HALMER, MARTINA MAGD · Coupled degassing and crystallization in open-system magma chambers

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Project objective

The aim is to develop models by incorporating crystallization and associated changes in magma viscosity an density in descending degassed magma, and by considering the convective stirring of degassing into the deep chamber. A convective overturn of dense degassed and less dense gas-rich magmas occurs easily in a vertical conduit linking surface volcanic activity and volatile degassing to a deeper magma chamber. Models involve convection of magma in a conduit connecting a deep chamber to the near surface. The bulk density of the magma in the shallow degassing zone is greater than that of volatile-rich deeper magma as a result of having lost gas bubbles and dissolved volatiles thus the degassed magma will sink. Degassing provides a driving force for convection. This convection is complicated because the loss of gas also induces large changes of viscosity and density due to crystallization. Degassed dense magma is expected to crystallize as it sinks due to pressure increase, an effect that has yet not been considered in any model. This process can have implications for the differentiation in magma chambers and for surface volcanic phenomena. Large volumes of degassed magma might be convectively stirred into the deep chamber and could provide a major driving force for fractional crystallization. Conventionally magma chambers are envisaged as evolving due to heat loss, but degassing and associated convective exchanges may be also significant. Radioisotopes of the decay of ^238U provide unique information about degassing in magmas because ^222Rn is a member of the decay sequence and ^210Pb is a daughter further down the chain. Thus models of magma degassing can potentially be developed which can be tested by comparison of predictions of the radioactive disequilibria with measurements. The full problem of degassing and convective exchange within the magma chamber and conduit system needs to be addressed.

Original text from CORDIS.

Participants

• UNIVERSITY OF BRISTOL · BRISTOL, CLIFTONCoordinatorUnited Kingdom

Links

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