THE ELECTRICAL-PROPERTIES OF A 2D CONDUCTIVE ZONE UNDER THE JUAN-DE-FUCA RIDGE

Vertical gradient electromagnetic sounding (VGS) on the Endeavour segm ent of Juan de Fuca mid-ocean ridge reveals the presence of a 2D ridge -parallel, conductivity anomaly. If the anomaly is caused mainly by me lt in a conventional upper mantle upwelling zone alone, then the condu ctivity of the Bone is about 0.6 S/m. The corresponding Archie's law m elt fraction exceeds 0.10. A significantly lower melt fraction require s a sheet-like, well interconnected melt. Upwelling zone conductivity can be reduced by a third if the anomaly is broadened and a crustal co nductor is added to the model.