HR: 09:00h
AN: V11A-05    [PDF]
TI: Nucleation and Growth Rates of Pyroxene, Plagioclase and Fe-Ti Oxides in Basalt
AU: * Burkhard, D J
EM: burkhard@itc-wgt.fzk.de
AF: Research Center Karlsruhe, Environment and Technique ITC-WGT, Karlsruhe, 76021 Germany
AU: * Burkhard, D J
EM: burkhard@itc-wgt.fzk.de
AF: University of Karlsruhe, Institute for Mineralogy and Geochemistry, Karlsruhe, 76131 Germany
AB: Rock textures and physical and chemical properties are determined by the time-temperature path of a magma, and the nucleation and growth rates (J, G) of crystallizing mineral phases. We applied the crystal size distribution theory (CSD) to derived J and G of pyroxene, plagioclase and of Fe-Ti oxides in basalt glass during heat treatment [1,2,3,4]. The glass was sampled from active Pu`u O`o, Kilauea, Hawaii, by hammer-dipping and subsequent quenching [5]. Temperature (T) and time (t) dependent heat treatment of the glass above temperature of nucleation and growth maxima, about 930$\deg$C, allows one to derive the activation energy of J and G, E$_{J}$, E$_{G}$, which are at steady state after about 100 hrs, at 180/200, 353/307, 292/343 kJ/mol (E$_{J}$/E$_{G}$, for pyroxene, plagioclase and Fe-Ti oxides). On a logarithmic scale, J and G are linear with t. A comparison with growth rates of lava cooled within a lava lobe, from top to bottom [6], suggests that independent of depth, all mineral phases crystallized at T $<$ 1000$\deg$C. According to our results of t and T dependent J and G, such rock textures should first crystallize pyroxene, and intersertal plagioclase which is, indeed, observed. Slow cooling or a hold at T $>$ 1000$\deg$C, should result in a first crystallization of plagioclase. This is reported in the literature [e.g., 7]. In agreement with this, we detected anorthite nuclei in the glass with HRTEM [8]. [1] Randolph R.D., Larson M.A (1979); Theory of particulate processes. Academic Press, New York. [2] Marsh B.D. (1988); Contrib.Mineral. Petrol. 99, 277-291. [3] Cashman K.V., Marsh (1988) Contrib. Mineral. Petrol. 99, 292-305. [4] Burkhard D.J.M. (2002); Contrib. Mineral. Petrol. 142, 724-527. [5] Burkhard D.J.M. (2001); J. Petrol. 42, 507-527. [6] Burkhard D.J.M. (2003; Bull. Volcanol. 65, 136-143. [7] Lofgren G.E 1983; J. Petrol., 24, 229-225. [8] Burkhard D.J.M., Wirth, R. (2001); EOS Trans. AGU, 82 (47), Fall Meet. Suppl., abstract V51B-1014.
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 5112 Microstructure
DE: 8494 Instruments and techniques
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting