THE INFLUENCE OF REGIONAL STRESS AND MAGMATIC INPUT ON STYLES OF MONOGENETIC AND POLYGENETIC VOLCANISM

A new model is proposed to relate the development of monogenetic and polygenetic volcanoes to magmatic input and regional stress in the lithosphere. Output-stress diagrams relate magmatic output rate and crustal deformation rate (or strain rate). The magmatic output rates of polygenetic volcanoes and monogenetic volcano fields, including lava fields and central (axial) volcanoes on the mid-oceanic ridge systems, are estimated. Crustal deformation rates obtained from the literature are used as indicators of differential stress (DELTAsigma). These data are normalized over time periods of 10(4) years, and over areas of 10(3) km2. The ratio of output rate to input rate, inferred from ophiolite sections, and from crustal deformation around volcanoes, is about 0.1 to 0.3. Based on the average ratio, an input-stress diagram may be obtained at some volcanoes. Polygenetic volcanoes are plotted in the region of both larger output rate and smaller DELTAsigma. Monogenetic volcano fields are plotted on a rift trend, or in the region of a small output (less-than-or-equal-to 1 km3/10(4) yr/10(3) km2). In some regions, polygenetic volcanoes and monogenetic volcanoes coexist, for example, during 0.1 m.y. periods, and within the area of 30 km x 30 km. The output-stress diagram indicates that coexistence of these volcano types results from variation in differential stress, or variation in production rate of magma in the mantle at different levels over periods of time less than 0.1 m.y. This is supported using extrusive volumes and crustal deformation data from the eastern volcanic zone, Iceland, Taupo Volcanic Zone, New Zealand, TransMexican Volcanic Belt, Mexico, and the volcanic field on and around the Izu peninsula, Japan. The observed relationship between deformation rate, magmatic output rate, and volcano type supports the crack interaction theory of magma-filled cracks. The output-stress diagram also indicates that the balance between local stress induced by magma accumulation and regional stress, and stress relaxation, govern the structure of a volcano.