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Hydroxylapatite (HA) nanoparticles were functionalized by depositing rare-earth-doped Y2O3Y2O3 nanoparticles on the surface, and the structural evolutions of both HA and Y2O3Y2O3 phases at different annealing temperatures were investigated by x-ray diffraction and transmission electron microscopy. Laser spectroscopy indicated that the surface functionalized HA nanoparticles exhibited strong visible emissions. No visible emissions were observed from rare-earth-doped Y2O3Y2O3 without any substrate, suggesting a doping-induced environmental change of optically active rare-earth elements in the functionalized HA nanoparticles. The luminescent hydroxylapatite nanoparticles may find important applications as a biodegradable substrate for biomarking and drug delivery.

We report a quantitative analysis of regional differences in the the oxygen isotope composition of river water and precipitation across the USA because data are now available to undertake a more geographically and temporally extensive analysis than was formerly possible. Maps of modern, mean annual?? 18 O values for both precipitation (?? 18 O PPT) and river water (?? 18 O RIV) across the 48 contiguous states of the USA have been generated using latitude and elevation as the primary predictors of stable isotope composition while also incorporating regional and local deviations based on available isotopic data. The difference between these two maps was calculated to determine regions where?? 18 O RIV is significantly offset from local?? 18 O PPT . Additional maps depicting seasonal and extreme values for?? 18 O RIV and?? 18 O PPT were also constructed. This exercise confirms the presence of regions characterized by differences in?? 18 O RIV and?? 18 O PPT and specifically identifies the magnitude and regional extent of these offsets. In particular, the Great Plains has?? 18 O RIV values that are more positive than precipitation, while much of the western USA is characterized by significantly lower?? 18 O RIV values in comparison with local?? 18 O PPT . The most salient feature that emerged from this comparison is the???catchment effect??? for the rivers. Because river water is largely derived from precipitation that fell upstream of the sample locality (i.e. at higher elevations)?? 18 O RIV values are often lower than local?? 18 O PPT values, particularly in catchments with high-elevation gradients. Seasonal patterns in the isotopic data substantiate the generally accepted notion that amplitudes of?? 18 O variation are greatly dampened in river water relative to those of local precipitation. Copyright?? 2005 John Wiley & Sons, Ltd.

???Coexisting muscovite and paragonite have been observed in an eclogite from the Sesia???Lanzo Zone (Western Alps, Italy). The P - T conditions of this eclogite reached 570???650?????C and 19???21 kbar and the rocks show several stages of mineral growth during their retrograde path, ranging from the subsequent lower- P eclogite facies to the blueschist facies and then the greenschist facies. Muscovite and paragonite are very common in these rocks and show two texturally different occurrences indicating equilibrium and non-equilibrium states between them. In one mode of occurrence they coexist in equilibrium in the lower- P eclogite facies. In the same rock muscovite????????albite also replaced paragonite during a greenschist-facies overprint, as evidenced by unique across??? (001) layer boundaries. The chemical compositions of the lower- P eclogite-facies micas plot astride the muscovite??? paragonite solvus, whereas the compositions of the greenschist-facies micas lie outside the solvus and indicate disequilibrium. The TEM observations of the textural relations of the greenschist-facies micas imply structural coherency between paragonite and muscovite along the layers, but there is a sharp discontinuity in the composition of the octahedral and tetrahedral sheets across the phase boundary. We propose that muscovite formed through a dissolution and recrystallization process, since no gradual variations toward the muscovite??? paragonite interfaces occur and no intermediate, homogeneous Na-K phase has been observed. Because a solid-state diffusion mechanism is highly unlikely at these low temperatures (300???500?????C), especially with respect to octahedral and tetrahedral sites, it is assumed that H 2 O plays an important role in this process. The across-layer boundaries are inferred to be characteristic of such non-equilibrium replacement processes. The characterization of these intergrowths is crucial to avoiding erroneous assumptions regarding composition and

Recrystallization and structural recovery in -decay damage in zircon samples have been studied using Raman spectroscopy. Fifteen zircon samples with different degrees of radiation damage have been thermally annealed between 600 K and 1800 K for up to 28 days and 8 hours. The experimental results from this study reveal that recrystallization in the damaged zircon samples is a multi-stage process that depends on the degree of initial damage of the samples. In partially damaged samples the lattice recovery of damaged crystalline ZrSiO4 takes place at temperatures as low as about 700 K, as shown by a remarkable band-sharpening and a significant increase in the frequencies of 1 and 3 Si-O stretching vibrations together with the external band near 357 cm-1 with increasing temperature. A dramatic increase of Raman scattering intensity of ZrSiO4 occurs in partially damaged samples near 1000 K due to a recrystallization process involving epitaxial growth. Heavily damaged samples tend to decompose into ZrO2 and SiO2 at high temperatures. Tetragonal ZrO2 has been observed under annealing between 1125 K and about 1600 K in heavily damaged samples while monoclinic ZrO2 appears above 1600 K. Weak signals from ZrSiO4 were detected at 1125 K in highly metamict zircon although the main recrystallization appears to occur near 1500 K accompanied by a decrease of the volumes of ZrO2 as well as SiO2 . This suggests that this recrystallization is associated with the reaction of ZrO2 with SiO2 to form ZrSiO4 . A possible intermediate phase has been observed, for the first time, by Raman spectroscopy in damaged zircons annealed at temperatures between 800 K and 1400 K. This phase is characterized by strong, broad Raman signals near 670, 798 and 1175 cm-1 . Prolonged isothermal annealing at 1050 K results in a decrease of these characteristic bands and eventually the disappearance of this intermediate phase.

Electron microbeam techniques have been used to examine submicroscopically intergrown paragonite, phengite and chlorite from the South Fork Mountain Schist of the Franciscan Terrane of northern California, which was subjected to blueschist facies metamorphism. The sample also contains quartz, albite, lawsonite, and rutile. The subassemblage albite-lawsonite-rutile requires metamorphic conditions on the low-temperature side of the equilibrium albite+lawsonite+rutile=paragonite+sphene+quartz+H 2 O (T<200?? C and P<7.4 kbars based on thermodynamic data of Holland and Powell 1990). The white micas appear to be optically homogeneous, but back-scattered electron images can distinguish two different micas by their slight difference in contrast. Electron microprobe analyses (EMPA) of micas show Na/(Na+K) ranging from 0.2 to 0.8. The two micas are resolved by transmission electron microscopy (TEM) as packets of phengite and paragonite that range from 20 to several hundred nm in thickness. The compositions, determined by analytical electron microscopy (AEM), constrain the limbs of the phengite-paragonite solvus to values of Na/(Na+K)=<0.02 and 0.97, representing less mutual solid solution than ever reported by EMPA. The textural relations imply that the sheet silicates were derived from reactions between fluids and detrital clays and that they are in an intermediate stage of textural development. We caution that microprobe analyses of apparently homogeneous sheet silicates may yield erroneous data and lead to faulty conclusions using phengite barometry and paragonite-muscovite thermometry, especially in fine-grained rocks that formed at relatively low temperatures.

