Fibrous quartz veins in deformed banded iron formation of the Amalia greenstone belt, southwestern Transvaal, are spatially related to gold–pyrite mineralization in both wallrock and vein inclusions. Poles to quartz vein orientations show a general parallelism with mineral elongation and fold plunges of the principal deformation in the wallrock. Quartz vein fibres show a consistent anticlockwise rotation, late components being subparallel to the elongation lineation, suggesting veining was probably synchronous with the principal deformation. Antitaxial fibrous veins, which dominate the mineralized banded iron formation, formed by the process of crack–seal which channelled mineralizing fluids along the vein walls, increasing the potential for fluid–wallrock interaction. Gold mineralization in quartz veins occurs in wall-parallel slivers of banded iron formation which have been plucked off the vein wall during antitaxial fibre growth. Mineralization can be explained by a process of fluid–wallrock interaction with sulphidation and gold precipitation.

Bipolar bivalve genera probably existed through the greater part of late Mesozoic (i.e. late Jurassic–late Cretaceous) time. Of the various theories put forward to account for their presence, those based on some form of global climatic zonation seem most appropriate. Although equatorial–polar temperature gradients were substantially less in late Mesozoic time than at the present day, high latitude regions were subjected to temperate (or even cool-temperate) climatic regimes. Macrobenthonic marine faunas may have been more susceptible to differentiation in response to these climatic patterns than nektonic ones. This is particularly so in the late Mesozoic strata of the Southern Hemisphere.

Comagmatic granitic and volcanic rocks are divided into two types depending on whether or not the primary magma contains restite crystals. Examples of both of these types are discussed from the Lachlan Fold Belt of southeastern Australia.

Volcanic rocks containing restite phenocrysts are chemically identical to the associated plutonic rocks containing the same amount of restite. The more mafic granitic rocks correspond in composition to the most phenocryst-rich volcanics (up to 60% phenocrysts), and thus cannot be cumulate rocks produced by fractional crystallization, but must represent true magma compositions. These restite-bearing magmas result from partial melting in a source region up to the rheological critical melt percentage, which we estimate to be about 40% in the S-type Hawkins Suite of volcanics.

Melts which escape their restite at the source, before the critical melt percentage is reached, are able to undergo fractional crystallization in high level magma chambers by heterogeneous crystallization on chamber walls. In this case volcanic products from the top of the chamber are more felsic than the plutonic products, the plutonics are crystal cumulates and the volcanics are composed of the complementary fractionated liquid. Those phenocrysts present in the volcanics were probably eroded from the chamber walls and are less abundant (< 20%) than in the restite-retentive volcanic products.

Basaltic, andesitic and rhyodacitic/rhyolitic volcanism was widespread during Ordovician time in the Welsh Basin. New chemical data are presented for Llanvirn to Caradoc lavas and tuffs from the Welsh Borderland which, during Ordovician time, formed the southeastern margin of the Welsh Basin. In view of the observed chemical alteration, immobile elements are used in the interpretation of the original geochemical character. The data indicate that the Llanvirn Stapeley volcanic group of the Shelve inlier was a bimodal basalt/basaltic andesite – rhyodacite/rhyolite association. The basalts have trace element contents of tholeiitic associations with a subduction-related character. The Caradoc Whittery and Hagley volcanic groups of the Shelve inlier comprise lavas and tuffs of calc-alkaline andesite. Blocks sampled from the Breidden Hills show that these were also derived from a calc-alkaline volcano. Associated Caradoc pumice- and ash-flow deposits from the Breidden Hills are probably of altered calc-alkaline rhyodacite/rhyolite composition. The Sibdon Carwood basalt flow, the only known example of Ordovician volcanism east of the Pontesford–Linley and Church Stretton lineaments, has transitional tholeiitic to alkaline character, with trace element contents influenced by subduction-related processes. The overall tholeiitic to calc-alkaline nature of the magmatism is consistent with the view that, during Llanvirn to Caradoc time, the Welsh Basin was an ensialic marginal basin.

The Precambrian–Cambrian boundary candidate section at Meishucun, China, has yielded trace fossils which are abundant at some horizons. The earliest occur in Unit 3 of the Zhongyicun Member approximately 8 m above the lower selected stratotype reference point for the boundary and include Arenicolites sp., Asteriacites sp., Neonereites biserialis, N. uniserialis and Sellaulichnus meishacunensis. The next trace-fossil-bearing horizon is in Unit 6 of the Zhongyicun Member where Cochlichnus sp., Monomorphichnus sp., Neonereites biserialis and N. uniserialis occur. Immediately above, in Unit 7, are Cruziana sp., Didymaulichnus miettensis, Monomorphichnus sp. and Rusophycus sp. In the Badaowan Member at the top of the section there are Didymaulichnus sp. and Taphrhelminthopsis circularis in Unit 9, Arenicolites sp., Diplocraterion sp., Gordia molassica, Skolithos sp. and T. circularis in Unit 11, and Gordia meandria, ? Plagiogmus sp., Skolithos sp. and T. circularis in Unit 12.

