The Juan de Fuca Ridge—Hot Spot—Propagating Rift System: New tectonic, geochemical, and magnetic data

Abstract

Underway geophysics, deep tow camera work, and preliminary geochemical and magnetic studies, from a 1980 cruise to the Juan de Fuca Ridge, allow the following interpretations: (1) the central third (between 45.5°N and 46.5°N) of the ridge is now actively spreading from a zone which is 10 to 20 km west of the axis bisecting the Brunhes‐Matuyama magnetic reversal boundary, (2) the apparent terminus of surficial igneous activity at the northern tip of the active ‘Cobb Propagator’ has been identified by dredging and camera work; the tip appears curved, or offset slightly, to the west, does not correspond to the northernmost tip of the central magnetic anomaly [Elvers et al., 1974], and spreading has been initiated beneath sediments farther north, and (3) iron and titanium in fresh glasses from the active volcanic zone exhibit a progressive enrichment northward, then a pronounced reversal to more ‘normal’ concentrations in the vicinity of the Cobb Offset.