At the submerged margins of the North Atlantic, andesitic to dacitic and basaltic volcanic rocks occur together. The silicic rocks were derived by processes requiring the presence of continental crust (crustal anatexis and/or contamination of mafic magmas) while the majority of the basaltic lavas had little or no contact with continental crust. We report 40Ar–39Ar incremental heating ages for several dacitic and basaltic rocks recovered from three offshore localities of the North Atlantic Igneous Province. Dacitic lavas and tuffs at the southeast Greenland margin and trachytic lavas in the Scottish Hebrides erupted contemporaneously with basaltic lavas at 62–61 Ma. In contrast, the silicic lavas from the northern Rockall Trough (offshore western Scotland) and the Vøring Plateau (offshore Norway) erupted at ∼55 Ma followed shortly by basaltic volcanism. At this time, silicic magmatism at the southeast Greenland margin had ceased and only oceanic basalts were erupted. Similarly, ∼55 Ma lavas on the southwest Rockall Plateau are wholly basaltic. The compositions of all of the dated silicic volcanic rocks are consistent with derivation from partial melting of either continental crust or sediments. The heat necessary for partial melting appears to have been provided by basaltic magmas. Therefore, the existence of the silicic rocks indicates the presence of continental crust as well as a stable tectonic environment that allowed the stagnation and pooling of basaltic melts within the crust. With this in mind, it is apparent that at 62–60 Ma, both western and eastern sides of the present North Atlantic margins were characterized by extensional environments within continental crust that were restrictive to the passage of mafic magmas. By 55 Ma, at the time of continental breakup, the proximal margins at southeast Greenland and the Rockall Plateau were devoid of continental crust. But the presence of 55 Ma silicic magmatism on the eastern North Atlantic margin can be attributed to a broader zone of magmatism and sediment-filled Mesozoic rift basins.

Central Cape Breton Island in Nova Scotia, Canada, is host to ∼700–630 Ma felsic and associated mafic volcanic rocks that are relatively rare in other parts of the Avalon Composite Terrane, occurring elsewhere only in the Stirling Block of southern Cape Breton Island and in parts of eastern Newfoundland. The mafic rocks of central Cape Breton Island are typically intraplate tholeiitic basalts generated by melting of a garnet-bearing mantle source. They lack a continental trace element and εNd imprint although they were emplaced on continental crust; they resemble oceanic island basalts. Contemporaneous volcanism in the Stirling Block is calc-alkaline and formed in a volcanic arc setting. In the absence of evidence for an intervening trench complex or suture, it may be inferred that the central Cape Breton tholeiites formed in a back-arc setting relative to the Stirling Block. This rifting may represent the initial stages of separation of an Avalonian arc from western Gondwana. The arc rifted further between ∼630–610 Ma when the younger Antigonish-Cobequid back-arc basin formed. Subsequently, the extensional arc became convergent, telescoping the back-arc basin. Northwestward migration of calc-alkaline arc magmatism may be related to shallowing of the associated Benioff zone through time.

Stable isotopic measurements have been made on both planktonic foraminifera and coccolithic matrix of Middle Cretaceous (Late Albian–Cenomanian) age from two Pacific low latitude sites. The degree of alteration of the foraminifera has been assessed through the application of chemical analyses, cathodoluminescence and Scanning Electron Microscopy (SEM). The rotaliporid foraminifera display an interspecies range of δ18O values from −2.29 to −3.01‰ at Deep Sea Drilling Project (DSDP) Site 463 and from −2.74 to −3.55‰ at DSDP Site 305. Hedbergellid foraminifera exhibit a δ18O interspecies variation of −2.52 to −3.02‰ at Site 305. Isotopic analysis of individual Hedbergella delrioensis and Rotalipora appenninica foraminifera from single samples shows H. delrioensis to have a surprisingly large spread of δ18O values (−2.492 to −3.097‰ from Site 463, −2.454 to −3.344‰ from Site 305), whilst δ13C values remain confined to a narrower range. Such a spread of oxygen values may be related to a number of factors, including subtle diagenetic alteration, a wide range of temperature-related depth habitats or growth related changes of primary skeletal calcite. The hedbergellids have consistently lighter oxygen and heavier carbon isotopic values than do the rotaliporid foraminifera and hence provide isotopically derived palaeotemperatures consistent with a thermally stratified ocean. At both sites the oxygen isotopic data are consistent with a gradual warming through Albian–Cenomanian time. However, the results suggest that Middle Cretaceous equatorial oceans were possibly only as warm as those of the present day (or slightly warmer), but did not reach the high temperatures claimed in older literature.

In extensional tectonic settings, vertical movements of the earth's surface are largely controlled by rates of strain. Extensional strain rates within the Larderello geothermal area, located in inner parts of the Northern Apennines, have been evaluated together with uplift rates and 40Ar/39Ar cooling ages. Results indicate that extensional strain rates have been relatively low (5.8×10−17 s−1), since the middle Pliocene. Differential uplift rates are estimated to have been high (c. 0.2 mm/year). Strain and uplift rates within the Larderello region are consistent with the regional tectonic framework. The low strain rate, rapid uplifting and high heat flow within southern Tuscany can be explained by an eastward dipping lithospheric shear maintained since at least middle Pliocene times.

