Termometría de dos piroxenos en condros de la condrita ordinaria Nuevo Mercurio H5, México

in this work we reconstructed the thermal history of some chondrules of nuevo mercurio h5 ordinary chondrite. we selected pyroxene-rich chondrules of different textural groups (rp, c and pp) showing diopsidic rims and exsolution textures and obtained 149 wds microprobe chemical analyses. in order to calculate the temperature, we used the quilf program for two-pyroxene thermometry, which yielded minimal values of crystallization because ca-poor pyroxene formed prior to ca-rich pyroxene. presence of contraction cracks, clinoenstatite raman spectra and enclosed olivine in enstatite phenocrysts suggest formation temperatures much greater than 1200 °c. the highest pyroxene temperatures were obtained for augite blebs and grains (1065-1232 °c), pigeonite lamellae (1037-1103 °c) and enstatite cores (1277-1284 °c). on the other hand, calculated temperatures for augite lamellae and diopsidic rims are 933-817 °c, whilst enstatite reached temperatures from 915-988 °c. we found in the five chondrules of nuevo mercurio that diopside rims and ca-rich augite lamellae reached a minimum temperature range between 817 °c and 933 °c, and interpreted this temperature range as the peak of thermal metamorphism. we conclude that pyroxene temperatures from nuevo mercurio chondrules had two origins: the highest, albeit minimum temperatures (1283-915 °c) preserved from chondrule formation, and the lowest temperatures (933-817 °c) reflecting prograde thermal metamorphism well inside the chondritic parental body, as suggested by the low cooling rate reported by other authors of 15 °c/ma. we performed mineragraphic analysis of troilite + fe-ni alloys in order to verify that the metamorphic peak did not reach the eutectic temperature of this opaque minerals association at 988 °c. x-ray diffraction data detected sodic plagioclase, a secondary recrystallization product confirming the thermal metamorphism grade 5.