The role of crystal frameworks in the preservation of enclaves during magma mixing

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doi: 10.1016/j.epsl.2006.06.030
Authors:Martin, Victoria M.; Pyle, David M.; Holness, Marian B.
Author Affiliations:Primary:
University of Cambridge, Department of Earth Sciences, Cambridge, United Kingdom
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 248(3-4), p.787-799. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:2006
Note:In English. 49 refs.; illus., incl. geol. sketch map
Summary:The dacitic lava flows of Nea Kameni, Santorini, Greece, contain a variety of partially-crystalline mafic enclaves. Each enclave type is derived from the break-up of a layer of replenishing magma, emplaced in the dacite chamber prior to eruption. Crystallisation-induced vesiculation of this layer, driven by the temperature contrast between the two magmas, was sufficient to drive upwelling and overturn of the layer, resulting in the formation of mafic enclaves within the host. The replenishing magmas are preserved as enclaves due to the presence of a plagioclase crystal framework. Spatial distribution pattern (SDP) analysis and melting experiments demonstrate that the plagioclase crystallinity and crystal aspect ratios observed in the Kameni enclaves are sufficient to form a touching framework of crystals. Observations on the coherence of the framework during exsolution of volatiles and enclave transport suggest that the morphology of the dominant framework-forming phase places a significant control on the strength and viscosity of the crystal framework, which in turn determines the extent to which the replenishing magmas will fragment and mix with the dacite host. Frameworks composed of high-aspect ratio crystals are weak, and respond to rapid vesicle expansion in a brittle manner. The replenishing magma then disaggregates to become a source of crystals dispersed throughout the host magma. In contrast, low-aspect ratio crystals form strong crystal frameworks that are more resistant to rapid vesicle expansion, resulting in preservation of the replenishing magma as vesicular enclaves. Abstract Copyright (2006) Elsevier, B.V.
Sections:Petrology
Subsections:Igneous rocks; Volcanology
Subjects:Crystallinity; Dacites; Eruptions; Experimental studies; Exsolution; Feldspar group; Fragmentation; Framework silicates; Igneous rocks; Lava flows; Mafic composition; Magma chambers; Magmas; Melting; Mixing; Plagioclase; Preservation; Rheology; Silicates; Spatial distribution; Textures; Vesicular texture; Viscosity; Volatiles; Volcanic rocks; Aegean Islands; Cyclades; Europe; Greece; Greek Aegean Islands; Mediterranean region; Southern Europe; Thera; Crystal frameworks; Enclaves; Kameni Islands
Coordinates:N362400 N362400 E0252700 E0252700
Abstract Numbers:06M/4032
Record ID:2007088405
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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