An 40 Ar/ 39 Ar thermochronological investigation of upper greenschist to granulite facies gneiss, amphibolite and marble was conducted in the Central Metasedimentary Belt (CMB), Ontario, to constrain its cooling history. Incremental 40 Ar/ 39 Ar release spectra indicate that substantial differential unroofing occurred in the CMB between ∼ 1000 and ∼ 600 Ma. A consistent pattern of significantly older hornblende and phlogopite 40 Ar/ 3 Ar cooling ages on the southeast sides of major northeast striking shear zones is interpreted to reflect late displacement due to extensional deformation. Variations in hornblende 40 Ar/ 39 Ar age plateaus exceeding 200 Ma occur over distances less than 50 km with major age discontinuities occurring across the Robertson Lake shear zone and the Sharbot Lake mylonite zone which separate the Sharbot Lake terrane from the Elzevir and Frontenac terranes. Extensional displacements of up to 14 km are inferred between the Frontenac and Elzevir terranes of the CMB. No evidence for significant post argon-closure vertical displacement is indicated in the vicinity of the Perth Road mylonite within the Frontenac terrane. Variations of nearly 100 Ma in phlogopite 40 Ar/ 39 Ar plateau ages occur in undeformed marble on either side of the Bancroft Shear Zone. Phlogopites from sheared and mylonitized marble within the shear zone yield 40 Ar/ 39 Ar diffusional loss profiles, but have older geologically meaningless ages thought to reflect incorporation of excess argon. By ∼ 900 Ma, southeast directed extension was occurring throughout the CMB, possibly initiated along previous zones of compressional shearing. An easterly migration of active zones of extension is inferred, possibly related to an earlier, overall easterly migration of active zones of regional thrusting and easterly migration of an ancient subduction zone. The duration of extensional shearing is not well constrained, but must have ceased before ∼ 600 Ma as required by the deposition of ove

Recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive Gibbs free energies for hedenbergite and pyrope. These were used to calculate the geobarometric equilibria

On December 12, 1992 a large earthquake (M s 7.5) occurred just north of Flores Island, Indonesia which, along with the tsunami it generated, killed more than 2,000 people. In this study, teleseismic P and SH waves, as well as PP waves from distances up to 123??, are inverted for the orientations and time histories of multiple point sources. By repeating the inversion for reasonable values of depth, time separation and spatial separation, a 2-fault model is developed. Next, the vertical deformation of the seafloor is estimated from this fault model. Using a detailed bathymetric model, linear and nonlinear tsunami propagation models are tested. The data consist of a single tide gauge record at Palopo (650 km to the north), as well as tsunami runup height measurements from Flores Island and nearby islands. Assuming a tsunami runup amplification factor of two, the two-fault model explains the tide gauge record and the tsunami runup heights on most of Flores Island. It cannot, however, explain the large tsunami runup heights observed near Leworahang (on Hading Bay) and Riangkroko (on the northeast peninsula). Massive coastal slumping was observed at both of these locations. A final model, which in addition to the two faults, includes point sources of large vertical displacement at these two locations explains the observations quite well.

The 9 March 1957 Aleutian earthquake has been estimated as the third largest earthquake this century and has the longest aftershock zone of any earthquake ever recorded???1200 km. However, due to a lack of high-quality seismic data, the actual source parameters for this earthquake have been poorly determined. We have examined all the available waveform data to determine the seismic moment, rupture area, and slip distribution. These data include body, surface and tsunami waves. Using body waves, we have estimated the duration of significant moment release as 4 min. From surface wave analysis, we have determined that significant moment release occurred only in the western half of the aftershock zone and that the best estimate for the seismic moment is 50???100??10 20 Nm. Using the tsunami waveforms, we estimated the source area of the 1957 tsunami by backward propagation. The tsunami source area is smaller than the aftershock zone and is about 850 km long. This does not include the Unalaska Island area in the eastern end of the aftershock zone, making this area a possible seismic gap and a possible site of a future large or great earthquake. We also inverted the tsunami waveforms for the slip distribution. Slip on the 1957 rupture zone was highest in the western half near the epicenter. Little slip occurred in the eastern half. The moment is estimated as 88??10 20 Nm, or M w =8.6, making it the seventh largest earthquake during the period 1900 to 1993. We also compare the 1957 earthquake to the 1986 Andreanof Islands earthquake, which occurred within a segment of the 1957 rupture area. The 1986 earthquake represents a rerupturing of the major 1957 asperity.

The heat capacity of cryolite (Na3AlF6) has been measured from 7 to 1000 K by low-temperature adiabatic and high-temperature differential scanning calorimetry. Low-temperature data were obtained on material from the same hand specimen in the calorimetric laboratories of the University of Michigan and U.S. Geological Survey. The results obtained are in good agreement, and yield average values for the entropy of cryolite of: S0298 = 238.5 J/mol KS0T-S0298 = 145.114 ln T+ 193.009*10-3T- 10.366* 105/T2- 872.89 J/mol K (273-836.5 K)[Delta]STrans = 9.9J/mol KS0T-S0298 =198.414 ln T+73.203* 10-3T-63.814*105/T2-1113.11 J/mol K (836.5-1153 K) with the transition temperature between [alpha]- and [beta]-cryolite taken at 836.5 K. These data have been combined with data in the literature to calculate phase equilibria for the system Na---Fe---Al---Si---O---F. The resultant phase diagrams allow constraints to be placed on the fO2, fF2, aSiO2 and T conditions of formation for assemblages in alkalic rocks. A sample application suggests that log fO2 is approximately -19.2, log fF2 is -31.9 to -33.2, and aSiO2 is -1.06 at assumed P/T conditions of 1000 K, 1 bar for the villiaumite-bearing Ilimaussaq intrusion in southwestern Greenland.

We have analyzed a suite of seventy-four formation-water samples from Mississippian and Pennsylvanian carbonate and siliciclastic strata in the Illinois basin for major, minor, and trace element concentrations and for strontium isotopic composition. A subset of these samples was also analyzed for boron isotopic composition. Data are used to interpret origin of salinity and chemical and Sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from Silurian-Devonian reservoirs. Systematics of Cl-Br-Na show that present Mississippian-Pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporation short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle Mississippian St. Louis Limestone, along with extensive dilution by mixing with meteoric waters. Additional diagenetic modifications in the subsurface interpreted from cation/Br ratios include K depletion through interaction with clay minerals, Ca enrichment, and Mg depletion by dolomitization, and Sr enrichment through CaCO3 recrystallization and dolomitization. Ste. Genevieve Limestone (middle Mississippian) formation waters show 87Sr/86Sr ratios in the range 0.70782-0.70900, whereas waters from the siliciclastic reservoirs are in the range 0.70900-0.71052. Inverse correlations between 87Sr/86Sr and B, Li, and Mg concentrations suggest that the brines acquired radiogenic 87Sr through interaction with siliciclastic minerals. Completely unsystematic relations between 87Sr/86Sr and 1/Sr are observed; Sr concentrations in Ste. Genevieve and Aux Vases (middle Mississippian) waters appear to be buffered by equilibrium with respect to SrSO4. Although there are many similarities in their origin and evolution, these formation waters are distinguished from Silurian-Devonian brines in the basin by elevated Cl/Br and Na/Br ratios and by unsystematic Sr isotope relationships. Thus waters

