Basaltic-volcano systems

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Abstract
This review and personal account of basaltic volcanism concentrates on the geological aspects and physical controls, unlike most others which concentrate on geochemistry. It serves as an update to reviews by Wentworth & Macdonald 20 to 40 years ago. The concept of volcanic systems is developed, a system including the plumbing, intrusions, and other accoutrements of volcanism, as well as the volcanic edifice. Five types of systems are described, namely lava-shield volcanoes, stratovolcanoes, flood-basalt fields, monogenetic-volcano fields, and central volcanoes (having silicic volcanics as well as basaltic). It is postulated that the system-type depends on (a) the magma-input rate and (b) the frequency with which magma-batches enter the system (or modulation frequency). These controls determine whether a hot pathway is maintained from the source to the high-level magma chamber, and hence if eruptions are concentrated in the central-vent system. Reviews are given on many aspects: the different kinds of rift zones that volcanoes exhibit, and their controls; the mostly small intrusions, including coherent-intrusion complexes, that occur in and under the volcanic edifices; the great sill swarms that are an alternative to flood basalts; the origin of the craters and calderas of basaltic volcanoes; high-level magma chambers, their locations, and cumulate prisms; the positive Bouguer gravity anomalies that are attributed to cumulates and intrusion complexes; the structures of basaltic lava flows; the characteristics of basaltic explosive volcanism and the consequences of participation by non-volcanic water; the products of underwater volcanism; the origin and significance of joints, formed either by contraction or expansion, in volcanic rocks; and the distribution of vesicles in basaltic rocks. A fairly extensive bibliography is included.