The occurrence of Zr-bearing amphiboles and their relationships with the pyroxenes and biotites in the teschenite and nepheline syenites of a differentiated dolerite boss, Islay, NW Scotland

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doi: 10.1180/002646100549526
Authors:Preston, R. J.; Hole, M. J.; Still, J.
Author Affiliations:Primary:
University of Aberdeen, Department of Geology and Petroleum Geology, Aberdeen, United Kingdom
Volume Title:Mineralogical Magazine
Source:Mineralogical Magazine, 64(3(424)), p.459-468. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:2000
Note:In English. 22 refs.; illus., incl. 2 tables, geol. sketch maps
Summary:The Cnoc Rhaonastil minor dolerite intrusion on Islay, NW Scotland represents a single body of alkali olivine basalt magma which differentiated in situ, from leucodolerite, through teschenite to minor nepheline syenite. The syenites occur as isolated nests and pegmatitic schlieren within the leucodolerite, and schlieren of gabbroic pegmatite also occur at the margin of the teschenite. The differentiated rocks contain pyroxene, amphibole and biotite of variable compositions which reflect both primary fractionation processes and late-stage deuteric alteration and reaction. Mafic phases within the gabbroic pegmatite, teschenite and syenite are typically rimmed and speckled with biotite, the composition of which is controlled by the local environment of crystallization. The nepheline syenites contain primary ferro-kaersutite which, where in contact with interstitial patches, has been altered to arfvedsonite, which occasionally contains up to 1.2 wt.% ZrO2. The occurrence of Zr-arfvedsonite (and of Zr-aegirine) in interstitial patches suggests that variably trace element-enriched domains existed within the residual melts on very small scales. [R.A.H.]
Sections:Mineral data
Subsections:Silicates
Subjects:Alkali gabbros; Amphibole group; Biotite; Chain silicates; Chemical fractionation; Diabase; Gabbros; Geochemistry; Igneous rocks; Metals; Mica group; Nepheline syenite; Plutonic rocks; Pyroxene group; Sheet silicates; Silicates; Syenites; Teschenite; Zirconium; Argyllshire Scotland; Europe; Great Britain; Hebrides; Inner Hebrides; Islay; Scotland; United Kingdom; Western Europe; Cnoc Rhaonastil Intrusion; Strathclyde region Scotland
Coordinates:N553500 N555500 W0060000 W0063000
Abstract Numbers:00M/4201
Record ID:2000062866
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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