Mississippi Valley-type (MVT) ore deposits are epigenetic carbonate-hosted Pb-Zn deposits that contain galena, sphalerite, fluorite, barite, dolomite, calcite, and quartz. Although they are thought to form from basinal brines, their exact origins are still unclear, partly because of the scarcity of reliable geochronological data. Rb-Sr dating of sphalerites has recently been shown to be a promising technique for the direct dating of ore minerals in MVT deposits. This paper reports the results of a reconnaissance study of sphalerites, their fluid inclusions, and associated minerals from MVT deposits of North America. Sphalerites from Immel mine, Mascot-Jefferson City district, east Tennessee, define a Rb-Sr age of 347 +/- 20 Ma consistent with a Rb-Sr age of 377 +/- 29 Ma for sphalerites from Coy mine in the same district, but inconsistent with models that ascribe their genesis to the effects of the late Paleozoic Alleghenian orogeny. Rb-Sr isotopic analyses of K-feldspar from Immel mine preclude the possibility that the Rb-Sr data reflect feldspar inclusions. Sphalerites from the main ore zone of Daniel's Harbour mine, New foundland, do not form a linear isochron and open behavior of the Rb-Sr system is suspected. Sphalerites from the Pine Point district, Northwest Territories, Canada, define a Rb-Sr age of 361 +/- 13 Ma, indicating that the mineralization took place shortly after the deposition of the middle Devonian host carbonate rocks. These results are not compatible with mineralization models based on regional fluid migration related to early Tertiary Cordilleran deformation. Sphalerites from northern Arkansas have very low Rb and Sr concentrations (less than 0.1 ppm). The Rb-Sr data do not form isochrons and the sphalerites have higher 87Sr/86Sr ratios than expected, given their Rb/Sr ratios and reasonable constraints on their ages. The sphalerites are suspected to contain clay inclusions; and it is likely that the Sr isotopic compositions of these sphalerite

The Pueblo Viejo district is one of the largest producers of precious metals in the world, yielding more than 11,000 kg of Au annually. Gold mineralization at Pueblo Viejo is hosted in spilite, and coarse clastic and finely laminated, fine grained carbonaceous sedimentary rocks of the Lower Cretaceous Los Ranchos Formation. Mineralization was accompanied by sulfidation as evidenced by (1) the occurrence of siderite distal to mineralization and pyrite proximal to mineralization, (2) increased S/Fe ratios associated with Au mineralization, (3) the occurrence of native S in and adjacent to mineralization, and (4) the presence of sulfidized organic matter (organo-S compounds) in mineralized rocks. Organic matter in the carbonaceous sedimentary rocks comprises vitrinite and pyrobitumen. Rock-Eval pyrolysis data indicate that this organic matter is overmature (HI 2S in the mineralizing fluid would have destabilized Au bisulfide complexes and caused deposition of gold. The restriction of S-rich organic matter to rocks in which all Fe occurs as pyrite indicates that sulfidation of organic matter postdates sulfidation of ferrous Fe and therefore, deposition of much of the Au.

The intrinsic oxygen fugacity (IOF) of olivine separates from the Salta, Springwater, and Eagle Station pallasites was measured between 850 and 1150[deg]C using oxygen-specific solid zirconia electrolytes at 105 Pa. The experimental apparatus consisted of a double-opposed electrolyte configuration with a CO-CO2 gas-mix bridging atmosphere. Four initial IOF measurements on Salta olivines revealed the effects of grain size and cell memory on experimental results; experiments with an IW cell memory and fine grain size (log fO2), contains Fa12.5 and Fe90.5Ni9.0; Springwater, of intermediate redox state (~IW), contains Fa18.0 and Fe87.5Ni12.1; Eagle Station, the most oxidized sample (IW + 0.5 logfO2), contains Fa20.5 and Fe85.0Ni14.6. Electron microbeam characterization of the starting materials and run products from these experiments have shown that olivine is the only phase present. Thermodynamic calculations of redox equilibria involving equilibrium pallasite assemblages are in good agreement with our experimental results and provide a lower limit to pallasite redox stability; others involving disequilibrium assemblages, suggest that pallasites experienced localized, late-stage oxidation and reduction effects. Consideration of the redox buffer metal-olivine-orthopyroxene utilizing calculated Eucrite Parent Body (EPB) mantle phase compositions indicates that small redox gradients may have existed in the EPB. Such gradients may have produced strong compositional variation within the EPB. In addition, there is apparently significant redox heterogeneity in the source area of Eagle Station Trio (EST) pallasites and Bocaiuva iron meteorites.

The Sr, Nd, and O isotopic compositions of garnet and clinopyroxene mineral separates from nine eclogite xenoliths from the Bellsbank kimberlite (erupted at 120 Ma) define three groups. Group A eclogites, considered to be mantle cumulates, are characterized by [delta]18O, and 87Sr/86Sr values typical of mantle-derived materials (+5.1 to +5.6[per mille sign] and 0.7042-0.7046, respectively), and very low Sm/Nd ratios, (apparent) Rb/Sr ratios and [epsilon]Nd[120] values (0.057-0.078, 0.00005-0.00136 and -14 to -16 respectively). The REE and isotopic data for these eclogites can be modelled in terms of crystallization from a Group II kimberlite magma at ~ 1-1.5 Ga. Group B and C eclogites, believed to be the metamorphosed products of ancient subducted oceanic crust, are characterized by low [delta]18O (+2.9 to +4.7), extremely high [epsilon]Nd[120] (~ +40 to +219), and radiogenic 87Sr/86Sr ratios (0.708-0.710). The Sm/Nd ratios of the Group B eclogites are very high (up to 1.6). The data for Group B and C eclogites define a linear correlation on Sm/Nd and 1/Nd vs. [epsilon]Nd[120] diagrams. These relationships are consistent with mixing of the Bellsbank kimberlite ([epsilon]Nd[120] = -10; Sm/Nd = 0.10) with a depleted eclogite end-member ([epsilon]Nd[120] +219; Sm/Nd = 1.6) during a cryptic metasomatic event. The Sr isotopic variations in Group B and C eclogites cannot be generated by simple two-component mixing. The Sr, Nd, and O isotope data for Group B and C eclogites probably reflect a complex sequence of depletion and enrichment events, in both crust and mantle settings. Enrichments which possibly affected the Group B and C eclogites include seawater-alteration of a MORB-like protolith, which lowered the [delta]18O and raised the 87Sr/86Sr ratio, but left the Nd isotopic compositions unchanged, and cryptic metasomatism by the magmatism that produced the Bellsbank kimberlite. The high Sm/Nd ratio of the depleted eclogite end-member cannot be generated by extraction

