Experiments are described, relevant to the problem of correlating quantitatively a Stark effect, or any alternative explanation of broadening in spectral lines, with physical state of an atmosphere. A particular difficulty is that of fitting any theoretical contour to an observed line when an unknown degree of self-absorption is suspected of distorting the broadened structure, as in solar flares or radiation from unknown depth in the expanded atmospheres of early-type stars. To study a Stark contour in the presence of self-absorption, the laboratory source chosen is a deep electrodeless plasma with unusually high charge density at low voltage. Contours of Hex are analysed by transmitting from a high-dispersion spectrometer into a photomultiplier through a slit of aperture small compared with line-width. The assumptions required in fitting theories of Stark broadening to contours are examined, to find conditions under which a degree of self-absorption in the core of the line may be estimated. Misfit in the extreme wings is related to some theories which have arisen in stellar physics.
The Fish Canyon Tuff, Colorado, forms one of the largest (3000 km3 known silicic eruptions in Earth history. The tuff is a homogeneous quartz latite consisting of 40% phenocrysts (plagioclase, sanidine, biotite, hornblende, quartz, magnetite, apatite, sphene, and ilmenite) in equilibrium with a highly evolved rhyolitic melt now represented by the matrix glass. Melt inclusions trapped in hornblende and quartz phenocrysts are identical to the newly analyzed matrix glass composition indicating that hornblende and quartz crystallized from a highly evolved magma that subsequently experienced little change. This study presents experimental phase equilibrium data which are used to deduce the conditions (P, T, fO2, fH2O, etc.) in the Fish Canyon magma chamber prior to eruption. These new data indicate that sanidine and quartz are not liquidus phases until 780°C temperatures are achieved, consistent with Fe-Ti oxide geothermometry which implies that the magmatic temperature prior to eruption was 760±30°C. Natural Fe-Ti oxide pairs also suggest that log fO2 was -12.4 (intermediate between the Ni-NiO and MnO-Mn3O4 oxygen buffers) in the magma chamber. This fO2.102 is supported by the experimentally determined variations in hornblende and melt Mg-numbers as functions of fO2 A new geobarometer based on the aluminum content of hornblendes in equilibrium with the magmatic assemblage hornblende, biotite, plagioclase, quartz, sanidine, sphene, ilmenite or magnetite, and melt is calibrated experimentally, and yields pressures accurate to ±0.5 kb. Total pressure in the Fish Canyon magma chamber is inferred to have been 2.4 kb (equivalent to a depth of 7.9 km) based on the Al-content of natural Fish Canyon hornblendes and this new calibration. This depth is much shallower than has been proposed previously for the Fish Canyon Tuff. Variations in experimental glass (melt) composition indicate that the magma was water-undersaturated prior to eruption. XH2O in the fluid phase that may have coexisted with the Fish Canyon magma is estimated to have been 0.5 by comparing the An-content of natural plagioclases to experimental plagioclases synthesized at different XH2O and Ptotals. This ratio corresponds to about 5 wt.% water in the melt at depth. The matrix glass chemistry is reproduced experimentally under these conditions: 760°C, 2.4 kb, XH2O=0.5, and log fo2=NNO+2 log units. The fugacity of SO2 (91 b) is calculated from the coexistence of pyrrhotite and magnetite. Maximum CO2 fugacity (2520 b) is inferred assuming the magma was volatile saturated at 2.4 kb.
