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Boletín de la Sociedad Geológica Mexicana Volumen 72, núm. 3, A120620, 2020 |
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Petrology and geochemistry of high-Al chromitites from the MedellÍn Metaharzburgitic Unit (MMU), Colombia
Petrología y geoquímica de cromititas ricas en Al de la Unidad Metaharzburgítica de Medellín (UMM), Colombia
Juan S. Hernández-González1,2, Lídia Butjosa1, Núria Pujol-Solà1,*, Thomas Aiglsperger3,
Marion Weber4, Mónica Escayola5, Carlos Ramírez-Cárdenas1, Idael F. Blanco-Quintero6,
José María González-Jiménez7, Joaquín A. Proenza1
1 Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, C/ Martí i Franquès s/n, 08028, Barcelona, Spain.
2 Departamento de Mineralogia e Geotectônica, Instituto de Geociências (GMG-IGc), Universidade de São Paulo, Rua do Lago 562, 05508-080, São Paulo, Brazil.
3 Department of Civil Engineering and Natural Resources, Division of Geosciences and Environmental Engineering, Luleå University of Technology, SE 97187, Luleå, Sweden.
4 Departamento de Geociencias y Medio Ambiente, Facultad de Minas, Universidad Nacional de Colombia, Avenida 80 # 65-223, 050034, Medellín, Colombia.
5 Instituto de Ciencias Polares y Ambientales ICPA, Universidad de Tierra del Fuego-CONICET, Fueguia Basket 251, 9410, Ushuaia, Tierra del Fuego, Argentina.
6 Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Carretera de San Vicente del Raspeig s/n, 03690, Alicante, Spain.
7 Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, 18002, Granada, Spain.
* Corresponding author: (N. Pujol-Solà) This email address is being protected from spambots. You need JavaScript enabled to view it.
How to cite this article:
Hernández-González, J.S., Butjosa, L., Pujol-Solà, N., Aiglsperger, T., Weber, M., Escayola, M., Ramírez-Cárdenas, C., Blanco-Quintero, I.F., González-Jiménez, J.M., Proenza, J.A., 2020, Petrology and geochemistry of high-Al chromitites from the Medellin Metaharzburgitic Unit (MMU), Colombia: Boletín de la Sociedad Geológica Mexicana, 72 (3), A120620. http://dx.doi.org/10.18268/BSGM2020v72n3a120620
Abstract
The Medellin Metaharzburgitic Unit (MMU), emplaced onto the western continental margin of Pangea during Triassic time, is located in the Central Cordillera of Colombia and consists of metaharzburgites, minor metadunites and chromitite bodies (Patio Bonito and San Pedro ore deposits). The ultramafic rocks contain relicts of mantle-derived olivine, chromian spinel and minor orthopyroxene, and a later metamorphic mineral assemblage composed by tremolite, chlorite, talc, fine-grained recrystallized olivine, serpentine-group minerals, magnetite, and secondary chromian spinel, formed during the thermal evolution of the unit. The Cr# [Cr/(Cr+Al) atomic ratio] of the accessory primary chromian spinel in the metaperidotites ranges from 0.58 to 0.62 and overlaps those of supra-subduction peridotites from ophiolites. According to textural and compositional variations, the accessory chromian spinel in the metaperidotites can be classified into three groups: i) partially altered chromian spinel with an Al-rich core, ii) porous, Cr-Fe2+-enriched and Al-Mg-depleted chromian spinel, and iii) homogeneous Fe3+-rich chromian spinel. These variations can be related to superimposed medium-T metamorphism that reached amphibolite facies (ca. 600 ºC). Chromitite bodies associated with the metaperidotites have massive and semi-massive textures, and mainly consist of chromian spinel crystals, which show large unaltered cores surrounded by thin alteration rims of ferrian chromian spinel and chlorite. Chromitites are Al-rich (#Cr <0.6) and strongly depleted in platinum group elements (ΣPGE <41 ppb). The primary petrological and geochemical characteristics preserved in the metaperidotites and chromitites indicate that the MMU formed at shallow levels of a suboceanic lithospheric mantle related to a supra-subduction zone (back-arc basin/incipient arc scenario), and that the chromitites crystallized from a tholeiitic magma (back-arc basin basalt type).
Keywords: Metaperidotite, chromian spinel, chromitite, ophiolite, supra-subduction zone, Colombia.
