April 2007 LIP of the Month

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Corresponds to event #18 in LIP record database.

The Kerguelen Large Igneous Province

Stephanie Ingle, SOEST - University of Hawaii
1680 East-West Road, POST 606
Honolulu, HI 96822

email: ingle@hawaii.edu

The Kerguelen Large Igneous Province is the second largest LIP on Earth. It covers an area of ~2.3 x 106 km2 and was constructed over a protracted time period beginning around 130 Ma in the nascent, eastern Indian Ocean. The oldest erupted lavas are the Bunbury Basalts in western Australia at ~132 – 123 Ma (Coffin et al.  2002). This was followed by volcanism in eastern India at ~118 Ma (Kent et al.. 1997) and the construction of the Southern Kerguelen Plateau beginning ~119 Ma (Duncan. 2002). The remainder of the plateau was constructed over the following 85 million years or so until spreading began on the Southeast Indian Ridge, dividing the Kerguelen Plateau from the Broken Ridge. At peak output, eruption volumes may have been 0.9 km3/y or more (Coffin et al. 2002); for comparison, Hawaii has a mass flux of ~0.15 km3/y (White. 1993). Kerguelen, Heard, and McDonald Islands are the most recent products of the Kerguelen hotspot which remains active today.

Many products of the early Kerguelen hotspot are derived from magmas that appear to have traversed and assimilated continental lithosphere during their ascent. Cretaceous Kerguelen Plateau basalts were previously considered as type-examples of the oceanic EM-1 mantle component. This now appears to be incorrect. Continental lithosphere is now known to underlie significant regions of the plateau, particularly at Elan Bank and the Southern Kerguelen Plateau (Fig. 1). Drilling at Elan Bank recovered a volcaniclastic conglomerate that contained cobble-sized fragments of rhyolite, basalt, trachyte, granitoid and gneisss (e.g., Frey et al.  2000). The gneiss contained garnet and biotite, providing strong evidence for its derivation from within continental crust, and it experienced metamorphism around 550 Ma (Nicolaysen et al. 2001). The cobble-sized clasts require transportation to be limited, ruling out their derivation from the nearest continents. Seismic investigations of Elan Bank have demonstrated that up to 80% of Elan Bank’s crust is characterized by velocities more typical of continental crust than oceanic crust (Borissova et al. 2003).

Figure 1: Physiographic map of the Indian Ocean and bathymetric map of the Kerguelen Plateau and Broken Ridge. The locations of the Bunbury Basalts and the Rajmahal Traps are noted on the physiographic map. Numbers on the bathymetric maps refer to drill sites. KA is Kerguelen Archipelago and HI is Heard Island.

Additional evidence suggests the influence of in-situ continental material in Kerguelen hotspot-derived basalts is widespread. Many workers have argued for continental crust contamination based on radiogenic isotopic data (e.g., Weis et al. 2001; Ingle et al. 2002b; Frey et al. 2002). With a few notable exceptions, nearly every drilled site on the Kerguelen Plateau and Broken Ridge records a ‘fingerprint’ of the continental contaminant in their Pb isotope compositions (Fig. 2). This is because the Pb concentrations in continental crust are up to 10x higher than those of mafic, mantle-derived magmas ensuring that even very small amounts (<<1%) of assimilation will be recorded in the Pb isotopic compositions of the lavas . In some cases, the contaminating crust may be the upper continental crust, characterized by high 207Pb/204Pb and 208Pb/204Pb, but in others, lower continental crust seems to be responsible for the lower 206Pb/204Pb values observed in a few places on the plateau.


Figure 2: Measured 207Pb/204Pb vs. 206Pb/204Pb drilled rocks from the Kerguelen Plateau and Broken Ridge and dredged rocks from (Keremis) seamounts between the Northern and Central Kerguelen Plateau. Also plotted are the Bunbury basalts from southwestern Australia, and Rajmahal Traps from eastern India. Fields for flood basalts from the Kerguelen Archipelago and Indian Ocean MORB are also shown as are the data for gneiss clasts from Site 1137 corrected to 120 Ma (Ingle et al. 2002a). Note the near-vertical trend of increasing 207Pb/204Pb centered around 206Pb/204Pb of ~18.0. This trend has been interpreted to reflect increasing amounts of assimilated continental crust by ascending magmas (Weis et al. 2001; Ingle et al. 2002a,b). Note also that the Bunbury basalts and Rajmahal Traps fall on this trend and their data bracket those of the basaltic rocks from the plateau. This may reflect a common mantle source for the rocks on this trend and a comparable continental contaminant (Ingle et al.  2003). The gneiss clasts plot at the end of this trend but it is not clear if their compositions are those of the actual contaminant. The lower 206Pb/204Pb found in rocks from Sites 738, 747, 750, and 1139 require, at the least, a different continental contaminant (Frey et al. 2002) or they may be sourced from a different mantle composition altogether from those forming the vertical Pb isotope trend (Ingle et al. 2003). Data sources are as follows: Site 738 (Mahoney et al.. 1995), Sites 747, 749, and 750 (Frey et al. 2002), Sites 1136, 1138, 1141, and 1142 (Neal et al. 2002), Site 1137 (Weis et al. 2001; Ingle et al. 2002a), Site 1139 (Kieffer et al. 2002, only data for mafic lavas are plotted), Site 1140 (Weis and Frey 2002), Kerimis Seamounts (Weis et al. 2002), Bunbury basalts (Frey et al. 1996), and Rajmahal Traps (Kent et al.. 1997). Indian Ocean MORB data are from Chauvel and Blichert-Toft 2001 and references therein. Note that, with the exception of some lavas from NKP Site 1140, these LIP basalts do not overlap with the MORB lavas. For some lavas from Sites 738, 747, and 1137, assimilation of continental crust is inferred (a typical trajectory for increasing continental contamination is shown by the red arrow).