Comparison of this trace-fossil distribution with that in key Precambrian–Cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary (e.g. Didymaulichnus, Neonereites, Planolites) but most appear only in the Cambrian. Different ichnogenera seem to appear at various levels above the boundary. Arenicolites and Asteriacites are among the first, while Taphrhelminthopsis circularis is only encountered higher in all sequences. Some have only been recorded at much higher levels and relatively close to the first appearance of trilobites (e.g. Cruziana, Diplocraterion, Rusophycus). This suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late Precambrian and early Cambrian strata.

The Forland Complex of Prins Karls Forland has been subjected to mid-Palaeozoic greenschist facies metamorphism and polyphase deformation. Metamorphism was initiated prior to D1 deformation and gave rise to a parallelism of stratigraphic and metamorphic reaction surfaces. D1 gave rise to imbricately thrust, southwest-directed fold nappes which have not noticeably disturbed the isograd surfaces. D2, interpreted as belonging to the mid-Cenozoic West Spitsbergen Orogeny (WSO) which was coaxial but not coplanar with D1, produced crenulation folds and pressure solution cleavages and some thrusting. D3 structures are related to the formation of the Prins Karls Forland–Forlandsundet–Oscar II horst and graben system which is a late expression of the WSO. The rejuvenation of the Prins Karls Forland horst along NNW–SSE faults, the large scale E–W flexures and ENE–WSW faults in the Forland Complex and Tertiary graben deposits are assigned to D3.

A suite of late-tectonic minor intrusive rocks in the Inner Hebrides of Scotland show a well developed internal tectonic fabric. This fabric has a similar orientation in adjacent intrusions and it is usually not seen in the wall rock. It is suggested that the intrusions' tectonic fabric records the effects of palaeostress over the cooling period of the intrusions and thus provides palaeostress trajectories over a geologically short period of time over the area occupied by the swarm of intrusions.

Conodont colour alteration index (CAI) values from Upper Paleozoic rocks in the Cantabrian zone of northern Spain show that temperatures during Hercynian metamorphism locally exceeded 300 °C. Various temperature domains have been defined, which are generally separated by fundamental structures. These domains do not correspond with the tripartite subdivision based on stratigraphic analysis.

The observed CAI values of conodonts are in general agreement with the mineral paragenesis. Areas with high CAI values display extensive alteration and mineralization, and where CAI values exceed 4–4.5 (>200 °C) slaty cleavage has developed.

The Cantabrian zone is an area of very low grade metamorphism, where peak conditions were reached in Upper Carboniferous to Lower Permian times. The characteristics of the metamorphism and its spatial relationship with major faults suggest that fluids were the main source for regional heating and that fluid transport was focussed along crustal-scale structural features.

The overall deformation regime in this part of the Variscan orogen of western Europe is interpreted to be large-scale transtension. This is in agreement with earlier proposed models for the formation of Upper Palaeozoic basins in this area.

Homa Mountain is a well developed ijolite/carbonatite complex of Miocene to Quaternary age. Late stage olivine melilitite occurs as a satellite plug, parts of which show strong deuteric alteration to carbonate resulting in complete pseudomorphing of the melilite.

A second satellite centre exposes a grey carbonate tuff and accompanying dykes, all of which exhibit relic textures after an elongate, rectangular mineral also formerly believed to be melilite. Comparison with other recently described occurrences indicates however that the second centre erupted alkali-carbonatite and that the chief mineral originally present was nyerereite (Na2Ca(CO3)2). The field relationships and petrographic characters of both rock types are described and criteria are given which permit distinction between carbonated melilite and calcitized nyerereite. It is concluded that olivine melilitite and alkalicarbonatite are closely related in space and time.

The swarm of Palaeocene inclined sheets around Loch Scridain in southwest Mull includes basaltic sheets which contain abundant metasedimentary xenoliths that show evidence for having been partially molten. In contrast with the majority of dyke-like conduits worldwide, which have essentially planar margins, the contact of one of these xenolithic sheets with Moine metasediments is irregular along a segment where it crosses interbedded psammites and pelites. Relatively fusible mica schists have been excavated by the magma, on either side of a massive refractory quartzite horizon. Furthermore, the dolerite of the sheet shows only a slight reduction of grain size, through a zone 0.5 m wide, adjacent to its margin, in contrast with the pronounced marginal chilling which characterizes most intrusions of the Loch Scridain swarm. These field relationships are interpreted as evidence that the basic magma which formed this sheet flowed with local turbulence during its emplacement. The estimated liquidus of the magma (1130 °C at 1 atm) is approximately 200 °C above the solidus of pelitic horizons in the country rock, but far below the solidus of the quartzites.

Radiometric dates on specimens of plutons of the Coastal Cordillera of Atacama span the period 300–110 Ma. A group of dates cluster around 190 Ma and evidence is presented which strongly suggests that they represent near crystallization ages. The geographic distribution of these plutons, adjacent to Liassic tuffs and lavas (Pan de Azúcar and Posada de los Hidalgo formations), suggests a genetic relationship between them, and that the plutons were the roots of the Lower Jurassic volcanic chain. The location of these granitoids to the west of the Liassic volcanic rocks, favours a previous idea that the Liassic basin extended eastwards as a back-arc or intra-arc basin. The host rocks to the Lower Jurassic plutons include Palaeozoic granitoids and metasedimentary rocks, indicating that the volcanic chain was founded on continental crust. The distance from the Liassic plutons to the present-day trench is less than 100 km, which indicates the possibility that part of the arc-trench system of that time is missing.