Petrology, phase equilibria modelling, noble gas chronology and thermal constraints of the El Pozo L5 meteorite

作者：Corona Chavez Pedro^*; Hernandez Bernal Maria Del Sol; Vignola Pietro; Lozano Santacruz Rufino; Morales Contreras Juan Julio; Reyes Salas Margarita; Sole Vinas Jesus; Molina Jose F

来源：Chemie der Erde, 2018, 78(2): 248-253.

DOI：10.1016/j.chemer.2017.12.003

• Ordinary chondrite
• El Pozo
• Petrology
• Metamorphism
• Phase equilibria modelling
• Thermobarometry
• Cosmogenic ages

We present the results of physical properties, petrography, bulk chemistry, mineral compositions, phase relations modelling and Noble gases study of the meteorite El Pozo. The petrography and mineral compositions indicate that the meteorite is an L5 chondrite with a low shock stage of S2-S3. Heterogenous weathering was preferentially along shock structures. Thermobarometric calculations indicate thermal equilibrium conditions between 768 degrees C and 925 degrees C at similar to 4 to 6 kb, which are substantially consistent with the petrological metamorphism type 5. A pseudosection phase diagram is relatively consistent with the mineral assemblage observed and PT conditions calculated. Temperature vs. fO(2) diagram shows that plagioclase compositional stability is very sensitive to Tschermack substitution in orthopyroxene, clinopyroxene and X-An plagioclase during the high temperature metamorphic process. Based on noble gases He, Ne, Ar and K contents a cosmogenic exposure age CRE of 1.9 Myr was calculated. The Ne-21 would be totally cosmogenic, with no primordial Ne. The Ne-21/Ne-22 value (0.97) is higher than solar value. According to the cosmogenic Ne content, we argue that El Pozo chondrite originally had a pre-atmospheric mass of 9-10 kg, which would have been produced by a later collision after the recognized collision of the L-chondrite parent body similar to 470 Ma ago.

• 出版日期2018