the metagabbros orthogneisses and paragneisses of the connemara complex western ireland although now largely disappeared within the 400 ma old galway granite the syntectonic connemara metagabbro gneiss complex which crystallized at 490 ma arenig is the largest intrusion into the dalradian rocks it is part of widespread cambro ordovician volcanism and plutonic injection into continental crust in the appalachian caledonide orogenic belt being synchronous in crystallization with the widely obducted 490 ma ophiolites within the orogeny the peridotites and hornblende gabbros were injected broken up and shouldered aside by quartz diorite granodiorite granite and trondhjemite gneisses and it is shown that these orthogneisses are not the in situ differentiation products of the gabbro magma the hornblende in the metagabbros is mainly igneous but is partly metamorphic and replaces olivine fo 75 92 orthopyroxene en 65 92 clinopyroxene wo 48 5 en 50 39 fs 5 14 and plagioclase typically an 80 92 range an 50 96 an aureole at least 10 km wide in the sillimanite zone was imposed and cordierite garnet sillimanite dalradian hornfelses were partially melted at temperatures up to 1000 o c near to the gabbros at 4 5 1 kbar corresponding to c 18 km depth this suggests that the complex forms part of the root of a now eroded batholith of calc alkaline affinities the gabbros corresponding to the transition zone to a basic bottom which is often supposed to underlie many batholiths within the orthogneisses are sheets of paragneiss formed from dalradian metasediments which have been folded up from the floor and down into sides of the magma chamber which process could be illustrative of the means by which basic magma can intimately interact with crustal material the 18 o 16 o d h nd and sr isotope evidence and the existence of inherited zircons in the gneisses indicate that the gabbro and gneiss magmas were significantly contaminated with crustal possibly dalradian material both before and after intrusion with the lowest initial 87 sr 86 sr at 490 ma being 0 708 even in samples far removed from metasediment the metagabbros are tholeiitic to high alumina basalt in character but the gneisses have distinct calc alkaline geochemistry the chemistry igneous hornblende and highly calcic plagioclase match many arc plutons in the western usa the syntectonic nature and the ubiquitous gneissic fabric in the quartz diorites trondhjemites and granites is a consequence of early movements which were probably in part connected with the separation of the connemara massif and which culminated in slicing off the largely inverted complex and carrying it southwards on the mannin thrust which underlies the whole of connemara the complex is thus a fragment of a now disrupted cambro ordovician continental magmatic arc or continent island arc environment which can be traced along the se edge of the laurentian continent

the provenance of granite boulders in conglomerates of the northern and central belts of the southern uplands of scotland rb sr whole rock isochrons from several suites of granite boulders which occur in ordovician and silurian conglomerates in the southern uplands of scotland yield ages of around 1200 ma 600 to 700 ma and 470 to 490 ma the plutonic and tectonic history recorded by these clasts corresponds more closely with that of nw newfoundland than with that of scotland the petrography of the clasts can also be matched with exposed granite plutons in newfoundland since the conglomerates were derived from the nw it is concluded that the southern uplands lay to the se of newfoundland a total of 1500 km strike slip displacement occurred between the caradoc and the early devonian consistent with oblique subduction of the iapetus ocean below the north american continental margin

deterministic seismic zoning of eastern cuba a deterministic seismic zoning of cuba is performed by modelling with modal summation the complete p sv and sh waves fields generated by point source earthquakes buried in flat layered anelastic media the results of the computation performed for periods greater than 1 second are presented in two sets of maps of maximum displacement d max maximum velocity v max and design ground acceleration dga obtained by using two different criteria in the definition of the input magnitude 1 values reported in the earthquake catalogue m obs and 2 values determined from seismotectonic considerations m max a comparison with the results of a previous probabilistic seismic zoning is made to test the possibility of making intensity ground motion conversion with the aid of log linear regressions

caledonian plutonism and major lineaments in the sw scottish highlands within the sw grampian highlands several ne sw trending shear zones and faults related to the caledonian transpressional collision are recognized as being distinct from an intersect ing set of nw se trending pre caledonian crustal lineaments which were reactivated during caledonian orogenesis the geochemical and isotopic characteristics of the 425 400 ma granitoids of this region show that they were derived by anatexis of the lower crust associated with a mantle component which provided an influx of mantle heat and or metasomatic fluids their spatial distribution suggests a close genetic relationship with caledonian shear zones having made the fundamental distinction between ascent transport and emplacement arrival configurations possible for granitoid magmas new data are presented for these plutons which show that i a common modal sequence of intrusive phases can be recognized ii these phases are all sited at shear zone or lineament intersections where transtensional zones allowed and facilitated ascent iii emplacement was often by a process of localized in situ ballooning the existence of such lineaments in these orientations in the sw highlands may indicate that the structure of the lower crust can be regarded as a series of blocks bounded by intersecting ductile zones of high strain the establishment of such a pattern of structural interactions within the lower crust could provide a mechanistic framework within which the location of anatectic zones siting and ascent pathways and any subsequent emplacement phenomena can be explained in orogenic belts

polyphase magnetization in lower carboniferous rocks of s scotland palaeomagnetic and tectonic considerations abstract lower carboniferous lavas and intrusives from the southern margin of the midland valley scotland have yielded a principal magnetization termed the b component with d i 192 12 95 5 9 this magnetization is thought to have formed essentially during the original cooling but evidence of low temperature mineralogical changes as well as the presence of dual polarity remanence structures suggest that the magnetization processes continued beyond the deuteric stage covering at least the time span of geomagnetic field inversions an overprinted magnetization the a1 component of inferred lower tertiary age has a mean direction of d i 188 49 95 3 5 this secondary magnetization is found principally in three sites two from silica veins and one from a basaltic neck located within the southern uplands fault zone at dunbar microscopic evidence suggests that the a1 overprint was acquired thermochemically through alpine tectonic re activation of the fault

