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Geochemistry and eruptive environment of metavolcanic rocks from the Mona Complex of Anglesey, North Wales, U.K

Published online by Cambridge University Press:  01 May 2009

R. S. Thorpe
R. S. Thorpe
Affiliation:
Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, U.K.
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Abstract

The late Precambrian–early Palaeozoic Monian Supergroup of the Mona Complex is a thick sequence of flysch-type sediments and metavolcanic rocks which were deposited during the late Precambrian–early Palaeozoic and deformed during the late Precambrian and Caledonian (Ordovician/Silurian) orogenies. The Monian Supergroup includes tectonically emplaced, geographically separated outcrops of metabasalt/andesite, gabbro and serpentinized ultramafic rocks all of ophiolite affinity. The major units of the Mona Complex are separated by important faults/fault zones which may represent terrane boundaries. New chemical analyses, together with existing ones, show that the metabasalts and meta-andesites from the older New Harbour Group of north Anglesey have characteristics of suprasubduction zone arc eruptives whereas the metabasalts from the younger Gwna Group of south Anglesey and Lleyn have MORB geochemistry. It is suggested that these volcanic rocks were produced during the late Precambrian–early Palaeozoic development of the lapetus Ocean and emplaced as separate terranes during its closure.

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 1 , January 1993 , pp. 85 - 91
Copyright
Copyright © Cambridge University Press 1993

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