We present the first experimental investigation of the fragmentation behavior of twophase (melt+gas) rhyolitic systems under rapid decompression. Two-phase samples have been generated by foaming water-oversaturated rhyolitic melts up to 900°C and up to 18 MPa prior to rapid decompression in a fragmentation bomb. The fragmented particles or experimental pyroclasts were recovered for analysis. Se...

Phillipsite has formecl from volcanic glass in saline, alkaline lakes both saturated and undersaturated with respect to gaylussite and trona. It has also formed from volcanic glass in saiine, alkaline soils of Olduvai Gorge, Tanganyika. Phillipsite occurs both as lath,shaped and as equant crystals, which are commonly zoned lvith refractive indices ranging between 1.438 and 1.490. Molecular SiOz...

the late eocene-early oligocene sarnowsar granitic rocks and many dacitic to rhyolitic dykesintruded in metamorphosed and metasomatized shale, sandstone, calcite and dolomite marbles andvolcaniclastic and pyroclastic rocks. as a result several million tons of iron ores formed within carbonaterocks in the sangan area. the sarnowsar granitic rocks are mainly granite to granodiorite, metaluminous,...

Abstract Extensional tectonics in the Late Paleozoic Central Europe was accompanied by rift magmatism that triggered voluminous intracontinental caldera-forming eruptions. Among these, Lower Permian Rochlitz Volcanic System (RVS) North Saxon Complex (Eastern Germany, Saxony) represents a supereruption (VEI 8, estimated volume of 1056 km 3 ) monotonous rhyolites followed intermediates. Mapping, ...

Quartz porphyry of rhyolitic composition though a volumetrically minor is an important component metavolcanic successions in the Gadag schist belt western Dharwar craton. The quartz porphyries are calc-alkaline, enriched light rare earth elements (Lan/Ybn ~ 10–20) and with strong negative Eu anomaly (Eu/Eu*N=0.45–0.58). These features, coupled high K2O/Na2O (0.8 to 1.46), low Nb/Th (<1), Lan/Sm...

Dissolved water is known to dramatically enhance oxygen diffusion in silicate melts, glasses and minerals. A quantitative theory has been developed to explain this phenomenon by transport via molecular H2O diffusion [Y. Zhang, E.M. Stolper, G.J. Wasserburg, Diffusion of a multi-species component and its role in the diffusion of water and oxygen in silicates, Earth Planet. Sci. Lett., 103 (1991)...

[1] Knowledge about the properties of silicate melts is needed by volcanologists and petrologists to evaluate the dynamics of volcanic eruptions and magmatic processes. These properties include the solubility and diffusivity of volatile components in silicate melts, silicate melt viscosity, and the fragmentation condition. Data and models of each property are reviewed and assessed. For rhyoliti...

Three voluminous rhyolitic ignimbrites have been identified along the southern margin of the central Snake River Plain. As a result of wide-scale correlations, new volume estimates can be made for these deposits: ~350 km for the Steer Basin Tuff and Cougar Point Tuff XI, and ~1,000 km for Cougar Point Tuff XIII. These volumes exclude any associated regional ashfalls and correlation across to th...

Magmatism during early Basin and Range extension in Trans-Pecos Texas consisted of widespread but volumetrically minor alkali basalts (24-17 Ma), an alkalic mafic to intermediate composition stratovolcano (28-27 Ma), and a dominantly rhyolitic, possibly bimodal, caldera complex in adjacent Chihuahua (3128 Ma). This magmatism contrasted sharply with the much more voluminous and compositionally m...