the british caledonides interpretations from cenozoic analogues recent interpretations of cenozoic arc systems and collision belts facilitate reinterpretation of some aspects of british caledonide evolution end cambrian grampian collision of the passive dalradian foreland following southeastwards subduction beneath an island arc was accompanied by initiation of the highland boundary fault as a high angle south directed oblique slip thrust mid ordovician to early devonian northwestward oblique subduction of the iapetus ocean beneath the grampian orogen resulted in a continental margin magmatic arc back arc thrusting and development of an accretionary prism while southeastward subduction led to arc magmatism and back arc extension followed by initiation of the rheic ocean as a back arc marginal basin this syn subduction n s asymmetry of the iapetus ocean margins was analogous to the e w asymmetry of the modern pacific closure of iapetus was diachronous earlier in the northeast during end silurian collision the southern caledonides behaved as a passive foreland post collision foreland thrusting resulted in deposition and deformation of lower old red sandstone foreland basin deposits in wales and probably in northwest directed back thrusting in the region of the longford down accretionary prism subsequent dextral movement in the suture zone juxtaposed the southern caledonides with scotland and northern ireland beneath which northwestward subduction had continued into the early devonian

ophiolitic melange separates ortho and para tectonic caledonides in western ireland the nature of the contact between the orthotectonic late pre cambrian to cambrian and the paratectonic ordovician and silurian caledonides has long been a source of discussion in western ireland this junction occurs in a complex zone which crops out along the southern shores of clew bay county mayo where dalradian middle cambrian and ordovician arenig rocks are separated by a pre silurian rock unit termed the deer park complex1 fig 1 the complex contains both meta sedimentary and meta igneous rocks and has been variously interpreted as representing a pre caledonian basement ridge1 an imbricate thrust zone2 related to the development of a major fault system the fair head clew bay line3 or an arenig ophiolite4 we report here geological geochemical and geophy sical studies on the deer park complex which indicate that it is a northerly dipping melange unit containing the components of a dismembered ophiolite these findings imply a source of ophiolitic rocks to the north possibly within the orthotectonic caledonides

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

the trace element and isotope geochemistry of the sabaloka igneous complex sudan the sabaloka igneous complex comprises 2 igneous centres of 9within plate9 magmatism intruded into precambrian gneisses in northern sudan the cauldron complex is the larger centre and was emplaced at 383 14 ma the earliest felsic magmas are highly fractionated peraluminous rhyolites with isotope and trace element characteristics indicative of either a biotite tonalite granodiorite source or of amphibole fractionation from a metalumi nous melt the rhyolites are overlain by ignimbrites which have similar trace element characteristics to the rhyolites but are less aluminous a mica granite boss intrudes both rhyolites and ignimbrites and has an unuaual trace element geochemistry which is ascribed to volatile loss during emplacement the cauldron complex is circumscribed by a microgranite ring dyke which has isotopic and trace element characteristics which allow the microgranite magma to be the source from which the rhyolites fractionated the microgranite itself requires a monzonite or syenite source the subsidiary tuleih complex was emplaced at 465 14 ma and is largely composed of a silica saturated marginally undersaturated syenite trace elements and isotopes from the syenite indicate a garnet eclogite source of mantle origin the sabaloka intrusions provide an example of several periods of magmatism contributing to the same igneous complex although not necessarily to the same igneous centre

the sedimentology of the south connemara group western ireland a possible ordovician trench fill sequence the stratigraphy of the ordovician south connemara group is described the group is approximately 3 km thick and includes sedimentary and volcanic rocks the sedimentary elements of the succession include conglomerates sandstones shales cherts and minor limestone breccias the lettermullen formation exhibits the thickest continuous sedimentary sequence in the group it is divided into five facies a conglomerate facies thick sandstone facies medium sandstone facies sandstone siltstone facies and chert facies the sedimentary features of these rocks include channelling and grading and are described in terms of bouma units where applicable the coarse elements of the formation are thought to represent deposition in or proximal to submarine channels feeding a more distal depositional site represented by the finer elements igneous rocks of the group include pillowed and non pillowed lavas massive amphibolites and minor tuffs often in conformable contact with the sediments petrography of conglomerate clasts and sandstones indicates derivation from a continental source area palaeocurrent analysis reveals a primary easterly mode with a subsidiary northerly mode it is suggested that the group exhibits some characteristics of trench fill sequences and the succession may be related to similar environments within the southern uplands accretionary wedge

syn orogenic alkaline magmatism and its relationship to the moine thrust zone and the thermal state of the lithosphere in nw scotland the alkaline complexes of nw scotland lie in a zone sub parallel to the moine thrust and represent the nw edge of the otherwise overwhelmingly calc alkaline late orogenic magmatism of the caledonian fold belt the emplacement of intrusives in assynt overlapped the thrust movements and new u pb zircon ages for the loch ailsh intrusion 439 4 ma provide are liable bracket when combined with existing age data for the loch borralan intrusion 430 4 ma for the main movements on the ben more thrust plane a detailed history of the main tectonic and igneous events in the moine thrust zone is tabulated zircons from the undeformed cnoc nan cuilean syenite emplaced in moine rocks near loch loyal give an age of 426 9 ma in contrast to the deformed glen dessary syenite for which earlier work gave 456 5 ma the linear distribution of the alkaline complexes to the west of the calc alkaline plutons and the ultra potassic character of the loch borralan complex the most westerly are consistent with but do not prove generation related to a w dipping subduction zone the persistence of the magmatism over 30 ma in a belt being shortened by thrusting suggests a source in the mantle lithosphere the absence of magmatism further to the nw and the production of calc alkaline magmas to the se of this zone is compatible with a model in which the thermal state of the lithosphere exercises the most important control on the nature of late caledonian magmatism