The high-silica rhyolite lavas of Glass Mountain, California, provide a detailed record of the evolution of the Long Valley magmatic system during the 1.4 m.y. prior to the catastrophic eruption of the voluminous zoned rhyolitic Bishop Tuff at 0.73 Ma. The older lavas of Glass Mountain are extremely evolved, and were erupted from 2.1 to 1.2 Ma with 87Sr/86Sr of 0.707-0.739 and [epsilon]Nd of -3 to -4, whereas the younger lavas are slightly less evolved and were erupted between 1.2 and 0.79 Ma with 87Sr/86Sr of 0.706-0.707 and [epsilon]Nd close to -1, essentially identical to the Sr and Nd isotopic compositions of the Bishop Tuff. Neither the older nor younger lavas display a relationship between the isotopic compositions of Sr and Nd. The Pb isotopic compositions are effectively uniform at 206Pb/204Pb = 19.13-19.17. A group of older lavas that outcrop in a northwest-trending band near the topographic rim of the caldera collectively define an apparent Rb---Sr isochron age (t) of 2.09 +/- 0.06 Ma with an intercept of 87Sr/86Sr = 0.7060 +/- 3, where analyzed older lavas outcropping outboard of this band define an isochron of 1.90 +/- 0.02 Ma (87Sr/86Sr)t = 0.7063 +/- 4) These isochron ages are identical to the K---Ar ages for oldest erupted rhyolites in the two regions, respectively. The younger lavas away from the caldera define an apparent Rb---Sr isochron age (t) of 1.14 +/- 0.08 Ma with the same (87Sr/86Sr)t as the older lavas. The agreement between the 87Sr/86Sr ratios of the rhyolite magmas when emplaced in the Long Valley magmatic system (0.706) and that of basaltic lavas in the region (0.7059-0.7062) suggests that the Sr isotopic compositions of these Sr-poor rhyolites may be totally dominated by Sr from mantle-derived components. K---Ar ages and stratigraphic relations for both the older and younger lavas seem to rule out the possibility that the Rb---Sr isochron ages record the times of eruption. The very low Sr concentrations of all the lavas (down to 0.1 ppm

The compositions of individual synthetic fluid inclusions in the systems NaCl-KCl, NaCl-CaCl2 and NaCl-KCl-CaCl2 have been semi-quantitatively determined by energy dispersive analysis of precipitates produced during thermal decrepitation. Inclusions containing known mixtures of 20 wt.% total salinity were synthesized by healing fractures in natural quartz at 600-700[deg]C and 5-7 kbars for 7-10 days. The two-phase, daughter-free inclusions homogenized at 170-250[deg]C, began to decrepitate after about 100[deg] of overheating and by 360-420[deg]C a significant number of decrepitates had formed on the polished surface. Peak heights generated by EDA (raster mode) of these decrepitates were standardized using both single and mixed salt standards evaporated to dryness in a vacuum. Although the mixed salt standards better approximated the decrepitate compositions, difficulties were encountered in producing micronscale homogeneity and the single salts yielded more reliable results. Eight different solutions of 20-23 wt.% total salinity were run and in all the samples the average compositions of 10-20 discrete, single inclusion decrepitates fell with 6 wt.% (0.2 to 5.2) of the actual composition, suggesting that the decrepitates were chemically representative of their precursor inclusions. However, not all decrepitates analyzed provided similarly accurate results. Electron mapping revealed that fracture-aligned decrepitates were often chemically inhomogeneous and thus had to be avoided. A sample decrepitated at 500[deg]C yielded spurious results suggesting that chloride volatility may become a significant problem when temperatures in excess of 450[deg]C are required for decrepitation. Decrepitates with diameters between 10 and 30 [mu]m yielded more consistent and accurate results than smaller or larger decrepitates on the same samples.

Intense intraplate seismic activity has recently been identified in the west-central Pacific, along a line extending from Samoa through the Gilbert Islands and the Ralik Fracture Zone to the Caroline Islands. Over the past 50 years, this seismic line has contributed an estimated 15-30% of the entire intraplate seismicity for the Pacific plate (Hawaii excepted). Focal mechanisms available for ten of the largest events during the 1981-1983 Gilbert Islands swarm, with horizontal compressional stress oriented at right angles to the direction of motion of the plate, cannot be reconciled with simple models of intraplate stresses. We speculate that they express large scale deformation of that part of the Pacific plate, related to incipient detachment of a microplate and relocation of the Pacific-Australian subduction zone some 1000 km to the north of its present position.

Chemical analysis (including H 2 , F 2 , FeO, Fe 2 O 3 ) of a Mg-vesuvianite from Georgetown, Calif., USA, yields a formula, Ca 18.92 Mg 1.88 Fe 3+ 0.40 Al 10.97 Si 17.81- O 69.0.1 (OH) 8.84 F 0.14 , in good agreement on a cation basis with the analysis reported by Pabst (1936). X-ray and electron diffraction reveal sharp reflections violating the space group P4/nnc as consistent with domains having space groups P4/n and P4nc. Refinement of the average crystal structure in space group P4/nnc is consistent with occupancy of the A site with Al, of the half-occupied B site by 0.8 Mg and 0.2 Fe, of the half-occupied C site by Ca, of the Ca (1,2,3) sites by Ca, and the OH and O(10) sites by OH and O. We infer an idealized formula for Mg-vesuvianite to be Ca 19 Mg(MgAl 7 )Al 4 Si 18 O 69 (OH) 9 , which is related to Fe 3+- vesuvianite by the substitutions Mg + OH = Fe 3+ + O in the B and O(10) sites and Fe 3+ = Al in the AlFe site. Thermodynamic calculations using this formula for Mg-vesuvianite are consistent with the phase equilibria of Hochella, Liou, Keskinen & Kim (1982) but inconsistent with those of Olesch (1978). Further work is needed in determining the composition and entropy of synthetic vs natural vesuvianite before quantitative phase equilibria can be dependably generated. A qualitative analysis of reactions in the system CaO-MgO-Al 2 O 3 -SiO 2 -H 2 O-CO 2 shows that assemblages with Mg-vesuvianite are stable to high T in the absence of quartz and require water-rich conditions (XH 2 O > 0.8). In the presence of wollastonite, Mg-vesuvianite requires very water-rich conditions (XH 2 O > 0.97).

