Kinetics of Sr and Nd exchange in silicate liquids: Theory, experiments, and applications to uphill diffusion, isotopic equilibration, and irreversible mixing of magmas

Journal Article · Tue May 10 04:00:00 EDT 1994 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JB00469· OSTI ID:135829

Lesher, C E ^[1]

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1. Univ. of California, Davis, CA (United States)

Diffusion coefficients that govern chemical and isotopic exchange of Sr and Nd were determined from compositional profiles developed between juxtaposed anhydrous basaltic and rhyolitic liquids. Analysis of simple diffusion couples involving isotopically enriched and normal tholeiitic basalt and metaluminous rhyolite recover Sr and Nd self-diffusion coefficients (D{sup *}) in the end-member compositions of contrasting polymerization. Self-diffusion of Sr is 7 times faster in basaltic melt than rhyolitic melt at 1255{degrees}C and 1 GPa, while self-diffusion of Nd is more than 1 order of magnitude greater in basalt than rhyolite. Also, at these conditions, D{sub Sr}{sup *} is a factor of 3 greater than D{sub Nd}{sup *} in basalt and an order of magnitude greater than D{sub Nd}{sup *} in rhyolite. The results of a Botlzmann-Matano analysis of {sup 87}Sr/{Sigma}Sr and {sup 144}Nd/{Sigma}Nd profiles of complex diffusion couples composed of isotopically normal basalt and enriched rhyolite yield diffusion coefficients for intermediate bulk compositions in agreement with interpolated values given by the relationships above. An important feature of the interdiffusion of basaltic and rhyolitic liquids is the equilibration of isotopic composition in advance of chemical homogenization. This behavior is best displayed by Sr in the present experiments and predicted for Nd. These results are considered in a magmatic context, where intimate blending of magmas during mixing is frustrated by large rheological contrasts and/or insufficient exposure time. Time-dependent diffusional exchange between mingling magmas leads to covariations in chemical and isotopic compositions that differ markedly from the expectations of bulk mixing. Examples presented offer alternative interpretations for the compositional relationships found among magmatic rocks of hybrid origin. 63 refs., 14 figs., 4 tabs.

• DOE Contract Number: FG03-92ER14240
• OSTI ID: 135829
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B5 Vol. 99; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
DIFFUSION
MAGMA
MIXING
NEODYMIUM
SILICATES
STRONTIUM
TRACER TECHNIQUES