We report the first systematic study of H2O speciation in dacitic melt with total dissolved H2O ranging from 1.4 to 2.6 wt%. Samples were heated in a one-atmosphere tube furnace at 480–590 °C for certain durations and then quenched in water or air. Species concentrations were measured with Fourier transform infrared (FTIR) spectroscopy. At a given temperature, the equilibrium constant for the r...

We report the first experimental study of the diffusion of H2O in dacitic melts. Dehydration experiments were conducted at 551–637 8C and 1–1450 bars for samples with ~0.8 to ~2.5 wt.% total dissolved H2O. The H2O diffusivity is proportional to total H2O contents at V0.8 wt.%, but increases exponentially with total H2O at higher H2O contents. The diffusivity of the total dissolved H2O (in Am /s...

We present the stratigraphy, lithology, volcanology, and age of the Acahualinca section in Managua, including a famous footprint layer exposed in two museum pits. The ca. 4-m-high walls of the main northern pit (Pit I) expose excellent cross sections of Late Holocene volcaniclastic deposits in northern Managua. We have subdivided the section into six lithostratigraphic units, some of which we c...

H2O diffusion in dacitic melt was investigated at 0.48–0.95 GPa and 786–893 K in a piston-cylinder apparatus. The diffusion couple design was used, in which a nominally dry dacitic glass makes one half and is juxtaposed with a hydrous dacitic glass containing up to 8 wt.% total water (H2Ot). H2O concentration profiles were measured on quenched glasses with infrared microspectroscopy. The H2O di...

The diffusion of water in dacitic and andesitic melts was investigated at temperatures of 1458 to 1858 K and pressures between 0.5 and 1.5 GPa using the diffusion couple technique. Pairs of nominally dry glasses and hydrous glasses containing between 1.5 and 6.3 wt.% dissolved H2O were heated for 60 to 480 s in a piston cylinder apparatus. Concentration profiles of hydrous species (OH groups an...

Volcán San Pedro in the Andean Southern Volcanic Zone (SVZ) Consequently, the role of young, unradiogenic hydrous gabbro in Chile, comprises Holocene basaltic to dacitic lavas with trace generating dacite and contaminating basalt may be underappreciated element and strontium isotope ratios more variable than those of in the SVZ. most Pleistocene lavas of the underlying Tatara–San Pedro complex....

Multiple volcanic eruptions occurred between 8500 and 9000 yr. B.P. from the central crater of CitiaitCpetl Volcano generating a series of pyroclastic flows that formed a deposit with a total volume of about 0.26 km3 (D.R.E.). The flows descended in all directions around the crater, but they were mostly controlled by topography and deposited in valleys or local topographic depressions up to abo...

Magmatic processes have usually been identified and evaluated using qualitative or semiquantitative geochemical or isotopic tools based on a restricted number of variables. However, a more complete and quantitative view could be reached applying multivariate analysis, mass balance techniques, and statistical tests. As an example, in this work a statistical and quantitative scheme is applied to ...