Physical geology of high-level magmatic systems: introduction

Christoph Breitkreuz, Nick Petford

Research output: Contribution to JournalArticlepeer-review


Despite their wide occurrence and structural importance for the development of the upper continental crust, the physical geology of high-level dykes, sills and laccoliths (so-called minor intrusions) has not received the level of detailed attention that it deserves. Factors determining the final emplacement level of subvolcanic intrusions are complex, and depend upon a range of physical parameters, including magma driving pressure, the local (and regional) stress field, and the physical properties (viscosity and density) of the intruding material (Breitkreuz et al. 2002). SiO2-poor magmas rise through tabloid or ring-shaped dykes, acting as feeder systems for Hawaiian to strombolian eruptions or for their phreatomagmatic to subaquatic equivalents. The ascent of silica-rich magmas leads to explosive eruptions, extrusion of lava or emplacement of subvolcanic stocks and laccoliths. The main reason for this variation in emplacement style appears to be the initial volatile content of the rising magma (e.g. Eichelberger et al. 1986). Despite this, and as shown in this volume, the resulting emplacement geometries are surprisingly limited in range, suggesting that interactions between magma pressures and local (and regional) stress fields act to minimize the degree of freedom available for space creation, irrespective of initial composition. Interaction between magmas and sediments is an important process in high-level intrusive complexes, and a number of papers address this topic. In the field, the distinction between subvolcanic intrusions and lavas, and even some high-grade rheomorphic ignimbrites, is not always clear cut, especially in the case of ancient units exposed in limited outcrop or in drill ... This 250-word extract was created in the absence of an abstract.\n
Original languageEnglish
Pages (from-to)1-4
Number of pages4
JournalGeological Society, London, Special Publications
Issue number1
Publication statusPublished - 30 Apr 2008


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