In summary, the Kerguelen Plateau likely represents the least “typical” large igneous province. Its protracted construction period conflicts with the model for LIP emplacement by a large mantle plume head; the integration of continental fragments in the plateau’s structure hamper efforts to understand its magma output history and emplacement environment; and contamination of the mafic lavas by continental crust make it a challenging place to work out the geochemical signature of its mantle source.

References

Borissova, I., M. F. Coffin, et al. (2003). Structure and development of a microcontinent: Elan Bank in the southern Indian Ocean. Geochemistry, Geophysics and Geosystems 4: 1071, doi:10.1029/2003GC000535.

Chauvel, C. and J. Blichert-Toft (2001). A hafnium isotope and trace element perspective on melting of the depleted mantle. Earth and Planetary Science Letters 190: 137-151.

Coffin, M. F., M. S. Pringle, et al. (2002). Kerguelen hotspot magma output since 130 Ma. Journal of Petrology 43: 1121-1139.

Duncan, R. A. (2002). A timeframe for construction of the Kerguelen Plateau and Broken Ridge. Journal of Petrology 43: 1109-1119.

Frey, F. A., M. F. Coffin, et al. (2000). Origin and evolution of a submarine large igneous province: the Kerguelen Plateau and Broken Ridge, southern Indian Ocean. Earth and Planetary Science Letters 176: 73-89.

Frey, F. A., N. J. McNaughton, et al. (1996). Petrogenesis of the Bunbury Basalt, Western Australia:  interaction between the Kerguelen plume and Gondwana lithosphere? Earth and Planetary Science Letters 144: 163-183.

Frey, F. A., D. Weis, et al. (2002). Involvement of continental crust in formation of the Kerguelen Plateau: new perspectives from ODP Leg 120 Sites. Journal of Petrology 43: 1207-1239.

Ingle, S., D. Weis, et al. (2003). Hf isotope constraints on mantle sources and shallow-level contaminants during Kerguelen hotspot activity since ~120 Ma. Geochemistry, Geophysics and Geosystems  4(8): 1068, doi:10.1029/2002GC000482.

Ingle, S., D. Weis, et al. (2002a). Indian continental crust recovered from Elan Bank, Kerguelen Plateau (ODP Leg 183, Site 1137). Journal of Petrology 43: 1241-1257.

Ingle, S., D. Weis, et al. (2002b). Relationship between the early Kerguelen plume and continental flood basalts of the paleo-Eastern Gondwanan margins. Earth and Planetary Science Letters 197: 35-50.

Kent, R. W., A. D. Saunders, et al. (1997). Rajmahal Basalts, eastern India: mantle sources and melt distribution at a volcanic rifted margin. Large Igneous Provinces:  Continental, Oceanic, and Planetary Flood Volcanism. M. Coffin and J. Mahoney. Geophysical Monograph 100: 145-182.

Kieffer, B., N. T. Arndt, et al. (2002). A bimodal alkalic shield volcano on Skiff Bank: its place in the evolution of the Kerguelen Plateau. Journal of Petrology 43: 1259-1286.

Mahoney, J. J., W. B. Jones, et al. (1995). Geochemical characteristics of lavas from Broken Ridge, the Naturaliste Plateau and southernmost Kerguelen Plateau:  Cretaceous plateau volcanism in the southeast Indian Ocean. Chemical Geology 120: 315-345.

Neal, C. R., J. Mahoney, et al. (2002). Mantle sources and the highly variable role of continental lithosphere in basalt petrogenesis of the Kerguelen Plateau and Broken Ridge LIP: results from ODP Leg 183. Journal of Petrology 43: 1177-1205.

Nicolaysen, K., S. Bowring, et al. (2001). Provenance of Proterozoic garnet-biotite gneiss recovered from Elan Bank, Kerguelen Plateau, southern Indian Ocean. Geology 29 (3): 235-238.

Weis, D. and F. A. Frey (2002). Submarine basalts of the Northern Kerguelen Plateau: interaction between the Kerguelen plume and the Southeast Indian Ridge revealed at ODP Site 1140. Journal of Petrology 43(7): 1287-1309.

Weis, D., F. A. Frey, et al. (2002). Trace of the Kerguelen Mantle Plume: evidence from seamounts between the Kerguelen Archipelago and Heard Island, Indian Ocean. Geochemistry, Geophysics and Geosystems 3: 10.1029/2001GC000251.

Weis, D., S. Ingle, et al. (2001). Origin of continental components in Indian Ocean basalts: Evidence from Elan Bank (Kerguelen Plateau, ODP Leg 183, Site 1137). Geology 29(2): 147-150.

White, R. S. (1993). Melt production rates in mantle plumes. Philosophical Transactions of the Royal Society of London 342: 137-153.