Magmatic processes in oceanic ridge and intraplate settings

Abstract

The global mid-ocean ridge (MOR) system is about 60 000 km in length and represents the single largest supply system of magma to the earth’s surface. The oceanic lithosphere also contains islands and archipelagos representing the effects of isolated, but durable, mantle melting anomalies. In attempting to review the processes of magma genesis and evolution in these distinctive environments, this chapter draws on existing syntheses of magmatic processes in the oceanic domain (e.g. BVSP, 1981; Wilkinson, 1982; Hekinian, 1982; Thompson, 1987). Within the oceanic domain, ‘magmatic processes’ include the partial melting of mantle, the physical extraction of melts from multiphase solid assemblages, and the combined effects of crystallization, mixing and wallrock reaction during the uprise and emplacement of magma. Realistic physical models provide the means to utilize erupted magma as a chemical and thermal probe of the mantle and to better understand the phenomenon of planetary melting. This chapter examines the chemical and petrographic variation of magmas generated at oceanic ridge and intraplate settings in terms of recent experimental results, current knowledge about the physical character of active ridge axes, and real-time studies of active volcanoes.