associated with most foreland-vergent thrust ramps, leading to quasi-symmetric uplift and a low critical taper for the wedge, typical of foreland fold and thrust belts with a weak basal decollement (Triassic anhydrites in the present case); (4) an important influence of basement faulting which, despite a general basement-cover decoupling, appears to control stress localization in the latter, producing linkage of basement and cover stuctures in a combination of thin- and thick-skinned tectonic styles; and (5) contrasting structural styles characterizing deep features, as imaged by seismic reflection profiles, and shallow ones. Deep stuctures consist of growth anticlines bounded by major thrust ramps and back limb back thrusts, separated by broader, open synclines, both involving a Mesozoic-Paleogene, mainly carbonate, passive margin succession. In the crestal zones of major anticlines, shallow structures, affecting Neogene terrigenous foredeep sediments, show a complex pattern of upright to recumbent folds (of tens to hundreds of meters wavelength) related to minor thrusts and backthrusts. Deformation of the Mesozoic-Paleogene multilayer appears to be dominated by thrust propagation in the cores of early formed anticlines developed by buckling instabilities. The overlying Neogene deposits are detached from the carbonate substratum along the base of the foredeep succession. Bedding-parallel slip occurring along this detachment level appears to be accommodated by the complex structures in the crests of major anticlines, where the thrusts lramp to the surface cutting up section. Complex shallow structures, interpreted to accommodate at shallow structural levels the deep deformation, would therefore represent a geometrical requirement for maintaining strain compatibility across the shallow detachment level located at the base of the foredeep succession.

The restoration of structures along balanced cross sections through the West Carpathian accretionary wedge and pseudo-3D restoration in the Smilno Tectonic Window area shows that various defined units contain sediments from Magura and Silesian depositional areas. The shortened Magura succession was detached at the Upper Cretaceous stratigraphic level. The shortened Silesian sedimentary package was detached at the Lower Cretaceous stratigraphic level. The Magura succession was the southwestern neighbor of the Silesian succession in a large depositional system. Both sedimentary packages were shortened during the Paleogene and the Magura succession was later thrust over the Silesian succession as an out-of sequence oblique thrust during the Neogene. The general shortening mode is piggy-back. Thrust geometries are created by both fault-bend and fault-propagation folding. The common out-of-sequence thrusting is caused by the involvement of the basement in the shortening and by interplay of friction and erosion. The influence of basal friction on thrust sheet length is validated by sand-box models. Variations in friction along the basal thrust include low friction, documented by subhorizontal veins with vertically grown fibers and long thrust sheets, medium friction, indicated by duplexing and high friction, indicated by antiformal stacks and back thrusting.

Four profiles across the obliquely convergent West Carpathian external zone, together with a field study of the area, indicate the interrelation of thrusting and strike-slip faulting in the transpressionally deformed wedge. In the front of the wedge, thrusting is dominant. Towards the hinterland a progressively greater proportion of strike-slip faulting is found. The resultant deformational paths are curvilinear, diverging from the parallel with the northeast-vergent orogen advance. The external zone of the West Carpathian arc consists of two parts: first, a zone of frontal compression perpendicular to the orogen advance vector; and second, a zone of lateral sinistral transpression, which is at a lower angle to the orogen advance vector. The displacement along correlated strike-slip faults progressively decreases towards the zone of frontal compression.

This paper describes palaeostresses calculated from fault-striae data, the inferred palaeostrain patterns and determines the inter-relation of the compression and extension during the Tertiary development of the West Carpathians. The calculated stress and inferred strain patterns for the Palaeogene–Burdigalian indicate that the ancestral West Carpathians formed a more-or-less straight orogenic belt. This belt underwent contraction and uplift in its narrow frontal zone, stretching along its strike during the Paleocene–Chattian, and regional contraction and uplift during the Chattian–Burdigalian. The strain/stress pattern is similar to the collision-related pattern known from the Eastern Alps for the Paleocene–Burdigalian. During the Burdigalian–Tortonian, the calculated and inferred West Carpathian stress and strain patterns indicate narrow frontal contractional and lateral sinistral transpressional zones in the orogenic front and broad extensional and dextral transtensional zones in the orogenic interior. The stress/strain pattern is similar to the subduction-related pattern known from areas such as the Hellenic or Sunda/Banda Arcs.

