Combined laboratory and numerical studies of the interaction between buoyant and plate‐driven upwelling beneath segmented spreading centers

Abstract

A combination of laboratory and numerical models are used to examine the mantle flow beneath a segmented ridge generated by the interaction of a linear, buoyant upwelling source with plate‐driven flow. In the absence of plate spreading, the linear buoyant source creates a very narrow (across‐axis), two‐dimensional upwelling pattern. The plate‐driven flow consists of a quasi‐linear sheet‐like upwelling that cuts beneath ridge‐transform inside corners and is not centered beneath the spreading segments. When buoyant and plate‐driven flows are combined, material rises beneath the inside corners and flows away from the axis asymmetrically. Near the ends of segments, this results in a geometrical misfit between the center of mantle upwelling and the ridge axis. If a similar pattern of mantle flow occurs beneath a segmented mid‐ocean ridge, the result will be a thinner crust toward segment ends and possibly a negative correlation between extent of mantle melting and average depth of melting. These results indicate that even with an essentially two‐dimensional source, in cases where it is oblique to the actual spreading segments, the upwelling beneath a segmented ridge will appear to be three‐dimensional along axis. Since slow spreading ridges are generally more segmented than fast spreading ridges, this effect is likely to be more important at slow spreading ridges.