Structural analysis of the Lower Allochthon in the north-central Scandinavian Caledonides has allowed the construction of restorable cross-sections consistent with the development of a foreland-propagating linked thrust system. The internal geometry of an antiformal stack, the Njakafjäll duplex, within the Lower Allochthon demonstrates tectonic shortening of c. 50% and suggests an overall predeformational width for the Lower Allochthon in this area of at least c. 130 km, and possibly considerably greater if the buried trailing edge of the Lower Allochthon lies in a comparable position to that farther south in Tröndelag. These results, combined with a stratigraphic analysis of the imbricates within the Lower Allochthon and of the adjoining Autochthon and Middle Allochthon, indicate the development, from Proterozoic through Cambrian times, of two sedimentary basins on the c. 200 km wide continental margin of Baltica bordering the Iapetus Ocean. The basins were separated by a region of basement relief, the Børgefjell domain, above which a reduced sequence of Vendian to Cambrian rocks accumulated. This Børgefjell basement high, and the similar Njakafjäll basement high to the east, subsequently became the sites of antiformal stack development. It is argued that the frequent incorporation of basement into the thrust sheets, together with the thin sedimentary fill of these basins, compared with the much greater fill in basins to the south in Jämtland and to the north of Finnmark, implies major palaeogeographic changes along the Baltoscandian margin, possibly related to early rift geometries. The apparent lack of subsequent foreland basin development in north-central Scandinavia compared with areas to the south may indicate a deeper level of thrust detachment beneath the Middle Allochthon to the north, such that any foreland basin sediments have been removed in the hangingwall and subsequently eroded. An alternative possibility is a primary absence of foreland basin development that may relate to a differing response to thrust loading by continental lithosphere which had been variably thinned during the earlier rift regime.

Crystal rich (∼ 70–98% phenocrysts) magmatic inclusions in pumices for compositionally heterogeneous ignimbrites from the Central Andes of northern Chile are interpreted as the products of crystal accretion at the sidewalls of the magma chambers. The inclusions are typically andesitic in composition and are found as ‘peppery textured’ lenses and bands, or as discrete ovoid ‘blobs’ within dacitic pumices from the early erupted portions of the ignimbrites. The inclusions have a bimodal gain size with large phenocrysts (> 1 mm), typical of those of the host pumice, set in a dominant finegrained framework (< 0.5 mm) of plagioclase, with lesser amounts of hornblende and biotite in equal proportions, and ubiquitous titanomagnetite in a matrix of vesiculated high-Si rhyolite glass. An igneous microgranular texture is defined by this framework. The mineralogy of the inclusions, as well as the compositions of the phenocrysts and glass, are very similar to those of the host pumices. These characteristics, in addition to available major, trace and REE data, are best reconciled if the inclusions represented samples of fractionated crystals and glass from the same magma as the host pumice. The restricted occurrence of these inclusions in the early erupted portions of the ignimbrites suggests that these crystal accumulations occurred in the upper portions of the magma chambers, at the sidewall; the dominantly fine grain size and crystal rich nature of the inclusions are considered to be the result of the higher thermal gradient in the boundary layer.

These inclusions may be an important link between the experimental and geochemical models for the origin of compositional layering in magma chambers by sidewall crystallization. The presence of similar inclusions in other ignimbrites and volcanics, as well as plutonics, suggest that they may be a common feature of silicic magmas.

The Neihart Quartzite is the basal quartz arenite unit (≍270m thick) of the Mid-Proterozoic Belt Supergroup of western North America. Petrographic studies indicate a source area with plutonic granitic, metamorphic and felsic volcanic rocks. Extreme textural maturity and bimodality indicate an episode of aeolian transport for the detrital quartz grains. The lower 80% of the Neihart Quartzite were probably deposited by braided streams, whereas the upper 20% were deposited in shoreline environments. Residual material that was ‘stored up’ on the pre-Beltian cratonic surface and underwent aeolian reworking was the likely source material for most of the Neihart Quartzite. Less mature sediments in the top portion of the Neihart Quartzite indicate uplift and erosion of new source material during Neihart deposition. Other known cratonic quartz arenites, such as the St. Peter Sandstone (Ordovician), Lamotte Sandstone (Cambrian) and Flathead Quartzite (Cambrian), are thin (tens of metres thickness) and exhibit sheet-like geometry. In contrast, the Neihart Quartzite and its probable lateral equivalents are considerably thicker and increase in thickness towards the central portions of the basin. It thus appears that Belt sedimentation began with accumulation of a basal quartz arenite unit, and that sand for that unit was transported by braided streams from the surrounding craton to a gradually subsiding Belt basin.

