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Fluid-rock reactions in the 1.3Ga siderite carbonatite of the GrOnnedal-ika alkaline complex, Southwest Greenland

Journal article
Authors E. Ranta
G. Stockmann
T. Wagner
T. Fusswinkel
Erik Sturkell
E. Tollefsen
A. Skelton
Published in Contributions to Mineralogy and Petrology
Volume 173
Issue 10
ISSN 0010-7999
Publication year 2018
Published at Department of Earth Sciences
Language en
Links dx.doi.org/10.1007/s00410-018-1505-...
Keywords Carbonatites, Ferrocarbonatite, Metasomatism, LA-ICP-MS, Gronnedal-Ika, bearing aqueous-solutions, field-strength elements, ablation icp-ms, rare-earth, gardar province, elevated-temperature, liquid immiscibility, crystal-chemistry, hill carbonatite, syenite complex, Geochemistry & Geophysics, Mineralogy, donough wf, 1995, chemical geology, v120, p223, nge mj, 1995, earth and planetary science letters, v131, p225
Subject categories Geochemistry, Geophysics, Mineralogy

Abstract

Petrogenetic studies of carbonatites are challenging, because carbonatite mineral assemblages and mineral chemistry typically reflect both variable pressure-temperature conditions during crystallization and fluid-rock interaction caused by magmatic-hydrothermal fluids. However, this complexity results in recognizable alteration textures and trace-element signatures in the mineral archive that can be used to reconstruct the magmatic evolution and fluid-rock interaction history of carbonatites. We present new LA-ICP-MS trace-element data for magnetite, calcite, siderite, and ankerite-dolomite-kutnohorite from the iron-rich carbonatites of the 1.3Ga GrOnnedal-ika alkaline complex, Southwest Greenland. We use these data, in combination with detailed cathodoluminescence imaging, to identify magmatic and secondary geochemical fingerprints preserved in these minerals. The chemical and textural gradients show that a 55m-thick basaltic dike that crosscuts the carbonatite intrusion has acted as the pathway for hydrothermal fluids enriched in F and CO2, which have caused mobilization of the LREEs, Nb, Ta, Ba, Sr, Mn, and P. These fluids reacted with and altered the composition of the surrounding carbonatites up to a distance of 40m from the dike contact and caused formation of magnetite through oxidation of siderite. Our results can be used for discrimination between primary magmatic minerals and later alteration-related assemblages in carbonatites in general, which can lead to a better understanding of how these rare rocks are formed. Our data provide evidence that siderite-bearing ferrocarbonatites can form during late stages of calciocarbonatitic magma evolution.

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