9714012 Scott Abstract This award supports a collaborative interdisciplinary project to characterize the carbonates and associated minerals in Martian meteorite ALH84001 toward an improved understanding of the conditions and mechanisms involved in their formation. It is supported by the Office of Polar Programs, the Chemistry Division, and the MPS Office of Multidisciplinary Activities. These chemically and isotopically heterogeneous carbonates have been described as possibly containing organic and inorganic fossils of ancient Martian biota. Understanding the origin of the carbonates is the key to evaluating these interpretations. Two models for the origin of the carbonates in ALH84001 will be studied: shock melting of carbonates at high temperatures, which would virtually preclude the presence of fossils of carbon-based life, and low-temperature deposition in pores and fractures from aqueous fluids. Petrologic studies using optical and electron microscopy and electron probe analysis of thin sections will focus on the effects of shock melting and shock metamorphism of minerals in ALH84001. Shock-formed silica and plagioclase glasses will be studied in pyroxene fractures, crushed zones and uncrushed regions and compared with analogous phases in other shocked meteorites and terrestrial analogs to constrain the shock and deformation history of ALH84001. Carbonate globules, disks and grains in pyroxene fractures, crushed and uncrushed regions and their associated oxides and sulfides will be studied to test whether carbonates could have crystallized from shock melts that formed and were partly mobilized during the impact that melted plagioclase and silica. Carbonates and shock-formed glasses will also be studied in sections with laser micro-Raman spectroscopy and FT-infrared microscopy to search for carbonate ions in glass and to understand the shock and thermal histories of glasses and carbonates. Carbonates, glasses and other phases will be studied on fracture surfaces of the rock with atomic force microscopy (AFM) to clarify the origin of the carbonate and its relationship to the glasses. AFM studies will focus on the distribution of organic phases in the carbonate, its crystallinity and the degree of rotational disorder of carbonate-ions. These features will help in distinguishing biogenic and abiogenic carbonate mineral phases.
