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An ‘Al-thermometer’ was applied to agate samples of volcanic parent rocks to provide information about the temperature of agate formation. The temperatures were calculated from concentrations of [AlO4]0 centres determined by electron paramagnetic resonance (EPR) measurements. The calculations for agate bands in some cases yield temperatures of up to 655°C, which are assumed to be invalid; they are thought to be artifacts resulting from non-equilibrium crystallization processes. In contrast, the formation temperatures (60–198°C) estimated for associated quartz incrustations within the agate geodes are in good accord with those calculated from oxygen isotope data. Direct estimation of the formation temperatures of agates is problematic. The best results will be obtained by analyses of associated phanerocrystalline quartz incrustations.

A suite of serpentinized peridotites from Leg 153 was analyzed for major and trace elements. All the rocks are less-refractory peridotites. The mineral chemistry of olivines (Mg# = 90.3), orthopyroxenes (Mg# = 90.4), clinopyroxenes (Mg# = 91.6), and some Cr spinels (Mg# = 68.4; Cr# = 29.7) shows the characteristic features of minerals from less-depleted mantle peridotites. Some geothermometric calculations gave temperatures for the pyroxene system of about 1300°C, reflecting the prekinematic to synkinematic crystallization of the pyroxenes, and gave a range from 1180° to 1075°C for the mineral pair orthopyroxene and spinel. Oxygen-isotope determinations show δ 18 θ values of about 6%c for olivine, orthopyroxene, and clinopyroxene; δ 18 θ values from chromian spinel/magnetite vary between 2.9%e and 3.8%o, values from serpentine vary between 2.8‰ and 5.3%e, and whole-rock values vary between 2.9%e and 4.6‰. Two temperatures could be calculated from the oxygenisotope exchange for the mineral pair clinopyroxene and spinel: about 1100° and about 900°C. The 1100°C value nearly corresponds to the data obtained using the orthopyroxene-spinel mineral thermometer, and may indicate subsolidus deformation and recrystallization. The temperature range of the serpentinization could only be estimated. It depends upon the rock/water ratio, and may not have exceeded ~300°C. Finally, a calculation of possible rock/water ratios is given.

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