Three-dimensional petrography of metal phases in equilibrated L chondrites—Effects of shock loading and dynamic compaction

• Published in: Earth and planetary science letters 2008-10, Vol.275 (1), p.172-180
• Main Authors: Friedrich, Jon M., Wignarajah, Douglas P., Chaudhary, Shahrukh, Rivers, Mark L., Nehru, C.E., Ebel, Denton S.
• Format: Article
• Language: English
• Subjects: asteroid; ASTEROIDS; chondrite; CHONDRITES; COMPACTING; DISTRIBUTION; DYNAMIC LOADS; foliation; GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; GRAIN ORIENTATION; GRAIN SIZE; Impact; IMPACT TESTS; IRON; LOADING; METALS; METEORITES; MORPHOLOGY; NICKEL; PETROGRAPHY; PRESSURE RANGE GIGA PA; RESOLUTION; SHOCK WAVES; THREE-DIMENSIONAL CALCULATIONS; TOMOGRAPHY; X RADIATION; X-ray microtomography
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2008.08.024

To examine the role of impacts in the evolution of asteroids as seen through their chondritic offspring, we have performed a quantitative three dimensional (3D) study of metal grains in a suite of increasingly shocked L chondrites with synchrotron X-ray microtomography (XMT). Our data allow rigorous quantification of size-number distributions and collective morphology of Fe(Ni) metal phases in chondritic meteorites. At the resolution of our XMT measurements (8.4–17.9 μm/voxel), the number of metal particles increase with higher degrees of petrographically identified shock loading, indicating a coalescing of Fe–Ni metal at or below this scale. Our results demonstrate that collective degrees of metal grain preferred orientation increase with greater degrees of impact-related compaction and shock loading. Ductile metal grains in L chondrites begin to show foliation at peak shock pressures < 5 GPa, pressures great enough to compact and indurate loosely bound chondritic material, and our results constitute evidence for multiple generations of impact events acting on the L parent body or bodies.