displaced terranes in britain and ireland a meeting entitled displaced terranes in britain and ireland was held at burlington house on 2 november 1988 this was the third terranes meeting held in britain since the inception of international geological correlation project no 233 terranes in the circum atlantic palaeozoic orogens the others having been held at cardiff in 1986 and glasgow in 1987 igcp 233 grew out of igcp 27 the caledonide orogen many of the developments promoted by which are recorded within two special publications of the geological society harris et al 1979 harris fettes1988 over the last few years research on displaced terranes in the british caledonides has accelerated with new data now challenging what have become traditional applications of plate tectonic theory to the british caledonides the reports of work in progress on caledonian terranes and it was thought appropriate to take advantage of the rapid publication facilities afforded by the short papers scheme because of the four page limit on short papers much introductory material has had to be omitted so that we provide here an introduction to the concept of displaced terranes and its applications to british palaeozoic geology displaced terranes the essential value of the terrane concept lies in its recognition of the likelihood of large scale lateral fault movements occurring along active plate margins the concept of terrane tectonics is therefore no more than a fuller appreciation of the kinematic implications of plate tectonic theory the impact of this recognition upon our perception of geotectonic processes in general and the

does the golden spike still glitter a modus operandi for precambrian stratigraphy is suggested which combines the geochronometrical scale and late proterozoic chronostratigraphy the development of phanerozoic stratigraphical classification is followed from the pioneering days of murchison through the growing understanding of fossils in relation to time and the later distinction of rock and time rock to the advent of the golden spike criticisms of chronostratigraphy global standard stratigraphy are assessed and its value upheld stratigraphical procedures such as those of event stratigraphy are useful in particular situations but correlative methods in the phanerozoic are dominated by biostratigraphy examples are taken of its use and potential in north american cordilleran palaeozoic stratigraphy in the triassic system as a whole and in the caledonides of britain and ireland

a magnetic deep structural geology interpretation of ireland a new 10 nt compilation of magnetic data for ireland and the immediately adjacent sea area shows distinct geophysical provinces of characteristic magnetic signature separated by major magnetic linears which can be related to important geological lines in the far northwest there is a structurally coherent grampian tectonic thermal zone bounded to the southeast by the fair head clew bay line between the fair head clew bay line and the western extension of the southern uplands line which forms the northern margin to the southern uplands of scotland is a segmented zone of relatively small magnetic anomalies and geological bodies of mixed crustal affinity grampian massifs lower palaeozoic sedimentary basins bounded by major shear faults relics of lower palaeozoic oceanic and related crust and possible older microcontinent fragments these separate areas have quite individual structural and metamorphic histories there is good evidence for the grampian massifs having undergone significant lateral movement during lower palaeozoic times and it can be inferred that many of the now adjacent bodies are only docked the original position of each block is now not known in the far southeast of ireland are relics of a cadomian craton which are now tectonically imbricated with lower palaeozoic rocks this is probably the segmented margin of the stable cadomian craton which is inferred beneath wales and south britain between the southern uplands line and the northernmost extent of the relics of the southern craton is a zone of deep seated low amplitude magnetic anomalies and major linears these are about 30 oblique to the southern margin of this vestiges of the iapetus ocean zone but are nearly parallel with the northern margin

crystallization and emplacement chronology of the fournier oceanic fragment canadian appalachians collision zones between the plates that form the earth s surface are commonly delineated by displaced fragments of oceanic crust and mantle these fragments are important because they can be used to constrain the timing of the generation and destruction of former oceans by means of radiometrie and fossil studies in the northern appalachian caledonian orogen of canada the united kingdom and scandinavia the majority of the oceanic fragments crystallized between 480 and 500 myr ago in basins marginal to the lapetus ocean and were emplaced onto continental margins at least 10 myr later here we report a significant exception u pb geochronology of zircons extracted from a plagiogranite in the fournier oceanic fragment of the canadian appalachians reveals a much younger crystallization age of 461 3 2 myr whereas fossil evidence indicates continental incorporation in the silurian some lapetan marginal basins therefore continued to develop or were created after the early ordovician

seismological evidence for shallow crystalline basement in southern uplands scotland new evidence is presented and old data re appraised to indicate that the southern uplands of scotland contain crystalline rocks of continental affinity at shallow depth 1 5 km in at least two zones roughly parallel to the caledonoid strike this is in contrast with earlier interpretations especially of the lispb seismic profile1 2 which suggested that the lack of such rocks implied a major discontinuity across the caledonides near the southern uplands fault the new interpretations suggest that basement indistinguishable seismologically from that below the midland valley continues 15 20 km southwards below the southern uplands and that another such crustal block underlies the eskdalemuir eka seismological array further to the south the existence of such blocks radically affects plate tectonic reconstructions of the caledonides especially the margins of the lapetus ocean3 6 only drilling is likely to show whether the contact between basement and the overlying lower palaeozoic greywackes and shales is structural igneous or least likely simple overstep

strain partitioning in transpression zones abstract transprcssional strain acting upon structurally anisotropic rocks can be partitioned into separate deformational domains of pure shear and simple shear this contrasts with homogeneous transpression in which both the pure shear and the simple shear strain components are uniformly distributed across the zone of deformation structural weaknesses capable of partially or fully accommodating one component of deformation include lithological contacts rheological heterogeneities and faults or shear zones situated within the deformation zone or lying along its boundaries partitioning of transprcssional strain can occur when stress is applied oblique to pre existing structural weaknesses or can occur during later stages of progressive strain when the early deformation of isotropic rocks imparts sufficient anisotropy to allow subsequent strain to be partitioned partitioning of transpressional strain into domains lying parallel to the deformation zone boundaries can be distinguished from fault stepped transpression in which strain is partitioned along the length of a segmented fault zone mesofracture analysis of rocks affected by mid devonian deformation on both sides of the highland boundary fault zone hbfz in central scotland shows that strain was not homogeneous the mesofracture data suggest that regional north south compression orientated oblique to the pre existing ne sw trending hbfz was partitioned into separate deformational domains the hbfz accommodated most of the simple shear component whilst the rocks flanking the zone were deformed predominantly by pure shear a contemporary example is the san andreas fault in central california where analyses of neo tectonic stresses show that the direction of principal compression is perpendicular to the fault zone many examples of the partitioning of transpressional strain have also been recognised at destructive plate margins where the direction of plate motion is oblique to the edge of the over riding plate

