Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..386l&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 386
Other
Meteorites, Snc, Neutron Activation Analysis, Trace Elements
Scientific paper
The parental magma of the ALHA 77005 meteorite, a shergottite of putative martian origin, remains poorly known. Electron microprobe and INAA analyses of magmatic inclusions in olivine suggest that the parental magma for ALHA 77005 had abundances of many elements (Na, Ca, Sc, REE) less than 3X greater than in the bulk meteorite, and had a REE pattern comparable to that of the bulk meteorite. Olivines in ALHA 77005 (an olivine-pyroxene-plagioclase cumulate) contain ovoid magmatic inclusions [1], relicts of magma trapped within growing crystals [2]. We have analyzed these inclusions to constrain ALHA 77005's parental magma composition. The ideal sample would be an entire inclusion and the olivine that had crystallized from the inclusion. However, we cannot distinguish this crystallized olivine from host olivine, and cannot always extract entire inclusions. Inclusions for analysis were extracted with a microcoring drill from a petrographic thin section as cores 95-340 micrometers in diameter. Seven samples of inclusion-free olivine and 15 containing inclusions were analyzed by micro-INAA [3]. Sample masses cannot be measured directly, and are calculated from INAA and EMP analyses for Na and Fe. Electron microprobe analyses of inclusions are close to 1.4% Na2O (approximately 3X the bulk meteorite value of 0.48 [4]), which was used to calculate inclusion masses. Sample masses were calculated from inclusion masses and EMP analyses for FeO in inclusions (10%) and olivines (26.5%, Fo71). Analyzed inclusions ranged from 0.02 to 1.44 micrograms, or 4-66% of the masses of the whole samples (0.5-5.4 micrograms). Calculated inclusion compositions are uncertain because of possible inhomogeneity and because the calculation involves differences between analyzed abundances. CaO abundances in the inclusions are near 10% (3X bulk meteorite), in agreement with EMP results. Rare-earth-element patterns are similar in all inclusions and similar to the bulk pattern: depleted in LREE and HREE with Lu/Tb ~~ 0.8 and La/Tb ~~ 0.3 [4]. REE abundances are 2-4X the bulk values. Scandium abundances scatter around 40 ppm (2X bulk), probably reflecting sample inhomogeneity. Abundances of K2O are even more scattered, ranging from 0.05 to 1.0% (EMP) or 0.1 to 2% (INAA). Alkalis in some inclusions are greatly enriched over the bulk rock, with average enrichments of about 30X for K, 150X for Rb, and 100X for Cs. For smaller inclusions, even enrichments at these levels may be below detection limits. Several of the alkali-enriched inclusions have positive Ce anomalies, which may suggest aqueous alteration, although there is no other geochemical or petrographic evidence for such alteration. Based on these preliminary analyses, the REE patterns and abundances in the inclusions appear to be consistent with earlier inferences from SIMS analyses of individual phases that the parent magma of ALHA 77005 had Tb ~ 15X CI and was depleted in LREE [4]. The similarity of REE patterns in the bulk rock and the inclusions suggests limited fractionation until most of the REE were in solid phases. Abundances of several elements (Na, Ca, Sc, REE) in the inclusions are approximately 3X the bulk meteorite values. Some of this enrichment may be caused by growth of olivine on the walls of the inclusion, so overall melt compositions must have been close to bulk rock values. Further work using thicker sections to obtain larger samples of entire inclusions is in progress. References: [1] Jagoutz E. (1989) GCA, 53, 2429-2441. [2] Harvey R. P. and McSween H. Y. Jr. (1992) EPSL, 111, 467-482. [3] Lindstrom D. J. (1990) Nucl. Instr. Meth. Phys. Res., A299, 584-588. [4] Lundberg L. L. et al. (1990) GCA, 54, 2535-2547.
Lindstrom David J.
Martinez Rafael
Treiman Allan H.
No associations
LandOfFree
Trace-Element Analysis of Magmatic Inclusions in ALHA 77005 by Micro-INAA does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Trace-Element Analysis of Magmatic Inclusions in ALHA 77005 by Micro-INAA, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Trace-Element Analysis of Magmatic Inclusions in ALHA 77005 by Micro-INAA will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1072366