The Stillwater Complex chromitites : the response of chromite crystal chemistry to magma injection
(Montanuniversität Leoben. Department of Mathematics and Geosciences)Garuti, G.
(Montanuniversität Leoben. Department Applied Geosciences and Geophysics)Zaccarini, F.
(Department Applied Geosciences and Geophysics)Cooper, R. W.
(Lamar University. Department of Geology)Princivalle, F.
(Università degli Studi di Trieste. Dipartimenti di Matematica e Geoscienze)
||Nineteen chromite crystals from the A, B, E, G, H, J and K chromitite layers of the Peridotite Zone of the Stillwater Complex (Montana, USA) have been studied by means of X-ray single crystal diffraction and microprobe analyses. The results show that samples from the basal A layer are quite different from the others showing very high oxygen positional parameter u (0. 2633-0. 2635) and Ti- contents (0. 059-0. 067apfu). Mg# values are within the range 0. 21-0. 23 while for the other chromites it is in the range 0. 45-0. 47. Moreover, for the other samples, according to the structural parameters, two groups have been identified. The first one comprises samples of layers B, E and G, the second includes H, J and K layer samples. It is supposed that high Fe2+ and Ti contents of A layer samples are due to the post-crystallization reaction with interstitial liquid. This fact allowed a very slow cooling rate as evidenced by the high u values. The fractionation of evolved magma from within the intrusion and pulse of a new magma bringing more chromium into the chamber lead to Cr- and Fe3+ -rich compositions and consequently to the increase of the cell edges. The decrease of u values seems to be related to the Cr+Fe3+ and/or Al contents.
||Tots els drets reservats
||article ; publishedVersion
X-ray single crystal diffraction ;
Structural refinement ;
||Geologica acta, Vol. 10, Núm. 1 (Març 2012) , p. 33-41, ISSN 1696-5728
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Record created 2012-04-13, last modified 2012-07-18