2 research outputs found
A reappraisal of the metamorphic history of the Tehuitzingo chromitite, Puebla state, Mexico
The Tehuitzingo ultramafic body (Acatlán 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 Fe-rich and Al-depleted porous chromite containing chlorite; ii) porous chromite corresponding to a chromite that was entirely transformed to Fe-rich and Al-depleted porous chromite; and iii) zoned chromite formed by modified cores surrounded by Fe-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 Fe-rich chromite by reaction of magmatic chromite with olivine between 584 and 449 °C; while the new thermodynamic calculations performed in the FMASH system shows that the Fe-rich non-porous chromite and magnetite rims in zoned chromites were formed at lower temperatures (i.e. 270–340 ÂşC 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 Fe-rich chromite (i.e. 560–700 ÂşC). These temperatures are more restricted than those estimated for chlorite hosted in partly altered (193–481 ÂşC) and porous chromite (158–255 ÂşC), and those reported in host serpentinite and associated eclogitic rocks (210–399 ÂşC). 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.This work was partially supported by the Consejo Nacional de Ciencia y TecnologĂa [155662]; DirecciĂłn General de Asuntos del Personal AcadĂ©mico, Universidad Nacional AutĂłnoma de MĂ©xico [IA101419]; European Regional Development Fund [00000]; Ministerio de EconomĂa y Competitividad [CGL2014-55949-R,CGL2015-65824-P,RYC-2015-17596