Aspects of magmatism and plate tectonics in the Precambrian of England and Wales

Thorpe, R. S.

doi:10.1002/gj.3350090202

Cited by 28 publications

(4 citation statements)

References 49 publications

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“…Hence we conclude that later Caledonian displacements between the terranes represented by these basement outcrops have not been on a scale to upset this general accordance between early Cambrian palaeomagnetic records, although they have probably been responsible for modifying it in detail. Close spatial continuity between these outcrops during early Cambrian times is also suggested by the common low grade metamorphic nature of their roots, the young isotopic signature of the derivative rocks, and the geochemical signature of the igneous suites (Thorpe 1974(Thorpe , 1979Thorpe et al 1984).…”

Section: Discussion 4a Lower Carnbriaia P W and Tectonic Integrity Ofmentioning

confidence: 97%

“…Geochronological data suggest approximate ages of 670,580-545, and >540 Ma for the above divisions (l), (3), and (4) (Cribb 1975;Patchett el al. 1980;Thorpe et al 1984), and the calc-alkaline nature of the igneous rocks (Thorpe 1974(Thorpe , 1979) implies a regional setting at a volcanic arc above subducting oceanic crust. A fundamental change in the palaeoenvironment to a passive marine shelf occurred during Lower Cambrian times (Paisecki et al 1980;Brasier and Hewitt 1979).…”

Section: Regional Settingmentioning

confidence: 99%

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A palaeomagnetic study of the Charnian, Caldecote, and Uriconian volcanics and plutons, central England

Piper¹,

Strange²

1989

Geological Journal

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This palaeomagnetic study has investigated intrusive and extrusive calc-alkaline igneous rocks comprising the preOrdovician 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. PostOrdovician 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 cu. 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.KEY WORDS Charnian Caldecote Uriconian Palaeomagnetism Cambrian 1. REGIONAL SETTING For the purposes of this paper the Late Precambrian-Lower Cambrian basement of England and Wales is regarded as that part of the geological column south of the Iapetus suture which predates deposition of the Lower Cambrian quartzites in a quiescent shelf environment during the latter part of Lower Cambrian times (ca. 535 Ma). This basement only appears as outcrop at a number of small and scattered locations. The exposed rock units fall into four broad divisions namely: (1) low grade metamorphic rocks, mostly of igneous derivation (the Malvernian, Stanner-Hanter Complex, Rushton schist, and Primrose Hill gneiss); (2) the Charnian sedimentary and volcanoclastic succession; (3) the Charnian, Caldecote, and Unconian volcanics and plutons; and (4) the Longmyndian sedimentary succession. Chemical and isotopic evidence imply a derivation of the igneous and metamorphic suites from crust with an antiquity no greater than ca. lo00 Ma (Thorpe et al. 1984). This terrane clearly contrasts with crust ...

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Section: Discussion 4a Lower Carnbriaia P W and Tectonic Integrity Ofmentioning

confidence: 97%

Section: Regional Settingmentioning

confidence: 99%

A palaeomagnetic study of the Charnian, Caldecote, and Uriconian volcanics and plutons, central England

Piper¹,

Strange²

1989

Geological Journal

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“…The severe inversion and sinistral transpression (Strachan, 2012) affecting the Longmyndian basin appears to have taken place rather abruptly, over a period of perhaps 5-10 Ma. Lavas of the Warren House Formation form a small (<1 km 2 ) outcrop on the eastern flank of the Malvern Hills (Penn and French, 1971;Thorpe, 1974). Altered basalt and basaltic andesite lavas, exhibiting small pillow structures occur with minor amounts of rhyolitic tuff, which have yielded concordant U-Pb zircon ages of 566 ± 2 Ma (Tucker and Pharaoh, 1991).…”

Section: Late Rifting and Marginal Basin Developmentmentioning

confidence: 99%

“…Although identical in age to the Uriconian lavas, the geochemical composition of basaltic components differs. The Uriconian basalts have a significant subduction-related component; the Warren House basalts have a much smaller subduction component and are chemically most similar to primitive marginal basin basalts (Thorpe, 1974;Pharaoh et al, 1987b).…”

