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Joint South-Central and North-Central Sections, both conducting their 41st Annual Meeting (11–13 April 2007)

Paper No. 7
Presentation Time: 1:40 PM-5:00 PM

PETROGENESIS OF WEST GREENLAND PICRITES: A MELT INCLUSION PERSPECTIVE


PEATE, David W.1, UKSTINS PEATE, Ingrid1, BEHANISH, Shane1 and KENT, Adam J.R.2, (1)Dept. of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, (2)Department of Geosciences, Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331-5506, david-peate@uiowa.edu

The 61 Ma Vaigat Formation represents the earliest phase of magmatism in the West Greenland flood basalt province. This c. 1 km thick sequence is comprised of thin lava flows and hyaloclastite breccias, and is unusual for its high proportion of picritic units. Pillow matrix glasses have MgO contents of 6.7-8.8%, but the presence of high-Fo olivines up to Fo93 suggest the existence of higher-MgO parental melts (Larsen et al. 2000). Graham et al. (1998) showed that olivine phenocrysts in some units had high 3He/4He values up to 30 R/RA. We have obtained the five samples studied by Graham et al. (1998) for an olivine melt inclusion study. Melt inclusions have the potential to preserve compositional diversity of melts present in the feeder systems, and thus provide critical information about the melting process and reactions between ascending melts and wall rocks (mantle or crustal).

Olivine-hosted melt inclusions were homogenised at 1200°C for 10 minutes under controlled redox conditions in a 1-atm gas-mixing furnace at Oregon State University. Host olivines are Fo 84-90, with a few crystals of Fo-92. We have analysed a total of 60 inclusions by electron microprobe. Correlations between inclusion FeO and host olivine Fo, and traverses across olivines adjacent to inclusions show that inclusion compositions have been modified by post-entrapment processes, which must be corrected for. Incompatible element ratios such as K/Ti are relatively unaffected by such processes. Most inclusions show a restricted range in K/Ti (0.13±0.03), but those in sample 332788 have higher average K/Ti and show more scatter (0.22±0.07). This sample has higher K/Ti (0.4) and lower 143Nd/144Nd than the other samples, consistent with assimilation of crustal material. The range in K/Ti in the inclusions suggests they potentially record different stages of the assimilation process, which will be evaluated by trace element data on the inclusions that we hope to obtain in the near future.

References: Graham et al. (1998) Earth and Planetary Science Letters, 160, 241-255. Larsen et al. (2000) Journal of Petrology, 41, 1071-1098.

Session No. 10--Booth# 20

Petrology (Posters)
Wednesday, 11 April 2007: 1:40 PM-5:00 PM
Geological Society of America Abstracts with Programs. Vol. 39, No. 3, p.11
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