Alkaline and ultramafic lamprophyre dykes at Aillik Bay on the coast of central Labrador exhibit features indicative of volatile-rich conditions at the time of emplacement. Aillikites (ultramafic lamprophyres) are flanked by closely spaced fracture systems whose formation was promoted by a carbonate-rich fluid moving ahead of the intruding magma. Sannaites (alkaline lamprophyres) frequently have horned termination structures which are interpreted to be partial reconnections between dyke segments which had separated at an earlier stage of intrusion.

The lamprophyre dykes comprise three sets which are interpreted as cone sheets and radial dykes related to an intrusive centre located beneath the Labrador Sea to the northeast of the coastal exposures. This complex is one of several on the margins of the Labrador Sea, and its position may be influenced by the Archean/Aphebian boundary and by a major oceanic structural feature represented by offsets in seafloor magnetic anomalies.

The earliest of four distinct phases of deformation recognized in the central part of the Proterozoic Mount Isa inlier involved brittle extensional faulting at shallow crustal levels. Extensional faulting produced stacks of imbricate fault slices, listric normal faults and characteristic tourmalinerich breccias. Structures belonging to this phase occur over a large part of the inlier and indicate an important phase of basin-forming crustal or lithospheric extension at 1750–1730 Ma. Late intense ductile deformation and tight folding of the imbricate systems destroyed part of these older structures, and obscures their existence in many parts of the inlier.

The brissid echinoid Amoraster (gen. nov.) is described from Miocene strata in southern Australia on the basis of two species: A. paucituberculata sp. nov., which ranges from the Batesfordian (latest Early Miocene) Bochara Limestone to the Bairnsdalian–Mitchellian (Middle–Late Miocene) Port Campbell Limestone in Victoria; and A. tuberculata sp. nov. from the Longfordian (Early Miocene) Mannum Formation in South Australia. Morphological changes which occurred with the evolution of A. paucituberculata from A. tuberculata are interpreted as being adaptations to the occupation of a finer grained sediment by the descendant species.

The Bwlch y Cywion microgranite intrudes an Ordovician sedimentary sequence in northeast Snowdonia, North Wales. Its age is recorded by hornfelses within its metamorphic aureole which give an Ordovician age of 454 ± 20 Ma. The whole-rock Rb–Sr isotope systems of the intrusion, however, and of an associated ash-flow tuff and a rhyolite of the Llewelyn Volcanic Group (Caradoc), were reset during low-grade metamorphism and give Devonian ages of 392±11 Ma, 392±5 Ma, and 405 ± 6 Ma, respectively.

At least 2000 km3 of relatively uniform dacitic magma have been erupted from the Cerro Galan caldera complex, northwest Argentina. Between 7 and 4 Ma ago several composite volcanoes predominantly of dacitic lava were constructed, and several large high-K dacitic ignimbrites were erupted. 2.2 Ma ago the > 1000km3 Cerro Galan ignimbrite was erupted. The predominant mineral assemblage in the ignimbrites is plagioclase-biotite-quartz-magnetite-ilmenite; the Cerro Galan ignimbrite also contains sanidine. Fe-Ti oxide minerals in the Cerro Galan ignimbrite imply temperatures of 801–816 °C. Plagioclase phenocrysts in the ignimbrites typically have rather homogeneous cores surrounded by complex, often oscillatory zoned, rims. Core compositions show a marked bimodality, with one population consisting of calcic cores surrounded by normally zoned rims, and a second of sodic cores surrounded by reversely zoned rims. The older ignimbrites do not show systematic compositional zonation, but the Cerro Galan ignimbrite exhibits small variations in major elements (66–69% SiO2) and significant variations in Rb, Sr, Ba, Th and other trace elements, consistent with derivation from a weakly zoned magma chamber, in which limited fractional crystallization occurred. The ignimbrites have 87Sr/86Sr = 0.7108–0.7181; 143Nd/144Nd = 0.51215–0.51225, and δ18O = + 10 to + 12.5, consistent with a significant component of relatively non-radiogenic crust with high Rb/Sr and enriched in incompatible elements. Nd model ages for the source region are about 1.24 Ga. 87Sr/86Sr measurements of separated plagioclases indicate that Anrich cores have slightly lower 87Sr/86Sr than less calcic plagioclases, suggesting a small degree of isotopic heterogeniety in different components within the magmas. Pb isotope data for plagioclase show restricted ranges (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb = 18.87–18.92, 15.65–15.69 and 39.06–39.16 respectively), and suggest derivation from Proterozoic crustal material(> 1.5 Ga).

