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Thermal limitations on incorporation of wall rock into magma

¹ Department of Geological Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3315, USA

Incorporation of solid wall rocks is an oft-cited process in the evolution of magmas, but this process is severely limited by the energy required to dissolve xenoliths. Disaggregation without melting has been proposed as an alternative process for incorporating xenoliths into magma because disaggregation avoids expending the energy required for melting. Analysis of these processes using enthalpy-composition diagrams shows that both processes rapidly lead to high crystal contents in the hybrid magma. For example, incorporation of 25% granite at 400 °C into basalt magma at 1125 °C produces a hybrid magma at 1050 °C with >50% crystals; if the granite disaggregates without melting, the crystal content is 65%–70%. Once the crystal content reaches 50% the viscosity of the magma is too high to allow further magma movement or xenolith incorporation. Thus, both processes are self-limiting and probably restricted in natural systems to at most a few tens of percent incorporation of xenoliths.

Key Words: magma • thermodynamics • igneous petrology • assimilation

This article has been cited by other articles:

				A. F. Glazner and J. M. Bartley Reply to comments on "Is stoping a volumetrically significant pluton emplacement process?" GSA Bulletin, July 1, 2008; 120(7-8): 1082 - 1087. [Full Text] [PDF]