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The enthalpies of synthesized multicomponent gas hydrates and the influence of guest molecules such as [C.sub.2][H.sub.6], [C.sub.3][H.sub.8], and C[O.sub.2] on their thermal behavior were determined. It was seen that when the difference in guest-to-cavity size ratio between the replaced methane and the replacing guest molecule is significant.

Whole-rock Chemical composition and [sup.11]B/[sup.10]B isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the Andean basement from the Palaeozoic to Mesozoic. In the basement (Cambrian to Ordovician high-grade paragneisses, migmatites and orthogneisses, the Eocambrian Puncoviscana Formation, and Paleozoic-Mesozoic granitoid igneous rocks) whole-rock B contents are generally below 100 ppm, but B contents of ~1 wt% are found in cogenetic aplite and pegmatite dikes and in tourmaline-quartz rocks. In the metasedimentary rocks, no systematic variation in B content because of metamorphic grade and no correlation of B with other incompatible elements are apparent. Tourmalines from the high-grade metamorphic basement yield [delta.sup.11]B values ranging from -11.2 to -6.8 [per thousand] and isotope fractionation during migmatisation was small. Metamorphic tourmalines from the Puncoviscana Formation have [delta.sup.11]B values between -6.3 and -5.8 [per thousand]. The calculated (corrected for fractionation) [delta.sup.11]B values of -6 to -2 [per thousand] for the sedimentary protolith of the metamorphic basement indicate a continental B source with subordinate marine input. Tourmalines from Palaeozoic and Mesozoic granitoids display an identical range of [delta.sup.11]B values from -12 to -5.3 [per thousand] and indicate a similarly homogeneous B source throughout time. Tourmalines from pegmatites and tourmaline-quartz rocks record the average [delta.sup.11]B values of the parental granitic magma. We assume that B in the Palaeozoic and Mesozoic granitoids is derived from the local metamorphic basement supporting the hypothesis that recycling of the lower Palaeozoic crust is the dominant process in granitic magma formation from Palaeozoic to Mesozoic.

The submersible Nautile completed 22 dives during the Nautilau cruise (R/V Nadir, April 17-May 10, 1989) for a detailed investigation of the southern Lau basin near Tonga. The objective of the scientific team from France, Germany, and Tonga was to understand the process of sea-floor ore fornation associated with hydrothermal circultion along the Valu Fa back-arc ridge behind the Tonga-Kermadec trench. The four diving areas, between lat 21[degrees]25'S and 22[degrees]40'S in water 2000 m deep, were selected on the basis of results from cruises of the R/V Jean Charcot and R/V Sonne. The Nadit cruise provided proof of hydrothermal activity--in all four areas, over more than 100 km--as indicated by the idespre widespread occurrence of hydrothermal deposits and by heat flow, conductivity, and temperature measurements near the sea bottom. The most spectaculr findings were high-temperature white and black smokers and associated fauna and ore deposits. Hydrothermal water chemistry and sulfide composition data presented here indicate that this hydrothermal field is very different from the hydrothermal fields in oceanic ridges. This difference is seen in the water chemistry of the hydrothermal fluid (pH = 2 and highmetal content) and the chemical composition of sulfides (enrichment in Ba, As, and Ph).

The phase behavior of multicomponent gas hydrate systems formed from primarily methane-propane and methane-ethane-propane gas mixtures were investigated. These systems showed interesting behavior at P-T conditions close to the decomposition line of pure methane hydrate during which the formation and decomposition of hydrate crystals could be seen and the morphology of the system changed from larger euhedral crystals to a fine crystal foamy mass.