Contemporaneous satellite scoria cones and lavas are high-K basalts, basaltic andesites and andesites with SiO2 = 51–57%; K2O = 2–3% and normative plagioclase compositions of An37–48, and may be derived from a mantle source containing both ‘subduction zone’ and ‘within plate’ components. 87Sr/86Sr ranges from 0.7055 to 0.7094 and 143Nd/144Nd from 0.51250 to 0.51290. Variation diagrams such as MgO: SiO2 show two trends, one indicating closed system fractional crystallization and the other crustal contamination. AFC modelling of the open system rocks indicates a parental mantle-derived mafic magma which is itself enriched in K, Rb, Ba, U, Ta/Sm, Ta/Th and Sr, and has 87Sr/86Sr = 0.705–0.706, while the contaminant need not be more radiogenic than the dacitic ignimbrites.

The Cerro Galan dacitic magmas are interpreted in terms of a deep and uniform region of the central Andean continental crust repeatedly melted by emplacement of incompatible-element-enriched, mantle-derived mafic magmas, a proportion of which may also have mixed with the dacite magmas. A component of the crustal material had a Proterozoic age. The magmas derived by crustal melting were also enriched in incompatible elements either by crystal/liquid fractionation processes, or by metasomatism of their source regions just prior to magma generation. Much of the crystallization took place in the source region during the melting process or in mid-crustal magma chambers. The magmas may have re-equilibrated at shallow levels prior to eruption, but only limited compositional zonation developed in high-level magma chambers.

Compositional variation in Lower Old Red Sandstone (ORS) detrital garnets can be used to evaluate potential source areas and to trace the pattern of early Devonian sediment dispersal. Garnets in northwesterly derived fans along the northern flank of the Midland Valley appear to duplicate spatial variation in the compositions of garnets in the adjacent Dalradian block. Whilst metamorphic clasts ‘resembling’ Dalradian lithologies occur in these fanglomerates, the strike-extent of Dalradian-type crust (c. 1000 km) makes simply matching the clasts a rather imprecise way of constraining source–basin displacement. The garnet data imply that the Ordovician separation inferred for crustal blocks juxtaposed along the Highland Boundary was removed by early Devonian times. Major Silurian displacements are thus invoked along the Highland Boundary with amalgamation largely achieved prior to the ‘Acadian’ transcurrent deformation seen in the slate belts to the south. Vertical changes in the composition of garnets in the thick Lower ORS sequence in the northeast Midland Valley are slight and it is not known to what extent these reflect migration of a differentiated source block or the involvement of recycled additions which become increasingly important towards the base of the ORS succession. The axially dispersed sandstones which interdigitate with the northwesterly derived fans are dominated by spessartine-rich almandines which resemble garnets fed laterally to the basin in the northwest Midland Valley. Although the large scale inferred for the axial fluvial system suggests that its drainage basin extended outside Scotland, almandine-pyropes which might have come from exhumed eclogites in western Norway are absent. Such compositions are widespread in Mesozoic sandstones in the northern North Sea and it is evident that these sediments do not represent the final repository for the 'lost' sediment stripped from Caledonian metamorphic terranes in Scotland. Garnet populations from the Anglo-Welsh Basin do not resemble those in the coeval axial sandstones of the Midland Valley, suggesting that the two basins were not linked at this time. The scale of the Midland Valley axial sandbodies are inconsistent with internal drainage of central Scotland and a route to the early Devonian shoreline must be sought. It may be that 'Acadian' strike-slip motions have displaced the Scottish basins from the coastal alluvial plains they originally fed.