Geochemical tracers demonstrate that elements are cycled from subducted sediments into the arc melting regime at subduction zones, although the transfer mechanism is poorly understood. Are key elements (Th, Be, Rb) lost during sediment dehydration or is sediment melting required? To investigate this question, we conducted phase equilibria and trace element partitioning experiments on a pelagic red clay for conditions appropriate to the slab beneath arc volcanoes (2–4 GPa, 600°–1000°C). Using both piston cylinders and multianvils, we determined the solidus, phase stabilities, and major element compositions of coexisting phases. The solidus (H 2 O + Cl fluid‐saturated) was located at 775 ± 25°C at 2 GPa, 810 ± 15°C at 3 GPa, and 1025 ± 25°C at 4 GPa with noevidence for complete miscibility between melt and fluid. This sediment composition produces a profusion of phases both above and below the solidus: garnet, jadeitic pyroxene, alkali‐rich amphibole, phengite, biotite, magnetite, coesite, kyanite, apatite, zircon, Cl‐rich fluids, and peraluminous to peralkaline granitic melts. At 2 GPa the phengite dehydration solidus is at 800°–825°C, while biotite breaks down between 850° and 900°C. To explore trace element partitioning across the solidus at 2 GPa, we used diamonds to trap fluids and melts. Both the bulk sediment residues and diamond traps were analyzed postexperiment by inductively coupled plasma–mass spectrometry (ICP‐MS) and inductively coupled plasma–atomic emission spectrometry (ICP‐AES) for 40 elements for which we calculated bulk partition coefficients (D = C solid /C fluid ). Below the solidus, Rb, Sr, Ba, and Pb showed the greatest mobility ( D ∼ 0.5–1.0), while at the solidus, Th and Be became notably partitioned into the melt ( D values changing from >2.0 to <1.0). K and Rb D values fall below 1.0 when the micas breakdown. Only at the solidus do Th and Rb attain similar partition coefficients, a condition required by arc data. Taken together, the experimental results indicate that critical elements (Th and Be) require sediment melting to be efficiently transferred to the arc. This conclusion is at odds with most thermal models for subduction zones, which predict slab temperatures more than 100°C lower than sediment solidi. Thus the condition of sediment melting (with oceanic crust dehydration) may provide new constraints on the next generation of thermal/geodynamical models of subduction zones.
Abstract : This study reviews the state of the art regarding plasma arc torch vitrification of waste. It provides background by describing the history and environmental benefits of vitrification and the history and design of plasma arc torches. It reviews current uses of a plasma torch to heat ex-situ furnaces, and develops a case study showing how such a furnace could be used by the Army to pyrolyze scrap tires. This pyrolysis process would benefit the Army by providing an additional source of revenue and ensuring an environmental solution to the destruction of the 16 million scrap tires the Army collects each year. An immediate research product is a computer model, which allows in-situ heat transfer to be investigated. These model results provide important constraints on in-situ applications of plasma arc technology. Finally, laboratory scale experiments and associated analytical work allowed direct study of in-situ vitrification using a plasma arc torch. These research results fill gaps in theoretical knowledge and inform general understanding of the thermal and geochemical changes caused by vitrification. The United States Army is actively seeking innovative and effective methods of treating the wastes associated with producing and using the technology today's Army requires. Plasma arc torch vitrification offers one potential solution. Before the Army can adapt this solution to its requirements, significant research directed at understanding the vitrification process must still be accomplished.
Research Article| September 01, 1989 Experimental calibration of the aluminum-in-hornblende geobarometer with application to Long Valley caldera (California) volcanic rocks Marie C. Johnson; Marie C. Johnson 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar Malcolm J. Rutherford Malcolm J. Rutherford 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar Geology (1989) 17 (9): 837–841. https://doi.org/10.1130/0091-7613(1989)017<0837:ECOTAI>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Marie C. Johnson, Malcolm J. Rutherford; Experimental calibration of the aluminum-in-hornblende geobarometer with application to Long Valley caldera (California) volcanic rocks. Geology 1989;; 17 (9): 837–841. doi: https://doi.org/10.1130/0091-7613(1989)017<0837:ECOTAI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A new geobarometer based on the Al content of igneous hornblendes in equilibrium with melt, fluid, biotite, quartz, sanidine, plagioclase, sphene, and magnetite or ilmenite has been calibrated experimentally. The calibration was performed by equilibrating the required phase assemblage over the pressure range 2-8 kbar at 740-780 °C, and then analyzing euhedral hornblendes in equilibrium with glass (melt). Experiments were performed on natural samples of both volcanic and plutonic rocks. Earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks. The experimental calibration differs from the empirical calibrations, especially above 5 kbar, and shows that the Al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought. The geobarometer's uncertainty is dramatically reduced. The derived equation is P (±0.5 kbar) = 3 -3.46 (±0.24) + 4.23 (±0.13) (AlT). The geobarometer is applied to post-Bishop Tuff volcanic rocks from Long Valley caldera, California, and reveals that most rhyodacites in this complex erupted from depths of about 6 km. These eruptions occurred over 500 000 yr, suggesting that the rhyodacitic magma reservoir beneath Long Valley had reached a steady P (depth)-T state. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
