Nuclear Instruments and Methods in Physics Research B 363 (2015) 79–85
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PIXE micro-mapping of minor elements in Hypatia, a diamond bearing carbonaceous stone from the Libyan Desert Glass area, Egypt: Inheritance from a cold molecular cloud? M.A.G. Andreoli a,⇑, W.J. Przybylowicz b,c, J. Kramers d, G. Belyanin d, J. Westraadt e, M. Bamford f, J. Mesjasz-Przybylowicz b, A. Venter g a
School of Geosciences, University of the Witwatersrand, P.O. Box 3, Wits 2050, South Africa iThemba LABS, National Research Foundation, P.O. Box 722, Somerset West 7129, South Africa c AGH University of Science and Technology, Faculty of Physics & Applied Computer Science, al. A. Mickiewicza 30, 30-059 Kraków, Poland d Department of Geology, University of Johannesburg, Auckland Park 2006, South Africa e Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth 6031, South Africa f Evolutionary Studies Institute, University of the Witwatersrand, P.O. Box 3, Wits 2050, South Africa g South African Nuclear Energy Corporation, P.O. Box 582, Pretoria 0001, South Africa b
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Article history: Received 9 April 2015 Received in revised form 1 September 2015 Accepted 1 September 2015 Available online 11 September 2015 Keywords: Hypatia Pre-solar dust Micro-PIXE Dynamic Analysis
a b s t r a c t Matter originating from space, particularly if it represents rare meteorite samples, is ideally suited to be studied by Particle Induced X-ray Emission (PIXE) as this analytical technique covers a broad range of trace elements and is per se non-destructive. We describe and interpret a set of micro-PIXE elemental maps obtained on two minute (weighing about 25 and 150 mg), highly polished fragments taken from Hypatia, a controversial, diamond-bearing carbonaceous pebble from the SW Egyptian desert. PIXE data show that Hypatia is chemically heterogeneous, with significant amounts of primordial S, Cl, P and at least 10 elements with Z > 21 (Ti, V, Cr, Mn, Fe, Ni, Os, Ir) locally attaining concentrations above 500 ppm. Si, Al, Ca, K, O also occur, but are predominantly confined to cracks and likely represent contamination from the desert environment. Unusual in the stone is poor correlation between elements within the chalcophile (S vs. Cu, Zn) and siderophile (i.e.: Fe vs. Ni, Ir, Os) groups, whereas other siderophiles (Mn, Mo and the Platinum group elements (PGEs)) mimic the distribution of lithophile elements such as Cr and V. Worthy of mention is also the presence of a globular domain (Ø 120 lm) that is C and metals-depleted, yet Cl (P)-enriched (>3 wt.% and 0.15 wt.% respectively). While the host of the Cl remains undetermined, this chemical unit is enclosed within a broader domain that is similarly Cpoor, yet Cr–Ir rich (up to 1.2 and 0.3 wt.% respectively). Our data suggest that the pebble consists of shock-compacted, primitive carbonaceous material enriched in cold, pre-solar dust. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Even before the Apollo 11 mission to the Moon delivered the first samples of the early lunar crust, scientists have pursued the quest to find the oldest materials of the Solar System from which not only the planets, but also the meteorites have evolved. This search identified a group of falls known as carbonaceous chondrites to be important because of their potential to shed light on organic compounds derived from interstellar clouds [1]. It was also found that such meteorites hosted minute amounts of even older material, known as presolar grains (nanodiamond, silicon carbide) ⇑ Corresponding author. E-mail address:
[email protected] (M.A.G. Andreoli). http://dx.doi.org/10.1016/j.nimb.2015.09.008 0168-583X/Ó 2015 Elsevier B.V. All rights reserved.
as well as refractory, early condensates (CAls or Calcium–Aluminium Silicate inclusions) from the hot proto-Sun [2]. On the other hand, minute grains of space dust known as interplanetary dust particles (IDPs) have been investigated as they are thought to represent the best available samples of outer Solar System primordial dust [3,4]. Finally, NASA (National Aeronautics and Space Administration) and ESA (European Space Agency) have sent deep space probes to study comets at close range. The latest of these expeditions, known as Rosetta, is particularly ambitious as it attempts to unravel the history of the comets by robotic sampling of their surfaces with a lander [5]. In the STARDUST mission, a probe traveling behind comet 81P/Wild 2 was able to trap, in an array of aerogel collectors, numerous lithic particles, now the
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M.A.G. Andreoli et al. / Nuclear Instruments and Methods in Physics Research B 363 (2015) 79–85
subject of extensive mineralogical studies despite their minute size (