The tectonostratigraphic analysis presented here aims to establish a broad stratigraphic framework within which the likely distribution of both reservoir and source rock intervals within the deep-water Voering and More basins can be evaluated. In terms of hydrocarbon potential, the Devonian to Triassic interval can be effectively discounted by its extreme depth of burial across most of the study area. The Middle Jurassic is interpreted to provide a potential reservoir target in the Gjallar Ridge area. The Cretaceous is seismically mappable across the region and has been divided into five tectonostratigraphic sequences. Late Cretaceous reservoirs are considered to offer targets in the Nyk High area. Six tectonostratigraphic sequences are described within the Cenozoic succession. Paleocene reservoirs are interpreted to offer targets over both the Ytterskallen and Ormen Lange areas of the More Basin. Source rock maturity is critical for exploration success. Mapping shows the Late Jurassic/earliest Cretaceous Spekk Formation to be overmature over most of the area, though the presence of possible DHIs indicates the probable presence of major gas accumulations in the region. Only on the western flank of the Vigrid Syncline does the Spekk shallow sufficiently to lie within the potential oil window. It is concluded that the region has the potential to become a significant new hydrocarbon province for the 21st century.

Field studies on the island of Elba and seismic lines from the Northern Tyrrhenian Sea, Italy, indicate that major extensional displacements were accommodated along east-dipping low-angle detachment faults. The rifting and subsidence in the Northern Tyrrhenian Sea basin have followed convergence and collision of the Corso-Sardinian block and the Apulian microplate. This collisional episode produced the Northern Apennines fold-and-thrust belt. Major extensional faults cut down-section through the stratigraphy and pre-existing west-dipping thrust faults. West-dipping thrusts can also be reactivated and form antithetic faults to the east-dipping detachments. Brittle deformation conditions predominated during the extensional phase. The geometry, internal structure and the fabrics (brittle and penetrative) associated with a well-exposed low-angle extensional detachment in Elba are presented in this paper. A geometrical model for the brittle extensional faulting is presented in which regional extension was accommodated on a system consisting of two sets of simultaneously active antithetic faults. The east-dipping detachment faults appear to have started at steeper angles, based on field and seismic observations, and rotated counter-clockwise to lower dips. Due to this rotation, and for space accommodation, antithetic west-dipping faults formed and rotated clockwise. A tectonic model is proposed whereby slowing of the convergence between Apulia and Corsica, as well as Tethys oceanic crust and Apulian crust subduction, led to the delamination of the Apulian litho-spheric mantle away from the crust. Accompanying asthenospheric upwelling and intrusion at the crust—mantle interface beneath the Tyrrhenian Sea caused late orogenic crustal stretching in the Northern Apennines internal zone.

The Limpopo Orogeny, which lasted from ∼ 2700 to ∼ 2600 Ma, was characterised by NNW-SSE directed shortening. This resulted in both crustal thickening, accommodated by folding and NNW-directed thrusting, and associated crustal extrusion whereby a number of crustal blocks, including the Central Zone of the Limpopo Belt, was displaced to the west-southwest along WSW-ENE trending shear zones. This was part of a regionally distributed phase of orogenic deformation which affected the adjoining Kaapvaal and Zimbabwe Cratons from the Witwatersrand Basin in the south to the Harare Greenstone Belt in the north. This deformation, which migrated northwards with time, postdated an earlier phase of crustal accretion during which the Archaean crustal unit now marked by the Kaapvaal and Zimbabwe Cratons and the Limpopo Belt, grew towards the north-northwest. Shortening of this unit during the Limpopo Orogeny may be regarded as the last stage of the crustal accretion process. This tectonic process of continental growth by accretion followed by crustal shortening with associated crustal extrusion has many features in common with Tibetan tectonics from the Mesozoic to the present.

Sea-floor palaeomagnetic data that reflect variations in rate and vector of Indian Plate movement and rotation suggest that initial collision between India and Asia occurred at about 50–55 Ma ago. As the pre-collisional Indian Plate was diamond shaped, with the northern margin comprised of two oblique boundaries, collision was earliest where these boundaries meet, or in what is now the northwest Himalaya. Oblique convergence along each of these two boundaries would generate rotation of thrust sheets as they climb on to the Indian Plate. The oroclinal shape of the main Himalayan chain to the east of the northwest Himalayan syntaxes reflects a combination of the effects of oblique convergence, post-collisional anticlockwise rotation of the Indian Plate, and the pinning of the main thrusts at their northwestern terminations by crust thickened during the earliest collisional stage. The Indian Plate rotation enhances a strike-slip component of movement along the western oblique margin, with the transpressively sinistral Chaman fault zone now acting as a continental escape structure.

