Granites and yet more granites forty years on

The theme of this synoptic review is the relationship between cause, process, source and the geological context during the genesis of the granitic rocks. A close environmental relationship occurs because granites can arise as the end-stage of several generative processes, involving different source rocks, each appropriate to a particular tectonic situation. Expressed in geological terms the differences can be used to erect a genetic classification, to set in perspective the intervention of basic magma, to reveal the importance of the volcanoplutonic interface, to evaluate the significance of the texture, to predict the type of mineralisation, to understand the mode of emplacement and to determine the contribution of the various source rocks.

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Zusammenfassung Das Thema dieser synoptischen übersicht behandelt das Verhältnis zwischen Ursache, Prozess, Herkunft und dem geologischen Rahmen während der Genese granitischer Gesteine.Es besteht hier eine enge Beziehung, weil Granite das Endstadium sehr unterschiedlicher Entstehungsprozesse sein können, die verschiedene Ausgangsgesteine einbeziehen und von denen jeder einer speziellen tektonischen Situation entspricht.Geologisch ausgedrückt kann man die Unterschiede dazu verwenden, eine genetische Klassifikation zu erstellen, um damit den Einflu\ basischen Magmas im richtigen Verhältnis zu sehen, die Bedeutung des vulkanisch-plutonischen Grenzbereiches aufzuzeigen, die Wichtigkeit der Textur herauszustreichen und den Typ der Mineralisation vorherzusagen. Auf diese Weise lä\t sich das Verständnis für den Modus der Platznahme erzielen und der Einflu\ verschiedener Ausgangsgesteine abschätzen.

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Résumé Cette revue synoptique a pour thème les relations entre la cause, le processus, la source et le contexte géologique au cours de la genèse des roches granitiques. Il existe entre ces facteurs des relations étroites, car les granites peuvent représenter le stade final de plusieurs processus de genèse, impliquant des roches de départ diverses, et appropriés chacun à une situation tectonique particulière.Exprimées en termes géologiques, les différences peuvent Être utilisées en vue d'établir une classification génétique, de mettre en évidence l'intervention du magma basique, d'exprimer l'importance de l'interface volcano-plutonique, d'estimer la signification de la texture de mise en place et de déterminer la contribution des diverses roches de départ.

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Saldanha Bay,South Africa III: new production and carrying capacity for bivalve aquaculture

Measurements of NH₄, NO₃, urea and HCO₃ uptake using 15N and 13C stable isotope tracers were undertaken in Saldanha Bay, South Africa, between January 2012 and January 2013. These studies provide the first direct measurements of N utilisation by the plankton in the bay. Primary production in the bay is driven predominantly by the advection of nutrients from the neighbouring shelf environment during upwelling events, with terrestrial and other sources providing minor inputs. New production (NO₃-based) was calculated from the f-ratio and total primary production and was used to provide estimates of potential carrying capacity for bivalve culture. Despite the apparent light limitation of NO3 uptake in the winter, the availability of NO₃ appeared to exert the major influence on new production throughout the year. In addition, new production was modulated by NH₄ availability as shown by the suppression of NO₃ uptake by concentrations higher than 1?1.5?mmol m^?3. The estimated areal new production of 0.60?g C m^?2 d^?1 yielded a bay-wide annual estimate of 9 811 t C ha^?1 y^?1, slightly higher than previous calculations based on physical models. It is estimated that the total annual production of mussels and oysters, respectively, for a 1 000-ha cultivation area is approximately 40 000–53 000 t y^?1 (mainly Mytilus galloprovincialis) and 4 600–6 000 t y^?1 (Crassotrea gigas). The combined total production figures constitute only 24–31% of the surplus new production. A combined harvestable carrying capacity of 74 000–82 000 t y^?1 can be calculated from this surplus. However, from a management and ecological perspective, bivalve culture should be limited to well below this theoretical maximum. Even with this constraint, there appears to be considerable scope for expansion of bivalve farming over the modest, present levels with little jeopardy to ecological integrity.