The Mull Paleocene dykes: some insights into the nature of major dyke swarms

At about 1000 km long and with a magmatic volume exceeding 850 km 3 , the Paleocene Mull Dyke Swarm qualifies as a giant dyke swarm. As such, it offers important insights into the nature of such swarms. Magma flowage laterally from the Mull Central Complex is supported by evidence of recent magma flowage in rift-related volcanic areas. Conduits were frequently used by more than one magma pulse at different times. Pre-heating of conduits by basaltic magma enabled salic magmas to propagate for >400 km from Mull. The Southern Upland Fault had a major influence on dyke propagation in the southern sector of the swarm, variably arresting magma migration or diverting magma vertically or laterally, in one case for 16 km laterally. A significant role for crustal heterogeneity in controlling dyke dynamics is advocated. Recent models point to important interactions between the dykes and adjacent Paleocene central complexes. The dyke swarm can potentially contribute significant information on the evolution of the Mull plumbing system, such as the formation of compositional zoning and the role of magma input in chamber rupture.