Two balanced cross-sections were constructed through the Outer Carpathians of Poland in order to restore the Early Cretaceous rifts. The rift fill is incorporated into the Tertiary Carpathian accretionary wedge. The data compiled for this study confirm that the Early Cretaceous rifting in the Silesian Basin area was followed by Late Cretaceous–Paleocene basin inversion, Eocene pelagic deposition, and Oligocene syn-orogenic deposition. The original width of the Silesian Basin is about 130–138 km. The overall wedge shortening ranges between 31 and 58% with 57 and 58% in the Silesian Nappe. The rifting commenced at the Jurassic/Cretaceous boundary and formed the horst and graben structures defined by NW–SE striking normal faults. Portions of the horsts become emergent at various times during rifting stages. Sedimentation rates in the grabens varied around 4.7, 2.1 and 1.3 cm/ka during three rifting stages, while sedimentation rates on their slopes varied around 0, 0–1.26 and 0 cm/ka. The altitude difference between horst tops and graben floors did not exceed 2 km. The reconstructed widths of the horsts range between 17.5 and 18.3 km. The reconstructed widths of several grabens in both cross-sections have values 14.5, 45.7, 57.7 and 79.3 km. The rifting-related extension, calculated from fault-striae data, was NE–SW directed. Sometimes, the very low ( σ 2 – σ 3 )/( σ 1 – σ 3 ) stress ratio of the driving stress configuration resulted in polydirectional extension when the value decreased below 0.1.

A structural model encompassing the southern North Sea Basin west of the Central Graben has been developed that combines gravity gliding of the postsalt cover with basement tectonics. The basin differs from many salt basins in that it forms a closed system. Section construction and balancing through the cover of the North Sea need to take into account thin-skinned and thick-skinned extensions and contractions. The North Sea salt formed in Permian time in two large oval basins separated by the Mid North Sea High. The shape of these basins reflects variable patterns of thermal subsidence. Subsequent salt tectonics was governed by local graben structures and by regional uplift and subsidence. Rifting initiated during the Triassic and allowed reactive and locally passive diapirs to develop in the postsalt cover. In the southern North Sea, the Dowsing graben system in the cover is offset from the Dowsing fault zone below the salt. This offset in extensional structures probably relates to the salt thickness and to the position of the surface hinge line that controlled the onset of gravity gliding in the postsalt section. Gravity gliding of the cover into the Triassic-Jurassic Sole Pit trough and away from zones of rift flank uplift was associated with Late Jurassic-Early Cretaceous extension in the Central North Sea; gliding caused asymmetric compressional pillows to develop downslope. Gravity spreading of the cover during the Late Cretaceous-early Tertiary was associated with tilting during thermal subsidence of the southern North Sea Basin, enhanced by pulses of tectonic inversion in the southern North Sea basement. The resultant glide tectonics formed new small grabens upslope and compressional pillows downslope. Where the compressional pillows were eroded sufficiently or faulted later, the salt broke through the thinned cover to produce new active and then passive diapirs, which drained the pillows to produce new rim synclines.

Reflection seismic data, well data, geochemical data, and surface geology suggest that a Cretaceous rift basin exists beneath the thrusted allochthonous sedimentary sequence of the Masirah graben, Oman. The Masirah graben is located east of the Huqf uplift, parallel to the southern coast of Oman. The eastern side of the northeast-trending Huqf anticlinorium is bounded by an extensional fault system that is downthrown to the southeast, forming the western edge of the Masirah graben. This graben is limited to the east by a large wedge of sea floor sediments and oceanic crust, that is stacked as imbricate thrusts. These sediments/ophiolites were obducted onto the southern margin of the Arabian plate during the collision of the Indian/Afghan plates at the end of the Cretaceou . Most of the Masirah graben is covered by an allochthonous sedimentary sequence, which is complexly folded and deformed above a detachment. This complexly deformed sequence contrasts sharply with what is believed to be a rift sequence below the ophiolites. The sedimentary sequence in the Masirah graben was stable until further rifting of the Arabian Sea/Gulf of Aden in the late Tertiary, resulting in reactivation of earlier rift-associated faults. Wells drilled in the Masirah graben in the south penetrated reservoir quality rocks in the Lower Cretaceous Natih and Shuaiba carbonates. Analyses of oil extracted from Infracambrian sedimentary rocks penetrated by these wells suggest an origin from a Mesozoic source rock.