The Mesoproterozoic Kibaran belt in southwest Rwanda (Central Africa) consists of two contrasting metamorphic sequences. The first is essentially composed of weakly deformed, low-grade pelitic rocks with many quartzitic intercalations and some volcano-sedimentary sequences. The second consists of medium- to high-grade metamorphic metasediments and gneisses, intruded by sheared granitoids. Existing geological maps are of limited use in understanding the evolution of this part of the Kibaran belt. A combination of airborne γ-spectrometry data with Landsat TM imagery readily distinguishes known lithologies, and in particular detects two distinct granite types. Trace element data for one granite type does not correspond with known petrochemical trends of Kibaran granites, and may belong to a pre-Kibaran basement. The combining of these data with a recently published schematic geological map of the northeast Kibaran belt and re-interpreted field structural data, suggests a model for the Kibaran orogenic evolution in terms of extensional detachment tectonics and associated metamorphic core complexes.

Little is known about the cleavage–fold relationships in the Lower Palaeozoic Brabant Massif, primarily because of the scarcity of suitable exposures. Moreover, to date, folds have only been described in the Ordovician and Silurian sequences along the southern extremity of the basement. However, excavation works for the construction of the TGV(railway)-track south of Brussels created an opportunity to study cleavage–fold relationships in the Lower Cambrian terrigenous series (Tubize Group) in a more central part of the Brabant Massif. The structural features observed seemed inconsistent with the suspected regional trends. Primarily, a divergent cleavage fan was observed in a region thought to have a regular cleavage attitude. The symmetrical but divergent disposition of the cleavage with regard to the fold hinges is explained by flexural folding of a pre-existing bedding-parallel compaction fabric. Cleavage development and folding are considered synchronous. The divergent cleavage fan reflects local strain variations. Also the steeply plunging hinge lines of the open, subangular folds are seemingly inconsistent with the regional trend characterized by subhorizontal fold hinges. Taking into account the structural position of the fold assemblage in the subvertical limb of a large-scale, upright, isoclinal fold structure, the fold assemblage is interpreted as an incongruous parasitic feature. The steeply plunging hinge lines are considered to be caused by fold hinge rotation during progressive coaxial deformation. Although this incongruous fold assemblage with its divergent cleavage fan is localized, it provides important information on both local and regional deformation circumstances in this part of the Anglo-Brabant Fold Belt.

Microfossils obtained from dissolution of a limestone horizon from the lower Cambrian Allt y Shed Sandstone of the Llangynog Inlier, Carmarthenshire, South Wales, are identified as agglutinated foraminiferans. Two genera and three species are represented and are figured. These microfossils add further to the scanty record of Cambrian foraminiferans, but do not resolve the problem of the precise age of the Allt y Shed Sandstone.

The Honningsvåg Intrusive Suite consists of several layered mafic/ultramafic intrusions and a transgressive body of igneous breccia that appears to represent a magma conduit. It is emplaced into a Silurian, flysch-type sedimentary sequence that is thermally metamorphosed to spotted slate, cordierite–andalusite or pyroxene hornfels and agmatitic migmatite. Folds and flattened reduction spots in the hornfelses suggest that emplacement took place after Caledonian deformation and development of a slaty cleavage. Tectonic rotation subsequent to emplacement has led to exposure of the Honningsvåg Intrusive Suite in a natural cross-section corresponding to ∼10 km of crustal depth. Basaltic magma was initially emplaced as a several-kilometre-tall pipe that crystallized to form Intrusion 1. A second magma chamber was initiated alongside this pipe and subsequently expanded laterally into a sill-like magma body as batches of olivine-saturated basalt were added. A later magma chamber, represented by Intrusion 4, developed largely within the cumulates forming the upper part of Intrusion 2 and appears to have been accompanied by opening of a broad inclined feeder into which blocks and slabs of older cumulates collapsed. The resulting igneous breccias of Intrusion 3 are chaotic and largely clast-dominated in the lower part of the conduit, but enclosed slabs are matrix supported and orientated parallel to an originally subhorizontal banding in the feldspathic peridotite matrix in the upper part. The core of the breccia body has a troctolite matrix and contains blocks of older breccia, suggesting re-opening of the conduit, either during the crystallization of Intrusion 4 or possibly during the development of chambers represented by the younger layered intrusions. The cumulates in Intrusion 4 subsided sufficiently to invert marginal parts of the Layered Series before a further magma chamber was initiated in its roof rocks. The last major magma chamber opened alongside Intrusion 5 and extended upwards as a pipe or broad dyke to the highest structural levels exposed. Cross-cutting relationships show that the Honningsvåg magma chambers were not active simultaneously but were emplaced sequentially, generally at successively higher structural levels. Olivine tholeiite magma initially pooled in a crustal zone where it had neutral buoyancy. Subsequent chambers are suggested to have been initiated by emplacement of magma along the density discontinuities that existed above and around crystallized intrusions and their associated hornfelses. Chambers evolved by fractional crystallization, assimilation of country rocks and periodic replenishment. The abandonment of magma chambers may have resulted from the expulsion of low-density residual melts.

