Ferrian tourmaline from Bungonia,New South Wales

New chemical, X‐ray and cell dimension data are presented for ferrian tourmaline in quartz‐tourmaline rock at three localities near Bungonia, New South Wales. The tourmaline is fine‐grained, normally euhedral, and forms up to 90% of the rock. It shows restricted solid solution between dravite and ferridravite, although some grains are zoned and others have an irregular, bipartite chemical variation. Tourma‐linisation is interpreted as being.related to late‐stage volatile emanations from the Marulan Batholith.     

Compositional variations in submarine volcanic ashes from the vicinity of the Vanuatu Island Arc: a response to ridge—arc collision?

The late Tertiary-Recent collision of the d'Entrecasteaux Zone with the Vanuatu (New Hebrides) Island Arc appears to have been associated with a shift to generally more potassic compositions. Glass shards analysed from Quaternary volcanic ashes recovered from ODP Leg 134 drill sites follow distinct shoshonitic and calc-alkaline trends, consistent with those previously recognised onshore. In the Aoba Basin (Site 832) a marked compositional change is recognised at 37 m below sea floor (mbsf). From estimates of sedimentation rates this is equivalent to an age of about 100 ka and may be associated with the development of the Central Basin volcanoes of Santa Maria, Aoba and Ambrym on fracture zones transverse to the island arc. Deeper than 37 mbsf differentiated compositions fall on a medium-K calc-alkaline trend but the associated basaltic glasses are strongly potassic. Conversely, above this level the differentiated glasses follow a shoshonitic trend but the basaltic glasses are medium-K calc-alkaline. Separate sources are envisaged, associated with subduction and rifting. Episodic subduction of the d'Entrecasteaux Zone exercises tectonic control over the release of magma from different depths. In contrast, shoshonitic glasses are sparsely represented in the Vanuatu forearc where relatively low-K calc-alkaline compositions probably correspond to the ashes in the lower part of the Aoba Basin sequence. This is consistent with their age (> 100 ka) estimated from lower sedimentation rates at these sites. The scarcity of younger shoshonitic ashes at the forearc sites is attributed to the influence of high-level westerly winds transporting ash from the Central Chain volcanoes eastwards across the North Fiji Basin.     

Electronic Microprobe Analysis and Scanning Electronic Microscopy in Geology, by S. J. B. Reed. Cambridge University Press, Cambridge, 1996. Hardback: {pound}50. Paperback: {pound}17.95.

Anyone in the Earth Sciences community involved in the trainingof postgraduate students new to electron microprobe and scanningelectron microscope instrumentation has, in the past, alwayshad problems answering the inevitable question regarding textsthat the student may study. There are a number of excellentbooks that could be recommended. Chapman (1986), Goldstein etal. (1992), Scott et al. (1995) and, dare I say it, Reed (1993)would feature on any reading list. Unfortunately, other thanChapman (1986), such books are for the specialist. They aretheoretical, comprehensively detailed, and highly numerical.When practical aspects are discussed (as in Goldstein et al.)these are heavily biased towards the materials scientist orbiologist. On the other hand,