Sigmoidal exsolution by internal shear stress in pyroxenes from chondritic meteorites |
| |
| Authors: | Ferraris C Folco L Mellini M |
| |
| Institution: | (1) Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, 53100 Siena, Italy;(2) Institute of Environmental Science Engineering, Nanyang Technological University, Innovation Centre Block 2, Unit 247, 18 Nanyang Drive, Singapore, 637723;(3) Museo Nazionale dell Antartide, Università di Siena, Via Laterina 8, 53100 Siena, Italy |
| |
| Abstract: | Pyroxenes of pigeonitic and augitic bulk compositions in H3–4 chondritic meteorites commonly exhibit sigmoidal precipitates, rather than the elsewhere common lamellar associations. Most often, submicrometric sigmoids with calcic clinopyroxene composition occur within clinoenstatite; more rarely, clinoenstatite sigmoids occur within calcic clinopyroxene. The sigmoids appear as  001 terminated lamellae, with terminations rotated in opposite directions towards the 100 orientation. Pre-exsolution pigeonite and augite formed at temperatures higher than 980 °C, whereas sigmoidal exsolution occurred between 990 and 830 °C. Local anomalous lattice parameters determined by electron diffraction suggest that lattice parameters are most strained where the exsolution texture is most poorly defined. Shear strain occurs during exsolution due to mismatching lattice parameters and variable  angles. In response to shear stress, the lamellae relax and assume sigmoidal strained morphologies. Sigmoidal exsolution is strongly controlled by (100) orthoenstatite stacking faults that possibly trigger exsolution. |
| |
| Keywords: | Exsolution Pyroxene Chondrule Sigmoids Shear stress |
| 本文献已被 SpringerLink 等数据库收录！ |
|