the northern belt of the longford down inlier ireland and southern uplands scotland an ordovician back arc basin the northern belt of the southern uplands longford down zone contains two compositionally distinct clastic petrofacies suites each ranging from mid to late ordovician age they extend throughout the length of the belt and are generally separated by a strike fault the northwestern metaclast petrofacies suite is characterized by felsic igneous and metamorphic detritus derived from a continental source to the nw whereas the southeastern basic clast petrofacies suite contains abundant calc alkaline detritus derived from an island arc and plutonic metamorphic root zone complex to the s or se a similar source but located to the north is indicated for younger clastic sequences of similar composition in the northern part of the central belt immediately south of a major sinistral shear zone which defines the boundary between the northern and central belts it is concluded in light of other facets of regional geology and possible palaeogeographic configurations that this pattern reflects a back arc basin in the northern belt margined by a volcanic arc massif which once occupied the space now represented by the shear zone and a fore arc basin to the se central and southern belts the northern belt back arc basin is postulated to have been closed and deformed at the end ordovician and subsequently overthrust northwestward by the allochthonous thrust stack imbricated central and southern belts fore arc sequence at the end silurian this in the northern belt resulted in the development of a major recumbent structure downward facing on regional end silurian cleavage

an oxygen and carbon isotopic study of multiple episodes of fluid flow in the dalradian and highland border complex stonehaven scotland the carbon and oxygen systematics of rocks north of stonehaven scotland were studied to provide new constraints on the nature and timing of metamorphic and post metamorphic fluid infiltration carbon and oxygen isotopic data were collected from carbonated spilites and carbonate bearing veins in the highland boundary fault from dalradian metacarbonate layers and pervasively carbonated schists and from three generations of carbonate bearing veins and a quartz porphyry dyke within the dalradian isotopic evidence for syn metamorphic fluid infiltration in the dalradian is preserved in quartz calcite veins in the upper chlorite zone and in staurolite zone metacarbonates 18 o values for coexisting quartz 18 o quartz 13 6 and calcite 18 o calcite 11 6 in a vein from the upper chlorite zone are consistent with precipitation of both minerals from a single fluid at c 375 c oxygen isotopic data from staurolite zone metacarbonate layers 18 o calcite 10 4 to 12 9 suggest major isotopic exchange with an external fluid equilibrated with a quartzo feldspathic reservoir such as the dalradian metasediments at metamorphic temperatures low negative carbon isotope data from these metacarbonate layers 13 c calcite 12 4 to 17 7 may indicate a component of oxidized organic material in the infiltrating fluid post metamorphic fluids derived from or equilibrated with a high temperature silicate reservoir such as felsic igneous rocks were responsible for precipitation of post metamorphic vein carbonate carbonation of pelitic schists and alteration of metamorphic feldspar porphyroblasts from barrow s famous spotted chloritoid schists in an area geographically associated with several carbonated quartz porphyry dykes some veins in the biotite and garnet zones have been conduits for multiple generations of fluid flow quartz from this generation of veins preserves a metamorphic isotopic signature 18 o quartz 11 2 to 13 2 whereas dolomite and calcite are considered to be post metamorphic based on textural evidence and isotopic data indicating extreme oxygen isotopic disequilibrium between vein quartz and carbonate minerals 18 o dolomite 23 7 to 24 2 18 o calcite 25 3 18 o quartz 11 2 to 13 2 variably depleted carbon isotopes from carbonate minerals in these veins 13 c dolomite 8 1 to 13 4 13 c calcite 12 2 may reflect input of oxidized organic material in the mineralizing fluid isotopic data from carbonate veins and variably carbonated spilites from the highland boundary fault are consistent with hydrothermal alteration of basalts by seawater which had its carbon isotope systematics modified by addition of magmatic co 2 and or oxidation of organic carbon such alteration may have occurred on the seafloor or during emplacement in the highland boundary fault

the deep structure of northern england and the iapetus suture zone from birps deep seismic reflection profiles the nec deep seismic reflection profile images structures in the lower crust which represent the iapetus suture zone beneath southern scotland and northern england on the basis of reflectivity characteristics of the lower crust and reflection moho we recognize four different crustal zones which correspond to four crustal terrane types midland valley zone a a sub continental subduction complex zone b lake district zone c and midland platform zone d the junctions between each of these zones are interpreted as being tectonic a and b originate from the northern continental margin of the iapetus ocean and are separated from c and d which are derived from a southern continent by strong northerly dipping reflections between approximately 15 and 30 km deep in the crust the structure responsible for these reflections does not displace the reflection moho north of the ab cd junction the base of zone b and base of the reflective crust is marked by a pair of parallel reflectors persistent for a horizontal length of about 55 km these reflectors are interpreted as the top and bottom of a slice of remnant oceanic crust at their northerly limit the deepest of the two parallel reflectors transects the moho to a depth of 6 7 km into the uppermost mantle we suggest that their termination delimits the northerly extent of a decollement or shear zone at the present continental moho the shear zone was active during the late stages of caledonian collision when mantle originally from beneath the southern continent underthrust old and newly created crust of the collision zone

