| 释义 |
ultrabasic, a. (n.) Petrol.|ʌltrəˈbeɪsɪk|
[f. ultra- 3 + basic a.]
Of an igneous rock: having a silica content that is lower than that of the basic rocks (cf. basic a. 2 b), spec. less than 45 per cent by weight. Also as n.
1881J. W. Judd Volcanoes (ed. 2) 317 There are some rarer materials..that present a most wonderful resemblance to the stony portions of meteorites. These materials we may call ‘ultra-basic rocks’. 1885― in Q. Jrnl. Geol. Soc. XLI. 354 Those rocks which contain an excessive proportion of the bases, especially magnesia and ferrous oxide, and are therefore composed largely of unisilicates, may be conveniently classed as ultra-basic rocks. 1893Geikie Text-bk. Geol. (ed. 3) vi. i. 681 Crystalline rocks, which range from amorphous masses..to basic or even what are called ‘ultra-basic’ compounds. 1898Nature 3 Feb. 315/2 He..had arrived at certain very definite views concerning the constant association of the crystalline form of carbon with the ultrabasic rocks. 1938R. W. Lawson tr. Hevesy & Paneth's Man. Radioactivity (ed. 2) xxv. 274 Stone meteorites are still more strongly basic than the ultrabasic terrestrial rocks. 1964Economic Geol. LIX. 804 In the low-lying regions the ultrabasics are largely masked by soil. 1970Nature 28 Mar. 1227/2 Most of the volcanics were basic, but during the upper Cretaceous ultrabasics..were intruded. 1977Sci. Amer. Mar. 96/3 In a typical greenstone belt early volcanic activity has produced ultrabasic and basic lavas. |