1,721,085 research outputs found
Accretionary orogen and evolution of the Japanese Islands: Implications from a Sr-Nd isotopic study of the Phanerozoic granitoids from SW Japan
No full textDabieshan UHP metamorphic terrane: Sr-Nd-Pb isotopic constraint to pre-metamorphic subduction polarity
No full textKomatiites: An early precambrian phenomenon
No full textUsing the presently accepted definition, komatiites are ultramafic volcanic rocks characterised by bladed and/or skeletal olivine texture (spinifex texture). Where textural evidence is absent,the geochemical definition is equivocal and as a result there is considerable ambiguity, particularly among the basaltic types. If the added control of Al2O3/TiO2 ? 25 is added to the definition, this eliminates rocks of the boninite group and also the low-Ti basalts found in some ophiolite complexes. The bulk of komatiites occur in the Archaean and the most obvious explanation is that the eruption of high (up to 30%) MgO melts was controlled by an enhanced geothermal gradient. There is some evidence to suggest that the high CaO/Al2O3 ratio characteristic of some komatiites (e.g. Barberton) is found only in those greenstone belts older than 3.0 b.y
REE distribution and petrogenesis of the Spanish peaks igneous complex, Colorado
No full textThe petrogenesis of the igneous complex in the Spanish Peaks region, Colorado, is reevaluated with Sr isotopic data (published and new) and new trace element data of REE and other transition metals. These data indicate that the diverse rock types ranging from ultrabasic lamprophyres to granitic porphyry of the igneous complex have independent origins.The lamprophyric magmas could be derived from the upper mantle by small degrees of partial melting of garnet peridotite source(s). Limited intra-type crystal fractionation is responsible for the small differences in REE and other elemental abundances. The intermediate syenodiorites were also derived by partial melting of some mantle sources with garnet as a residual phase. However, the major and trace element data suggest that the source for the syenodiorites is distinctly different from that of the lamprophyres. The narrow range of K/Rb ratios observed in minettes (449–464), camptonites (384–450) and syenodiorites (370–460) suggest that amphibole fractionation is not important in the generation of these intra- and intertype rocks.The granitic rocks were derived by melting of a lower crust whose composition varied from that of a granodioritic granulite to an amphibolite. It is suggested that the high alkali contents of the granitic porphyries are due to the introduction of alkalis into the source granulites shortly prior to the melting
Diverse PT paths of the northern Dabie complex in central China and its reworking in the early Cretaceous
No full textContinental accretion and intra-continental deformation of the Central Asian Orogenic Belt
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Petrologic and geochemical constraints on the petrogenesis of Permian–Triassic Emeishan flood basalts in southwestern China
No full textAssemblages and textural evolution of UHP eclogites from the Chinese Continental Scientific Drilling main hole
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