Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6437146 | Geochimica et Cosmochimica Acta | 2016 | 14 Pages |
Cosmic spherules collected from deep sea sediments of the Indian Ocean having different textures such as scoriaceous (4), relict-bearing (16), porphyritic (35) and barred olivine (2) were investigated for petrography, as well as high precision oxygen isotopic studies on olivine grains using secondary ion mass spectrometry (SIMS). The oxide FeO/MgO ratios of large olivines (>20 μm) in cosmic spherules have low values similar to those seen in the olivines of carbonaceous chondrite chondrules, rather than matching the compositions of matrix. The oxygen isotope compositions of olivines in cosmic spherules have a wide range of δ18O, δ17O and Î17O values as follows: â9 to 40â°, â13 to 22â° and â11 to 6â°. Our results suggest that the oxygen isotope compositions of the scoriaceous, relict-bearing, porphyritic and barred spherules show provenance related to the carbonaceous (CM, CV, CO and CR) chondrites. The different types of spherules that has experienced varied atmospheric heating during entry has not significantly altered the Î17O values. However, one of the relict-bearing spherules with a large relict grain has Î17O = 5.7â°, suggesting that it is derived from 16O-poor material that is not recognized in the meteorite record. A majority of the spherules have Î17O ranging from â4 to â2â°, similar to values in chondrules from carbonaceous chondrites, signifying that chondrules of carbonaceous chondrites are the major contributors to the flux of micrometeorites, with an insignificant fraction derived from ordinary chondrites. Furthermore, barred spherule data shows that during atmospheric entry an increase in â¼10â° of δ18O value surges Î17O value by â¼1â°.