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The effects of superheating and cooling rate on olivine growth in chondritic liquid

Auxerre, M. ; Faure, F. ; Lequin, D., Meteoritics & Planetary Science

The effects of superheating and cooling rate on olivine growth in chondritic liquid

Auxerre, M. ; Faure, F. ; Lequin, D.

Meteoritics & Planetary Science, 2022, 1-22

Abstract :

Chondrules, the major constituent of chondrites, are millimeter-sized igneous objects resulting from the crystallization of silicate liquids produced by the partial orcomplete melting of chondritic precursors, whose exact nature remains disputed. Variouschondrule textures are observed as a function of the extent of the initial melting event.Here, we report dynamic crystallization experiments performed with a broad range ofcooling rates (2–750°Ch−1) from superliquidus or subliquidus initial conditions todemonstrate the control of nucleation on the final chondrule texture. Classical crypto-porphyritic, micro-porphyritic, and porphyritic olivine textures were reproduced insubliquidus experiments in which heterogeneous nucleation dominates. In contrast, we wereunable to reproduce barred olivine textures, regardless of the cooling rates investigated fromsuperliquidus conditions ; instead, macro-porphyritic textures were systematically obtained atlow cooling rates (<10°Ch−1). The small number and large size of crystals in the macro-porphyritic texture are consistent with the initial step of superheating and the presence oflong embayments that indicate an initial episode of rapid growth due to delayed nucleation.Crystals then acquired polyhedral shapes during a subsequent episode of slow growth.When the growth rate is too slow to decrease the degree of supersaturation in the liquid, anew episode of rapid growth produces a new generation of melt inclusions

Voir en ligne : https://doi.org/10.1111/maps.13830




publié jeudi 9 juin 2022