Petrology and geochemistry of the recent eruption history at Rabaul Caldera, Papua New Guinea : implications for magmatic processes and recurring volcanic activity

Abstract

The initial phase (Phase 1 - 19 September 1994 to 16 April 1995) of the current (1994-2003) eruption at Rabaul Caldera occurred with synchronous vulcanian and vulcanian-plinian eruptions from Tavurvur and Vulcan, respectively, on opposing sides of the caldera. A second phase of activity (Phase 2), beginning on 28 November 1995 and continuing until the present (2003), is characterised by intermittent vulcanian and strombolian eruptions that are restricted to Tavurvur, on the northeastern side of Rabaul Caldera...Comparison with dacite magma compositions erupted in 1937-1943, 1878, and during the recent prehistoric era and the presence of plagioclase phenocrysts reflecting older basalt-dacite magma interaction events (i.e., anorthite cores overgrown with thick andesine rims). The petrologic and geochemical observations made in this study indicate the shallow magma system at Rabaul Caldera has been subject to repeated mafic magma injection since, and also during, the latest caldera-fonning eruption about 1400 years BP. The frequency and repeated occurrence of these injections may maintain a near steadystate system that is characterized by the persistent eruption of similar, crystal-poor dacite compositions over the last 1400 years, and the presence at shallow level of a large volume of dacite magma beneath Rabaul Caldera (Finlayson et al., 2003; Mori et al., 1989).