Petrography, classification, oxygen isotopes, noble gases, and cosmogenic records of Kamargaon (L6) meteorite: The latest fall in India

Abstract

A single piece of meteorite fell on Kamargaon village in the state of Assam in India on November 13, 2015. Based on mineralogical, chemical, and oxygen isotope data, Kamargaon is classified as an L‐chondrite. Homogeneous olivine (Fa: 25 ± 0.7) and low‐Ca pyroxene (Fs: 21 ± 0.4) compositions with percent mean deviation of <2, further suggest that Kamargaon is a coarsely equilibrated, petrologic type 6 chondrite. Kamargaon is thermally metamorphosed with an estimated peak metamorphic temperature of ~800 °C as determined by two‐pyroxene thermometry. Shock metamorphism studies suggest that this meteorite include portions of different shock stages, e.g., S3 and S4 (Stöffler et al. ); however, local presence of quenched metal‐sulfide melt within shock veins/pockets suggest disequilibrium melting and relatively higher shock stage of up to S5 (Bennett and McSween ). Based on noble gas isotopes, the cosmic‐ray exposure age is estimated as 7.03 ± 1.60 Ma and nitrogen isotope composition (δ15N = 18‰) also correspond well with the L‐chondrite group. The He‐U, Th, and K‐Ar yield younger ages (170 ± 25 Ma 684 ± 93, respectively) and are discordant. A loss of He during the resetting event is implied by the lower He‐U and Th age. Elemental ratios of trapped Ar, Kr, and Xe can be explained through the presence of a normal Q noble gas component. Relatively low activity of 26Al (39 dpm/kg) and the absence of 60Co activity suggest a likely low shielding depth and envisage a small preatmospheric size of the meteoroid (<10 cm in radius). The Kr isotopic ratios (82Kr/84Kr) further argue that the meteorite was derived from a shallow depth.

Spectroscopy and Mineralogy of a New Meteorite Kamargaon (L6) Chondrite

“…The overall spectroscopic analysis of Kamargaon is consistent with the geochemical compositional analysis. While this manuscript was under review, a report on the fall of the Kamargaon meteorite has been reported by Ray et al (2017). Our present study confirms the classification of the meteorite as L6 chondrite.…”

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“…The presence of plagioclase indicates to weak nature shock 28 in Kamargaon, which have been already reported. 2 The antisymmetric Si-O stretching vibrations and antisymmetric O-Si(Al)-O deformations exhibits in the mid infrared spectra of Kamargaon correspondingly between 800 to 1150cm −1 and 400cm −1 to 500cm −1 . These band profiles are generally depends on the crystalline structure of the silicates and can therefore be used to identify the mineral phases.…”

“…The Kamargaon chondrite ( Figure 1) is a single fall (Kamargaon: 26°39ˊ01 ̋ N and 93° 46ˊ 02 ̋ E), on 13th November, 2015; its total known weight 12.095kg. [1][2][3] Earlier studies focused on the compositional analyses of the meteorite and assigned Kamargaon as an L6 ordinary chondrite. [1][2][3] A cosmic ray exposure age of Kamargaon is 7 Ma.…”

“…[1][2][3] Earlier studies focused on the compositional analyses of the meteorite and assigned Kamargaon as an L6 ordinary chondrite. [1][2][3] A cosmic ray exposure age of Kamargaon is 7 Ma. 2 Presence of irregular fractures of olivine and pyroxene grains observed previous authors 2 and entails the stage of shock metamorphism of Kamargaon is S3.…”

“…[1][2][3] A cosmic ray exposure age of Kamargaon is 7 Ma. 2 Presence of irregular fractures of olivine and pyroxene grains observed previous authors 2 and entails the stage of shock metamorphism of Kamargaon is S3. The Raman, infrared and X-ray diffraction processes are the most essential tools in mineralogical research.…”