Abstract The primary goal of this study was to apply an innovative analytical method based on a gas membrane sensor (GMS) to quantify the concentrations of CO 2 and CH 4 gas in water columns from volcanic lakes. For this purpose, dissolved CO 2 and CH 4 from the Monticchio Grande and Piccolo (Mt Vulture, Italy) and Pavin (Massif Central, France) lakes, characterized by depths of 35, 38 and 92 m, respectively, were measured using two different approaches: GMS and SH (single hose), the latter being an independent conventional method. The CO 2 and CH 4 concentrations recorded via the GMS and SH techniques were within the analytical errors of the two methods. These test measurements demonstrated that the GMS method can be successfully used to produce highly accurate in situ measurements of dissolved gas composition along the vertical profiles of lakes.

Ultramafic and mafic xenoliths entrained in late Oligocene dikes of intraplate origin provide information about the composition of the lower crust and the processes operating beneath the eastern Rhodope metamorphic core complexes Biala Reka and Kesebir, in southeastern Bulgaria. The cumulates comprise a series of high- to medium-pressure rocks represented by olivine websterites, orthopyroxenites, clinopyroxenites, websterites, and gabbros. Thermobarometric studies and comparison with experimental works suggest that the cumulate sequence formed from hydrous (>3 wt%) mafic magma at pressures of 14–9 kilobars (45–30 km) and temperatures of 1200–850 °C. It is inferred that underplating of such hot, wet mafic intrusions modified the thermal and mechanical properties of the lower and middle crust, as is reflected in thermal metamorphism, associated extension, and hydrothermal activity producing low-sulfidation Au deposits. Findings of similar xenoliths in the alkaline basalts from other extended regions such as the eastern Mediterranean and the Basin and Range Province indicate that underplating of mafic magma plays an important role in core complex formation.