During the past half-century, the nuclear fuel cycle has generated approximately 1400 metric tons of plutonium and substantial quantities of the “minor” actinides, such as Np, Am, and Cm. The successful disposition of these actinides has an important impact on the strategy for developing advanced nuclear fuel cycles, weapons proliferation, and the geologic disposal of high-level radioactive waste. During the last decade, there has been substantial interest in the use of the isometric pyrochlore structure-type, A2B2O7,A2B2O7, for the immobilization of actinides. Most of the interest has focused on titanate-pyrochlore because of its chemical durability; however, these compositions experience a radiation-induced transition from the crystalline-to-aperiodic state due to radiation damage from the alpha-decay of actinides. Depending on the actinide concentration, the titanate pyrochlore will become amorphous in less than 1000 years of storage. Recently, systematic ion beam irradiations of a variety of pyrochlore compositions has revealed that many zirconate pyrochlores do not become amorphous, but remain crystalline as a defect fluorite structure-type due to disordering of the A- and B-site cations. The zirconate pyrochlores will remain crystalline even to very high doses, greater than 100 displacements per atom. Systematic experimental studies of actinide-doped and ion beam-irradiated pyrochlore, analyses of natural U- and Th-bearing pyrochlore, and simulations of the energetics of the disordering process now provide a rather detailed understanding of the structural and chemical controls on the response of pyrochlore to radiation. These results provide a solid basis for predicting the behavior and durability of pyrochlore used to immobilize plutonium. © 2004 American Institute of Physics.

We theoretically document the stability of hcp iron for pressure–temperature conditions of the Earth’s inner core by separately computing the electronic and phonon contributions to the free energy. These pseudopotential-based quasi-harmonic calculations reveal that the hcp phase remains stable compared to bcc and that the c/a ratio of lattice parameters exhibits only a modest temperature dependence at inner-core conditions.

??-decay damage and recrystallization in natural zircon (with dose ranging from 0.06 to 23.3??1018??-events??g -1) were studied using polarized reflection infrared spectroscopy. The experimental results show that??-decay damage leads to a gradual decrease in reflectivity and a loss of anisotropy of IR spectra. Recrystallization of damaged zircon is found as a multi-stage process with a strong dependence on the initial degree of damage. In weakly and moderately damaged samples the major recrystallization takes place near 1000??K. Annealed samples recrystallize epitaxially along their original crystallographic orientations. A highly damaged zircon with radiation dose of 15.9??1018??-events??g -1 decomposes into SiO2 and ZrO2 near 1100??K. In this sample the growth of ZrSiO4 from the binary oxides occurs between 1400 and 1500??K. An additional IR signal peaked near 790??cm -1 is detected in moderately damaged samples annealed at temperatures higher than 800??K. This peak is sharp and isotropic. The peak tends to disappear at temperatures above 1400??K. This signal may be related to an unknown intermediate phase caused by heating of radiation-damaged zircon. Alternatively, the signal may be due to the structural distortions near the boundaries between the amorphized and crystalline regions.

Stable isotope analyses of rocks and minerals associated with the detachment fault and underlying mylonite zone exposed at Secret Creek gorge and other localities in the Ruby-East Humboldt Range metamorphic core complex in northeastern Nevada provide convincing evidence for meteoric water infiltration during mylonitization. Whole-rock?? 18 O values of the lower plate quartzite mylonites (???95% modal quartz) have been lowered by up to 10 per mil compared with structurally lower, compositionally similar, unmylonitized material. Biotite from these rocks has??D values ranging from -125 to -175, compared to values of -55 to-70 in biotite from unmylonitized rocks. Mylonitized leucogranites have large disequilibrium oxygen isotope fractionations (?? quartz-feldspar up to???8 per mil) relative to magmatic values (?? quartz-feldspar???1 to 2 per mil)). Meteoric water is the only major oxygen and hydrogen reservoir with an isotopic composition capable of generating the observed values. Fluid inclusion water from unstrained quartz in silicified breccia has a??D value of-119 which provides a plausible estimate of the??D of the infiltrating fluid, and is similar to the isotopic composition of present-day and Tertiary local meteoric water. The quartzite mylonite biotites would have been in equilibrium with such a fluid at temperatures of 480???620?? C, similar to independent estimates of the temperature of mylonitization. The relatively high temperatures required for isotopic exchange between quartz and water, the occurrence of fluid inclusion trails and deformed veins in quartzite mylonites, and the spatial association of the low- 18 O, low-D rocks with the shear zone all constrain isotopic exchange to the mylonitic (plastic) deformation event. These observations suggest thata significant amount of meteoric water infiltrated the shear zone during mylonitization to depths of at least 5 to 10 km below the surface. The depth of penetration of meteoric fluids into the lower

The transition between rutile and??-PbO 2 structured TiO 2 (TiO 2 II) has been investigated at 700???1,200????C and 4.2???9.6??GPa. Hydrothermal phase equilibrium experiments were performed in the multi-anvil apparatus to bracket the phase boundary at 700, 1,000, and 1,200????C. The equilibrium phase boundary is described by the equation: P (GPa)=1.29+0.0065 T (????C). In addition, growth of TiO 2 II was observed in experiments at 500 and 600????C, although growth of rutile was too slow to bracket unambiguously the equilibrium boundary at these temperatures. Water was not detected in either rutile or TiO 2 II, and dry synthesis experiments at 1,200????C were consistent with the phase boundary determined in the fluid-bearing experiments, suggesting that the equilibrium is unaffected by the presence of water. Our bracket of the phase boundary at 700????C is consistent with the reversed, dry experiments of Akaogi et al. (1992) and the reversals of Olsen et al. (1999). The new data suggest that the phase boundary is linear, in agreement with Akaogi et al. (1992), but in striking contrast to the phase diagram inferred by Olsen et al. (1999). The natural occurrence of TiO 2 II requires formation pressures considerably higher than the graphite???diamond phase boundary.

???Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes that formed during late???magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a?? 18 O value of???5.8??? and a??D value of???158???. These low values reflect subsolidus alteration by low????? 18 O, low?????D hydrothermal fluids of meteoric origin. The??D value is lower than the???146 to???112??? values previously reported for amphiboles from other early Tertiary meteoric???hydrothermal systems in East Greenland and Scotland, indicating that the meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is??D=???110?????10???,?? 18 O??????15???. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have?? 18 O values between???6.0 and???3.8??? and??D values between???155 and???140???. These are both much lower than typical values of fresh basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low????? 18 O partial melts of xenoliths that had been hydrothermally altered and depleted in 18 O prior to stoping. The pegmatitic minerals may hav

???Alkali basalts and nephelinites from the volcanic province of northern Tanzania contain pyroxene and nepheline that show evidence for chemical and/or isotopic disequilibria with their host magmas. Olivine, pyroxene, nepheline and plagioclase all appear to be partially xenocrystic in origin. Five whole rock/mineral separate pairs have been analyzed for Sr, Nd, and Pb isotopic compositions. The 206 Pb/ 204 Pb ratios are distinct by as much as 20.94 (whole rock) vs. 19.10 (clinopyroxene separate). The Sr and Nd isotopic disequilibria vary from insignificant in the case of nepheline, to?? 87 Sr/ 86 Sr of 0.0002 and???? Nd of 0.7 in the case of clinopyroxene. The mineral chemistry of 25 samples indicates the ubiquitous presence of minerals that did not crystallize from a liquid represented by the host rock. The northern Tanzanian magmas are peralkaline and exhibit none of the xenocrystic phases expected from crustal assimilation. The disequilibria cannot be the result of mantle source variations. Rather the xenocrystic phases present appear to have been derived from earlier alkali basaltic rocks or magmas that were contaminated by the crust. Material from this earlier magma was then mixed with batches of magma that subsequently erupted on the surface. Disequilibrium in volcanic rocks has potentially serious consequences for the use of whole rock data to identify source reservoirs. However, mass balance calculations reveal that the 206 Pb/ 204 Pb isotopic compositions of the erupted lavas were changed by less than 0.25% as a result of this indirect crustal contamination.

