Some aspects of magmatic evolution

摘要: Summary The address is concerned with some aspects of magmatic evolution in volcanic successions, and includes particularly a discussion the nature genetic relations primary derivative basic intermediate magmas. Among associations oceanic areas, those Hawaiian archipelago provide data critical importance study basaltic evolution. established chronological succession magmas these islands makes it probable that alkali-poor tholeiites to be recognized lavas primitive shield volcanoes form closest approach magma ocean basins, from them derive by fractional crystallization processes alkali series olivine-basalt, mugearite (so-called andesite) trachyte. course variation there exhibited provides new orientation Tertiary igneous Brito-Icelandic province, leads conception Hebridean derives through as an alternative line descent. tholeiite great layered intrusion its final product granophyre illustrative flexibility descent which fractionation permit. Derivation differentiation convecting system comparable demonstrated intrusions seems, indeed, most likely mechanism for genesis sialic layer crust itself. problem successions orogenic belts petrogenic theory. Though appear competent give liquid andesite rhyolite, normal does not reflect chemistry (tholeiitic) differentiation. Consideration devoted andesites, though ultimately parentage, have derived part contamination. testing assemblages within basalt-andesite range suites orogens remains one important problems petrogenesis. Systematic attack intimate phase analysis geochemical may will go far solve, only status voluminous andesite, but general rock