MULTICOMPONENT DIFFUSION IN BASALTIC MELTS

Citation
V. Kress et Ms. Ghiorso, MULTICOMPONENT DIFFUSION IN BASALTIC MELTS, Geochimica et cosmochimica acta, 59(2), 1995, pp. 313-324
Citations number
55
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
00167037
Volume
59
Issue
2
Year of publication
1995
Pages
313 - 324
Database
ISI
SICI code
0016-7037(1995)59:2<313:MDIBM>2.0.ZU;2-6
Abstract
Experimental results are presented for eighteen experiments exploring multicomponent chemical-diffusion in basaltic liquids. Experiments wer e performed in Columbia River Basalt (CRB) composition doped with abou t 5 wt% SiO2, TiO2, Al2O3, FeO, MgO, and CaO, under reducing condition s at 1 atm., at 1473 K, 1573 K, and 1723 K. Results indicate that diff usion behavior in CRB compositions is consistent with a simple Fick's law formulation. This Fickian behavior in CRB compositions contrasts w ith more complicated diffusion behavior observed in MgO-Al2O3-SiO2 and CaO-MgO-Al2O3-SiO2 melts. Results of CRB experiments are combined to calibrate a diffusion matrix (D) in CRB liquids at 1473 K, 1573 K, and 1723 K. Our D estimates indicate negative coupling between CaO and bo th FeO and Al2O3 components, though diagonal elements still dominate. These general features persist across the temperature range considered . Self- and tracer-diffusion data from the literature are used with th e predictive model of Richter (1993) to estimate a D matrix at 1573 K. The resulting matrix does not compare well with our measured 1573 K d iffusion matrix. It cannot be established if this discrepancy indicate s a failure of the Richter (1993) model, or merely reflects deficienci es in the available tracer- and self-diffusion data, or limitations in the melt activity model. Effective Binary Diffusion Coefficients (EBD C) were also estimated for TiO2, Al2O3, FeO, MgO, CaO at 1473 K, 1573 K, and 1723 K. These EBDC estimates are used to constrain a polytherma l Arrhenian model for the prediction of EBDC values at super-liquidus temperatures. Results of experiments on alkali diffusion in CRB compos itions are included to add Na2O and K2O to the polythermal EBDC model.