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A Textural Record of Solidification and Cooling in the Skaergaard Intrusion, East Greenland |
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| Authors: | Holness Marian B; Tegner Christian; Nielsen Troels F D; Stripp Gemma; Morse Stearns A |
| Institution: | 1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK 2Department of Earth Sciences, University of Aarhus, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark 3Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark 4Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst, MA 01003-9297, USA |
| Abstract: | The clinopyroxene–plagioclase–plagioclase dihedralangle,  cpp, in gabbroic cumulates records the time-integratedthermal history in the sub-solidus and provides a measure oftextural maturity. Variations in cpp through the Layered Seriesof the Skaergaard intrusion, East Greenland, demonstrate thatthe onset of crystallization of clinopyroxene (within LZa),Fe–Ti oxides (at the base of LZc) and apatite (at thebase of UZb) as liquidus phases in the bulk magma is recordedby a stepwise increase in textural maturity, related to an increasein the contribution of latent heat to the total heat loss tothe surroundings and a reduction in the specific cooling rateat the crystallization front of the intrusion. The onset ofboth liquidus Fe–Ti oxide and apatite crystallizationis marked by a transient increase in textural maturity, probablylinked to overstepping before nucleation. Textural maturationat pyroxene–plagioclase–plagioclase triple junctionseffectively ceases in the uppermost parts of the Layered Seriesas a result of the entire pluton cooling below the closure temperaturefor dihedral angle change, which is  1075°C. Solidificationof the Layered Series of the Skaergaard intrusion occurred viathe upwards propagation of a mush zone only a few metres thick. KEY WORDS: magma; partial melting; asthenosphere; olivine; mantle |
| Keywords: | : magma partial melting asthenosphere olivine mantle |
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