accretion and collision related deformation in the southern uplands accretionary wedge southwestern scotland recent models for the tectonic development of the southern scottish caledonides are reviewed in terms of the deformation sequence observed within the southern uplands of scotland the early stages of this history are consistent with deformation within an accretionary prism formed above a northwest directed subduction zone later stages show a reversal in transport direction and also evidence for sinistral shear a deformational history for the area is proposed in terms of recent data on the deep structure of the southern uplands and adjacent regions the southern uplands is considered to be a large scale popup structure between a forethrust the iapetus suture and a backthrust which partially obducted it toward the northwest

the geology of the western part of the fintona block northern ireland evolution of carboniferous basins the western part of the fintona block is divided into four fault bounded segments that contain red bed sediments formerly assigned to the lower old red sandstone dating by miospores indicates the presence of deposits of early devonian age in the irvinestown segment late visean early silesian age in the tempo lisbellaw segment and late visean early silesian and late silesian ages in the milltown segment northward migration of the early carboniferous marine transgression in the northern part of ireland coincided with the sequential propagation of back stepping faults and resulted in the development of diachronous facies belts between late courceyan and arundian times tectonic uplift of a possible southwesterly extension of the tyrone igneous complex gave rise to the deposition of asbian to pendleian red beds to the south of a massif an interface between these red beds and contemporaneous marine sediments farther to the south is recognized and dated a new non marine basin containing brigantian and pendleian red beds also developed to the north of the massif a waterlogged floodplain that developed during westphalian a times may be coeval with more widespread coal bearing sequences elsewhere in ireland alluvial fans prograded southwards over this plain during westphalian b times when faults bordering a northern landmass were reactivated

is the southern uplands of scotland really an accretionary prism we argue that there is little which demands the accretionary prism model for the widespread silurian rocks of the southern uplands of scotland and ireland with new data from ireland we reinterpret these rocks as the turbidite fill of a successor basin that formed after the subduction of iapetus oceanic crust finally stopped at the end of the ordovician the structure of the basin is a sinistral transcurrent imbricate stack the result of oblique terminal collision of cadomia with laurasia at the end of the silurian

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

a tectonic model for the emplacement of the main donegal granite nw ireland the main donegal granite is shown to lie in a major late stage ne sw trending transcurrent sinistral shear zone in the caledonides of nw ireland the zone which is bent both laterally and upwards around the pluton has displacements which diminish sw along its length from a maximum of approximately 20 km at the ne end of the pluton the granite has also been deformed by this sinistral shear but it has a strain component of its own the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone strain variations between granite and wall rock and an early plagioclase fabric associated with the petrographic banding of the granite suggest that intrusion and deformation were more or less synchronous at around 400 ma it is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend split lengthwise and progressively create an internal low pressure zone into which the main granite was emplaced the wide variety of emplacement styles of the other radiometrically synchronous plutons of the batholith can be attributed to the progressive development of the shear zone thorr and fanad in tension between the zone and a complimentary structure to the n ardara and toories in local compression at the shear zone termination rosses in tension on the outer arc of the bending zone and trawenagh bay as displaced main granite magma in a similar tensional setting during the final stages of deformation

geological constraints structural evolution and deep geology of the northwest scottish caledonides the front of the caledonian orogenic belt in nw scotland is marked by a zone of foreland thrusting which contains imbricates of lewisian basement proterozoic cover and cambrian shelf sediments faults within this moine thrust belt in most localities propagated in a foreland directed sequence therefore the earliest of these thrusts was the moine thrust which carried a basement assemblage of moine and lewisian rocks over the cambrian shelf the development of large duplex and imbricate structures in the footwall postadted movement on this thrust hence a restoration of these imbricates provides a minimum estimate of the eastern extent of the cambrian shelf no synsedimentary or prethrust extensional features are recognised within the cambrian succession which displays a remarkable stratigraphic and thickness consistency this implies a corresponding consistency in crustal structure beneath these cover rocks immediately prior to caledonian thrusting a balanced cross section constructed across the northern part of the moine thrust belt has given a restored width for the cambrian shelf of 54 km geophysical data suggest that the present foreland crustal thickness is 28 km if this is taken to be the crustal thickness beneath the cambrian shelf during caledonian thrusting a minimum cross sectional area of 1512 km of lewisian rocks must remain beneath the present outcrop of the moine thrust sheet this foreland basement wedge may have been imbricated subsequent to the development of the cambrian imbricates caledonian structures within the moine thrust sheet are interpreted as forming an imbricate stack with the moine thrust acting as a floor thrust the ductile imbricate thrusts possibly roofed into the naver slide late open folds which warp foliation slides and metamorphic isograds within the moine sheet may represent culminations in the foreland lewisian imbricates beneath the moine thrust these postulated culminations may have been sufficient to initiate gravity driven structures this may explain late movements on high level faults within the moine thrust belt

palaeozoic terrane accretion in the western irish caledonides the southern boundary of the early caledonides in the british isles the dalradian supergroup is represented by the major highland boundary fair head clew bay line in the west of ireland accretion along this laurasian margin occurred by sinistral strike slip during two phases the earliest was responsible for the docking of the connemara terrane a displaced part of the dalradian outboard of the south mayo trough in the llanvirnian llandeilian this event is recorded independently by radiometrically dated sinistral strike slip deformation in the ox mountains of western ireland following deposition of a silurian overlap sequence sinistral movements were renewed between the upper llandoverian and the siegennian this event is part of a major phase of sinistral strike slip throughout the british isles involving accretion of the cadomian terrane and the devonian accretion of the avalon terrane in the northern appalachians

