P total,P_{H_2 O} and the occurrence of cummingtonite in volcanic rocks

The phenocryst assemblage of cummingtonite, orthopyroxene, quartz, titanomagnetite and ilmenite in rhyolites of New Zealand has been used to calculate P _total and . The values of P _total and depend strongly upon whether an ideal mixing, or an ordered, model is used for the solid-solutions, but in both cases P _total.The rhyolite magma contained over 9 per cent water (by weight) when the cummingtonite phenocrysts precipitated, and possibly as much as 12 per cent, so that it is surprising that one of these rhyolites is a coherent lava. The calculated values of P _total and are very sensitive to uncertainty in both the composition of the solid-solutions and temperature. Calculations show that >0.7–0.8 P _total for cummingtonite to precipitate in rhyolites, and that iron-rich olivine and cummingtonite could only exist in rhyolites over a small temperature range at a pressure near 5 kilobars. Hornblende phenocrysts co-existing with fayalitic olivine in rhyolites accordingly have a very low activity of Mg₇Si₈O₂₂(OH)₂.     

Toxins in the red Whelk

A case of poisoning following consumption of Neptunea occurred in Scotland in 1970. The organism is caught in traps with the Edible Whelk where it constitutes less than 0·5% of the catch. Toxin in the salivary gland demonstrated by mouse bioassay could be distinguished from PSP toxin. It is concluded that the public health risk from consumption of the Edible Whelk is negligible.     

The economic analysis of raft foundations

An approximate method, using a simplified soil model, for predicting the behaviour of raft foundations subjected to applied vertical forces and moments will be outlined. Results obtained for circular rafts of finite rigidity are compared with those obtained, from more rigorous solutions, by other authors. Satisfactory agreement is obtained for the surface settlements and raft bending moments over a wide range of soil inhomogeneity. Finally, the versatility of the method of analysis is illustrated for an unusual asymmetrical structure. Computed total and differential settlements are shown to be in reasonable agreement with measured values and those predicted by an independent plane strain finite element analysis.     

The interstellar dust as a precursor of Ca,Al-rich inclusions in carbonaceous chondrites

(1) The observed anomalies in meteoritic oxygen isotope compositions are not due to an incomplete mixing of several dust or gas-plus-dust components in the solar nebula. If they were, other elements would display similar anomalies. (The FUN inclusions in Allende appear to be exceptions to this premise.) (2) The anomalies must therefore stem from differing degrees of incomplete exchange of oxygen isotopes between the primordial gas and dust components of the nebula. The dust is more likely to have been the¹⁶O-enriched component. (3) Since the isotopic difference between dust and gas probably could not have been preserved if the dust was ever completely vaporized in the nebula, the Ca,Al-rich inclusions (CAI's) in carbonaceous chondrites are unlikely to be condensates, but instead are distillation residues. (4) If so, the observed depletion of super-refractory elements in the Group II CAI's cannot have been accomplished by fractional condensation in the solar nebula. (5) Then this depletion, and a number of other properties of the components of primitive meteoritic material, must be relics of pre-solar system fractionations among different populations of interstellar dust grains.     

Relations between surface deformation,fault geometry,seismicity, and rupture characteristics during the El Asnam (Algeria) earthquake of 10 October 1980

The El Asnam earthquake of October 10, 1980 (M_s=7.3) produced surface faulting on a northeast-trending thrust fault of 30 km length with displacements of up to 6.5 m, though average displacements were about 3 m. In addition, widespread tensional features were formed, some in clear association with folding above the thrust, and others, in an area beyond the exposure of the thrust at the surface, which may be related to buried reverse faults.The observed thrust fault is split into southern, central and northern segments. Local and teleseismic data are examined to show that the main shock nucleated at the southwest end of the fault, and propagated 12 km northeast where a second rupture of approximately equal moment occurred, continuing the faulting a further 12 km northeast along the central segment. Both ruptures nucleated at about 8–10 km depth. Displacements were largest on the central segment, where they were probably enlarged by aftershocks, including one of m_b=6.1 three hours after the main shock. The northern segment was much shorter than the other two, and showed smaller displacement.The junctions between fault segments are marked by distinct geomorphological characteristics and a change in strike of the faulting, as well as a sudden drop in the observed displacement. It appears that the rupture development is influenced by the changes in fault geometry between segments, and that such junctions or barriers have persisted through much of the late Quaternary.     

