Discipline: Ecology Environmental and Earth Sciences
Subcategory: Geosciences and Earth Sciences
Lucia Mallozzi - Stony Brook University
Co-Author(s): Glenn MacPherson, Smithsonian National Museum of Natural History, Washington, D.C.; Cari Corrigan, Smithsonian National Museum of Natural History, Washington D.C.
Chondrites are a category of meteorites that contain highly refractory inclusions such as CAIs (Calcium Aluminum Inclusions), AOAs (Amoeboid Olivine Aggregates), and chondrules (olivine-pyroxene glass). These components are planetary building blocks that predate planetary formation, forming bodies that are currently recognized as asteroids, moons and terrestrial planets. CVs, Carbonaceous Vigarano-like chondrites, are a chondrite group noted for their high abundance of large CAI’s (up to ~2 cm) and chondrules. In understanding their signature features, mineralogical, textural and petrological deviations from these understood “norms” can provide unique insight into secondary processes that took place on its parent body after its formation. When classifying chondtires, a numerical petrologic type from 1 to 6 is given to account for these deviations: 1-2 representing degrees of aqueous alteration, 3.0-3.9 representing degrees of “pristine” or unaltered components, and a 4-6 type representing degrees of thermal metamorphism. Of the classified CV chondrites, all have been classified as a petrologic type 3. However, in CV chondrite NWA 8418, there are distinct features that suggest thermal alteration in what could be the first CV4 chondrite. The existence of a CV4 chondrite would allow for unique insight into secondary processing on asteroidal parent bodies that was once unavailable to scientists. To test for type 4, data for NWA 8418 was collected using optical microscopy in both plane and cross-polarized light, backscattered electron (BSE) imaging, and X-ray elemental area mapping. The images were produced by a FEI Nova NanoSEM 600 at the Smithsonian Institution, operating at 15 keV, with a spot size between 4.5-5.5 and a ≤5% dead time. Images were processed using Noran System Six software. The preliminary data yielded results that are highly suggestive of “4” petrologic type. The evidence includes the replacement of melilite with Na-rich plagioclase within NWA 8418 CAIs, rounded and relatively homogenized matrix olivine grains, and the breakdown of chondrules from glass into constituent mineral crystals such as enstatite. The preliminary data for NWA 8418 warrants further testing to confirm that is a CV4. Future test includes Al/Mg isotopic testing, electron hyper probe analysis, as well other investigative techniques before it can be officially classified as a CV4.
Funder Acknowledgement(s): National Science Foundation
Faculty Advisor: Cari Corrigan, email@example.com
Role: For this project, I collected all SEM data and X-ray spectra under the supervision of my mentor. I also processes the images and spectra that we collected using the Noran Six Software.