the glen kyllachy granite and its bearing on the nature of the caledonian orogeny in scotland the tomatin findhorn granite in the nw grampian highlands has been separated into two distinct complexes a late tectonic glen kyllachy granite tectonically foliated and a post tectonic findhorn granite flow foliated for the glen kyllachy complex rb sr analyses of muscovites from the granite and from an associated suite of cross foliated pegmatites yield an emplacement age of 443 5 15 ma whole rock rb sr data support field and textural evidence that the pegmatite and granite emplacement was late tectonic to the last f3 phase of caledonian folding initial granite 87 sr 86 sr of 0 7176 supports field and geochemical evidence of derivation from upper crustal metasediments first metamorphosed during the grenville event for the findhorn granite concordant rb sr and k ar mineral data establish an age of 413 5 ma and an initial 87 sr 86 sr of c 0 706 indicates a lower crustal and or mantle source this age and isotopic contrast between these granites is characteristic of the whole grampian region in which a plutonic hiatus between c 440 and 415 ma coincides with the peak of sedimentary accretion in the southern uplands and may be explained in terms of the lack of hydrous materials passing down the associated subduction zone structural metamorphic and radiometric evidence suggests a that the late f3 glen kyllachy pegmatites are comparable with the 442 7 ma old syn f3 pegmatites in the n highlands both pegmatite suites are situated in the axial zone of the metamorphic caledonides displaced by the great glen fault and b that the caledonian c 454 ma old peak tectonic metamorphic event d2 previously documented in the n highlands coincides with a caradocian basin closure along the highland boundary fault for silurian events in the n highlands we propose a separate subduction history in this region the peak of calc alkaline plutonism was accompanied by continuous folding and westward thrusting at the same time as a plutonic hiatus in the grampian highlands current evidence suggests that the c 160 km or greater sinistral movements on the great glen fault were not initiated until late silurian early devonian time

response of continental magmatic arcs to regional tectonic changes recorded by synorogenic plutons in the middle crust an example from the coast mountains of british columbia abstract the coast mountains of british columbia record an increase in magmatic activity acceleration in exhumation rate and a change from transpression to extension between 60 and 52 ma structural analysis of fabrics in three mid crustal plutons and country rocks leads to conclusions about pluton emplacement mechanisms and strain partitioning during changing tectonic conditions the quottoon and kitlope plutons 60 ma have steep foliations and lineations consistent with partitioned transpressional deformation the chief matthew s pluton 57 55 ma intruded during the formation of a sub horizontal transposition foliation and has radially distributed lineations consistent with sub vertical flattening during extension the change in orientation of the foliation represents an almost orthogonal rotation of the shortening direction from sub horizontal to sub vertical the chief mathew s pluton is interpreted to intrude initially into gently dipping fractures perpendicular to the steeply dipping foliation these melt filled fractures acted as conduits for melt triggering horizontal flow and eventually formed kilometer scale sills the steeply dipping fabrics of the coast shear zone provided pathways for melt to ascended from lower to middle crustal depths partitioning deformation into three dimensional domains of flattening simple shear and constrictional strain created the space for plutons this pattern of deformation reflects the interaction of regional deformation with magma emplacement

the pontesford lineament welsh borderland the ne trending pontesford lineament centres on the pontesford linley and adjacent faults in the shelve longmynd inlier to the ne it is usually drawn along the se edge of the cheshire basin and to the sw along a variety of lines parallel to or converging with the church stretton fault new mapping and reassessment of published data suggest that sw of the pontesford linley fault the lineament is logically drawn along the clun forest disturbance a post pridoli late silurian fold fault belt then across the nw side of the llandrindod inlier to flank the tywi lineament the lineament was intermittently active at least from mid ordovician through to triassic time with both strike slip and dip slip displacements that involved the upper part of the precambrian basement late ordovician and early silurian strike slip was particularly important the lineament controlled the sites of several silurian sedimentary basins ordovician contrasts across the lineament can be explained either by contemporary fault control or by subsequent large displacements juxtaposing unlike terranes the long history of reactivation and basement control on the pontesford lineament is typical of lineaments throughout wales and the borderland it suggests that both caledonian and variscan structural trends n of the variscan front may be inherited from older pre silurian or even precambrian basement structures

snowdon basalts and the cessation of caledonian subduction by the longvillian basalts of the bedded pyroclastic formation snowdon volcanic group north wales of longvillian caradoc age are heterogeneous in trace element composition forming a mixing trend between ocean island basalt oib type and magmatic arc basalt the two end member compositions were partial melts of two distinct upper mantle sources the oib end member is similar to icelandic oib and is the only known example of basalt of this type in the ordovician silurian welsh basin since ocean island basalt magma type is thought never to erupt above well established subduction zones the eruption of the longvillian oib provides a minimum age for the end of subduction of iapetus oceanic lithosphere below the welsh basin a model for the evolution of the mantle below the welsh basin is proposed which accounts for the geochemistry of magmas erupted from the tremadoc to the early silurian

the loch quoich line a limit of early palaeozoic crustal reworking in the moine of the northern highlands of scotland the loch quoich line a major structural line at least 60 km in length within the moine of the northern highlands of scotland has hitherto been variously interpreted as a major tectonic dislocation the root zone of a nappe and an unconformity the work reported here was carried out at the type locality of the line and was directed at resolving these ambiguities the lithostratigraphic succession established by sedimentary structures shows that the rocks of the glenfinnan division are older than but are stratigraphically continuous into those of the loch eil division rocks of the loch eil division crop out extensively to the w of the loch quoich line and are not restricted in outcrop to the area e of the line as was previously thought the early d 1 d 2 structures were initially sub horizontal steeply inclined nne trending d 3 structures are weakly developed e of the axial trace of a major fold the beinn beag synform in this area the metasediments remain essentially in their post d 2 gently inclined attitude w of the axial trace of the synform the earlier folds and fabrics were severely reworked into steep attitudes during d 3 producing nne trending zones of 9platy9 rocks which mark regions of severe strain on d 3 fold limbs earlier d 1 d 2 structures are clearly preserved in d 3 hinge zones which mark zones of low d 3 strain it is concluded that the loch quoich line coincides with the axial trace of the beinn beag synform and that it is the eastern limit of severe tectonic reworking probably caledonian over printing early probably precambrian structures recognition of structural and stratigraphic continuity between the glenfinnan and loch eil divisions implies that the loch quoich line cannot be correlated across the great glen fault with the putative unconformity separating the grampian cover and central highland basement divisions in the moine rocks of the central highlands

