Preliminary study of the sandstones in the Torlesse terrane,New Zealand (鮫島輝彦先生追悼論文集)

概要

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Heavy fractions of minerals in the sandstones from the Torlesse terrane are composed mainly of metamorphic minerals such as epidote, titanite and pumpellyite with subordinate amounts of detrital minerals such as zircon, garnet, apatite and ilmenite. Although metamorphism has been considered to be continuous within the Torlesse terrane, modal proportions of metamorphic minerals, especially pumpellyite and epidote, are depleted in the centreil region. Compositions of detrital garnets vary consistently with the geological age of their host sandstones. Jurassic-Cretaceous sandstones contain garnets with a wide compositional range, whereas garnets in Triassic rocks have a narrow compositional range. Rocks of both ages contain Mg-rich and Ca-rich garnets, whereas Permian gar-nets are usually rich in Mn. Although dissolution of garnets is common in the sandstones due to diagenesis and metamorphism, the difference of the garnet com-position reflects compositional differences in the source rocks. Garnets in the Permian rocks were predominantly derived from granitic rocks, whereas those in the Triassic to Cretaceous rocks were derived from garnet amphibolite and gneiss which should be lower in metamorphic grade than metamorphic rocks in the eastern Antarctic.
静岡大学の論文