Opaque assemblages in CR2 Graves Nunataks (GRA) 06100 as indicators of shock‐driven hydrothermal alteration in the CR chondrite parent body

Citations Over TimeTop 17% of 2013 papers

Abstract

Abstract We have studied the petrologic characteristics of sulfide‐metal lodes, polymineralic Fe‐Ni nodules, and opaque assemblages in the CR 2 chondrite Graves Nunataks ( GRA ) 06100, one of the most altered CR chondrites. Unlike low petrologic type CR chondrites, alteration of metal appears to have played a central role in the formation of secondary minerals in GRA 06100. Differences in the mineralogy and chemical compositions of materials in GRA 06100 suggest that it experienced higher temperatures than other CR 2 chondrites. Mineralogic features indicative of high temperature include: (1) exsolution of Ni‐poor and Ni‐rich metal from nebular kamacite; (2) formation of sulfides, oxides, and phosphates; (3) changes in the Co/Ni ratios; and (4) carbidization of Fe‐Ni metal. The conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 °C. Opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides, Fe‐rich carbonates, including endmember ankerite, and the sulfide‐silicate‐phosphate scorzalite. We suggest that these materials formed via impact‐driven metamorphism. Mineralogic features indicative of impact metamorphism include (1) the presence of sulfide‐metal lodes; (2) the abundance of polymineralic opaque assemblages with mosaic‐like textures; and (3) the presence of suessite. Initial shock metamorphism probably resulted in replacement of nebular Fe‐Ni metal in chondrules and in matrix by Ni‐rich, Co‐rich Fe metal, Al‐Ti‐Cr‐rich alloys, and Fe sulfides, while subsequent hydrothermal alteration produced accessory oxides, phosphates, and Fe carbonates. An extensive network of sulfide‐metal veins permitted effective exchange of siderophile elements from pre‐existing metal nodules with adjacent chondrules and matrix, resulting in unusually high Fe contents in these objects.

Related Papers

• → Iron and iron-nickel sulfides in chondritic interplanetary dust particles(1995)81 cited
• → PIANCALDOLI METEORITE: CHEMISTRY, MINERALOGY AND PETROLOGY(1976)4 cited
• → The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite from South Australia(2009)
• Euhedral awaruite in the Allende meteorite: Implications for the origin of awaruite- and magnetite-bearing nodules in CV3 chondrites(1991)
• МЕТЕОРИТ З УМОВНОЮ НАЗВОЮ “ВЕЛИКА БАЛКА”: МІНЕРАЛОГІЧНА ХАРАКТЕРИСТИКА І КЛАСИФІКАЦІЯ(2021)