| 释义 |
peralkaline, a. Petrol.|pɜːrˈælkəlaɪn|
[f. per-1 4 + alkaline a.]
Of a rock: containing a high proportion of soda and potash; now spec. (see quot. 1931).
1913A. N. Winchell in Jrnl. Geol. XXI. 210 Along this co-ordinate igneous rocks are classified as normal or alkali-calcic.., alkaline, and peralkaline. Ibid. 211 Peralkaline rocks are characterized mineralogically by the presence of feldspathoids (or lenads)... Chemically they are distinguished by insufficient silica to combine with the abundant alkalies to form feldspars after saturation of other available bases as orthosilicates. 1927S. J. Shand Eruptive Rocks vii. 128 The following groups of rocks stand out as chemically distinct:— (a) A peraluminous group, characterised by primary muscovite, biotite, corundum, tourmaline, topaz, almandine, or spessartite. (b) A peralkaline group, characterised by soda-pyroxenes or soda-amphiboles,..and by the virtual absence of anorthite... (c) A group characterised by common pyroxenes, amphiboles, olivine, [etc]. 1931― Study of Rocks iv. 52 Peraluminous rocks... The molecular proportion of alumina exceeds the molecular proportions of soda, potash and lime combined... Peralkaline rocks... The molecular proportion of alumina is less than that of soda and potash combined. 1950Rep. 18th Internat. Geol. Congr. 1948 ii. 129 Peralkaline rocks..only occur in stable parts of the earth's crust, outside active orogenic zones. 1974Nature 24 May 315/1 Alkaline and peralkaline igneous rocks were intruded and extruded in distinct nodes. 1974[see peraluminous a.].
Hence ˌperalkaˈlinity, the state of being peralkaline.
1969Amer. Jrnl. Sci. CCLXVII. 242 A quadrilateral diagram in which molecular alumina is plotted against soda/potash ratio can then be employed to show the variation in alkali ratio in whole rocks..with changes in silica content and peralkalinity. 1974Bowden & Turner in H. Sørensen Alkaline Rocks iv. viii. 334/2 The variation in the coloured mineral content is dependent on the peralkalinity of the granites. |