Section: Late Rifting and Marginal Basin Developmentmentioning

confidence: 99%

The Anglo-Brabant Massif: Persistent but enigmatic palaeo-relief at the heart of western Europe

Pharaoh

2018

Proceedings of the Geologists' Association

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The research collaborations established resulted in numerous further publications, including a special publication of the Geological Society (Winchester et al., 2002). One of the most significant results was the elucidation of the history of the Anglo-Brabant Deformation Belt (not to be confused with the ABM) which links the Caledonides of England and Belgium. Many of the same authors contributed to the Southern Permian Basin Atlas (SPBA) published by TNO and EAGE (Pharaoh et al., 2010; De Vos et al., 2010). 2. Crustal and lithospheric structure The crustal structure of the ABM is less well known than that of surrounding regions, e.g. northern England and the region south of the Variscan Front. It was recognised from the exploration boreholes drilled in the pre-seismic era (1940s-1950s) that although coal-bearing basins are locally present on its northern margins, the massif is poorly prospective for oil and gas (Lees and Taitt, 1946; Falcon and Kent, 1960). Thus the dense networks of seismic reflection data acquired since 1970 in northern and southern England, which are so informative about the upper crustal and sedimentary basin structure in those areas (e.g. Whittaker, 1985; Kirby et al., 2000; Smith et al., 2005; Pharaoh et al., 2011) are largely absent over the massif. Significant coverage is only present in the NW (Staffordshire), the Worcester Graben and Oxfordshire Concealed Coalfield areas (Butler, in press). A small number of seismic reflection profiles, gathered by the British Geological Survey (Chadwick, 1985; Chadwick and Smith, 1988) and academic institutions (e.g. Maguire, 1987) provide limited insights to crustal structure. The massif is crossed by only one long lithospheric-scale seismic refraction profile (Lithospheric Seismic Profile in Britain, LISPB) acquired in 1974 (Bamford et al., 1976). The GAMMA segment ends in Buxton, just beyond the northern edge of the massif (Barton, 1992). The DELTA segment extends from North Wales to the Isle of Portland and an interpretation was published by Maguire et al. (2011). The segment crosses the massif in its west central part, intersecting shorter refraction profiles in the Bristol Channel area (Mechie and Brooks, 1984). Deep seismic reflection data, recorded to 12 or 15 s Two-Way Travel Time (TWTT) by the British Institutions Reflection Profiling Syndicate (BIRPS), based at Cambridge University, cover only the offshore area (Klemperer and Hobbs, 1991). These profiles are nevertheless useful in assessing the tectonic milieu of the massif. Deep seismic reflection data from northern France (Cazes and Toreilles, 1988) and Belgium (Bouckaert et al., 1988; Meissner and Bortfeld, 1990) demonstrate a gently southward-dipping Variscan detachment, with the crust of the ABM forming a tapering wedge in the footwall (Blundell, 1993). The latter extends some 60 to 100 km south of the Variscan Front, and its nature is confirmed by the continuity of the South Central England Magnetic Anomaly beneath the Variscan nappes (Beamish et al., 2016). Interpretations of crustal...

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A palaeomagnetic investigation of the Malvernian and Old Radnor Precambrian, Welsh Borderlands

Piper

1982

Geological Journal

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The late Prccambriarrcam brian palaeomagnetic record (ca 700-500 Ma) of England and W a l e s is compand with data from \he Annorican Massif. Although the apparent polar wander (a.p.w.) paths an widely dissimilar prior to 550 Ma, the two rcgiorrr had similar latitudes and went through similar palatolatitudinal movements throughout this interval. The palaeomagnctic data support models involving tectonic rotations but little dosurc across this part of the Hercynian Belt.

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Aspects of magmatism and plate tectonics in the Precambrian of England and Wales

Cited by 28 publications

References 49 publications

A palaeomagnetic study of the Charnian, Caldecote, and Uriconian volcanics and plutons, central England

A palaeomagnetic study of the Charnian, Caldecote, and Uriconian volcanics and plutons, central England

The Anglo-Brabant Massif: Persistent but enigmatic palaeo-relief at the heart of western Europe

A palaeomagnetic investigation of the Malvernian and Old Radnor Precambrian, Welsh Borderlands

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