Canadian meteorites: a brief review1
Transcription
Canadian meteorites: a brief review1
4 Canadian meteorites: a brief review1 Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Graham C. Wilson and Phil J.A. McCausland Abstract: We present a brief overview of Canadian meteorites with a focus on noting significant recent falls, finds, and research developments. To date, 60 Canadian meteorites have received official international recognition from the Nomenclature Committee of the Meteoritical Society, while at least 13 more are “in process” for submission to the Meteoritical Bulletin, that organization’s official database of the world’s meteorites. The 60 meteorites (44 finds and 16 falls since the recognition of the Madoc iron in 1854) include 25 irons, 3 pallasite stony-irons, and 32 stony meteorites. The latter include 14, 11 and 3 H, L and LL chondrites, 2 carbonaceous chondrites and 2 enstatite chondrites, but no achondrites. The most intensively researched meteorites are Tagish Lake (C2 ungrouped) and Abee (EH5), followed by Bruderheim (L6) and Springwater (pallasite). Bruderheim, a 1960 fall, is widely distributed, being the most massive reported Canadian meteorite at 303 kg total known weight (TKW). Seven Canadian meteorites exceed 100 kg TKW, 36 are between 1 and 50 kg, and 17 are <1 kg. Recent years have seen the addition of the Tagish Lake, Buzzard Coulee and Grimsby meteorite falls, all of which have well-determined fireball trajectories and therefore well-known orbits, a striking Canadian addition to the handful that are known worldwide. The discovery of the Holocene Whitecourt iron impact crater is similarly a significant recent development in understanding the impactor flux. The lessons learned on meteorites can be applied to newly recovered samples from the Moon, Mars, asteroids, and comets. Résumé : Nous présentons une brève vue d’ensemble des météorites canadiennes tout en ciblant les plus récentes chutes importantes, les trouvailles et les résultats de la recherche. À ce jour, 60 météorites canadiennes ont été officiellement reconnues par le comité de nomenclature de la Meteoritical Society, alors qu’au moins 13 autres sont « en traitement » pour être soumises au Meteoritical Bulletin, la base de données officielle de cette organisation pour les météorites mondiales. Les 60 météorites (44 trouvailles et 16 chutes depuis la reconnaissance de la météorite ferreuse Madoc en 1854) comprennent 25 météorites ferreuses, 3 pallasites mixtes et 32 météorites pierreuses. Ces dernières comprennent 14, 11 et 3 chondrites H, L et LL, 2 chondrites carbonées et 2 chondrites à enstatite, mais pas d’achondrites. Les météorites les plus étudiées sont celles du lac Tagish (C2 non groupée) et d’Abee (EH5), suivies de Bruderheim (L6) et de Springwater (pallasite). Bruderheim, une pluie météorite à grande distribution, datant de 1960, est la météorite canadienne la plus massive, avec un poids total connu de 303 kg. Sept météorites canadiennes ont un poids total connu de plus de 100 kg, 36 pèsent entre 1 et 50 kg et 17 ont un poids inférieur à 1 kg. Au cours des dernières années, les chutes des météorites du lac Tagish, de Buzzard Coulee et de Grimsby, toutes avec des trajectoires bien déterminées de globes de feu et donc des orbites bien connus, ont été des ajouts canadiens remarquables à la poignée de météorites connues mondialement. La découverte du cratère d’impact de la météorite ferreuse Whitecourt (datant de l’Holocène) constitue aussi un développement important récent dans la compréhension du débit des impacteurs. Les leçons apprises sur les météorites peuvent être appliquées à des échantillons nouvellement récupérés de la lune, de Mars, des astéroïdes et des comètes. [Traduit par la Rédaction] Introduction The history of modern meteorite research in Canada arguably dates to the time of recognition of the first meteorite in the country 13 years prior to Confederation, near Madoc, southern Ontario in 1854. The 167.5 kg single mass of iron meteorite was acquired by William Logan, first director of the fledgling Geological Survey of Canada (Hunt 1855). The 4th edition of the Natural History Museum catalogue of meteorites (Graham et al. 1985), lists only 46 authenticated meteorites for Canada, the world's second-largest country. The