Leg 183 snthesis: Kerguelen Plateau-Broken Ridge-a large igneous province

• Main Authors: Frey, FA, Coffin, MF, Wallace, PJ, Weis, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: Texas A & M University, Ocean Drilling Program 2003
• Subjects: Earth Sciences; Geology; Marine Geoscience; Broken Ridge; Elan Bank; Indian; Kerguelen; Southern Ocean; Antarc*; Antarctica
• Online Access: https://doi.org/10.2973/odp.proc.sr.183.015.2003; http://ecite.utas.edu.au/73830

The Kerguelen Plateau and Broken Ridge form a large igneousprovince (LIP) in the southern Indian Ocean. The main objectives ofOcean Drilling Program Leg 183 were to understand the origin and evolutionof this LIP and the impact of its formation on the environment.Igneous basement (33 to 233 m of penetration) has been recoveredfrom 11 drill sites on the LIP, and 7 are Leg 183 sites. Studies of the basementand 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 119110 and 10595 Ma.Although an important caveat is that we have access only touppermost basement of a thick (~20 km) igneous crust, theseresults are inconsistent with massive volcanism associated witha single plume head and continental breakup.2. The uppermost igneous basement is dominantly tholeiiticbasalt. Based on the physical characteristics of the lava flows,which indicate subaerial eruption, and the occurrence of overlyingterrestrially derived sediments containing wood fragments,fern remains, and terrestrial palynoflora, much of the LIP wasabove 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 basalterupted at each site. These differences are attributed to varyingproportions of components derived from the Kerguelen plume,depleted MORB-related asthenosphere, and continental lithosphere.4. Based on radiogenic isotopic ratios and incompatible elementabundances, tholeiitic basalt of Cretaceous age from spatiallydiverse locations (Site 738 in the SKP, Site 1137 on Elan Bank,Site 747 in the Central Kerguelen Plateau (CKP), and Site 1142on Broken Ridge) contains up to ~5% of a component derivedfrom continental crust. The Proterozoic-age zircon and monazitein clasts of garnet-biotite gneiss in a conglomerate intercalatedwith basalt at Site 1137 demonstrate that continental crust fragmentsare present in the Indian Ocean lithosphere.5. Surprising new results for oceanic LIPs are the dominance ofalkalic lavas, trachybasalt to trachyte and rhyolite, at Skiff Bankand the pyroclastic deposits present on Skiff Bank, Elan Bank,and the CKP. Explosive subaerial volcanism at high latitudes cancontribute volatiles to the stratosphere; therefore, LIP volcanismmay have had a significant environmental impact.6. Flora and fauna preserved in Kerguelen Plateau sedimentsprovide a long-term record of the plateaus environment, beginningwith terrestrial and shallow-marine deposition followed byequable Cretaceous paleoceanographic conditions, the abruptCretaceous/Tertiary boundary, the Late Paleocene ThermalMaximum, and cooling of the Southern Ocean through Tertiarytime.