TY - JOUR

T1 - Crystallization of quartz dioritic magmas at 2 and 1 kbar

T2 - Experimental results

AU - Pietranik, Anna

AU - Holtz, Francois

AU - Koepke, Jürgen

AU - Puziewicz, Jacek

N1 - Funding information: This work was supported by a DAAD fellowship to AP and by the DAAD exchange program between the Leibniz University of Hannover and the University of Wroc?aw, Poland. AP thanks Roman Botcharnikov, Sandrin Feig and Kevin Klimm for invaluable advice on how to prepare experiments. AP also thanks Otto Diedrich and other people from the workshop. Kirsten Drüppel and Bruno Scaillet are thanked for helpful comments on the manuscript.

PY - 2009/8/5

Y1 - 2009/8/5

N2 - Crystallization experiments were performed on quartz diorite (~55 wt.% SiO2, 3.1-8.4 wt.% MgO) from the Gȩsiniec Intrusion (Bohemian Massif, SW Poland) at 1-2 kbar, 750-850°C, various mole fractions of water and with fO2 buffered by the NNO buffer. The two natural quartz diorites (leucocratic poikilitic quartz diorite - 'LPD' and melanocratic quartz diorite - 'MD') differ in whole rock and mineral composition with MD being richer in MgO and poorer in CaO than LPD, probably due to accumulation of mafic minerals or melt removal in MD. LPD represents melt composition and is used to reconstruct crystallization conditions in the Gȩsiniec Intrusion. The crystallization history of LPD magma, deduced from experimental and natural mineral compositions, includes a higher pressure stage probably followed by emplacement at ~2 kbar of partly crystallized magma at temperatures ~850-800°C and quick cooling. The mineral assemblage present in LPD requires water contents in the magma of at least 5 wt% and oxygen fugacity below that controlled by the NNO buffer. The compositions of mafic minerals in the MD composition were equilibrated at temperatures below 775°C and at subsolidus conditions. The equilibration was probably due to the reaction between water-rich, oxidizing residual melt and the cumulatic-restitic mineral assemblage. MD is characterized by occurrence of the euhedral cummingtonite and increasing anorthite content in the rims of plagioclase. A similar reaction was reproduced experimentally in both LPD and MD compositions indicating that cummingtonite may be a late magmatic phase in quartz dioritic systems, crystallizing very close to solidus and only from water saturated magma.

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

UR - http://www.scopus.com/inward/record.url?scp=67949104728&partnerID=8YFLogxK

U2 - 10.1007/s00710-009-0070-5

DO - 10.1007/s00710-009-0070-5

M3 - Article

AN - SCOPUS:67949104728

VL - 97

SP - 1

EP - 21

JO - Mineralogy and Petrology

JF - Mineralogy and Petrology

SN - 0930-0708

IS - 1-2

ER -