Basaltic glass and alteration mineralogy: Terrestrial impact site analogs
Abstract
Lonar Crater, India provides a unique analog impact site with primary and secondary minerals contained in fresh and altered basalts. Both are transformed to a range of impact glasses. Our sample collection from the Lonar ejecta blanket contains alteration minerals of importance for Mars exploration because of their implications for water-rock interactions. Fieldwork and corresponding laboratory sample analyses suggest further studies are warranted and will benefit the goals of the Mars Program. Lonar Crater is seen as a good Mars analog site because of the basaltic host rock, an interlayer development of baked zones/boles and soil. The lower three of six flows were aqueously altered to produce products similar to what is seen on Mars: hematite, chlorite, serpentine, zeolite, and palagonite as well as impactites. Fieldwork shows that the ejecta consists of two layers: 1 m of suevite breccia with clasts from a large range of shock pressures, which overlies 8 m of lithic breccia comprised of relatively unshocked clasts. The alteration mineralogy of every ejecta lobe is being mapped at a detailed scale similar to that for Meteor Crater, Arizona by Shoemaker. Several types of pre-impact alteration (generally named by their color or alteration mineral listed above) are categorized to compare to their shocked equivalents. Laboratory analysis includes thermal infrared (TIR) emission spectroscopy of the unshocked and shocked basalts as well as a new approach gathering TIR emission spectra of samples directly undergoing melting via a microfurnace. Both fresh and altered (unshocked) basalts are measured at temperatures up to and above their liquidus. This ultimately forms a glass with the composition of the original starting material that is compared to the impact-related glasses. The melting approach also allows for mineralogical changes to be measured as a function of temperature. We are examining ratios of augite:labradorite:glass that would differentiate between glasses produced by impact versus volcanic origins. For example, augite and calcic labradorite have a range of melting temperatures that we are attempting to pinpoint for Deccan basalt. However, because the Hugoniot Elastic Limit for labradorite is lower than for augite, maskelynite-bearing basalts still have crystalline, albeit highly fractured, augite.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P31H3804W
- Keywords:
-
- 5464 Remote sensing;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5470 Surface materials and properties;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5494 Instruments and techniques;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5499 General or miscellaneous;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS