Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by CHEN, M. Articles by GILLET, P. Search for Related Content GeoRef GeoRef Citation

Melting experiments of a chondritic meteorite between 16 and 25 GPa

¹ Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, P.R. China.
² Max-Planck-Institut für Chemie, D-55128 Mainz, Germany
³ Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany
⁴ Ecole Normale Superieure de Lyon, F-69364 Lyon Cedex, France

^* Corresponding author, e-mail: mchen{at}gig.ac.cn

Melting experiments at high-pressure and temperature were conducted at pressures from 16 to 25 GPa using chondritic starting material but with slightly enhanced Na- and K-contents while keeping the chondritic Na/K ratio constant. The experiments revealed that majorite garnet contains enhanced concentrations of Na (3.75–4.71 wt.% Na₂O) and moderately enhanced concentrations of K (0.3–0.46 wt.% K₂O) from 16 to 20 GPa and it is therefore the Na- and K-bearing phase at this pressure range. The Na₂O/K₂O ratio (8–15) in garnet is close to the initial chondritic ratio (7) of the starting material, which might indicate that at these pressures only little Na/K fractionation takes place. At pressures above 21 GPa, the high-pressure phases enriched in Na include majorite garnet (3.08–6.22 wt.% Na₂O), magnesiowiistite (1.83–3.3 wt.% Na₂O), and (Mg, Fe)SiO₃-perovskite (0.43–1.25 wt.% Na₂O). These phases contain only small amounts of K (<0.1 wt.% K₂O). The Na₂O content of magnesiowüstite progressively increases with increase of pressure, whereas Na₂O contents of garnet and perovskite are negatively correlated with pressures between 23 and 25 GPa. Na/K fractionation takes place among the high-pressure phases (Na₂O/K₂O ratio: 56–102 in garnet, 5–20 in perovskite, and 43–94 in magnesiowüstite), and between the high-pressure phases and the residual silicate melt above 21 GPa, and most of the K is partitioned into the residual melt. The hollandite-stractured, high-pressure KAlSi₃O₈polymorph crystallizes from the liquid at 23 GPa. These results demonstrate that Na/K fractionation at P > 21 GPa should have taken place in the early accretional period in the primitive chondritic mantle of the Earth.

Key-words: melting experiment, high pressure, chondritic meteorite, alkali element, fractionation.

This article has been cited by other articles:

				P. Gillet, A. El Goresy, P. Beck, and M. Chen High-pressure mineral assemblages in shocked meteorites and shocked terrestrial rocks: Mechanisms of phase transformations and constraints to pressure and temperature histories Geological Society of America Special Papers, January 1, 2007; 421(0): 57 - 82. [Abstract] [Full Text] [PDF]