Modeling dislocation creep as a near-field material transfer process during spherical pluton expansion: implications for strain rates and their preservation in pluton aureoles

摘要

In this paper we model coupled spatial and temporal changes in stress and temperature to calculate dislocation creep strain rates in host rock associated with spherical magma chamber expansion with and without material removal by stoping and/or assimilation. Given a constant magma-chamber pressure of 100 MPa, we show that stress and temperatures in the host rock range from 100 to 10 MPa and 800 to 300℃, respectively. Using a flow law for dislocation creep of wet quartzite with recently calibrated parameters, maximum dislocation creep strain rates on the order of ca. 10~(-10) s~(-1) occur only close to the pluton margin. Despite the simple geometry relative to real plutons, the models yield several thought-provoking predictions. If the outer portions of the pluton are allowed to cool, a wide thermal and structural aureole forms. Maintaining the liquidus temperature in the entire pluton allows for rapid aureole deformation, resulting in a narrow thermal and structural aureole, because the deformation outpaces heat conduction. Dislocation creep strain rates in the inner portions of aureoles are extremely sensitive to pressure changes only, potentially resulting in large transient variations in strain rate under isothermal conditions. Evidence for elevated strain rates in pluton aureoles may not be preserved in host rock aureoles if solidified pluton participates in the deformation or it may be completely removed.