New forms of abundant carbonatite–silicate volcanism: recognition criteria and further target locations

AbstractIn the Calatrava province of central Spain, numerous Quaternary pyroclastic vents have erupted carbonatite magmas carrying silicate melt fragments, mantle debris and megacrysts. Lava flows are rare. Maar and scoria deposits have carbonate matrices and pass into tuff sheets with carbonate contents >50%, which are spread widely away from the eruptive centres and constitute the most abundant form of effusive carbonate. Immense quantities of mantle debris are present in the erupted material. The tuffs have a distinctive fabric, which consists of a pale matrix carrying black silicate glass clasts that contain globules of immiscible carbonate and carbonate phenocrysts. There is evidence of similar volcanism in the Limagne province of central France and in other intra-continental provinces in Europe and Africa. About 500 vents have been identified in France and Spain: all the vents examined to date have erupted carbonatite magma. Such eruptions are not generally recognized in classical volcanology. As pyroclastic carbonatite was not previously recognized in Spain and France, a detailed examination of other mafic and ultramafic alkaline provinces, where research has traditionally concentrated on lava flows, is vital. For any search to be successful, evidence from the pyroclastic rocks will be required.

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Extensive dolomitic volcanism through the Limagne Basin, central France: a new form of carbonatite activity

Mineralogical Magazine ◽

10.1180/0026461067020327 ◽

2006 ◽

Vol 70 (2) ◽

pp. 231-236 ◽

Cited By ~ 20

Author(s):

K. Bailey ◽

S. Kearns ◽

J. Mergoil ◽

J. Mergoil Daniel ◽

B. Paterson

Keyword(s):

High Temperature ◽

Silicate Glass ◽

Silicate Melt ◽

Central Spain ◽

Deep Mantle ◽

First Case ◽

New Findings ◽

New Form ◽

Active Research

AbstractRecognition of widespread carbonate volcanism in central Spain has led to another case in France, of similar age (23–0 Ma) but with entirely new features. More than 100 new carbonate volcanoes are indicated already, adding a wholly unexpected dimension to this form of activity. Eruptions form layers, mostly of glassy nephelinite fragments in a dolomitic matrix, but some layers are largely dolomite. Major new findings are phenocrysts of dolomite, magnesite and calcite in silicate glass, and spectacular dolomite-nephelinite melt immiscibility, neither recorded previously. Most volcanic carbonatites are Ca rich, and dolomite is rare. The Limagne dolomites share links with those in Spain and Zambia, with chromite a hallmark in all three. Limagne is exceptional in being the first case where dolomite has erupted with co-genetic silicate melt. Mantle debris and magnesite indicate a source within ∼ 100–150 km. Chromite in the dolomite globules, and in the enclosing silicate glass, is similar to that in high-temperature kimberlites, indicating immiscibility in the deep mantle. Recognition of two large, previously undetected provinces of carbonate volcanism in Europe, where there has been active research for >200 y, must lead to the inference that similar cases may await discovery on other continents.

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The Amisk Group: An Aphebian(?) Island Arc Deposit

Canadian Journal of Earth Sciences ◽

10.1139/e75-179 ◽

1975 ◽

Vol 12 (12) ◽

pp. 2021-2035 ◽

Cited By ~ 21

Author(s):

Mel R. Stauffer ◽

A. C. Mukherjee ◽

J. Koo

Keyword(s):

Major Element ◽

Regional Metamorphism ◽

Island Arc ◽

Lava Flows ◽

Chemical Analyses ◽

Pyroclastic Rocks ◽

Andesitic Lava ◽

Ore Bodies ◽

Flin Flon ◽

Garnet Zone

The Amisk Group (Aphebian?) near Flin Flon, Manitoba, consists dominantly of andesitic lava flows and pyroclastic rocks, with minor basalt, dacite, rhyolite, and epiclastic rocks. These have undergone regional metamorphism ranging from chlorite to garnet zone, and locally have been sheared intensely.Major element chemical analyses indicate that intensely sheared Amisk rocks near the Flin Flon and Schist Lake Cu–Zn ore bodies have undergone considerable metasomatism. The unsheared, regionally metamorphosed rocks have undergone significantly less metasomatism, and the compositions of the least-altered of these suggest an island arc tholeiite chemical affinity.The lithology, primary structures, and major-element compositions of lavas within the Amisk Group suggest deposition may have been in an island arc environment.

