East Scotia Ridge unsecured

1977 tarney et al 1977 saunders tarney 1979 muenow

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: compositions of lavas dredged at the four locations D20 and D22–24 have been reported in earlier studies (Hawkesworth et al., 1977; Tarney et al., 1977; Saunders & Tarney, 1979; Muenow et al., 1980; Cohen & O’Nions, 1982a; Saunders et al., 1982; Mattey et al., 1984; Newman & Stolper, 1996; Eiler et al., 2000). These studies showed that the lavas have an intermediate 1436 FRETZDORFF et al. PETROGENESIS OF EAST SCOTIA RIDGE Fig. 1. (a) Tectonic setting of the East Scotia Ridge within the Scotia Sea area. (b) Sketch map of the South Sandwich subduction zone with the location of the East Scotia Ridge segments (E1–E9) and South Sandwich Islands (after Leat et al., 2000). The arrows mark the spreading direction along the East Scotia Ridge and the relative movement of the subducting plate. geochemical composition between MORB and islandarc tholeiite, leading to the suggestion that fluids and/ or sediments derived from the subducting slab influence the mantle source of the East Scotia Ridge basalts (e.g. Saunders & Tarney, 1979; Tarney et al., 1981; Saunders et al., 1982). More recently, Pearce et al. (2001) reanalysed a suite of samples from dredge sites on segments E3 and E9. They showed that the back-arc lavas have Pb and Nd isotope characteristics of South Atlantic, rather than Pacific mantle. This implies that any outflow of Pacific MORB through the Drake Passage as suggested by Alvarez (1982) does not extend as far as the East Scotia Ridge. Most of the back-arc lavas have lower 206Pb/204Pb ratios than those of the South American–Antarctic Ridge (Pearce et al., 2001). The characteristic geochemical signature of the South American–Antarctic Ridge basalts is interpreted to be the result of a westward asthenospheric flow of enriched mantle from the Bouvet plume along the ridge axis (e.g. Le Roex et al., 1985). Pearce et al. (2001) suggested that this Bouvet plume component is also present in the East Scotia Ridge mantle source as a result of asthenospheric inflow into the back-arc region from the north and south. Leat et al. (2000) carried out a detailed geochemical study of the E2 segment. Their results support the interpretation of Pearce et al (2001) 1437 JOURNAL OF PETROLOGY VOLUME 43 NUMBER 8 AUGUST 2002 Fig. 2. HAWAII-MR1 bathymetry of the East Scotia Ridge, showing sample locations occupied during British Antarctic Survey (BAS) cruises JR09 (dredged samples: red triangles), JR12 (wax core samples: red circles; dredged samples: red triangles), JR39b (wax core samples: yellow circles) and the German Polarstern cruise PS47 (dredged samples: red squares). 1438 FRETZDORFF et al. PETROGENESIS OF EAST SCOTIA RIDGE that material from the Bouvet mantle plume is migrating westwards into the back-arc, and showed that lavas from the flanks of segment E2 have a higher plume influence than axial lavas. Furthermore, they demonstrated the contribution of a slab-derived component to most E2 lavas. Sampling Sampling stations on the active part of the back-arc spreading ridge were selected on the basis of detail...
View Full Document

This document was uploaded on 02/01/2014.

Ask a homework question - tutors are online