Results 131 to 140 of about 1,332 (160)
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1991
The mineralogy of the lamproite clan is perhaps one of the most exotic of all alkaline rocks. The perpotassic and peralkaline traits of the magmas lead to a distinctive mineral assemblage that is virtually unparalleled. The paragenesis and composition of the minerals comprising lamproites are detailed in this chapter.
Roger H. Mitchell, Steven C. Bergman
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The mineralogy of the lamproite clan is perhaps one of the most exotic of all alkaline rocks. The perpotassic and peralkaline traits of the magmas lead to a distinctive mineral assemblage that is virtually unparalleled. The paragenesis and composition of the minerals comprising lamproites are detailed in this chapter.
Roger H. Mitchell, Steven C. Bergman
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1991
Igneous rock classifications have never been graced with the elegance and simplicity of terminology employed in other branches of science. Consequently rock names present us with a bewildering plethora of unrelated, noninformative, and commonly unpronounceable terms.
Roger H. Mitchell, Steven C. Bergman
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Igneous rock classifications have never been graced with the elegance and simplicity of terminology employed in other branches of science. Consequently rock names present us with a bewildering plethora of unrelated, noninformative, and commonly unpronounceable terms.
Roger H. Mitchell, Steven C. Bergman
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1991
The development of realistic hypotheses for the petrogenesis of potassic rocks has been hindered, until recently, by the tendency of petrologists to consider all leucite-bearing K-rich rocks as being related. Sufficient geological, geochemical, and mineralogical evidence (see Chapter 2) has now accumulated to show that this assumption is not correct ...
Roger H. Mitchell, Steven C. Bergman
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The development of realistic hypotheses for the petrogenesis of potassic rocks has been hindered, until recently, by the tendency of petrologists to consider all leucite-bearing K-rich rocks as being related. Sufficient geological, geochemical, and mineralogical evidence (see Chapter 2) has now accumulated to show that this assumption is not correct ...
Roger H. Mitchell, Steven C. Bergman
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Petrology of Lamproites from the Nuapada Lamproite Field, Bastar Craton, India
2013This work presents the first mineralogical, geochemical and 40Ar/39Ar geochronological data on hypabyssal facies lamproites near Kalmidadar and Darlimunda in the Nuapada Lamproite Field of the Bastar Craton. The Kalmidadar lamproite is a diamondiferous intrusion with surface dimension of ~320 m × 160 m, whereas the Darlimunda lamproite is a dyke swarm ...
N. Sahu +6 more
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The Geochemistry of Lamproites
1991Relative to other mafic alkaline rocks lamproites are distinguished by their high K2O, TiO2, P2O5, and MgO contents, K2O/Na2O ratios and low Al2O3 and CaO contents. The general characteristics of the lamproite clan have been outlined in Section 2.6. In this section the compositional averages and ranges of lamproites are compared with those of other ...
Roger H. Mitchell, Steven C. Bergman
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Fluorine-bearing phases in lamproites
Mineralogy and Petrology, 1991The distribution of F between phlogopite, amphibole, apatite, and glass has been determined for 261amproites from Leucite Hills, Wyoming; West Kimberley, Western Australia; Smoky Butte, Montana; Prairie Creek, Arkansas; and Gaussberg, Antarctica. The F contents of these phases are inconsistent in different lamproite localities, with distinct variations,
A. D. Edgar, H. E. Charbonneau
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Description of Lamproite Occurrences
1991Lamproites have been recognized in over 25 occurrences (provinces or fields) on all continents (Figure 3.1). In common with kimberlites, they are restricted to continental environments. As noted in Chapter 4, the formation of both kimberlite and lamproite magmas has occurred from the Precambrian to the Cenozoic, although the Mesozoic Era was the time ...
Roger H. Mitchell, Steven C. Bergman
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Tectonic Framework of Lamproite Genesis
1991Lamproites are temporally and spatially widespread; however, they form only volumetrically minor igneous occurrences relative to most, if not all, other mantle-derived alkaline rocks. In fact, all presently known lamproite bodies comprise an aggregate volume of merely 75 km3, corresponding to a sphere with a radius of under 3 km or a 20-m-thick layer ...
Roger H. Mitchell, Steven C. Bergman
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The oxidation state of lamproitic magmas
TMPM Tschermaks Mineralogische und Petrographische Mitteilungen, 1985Olivine leucitites from the Gaussberg volcano, Antarctica are primitive members of the lamproite group of ultrapotassic rocks. They are glass rich, have an Mg number of around 70, and carry spinel lherzolite xenoliths. Liquidus phase fields and compositions were studied experimentally at atmospheric pressure with controlled oxygen fugacities.
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Lamproites and Kimberlites in India
Journal of the Geological Society of India, 1989Abstract New petrographic and mineral chemistry data are presented to show that the Majhgawan and Hinota pipes are olivine lamproite lapilli tuffs and not kimberlites as suggested elsewhere. These bodies, therefore, comprise a newly recognized province of diamondiferous olivine lamproites.
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