Computer Science
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004m%26ps...39..711l&link_type=abstract
Meteoritics & Planetary Science, Vol. 39, No. 5, p.711-722
Computer Science
4
Scientific paper
Transmission electron microscopy was used to examine pyroxene microstructure in the Northwest Africa (NWA) 856 martian meteorite to construct its cooling and shock histories. All pyroxenes contain strained coherent pigeonite/augite exsolution lamellae on (001). The average width and periodicity of lamellae are 80 and 400 nm, respectively, indicating a cooling rate below 0.1 °C/hr for the parent rock. Pigeonite and augite are topotactic, with strained coherent interfaces parallel to (001). The closure temperature for Ca-Fe, Mg interdiffusion, estimated from the composition at the augite pigeonite interface, is about 700 °C. Tweed texture in augite reveals that a spinodal decomposition occurred. Locally, tweed evolved toward secondary pigeonite exsolutions on (001). Due to the decreasing diffusion rate with decreasing temperature, "M-shaped" concentration profiles developed in augite lamellae. Pigeonite contains antiphase boundaries resulting from the C2/c to P21/c space group transition that occurred during cooling. The reconstructive phase transition from P21/c clinopyroxene to orthopyroxene did not occur. The deformation (shock) history of the meteorites is revealed by the presence of dislocations and mechanical twins. Dislocations are found in glide configuration, with the [001](100) glide system preferentially activated. They exhibit strong interaction with the strained augite/pigeonite interfaces and did not propagate over large distances. Twins are found to be almost all parallel to (100) and show moderate interaction with the augite/pigeonite interfaces. These twins are responsible for the plastic deformation of the pyroxene grains. Comparison with microstructure of shocked clinopyroxene (experimentally or naturally shocked) suggests that NWA 856 pyroxenes are not strongly shocked.
Cordier Patrick
Devouard Bertrand
Guyot Francois
Leroux Hugues
No associations
LandOfFree
Pyroxene microstructure in the Northwest Africa 856 martian meteorite does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Pyroxene microstructure in the Northwest Africa 856 martian meteorite, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pyroxene microstructure in the Northwest Africa 856 martian meteorite will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1060705