The Anglo-Brabant Massif: persistent but enigmatic palaeo-relief at the heart of western Europe Tim Pharaoh British Geological Survey, Keyworth, Nottingham, NG12 5GG
[email protected] ABSTRACT The surface geology of central England and Belgium obscures a large ‘basement’ massif with a complex history and stronger crust and lithosphere than surrounding regions. The nucleus was forged by subduction-related magmatism at the Gondwana margin in Ediacaran time, and partitioning into platform and basin was already evident in Cambrian/earliest Ordovician time. The accretion of the Monian Composite Terrane during the Penobscotian deformation phase preceded late Tremadocian rifting, and Floian separation, of the Avalonia Terrane from the Gondwana margin. Late Ordovician magmatism in a belt from the Lake District to Belgium records subduction beneath Avalonia of part of the Tornquist Sea. This ‘Western Pacific-style’ oceanic basin closed in latest Ordovician time, uniting Avalonia and Baltica. Closure of the Iapetus Ocean in early Silurian time was soon followed by closure of the Rheic Ocean, recorded by subduction along the southern margin of the massif. The causes of late Caledonian deformation are poorly understood and controversial. Partitioned behaviour of the massif persisted into late Palaeozoic time, when both late Devonian and Carboniferous sequences show strong onlap, and during the Variscan Orogeny, when a wedge-shaped mountain foreland uplift was driven by orogenic indentation. Permian to Mesozoic sequences persistently exhibit onlap onto the massif. Keywords: Anglo-Brabant Tectonics Palaeo-relief Avalonia Caledonian Variscan 1. Introduction 1.1 Location The Anglo-Brabant Massif (ABM) is a long-lived component of the crust of central England and Belgium (Fig.