A structural model encompassing the southern North Sea basin west of the Central Graben has been developed. This model consists of a rift system affecting the post-salt section around the basin margin and a large area of detached compressional buckle folds within the basin. This pattern is initially a response to gravity sliding of the post-salt section on the salt within the basin during the late Triassic to late Jurassic. A close relationship between the location and trend of the peripheral graben system and basement structures in the pre-salt is noted. Pre-Jurassic extension across the peripheral graben systems was balanced by the sum of fault heaves at the pre-salt (Rotliegend) level and shortening across salt-cored buckle folds in the post-salt section. Salt pillows and swells passively infilled the cores of these gravity-induced buckle folds. Cretaceous and Tertiary inversion involved basin tilt and renewed movement on basin-bounding basement faults; notably, reverse movements did not propagate from basement structures up into the peripheral graben systems. The post-salt sedimentary section experienced gravity spreading in response to inversion-related uplift, resulting in syn-inversion extensional faulting in the Sole Pit High, where the Mesozoic section was thickest. This extension, combined with a loss of fault heave in the pre-salt section, was balanced by amplification of salt-cored buckle folds in the centre of the basin. In the context of the model described here, salt pillows represent passive infill of thin-skinned, compressional buckle folds which later amplified during thick-skinned basement shortening. Crestal collapse of such folds occurs via normal faulting, accompanied by reactive diapirism. Such reactive diapirs establish conduits through which salt may leak, leading to pillow deflation and ultimately conduit preservation as a salt wall (flanked by rim synclines in areas where the buckle folds were emergent). The salt structures described here are related to cover folds and faults, which in turn reflect episodes of basin extension, tilting and inversion. Hence individual salt structures can be said to be only remotely connected with regional, intraplate stresses.

In North Pakistan the dominant transport direction throughout Himalayan collision has been to the S or SSE. Southward propagation of thrusts within the thickened Indian Plate has, however, been impeded by interference with SW-verging thrusts in Kashmir, at the western end of the main Himalayan oroclinal chain. As a result of this interference, thrusts within both the Pakistani and Kashmiri systems have become pinned at their lateral terminations. Lineation and palaeomagnetic data document substantial rotations of whole thrust sheets, of up to 40° around the pinned terminations, anticlockwise in Pakistan and clockwise in Kashmir. Although such rotations are best seen within the Pliocene to Recent structures of the external zones, similar rotations can be determined within Oligocene structures in the internal zones. The NW Himalayan syntaxes are crustal scale folds which have grown within the zone of convergence between the two thrust systems. The main Himalayan thrust system is interpreted as having been pinned within the Himalayan chain, rather than at its western termination, due to early thickening of the northwestern Indian Plate having acted as a mechanical impediment to the lateral propagation of the main Himalayan thrusts.

The Kamila Shear Zone is a deep to mid crustal structure developed within the Kohistan island arc complex of North Pakistan prior to Himalayan collision between Kohistan and India. Meta-gabbros of the Chilas complex were transported southwards across the shear zone onto a stack of high pressure rocks that had been assembled in the hanging wall of the Tethyan subduetion zone. The shear zone is constituted by an anastomosing array of amphibolite facies ductile high strain zones within which fabric intensity varies although mylonitic zones are common. Shear criteria and kinematic indicators have a consistent SW-vergence. Little microstructural evidence for the high temperature ductile shearing is preserved, fabrics having been over-printed by post-deformational processes of recrystallisation, annealing and grain growth. A subsequent history of exhumation during decreasing temperature is documented by a progressive sequence of down temperature retrogression and deformation in superimposed shear zones which predominantly affected coarse grained rocks unaffected by the earlier crystal plastic deformation. The shearing involved dominantly cataclastic amphibolite to greenschist facies deformation culminating in lower greenschist facies shearing and mylonitisation, and the development of a distributed network of minor cataclastic and gouge-filled fault rocks.

