Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland
The 1·13 Ga Il i ´ maussaq intrusive complex, South Greenland, is composed of various types of alkali granite and silica-undersaturated alkaline to agpaitic nepheline syenites related to three subsequently intruded magma batches. Mineral chemistry indicates continuous fractionation trends within eac...
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fthighwire:oai:open-archive.highwire.org:petrology:42/12/2231 2023-05-15T16:28:40+02:00 Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland MARKL, GREGOR MARKS, MICHAEL SCHWINN, GREGOR SOMMER, HOLGER 2001-12-01 00:00:00.0 text/html http://petrology.oxfordjournals.org/cgi/content/short/42/12/2231 https://doi.org/10.1093/petrology/42.12.2231 en eng Oxford University Press http://petrology.oxfordjournals.org/cgi/content/short/42/12/2231 http://dx.doi.org/10.1093/petrology/42.12.2231 Copyright (C) 2001, Oxford University Press ARTICLES TEXT 2001 fthighwire https://doi.org/10.1093/petrology/42.12.2231 2015-02-28T20:43:44Z The 1·13 Ga Il i ´ maussaq intrusive complex, South Greenland, is composed of various types of alkali granite and silica-undersaturated alkaline to agpaitic nepheline syenites related to three subsequently intruded magma batches. Mineral chemistry indicates continuous fractionation trends within each rock type, but with distinct differences among them. The last, peralkaline magma batch is the most fractionated in terms of <rm>X</rm> Fe mafic mineral , feldspar composition and mineral assemblage. This indicates that an evolving magma chamber at depth discontinuously released more highly fractionated alkaline melts. Fluid inclusions in some sodalites record a pressure drop from 3·5 to 1 kbar indicating that crystallization started during magma ascent and continued in the high-level magma chamber. On the basis of phase equilibria and preliminary fluid inclusion data, crystallization temperature drops from >1000°C (augite syenite liquidus) to <500°C (lujavrite solidus) and silica activity decreases from ∼0·8 to <0·3. An almost pure methane fluid phase at high temperatures and an almost pure aqueous fluid phase in the last crystallization stages of the agpaitic rocks indicate a strong increase in water activity. NaCl activity drops from 0·4 during magmatic sodalite crystallization to <0·01 (3 wt % NaCl equiv ) in the late magmatic aqueous fluids. Relative oxygen fugacity [ΔFMQ, where FMQ is fayalite–magnetite–quartz)] depends on silica and water activity via two solid–solid buffer reactions. It decreases during fractionation in the augite syenite from about FMQ – 1 to below FMQ – 4, but increases in the peralkaline stage. The extreme peralkaline fractionation trend appears to be governed by low water activity and low SiO 2 activity in the parental melt. Only then is methane a stable fluid phase during most of the crystallization history, which prevents early unmixing of an aqueous NaCl-bearing fluid phase. Text Greenland HighWire Press (Stanford University) Greenland Ilimaussaq ENVELOPE(-45.900,-45.900,60.983,60.983) Journal of Petrology 42 12 2231 2257 |
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HighWire Press (Stanford University) |
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English |
topic |
ARTICLES |
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ARTICLES MARKL, GREGOR MARKS, MICHAEL SCHWINN, GREGOR SOMMER, HOLGER Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland |
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ARTICLES |
description |
The 1·13 Ga Il i ´ maussaq intrusive complex, South Greenland, is composed of various types of alkali granite and silica-undersaturated alkaline to agpaitic nepheline syenites related to three subsequently intruded magma batches. Mineral chemistry indicates continuous fractionation trends within each rock type, but with distinct differences among them. The last, peralkaline magma batch is the most fractionated in terms of <rm>X</rm> Fe mafic mineral , feldspar composition and mineral assemblage. This indicates that an evolving magma chamber at depth discontinuously released more highly fractionated alkaline melts. Fluid inclusions in some sodalites record a pressure drop from 3·5 to 1 kbar indicating that crystallization started during magma ascent and continued in the high-level magma chamber. On the basis of phase equilibria and preliminary fluid inclusion data, crystallization temperature drops from >1000°C (augite syenite liquidus) to <500°C (lujavrite solidus) and silica activity decreases from ∼0·8 to <0·3. An almost pure methane fluid phase at high temperatures and an almost pure aqueous fluid phase in the last crystallization stages of the agpaitic rocks indicate a strong increase in water activity. NaCl activity drops from 0·4 during magmatic sodalite crystallization to <0·01 (3 wt % NaCl equiv ) in the late magmatic aqueous fluids. Relative oxygen fugacity [ΔFMQ, where FMQ is fayalite–magnetite–quartz)] depends on silica and water activity via two solid–solid buffer reactions. It decreases during fractionation in the augite syenite from about FMQ – 1 to below FMQ – 4, but increases in the peralkaline stage. The extreme peralkaline fractionation trend appears to be governed by low water activity and low SiO 2 activity in the parental melt. Only then is methane a stable fluid phase during most of the crystallization history, which prevents early unmixing of an aqueous NaCl-bearing fluid phase. |
format |
Text |
author |
MARKL, GREGOR MARKS, MICHAEL SCHWINN, GREGOR SOMMER, HOLGER |
author_facet |
MARKL, GREGOR MARKS, MICHAEL SCHWINN, GREGOR SOMMER, HOLGER |
author_sort |
MARKL, GREGOR |
title |
Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland |
title_short |
Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland |
title_full |
Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland |
title_fullStr |
Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland |
title_full_unstemmed |
Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilimaussaq Complex, South Greenland |
title_sort |
phase equilibrium constraints on intensive crystallization parameters of the ilimaussaq complex, south greenland |
publisher |
Oxford University Press |
publishDate |
2001 |
url |
http://petrology.oxfordjournals.org/cgi/content/short/42/12/2231 https://doi.org/10.1093/petrology/42.12.2231 |
long_lat |
ENVELOPE(-45.900,-45.900,60.983,60.983) |
geographic |
Greenland Ilimaussaq |
geographic_facet |
Greenland Ilimaussaq |
genre |
Greenland |
genre_facet |
Greenland |
op_relation |
http://petrology.oxfordjournals.org/cgi/content/short/42/12/2231 http://dx.doi.org/10.1093/petrology/42.12.2231 |
op_rights |
Copyright (C) 2001, Oxford University Press |
op_doi |
https://doi.org/10.1093/petrology/42.12.2231 |
container_title |
Journal of Petrology |
container_volume |
42 |
container_issue |
12 |
container_start_page |
2231 |
op_container_end_page |
2257 |
_version_ |
1766018350979219456 |