Comprehensive imaging and Raman spectroscopy of carbonate globules from Martian meteorite ALH 84001 and a terrestrial analogue from Svalbard

Abstract

Abstract-We report a comprehensive imaging study including confocal microRaman spectroscopy, scanning electron microscopy (SEM), and 3-D extended focal imaging light microscopy of carbonate globules throughout a depth profile of the Martian meteorite Allan Hills (ALH) 84001 and similar objects in mantle peridotite xenoliths from the Bockfjorden volcanic complex (BVC), Svalbard. Carbonate and iron oxide zoning in ALH 84001 is similar to that seen in BVC globules. Hematite appears to be present in all ALH 84001 carbonate-bearing assemblages except within a magnesite outer rim found in some globules. Macromolecular carbon (MMC) was found in intimate association with magnetite in both ALH 84001 and BVC carbonates. The MMC synthesis mechanism appears similar to established reactions within the Fe-C-O system. By inference to a terrestrial analogue of mantle origin (BVC), these results appear to represent the first measurements of the products of an abiotic MMC synthesis mechanism in Martian samples. Furthermore, the ubiquitous but heterogeneous distribution of hematite throughout carbonate globules in ALH 84001 may be partly responsible for some of the wide range in measured oxygen isotopes reported in previous studies. Using BVC carbonates as a suitable analogue, we postulate that a low temperature hydrothermal model of ALH 84001 globule formation is most likely, although alteration (decarbonation) of a subset of globules possibly occurred during a later impact event.

Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments

“…One hypothesis contends that the ALH 84001 carbonates have a number of characteristics that indicate their low temperature (< ∼100 • C) deposition in a dynamic environment during perhaps several different episodes (Corrigan and Harvey 2004;Halevy et al 2011;Holland et al 2005;McSween and Harvey 1998;Niles et al 2005Valley et al 1997;Warren 1998). Another hypothesis suggests that the carbonates formed in a rapidly cooling environment which was initially at higher temperature (>150°C) and cooled to ∼30°C (Eiler et al 2002;Leshin et al 1998;Romanek et al 1994;Steele et al 2007), although this is now directly disputed by recently reported clumped isotope results (Halevy et al 2011).…”

“…Hydrothermal alteration of basaltic crust could produce CH 4 and sequester CO 2 in carbonates: the low intrinsic oxygen fugacity (fO 2 ) of martian basalt may force oxidized carbon supplied by magmatic degassing or crustal carbonates to reduce to CH 4 during water-rock interaction (Lyons et al 2005). Steele et al (2007) argued that the carbonates in ALH 84001 formed under similar high temperature, low fO 2 conditions resulting in the simultaneous formation of carbonates and macromolecular carbon.…”

A Raman spectroscopic study of a fulgurite

“…A previous study investigating the gases in a bubble inside a fulgurite reports finding carbon dioxide and carbon monoxide, the origin of these gases were attributed to the plant matter at the point of a lightning strike (Navarro-Gonzalez et al 2007). Similarly, Steele et al (2006) have reported that they identified polyaromatic compounds from a glassy region of the Shergottite, Nakhite, Chassignite Martian meteorite Alan Hills 84001 and from a volcanic basalt specimen from the Svalbard Arctic Mars analogue site.…”

“…Clearly, the presence of polyaromatics, albeit unidentified on a molecular basis, in a meteorite and a volcanic glass (Steele et al 2006) lends credence to the assertion that PAHs could also have survived the thermal shock of a terrestrial lightning strike. This is the first observation, as far as we can ascertain, of the nondestructive detection, identification and location of organic material incorporated into the matrix of a fulgurite.…”

Laser mass spectrometric detection of extraterrestrial aromatic molecules: Mini-review and examination of pulsed heating effects

“…A similar analysis of PAHs in the Allan Hills (ALH) Martian meteorite 84001 uncovered PAHs localized in and around carbonate globules (15,16). This was perhaps the most controversial observation made using L 2 MS, because interpretation of how these PAHs were generated is a matter of continuing debate and has stimulated a significant amount of work (17,18). PAHs were not detected in ALH84001 fusion crust, nor were they found to be depth-dependent, as would be expected for terrestrial contaminants.…”