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Magnetite in the carbonatites from the Jacupiranga Complex, Brazil

Gaspar, Jose C. and Wyllie, Peter J. (1983) Magnetite in the carbonatites from the Jacupiranga Complex, Brazil. American Mineralogist, 68 (1-2). pp. 195-213. ISSN 0003-004X. https://resolver.caltech.edu/CaltechAUTHORS:20160203-110819188

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Abstract

Electron microprobe analyses of magnetites from five carbonatite intrusions (C_1, oldest, to C_5, youngest) constituting the carbonatite plug in the Jacupiranga complex confirm previous results from Jacupiranga giving compositions in the magnesioferrite-magnetite series very close to Fe_3O_4. Magnetites from other carbonatites are similar with somewhat more Ti and less Mg. MgO in Jacupiranga magnetites reaches no more than 10 wt.%. All analyzed grains are zoned, with Fe_3O_4 increasing toward the rim. In magnetites from C_2 to C_5, Fe_2O_3 replacement is mainly by Al_2O_3 and less by TiO_2; in C_1 magnetites TiO_2 replacement is more important. Despite their limited range of compositions, the cores of magnetites in each of the five intrusions are chemically distinct and distinguishable from each other as indicated by projections from within the Cr-free spinel prism, MgFe_2O_4-Mg_2TiO_4-MgAl_2O_4-Fe_3O_4-Fe_2TiO_4-FeAl_2O_4, and a plot of Mn ys. Mg. Magnetites from special locations such as dikes, banded reaction zones between carbonatite and jacupirangite, and in intergrowths with pyrite, are chemically related but distinct from the carbonatite magnetites. The systematic chemical variation and zoning of magnetites in the five carbonatite intrusions indicate magmatic origin. Magnetite crystals nucleated throughout the crystallization interval of the carbonatites, but most of them show evidence of marginal resorption. The oldest carbonatite, C_1, was probably derived from a magma somewhat different chemically from those producing carbonatites C_2 through C_5. The precipitation of carbonatite C_2 probably went to completion independently of C_3 through C_5, whereas carbonatites C_3 through C_5 probably were precipitated from successive batches of magma representing a continuum in time and magmatic evolution.


Item Type:Article
Related URLs:
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http://www.minsocam.org/msa/collectors_corner/amtoc/toc1983.htmPublisherIssue Table of Contents
Additional Information:© 1983 Mineralogical Society of America. Manuscript received, February 11, 1982; accepted for publication, September 7, 1982. We thank Serrana S/A de Mineração, G. C. Melcher, and V. A. V. Girardi for making possible the field work of JCG, I. M. Steele for invaluable assistance with microprobe analyses and for the computer program to calculate Fe3+, and J. V. Smith for assistance with the microprobe. Financial support was provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) PROC 201.158/80 and PROC 40.1410/81, Fundação de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP) PROC 80/470 and PROC 81/0168-8, and the Earth Science Division of the National Science Foundation Grants EAR 76-20410, and EAR 81-08599.
Funders:
Funding AgencyGrant Number
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)PROC 201.158/80
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)PROC 40.1410/81
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)PROC 80/470
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)PROC 81/0168-8
NSFEAR 76-20410
NSFEAR 81-08599
Issue or Number:1-2
Record Number:CaltechAUTHORS:20160203-110819188
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160203-110819188
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64196
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Feb 2016 23:08
Last Modified:03 Oct 2019 09:35

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