The lithological and biotic succession across the late Precambrian to early Cambrian interval is outlined for the Dalir and Valiabad successions of the Elburz Mountains of Iran. The Lower Dolomite Member contains an assemblage of phosphatic tubes and other poorly preserved remains. The succeeding Lower Shale Member bears macroscopic chuariamorphid algae. Early skeletal fossil diversity rises through the Middle Dolomite Member, with the successive appearance of Protohertzina anabarica, Cambrotubulus decurvatus and Anabarites trisulcatus, culminating near the top of the dolomites with the appearance of Purella sp., Maikhanella multa, Tiksitheca licis and circothecids. This succession is compared with lower to upper parts of the Nemakit-Daldyn Formation of Siberia. The overlying Upper Shale Member bears phosphatic beds at its base with allathecids and an uncoiled pelagiellid (?Aldanella sp.) that suggest comparison with lower Tommotian strata and the Precambrian–Cambrian boundary phosphorite event of southern and central Asia. A rich assemblage of molluscs appears high in the Upper Shale Member, including the Latouchella korobkovi group and the Pelagiella lorenzi group. The succession is broadly homotaxial with those from the Siberian Platform and Mongolia and those platforms bordering Gondwana (India, Kazakhstan, South China).

Basaltic hawaiite lavas are virtually absent in the Eocene Skye Main Lava Series, in contrast to relatively abundant basalts and hawaiites. Fractional crystallization from basalt to basaltic hawaiite involves extraction of a large proportion of plagioclase, and liquid densities thereby increase. From basaltic hawaiite to hawaiite titanomagnetite is a significant fractionating phase, and liquid densities decline. The coincidence between a gap in erupted compositions and a density maximum implies that liquid density exerted a strong control on ‘eruptibility’ of magmas; basaltic hawaiites were too dense to be erupted. Density maxima occur in basalt suites if plagioclase fractionates before Fe–Ti oxides, and may explain compositional gaps in erupted magmas. Compositional gaps are not the inevitable result of density maxima; the density of the rock column above, and the fluid dynamics within, the magma chamber where differentiation occurs are also critical factors.

Construction of cross-sections in Bellsund and Hornsund, southern Spitsbergen, using offshore and onshore structural data illustrate the main tectonic units of the region. From west to east these are: a wedge of late Cenozoic clastic sediments; a series of late Palaeozoic to early Mesozoic grabens controlled by basement faults along the west Spitsbergen margin; the Basement Horst, comprising late Precambrian to early Palaeozoic rocks deformed and metamorphosed during a mid-Palaeozoic orogeny; the Fold Belt, which forms a narrow NNW–SSE striking zone of eastward verging folds and thrusts attributed to Eocene inversion of a pre-Cenozoic basin; the Palaeogene Central Basin, deformed into a broad synclinorium and bound to the east by the Billefjorden Fault Zone. This basement lineament shows evidence of Palaeogene reactivation and may be linked to the Fold Belt by a detachment zone beneath the Central Basin. East of Spitsbergen, there is an offshore basin of possible Carboniferous age controlled by the Storfjorden Fault Zone which shows evidence of later inversion to form a positive flower structure.

A well-known tectonic event affecting the East Mediterranean region, generally referred to as ‘the’ Miocene–Pliocene phase, occurs at, or near the Miocene–Pliocene boundary. Recent sedimentological studies in Cyprus indicate that this ‘event’, in fact, is complex. The Tortonian–Lower Pliocene period is marked by a stress involving an N20 extension in the Polemi and Pissouri basins and by an N100 extension in the Psematismenos basin. Sedimentological studies have demonstrated three tectonic pulsations during Messinian time, prior to the Pliocene transgression. These are expressed by two episodes of seismic brecciation, and a palaeo-emersion is indicated by palaeosols and detrital discharges. These phenomena suggest brief tectonic instability during Messinian time. Microtectonic studies in the South Troodos basins of Cyprus reveal that the main change in tectonic stress does not coincide with the Miocene–Pliocene contact but occurs at the end of Lower Pliocene time. The authors conclude that the so-called Miocene–Pliocene ‘event’, in reality, is a series of subtle tectonic pulsations recorded clearly by sedimentary parameters.

