The trace element evolution of the Fongen-Hyllingen Intrusion has been studied on the basis of ICP-MS analyses of 21 whole rocks and 12 plagioclase separates. Emphasis has been placed on Stage IV of the intrusion that crystallized essentially after magma addition had ceased. Whereas the compositions of minerals and rocks in Stage IV exhibit strong normal fractionation trends, crustal contamination is evident in a wide range of incompatible element ratios that should be relatively constant if simple fractional crystallization prevailed. Crustal contamination in Stage IV is confirmed by isotopic studies. The distribution of incompatible elements in Stage IV can be successfully explained by AFC modelling. Olivine compositions and isotopic ratios in the most primitive cumulates together with the slight LREE-enrichment in their coexisting melts suggest that the FHI parental magma was subjected to at least olivine fractionation during ascent to the magma chamber. This resulted in a decrease in the Mg-number of the melt without changing its isotopic ratio and incompatible trace element ratios. The slight enrichment in LREE and relatively low Zr/Y ratios in the melt coexisting with the most primitive cumulates imply that the FHI primary melt was derived from garnet-free mantle. The relative abundance of incompatible elements in the most primitive calculated melts, geochemically similar to low-Ti continental flood basalts, suggest that a subcontinental mantle source was most probable for the parental melt for FHI.

抄録全体を表示

Duwi Formation that crops out between Qena to the north and Idfu to the south is composed of a number of phosphorite beds intercalated with shales, marls, cherts, and limestones. The shale intercalations were subjected to field and petrographic, mineralogical and geochemical investigations in order to examine their rock composition and origin. Shales are mainly fossiliferous and composed essentially of argillaceous materials, quartz, feldspar, phosphatic pelloids and skeletal fragments. The light fraction of the separated sand fraction is composed of quartz, plagioclase and microcline. The heavy fraction consists of opaque minerals, zircon, tourmaline, epidote, garnet, rutile and phosphates. X-ray diffraction analyses of bulk rocks identified quartz, francolite, gypsum, anhydrite, microcline, albite, halite, goethite and limonite as non-clay minerals. The clay minerals are smectite, kaolinite, and illite. The study have revealed that the constituents of these shales were inherited from the weathering of mafic igneous rocks as well as quartzose sedimentary rocks situated to the south and southeast of the study area, transported via a fluvial system into shallow marine environment. The abundance of smectite suggests the deposition of those shales in a period of transgression and arid to semi-arid climatic conditions.

抄録全体を表示

The editorial office apologizes for mistakenly writing the year of receipt of the manuscript as 2001 instead of 2002 on page 288. 2002 is crrect. Wrong:The year of receipt of the manuscript: 2001
Right:The year of receipt of the manuscript: 2002

抄録全体を表示