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A palaeomagnetic study of the Charnian, Caldecote, and Uriconian volcanics and plutons, central England
Author(s) -
Piper J. D. A.,
Strange Theresa M.
Publication year - 1989
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350240407
Subject(s) - geology , ordovician , paleontology , terrane , gondwana , outcrop , pluton , overprinting , volcanic rock , igneous rock , basement , paleomagnetism , orogeny , geochemistry , tectonics , archaeology , volcano , geography
This palaeomagnetic study has investigated intrusive and extrusive calc‐alkaline igneous rocks comprising the pre‐Ordovician basement of central England and the Welsh Borderlands and dated ca . 560–530 Ma. Demagnetization studies resolve a range of magnetic components in both the older volcanic successions comprising the eastern Uriconian volcanics, and in the younger intrusive episodes comprising the Charnwood and South Leicestershire outcrops. Post‐Ordovician overprinting is largely absent and the remanence record dates from ca . 560–420 Ma. Within this time interval field tests are inadequate to confirm a primary origin and some components may be overprints acquired in immediate post‐Uriconian (Cadomian) or during late Ordovician (early Caledonian) thermotectonic events. A first order continuity is recognized on a palaeomagnetic scale between the data from the Midlands‐Welsh Borderlands and the terranes exposed in Anglesey and Southwest Wales. The British terranes moved through low latitudes during the interval represented by the Uriconian episode; they crossed the palaeoequator during the folding of these rocks and prior to emplacement of the later intrusive suite. Collectively they had rotated through ca . 170° and moved into intermediate latitudes by mid‐Lower Cambrian times. Post‐Lower Cambrian movements on the Malvernian lineament are a possible explanation for second order differences between the palaeomagnetic records of the English Midlands and the Welsh Borderlands; the largest possible regional rotation here is a ca . 90° movement of the Charnwood block with respect to the other outcrops. Correlation with the Gondwana APW path places the Anglo‐Welsh basement in the vicinity of a comparable calc‐alkaline volcanic province linked to a subducting plate margin in the Afro‐Arabian area. Subsequent continental breakup led to termination of this volcanic activity and establishment of a passive marine shelf environment later in Lower Cambrian times.