The Periadriatic Lineament Zone which forms the boundary between the Eastern and Southern Alps in the Karawanken region of Austria has a complex history spanning the Variscan and Alpine orogenies. Variscan regional metamorphism and polyphase deformation followed by Late to Post Variscan intrusive activity with accompanying contact metamorphism affects a belt of structurally complex rocks referred to as the Eisenkappel Zone to the north of the lineament. Weak Early Alpine deformation in the Southern Alpine rocks can also be recognized in the Eisenkappel Zone. The Young Alpine intrusion of the Karawanken Tonalite was followed by lateral fault displacements associated with the formation of the Periadriatic Lineament. Late Tertiary sediments, caught up in the northward directed thrusting responsible for the uplift of the Karawanken chain, record the youngest deformation in the area.

A regional Tertiary basaltic dyke swarm intensifies within a Caledonian granite at Barnesmore, Co. Donegal. Rapid heating along the contact of one (possible feeder) dyke resulted in disequilibrium partial melting of granite wall-rock and the generation of a range in melt composition by the in situ melting of feldspar. The compositional variability of the melt is preserved in a glass containing feldspar spherulites and other quench phases which suggest rapid cooling. During partial melting the trace elements, Rb, Sr, and Ba were mobile and have been concentrated in glassy melted granite close to the contact of one dyke. The textures, mineralogy and geochemistry of dolerite in two dykes indicate localized bulk contamination and mixing with melted granite. This had a particularly marked effect on the crystallization of pyroxene and resulted in a wide range in mineral composition reflecting the degree of contamination. The intensification of a regional dyke swarm in well-jointed granite might control the siting of some major intrusive centres. Granite melted and mixed with basaltic magma may contribute to the evolution of granites in such centres.

The NW–SE Cornubian fault zones (FZs) continue to southwest Wales, where they caused dextral offsets during the late Stephanian. A fault bounded area of Devonian–Carboniferous strata, intruded by the Tertiary Lundy Igneous Complex, forms the Lundy Rhomboid. It originated as the Lundy Rhomb Graben, created by 28–40 km of Tertiary sinistral strike–slip faulting along the left-stepping NW–SE Sticklepath–Lustleigh FZ (SLFZ). Tertiary sedimentation in the graben was accompanied by intrusion of the 2.5–4.0 km thick igneous complex into its basement. Sedimentation later spread beyond the graben to form a ‘steer's horns’ basin, of which the Stanley Bank and West Lundy basins are remnants. The strata of the rhomb graben and the ‘steer's horns’ basin constituted the perhaps 4 km deep Lundy Pull-Apart Basin. Subsequent relatively minor dextral faulting on the left-stepping SLFZ inverted the graben into the Lundy Rhomb Horst; the basement of the graben was uplifted ≮ 1–2 km (net) and exposed by erosion of the Tertiary strata. The pull-apart basin developed at the intersection of reactivated Hercynian NW–SE transform FZs, and E–W subduction zone thrusts. Cenozoic N–S tensional and compressional reactivations of the thrusts were respectively associated with transtensional development of the pull-apart basin, transpressional of the rhomb horst.

If historical earthquake data are to be used in studies of regional seismotectonics, it is essential to include information on likely locational uncertainty. Contributory factors include both geophysical parameters and the social environment of the event. A reconstruction of how a recent earthquake might have appeared had it occurred 300 years ago is used to demonstrate the effects of documentary survival. Limits of uncertainty are estimated for two historical earthquakes (7 October 1690 and 28 November 1880) and shown to be large. It is recommended that such events should be shown on epicentral maps as areas rather than points.

The Loch Monar Synform folds the Sgurr Beag slide in the central northwest Highlands of Scotland. The east–west trend of the synform is oblique to the regional trend of the slide. However, when late-stage strain effects associated with superimposed folds on the synform are removed using computer techniques, the trace of the synform axial surface becomes perpendicular to the regional trace of the slide. The synform also becomes tighter and recumbent in attitude. The synform axis is parallel to strongly developed lineations. Folds of this generation appear to be localized in the vicinity of the slide. These observations suggest a model of folding associated with movement of the slide, followed by locking up of the slide and internal strain resulting in the superimposed folds and rotation of the synform.

Silicified flake conglomerates and in situ stratiform stromatolites of the Upper Proterozoic (c. 700–800 Ma) Limestone-Dolomite ‘Series’, central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages is Siphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder, Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively by Siphonophycus kestron. Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new: Myxococcoides stragulescens n.sp. and Scissilisphaera gradata n. sp.