ABSTRACT
Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature. The two mechanisms are not mutually exclusive. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid-melt phase. By incorporating constraints from a collocated seismic study into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.
ABSTRACT
A methodology for evaluating the accuracy and reproducibility of calculated T1's and T2's has been developed and applied to a General Electric 1.5 T Signa System. Specifically studied were absolute accuracy and temporal stability of image derived T1's and T2's as well as the dependence of calculated relaxation times on position in the scan plane, position along the axis of the magnet bore, the scan plane orientation (axial, sagittal, coronal), and the center frequency. The results of this study of the accuracy and reproducibility of image relaxation times have direct bearing on the design of clinical investigations assessing the diagnostic usefulness of these values.