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Formation of the Denchai gem sapphires, northern Thailand: evidence from mineral chemistry and fluid/melt inclusion characteristics

Mineralogical Magazine ◽

10.1180/0026461016560004 ◽

2001 ◽

Vol 65 (6) ◽

pp. 725-735 ◽

Cited By ~ 23

Author(s):

P. Limtrakun ◽

Khin Zaw ◽

C. G. Ryan ◽

T. P. Mernagh

Keyword(s):

Silicate Glass ◽

Melt Inclusions ◽

Melt Inclusion ◽

Vapour Phase ◽

Silicate Melt ◽

Alkaline Magmatism ◽

Type I ◽

Northern Thailand ◽

Pixe Analysis ◽

Solid Phases

AbstractThe Denchai gem sapphire deposits in Phrae Province, northern Thailand are closely associated with late Cenozoic alkaline basaltic rocks. The sapphires occur in alluvial placer deposits in palaeo-channels at shallow depths. Electron microprobe analysis of minor and trace element contents (Fe, Ti, Cr, Ga and V) of the sapphires indicate the following oxide abundances: Fe2O3 (0.32–1.98 wt.%), TiO2 (0.01–0.23 wt.%), Cr2O3 (<0.01 wt.%), Ga2O3 (0.01–0.03 wt.%) and V2O5 (<0.03 wt.%). Optical studies of sapphires revealed three types of primary fluid/melt inclusions. CO2-rich inclusions (Type I) contain three phases (LH2O + LCO2 + V) with the vapour phase comprising <10–15 vol.%. The presence of CO2 was confirmed by microthermometry and laser Raman analysis. Polyphase inclusions (Type II) (vapour + liquid + solid) contain a fluid bubble (20–30 vol.%), an aqueous phase (10–15 vol.%) and several solid phases. Silicate-melt inclusions (Type III) comprise vapour bubbles, silicate glass and solid phases. Proton-induced X-ray emission (PIXE) analysis revealed high concentrations of K (~;4 wt.%) as well as Ca (~;0.5 wt.%), Ti (~;1 wt.%), Fe (~;2 wt.%), Mn (~;0.1 wt.%), V (<0.03 wt.%), Rb (~;70 ppm) and Zr (~;200 ppm) in the silicate glass. The Ga2O3 abundances and Cr2O3/Ga2O3 values (<1) of the sapphires favour their formation by magmatic processes. The presence of CO2-rich fluids and high K concentrations in the silicate melt inclusions link the origin of the Denchai gem sapphires to CO2-rich alkaline magmatism.

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Information about open-system magma chambers derived from textures in magmatic enclaves: the Kameni Islands, Santorini, Greece

Geological Magazine ◽

10.1017/s0016756805001172 ◽

2005 ◽

Vol 142 (6) ◽

pp. 637-649 ◽

Cited By ~ 9

Author(s):

M. B. HOLNESS ◽

V. M. MARTIN ◽

D. M. PYLE

Keyword(s):

Major Element ◽

Detailed Examination ◽

Lava Flows ◽

Dihedral Angles ◽

Distinct Population ◽

Magma Chambers ◽

Original Population ◽

Mafic Enclaves ◽

The Past ◽

Dacitic Lava

Post-caldera eruptions of Santorini, Greece, over the past 3000 years resulted in the formation of the Kameni Islands, which comprise a series of compositionally similar dacitic lava flows. Each lava flow has a distinct population of partially-crystalline mafic enclaves, which we propose were derived from the break-up of a layer of replenishing magma responsible for triggering the eruption. Five of the recent flows (erupted in 1570, 1939, 1940, 1941 and 1950) include enclaves of essentially identical andesitic bulk compositions, which formed by crystallization of originally aphyric melts prior to eruption. Detailed examination of angles subtended at the junctions between pairs of plagioclase grains demonstrates that enclaves from each flow have a characteristic textural signature, with distinct differences in the extent of quench-related modification of the original population of dihedral angles formed by impingement of growing grains. These variations suggest that the temperature difference between the host dacite and the replenishing andesite at the time of layer overturn and eruption differed between flows. The uniformity of major element compositions of both the replenishing magma and the host dacitic lava flows demonstrates that the critical parameter in determining the timing of layer-overturn is the pre-eruptive H2O content of both host dacite and replenishing magma. We suggest that the replenishing magma responsible for two of the three eruptions in the period 1939–1941 was significantly wetter than that responsible for the later 1950 eruption. The enclaves with the least amount of quench-related modification occur in the 1570 flow. We suggest that in this case the intruding magma was relatively dry.

