Search and study of Antarctic meteorites, Belgian contribution (DWTC253)

The importance of meteorites. Meteorites are the left over building blocks of the Solar System. As such they provide valuable clues to its origin and evolution as well as to the formation of the planets. The majority comes from the asteroid belt between Mars and Jupiter, extremely rare ones were ejected from the deep crust of the Moon and Mars during large impact events. The meteorites are classified in groups corresponding to different evolution-phases of the Solar Nebula. The most primitive, the carbonaceous chondrites, together with the other chrondrites, originated from the break-up of small size undifferentiated planetary bodies. The Orgueil carbonaceous chondrite has almost the same chemical composition as the sun and resulted from the condensation of the solar nebula, almost without any fractionation. The chondrules and Ca - Al Inclusions (CAI) found in these meteorites were the first refractory phases to condensate out of the Nebula. The dating of CAI from the Acfer 059 meteorite (in situ U/Pb) places the origin of the Solar System at 4567.2 ± 0.6 Ma. Carbonaceous chondrites also contain complex organic compounds (ex. amino acids) and contribute to understand the origin of life on Earth. The other groups of meteorites (iron, stony-iron and achondrites) originate from more evolved planetary bodies that have undergone several episodes of differentiation comparable to the formation of the core, mantle and crust on Earth, and well as episode(s) of shock metamorphism during planetary collisions.The value of meteorites to document astronomical, solar system and terrestrial processes does not have to be further demonstrate. They have and continue to provide data on stellar evolution and nucleosynthesis, the chronology of the solar system, the formation of planets, cosmic rays bombardment, the deep crust of Mars and the Moon, the different types of asteroids and are often used to "calibrate" the instruments of the orbiters and landers used in planetary exploration (for example Spirit or Pathfinder). Meteorites in Antarctica.In 1970 less than about 2000 meteorites had been recovered all over the entire land surface of the Earth. In 1969, a Japanese glaciologist discovered 9 different meteorites in the region of the Yamato Mountain. In the last 35 years, the samples collected in Antarctica have more than tripled the world's collection of meteorites. The ice fields of Antarctica do concentrate rare and precious meteorites. This concentration occurs when the flowing ice is stopped or slowed down by a barrier, such as mountains. When a meteorite falls over Antarctica, it is buried in snow, and sinks deeper over the seasons to end up enclosed in ice as the snow crystallizes under pressure. Ice flows as a sluggish hydraulic system. The meteorite follows the ice movement outward towards the edge of the continent, and ultimately into the ocean. When the ice flow is stopped or slowed down by an obstacle, the wind strips the superficial snow and leads to the slow ablation of the ice. Over time, the meteorites trapped deep in the ice layers are brought to the surface as the lost by ablation is replenished by upstream ice at depth. The patches of stagnant ice flow are referred to as meteorite stranding surfaces. The low temperature reduces the weathering of the exposed meteorites. With patience and a good eye, numerous meteorites can be collected in the ice fields of Antarctica. In the last thirty-five years, Japanese expeditions have collected meteorites in the Yamato Mountains while US teams concentrated on the region around the MacMurdo base. Several rare and precious samples such as Martian and Lunar meteorites and carbonaceous chondrites were recovered in the Yamato mountain region. They have contributed to major advancements in planetary sciences. More samples remain to be found in this region, the goal of this proposal is to recover and study them. The recovered samples would then be shipped to Belgium and Japan (MOU between BELSPO-IPF-NIPR; and meteorite study curation between NIPR - VUB) and be made available for study by collaborating Belgian and Japanese scientists as well as to the rest of the community according to the proposal system currently used by meteorite curation facilities.Exploration of the ice field around the Belgian base will provide new meteorites that will contribute to further the understanding of the evolution of the Solar System and the planets. The recovered meteorites will be described and classified according to the standard procedure. Petrography, and geochemistry will document the evolution and timing of the magmatic and shock-metamorphic processes that took place in the parent body or, if such samples are found, during the crustal evolution of the Moon and Mars. The mineral phases and their zonations will be analyzed at a small scale to reconstruct the chronology of the condensation, fusion/crystallization, and differentiation processes having taken place. To do so, the most modern techniques of in-situ analyses and mass spectrometry will be applied (for example laser ablation with multi-cup inductively coupled plasma mass spectrometry to determine Pb and Sr isotopic ratio at a micrometer scale). The platinum group element (PGE) composition of the meteorites will be measured and compared with the PGE ratios measured on terrestrial impactites (see Tagle and Claeys, 2005) to determine the type of impact projectile. The following isotopic systems will be used to unravel the evolution of the meteorites parent-bodies: Mn-Cr, Hf-W, Sm-Nd, Rb-Sr, U-Pb. These systems are currently operational or in development at the ULB and VUB.Expected results.The outcome of this proposal depends highly on the type and abundance of the meteorites recovered from the ice fields, and in particular the possible presence of rare or unique specimens (ex. Mars and Lunar samples, or rare types of chondrites etc.). Previous NIPR mission of this type brought back between 100 and several thousands specimens. Every new contribution to the existing meteorite collection has in the past seen major progress in our understanding of planetary processes, including the evolution of Early Earth. In terms of outreach, the collected Antarctic meteorites will be exposed and described in details for a large public, most likely in the Royal Institute of Natural Sciences in Brussels.

Keywords:Geology, Meteorites, Antactica

Disciplines:Extraterrestrial geology, Palaeontology, Mineralogy and crystallography, Stratigraphy, Sedimentology