Petrological and geochemical features of recently discovered basalts of the Troodos Massif, Cyprus — a dyke in the Basal Group and altered pillow lavas in the Lower Pillow Lavas — suggest that all the lavas are part of a single volcanic suite.

The ultramafic—mafic complex at North Cape lies in a Mesozoic—Lower Tertiary tectonic belt linking New Zealand with New Caledonia and Papua New Guinea. The complex is faulted against Cretaceous submarine tholeiites and contains (1) serpentinized harzburgite and lherzolite of probable cumulus origin (and intruded by more Fe-rich wehrlitic veins and dykes), overlain by (2) layered olivine- and orthopyroxene-gabbro subvolcanic cumulates which are themselves host for (3) a sheeted dyke swarm of mainly quartz-diorite composition. It is suggested that the complex was emplaced with the Cretaceous volcanics by obduction of Mesozoic oceanic crust during the Lower Tertiary.

A vertical channel structure within a layered dolerite dyke resulted from differential magmatic flow. Layering in both dyke and channel is formed of more feldspathic dolerite attributed to fluctuations in water vapour pressure and supercooling during crystallization.

Field, petrographic and chemical evidence from the cumulates of western Lilloise suggest a substantially higher level of exposure in the cumulus pile than is seen on the E side, due to relative subsistence of the western half of the intrusion. It is suggested that the subsistence started while both cumulus pile and the surrounding basalts were still hot and not fully consolidated. When, later, reactivation occurred, the rocks were in a more cohesive state and ‘syenitic’ magma was available for intrusion as discrete sheets and veins.

Clastic dykes are described from a late Precambrian sequence of shallow water sediments — the Porsangerfjord Group of Finnmark, North Norway. The dykes are from one stratigraphic member of the Group and only occur where this member outcrops in a zone where sedimentation was thought to have been affected by recurrent earthquake shock. The dykes consist of poorly defined sandstone clasts in a muddy matrix. They exhibit no significant internal sedimentary structures. It is suggested that the dykes were intruded due to remobilization of sediment affected by a combination of tectonic shock and hydrostatic load. The dykes bear no genetic relationship to tectonic structures (cleavage and jointing) and evidence suggests that dewatering was virtually complete before the formation of the first cleavage.

The formation of a rift valley and its zigzag fault patterns is simulated by a model experiment. A stress analysis of the model shows how the rift valley and its fault pattern are formed on two oppositely inclined boundaries in the stress field.

Cleavage structures from two localities in the Northern Lake District, England, are described, and they are discussed critically in relation to the tectonic de-watering hypothesis. It is concluded that, whilst tectonic de-watering may aid in the formation of a slaty cleavage, strain is the primary mechanism for producing such structures.

Previous mechanisms of syntectonic growth of porphyroblasts, leading to sigmoidal inclusion patterns, are thought to be based on invalid assumptions. A new mechanism, which involves the formation of extension fractures, is outlined.

Quartz nodules and geodes, known as Bristol Diamonds, occur in the Triassic Dolomitic Conglomerate of the Bristol district of England. They are composed of either, megaquartz, milky in the outer part and clear towards the centre, or fibrous quartz, chalcedony and lutecite. Much of the quartz, particularly in the outer parts, is full of anhydrite inclusions which are relics of larger lath-shaped anhydrite crystals. The Bristol Diamonds formed by silica replacement of anhydrite nodules, with replacement proceeding from the outside inwards. In many cases anhydrite solution was faster than silica replacement, so that a central void developed into which grew crystals with fine terminations. The anhydrite formed by precipitation of sulphate from hypersaline sediment-porewaters, probably in a marginal playa situation.

Charges of Fe-tremolite, sulphur and water sealed in gold capsules and run at 600°C and 1 kb confining pressure for one month yielded talc, anhydrite, pyrite and quartz as principal mineral phases. It is concluded that in a S-rich environment talc is stabilized rather than diopside by the strong preference of Ca to form anhydrite.