¹Davide Lenaz,²Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12885]
¹Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy
²Division of Nuclear Physics, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

Six Cr-spinel grains from NWA 6077 brachinite-like and NWA 725 winonaite achondrites have been studied by single-crystal X-ray diffraction and structural refinement. From a chemical point of view, spinels from NWA 6077 show Cr/(Cr + Al) (i.e., Cr#) and Mg/(Mg + Fe2+) (i.e., Mg#) values similar to other brachinites, while the Cr# of NWA 725 is lower than that of literature winonaites. Spinels from NWA 6077 and NWA 725 meteorites show similar cell edges, while the oxygen positional parameter is rather different being about 0.2629 for NWA 6077 and 0.2622 for NWA 725. Considering both parameters, NWA 725 shows structural features that are close to some terrestrial spinel occurrences as in komatiites, kimberlites, or included in diamonds; those from NWA 6077 show values that have no terrestrial analogs. Olivine-chromite closure temperature ranges from ~737 to ~765° C for NWA 725, being similar to that of literature winonaites and ~846 to ~884° C for NWA 6077. The logfO2 ranges from −19.8 to −20.5 and −17.0 to −17.9 for the two meteorites, respectively. The u values for terrestrial samples can give information about the cooling history of the samples. For the extraterrestrial samples, it seems that it can give information about the cooling only for spinels where it is lower than 0.2625. For higher values, it appears related only to the chemistry of the spinels.

¹Dwijesh Ray,²Dewashish Upadhyay,³Saumitra Misra,⁴Horton E. Newsom,¹Sambhunath Ghosh
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12881]
¹Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, India
²Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
³Discipline of Geological Sciences, SAEES, University of KwaZulu-Natal, Durban, South Africa
⁴Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

The Lonar impact crater, India, is one of the few known terrestrial impact craters excavated in continental basaltic target rocks (Deccan Traps, ~65 Ma). The impactites reported from the crater to date mainly include centimeter- to decimeter-sized impact-melt bombs, and aerodynamically shaped millimeter- and submillimeter-sized impact spherules. They occur in situ within the ejecta around the crater rim and show schlieren structure. In contrast, non–in situ glassy objects, loosely strewn around the crater lake and in the ejecta around the crater rim do not show any schlieren structure. These non–in situ fragments appear to be similar to ancient bricks from the Daityasudan temple in the Lonar village. Synthesis of existing and new major and trace element data on the Lonar impact spherules show that (1) the target Lonar basalts incorporated into the spherules had undergone minimal preimpact alteration. Also, the paleosol layer as preserved between the top-most target basalt flow and the ejecta blanket, even after the impact, was not a source component for the Lonar impactites, (2) the Archean basement below the Deccan traps were unlikely to have contributed material to the impactite parental melts, and (3) the impactor asteroid components (Cr, Co, Ni) were concentrated only within the submillimeter-sized spherules. Two component mixing calculations using major oxides and Cr, Co, and Ni suggest that the Lonar impactor was a EH-type chondrite with the submillimeter-sized spherules containing ~6 wt% impactor components.