Paper No. 189-3
Presentation Time: 8:45 AM
COOLING AND CRYSTALLIZATION HISTORIES OF MAGMATIC BODIES FROM IN-SITU MG-FE ISOTOPIC ANALYSES IN OLIVINES: TELLING ZONED FROM ZONED
SIO, Corliss Kin I., Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave, Chicago, IL 60615, DAUPHAS, Nicolas, Department of the Geophysical Sciences and Enrico Fermi Institute, University of Chicago, 5734 S. Ellis Ave, Chicago, IL 60637, TENG, Fang-Zhen, Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195-1310, CHAUSSIDON, Marc, Institut de Physique du Globe de Paris, Université Paris Diderot, Paris, F-75005, France, RICHTER, Frank M., Department of the Geophysical Sciences, University of Chicago, 5734 S Ellis Ave, Chicago, IL 60637, HELZ, Rosalind T., US Geological Survey, M.S. 926A, Reston, VA 20192, ROSKOSZ, Mathieu, Unite Materiaux et Transformations, Universite ́ de Lille 1, Bat. C6, Villeneuve d’Ascq, 59655, France, MA, Chi, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 and SAUTTER, Violaine, Laboratoire de Minéralogie et Cosmochimie du Muséum, Museum National d'Histoire Naturelle, Paris, 75005
In the field of diffusion-based geospeedometry, a challenging task is to identify diffusive transport in chemically zoned minerals. The difficulty comes from the fact that diffusion profiles may not be easily distinguished from concentration gradients inherited during crystal growth. Teng et al. (2011) and Dauphas et al. (2010) recognized that Mg-Fe isotopic analyses could be used to identify diffusive transport in olivine. From analyzing olivine fragments from Kilauea Iki lava lake, HI, Teng et al. (2011) showed that Mg-Fe isotopic compositions in these olivines are negatively correlated. This observation can only be explained by Mg-Fe interdiffusion as light isotopes diffuse faster than their heavier counterparts (Richter et al., 2009). This discovery led Sio et al. (2013) to use micro-analytical techniques to spatially resolve Mg-Fe isotopic profiles in a zoned olivine phenocryst from Kilauea Iki lava lake, showing unambiguous evidence that diffusive transport in olivine is accompanied by large and negatively coupled Mg-Fe isotopic profiles.
Laser ablation MC-ICPMS and SIMS techniques have been developed to analyze Mg-Fe isotopes in chemically zoned olivines, providing spatial resolutions of ~50 microns and precisions of ~0.2 ‰ in δ56Fe and δ26Mg (1 SD). These techniques have been validated by good agreements with Mg-Fe isotopic data obtained using microdrilling followed by MC-ICPMS on the same zoned olivines.
Using these in-situtechniques, diffusive transport has been recognized in martian olivines. Diffusion calculations have been performed to evaluate the effects of melt evolution, crystal growth history, and crystal geometry on Mg-Fe isotopic fractionations. The formulations developed can be used to model chemical-isotopic compositions of zoned olivines to constrain thermal histories.
[1] Teng et al., (2011). EPSL, 308(3), 317-324. [2] Dauphas et al., (2010), 74(11), 3274-3291. [3] Richter et al., (2009) Chemical Geology, 258(1), 92-103. [4] Sio et al., GCA, 123, 302-321.
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