The thermal regime in the moist surficial peat layer of a palsa, measured during a clear and calm July day in arctic Alaska, indicates that coupled heat and water flow retard ablation of the ice core. A simulation model of coupled-flow effects was constructed using rough estimates of meteorological boundary conditions and material properties. The model indicates that ablation is inhibited by advection of cold water above the ice/peat interface, and by internal evaporation near the surface. Evaporation also limits thermal maxima near the surface; because the ratio of the heat of evaporation to the heat of fusion is approximately 7.5, the coupled-flow regime effectively retards ablation of the palsa's ice core. Das Temperaturregime in der feuchten, oberfl??chennahen Torfschicht eines Pals wurde w??hrend eines klaren und windstillen Julitages in der Arktis von Alaska vermessen. Es wird gezeigt, da?? der gekoppelte W??rme- und Wasserstrom die Ablation des Eiskernes verz??gert. Ein Simulationsmodell der gekoppelten Stromeffekte wurde konstruiert, wobei grobe Absch??tzungen der meteorologischen Grenzbedingungen und der Bodenbeschaffenheit angebracht wurden. Das Modell deutet an, da?? die Ablation durch Advektion von kaltem Wasser oberhalb der Eis-Torf-Grenzschicht und durch interne Verdunstung nahe der Oberfl??che behindert wird. Verdunstung beschr??nkt au??erdem die Temperaturmaxima nahe der Oberfl??che. Da das Verh??ltnis der latenten W??rmen der Verdunstung und der Sublimation ungef??hr 7,5 betr??gt, verz??gert das gekoppelte Stromregime effektiv die Ablation des Eiskernes der Pals.

While the biomechanical properties of bone are reasonably well understood at many levels of structural hierarchy, surprisingly little is known about the response of bone to loading at the ultrastructural and crystal lattice levels. In this study, our aim was to examine the response (i.e., rate of change of the vibrational frequency of mineral and matrix bands as a function of applied pressure) of murine cortical bone subjected to hydrostatic compression. We determined the relative response during loading and unloading of mineral vs. matrix, and within the mineral, phosphate vs. carbonate, as well as proteinated vs. deproteinated bone. For all mineral species, shifts to higher wave numbers were observed as pressure increased. However, the change in vibrational frequency with pressure for the more rigid carbonate was less than for phosphate, and caused primarily by movement of ions within the unit cell. Deformation of phosphate on the other hand, results from both ionic movement as well as distortion. Changes in vibrational frequencies of organic species with pressure are greater than for mineral species, and are consistent with changes in protein secondary structures such as alterations in interfibril cross-links and helix pitch. Changes in vibrational frequency with pressure are similar between loading and unloading, implying reversibility, as a result of the inability to permanently move water out of the lattice. The use of high pressure Raman microspectroscopy enables a deeper understanding of the response of tissue to mechanical stress and demonstrates that individual mineral and matrix constituents respond differently to pressure.

Das Tr??gergestein der Chapada Kupferlagerst??tte in Goi??s ist in metamorpher Hoch-Amphibolitfazies ausgebildet. Gesamtgesteins- und individuelle Mineral Rb-Sr-Isochronen mit einem 87 Sr/ 86 Sr-Initialwert (I) von 0,70414??0.00005 ergeben f??r die Kristallisation der Vulkanite und Magmatite, die die Metamorphose vordatieren, ein Alter von 561??9 Mio Jahre. Die Datierung der Metamorphose w??hrend der panafrikanisch/brasilianischen Orogenese (700 bis 450 Mio Jahre) ergibt 532??1 Mio Jahre. Das Mineral-Isochronenalter eines Dioritk??rpers porphyrischen Gef??ges, der in die Schiefer intrudierte, betr??gt 534??16 Mio Jahre (I=0,70415 ??0,00004). Das Ergebnis niedriger Initial-Werte dieser Isochronen ergibt f??r die Schiefer bei Chapada ein Ausgangs-Material im Bereich des oberen Mantels oder der tieferen Kruste; diese Ausgangswerte sind charakteristisch f??r magmatische T??tigkeit in Verbindung mit Inselb??gen. Das unterkambrische Alter des Tr??gergesteins bei Chapada steht im Widerspruch zu dem bisher angenommenen mittelproterozoischen Alter und ist ein Hinweis auf eine m??gliche Phase intensiverer pan-afrikanisch/brasilianischer magmatischer Aktivit??t in Zentral-Brasilien als urspr??nglich angenommen wurde. Whole rock and mineral Rb-Sr isochrons from the upper amphibolite grade metamorphic host rocks of the Chapada copper deposit in Goi??s, Brazil, yield an age of 561??9 Ma, with a 87 Sr/ 86 Sr initial (I) of 0.70414??0.00005, for the crystallization of pre-metamorphic volcanic and igneous rocks and 532 ??1 Ma for their metamorphism during the Pan-African/Brasiliano orogeny (700-450 Ma). A porphyritic diorite stock which intruded the host schists yields a mineral isochron age of 534??16 Ma (I=0.70415??0.00004). The low I values determined from these isochrons suggest that the host schists at Chapada were derived from upper mantle or lower crust material and are characteristic of magmatic products associated with island arcs. The Early Cambrian age of the host rocks a

Subduction-related volcanism in the Nevados de Payachata region of the Central Andes at 18??S comprises two temporally and geochemically distinct phases. An older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late Miocene age. The Pleistocene to Recent phase (???0.3 Ma) includes the twin stratovolcanoes Volcan Pomerape and Volcan Parinacota (the Nevados de Payachata volcanic group) and two small centers to the west (i. e., Caquena and Vilacollo). Both stratovolcanoes consist of an older dome-and-flow series capped by an andesitic cone. The younger cone, i. e., V. Parinacota, suffered a postglacial cone collapse producing a widespread debris-avalanche deposit. Subsequently, the cone reformed during a brief, second volcanic episode. A number of small, relatively mafic, satellitic cinder cones and associated flows were produced during the most recent activity at V. Parinacota. At the older cone, i. e., V. Pomerape, an early dome sequence with an overlying isolated mafic spatter cone and the cone-forming andesitic-dacitic phase (mostly flows) have been recognized. The two Nevados de Payachata stratovolcanoes display continuous major- and trace-element trends from high-K 2 O basaltic andesites through rhyolites (53%???76% SiO 2) that are well defined and distinct from those of the older volcanic centers. Petrography, chemical composition, and eruptive styles at V. Parinacota differ between pre- and post-debris-avalanche lavas. Precollapse flows have abundant amphibole (at SiO 2> 59 wt%) and lower Mg numbers than postcollapse lavas, which are generally less silicic and more restricted in composition. Compositional variations indicate that the magmas of the Nevados de Payachata volcanic group evolved through a combination of fractional crystallization, crustal assimilation, and intratrend magma mixing. Isotope compositions exhibit only minor variations. Pb-isotope ratios are relatively low (206 Pb/ 204 Pb = 17.95???18.20 and 208 Pb

Located at the volcanic front in the western Mexican arc, in the Colima Rift, is the active Volc??n Colima, which lies on the southern end of the massive (???450??km 3) Colima-Nevado volcanic complex. Along the margins of this andesitic volcanic complex, is a group of 11 scoria cones and associated lavas, which have been dated by the 40 Ar/ 39 Ar method. Nine scoria cones erupted???1.3??km 3 of alkaline magma (basanite, leucite-basanite, minette) between 450 and 60??ka, with>99% between 240 and 60??ka. Two additional cones (both the oldest and calc-alkaline) erupted <0.003??km 3 of basalt (0.5??Ma) and <0.003??km 3 of basaltic andesite (1.2??Ma), respectively. Cone and lava volumes were estimated with the aid of digital elevation models (DEMs). The eruption rate for these scoria cones and their associated lavas over the last 1.2??Myr is???1.2??km 3 /Myr, which is more than 400 times smaller than that from the andesitic Colima-Nevado edifice. In addition to these alkaline Colima cones, two other potassic basalts erupted at the volcanic front, but???200??km to the ESE (near the historically active Volc??n Jorullo), and were dated at 1.06 and 0.10??Ma. These potassic suites reflect the tendency in the west-central Mexican arc for magmas close to the volcanic front to be enriched in K 2 O relative to those farther from the trench.

The oxygen fugacities (fO 2 's) of magnetically-concentrated fractions (MCF) of three rock samples from the Skaergaard Layered Intrusion were measured between 800???1150?? C using oxygen-specific, solid zirconia electrolytes at atmospheric pressure. Two of the bulk rock samples (an oxide cumulate and an oxide-bearing gabbro) are from the Middle Zone (MZ) and the other (an olivine plagioclase orthocumulate) is from the Lower Zone (LZ). All MCF define fO 2 versus T arrays that lie 1.5???0.5 log units above the fayalite-magnetite-quartz (FMQ) buffer. Experiments with different cell-imposed initial redox states (one from a reduced direction and one from an oxidized direction) were run on each sample in an attempt to achieve experimental reversibility. This was accomplished by imposing a known redox memory on the galvanic cell prior to loading each sample. Reversibility for each sample agreed to better than 0.2 of a log unit. Irreversible autoreduction of 0.2 of a log unit was observed on the two MZ samples at temperatures exceeding 1065?? C. Scanning electron microscope and electron microprobe study of pre- and post-run products shows that reaction and textural re-equilibration occurred among the oxide phase assemblages under the experimental conditions employed. Careful characterization of pre- and post-run assemblages is clearly necessary before adequate interpretation of the experimental results can be made in these types of electrochemical studies. Different approaches to investigations of the fO 2 of the Skaergaard Intrusion, be it thermodynamic calculations or experimental methods, should yield concordant results or at least understandable discrepancies. Calculated fO 2 's using thermobarometry applied to the ilmenite-magnetite pairs in the post-experimental assemblages agree with the experimentally determined fO 2 's to within one log unit at a given temperature. These results are also consistent with previously calculated fO 2 values (Buddington and Lindsley 196

A wide variety of rock types are present in the O'Leary Peak and Strawberry Crater volcanics of the Pliocene to Recent San Francisco Volcanic Field (SFVF), AZ. The O'Leary Peak flows range from andesite to rhyolite (56???72 wt % SiO 2) and the Strawberry Crater flows range from basalt to dacite (49???64 wt % SiO 2). Our interpretation of the chemical data is that both magma mixing and crustal melting are important in the genesis of the intermediate composition lavas of both suites. Observed chemical variations in major and trace elements can be modeled as binary mixtures between a crustal melt similar to the O'Leary dome rhyolite and two different mafic end-members. The mafic end-member of the Strawberry suite may be a primary mantle-derived melt. Similar basalts have also been erupted from many other vents in the SFVF. In the O'Leary Peak suite, the mafic end-member is an evolved (low Mg/(Mg+ Fe)) basalt that is chemically distinct from the Strawberry Crater and other vent basalts as it is richer in total Fe, TiO 2, Al 2 O 3, MnO, Na 2 O, K 2 O, and Zr and poorer in MgO, CaO, P 2 O 5, Ni, Sc, Cr, and V. The derivative basalt probably results from fractional crystallization of the more primitive, vent basalt type of magma. This evolved basalt occurs as xenolithic (but originally magmatic) inclusions in the O'Leary domes and andesite porphyry flow. The most mafic xenolith may represent melt that mixed with the O'Leary dome rhyolite resulting in andesite preserved as other xenoliths, a pyroclastic unit (Qoap), porphyry flow (Qoaf) and dacite (Darton Dome) magmas. Thermal constraints on the capacity of a melt to assimilate (and melt) a volume of solid material require that melt mixing and not assimilation has produced the observed intermediate lavas at both Strawberry Crater and O'Leary Peak. Textures, petrography, and mineral chemistry support the magma mixing model. Some of the inclusions have quenched rims where in contact with the host. The intermediate rocks

The low-temperature heat capacity (C p) of KAlSi 3 O 8 with a hollandite structure was measured over the range of 5???303??K with a physical properties measurement system. The standard entropy of KAlSi 3 O 8 hollandite is 166.2??0.2??J??mol???1??K???1, including an 18.7??J??mol???1??K???1 contribution from the configurational entropy due to disorder of Al and Si in the octahedral sites. The entropy of K 2 Si 4 O 9 with a wadeite structure (Si-wadeite) was also estimated to facilitate calculation of phase equilibria in the system K 2 O???Al 2 O 3???SiO 2 . The calculated phase equilibria obtained using Perple_x are in general agreement with experimental studies. Calculated phase relations in the system K 2 O???Al 2 O 3???SiO 2 confirm a substantial stability field for kyanite???stishovite/coesite???Si-wadeite intervening between KAlSi 3 O 8 hollandite and sanidine. The upper stability of kyanite is bounded by the reaction kyanite (Al 2 SiO 5)??=??corundum (Al 2 O 3)?? +??stishovite (SiO 2), which is located at 13???14??GPa for 1,100???1,400??K. The entropy and enthalpy of formation for K-cymrite (KAlSi 3 O 8??H 2 O) were modified to better fit global best-fit compilations of thermodynamic data and experimental studies. Thermodynamic calculations were undertaken on the reaction of K-cymrite to KAlSi 3 O 8 hollandite??+?? H 2 O, which is located at 8.3???10.0??GPa for the temperature range 800???1,600??K, well inside the stability field of stishovite. The reaction of muscovite to KAlSi 3 O 8 hollandite??+??corundum??+??H 2 O is placed at 10.0???10.6??GPa for the temperature range 900???1,500??K, in reasonable agreement with some but not all experiments on this reaction.