Gabbroic rocks crop out commonly in different localities of the Central Anatolian Crystalline Complex and are interpreted by many researchers as the remnants of a Neotethyan ophiolitic suite now observed as roof-pendants in the granitoids of the complex. In this study, the structural position of the gabbroic rocks within one of the granitoids of the Central Anatolian Crystalline Complex, namely the Ağaçören Granitoid, is determined by geological and aeromagnetic data from the central part of the pluton. The gabbroic rocks have sinuous contacts with the Ağaçören Granitoid and they display a gradual change in composition and texture from gabbro at the top of the hills to diorite at the foot of the hills towards the contact with granitoid. Power spectra, high- and low-pass filtered aeromagnetic and pseudogravimetric anomalies were produced using geophysical methods. A two-dimensional model constructed from the high pass-filtered anomalies, with the control of the in situ susceptibility data and the low-pass filtered anomaly, suggests existence of a shallow conical-shaped and deeply buried gabbroic body. The deep body extends down to deeper levels of the upper crust and, given the textural and compositional features which suggest magma mixing, is interpreted as an intrusion coeval with the Ağaçören Granitoid.

The Almazán Basin (northern Spain) is a Tertiary basin, 90×45 km wide, located in the western part of the Iberian Chain. It is filled with folded Palaeogene (2500–3000 m thick) and horizontal Neogene (500 m) beds. From the study of a satellite image, more than 2300 lineaments have been identified in the Neogene horizontal rocks. Their absolute orientation maximum is 060–070, and relative maxima are 100–110 and 120–140. Some spatial variations in the regional trends can be observed: (1) Throughout the central part of the basin, the east–northeast trending lines are the most representative. (2) Near the eastern border of the Basin the northwest–southeast set (parallel to the trend of thrust and folds in the older rocks) is dominant. (3) In the northwestern part of the basin the northwest–southeast and WNW–ESE sets coexist with the main east–northeast set. The maximum density of lineaments is found along a WNW–ESE line that corresponds with the axis of maximum thickness for the Tertiary units. A detailed field study of fracturing at the outcrop scale (more than 2300 fractures measured) was carried out. The orientation distribution of lineaments coincides with the orientation of left-lateral faults at the outcrop scale, and differences are greater when considering all kinds of fractures in different sectors. The origin of fracturing at different scales in the Almazán Basin can be related to the Neogene stress field and the influence of previous structures: (1) The northwest–southeast set of fractures formed as a result of reactivation of older faults, inherited from the late Variscan fracturing. (2) The main ENE–WSW set of fractures corresponds to neoformed left-lateral joints and faults under the northeast–southwest Neogene compression, the dextral conjugate set of joints within this system (NNE–SSW) being much less developed.

Well-preserved soft sediment deformation structures were observed at six sites along the course of the Baldi Nadi in the Doon valley of the Garhwal Himalaya. These deformed structures lie in mid- and side-channel bars of the braided Baldi stream. The deformed sediments are composed of unconsolidated alternations of mud, silt and very fine sand with ripple lamination. Deformation is restricted to a single stratigraphic layer bounded by undeformed beds, suggesting synsedimentary deformation. These features can be traced laterally along the course of the braided Baldi Nadi, over a distance of 7 km in isolated bar deposits at one stratigraphic level, 1.5–2 m above the lean season water level. The deformed features display over-steepening of sedimentary strata, folding, graben-type faulting, plume-like intrusion, flame structure, slumping related to disrupted bedding and pear-drop structure. The style and type of deformation vary considerably in the different segments within a single bed, while the intensity may be same at one site. The deformation features of the Baldi Nadi are interpreted to be the product of liquefaction and fluidization of unconsolidated mud and silt during historic earthquake(s), related to the past seismic activity of the Main Boundary Thrust (MBT) and the Himalayan Frontal Fault (HFF) or blind thrust. The intensity of deformation provides an opportunity to reconstruct the felt area magnitude of large historic earthquake(s) and helps in tracing the palaeoearthquake epicentre. The observed earthquake-induced soft sediment deformation features indicate that in addition to the 1905 ‘great’ earthquake, the Doon valley was also affected by historic earthquake(s) of magnitude ∼7, possibly corresponding to those of 1803 and/or 1720, if not older.

The expression ‘fault-fin landscape’ is proposed for topography marked by sets of blade-like fins and walls of rock, controlled by deformation band shear zones, which project metres above upland surfaces of porous sandstone. Dramatic examples occur along monoclines of Navajo Sandstone in the Colorado Plateau region of southern Utah, USA. The fins express differential rates of erosion of porous (20–25%) host sandstone relative to deformation band shear zones (<1% to 5% porosity), which are made highly resistant by collapse of porosity, cataclasis of quartz grains, and silica precipitation.