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

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.