High-pressure crystal chemistry of large ions with attention to their distribution in the upper mantle

Large ions, such as K⁺, are considered to be relatively volatile and lithophile, contributing to melt processes in the Earth and their ultimate concentration in the crust. Nevertheless, the mantle retains some of these elements in heterogeneous reservoirs and subduction and collisional tectonics lead to high-pressure reprocessing of crustal components, including the large ions, with some recycling into the mantle. The research involves experimental investigation at high pressure and temperature of potassium-, fluorine-, and “water”-bearing phases potentially stable in Earth’s upper mantle. Results have shown the P-dependence of K uptake in clinopyroxene and amphibole, the stability of KMgF₃, a perovskite phase, as a breakdown product of F-bearing phlogopite, the enhanced pressure-stability of chondrodite and clinohumite with increasing F-content. Present studies with research scientist Rondi Davies have been determining the high pressure stability limits of K-cymrite (KAlSi₃O₈•nH₂O; n≤1), the hydrous analog of K-feldspar, which is stable to at least 9 GPa and 1100 °C, with evidence that melting occurs without the presence of K-cymrite where H₂O > KAlSi₃O₈. Results from the research are being used to improve predictions of the storage of potassium, fluorine, and water in reservoirs in the mantle as compared to the elements’ partitioning into fluids and melts. This research was supported by the National Science Foundation under Grants No. 9903203 and 9314819.

Recent papers and abstracts:

Harlow, G. E. (1997) Potassium in clinopyroxene at high pressure and temperature: An experimental study. American Mineralogist, 82, 259-269.

Harlow, G.E. (1999) Interpretation of Kcpx and CaEs in Clinopyroxene from Diamond Inclusions and Mantle Samples. In: Proceedings of Seventh International Kimberlite Convention (J.J. Gurney, J.L. Gurney, M.D. Pascoe & S.H. Richardson, eds.), Redroof Design Cc, Cape Town; Vol. I, 321 - 331.

Davies, R. and Harlow, G.E. (2002) The High Pressure Stability of K-Cymrite and Phases in the System Or-H₂O. EOS Transactions AGU, 83, Fxxx.

Harlow, G.E. (2002) Diopside + F-rich phlogopite at high P and T: Systematics, crystal chemistry and the stability of KMgF₃, clinohumite and chondrodite. Geological Materials Research v4n3. (http://gmr.minsocam.org/Papers/v4/v4n3/v4n3abs.html)

Mancini, F., Harlow, G.E., and Cahill, C. (2002) The crystal structure and cation ordering of Phase-X — (K_1-x-n)₂(Mg_1-n[Al,Cr]_n)₂Si₂O₇H_2x: A potential K-bearing phase in the mantle. American Mineralogist, 87, 302-306.

Origlieri, M.J., Downs, R.T., Thompson, R.M., Pommier, C.J.S., Denton, M.B., and Harlow, G.E. (2003) High-pressure crystal structure of kosmochlor, NaCrSi₂O₆, and systematics of anisotropic compression in pyroxenes. American Mineralogist 88, 1025-1032.

Harlow, G.E., and Davies, R. (2004) Status report on K-rich phases at mantle conditions. Selected Papers from the Eighth International Kimberlite Conference. Volume 2: The J. Barry Hawthorne Volume , Lithos 77, 647-653.

Davies, R., Fei, Y., and Harlow, G.E. (2004) Minor and trace element partitioning between α-, β- and γ-(Mg,Fe)₂SiO₄ in fertile peridotite KLB-1: a high pressure experimental study. Eos Trans. AGU Fall 85(47), Fall Meet. Suppl., Abstract V41C-1413.

Harlow, G.E., and Davies, R. (2005) Diamonds. Elements 1(2), 67-70.

Bindi, L., Downs, R.T. Harlow, G.E. Safonov, O.G. Litvin, Y.A., Perchuk, L.L., Uchida, H., and Menchetti, S. (in press) Compressibility of synthetic potassium-rich clinopyroxene: In situ high-pressure single-crystal X-ray study. American Mineralogist.