Relationships between Campi Flegrei and Mt. Somma volcanism: evidence from melt inclusions in clinopyroxene phenocrysts from volcanic breccia xenoliths

Summary We present compositions of reheated melt inclusions in clinopyroxene phenocrysts from three mafic xenoliths in Breccia Museo, Campi Flegrei, Italy. Melt inclusion compositions are remarkably different from the compositions of known contemporary Campi Flegrei lavas, being significantly enriched in K₂O and depleted in Na₂O. Some differences are also evident in FeO^* (total Fe as FeO) and TiO₂ contents. The clinopyroxene phenocrysts could not have crystallised from Campi Flegrei magmas. We suggest that they originated from a volcanic system genetically very similar to, and possibly linked with, the >14 ka volcanic system of Mt. Somma, another Campanian volcano ∼ 30 km east from Campi Flegrei, from which Vesuvius subsequently developed. This result indicates a close relationship (or link) between the two volcanic systems which have until now been considered separate. We speculate that the link was established prior to eruption of the Neapolitan Yellow Tuff (NYT) (∼ 12 ka). The xenoliths were derived from a volcanic system older than the host breccias themselves. We suggest that this older volcanism had close similarities with the volcanism of the older products of Mt. Somma (∼25 ka). Received March 20, 2000; accepted November 2, 2000     

Slow changes of solar irradiance and energetics of active regions

A new numerical technique is applied to study long-term variations of total solar irradiance. The background solar flux is estimated not from, e.g., a running mean but as the mode on a moving short time interval. Statistical properties of short-term variations with respect to the running mode are studied. The probability distribution function describing the data from Nimbus-7 is asymmetric and departs from a Gaussian.The ratio of time-integrated short-term negative and positive deviations shows that the energy re-radiated from faculae makes up about 40% of the energy blocked by sunspots. The amplitude and phase relations are studied between deviations which decrease and increase the irradiance. They characterize the mechanism of energy transformation with frequency. The cross-covariance analysis reveals that some parts of the energy blocked by sunspots come to the surface of the Sun after long delays.     

Neutron background in large-scale xenon detectors for dark matter searches

Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10⁻⁹–10⁻¹⁰ pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.     

Pre-collisional high pressure metamorphism and nappe tectonics at active continental margins: a numerical simulation

The evolution of a subduction channel and orogenic wedge is simulated in 2D for an active continental margin, with P-T paths being displayed for selected markers. In our simulation, subduction erosion affects the active margin and a structural pattern develops within a few tens of millions of years, with four zones from the trench into the forearc: (i) an accretionary complex of low grade metamorphic sedimentary material, (ii) a wedge of nappes with alternating upper and lower crustal provenance, and minor interleaving of oceanic or hydrated mantle material, (iii) a megascale melange composed of high pressure (HP) and ultra-high pressure (UHP) metamorphic rocks extruded from the subduction channel, and (iv) the upward tilted frontal part of the remaining lid. The P–T paths and time scales correspond to those typically recorded in orogenic belts. The simulation shows that HP/UHP metamorphism of continental crust does not necessarily indicate collision, but that the material can be derived from the active margin by subduction erosion and extruded from the subduction channel beneath the forearc during ongoing subduction.     

Inverted echo sounder measurement of dynamic height through an ENSOcycle in the central equatorial Pacific

A four-year record from an inverted echo sounder deployed near Palmyra Island at 6°N in the central Pacific Ocean is compared with a simultaneous record of subsurface pressure from this island lagoon. A factor m, converting round-trip acoustic travel time to surface dynamic height relative to a deep pressure level, was estimated from the ratio of the spectra of the two records in the energetic synoptic oscillation band. Year-to-year variation in m was not statistically significant. For the overall record, m was found to be -70±8 dynamic m/s, where the error bounds represent a 90% confidence interval. This is consistent with first-baroclinic-mode excitation