Earthquake response of a steel frame building

A study has been made of the response, during the San Fernando earthquake 9 February 1971, of the nine-storey steel frame Building 180, located at the California Institute of Technology, Jet Propulsion Laboratory, Pasadena. The analysis throws light on the actual dynamical properties of the building during the earthquake, and also demonstrates that it is possible, when the ground motion is specified, to make accurate predictions of building motions during moderate earthquakes by using a linear viscously damped model. Methods of evaluating the lower mode periods and damping ratios from the earthquake records are described and the values obtained are compared with results from dynamic testing before and after the earthquake and with the periods computed from computer models of the building. Although no structural damage occurred and computed stresses in the steel frame were less than yield stresses, the periods measured by an ambient vibration test after the earthquake were of the order of 10 per cent higher than the pre-earthquake values. The maximum periods during the earthquake were found to be about 30 per cent higher than the post-earthquake periods.     

The Otago schist megaculmination: Its possible origins and tectonic significance in the Rangitata orogen of New Zealand

In South Island, New Zealand, the Otago schist, 30,000 square km in extent, consists mainly of greenschist facies quartzo-feldspathic metagreywacke and meta-argillite with minor metavolcanics and metacherts. Before metamorphism the sediments were probably Carboniferous to Jurassic; the flanking, steeply dipping greywackes are Triassic in the northeast and southeast, and Permian in the west and southwest.Regional metamorphism culminating in the Late Jurassic was accompanied by pervasive deformation generating a variety of interrelated folds on all scales. The scarcity of distinctive reference units makes recognition of macroscopic structures difficult, and much progress has depended on observations of vergence of mesoscopic folds interpreted as defining macroscopic folds having axial plane separation of between 2 km and 6 km.At least two phases of synmetamorphic deformation are distinguishable locally, but regionally have an overlapping multiphase relationship. The regional schistosity structure is an irregular flat-crested antiform trending S and SE. The internal megascopic structure defined by the mesoscopic folds, appears to consist of a stack of nappe-folds facing east and northeast, which pass into reclining isoclinal folds in the west, southwest and north-east, and is interpreted to be a megaculmination. Mineral and textural metamorphic zones were developed during deformation, and a relatively simple regional pattern established at a late stage by continuing recrystallisation.The Otago schist originated in a complex sequence of Paleozoic—Mesozoic plate interactions near the southwest Pacific margin of Gondwanaland. It included part of a volcaniclastic frontal arc-basin assemblage (Murihiku and Caples Terranes) lying north or northeast of an older crystalline foreland, and a quartzo-feldspathic assemblage of plutonic-metamorphic provenance lying further to the northeast (Torlesse Terrane). Parts of these terranes underwent mainly greenschist facies metamorphism during Late Jurassic subduction-collision to form the Haast Schist Terrane of which the Otago schist is a major part.The earliest Torlesse sediments are thought to have prograded as a vast fan complex onto oceanic crust from the southwesterly crystalline foreland in the Carboniferous, then in the Permian were separated from their source by a spreading zone which thereafter isolated them from the sedimentary province of the newly developing arc system. Tectonic recycling of these sediments at a Permian to Jurassic oceanic subduction zone is considered to have developed the westward progradation features and the products of limited vulcanism found in the present Torlesse Terrane. The New Zealand Geosyncline appears to have consisted of a spreading zone between two inwardly facing convergent zones, one flanked by a foreland to the southwest, the other wholly oceanic.The metamorphic climax of the Rangitata Orogeny was the result of the medial spreading zone passing into the westerly subduction zone, so permitting the convergent zones to collide, with the Torlesse sediments caught between them.The mantle system driving the spreading zone appears to have continued to function, and soon after the collisional climax caused Late Jurassic—Cretaceous rifting of the sialic edge of Gondwanaland, igneous activity, differential shear of the New Zealand region, and initiation of the Alpine Fault. It subsequently commenced sea-floor spreading in the Tasman Sea, and later in the southwest Pacific Ocean.