Sodic plagioclase thermometry of type 6 ordinary chondrites: Implications for the thermal histories of parent bodies

Details Sodic plagioclase thermometry of type 6 ordinary chondrites: Implications for the thermal histories of parent bodies Sodic plagioclase thermometry of type 6 ordinary chondrites: Implications for the thermal histories of parent bodies

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999m%26ps...34..763n&link_type=abstract

Meteoritics & Planetary Science, vol. 34, no. 5, pp. 763-772 (1999).

Computer Science

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Scientific paper

The structural states of sodic plagioclase crystals of about 50 microns in size from three H6, two L6 and one LL6 chondritic meteorites have been determined by measuring the delta 131 parameter with a Gandolfi camera after analyzing chemical compositions. The temperature for each sodic plagioclase crystal has been determined by plotting the delta 131 parameter, corrected for the influence of K, on the relation diagram between the delta 131 parameter and temperature of synthesis of sodic plagioclase by Smith (1972). The temperature obtained is assigned to the crystallization temperature of sodic plagioclase and the maximum plagioclase temperature for each meteorite can be assumed to correspond to the maximum temperature attained by each meteorite during metamorphism. The maximum metamorphic temperatures estimated are 725-742 degC for H6, 808-820 degC for L6 and 800 degC for LL6 chondrites. These temperatures are lower than those based on Ca contents of clinopyroxenes (Dodd, 1981; McSween et al., 1988), but are consistent with those based on Ca contents of orthopyroxenes (McSween and Patchen, 1989; Langenhorst et al., 1995; Jones, 1997). The K content of sodic plagioclase correlates with the temperature obtained from the structural state. This positive correlation suggests that sodic plagioclase has formed in the course of equilibration processes of alkali elements in prograde metamorphism, i.e. during heating processes. The results of this study, i.e. the maximum metamorphic temperature of the H6 chondrite is lower than that of the L6 chondrite by about 80 degC and the meteorites of the same chemical group show very similar maximum metamorphic temperatures, are in accordance with the predictions of calculations based on the 26Al heat source and the onion-shell structure model of the parent bodies.

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