Abstract

Recent studies have suggested that many large diabase dikes have been emplaced laterally rather than vertically. These studies report only unidirectional flow, which is usually based on measurements of anisotropy of magnetic susceptibility. However, in the 250-km-long Higganum dike of southern New England (United States), seven independent flow-direction indicators record a complex history of forward- and backward-moving magma. We would expect other similar-size dikes to have had equally complex histories. Measurements within one en echelon segment of the Higganum dike show that as the magma rose, it spread laterally toward the ends of the segment and that backflow was in the reverse direction of the forward flow. The Higganum dike is interpreted to have formed from a linear array of intrusive fingers, each finger spreading laterally to form an en echelon dike segment as it rose through the lithosphere.

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