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Electron Irradiation Effects in Polyoxymethylene Crystals Grown Inside Trioxane Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010006444x ◽

1971 ◽

Vol 29 ◽

pp. 78-79

Author(s):

J. P. Colson ◽

D. H. Reneker

Keyword(s):

Cross Section ◽

Cross Sections ◽

Detailed Examination ◽

The Other ◽

Electron Micrograph ◽

Irradiation Effects ◽

Threefold Axis ◽

Typical Sample ◽

Polymer Crystals ◽

Chain Axis

Polyoxymethylene (POM) crystals grow inside trioxane crystals which have been irradiated and heated to a temperature slightly below their melting point. Figure 1 shows a low magnification electron micrograph of a group of such POM crystals. Detailed examination at higher magnification showed that three distinct types of POM crystals grew in a typical sample. The three types of POM crystals were distinguished by the direction that the polymer chain axis in each crystal made with respect to the threefold axis of the trioxane crystal. These polyoxymethylene crystals were described previously.At low magnifications the three types of polymer crystals appeared as slender rods. One type had a hexagonal cross section and the other two types had rectangular cross sections, that is, they were ribbonlike.

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A new dissociation mode for dislocations in silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108878 ◽

1978 ◽

Vol 36 (1) ◽

pp. 346-347

Author(s):

A. Ourmazd ◽

G.R. Booker ◽

C.J. Humphreys

Keyword(s):

Detailed Examination ◽

Experimental Results ◽

Dislocation Network ◽

Weak Beam ◽

Phosphorus Doped

A (111) phosphorus-doped Si specimen, thinned to give a TEM foil of thickness ∼ 150nm, contained a dislocation network lying on the (111) plane. The dislocation lines were along the three <211> directions and their total Burgers vectors,ḇt, were of the type , each dislocation being of edge character. TEM examination under proper weak-beam conditions seemed initially to show the standard contrast behaviour for such dislocations, indicating some dislocation segments were undissociated (contrast A), while other segments were dissociated to give two Shockley partials separated by approximately 6nm (contrast B) . A more detailed examination, however, revealed that some segments exhibited a third and anomalous contrast behaviour (contrast C), interpreted here as being due to a new dissociation not previously reported. Experimental results obtained for a dislocation along [211] with for the six <220> type reflections using (g,5g) weak-beam conditions are summarised in the table below, together with the relevant values.

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Communication Sciences and Disorders PhD Graduates' Perceptions of Their PhD Program

Perspectives of the ASHA Special Interest Groups ◽

10.1044/2020_persp-19-00107 ◽

2020 ◽

Vol 5 (2) ◽

pp. 463-478

Author(s):

Elizabeth Crais ◽

Melody Harrison Savage

Keyword(s):

Detailed Examination ◽

Career Expectations ◽

Doctoral Preparation ◽

Creative Solutions ◽

Phd Education ◽

Doctor Of Philosophy ◽

First Time ◽

Students Success ◽

Phd Program

Purpose The shortage of doctor of philosophy (PhD)–level applicants to fill academic and research positions in communication sciences and disorders (CSD) programs calls for a detailed examination of current CSD PhD educational practices and the generation of creative solutions. The intended purposes of the article are to encourage CSD faculty to examine their own PhD program practices and consider the perspectives of recent CSD PhD graduates in determining the need for possible modifications. Method The article describes the results of a survey of 240 CSD PhD graduates and their perceptions of the challenges and facilitators to completing a PhD degree; the quality of their preparation in research, teaching, and job readiness; and ways to improve PhD education. Results Two primary themes emerged from the data highlighting the need for “matchmaking.” The first time point of needed matchmaking is prior to entry among students, mentors, and expectations as well as between aspects of the program that can lead to students' success and graduation. The second important matchmaking need is between the actual PhD preparation and the realities of the graduates' career expectations, and those placed on graduates by their employers. Conclusions Within both themes, graduate's perspectives and suggestions to help guide future doctoral preparation are highlighted. The graduates' recommendations could be used by CSD PhD program faculty to enhance the quality of their program and the likelihood of student success and completion. Supplemental Material https://doi.org/10.23641/asha.11991480

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