mavis an upper crustal seismic refraction experiment in the midland valley of scotland summary the results of the midland valley investigation by seismology mavis are described the experiment consists of three refraction profiles of between 80 and 100 km length across the upper palaeozoic basins of the scottish midland valley three refractors are recognized thus defining four upper crustal layers the top two layers are interpreted as carboniferous plus upper old red sandstone and lower old red sandstone plus lower palaeozoic the structure of the refractor an unconformity separating the two layers mirrors surface structure deeper refractors associated with midland valley crystalline basement show no correlation with surface structure the mavis survey allows the refinement of earlier gross interpretation of upper crustal structure in the midland valley but confirms the existence of anomalously shallow 6 4 km s basement and shows in conjunction with results of previous work that a large area of the central and southern midland valley is characterized by one velocity signature probably indicative of a single terrane

a sequential back arc and foreland basin thrust duplex model for the southern uplands of scotland thrust imbrication of ordovician and silurian submarine fan sequences overlapping pelagic deposits in the southern uplands has been interpreted in terms of an accretionary prism formed above a nw directed subduction zone structural features invoked to support accretion are not definitive and could be explained in terms of a thin skinned thrusting model new palaeocurrent and compositional evidence from llandeilo to mid llandovery age turbidites in the northern part of the southern uplands proves interdigitation of sediments with strongly contrasting petrography turbidites derived from the south contain significant quantities of fresh andesitic detritus whereas those from the north form more mature quartz rich formations this implies a back arc situation the turbidites being deposited in a basin with a relatively mature continental landmass to the north and a rifted continental fragment containing an active volcanic arc to the south oblique collision of the opposing continental margins of the iapetus ocean during the llandovery caused the cessation of subduction underthrusting of the southern margin initiated a se propagating thrust stack which deformed the back arc basin sequence and may eventually have ramped over the eroded and faulted remains of the volcanic arc a southward migrating foreland basin formed ahead of the rising thrust stack and is now represented by the late llandovery hawick group and wenlock sequences mid to end silurian sinistral strike slip resulted from oblique collision and produced a transpressional regime during which reactivation of deep seated structures allowed the intrusion of lamprophyre dykes and granites

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

structural evolution in the moine of northwest scotland a caledonian linked thrust system a model is proposed whereby the caledonian metamorphic basement cover complex of northwest scotland the moine is considered as a linked thrust system this system lies between the moine thrust at its base and the naver sgurr beag slide at its top ductile fold and thrust zones which developed at mid crustal levels at metamorphic grades from greenschist to amphibolite facies are interpreted as decoupling from a detachment presently situated at relatively shallow depths this model is illustrated by two preliminary balanced cross sections these imply shortening across the northwest scottish caledonides in excess of 130 km and probably over 200 km when these structures are restored onto a crustal template a considerable quantity of lower crust is found to be required at depth the most likely location for the lower crustal wedge is beneath the grampian highlands

jurassic dextral and cretaceous sinistral movements along the hida marginal belt abstract the hida marginal belt hmb which consists of various kinds of fault bound blocks is located between the continental massif of the hida belt and the mesozoic accretionary complex of the mino belt in central japan detailed field investigation reveals that the hmb had grown through the two different movements i e jurassic dextral and cretaceous sinistral movements the jurassic dextral ductile shear zones run in the southern marginal part of the hida belt and the northern part of the hmb whereas the cretaceous sinistral cataclastic shear zones occur in the southern part of the hmb and the northern marginal part of the mino belt geologic map and field evidence seem to suggest that the jurassic dextral movement form the fault bound blocks of the hmb to form the basic structure of the hida marginal belt i e formation of the proto hmb following the dextral movement the sinistral one restructured the proto hmb to complete the present feature of the hida marginal belt the cretaceous sinistral movement might result in the sinistral collision between the proto hmb and the mino belt

major southward thrusting of the dalradian rocks of connemara western ireland the connemara schists are of dalradian late precambrian cambrian age and since the work of kilburn et al 1 it has been apparentthat they occupy an anomalous geographical position south southeast of the strike continuation of the dalradian rocks of scotland and ireland and south of the inferred position of the highland boundary fault fig 1 also the connemara schists are unusual in having reached a higher metamorphic grade and having had a different metamorphic history from most other parts of the dalradian the model which we propose here for the connemara dalradian that of an allochthonous thrust sheet offers an explanation for these anomalies and highlights hitherto unsuspected similarities between the tectonic histories of the south east margins of the metamorphic caledonides in the british isles and scandinavia

