( 210 Pb/ 226 Ra) variations during the 1994-2001 intracaldera volcanism at Rabaul Caldera

Determining the timing and source of gas transfer during intermittent intracaldera volcanism can aid in our understanding of degassing in these large systems. Using (210Pb/226Ra) ratios, (parentheses denote activity ratios) as a time-sensitive tracer, injections of 222Rn and the subsequent time scales of gas accumulation and loss can be determined. Variations in (210Pb/226Ra) have been measured for 15 volcanic products erupted at Rabaul Caldera over the period 1994 to 2001. In addition, one basaltic enclave from the 1937 eruption was also analyzed. Water and carbon dioxide contents determined from olivine hosted melt inclusions erupted in 1997 are < 1% and suggest extensive shallow-level degassing. Both 210Pb excesses and deficits are found in andesites and dacites, whereas the basaltic enclave displays an (210Pb/226Ra)0 ratio of 7. Between 1994 and 1997 three samples with (210Pb/226Ra) deficits were erupted which indicate open system gas loss since 1992 and 1994. No correlation exists between (210Pb/226Ra) and lava chemistry, eruptive style or date. 210Pb excesses are more common than deficits in Rabaul samples but cannot be explained by plagioclase feldspar accumulation, Pb sublimate accumulation or differentiation. Instead, a model of intra-magma 222Rn transfer can produce 210Pb excesses of the appropriate magnitude if gas transfer occurs over 1-5 years from an underlying body of magma that is 2-10 times larger than the volume of erupted material and that is consistent with geophysical estimates. Although intermittent gas transfer events can be inferred by the development of 210Pb excess, there is no evidence at Rabaul for a direct link between eruptive style, gas flux and (210Pb/226Ra)

Temporal variations in U-series disequilibria in an active caldera, Rabaul, Papua New Guinea

Intra-caldera eruptions have been speculated to sample the last batches of magma remaining from earlier caldera-forming eruptions. Rabaul Caldera, New Britain, Papua New Guinea has erupted several times since the last caldera-forming eruption in ad 640, with the most recent intra-caldera eruptions in 1878, 1937-1941 and 1994-present from the Tavurvur and Vulcan vents. U-series isotopes, in conjunction with 87Sr/86Sr and 143Nd/144Nd, were analyzed on 16 samples collected from 1994 to 2001 to monitor short-term changes in magma composition to model magmatic processes and to test whether there is evidence of recent fresh magma input. Inflections on MgO diagrams imply that fractional crystallization is an important process in long-term magma evolution, and the homogeneity in 87Sr/86Sr and 143Nd/144Nd shows that assimilation of isotopically distinct material has not occurred. A vertical array on a 230Th-238U isochron diagram requires open-system behavior and could support a model of differentiation of multiple magma batches over 26 kyr. However, the presence of (226Ra/230Th) excesses requires introduction of new magma within the past 8000 years and is permissible of a model in which the currently erupting magmas were emplaced at or since the last caldera-forming event. Other than the presence of mafic enclaves in the 1878 and 1937 eruptions, no evidence exists to suggest open-system magma injection. Systematic variation in U-series disequilibria between 1994 and 2001 is lacking, which may indicate that the system is broadly in steady state or that the processes acting to produce the limited compositional variation have time scales that are too short to be resolved by Ra isotopes (i.e. are less than a few hundred years)

(²¹⁰Pb/²²⁶Ra) variations during the 1994-2001 intracaldera volcanism at Rabaul Caldera

