Petrogenetic implications from biotite compositional variations in the Cornubian granite batholith

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doi: 10.1180/002646100549580
Authors:Stone, M.
Author Affiliations:Primary:
University of Exeter, Camborne School of Mines, Redruth, United Kingdom
Volume Title:Carbonatite thematic set
Volume Authors:Jones, A. P.
Source:Mineralogical Magazine, 64(4(425)), p.729-735; Tenth carbonatite workshop, London, United Kingdom, Feb. 19, 1999, A. P. Jones. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:2000
Note:In English. 14 refs.; illus., incl. 2 tables
Summary:Lithium oxide contents of biotites in some Cornubian granites which have been studied by electron microprobe are estimated from their SiO2 and F contents using samples formerly analysed by XRF and wet chemistry. Better formulae which include Li show that most of these biotites are lithian siderophyllites/lithian Al-annites although some Dartmoor samples, especially those in the basic microgranite (ME) enclaves, are closer to Al-annites. Dartmoor samples are slightly more basic and poorer in Alvi than those from the Isles of Scilly and Carnmenellis granites agreeing with the broad differences in the host rocks. Biotites in volcanic clasts from the New Red Sandstone are significantly different in having much higher Si, Ti, Mg , F and ΣY and lower Alvi contents than those of the granite biotites: these are lithian Fe-Mg biotites. These clasts are believed to be the volcanic equivalents of an evolving Dartmoor magma (Awad et al., 1996). If so, their biotites reflect the composition of the granite biotites at the time of magma emplacement. They subsequently evolved as they equilibrated with the cooling granite to give the present biotite compositions of the Dartmoor granites.
Sections:Mineral data
Subjects:Biotite; Carnmenellis Granite; Chemical composition; Clasts; Crystal chemistry; Electron probe data; Genesis; Geochemistry; Granites; Igneous rocks; Mica group; Plutonic rocks; Sheet silicates; Silicates; Variations; Volcanic rocks; Cornubian Batholith; Dartmoor; Devon England; England; Europe; Exeter England; Great Britain; United Kingdom; Western Europe; Isles of Scilly Granite; Lithium oxide
Abstract Numbers:01M/2020
Record ID:2000066408
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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