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

strike slip terranes and a model for the evolution of the british and irish caledonides evidence is presented that many of the major strike faults in the british and irish caledonides were active as sinistral strike slip zones in the end silurian to pre mid devonian period some such as the highland boundary fault moved in this way at an earlier stage in the ordovician these data allow the caledonian rocks lying between the laurentian miogeocline whose basement is represented by the lewisian moine and possibly the dalradian and the gondwanaland miogeocline midland platform and welsh basin to be re analysed as a group of disorganized terranes which originated to the southwest in north america and southwest europe africa prior to the silurian the highland border terrane and northern belt terrane are interpreted as duplicated pieces of a mid ordovician sequence which was a back are to northwest subduction the midland valley terrane is interpreted as a slice of laurentian foreland onto which ophiolites were obducted in the lower ordovician but which became the basement of a continental margin arc to northwest subduction in the mid ordovician the cockburnland terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip the connemara terrane is regarded as an allochthonous piece of the dalradian miogeocline and the south mayo terrane as a remnant of an early ordovician arc and fore arc which in mid ordovician times became a back arc marginal basin to northwest subduction the lake district wexford terrane is part of an arc to southeast subduction under gondwanaland whose activity climaxed in the mid ordovician the central terrane is interpreted as a silurian overstep assemblage which blankets the junction between laurentian and gondwanaland derived oceanic terranes and therefore iapetus is regarded as an ordovician ocean which closed prior to the silurian the model suggests that at the end of the silurian a clockwise rotating gondwanaland having carried laurentia into collision with baltica broke free and created a major sinistral strike slip zone which disrupted the ordovician palaeogeography in the british isles north american sector of iapetus

an ordovician ophiolite in county tyrone ireland ophiolites are regarded widely by geologists as remnants of old oceanic crust that has been obducted onto the continental margins during ocean or marginal basin closure and orogeny therefore they provide evidence for the existence of old oceans and oceanic basins and are a key to the extension of plate tectonic modelling into pre mesozoic rock assemblages in the caledonide appalachian orogen ophiolites are known although very few of these are dated well enough to provide accurate constraints on plate tectonic kinematics we report here the discovery of an ophiolitic sequence within the rocks of the tyrone igneous complex in northern ireland u pb dating combined with field evidence indicates that the tyrone ophiolite was formed and then obducted onto the northern margins of the iapetus ocean close to 470 myr bp arenig

the newer granite problem a geotectonic view the siluro devonian suite of granitic plutons in the british caledonides known as the newer granites together with their associated extrusive rocks represent one of the most extensively researched examples of calc alkaline magmatism apparently related to orogeny although recent chemical studies have credibly interpreted some of the scottish intrusions and volcanic rocks as part of a continental margin magmatic arc generated by the subduction of lapetus oceanic lithosphere beneath laurentia insurmountable problems of distribution and timing arise when attempts are made to relate the magmatic activity as a whole to a traditional two plate collision model for the orogeny newer granite magmatism is here discussed in the context of more mobilistic models for the post grampian evolution of the british caledonides which involve e w closure between laurentia and baltica terminated by collision in the silurian followed by the northward accretion of gondwana derived terranes in the early devonian the former produced the main caledonian tectonometamorphism of the northern highlands of scotland the latter the late caledonian deformation of the slate belts in the paratectonic caledonides these models imply much more complex convergence geometries which can in principle account for the whole newer granite suite as a series of subduction generated magmatic arcs overlapping in space and time the model proposed involves three late caledonian magmatic arcs in addition to the ordovician borrowdale arc which is not considered in this paper one is related to laurentia baltica convergence with westward subduction beneath the scottish sector of the laurentian margin in the ordovician and early silurian which generated the early members of the newer granite suite in the highlands a second is related to northward silurian early devonian subduction at the solway line which generated the younger newer granites and volcanic rocks north of the highland border and a third related to northward accretion of the armorican terrane in early devonian time produced intrusive and extrusive magmatism as far south as southeast ireland and the english midlands

the origin and significance of the delaney dome formation connemara ireland dalradian meta sediments of the laurentian margin and mafic intrusions thereof in sw connemara ireland tectonically overlie meta rhyolites of the delaney dome formation the two units are separated by the mannin thrust a new u pb age of 474 6 5 5 ma shows that the delaney dome formation is a temporal equivalent of arc volcanic rocks preserved in the adjacent south mayo trough the tourmakeady volcanic group erupted during the collision of an oceanic island arc with the laurentian margin in the grampian orogeny new rare earth and high field strength element data show that the delaney dome formation and tourmakeady volcanic group are chemically similar and arc like in character this suggests that the delaney dome formation is an along strike equivalent of the tourmakeady group strike slip faulted south of the south mayo trough during or after the grampian orogeny further correlation of these units with northern appalachian rhyolites is also possible the delaney dome formation is an extrusive temporal equivalent of intrusions that penetrate the connemara dalradian thus movement along the mannin thrust brought mid crustal plutons and dalradian country rocks tectonically above the extrusive volcanic sequence the mannin thrust is identified as a major imbricating structure within a continental arc but not a terrane boundary

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

the significance of a reliable ordovician age for some highland border rocks in central scotland a lower arenig fauna with north american affinities has been rediscovered at dounans aberfoyle central scotland this discovery makes part of the highland border complex younger than the adjacent dalradian rocks and suggests a provenance from the s

the ochil fault and the kincardine basin key structures in the tectonic evolution of the midland valley of scotland the ochil fault one of the most prominent tectonic features in the midland valley of scotland juxtaposes lower devonian volcanic rocks against late westphalian strata implying a possible vertical displacement of up to 4 km the kincardine basin in its hanging wall although actively subsiding during the greater part of the silesian trends generally n s perpendicular to the ochil fault and its silesian sedimentary record shows little sign of tectonic control by that fault it is proposed that the ochil fault was initiated possibly as a sinistral strike slip feature in the devonian but acted as a sidewall fault during the early evolution of the kincardine basin attributed to extension on a hypothetical pre brigantian fault along the bo9ness line on the east side of the basin until late namurian times when active extension ceased both faults were probably buried during late namurian and westphalian times reactivation of the ochil fault during end carboniferous n s extension dated by quartz dolerite emplacement was responsible for probably at least 2 km displacement including the presently visible footwall uplift it is suggested that the hanging wall may have contained a permian basin now removed