Dating the Late Precambrian volcanicity of England and Wales

Abstract

Ages for volcanism in the British Late Precambrian have been inferred from interpretations of SHRIMP zircon ages as follows: 559.3 ± 2.0 Ma for a tuff from the Beacon Hill Formation of the Charnian Supergroup; 566 ± 3 Ma for a tuff at Bardon Hill also in the Charnwood Forest area with abundant inherited grains at 590.5 ± 1.6; 566.6 ± 2.9 Ma and 555.9 ± 3.5 Ma for bentonite and tuff in the Stretton Group of the Longmyndian Supergroup; 604.7 ± 1.6 Ma for an ignimbrite of the Padarn Tuff Formation of the Arfon Group, and 572.5 ± 1.2 Ma for a tuff within the Fachwen Formation of the Arfon Group. These ages confirm that there were two major phases of volcanic activity in the English Midlands and Wales, one about 620–590 Ma and another about 575–550 Ma. This was followed in most of England and Wales by a major phase of tectonism before the Cambrian (Tommotian) transgression across the Midland Platform. Within the depocentre of the Welsh early Palaeozoic basin, however, sedimentation started within the second period of volcanism and may have continued without interruption well into the Cambrian Period. It is probable that the late phases of the Avalonian Orogeny lasted until after the beginning of the Cambrian. These new data show that the terranes of the Avalonian of England and Wales are comparable with those of eastern Canada and New England. The age estimate for the Charnia horizon is broadly similar to those obtained elsewhere in the world on rocks containing the earliest Ediacaran fauna and adds to the building of an extended time-scale for the global Ediacaran.

U-Pb geochronology and global context of the Charnian Supergroup, UK: Constraints on the age of key Ediacaran fossil assemblages

“…Formation. Additional constraint on the age of this formation is given by the volcaniclastic 562 sequence in the Bardon Hill Quarry (JNC 907), dated at 565.2 ± (0.3, 0.7, 0.9) Ma (cf 566.1 ± 563 3.1 Ma, Compston et al, 2002). 564…”

Does the Meguma Terrane Extend into SW England?

“…But if both these correlations and that with SW England are correct, an interesting situation emerges with respect to the distribution of the Meguma terrane, which would come to lie both inboard and outboard of established Avalonia in the Welsh Borderlands and the British Midlands (e.g. Tucker and Pharaoh 1991;Compston et al 2002). Waldron et al (2011) proposed several paleogeographic scenarios to account for the possible existence of the Meguma terrane (their Megumia) inboard of Avalonia (Fig.…”

Global Neoproterozoic petroleum systems: the emerging potential in North Africa

“…Late Ediacaran -Cambrian magmatism in the Himalaya (Cawood et al 2007), Iran (Ramezani & Tucker 2003;Hassenzadeh et al 2008), SE Turkey (Ustaömer et al 2008), west Turkey (Compston et al 2002;Strachan et al 2007) and into Avalonia suggests that the northern margin of Gondwana was very active until at least the mid-Cambrian (Collins pers. comm.…”