A reappraisal of the metamorphic history of the Tehuitzingo chromitite, Puebla state, Mexico
Por:
Colas, Vanessa, Maria Gonzalez-Jimenez, Jose, Camprubi, Antoni, Proenza, Joaquin A., Griffin, William L., Fanlo, Isabel, O'Reilly, Suzanne Y., Gervilla, Fernando, Gonzalez-Partida, Eduardo
Publicada:
22 sep 2019
Categoría:
Geology
Resumen:
The Tehuitzingo ultramafic body (Acatlan Complex, southern Mexico) is a
strongly serpentinized harburgitic body that encloses chromitite bodies
and blocks of eclogitic rocks. Hydrous retrograde metamorphism on
chromitite bodies resulted in the formation of: i) partly altered
chromite characterized by unaltered cores surrounded by Fe2+-rich and
Al-depleted porous chromite containing chlorite; ii) porous chromite
corresponding to a chromite that was entirely transformed to Fe2+-rich
and Al-depleted porous chromite; and iii) zoned chromite formed by
modified cores surrounded by Fe3+-rich non-porous chromite and magnetite
rims. The content of minor and trace elements (Ga, Ti, Ni, Zn, Co, Mn,
V, Sc) in the cores of partly altered chromite preserves the magmatic
fingerprint of back-arc-bearing chromitites, while the cores of zoned
chromite are enriched in Zn, Co and Mn but depleted in Ga, Ti, Ni and
Sc, and display a metamorphic signature. P-T pseudosections performed in
the system CrMFASH allow us to constrain the temperature of formation of
Fe2+-rich chromite by reaction of magmatic chromite with olivine between
584 and 449 degrees C; while the new thermodynamic calculations
performed in the FMASH system shows that the Fe3+-rich non-porous
chromite and magnetite rims in zoned chromites were formed at lower
temperatures (i.e. 270-340 oC and < 20 kbar). Temperatures of alteration
obtained using our new thermodynamic model are in agreement with the
qualitative estimation that use minor and trace elements in Fe2+-rich
chromite (i.e. 560-700 oC). These temperatures are more restricted than
those estimated for chlorite hosted in partly altered (193-481 oC) and
porous chromite (158-255 oC), and those reported in host serpentinite
and associated eclogitic rocks (210-399 oC). A comparison of P-T
conditions estimated by our new thermodynamic models and the
distribution of minor and trace elements in the different zones of
chromites allow us to infer that the alteration took place during the
hydrous retrograde metamorphism, and that the high-pressure metamorphism
did not modify the composition of chromites. Thus, the microstructural
zoning displayed by chromite grains was formed during the exhumation of
a segment of a back-arc-related oceanic lithosphere, at similar
temperature conditions than the Tehuitzingo serpentinite.
Filiaciones:
Colas, Vanessa:
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, Mexico City 04510, DF, Mexico
Maria Gonzalez-Jimenez, Jose:
Univ Granada, Fac Ciencias, Dept Mineral & Petrol, Granada, Spain
Camprubi, Antoni:
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, Mexico City 04510, DF, Mexico
Proenza, Joaquin A.:
Univ Barcelona, Dept Mineral Petrol & Geol Aplicada, Barcelona, Spain
Griffin, William L.:
Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst CCFS, Dept Earth & Planetary Sci, Sydney, NSW, Australia
Macquarie Univ, GEMOC Natl Key Ctr, Sydney, NSW, Australia
Fanlo, Isabel:
Univ Zaragoza, Dept Ciencias Tierra, Zaragoza, Spain
O'Reilly, Suzanne Y.:
Macquarie Univ, ARC Ctr Excellence Core Crust Fluid Syst CCFS, Dept Earth & Planetary Sci, Sydney, NSW, Australia
Macquarie Univ, GEMOC Natl Key Ctr, Sydney, NSW, Australia
Gervilla, Fernando:
Univ Granada, Fac Ciencias, Dept Mineral & Petrol, Granada, Spain
Univ Granada, CSIC, Inst Andaluz Ciencias Tierra, Granada, Spain
Gonzalez-Partida, Eduardo:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Queretaro, Mexico
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