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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
Sampling stations on the active part of the back-arc
spreading ridge were selected on the basis of detail...
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This document was uploaded on 02/01/2014.
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