Phase relations and liquid lines of descent of an iron-rich peralkaline phonolitic melt: an experimental study   总被引：1，自引：1，他引：0  

Christopher Giehl  Michael Marks  Marcus Nowak 《Contributions to Mineralogy and Petrology》2013,165(2):283-304

We experimentally investigated the phase relations of a peralkaline phonolitic dyke rock associated with the Ilímaussaq plutonic complex (South Greenland). The extremely evolved and iron-rich composition (magnesium number = 2, alkalinity index = 1.44, FeO* = 12 wt%) may represent the parental magma of the Ilímaussaq complex. This dyke rock is therefore perfectly suited for performing phase-equilibrium experiments, since in contrast to the plutonic rocks of the complex, no major cumulate formation processes complicate defining a reasonable starting composition. Experiments were carried out in hydrothermal rapid-quench cold-seal pressure vessels at P = 100 MPa and T = 950–750 °C. H₂O contents ranging from anhydrous to H₂O saturated (~5 wt% H₂O) and varying fO₂ (~ΔlogFMQ ?3 to +1; where FMQ represents the fayalite–magnetite–quartz oxygen buffer) were applied. Reduced and dry conditions lead to substantial crystallization of alkali feldspar, nepheline, hedenbergite-rich clinopyroxene, fayalite-rich olivine and minor amounts of ulvøspinel-rich magnetite, which represent the phenocryst assemblage of the natural dyke rock. Oxidized and H₂O-rich conditions, however, suppress the crystallization of olivine in favor of magnetite and clinopyroxene with less or no alkali feldspar and nepheline formation. Accordingly, combined low fO₂ and aH₂O force the evolution of the residual melt toward decreasing SiO₂, increasing FeO* and alkalinity index (up to 3.55). On the contrary, high fO₂ and aH₂O produce residual melts with relatively low FeO*, high SiO₂ and a relatively constant alkalinity index. We show that variations of aH₂O and fO₂ lead to contrasting trends regarding the liquid lines of descent of iron-rich silica-undersaturated peralkaline compositions. Moreover, the increase in FeO* and alkalinity index (reduced and dry conditions) in the residual melt is an important prerequisite to stabilize late-magmatic minerals of the dyke rock, for example, aenigmatite (Na₂Fe₅TiSi₆O₂₀), coexisting with the most evolved melts at 750 °C. Contrary to what might be expected, experiments with high aH₂O and interlinked high fO₂ exhibit higher liquidus T’s compared with experiments performed at low aH₂O and fO₂ for experiments where magnetite is liquidus phase. This is because ulvøspinel-poor magnetite crystallizes at higher fO₂ and has a higher melting point than ulvøspinel-rich magnetite, which is favored at lower fO₂.  相似文献   

Groundwater supply of lakes: the case of Lake Raduńskie Górne (northern Poland,Kashubian Lake District)     

Roman Cieśliński  Jacek Piekarz  Marcin Zieliński 《水文科学杂志》2013,58(13):2427-2434

ABSTRACT

The aim of the study was to locate and describe groundwater outflows in a selected lake basin and measure the spring output of water and the physical characteristics of the studied waters (temperature and conductivity). The final aim was to gauge the effects of the spring output on the lake hydrology. The time scope of the work included the period from January 2011 to September 2012. The spatial scope of the work included the area of Lake Raduńskie Górne and its direct catchment located in the Kashubian Lake District in northern Poland. Four groundwater outflows were located in the course of the study. Their total output was 4.6 L s^?1 and ranged between 0.5 and 2.5 L s^?1. This produces an annual yield of about 145 000 m³ year^?1. These results confirm that one of the forms of supply to the lakes are the under-lake springs. For lakes located in the area of young glacial accumulation this can be decisive.