Paper No. 132-0
DE, Subarnarekha, NRC Associate, Exobiology Branch, MS-239-4, NASA Ames Research Center, Moffett Field, CA 94035-1000,, BUNCH, Ted, Exobiology Branch, NASA Ames Research Center, Moffett Field, CA 94035, TREIMAN, Allan H., Lunar and Plantery Institute, 3600 Bay Area Blvd, Houston, TX 77058, AMUNDSEN, Hans E.F., Earth and Planetary Exploration Svcs, Jac Aalls gt44b, Oslo, N0364, Norway, and BLAKE, David F., NASA Ames Research Center, Exobiology Branch MS-239/4, Moffett Field, CA 94035-1000

Pleistocene volcanic centers in NW Spitsbergen, Norway host one of the worlds richest occurrences of mantle xenoliths. The xenoliths comprise varieties of spinel lherzolites and pyroxenites. Some of these xenoliths (and their host basalts) contain 10-100 m globules of ankeritic-magnesitic carbonates (AMC) [Amundsen et al. 1987]. In composition, mineralogy and petrology the AMC globules from Spitsbergen are strikingly similar to the carbonate globules in ALH84001. The AMC globules occur within interstitial quenched glass and as fracture fillings, although we have not seen replacement fabrics analogous to carbonate rosettes replacing glass in ALH84001. Siderite/ankerite forms the core of these concentrically zoned globules while rims are predominantly magnesite. Clay minerals can occasionally be found within and around the globules.

Aside from the clay minerals, the principal mineralogical difference between the AMCs and the ALH84001 carbonate rosettes is the presence of concentrated zones of nanophase magnetite in the rosettes, notably absent in the AMCs. However, carbonate globules containing nanophase magnetite have been produced inorganically by hydrothermal precipitation of carbonates and subsequent heating [Golden et al. 2001]. We heated Spitsbergen AMC at 585C in a reducing atmosphere to determine whether magnetite could be produced. Optical micrographs of the heated Spitsbergen AMC show dark concentric zones within the AMC. High resolution SEM images of those areas reveal 150-200 nm euhedral crystals that exhibit various morphologies including octahedra and elongated prisms. EDS analyses of areas where the crystals occur contain Fe, O and minor Si, and P. However, the probe integrates over volumes of material, which also include the surrounding matrix. We have begun TEM observations of both the heated and unheated Spitsbergen AMC to characterize the microstructures of the carbonates, establish the presence/absence of magnetite and determine the relationship of the clay minerals to the carbonates and host rock.

References: 1. Amundsen H. E. F. et al. (1987) Nature, 327, 692-695. 2. Golden, D. C. et al. (2001) Amer. Mineral., 86, 370-375.

GSA Annual Meeting, November 5-8, 2001
General Information for this Meeting
Session No. 132
Planetary Geology (Posters)
Hynes Convention Center: Hall D
1:30 PM-5:30 PM, Wednesday, November 7, 2001

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