Rare earth element behaviour during evolution and alteration of the Dartmoor Granite, SW England

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Authors:Ward, C. D.; McArthur, J. M.; Walsh, J. N.
Author Affiliations:Primary:
Royal Holloway and Bedford New College, Department of Geology, Egham, United Kingdom
Other:
University College London, United Kingdom
Volume Title:Journal of Petrology
Source:Journal of Petrology, 33(4), p.785-815. Publisher: Clarendon Press, Oxford, United Kingdom. ISSN: 0022-3530
Publication Date:1992
Note:In English. 56 refs.; illus. incl. 6 tables, geol. sketch map
Summary:The distribution of REE within the compositionally zoned Dartmoor pluton is used to constrain models of granite evolution and to assess the effects of pervasive hydrothermal alteration on REE mobility. The main process of magma evolution was crystal fractionation of early plagioclase, biotite and accessory apatite, monazite, zircon and xenotime. Concentrations of REE and other elements (Fe, Mg, Ca, Ti, Zr, Ba, Sr) decrease strongly with evolution of the pluton from 71 to 74% SiO2. These trends, and the inward zoning of the pluton, are compatible with differentiation by crystal fractionation at the level of emplacement, a process that gave rise to a marginal cumulate granite (CGM) modified by assimilation of country rock, a body of inner granite (PM) and a late-stage evolved granite (FG) that intruded the earlier types. REE modelling on the basis of fractional crystallization of REE-enriched accessory minerals from a parent PM granite shows that the FG granite cannot have formed from a residual liquid left by crystallization of the CGM granite. Two discrete stages were: 1) side-wall cumulate CGM granite crystallization dominated by LREE-enriched monazite fractionation followed by 2) a late-stage mobile residual FG granite in which fractionation was dominated by HREE-enriched apatite and zircon. Large-scale assimilation of country rock was not a dominant process. Pervasive hydrothermal alteration locally affected all types of Dartmoor granite, REE being mobilized over distances of centimetres only into the secondary alteration products sericite, chlorite, tourmaline, allanite and sphene. [R.A.H.]
Subjects:Geochemistry; Granites; Hydrothermal alteration; Igneous rocks; Metals; Metasomatism; Petrology; Plutonic rocks; Rare earths; Cornwall England; Devon England; England; Europe; Great Britain; United Kingdom; Western Europe; Dartmoor Granite; Evolution; Southwestern England
Abstract Numbers:93M/1917
Record ID:1992070446
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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