Leg 183 snthesis: Kerguelen Plateau-Broken Ridge-a large igneous province
Frey, FA and Coffin, MF and Wallace, PJ and Weis, D, Leg 183 snthesis: Kerguelen Plateau-Broken Ridge-a large igneous province, Proceedings of the Ocean Drilling Program, Scientific Results, 183 pp. 1-48. ISSN 1096-7451 (2003) [Refereed Article]
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The Kerguelen Plateau and Broken Ridge form a large igneous
province (LIP) in the southern Indian Ocean. The main objectives of
Ocean Drilling Program Leg 183 were to understand the origin and evolution
of this LIP and the impact of its formation on the environment.
Igneous basement (33 to 233 m of penetration) has been recovered
from 11 drill sites on the LIP, and 7 are Leg 183 sites. Studies of the basement
and sediment cores lead to the following conclusions.
1. Formation of the LIP postdated breakup between India and Antarctica,
with eruption ages (40Ar/39Ar) ranging from ~119 Ma in the southern Kerguelen Plateau (SKP) to ~34 Ma in the northern Kerguelen Plateau. Apparently, peaks in magmatic output (~0.9 km3/yr) occurred in the intervals of 119–110 and 105–95 Ma.
Although an important caveat is that we have access only to
uppermost basement of a thick (~20 km) igneous crust, these
results are inconsistent with massive volcanism associated with
a single plume head and continental breakup.
2. The uppermost igneous basement is dominantly tholeiitic
basalt. Based on the physical characteristics of the lava flows,
which indicate subaerial eruption, and the occurrence of overlying
terrestrially derived sediments containing wood fragments,
fern remains, and terrestrial palynoflora, much of the LIP was
above sea level when magmatic output was high.
3. The geochemical characteristics of basalt forming the LIP are unlike mid-ocean-ridge basalt (MORB). There are, however significant geochemical differences between tholeiitic basalt
erupted at each site. These differences are attributed to varying
proportions of components derived from the Kerguelen plume,
depleted MORB-related asthenosphere, and continental lithosphere.
4. Based on radiogenic isotopic ratios and incompatible element
abundances, tholeiitic basalt of Cretaceous age from spatially
diverse locations (Site 738 in the SKP, Site 1137 on Elan Bank,
Site 747 in the Central Kerguelen Plateau (CKP), and Site 1142
on Broken Ridge) contains up to ~5% of a component derived
from continental crust. The Proterozoic-age zircon and monazite
in clasts of garnet-biotite gneiss in a conglomerate intercalated
with basalt at Site 1137 demonstrate that continental crust fragments
are present in the Indian Ocean lithosphere.
5. Surprising new results for oceanic LIPs are the dominance of
alkalic lavas, trachybasalt to trachyte and rhyolite, at Skiff Bank
and the pyroclastic deposits present on Skiff Bank, Elan Bank,
and the CKP. Explosive subaerial volcanism at high latitudes can
contribute volatiles to the stratosphere; therefore, LIP volcanism
may have had a significant environmental impact.
6. Flora and fauna preserved in Kerguelen Plateau sediments
provide a long-term record of the plateau’s environment, beginning
with terrestrial and shallow-marine deposition followed by
equable Cretaceous paleoceanographic conditions, the abrupt
Cretaceous/Tertiary boundary, the Late Paleocene Thermal
Maximum, and cooling of the Southern Ocean through Tertiary