Kerguelen Archipelago (T.A.A.F.)
(Indian Ocean)
The Kerguelen Archipelago on the northern Kerguelen Plateau (Fig. 1a) has a ~40 to 0.1 Ma history of volcanism that is attributed to the Kerguelen plume. Prior to forming the Kerguelen Archipelago and perhaps Heard Island which are on the Antarctic plate, the long-lived (~115 my) Kerguelen plume formed a very large igneous province (Kerguelen Plateau) followed by a ~5000 km hotspot track (Ninetyeast Ridge). The plume is geochemically distinctive because it has DUPAL isotopic characteristics.
Sketch map of the Eastern Indian Ocean showing the major features related to the Kerguelen Plume (figure adapted from Mahoney et al., 1995).
Plume head: Kerguelen Plateau - Broken Ridge: 115-85 Ma
(ODP Legs 119 & 120: 738, 747, 748, 749, 750)
Hotspot track: Ninetyeast Ridge: 82-38 Ma
(ODP-DSDP sites: Leg 121: 756, 757 and 758; Legs 22 & 26: 214, 216, 253, 254)
Kerguelen Archipelago: 40 Ma - recent.
Schematic melt production diagram of the Kerguelen hotspot
(basalt production in km3/yr). The data are from Pringle et al.
(1994) and from Coffin and Pringle (unpublished). Additional drilling
on the Kerguelen Plateau (Leg 183) will help to refine these values,
especially the age and rate of basalt production on the northern
Kerguelen Plateau. Magma supply rate has evidently decreased from
a relatively high rate, >1.5 km3/yr, during the growth of the
Kerguelen Plateau to a much lower rate during the ~40 million
year growth of the Kerguelen Archipelago (Saunders et al., 1994).
The Kerguelen Archipelago flux, over 40 Ma, is estimated at 0.06
km3/yr which incorporates the northern part of the Kerguelen Plateau
in the production. These systematic long-term changes in magma
compositions and supply rates may represent the evolutionary stages
of plume-derived volcanism; initial high-volume magmatism derived
from a plume-head (Kerguelen Plateau) followed by long-term magmatism
derived from the plume-tail (Ninetyeast Ridge) followed by a gradual
decrease in plume-derived volcanism as the supply of plume material
is strongly reduced (Kerguelen Archipelago). The alkalic magmatism
and diminished magma supply rate represented by the archipelago
may also reflect a changing tectonic environment (Storey et al.,
1988; Gautier et al., 1990; Saunders et al., 1994). Specifically,
if the archipelago formed on the thick Cretaceous lithosphere
of the Kerguelen Plateau, the effects of thickened lithosphere
on plume-derived magmatism would be to lower the extents of melting
and increase the mean pressures of melt segregation (e.g., Ellam,
1992). The result is transitional to alkalic parental magmas showing
the effects of residual garnet during partial melting, as indicated
by La/Yb >10 in archipelago lavas compared to <4 in Ninetyeast
Ridge tholeiites (Weis et al., 1992; Frey and Weis, 1995; Saunders
et al., 1994). The small insets are chondrite-normalized REE diagrams
for the lavas formed by the Kerguelen Plume. Note the difference
of scale for each of them, with an increase in LREE enrichment
with decreasing age. Data are from Mahoney et al., 1995; Frey
et al., 1991; Gautier et al., 1990; Weis et al., 1993; Yang et
al., 1998.
Geological sketch map of the Kerguelen Archipelago (adapted from Nougier, 1970).
The flood basalts cover about 85% of the surface of the archipelago while the plutonic complexes represent less than 5%.
Mount Ross is the summit at 1800 m.
Dating information for the Kerguelen Archipelago.
References as indicated and unpublished work by K.
Nicolaysen.