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 reports in air and below excessive pressures concerning the main fascinating 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 many 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 comprise anomalous focus of many such parts as ok, Rb, Sr, U, F, P, etc., besides Ni, Co and Cr indicating a mix of crust and mantle fabrics. even supposing those rocks ensue not often in old geologic time, they've been erupting in general in sleek geological historical past (less than final a hundred and twenty Ma or so). Are the previous age information actual or the results of a sampling challenge? glossy observations depart without doubt that sediments needs to be subducted on a wide scale. there's now facts that the higher mantle (and even perhaps the decrease mantle) isn't really homogeneous yet just 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 unencumber of those strange rocks clearing the mantle of left over subduction fabrics? This quantity, written for these drawn to the geochemistry of K-rich melts from the deep Earth, reports the current country of information of those certain igneous rocks. the writer is knowledgeable within the box of Igneous Petrology and the publication will function a important reference ebook for researchers and academicians within the discipline.

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2. 3. Lamproite Minette Minette 1 Ma 28–19 Ma 27–26 Ma. 4 Ma 6. 7. 8. 9. 10. 11. 12. A. A. A. A. A Colima Graben, Mexico Alto-Paranaiba, Brazil Matheson, Ontario, Canada Gaussberg, Antarctica Virunga province, Zaire and Ruanda Vera, SE Spain Minette Minette, Kamafugitic rocks Minette Lamproite Leucitetephrite Lamproite 13. 14. Roman Province Italy Scotland and Northern England K-rich volcanics Minette 15. 16. 17. 18. Devon, SW England Western Alps, Switzerland, Italy Aeolian Arc East Eifel, Germany Lamproite Minette K-rich volcanics K-rich volcanics 19.

Letters a–g and h–k indicate analyses of clinopyroxenes and olivine respectively (after Luhr and Giannetti 1987) the Brown Leucite Tuffs also contain diopside aggregates (Fig. 6). The range of salite composition is as follows: Ca49–51Mg31–34Fe16–19, whereas, diopside composition plots near Ca47Mg47Fe6. High K-series rocks (leucite basanite, leucitite, tephritic leucitite, and leucite phonolite) of Vulsini are characterised by pyroxenes, ranging in composition from diopside to salite. The compositional plot of clinopyroxenes from leucite phonolites, trachyte and tephritic leucitites is shown in Fig.

These pyroxenes also contain more than enough Al to balance silica deficiency in the tetrahedral site, and substitutional relation is of the following type: Mg2+ + Si4+ ≈ Al3+ + Al3+. In addition to the CaAl2SiO6 molecule, the pyroxenes also contain CaFe3+AlSiO6 (ferri-Tschermak’s component). The pyroxenes from leucite phonolites and trachytes (Fig. 7) do not show discontinuous zoning like the ones from tephritic leucitites. The presence of two types of pyroxenes such as salite and diopside in some Vulsini lavas have been ascribed to variation in f(H2O) and f(O2) conditions in the same magma chamber by Luhr and Giannetti.

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