Extinct 129I in halite from a primitive meteorite: Evidence for evaporite formation in the early solar system

Science

Volumn 288, Issue 5472, 2000, Pages 1819-1821

  Whitby, James ^a   Burgess, Ray ^a   Turner, Grenville ^a   Gilmour, Jamie ^a   Bridges, John ^b  

^a UNIVERSITY OF MANCHESTER   (United Kingdom)

^b DEPARTMENT OF LIFE SCIENCES   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

IODINE 129; XENON;

EVAPORITE; HALITE; IODINE; METEORITE; SOLAR SYSTEM; XENON;

ARTICLE; ASTRONOMY; CHEMICAL ANALYSIS; EVAPORATION; FOSSIL; GEOLOGY; PRIORITY JOURNAL;

EID: 0034625660     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.288.5472.1819     Document Type: Article

References (23)

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4. This study used material separated from a 15 cm by 10 cm cut slice of Zag (Natural History Museum specimen 1999, M34). The meteorite slice shows a brecciated texture and consists of about 70% light-colored, crystalline clasts of petrographic type 6 and 30% surrounding gray matrix of petrographic type 4 that contains recognizable chondrules. Lesser amounts of a third dark clast type that has not yet been sectioned are also present in the hand specimen. Ten halite grains (≤3 mm diameter) have been identified on the cut surfaces of the Zag specimen, and four others have been found in thin sections; all fourteen are within the gray matrix. The grains are not present along obvious veins, although some of their outlines (i.e., rhombohedral in the case of the largest one) indicate that they crystallized within opening fractures. Some of the halite grains also show signs of having undergone subsequent fracturing and recrystallization. Both the matrix and light clasts were found to be weakly shocked - S3 by the classification of (20). The halite grains have mottled colors varying from colorless to blue (predominant) and dark blue. Zolensky et al. (1) suggested that similar colors seen in Monahans (H5) halite grains - also present within a gray matrix - were a resuit of exposure to cosmic rays before the meteorite fall. No other minerals within Zag that might have a related paragenesis to the halite, e.g., carbonates, sulfates, or clay veins, have been found; the textures and major mineral assemblages seen in thin section are typical of equilibrated H group chondrite. There are no signs of any reaction between the halite and surrounding silicate phases. The halite was found to contain primary and secondary fluid inclusions, and these are the subject of a separate study. Olivine and pyroxene mineral compositions (Hitachi 2500 SEM/EDS, 15 kV, 2 nA) are equilibrated Fo82, En83 in the light clasts and the matrix. However, the meteorite has previously been classified as H3-5 (2), indicating the presence of unequilibrated material. Therefore, Zag is heterogeneous on a coarse scale in respect to the range of petrographic types present within its components. The halite is nearly pure NaCl as K, S, and Ca were not detected (on the basis of multiple analyses within two separated grains and three grains in thin section; Cameca SX50 wds probe, 15 kV, 20 nA).
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23. We thank B. Clementson, C. Davies, and D. Blagburn for their skilled technical support. This work was funded by the Royal Society and the Particle Physics and Astronomy Research Council.