This paper describes the suture zone between the Asian plate and the accreted Kohistan island arc in the Chitral district of NW Pakistan.The southern part of the Asian plate consists of two tectonic units separated by the N-dipping Reshun fault. The northwestern unit comprises Devonian carbonates and quartzites overlain by Devonian to Permian shales and slates with some limestones (Lun shales). Its structure is complex with S-verging thrusts and isoclinal folds. Along the Reshun fault, the relatively undeformed Reshun Formation may represent molasse. The central unit includes N-dipping Upper Palaeozoic slates and quartzites (Darkot Group), probably faulted against an antiformal tract of slates, schists derived from a volcanic assemblage and Cretaceous limestones (Chitral slate, Koghozi greenschist, Krinj and Gahiret limestones). Asian plate sediments are intruded by granitic and granodioritic plutons, variably deformed and locally porphyritic.The Northern suture melange of volcanic, sedimentary and serpentinite blocks in a slate matrix separates the Asian plate from the southeastern unit, the Kohistan arc. This comprises Cretaceous volcanic rocks with some sediments (Shamran Volcanic Group, Drosh, Purit and Gawuch Formations) intruded by aphyric diorites, tonalites and granites. These intermediate plutonic rocks pass southwards into a mafic layered complex and amphibolites representing deep levels of the arc. The volcanic rocks and sediments dip to the N and have a horizontal lineation. The structural history of southern Asia and Kohistan is consistent with an originally curved Northern suture: motion of the arc was initially to the NE relative to Asia and subsequently to the NW.

India collided with a northern Kohistan-Asian Plate at about 50 Ma ago, the time of ocean closure being fairly accurately defined from syntectonic sediments as well as the effect on magnetic stripes on the Indian Ocean floor. Since collision, Asia has over-ridden India, developing a wide range of thrust scrapings at the top of the Indian Plate. Sections through the imbricated sedimentary cover suggest a minimum displacement of over 500 km during Eocene to recent plate convergence. This requires the Kohistan region to the north to be underlain by underthrusted middle to lower Indian crust, deformed by ductile shears and recumbent folds. These structures are well seen in the gneisses immediately south of the suture, where they are uplifted in the Indus and Nanga Parbat syntaxes. Here there are several phases of thrust-related small-scale folding and the development of a large folded thrust stack involving basement rocks, the imbrication of metamorphic zones and the local development of large backfolds. Some of the important local structures: the large late backfolds, the Salt Ranges and the Peshawar Basin, can all be related to the necessary changes in thrust wedge shape as it climbs through the crust and the three dimensional nature of the thrust movements associated with interference between the Kohistan and western Himalayan trends.

West Himalayan tectonics involve the Collision of microplates between the Indian and Asian Plates. The Kohistan Complex consists largely of tightly folded basic volcanics and sediments generated as Late Jurassic to Late Cretaceous island arcs. These were intruded by post-folding Mid-Cretaceous Eocene plutonics produced from continued subduction of the Indian Plate after closure of a suture between Kohistan and the Karakorum. The Himalayan structures show major thrust sheets and the Kohistan Arc is essentially a crustal 'pop-up' with southward-upright and northward-verging structures developed above a thick ductile decoupling zone (the Indus Suture), which can be traced for >100 km beneath Kohistan on large reentrants. This pop-up formed by a two stage process, closure of the Northern Suture followed by closure of the southern Indus Suture. Granitic rocks of the Kohis tan-Ladakh Batholith (dated at = 100-40 Ma) post-date most of the structures related to the Northern Suture but were deformed and carried southwards on shear structures related to the Indus Suture. Postcollisional deformation carried this Kohistan Complex on deep decoupling zones over the Indian Plate on a series of imbricated gneiss sheets, the thrusts climbing up section in the movement direction so that in the far S some override their own molasse debris. Folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms--i.e. the Nanga Parbat and Hazara Syntaxes. The Nanga Parbat Syntaxis probably formed due to a shear couple near a branch line where one of the main Himalayan thrusts joined the Indus Suture beneath Kohistan. Crustal delamination, to produce the imbricated gneiss sheets, could not account for all the displacement of India into Asia, suggested by palaeomagnetic data. There must also have been lateral displacement as demonstrated by the large oblique-slip shear zone in the Hunza Valley, N of Kohistan.

The 1985 Chinese/British expedition to the Tibetan Plateau attempted to solve the question of the origin of the very thick crustal rocks in this region. Continuing northwards movement of the Indian plate over the past 38 Myr has given rise to severe folding and thrust faulting, causing crustal thickening by internal deformation. Previous collisions of microplate terranes derived from Gondwanaland occurred during Mesozoic times but the Kun Lun terrane of northern Tibet was already part of Laurasia by the Carboniferous

Positive structural inversion involves the uplift of rocks on the hanging-walls of faults, by dip slip or oblique slip movements. Controlling factors include the strike and dip of the earlier normal faults, the type of normal faults — whether they were listric or rotated blocks, the time lapsed since extension and the amount of contraction relative to extension. Steeply dipping faults are difficult to invert by dip slip movements; they form buttresses to displacement on both cover detachments and on deeper level but gently inclined basement faults. The decrease in displacement on the hanging-walls of such steep buttresses leads to the generation of layer parallel shortening, gentle to tight folds — depending on the amount of contractional displacement, back-folds and back-thrust systems, and short-cut thrust geometries — where the contractional fault slices across the footwall of the earlier normal fault to enclose a “floating horse”. However, early steeply dipping normal faults readily form obliq...

The northern part of the Indian Plate in North Pakistan is composed of a number of large-scale crustal nappes, each of which are stratigraphically distinct, and which were stacked late in the main phase of southeasterly directed thrusting associated with the Himalayan event. The major nappes recognised in the Swat to Kaghan area of North Pakistan are the Besham, Swat, Hazara, Banna, Lower Kaghan and Upper Kaghan nappes. Metamorphism was synchronous with early stages of deformation. Within each nappe the metamorphic grade increases upwards, an overall inversion that represents post-metamorphic imbrication within individual nappes, synchronous with the main phase of nappe stacking, rather than a “hot iron” type inversion as described under the MCT in Nepal and India. As a result of this “within-nappe” imbrication each thrust slice within any particular nappe contains rocks of a higher metamorphic grade than those in the slice below, with sharp metamorphic breaks across the imbricating thrusts as well as across the major shears that bound the crustal-scale nappes. Uplift along these imbricating thrusts initiated cooling of the stack. K-Ar mica and hornblende cooling ages imply that much of this uplift was completed by 30 Ma, or within 20 Ma of the collision.

Mica and hornblende K-Ar and Ar-Ar data are presented from each of the three crustal components of the Himalayan collision zone in North Pakistan: the Asian plate, the Kohistan Island Arc, and the Indian plate. Together with U-Pb and Rb-Sr data published elsewhere these new data (1) date the age of suturing along the Northern Suture, which separates Kohistan from Asia, at 102–85 Ma; (2) establish that the basic magmatism in Kohistan, which postdates collision along the Northern Suture, predates 60 Ma, and that the later granite magmatism spanned a range of 60–25 Ma; (3) show that uplift amounts within Kohistan are greater toward the Nanga Parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 Ma to a current figure of about 5.5 mm a year; (4) show that much of southern Kohistan had cooled to below 500°C by 80 Ma and that the major deformation which imbricated Kohistan probably predated 80 Ma and certainly predated 60 Ma and was related to the Kohistan-Asia collision rather than the Kohistan-India one; (5) imply that uplift along the Hunza Shear in the Asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 Ma and was associated with breakback thrusting in the hanging wall of the Main Mantle Thrust; (6) suggest that the Indian plate has a lengthy pre-Himalayan history with an early metamorphism at about 1900 Ma, major magmatism at 500–550 Ma and early Jurassic lithospheric extension or inversion; and (7) show that the Indian plate rocks were metamorphosed shortly after the collision within Kohistan, which occurred at circa 50 Ma, and subsequently cooled back through 500°C at circa 38 Ma and 300°C at 30–35 Ma with ages of cooling through 200° and 100°C (as determined by fission track data) locally controlled by Nanga Parbat related uplift tectonics.