Determining the timing and source of gas transfer during intermittent intracaldera volcanism can aid in our understanding of degassing in these large systems. Using (²¹⁰Pb/²²⁶Ra) ratios, (parentheses denote activity ratios) as a time-sensitive tracer, injections of ²²²Rn and the subsequent time scales of gas accumulation and loss can be determined. Variations in (²¹⁰Pb/²²⁶Ra) have been measured for 15 volcanic products erupted at Rabaul Caldera over the period 1994 to 2001. In addition, one basaltic enclave from the 1937 eruption was also analyzed. Water and carbon dioxide contents determined from olivine hosted melt inclusions erupted in 1997 are < 1% and suggest extensive shallow-level degassing. Both ²¹⁰Pb excesses and deficits are found in andesites and dacites, whereas the basaltic enclave displays an (²¹⁰Pb/²²⁶Ra)0 ratio of 7. Between 1994 and 1997 three samples with (²¹⁰Pb/²²⁶Ra) deficits were erupted which indicate open system gas loss since 1992 and 1994. No correlation exists between (²¹⁰Pb/²²⁶Ra) and lava chemistry, eruptive style or date. ²¹⁰Pb excesses are more common than deficits in Rabaul samples but cannot be explained by plagioclase feldspar accumulation, Pb sublimate accumulation or differentiation. Instead, a model of intra-magma ²²²Rn transfer can produce ²¹⁰Pb excesses of the appropriate magnitude if gas transfer occurs over 1–5 years from an underlying body of magma that is 2–10 times larger than the volume of erupted material and that is consistent with geophysical estimates. Although intermittent gas transfer events can be inferred by the development of ²¹⁰Pb excess, there is no evidence at Rabaul for a direct link between eruptive style, gas flux and (²¹⁰Pb/²²⁶Ra).11 page(s

Mineralogical analyses and in vitro screening tests for the rapid evaluation of the health hazard of volcanic ash at Rabaul volcano, Papua New Guinea

The continuous ash and gas emissions from the Tavurvur cone in Rabaul caldera, Papua New Guinea, during 2007-08, raised concerns regarding how exposure would affect the respiratory health of nearby populations and impact on the environment. As part of a formal evaluation of the effects of volcanic emissions on public health, we investigated the potential health hazard of the ash using a suite of selected mineralogical analyses and in vitro toxicity screening tests. The trachy-andesitic ash comprised 2.1-6.7 vol.% respirable (sub-4 mu m diameter) particles. The crystalline silica content was 1.9-5.0 wt.% cristobalite (in the bulk sample) with trace amounts of quartz and/or tridymite. Scanning electron microscopy showed that the ash particles were angular with sparse, fibre-like particles (similar to 3-60 mu m max. diameter) observed in some samples, which we confirmed to be CaSO4 (gypsum, a

Fetal and Maternal Brain and Plasma Levels of Cocaine and Benzoylecgonine Following Chronic Subcutaneous Administration of Cocaine During Gestation in Rats

The distribution of cocaine and the cocaine metabolite benzoylecgonine (BE) in brain and plasma of Sprague-Dawley rat dams and their near-term fetuses was assessed 0.5 and 2 h post-injection on gestational day 20 following chronic daily subcutaneous injections of 10, 20, or 40 mg/kg/3 ml cocaine hydrochloride beginning on gestational day 8. Plasma concentrations of cocaine reached in the dams were found to be in the range of, or to exceed, those reported in human cocaine users. Dose-related increases in plasma and brain levels of cocaine in the dams and the fetuses were observed, particularly at 2 h post-injection. Fetal concentrations of cocaine in brain and plasma were approximately 2–3-fold less than those of the dams, suggesting that the placenta may somewhat restrict cocaine entry into fetal circulation. Brain/plasma cocaine ratios, however, were generally equivalent in the dams and fetuses, suggesting that once cocaine enters the circulation, its affinity for brain tissue is similar in the fetus and dam. Whereas plasma levels of BE, like cocaine levels per se, were greater in the dams than fetuses, BE concentrations in fetal brain were greater than those observed in maternal brain. These high levels of BE may contribute to the production of neurobehavioral alterations in cocaine-exposed offspring, given that this active cocaine metabolite has been shown to form molecular complexes with calcium ions (Misra and Mule 1975), thereby having the potential to influence a multiplicity of calcium-regulated developmental events. Taken together, the results of the present study suggest that the subcutaneous route may prove to be an appropriate means in rats for administering cocaine prenatally in investigations designed to assess potential neurobehavioral ramifications of gestational cocaine exposure