Fluid inclusions in apatite from Jacupiranga calcite carbonatites: Evidence for a fluid-stratified carbonatite magma chamber

Lithos ◽  
2006 ◽  
Vol 91 (1-4) ◽  
pp. 208-228 ◽  
Author(s):  
A COSTANZO ◽  
K MOORE ◽  
F WALL ◽  
M FEELY
Keyword(s):  
Magma Chamber ◽  
Fluid Inclusions ◽  
Calcite Carbonatites ◽  
Carbonatite Magma

Potassic glass and calcite carbonatite in lapilli from extrusive carbonatites at Rangwa Caldera Complex, Kenya

2003 ◽  
Vol 67 (5) ◽  
pp. 931-955 ◽  
Author(s):  
G. Rosatelli ◽  
F. Wall ◽  
M. J. Le Bas
Keyword(s):  
Direct Relationship ◽  
Country Rock ◽  
Western Kenya ◽  
History Museum ◽  
Complex Part ◽  
Silicate Carbonate ◽  
Calcite Carbonatites ◽  
Carbonatite Magma ◽  
Carbonate Melt ◽  
Metasomatized Mantle

AbstractThe ∽16 Ma Rangwa Caldera Complex, part of the large Kisingiri nephelinite-carbonatite volcano, Homa Bay District, western Kenya (0º34’S; 34º09’E) contains carbonatitic lapilli and ash tuffs, agglomerate and tuffisite, and a number of intrusive calcite carbonatites. A detailed petrographic and electron microprobe study has been performed on 20 fresh samples from the collection at The Natural History Museum, London.Most of the juvenile lapilli and ash particles are either predominantly composed of devitrified silicate glass (now biotite/phlogopite but probably also originally potassic silicate) or calcite carbonatite, which suggests that two molten liquids were erupted simultaneously. Some 10 mm-diameter lapilli contain quench-textured calcite crystals set in devitrified glass. They are interpreted as having crystallized from a molten silicate-carbonate melt at, or very near, the surface.The extrusive carbonate is mostly composed of calcite, consistent with intrusive calcite compositions at Rangwa. Other key minerals are magnetite, two types of mica (magnesian-biotite phenocrysts and phlogopite xenocrysts) and fluorapatite.The pyroclastic rocks contain many calcite carbonatite clasts, and fragments of calcite, aegirine and diopside, fluorapatite, magnetite, plus some phlogopite, titanite, K-feldspar, fenite and glimmerite; ijolite lithics are rare. Thus, there is no evidence for a cognate nephelinitic (ijolitic) or melilitic magma nor evidence for a direct relationship with the nephelinites of the Kisingiri volcano.Two hypotheses are discussed. A rising silicate and K-rich carbonatite liquid may have evolved towards a carbonate-rich K-silicate liquid after crystallization of calcite, phlogopite, apatite and magnetite. Preservation of the the potassic component may be rare, with a more usual scenario being that potassic component separates as fenitizing fluids. The alternative is that the silicate component is remobilized fenite, formed from country rock that was mobilized by supercritical K-rich, fenitizing fluids associated with the carbonatite. Both scenarios require generation of a K-rich carbonatite magma, probably from a carbonated phlogopite-rich metasomatized mantle.

Characterization of submicrometer fluid Inclusions in minerals by Analytical/Transmission Electron Microscopy and electron diffraction

1990 ◽  
Vol 48 (4) ◽  
pp. 424-424
Author(s):  
George Guthrie ◽  
David Veblen
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Light Microscopy ◽  
Fluid Inclusions ◽  
Energy Dispersive Spectrometer ◽  
Analytical Transmission Electron Microscopy ◽  
Transmission Electron

The nature of a geologic fluid can often be inferred from fluid-filled cavities (generally <100 μm in size) that are trapped during the growth of a mineral. A variety of techniques enables the fluids and daughter crystals (any solid precipitated from the trapped fluid) to be identified from cavities greater than a few micrometers. Many minerals, however, contain fluid inclusions smaller than a micrometer. Though inclusions this small are difficult or impossible to study by conventional techniques, they are ideally suited for study by analytical/ transmission electron microscopy (A/TEM) and electron diffraction. We have used this technique to study fluid inclusions and daughter crystals in diamond and feldspar.Inclusion-rich samples of diamond and feldspar were ion-thinned to electron transparency and examined with a Philips 420T electron microscope (120 keV) equipped with an EDAX beryllium-windowed energy dispersive spectrometer. Thin edges of the sample were perforated in areas that appeared in light microscopy to be populated densely with inclusions. In a few cases, the perforations were bound polygonal sides to which crystals (structurally and compositionally different from the host mineral) were attached (Figure 1).

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