The Cabo de Gata volcanic field of southeastern Spain contains several recently-recognized calderas. Some of the calderas are mineralized with epithermal gold, alunite, and base metal deposits, and others are barren, and yet they formed under generally similar conditions. Comparison of the magmatic, geochemical, and physical evolution of the Los Frailes, Rodalquilar, and Lomilla calderas provides insight into the processes of caldera evolution that led to precious-metal mineralization. The Los Frailes caldera formed at 14.4 Ma and is the oldest caldera. It formed in response to multiple eruptions of hornblende dacite magma. Following each eruption, the area collapsed and the caldera was invaded by the sea. Dacite domes fill the lower part of the caldera. Pyroxene andesites were erupted through the solidified core of the caldera and were probably initially responsible for magma generation. The Los Frailes caldera did not evolve to rhyolites nor was it subjected to the amount of structural development that the younger, mineralized Rodalquilar and Lomilla calderas were.

Heterogeneous fault motion of the 1993 Hokkaido Nansei-Oki earthquake is studied by using seismic, geodetic and tsunami data, and the tsunami generation from the fault model is examined. Seismological analyses indicate that the focal mechanism of the first 10 s, when about a third of the total moment was released, is different from the overall focal mechanism. A joint inversion of geodetic data on Okushiri Island and the tide gauge records in Japan and Korea indicates that the largest slip, about 6 m, occurred in a small area just south of the epicenter. This corresponds to the initial rupture on a fault plane dipping shallowly to the west. The slip on the northernmost subfault, which is dipping to the east, is about 2 m, while the slips on the southern subfaults, which are steeply dipping to the west, are more than 3 m. Tsunami heights around Okushiri Island are calculated from the heterogeneous fault model using different grid sizes. Computation on the smaller grids produces large tsunami height that are closer to the observed tsunami runup heights. Tsunami propagation in the nearly closed Japan Sea is examined as the free oscillation of the Japan Sea. The excitation of the free oscillation by this earthquake is smaller than that by the 1964 Niigata or 1983 Japan Sea earthquake.

While most aspects of subduction have been extensively studied, the process of subduction initiation lacks an observational foundation. The Macquarie Ridge complex (MRC) forms the Pacific-Australia plate boundary between New Zealand to the north and the Pacific-Australia-Antarctica triple junction to the south. The MRC consists of alternating troughs and rises and is characterized by a transitional tectonic environment in which subduction initiation presently occurs. There is a high seismicity level with 15 large earthquakes (M>7) in this century. Our seismological investigation is centered on the largest event since 1943: the 25 MAY 1981 earthquake. Love, Rayleigh, and P waves are inverted to find: a faulting geometry of right-lateral strike-slip along the local trend of the Macquarie Ridge (N30??E); a seismic moment of 5??10 27 dyn cm (M w =7.7) a double event rupture process with a fault length of less than 100km to the southwest of the epicenter and a fault depth of less than 20km. Three smaller thrust earthquakes occurred previous to the 1981 event along the 1981 rupture zone; their shallow-dipping thrust planes are virtually adjacent to the 1981 vertical fault plane. Oblique convergence in this region is thus accommodated by a dual rupture mode of several small thrust events and a large strike-slip event. Our study of other large MRC earthquakes, plus those of other investigators, produces focal mechanisms for 15 earthquakes distributed along the entire MRC; thrust and right-lateral strike-slip events are scattered throughout the MRC. Thus, all of the MRC is characterized by oblique convergence and the dual rupture mode. The???true??? best-fit rotation pole for the Pacific-Australia motion is close to the Minster & Jordan RM2 pole for the Pacific-India motion. Southward migration of the rotation pole has caused the recent transition to oblique convergence in the northern MRC. We propose a subduction initiation process that is akin to crack propagation; the

The early P wave coda (5???15 sec after the first arrival) of underground explosions at the Nevada Test Site is studied in the time domain using 2082 teleseismic short-period recordings, with the intent of identifying near-source contributions to the signals in the frequency range 0.2???2.0 Hz. Smaller magnitude events tend to have relatively high coda levels in the 0.4???0.8 Hz frequency band for both Yucca Flat and Pahute Mesa explosions. Coda complexity in this low-frequency passband is negatively correlated with burial depth for Pahute Mesa events but is only weakly correlated with depth for Yucca Flat events. Enhanced excitation of relatively long-period scattered waves for smaller, less deeply buried events is required to explain this behavior. Coda complexity in the 0.8???1.1 Hz band is positively correlated with magnitude and depth for Pahute Mesa events, but has no such dependence for Yucca Flat events. This may result from systematic variations between the spectra of direct signals and coda arrivals caused by pP interference for the largest events, all of which were detonated at Pahute Mesa. Another possible explanation is a frequency-dependent propagation effect on the direct signals of the larger events, most of which were located in the center of the mesa overlying strong lateral velocity gradients in the crust and upper mantle. Event average complexity varies spatially for both test sites, particularly in the 0.8???1.1 Hz band, providing evidence for frequency-dependent focussing or scattering by near-source structure. Both the direct arrivals and the early coda have strong azimuthal amplitude patterns that are produced by defocussing by mantle heterogeneity. The direct arrivals have stronger coherent azimuthal patterns than the early coda for Pahute Mesa events, indicating more pronounced deep crustal and shallow mantle defocussing for the direct signals. However, for Yucca Flat events the direct arrivals have less coherent azimuthal patterns than the

The post-glacial history of the Great Lakes has involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, outlet incision and isostatic rebound. The final lowering of lake levels occurred at approximately 7600 14 C yr BP, after which lake levels began to rise again to the Nipissing highstand at approximately 4700 14 C yr BP. During this time of rising lake levels, black bands of iron sulfide were being formed in the sediments of all five of the Great Lakes. These bands signify suboxic to anoxic conditions, at least within the sediments and possibly at the sediment-water interface, during the middle Holocene warm interval. During this interval, the climate was warmer and drier than present, possibly resulting in the occasional absence of seasonal turnover in the lakes. We examined a series of piston cores from northern Lakes Michigan and Huron and found that the black bands are correlatable among cores taken from within the same basin. The observation that the banding can be correlated suggests a basin-wide cause, near-bottom or sub-bottom anoxia in the northern Michigan and northern Huron sediments during the mid-Holocene warm period. The sedimentary and geochemical processes in the Great Lakes during the middle Holocene warm interval are good indicators of possible future scenarios for the lakes as a result of global warming, as 21 st -century temperatures are predicted to reach similar levels due to increased concentrations of greenhouse gases.