Origin of Potassium-rich Silica-deficient Igneous Rocks by Alok Krishna Gupta

By Alok Krishna Gupta

The e-book summarizes the incidence, geochemistry, mineralogy, petrology and phase-equilibria stories in air and lower than excessive pressures concerning the main exciting crew of potassium-rich mafic and ultramafic rocks, frequently together with host of unique mineral assemblages together with feldspathoids. Mantle-derived K-rich melts had intrigued lots of the founders of Geology and lots of of the later specialists within the box of Igneous Petrology, simply because they're occasionally linked to carbonatites or even diamond. they have a tendency to include anomalous focus of many such parts as okay, Rb, Sr, U, F, P, etc., in addition to Ni, Co and Cr indicating a mix of crust and mantle fabrics. even supposing those rocks happen hardly in historic geologic time, they've been erupting commonly in smooth geological historical past (less than final one hundred twenty Ma or so). Are the previous age info actual or the results of a sampling challenge? glossy observations go away doubtless that sediments has to be subducted on a wide scale. there's now proof that the higher mantle (and even perhaps the reduce mantle) isn't really homogeneous yet a bit like a fruit cake, and that there are thermal anomalies within the mantle caused by deep mantle plumes or subduction. is that this relating to liberate of those strange rocks clearing the mantle of left over subduction fabrics? This quantity, written for these attracted to the geochemistry of K-rich melts from the deep Earth, reports the current nation of information of those certain igneous rocks. the writer is knowledgeable within the box of Igneous Petrology and the e-book will function a precious reference publication for researchers and academicians within the discipline.

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Extra resources for Origin of Potassium-rich Silica-deficient Igneous Rocks

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0 wt%. 057 wt% even in leucites from the same rock specimen. A phenocrystal core has higher Na/K ratio than the rim. This observation is in agreement with the leucite data of Carmichael et al. (1974) from the similar lava type of the Roman region. The Vico leucites, however, show excess silica over the experimentally determined leucite solid solution (Fudali 1963). 0 wt% (Cundari 1975). Excess silica in leucite has also been reported by Brown and Carmichael (1969) from Korath Range and by Cundari (1973) from New South Wales.

The limited solid solution between natural analcime and leucite must be attributed to energetically favored heterogeneous equilibria involving minerals such as feldspars and other feldspathoids, and there is limited immiscibility between the end-members. Leucite incorporates up to 28 wt% NaAlSi2O6 (Fig. 1 GPa [P(H2O) = P (Total)] and 800 °C in the join KAlSi2O6–NaAlSi2O6 (Fudali 1963). Natural leucite does not contain more than 10 wt% NaAlSi2O6. Leucites from Leucite Hills incorporate excess silica and alkali over alumina and ferric ion (Carmichael 1967; Barton 1979).

Sisco (Corsica), Mount North (West Kimberley, Australia) and Orciatico (Pisa, Italy) mostly plot in the endiopside field of the pyroxene quadrilateral (Wagner and Velde 1986). This mineral constitutes 6–22 wt% in a lamproite. 3 wt% Cr2O3. 93 atom (Wagner and Velde 1986). The vacancy may be filled by remaining Fe3+, when structural formula is calculated in terms of four cations and six oxygens. A. (Carmichael 1967) and West Kimberley, Australia (Jaques et al. 1984). Acmite is present in many samples as a thin rim around diopside crystals.

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