HR: 1340h
AN: V23A-0684    [Abstracts]
TI: Evidence for Extended (5-10 Ma) Emplacement of Ferrar Dolerite from 40Ar-39Ar Geochronology
AU: * Knight, K B
EM: kbk@berkeley.edu
AF: Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720-4767 United States
AU: Renne, P R
EM: prenne@bgc.org
AF: Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720-4767 United States
AU: Renne, P R
EM: prenne@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AB: Antarctica's Ferrar large igneous province (LIP) is dominated by dolerites linked in time, space and geochemical character with the nearby Kirkpatrick basalts, and more broadly, with magmas preserved in Dronning Maud Land (Antarctica), the Karoo LIP (southern Africa) and the Chon Aike LIP (Patagonia). Together, these magmatic bodies represent an estimated emplacement volume of ~3 x 10⁶ km³, correlated with the break-up and post-break-up activity of the Gondwana supercontinent in the middle Jurassic. Plagioclase separates from 9 Ferrar dolerites exposed across the Dry Valleys of the Transantarctic Mountains were analyzed using the ⁴⁰Ar-³⁹Ar method. Detailed apparent age spectra reveal a range of well-defined plateau ages. Four samples yield indistinguishable ages with a weighted mean age 180.0 ± 0.5 Ma. The remaining 5 samples yield statistically distinct and significantly younger plateau ages, decreasing to as young as ca. 173 Ma. These ages may represent emplacement and/or cooling ages (below ~300°C, the approximate closure temperature for argon in plagioclase). Spectacular exposure and preservation of the Ferrar intrusive complex has led to increased interest in development of models of magma mush formation and emplacement. These data provide quantitative constraints for models of magma emplacement for the Ferrar, suggesting either the presence of long-lived magma chambers or sufficient thermal insulation or input to allow heterogeneous slow cooling of the Ferrar dolerites. The suggestion of protracted (5-10 Ma) intrusive activity supports previous geochronology data reported from Dronning Maud Land and the Ferrar, as well as the broad temporal picture arising around the time of Gondwana break-up.
DE: 1115 Radioisotope geochronology
DE: 3642 Intrusive structures and rocks
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 9310 Antarctica (4207)
DE: 9611 Jurassic
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005