The 1:500,000 coloured geological map of the traverse route combines observations from the Geotraverse, previous mapping, and interpretation of orbital images. The position of all localities visited by Geotraverse participants and basic geological data collected by them along the traverse route are shown on a set of maps originally drawn at 1:100,000 scale, reproduced on microfiche for this publication. More detailed mapping, beyond a single line of section, was achieved in five separate areas. The relationships between major rock units in these areas, and their significance, are outlined in this paper. Near Gyanco, (Lhasa Terrane) an ophiolite nappe, apparently connected with outcrops of ophiolites in the Banggong Suture about 100 km to the north, was under thrust by a discontinuous slice of Carboniferous—Permian clastic rocks and limestone, contrary to a previous report of the opposite sequence. At Amdo, a compressional left-lateral strike-slip fault zone has modified relationships along the Banggong Suture. Near Wuli, (northern Qiangtang Terrane) limited truncation of Triassic strata at the angular unconformity below Eocene redbeds demonstrates that most of the folding here is of Tertiary age. The map of the nearby Erdaogou region displays strong fold and thrust-shortening of the Eocene redbeds, evidence of significant crustal shortening after the India- Asia collision began. In the Xidatan-Kunlun Pass area, blocks of contrasting Permo—Triassic rocks are separated by east-trending faults. Some of these faults are ductile and of late Triassic — early Jurassic age, others are brittle and part of the Neogene—Quaternary Kunlun leftlateral strike-slip fault system. Some more significant remaining problems that geological mapping might help to solve are discussed briefly, including evidence for a possible additional ophiolitic suture within the Qiangtang Terrane.

In the Karakorum Range there is a structurally complicated Cretaceous are comprising the Kohistan sequence. On its northern side the Northern Suture consists of a mega-melange and is bounded to the S by tightly folded pillow-bearing volcanics and sediments. To the S the Kohistan Plutonic Belt consists of (southwards): (a) early foliated and late post-tectonic tonalites and diorites, (b) aplites and pegmatites (up to 30% of rock volume), (c) basic dykes up to 10 m thick, (d) the Chilas Complex, a stratiform cumulate body over 300 km long and 8 km thick (chromite-layered dunites, gabbros and norites) with a low pressure granulite-facies mineral fabric of tectonic origin, (e) an amphibolite belt with a complex mixture of other rocks, and (f) the Jijal Complex, a 200 km 2 tectonic wedge of high pressure granulites and chromite-layered dunites. Cumulate graded units in the Chilas Complex show that it is folded by an isoclinal anticline (F 1 ). The mid-upper crust of the are is folded by a 50 km half-wavelength F 2 , syncline. The whole Kohistan sequence with its two phases of isoclinal folds was tilted during Himalayan collision so that the structures are now subvertical. The Southern Suture (Main Mantle Thrust) has a wedge of glaucophane schists. The Indian plate contains a basement of psammites and schists intruded by Cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales.

The Variscan structures in SW England, apart from the high-level structures in the Culm synclinorium of N Devon, are recumbent with an overall gentle southward dip of cleavages, thrusts and recumbent folds. Translation was towards the NNW. The structures are interpreted on a thin-skinned model, with a basal decollement dipping gently S, related to a S-dipping subduction zone S of the Lizard. The granites are thought to have been generated to the S of their present position and injected northwards above the decollement zone.

The tectonic history of Kohistan, northern Pakistan, involves two collisional events. Cleavage and folding developed at 90-100 Ma along the northern suture between the Kohistan island arc and the Asian plate. At the same time there was major folding and shearing of the lower part of the Kohistan arc, approximately 100 km south of the suture. This deformation was followed by ocean subduction south of the Kohistan arc, generating the Kohistan calc-alkaline batholith, with subsequent ocean closure during the Eocene and obduction of the Kohistan arc, together with the adjacent part of the Asian plate, over the Indian continental crust. The construction of balanced cross-sections through the imbricated upper part of the Indian continental crust, in the footwall to this southern suture indicates a minimum displacement of 470 km, requiring the western Himalayan hinterland to be underlain by a large wedge of Indian middle to lower crust. There is some shortening of the overriding Kohistan and Asian plates by thrusts and shear zones, but it is insufficient to satisfy the palaeomagnetic data; there must be major crustal shortening, involving thrusts, in the Hindu Kush and Pamirs north of Kohistan. The post-Eocene thrust direction, which for most of Pakistan is towards 160°, is almost perpendicular to that immediately to the east in the Himalayan belt, generating complex refolded thrust patterns in the Hazara syntaxis and large scale folding and rapid uplift with associated brittle faulting and seismic activity adjacent to the Nanga Parbat syntaxis. These different thrust trends indicate that major thrust movement as well as the folds and deformation fabrics, cannot always be related to plate movement vectors, but are modified by, or develop from, complex rotations during place collision or from the gravitational spreading of a thickened crust. A regional approach is required to recognize and correctly attribute the various components in thrust displacements.

