. Bulletin of the British Museum (Natural History), Mineralogy. FROM THE BORRALAN COMPLEX, SCOTLAND 319 Text-fig. 9 emphasizes the strong reciprocal relationship of soda and potash in South-eastern Tract rocks. Coombs and Wilkinson (1969, Figs. 8 & 9) on similar diagrams give the trends for some 20 provinces and separate intrusions and in all of these soda and potash rise sympathetically, though the Shonkin Sag intrusion, over part of its range, shows some decrease of soda against potash. Even highly potassic provinces such as the Roman Comagmatic region, South-west Uganda and Java show '
. Bulletin of the British Museum (Natural History), Mineralogy. FROM THE BORRALAN COMPLEX, SCOTLAND 319 Text-fig. 9 emphasizes the strong reciprocal relationship of soda and potash in South-eastern Tract rocks. Coombs and Wilkinson (1969, Figs. 8 & 9) on similar diagrams give the trends for some 20 provinces and separate intrusions and in all of these soda and potash rise sympathetically, though the Shonkin Sag intrusion, over part of its range, shows some decrease of soda against potash. Even highly potassic provinces such as the Roman Comagmatic region, South-west Uganda and Java show ' normal' trends ( 9, inset diagram), the only exception encountered being the Kimberley province, Australia (Wade & Prider 1940; Prider i960). The mechanism which determined the well-defined Borralan trend is not, therefore, usually operative in the majority of igneous provinces. Na20 (Wt%) 5 _ 4 _ 3 2 1 A Na-,0 J I I I L. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 K20 (Wt%) Fig. 9. Plot of soda against potash for pseudoleucite and lower suite rocks. Filled circles, pseudoleucite borolanites ; half-filled circles, biotite-magnetite group ; open circles, muscovite group ; open squares, pyroxene group ; half-filled squares, horn- blende group ; filled squares, borolanites of lower suite ; open triangles, vullinite and pyroxene-microcline xenolith ; filled triangles, andradite borolanite. Inset diagram shows trends of soda against potash for (a) southwest Uganda volcanic province, (b) Java volcanic province and (c) Roman comagmatic region. In Text-fig. 10 the pseudoleucite rocks are shown plotted according to their normative Qz - Ne - Ks, normative anorthite being relatively small in these rocks. They he along a path between potassic feldspar and the nepheline compo- sitions defined by Morozewicz (1930) and Buerger et al. (1947). Also plotted are the nepheline syenite and its constituent nepheline and feldspar from near Loyne at the northwest end of the Borralan Complex
Size: 1771px × 1411px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorbritishmuseumnaturalhistory, bookcentury1900, bookcoll
