Controls on crustal accretion along the back-arc East Scotia Ridge: constraints from bathymetry and gravity data

Abstract

This study investigates crustal accretion processes along the East Scotia Ridge (ESR), an intermediate-rate back-arc spreading center with ten segments (E1–E10) that strike north–south. Mantle Bouguer anomaly (MBA) was calculated for the ESR region using satellite-derived and shipboard data sources. De-trended MBA (MBAdet) was determined by removing a residual plane from the MBA map, and ΔMBAdet was defined as the along-segment change in MBAdet. ΔMBAdet, as well as segment-averaged values of Na8, Fe8, and 87Sr/86Sr obtained from the published literature, generally appear to be better correlated with distsst (the distance from each segment center to the nearest point on the South Sandwich Trench) than with spreading rate. For each of the northern segments E2 through E6, MBAdet has a central low. MBAdet values also form a broad, longer-wavelength low from segments E2 through E6. Generally speaking, these findings are consistent with earlier studies such as Livermore et al. (Earth Planet Sci Lett 150:261–275, 1997) in suggesting that the region around segment E2 is a center for focused accretion along the ESR. On the other hand, southern segments E7 and E8 have central MBAdet highs, and MBAdet decreases somewhat linearly from segment E7 to E9, notwithstanding intrasegment variations. The quasi-linear MBAdet trend along these ESR segments is similar to that observed for the southernmost Lau spreading centers (e.g., Martinez and Taylor in Nature 416:417–420, 2002). Overall, plate boundary geometry and three-dimensional mantle flow may play a significant role in melting processes along the ESR, especially if the spreading center is processing geochemically heterogeneous South Atlantic mantle.