LABORATORY MODELS OF TIME-VARYING, THREE-DIMENSIONAL FLOW AND DEFORMATION OF THE MANTLE IN SUBDUCTION ZONES

We report on results of laboratory experiments that show how important subduction is in controlling vertical thermal and chemical fluxes from Earth’s upper mantle to the base of the lithosphere. Models of subduction-induced circulation produce a variety of spatial-temporal patterns in heat flux to the overriding lithosphere in convergent margins, and episodic pulses in melt production within the underlying mantle wedge. We use laboratory fluid dynamics experiments to characterize three-dimensional (3D) flow fields in convergent margins in response to a range of subduction and back-arc deformation styles, and how these flows interact with buoyant upwellings. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000 km of the mantle. Subducting lithosphere is modeled with a descending Phenolic plate and back-arc extension is produced by moving Mylar sheets. Thermally buoyant upwellings are generated from a pressurized, temperature controlled source. Our results show that naturally occurring transitions from downdip- to rollback-dominated subduction produce conditions that favor both widespread decompression melting in the mantle wedge and short-lived pulses of extensive slab melting. Results show that different subduction styles also produce distinct patterns in the thermal erosion of the overlying lithospheric plate. For cases of plume-subduction interaction, 3D slab-induced flow quickly converts active upwellings to passive thermal-chemical anomalies whose interaction patterns with the overlying lithosphere do not resemble simplified conceptual models (e.g., LIPs with linear age-progressive tracks). Results are discussed with regards to systems such as the Cascades-Yellowstone and the Tonga-Samoa subduction zones.