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GEOREF RECORD

The Eycott volcanic group, an Ordovician continental margin andesite suite in the English Lake District

D. Millward, G. F. Marriner and B. Beddoe-Stephens
The Eycott volcanic group, an Ordovician continental margin andesite suite in the English Lake District
Proceedings of the Yorkshire Geological Society (November 2000) 53, Part 2: 81-96

Abstract

The Eycott Volcanic Group, at the northern margin of the Lower Palaeozoic inlier in the Lake District, is the smaller of two substantial middle Ordovician (Caradoc) subduction-related volcanic successions that stratigraphically separate marine sedimentary successions of the Skiddaw Group and Windermere Supergroup. Tabular lavas and subordinate sills, in a sequence up to 2400 m thick, mainly comprise porphyritic basalt, basaltic andesite, andesite and dacite, and are locally interbedded with thin units of volcaniclastic sandstone and pyroclastic rocks; these are overlain by 800m of acid andesitic pyroclastic rocks. The distribution and form of the lava/sill facies association are consistent with emplacement as a lava plateau sequence, remarkably similar to the Birker Fell Formation, the lower part of the Borrowdale Volcanic Group in the central Lake District. The Eycott Volcanic Group rocks are geochemically coherent with characteristics transitional between medium-K, continental-margin tholeiitic, and calc-alkaline andesite suites. Rocks within the suite can be linked by fractionation of an assemblage of plagioclase, pyroxene, Fe-Ti oxide and apatite. A prominent compositional gap between about 58 and 65% SiO (sub 2) is attributed to the rapid precipitation and segregation of Fe-Ti oxide. Incompatible element concentrations in the mafic members suggest that magmas were derived possibly from a subcontinental lithosphere source, similar to that of the Borrowdale Volcanic Group. The geochemical differences between these two suites arose through the incorporation of different amounts of the subduction component and different fractionation histories.


ISSN: 0044-0604
EISSN: 2041-4811
Coden: PYGSAB
Serial Title: Proceedings of the Yorkshire Geological Society
Serial Volume: 53, Part 2
Title: The Eycott volcanic group, an Ordovician continental margin andesite suite in the English Lake District
Affiliation: British Geological Survey, Murchison House, Edinburgh, United Kingdom
Pages: 81-96
Published: 200011
Text Language: English
Publisher: Yorkshire Geological Society, Leeds, United Kingdom
References: 68
Accession Number: 2004-061487
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch map, 4 tables, sect.
N50°00'00" - N55°45'00", W06°30'00" - E01°30'00"
Secondary Affiliation: University of London, GBR, United Kingdom
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200418
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