The Arequipa Massif, between the Andes and the Pacific, is an extensive pre-Devonian metamorphic complex. The sequence of deformations, metamorphisms and magmatism in this complex has been established. Mollendo, Atico and Marcona events are distinguished by structural and metamorphic methods and dated by Rb-Sr whole-rock isochrons, at about 1918, 440 and 392 Ma respectively. The Mollendo event led to partial melting, followed by granulite-facies metamorphism, in sediments buried to about 30 km. Further NW, sillimanite-bearing migmatites and staurolite-andalusite schists are thought to represent the same event. The tectonic trend is uncertain but the structures and metamorphism suggest a collision orogeny which probably pre-dated the Pacific Ocean. The early Caledonian Atico and Marcona events are associated with coast-parallel batholiths, amphibolite- to greenschist-facies metamorphism and penetrative deformations. The Atico and Marcona events are separated by the deposition of the Marcona Formation, which is therefore thought to be Lower Palaeozoic (between about 440 and 392 Ma). The early Caledonian deformations are attributed to a subduction zone near the present Pacific margin. There is no penetrative Hercynian or Andean deformation in the Arequipa Massif. Palaeomagnetic study of Jurassic andesites and dykes suggests that there has been no latitudinal motion of the Arequipa Massif relative to the Brazilian shield during the evolution of the Andes.

South of the Main Mantle Thrust in north Pakistan, rocks of the northern edge of the Indian plate were deformed and metamorphosed during the main southward thrusting phase of the Himalayan orogeny. In the Hazara region, between the Indus and Kaghan Valleys, metamorphic grade increases northwards from chlorite zone to sillimanite zone rocks in a typically Barrovian sequence. Metamorphism was largely synchronous with early phases of the deformation. The metamorphic rocks were subsequently imbricated by late north-dipping thrusts, each with higher grade rocks in the hanging wall than in the footwall, such that the metamorphic profile shows an overall tectonic inversion. The rocks of the Hazara region form one of a number of internally imbricated metamorphic blocks stacked, after the metamorphic peak, on top of each other during the late thrusting. This imbrication and stacking represents an early period of post-Himalayan uplift.

Recent geological and geophysical data from southern Tibet allow refinement of models for the closing of southern (Neo-) Tethys and formation of the Himalaya. Shelf sediments of the Indian passive continental margin which pass northward into deep-sea Tethyan sediments of the Indus-Tsangpo suture zone were deposited in the Late Cretaceous. An Andean-type margin with a 2,500-km-long Trans-Himalayan (Kohistan-Ladakh-Gangdese) granitoid batholith formed parallel to the southern margin of the Lhasa block, together with extensive andesites, rhyolites, and ignimbrites (Lingzizong Formation). The southern part of the Lhasa block was uplifted, deformed, and eroded between the Cenomanian and the Eocene. In the western Himalaya, the Kohistan island arc became accreted to the northern plate at this time. The northern part of the Lhasa block was affected by Jurassic metamorphism and plutonism associated with the mid-Jurassic closure of the Bangong-Nujiang suture zone to the north. The timing of collision between the two continental plates (ca. 50-40 Ma) marking the closing of Tethys is shown by (1) the change from marine (flysch-like) to continental (molasse-like) sedimentation in the Indus-Tsangpo suture zone, (2) the end of Gangdese I-type granitoid injection, (3) Eocene S-type anatectic granites and migmatites in the Lhasa block, and (4) the start of compressional tectonics in the Tibetan-Tethys and Indus-Tsangpo suture zone (south-facing folds, south-directed thrusts). After the Eocene closure of Tethys, deformation spread southward across the Tibetan-Tethys zone to the High Himalaya. Deep crustal thrusting, Barrovian metamorphism, migmatization, and generation of Oligocene-Miocene leucogranites were accompanied by south-verging recumbent nappes inverting metamorphic isograds and by south-directed intracontinental shear zones associated with the Main Central thrust. Continued convergence in the late Tertiary resulted in large-scale north-directed backthrusting along the Indus-Tsangpo suture zone. More than 500 km shortening is recorded in the foreland thrust zones of the Indian plate, south of the suture, and > 150 km shortening is recorded across the Indian shelf (Zanskar Range) and the Indus suture in Ladakh. There was also large-scale shortening of the Karakoram and Tibetan microplates north of the suture; as much as 1,000 km shortening occurred in Tibet. The more recent deformation, however, involved the spreading of this thickened crust and the lateral motion of the Tibetan block along major approximately east-west–trending strike-slip fault zones.