Crystallization of quartz dioritic magmas at 2 and 1 kbar: experimental results

摘要: Crystallization experiments were performed on quartz diorite (~55 wt.% SiO2, 3.1–8.4 MgO) from the Gesiniec Intrusion (Bohemian Massif, SW Poland) at 1−2 kbar, 750–850°C, various mole fractions of water and with fO2 buffered by NNO buffer. The two natural diorites (leucocratic poikilitic - ‘LPD’ melanocratic ‘MD’) differ in whole rock mineral composition MD being richer MgO poorer CaO than LPD, probably due to accumulation mafic minerals or melt removal MD. LPD represents is used reconstruct crystallization conditions Intrusion. history magma, deduced experimental compositions, includes a higher pressure stage followed emplacement ~2 kbar partly crystallized magma temperatures ~850−800°C quick cooling. assemblage present requires contents least 5 wt% oxygen fugacity below that controlled compositions equilibrated 775°C subsolidus conditions. equilibration was reaction between water-rich, oxidizing residual cumulatic-restitic assemblage. characterized occurrence euhedral cummingtonite increasing anorthite content rims plagioclase. A similar reproduced experimentally both indicating may be late magmatic phase dioritic systems, crystallizing very close solidus only saturated magma.