official catalogue of the world’s meteorites is now published on-line as the Meteoritical Bulletin, and (as of early 2012) lists 60 officially recognized Canadian meteorites. These we focus on here, though it may be noted that many years can pass between the first recovery of a meteorite and its recognition as such by science. Even then, a proper classification must be carried out, and a suitable amount of material deposited with a recognized scientific depository (such as a major museum or university department active in meteorite research). The first author of this paper has main- Received 27 January 2012. Accepted 16 May 2012. Published at www.nrcresearchpress.com/cjes on 12 December 2012. Paper handled by Associate Editor Richard Leveille. G.C. Wilson. Turnstone Geological Services Limited, P.O. Box 1000, Campbellford, ON K0L 1L0, Canada. P.J.A. McCausland. Department of Earth Sciences, Western University, London, ON N6A 3K7, Canada. Corresponding author: Graham C. Wilson (e-mail: turnstonerocks@yahoo.ca). 1This article is one of a series of papers published in this CJES Special Issue on the theme of Canadian contributions to planetary geoscience. Can. J. Earth Sci. 50: 4–13 (2013) doi:10.1139/E2012-036 Published by NRC Research Press Wilson and McCausland Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Fig. 1. The Springwater main-group pallasite, showing coarse rounded olivine in metal (kamacite) with minor iron–nickel phosphide (schreibersite) at the metal–silicate interface. Note metric scale bar in centimetre, subdivided to millimetres. Fig. 2. The Dresden (Ontario) H6 (S2) chondrite, displaying the classic contrast, in a freshly recovered fragment, of black melted glassy fusion crust ≤1 mm thick around the pale, metal-flecked, silicate-dominated interior. Coin diameter = 23 mm. 5 Fig. 3. A photomicrograph of the Red Deer Hill L6 (S3) chondrite. A glassy shock melt vein, up to 0.25 mm thick, containing abundant micron-scale troilite (FeS) globules. Coarse troilite, as a typical aggregate of recrystallized polygonal domains (best seen in crosspolarized reflected light), occurs left of the vein, while a small angular grain of white kamacite, and minor patches of secondary oxide (goethite) are visible to the right. Nominal magnification 200×, long-axis field of view 0.4 mm, in plane-polarized reflected light. tained a modest database of these official meteorites plus other finds “in process”, the latter currently numbering 13 to 15 (most of these are listed at: http://www.turnstone.ca/canamet4.pdf, 10 April 2012) — which we hope will be added to the true tally before long. Before considering the 60 meteorites, and describing the significance of a few, we should first answer two questions, namely: (1) why study meteorites? and (2) what does Canada gain from its meteorites, and vice versa? The importance of meteorites Quite recently, meteorites were still rare. The total, historical worldwide haul of meteorites consisted of one or more fragments from some 2000 distinct meteorite finds or witnessed meteorite falls (e.g., the 2611 “reasonably authenticated meteorites” of Graham et al. 1985). This last total did not include the growing number of recoveries from the cold deserts of Antarctica, and preceded the impressive recoveries from the hot deserts of North Africa and the Middle East in the past two decades. The Meteoritical Bulletin (with 98 published editions through 2010, and now available as on-line updates alone) cited, as of 17 January 2012, some 41 714 valid entries, and 12 128 provisional names. This explosive growth of the meteorite inventory, roughly a 20-fold increase in a quarter-century, has been accompanied by a steady growth in the science of meteoritics, and associated fields of observational smallbody astronomy, cosmochemistry, and astrobiology. The field has long been at the forefront of developments in geochemical and mineralogical analysis of small and valuable samples, particularly in clean sample handling, mass spectrometry, and electron microscopy (e.g, Mason 1963; Clayton 1993; Bogard 1996). A multidisciplinary approach to a well-defined problem, such as the documentation and interpretation of a photoPublished by NRC Research Press 6 Can. J. Earth Sci., Vol. 50, 2013 Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Fig. 4. Field photo of site location EG-06 in the Tagish Lake C2 chondrite strewnfield, recovered in April 2000 from the frozen lake surface (Hildebrand et al. 2006). The dark carbonaceous chondrite was heated during the daytime and tended to melt and disaggregate into the ice within distinctive melt holes. In this view, one of the meteorite-bearing melt holes has been chainsawed out of the ice as a keystone block and tipped onto its side for viewing. The meteorite can be seen inside the ice block, having descended and formed a dark pancake of material ~10 cm below the snow-covered top of the block. Some dark debris can be seen to have continued downward along small holes much deeper into the ice. Fig. 5. The Grimsby H5 chondrite 21.9 g fragment “HP-1” as it was discovered two weeks after the 25 September 2009 fall, resting lightly on a grassy field in the west end of Grimsby, Ontario. This is one of only 13 pieces recovered from the fall. Note the dark, millimetre thick fusion crust and incipient rusting of FeNi metal on the fractured surfaces (McCausland et al. 2010). This fragment of Grimsby is evidently part of a larger, post-ablation individual that survived the fireball, but its sister fragments have not to date been found. Coin diameter = 23 mm. Published by NRC Research Press Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Wilson and McCausland graphed meteorite fall, can provide interesting opportunities for a diverse scientific team (e.g., Brown et al. 2000). Although there is now an almost unlimited supply of the most abundant classes of chondritic meteorite, the recognition of rare classes of igneous (achondritic) meteorites, some of them attributed to parent bodies such as the Earth’s moon, Mars, and asteroid 4 Vesta, means that the sample-conservative approach to analysis of small samples remains valid. The study of meteorites, particularly with the parallel evolution of geochemistry to handle the requirements of the Apollo and Luna sample-return programs in the late 1960s and early 1970s, has had concrete benefits, in terms of widely applicable technologies and also specific contributions to materials science, discovery of new minerals, and a refinement of our picture of the evolution of the solar system (McSween 1999; Hutchison 2004). Since the productive 1969 fall of the Allende carbonaceous chondrite in Mexico, it has become clear that the most “primitive” early constituents of the solar nebula are preserved in certain meteorite classes that have escaped significant metamorphism or aqueous alteration, casting light onto an epoch that predates the Earth’s oldest known rocks by hundreds of millions of years. Presolar grains of phases such as graphite, diamond, SiC, and corundum offer glimpses into a remote past, right back to the origin of the chemical elements (nucleosynthesis), in a generation of stars that predated our Sun. Meteorites provide also a wealth of clues to the origins and evolution of their parent bodies, ejection of the meteoroid from the parent body, and cosmic ray interactions with the meteoroid prior to its fall through Earth’s atmosphere (Hutchison 2004). Meteorites in Canadian science The 60 officially-sanctioned meteorites in Canada that were found or seen to fall before being recovered are listed in order of class and name in Appendix A Table A1. Note that one of the Canadian attributions of Graham et al. (1985), the Leeds iron, has been discredited, recognized by scientific detective work as a synonym of the large Toluca iron from Mexico (Kissin et al. 1999). The largest public collections in Canada, as of 2012, include: the National Collection, curated at the Geological Survey of Canada in Ottawa; the University of Alberta at Edmonton; and the Royal Ontario Museum in Toronto. The latter may be smaller in numerical terms, but has a very active acquisitions program and a remarkable diversity of the rarer achondritic classes of meteorite, including many specimens from the hot deserts of North West Africa (the numbered NWA series) and some notable Canadiana, including the recently unearthed main mass of the Springwater pallasite. The National Collection (Herd 2002; Herd et al. 2010) has the widest selection of Canadian meteorites, and more than 2700 samples of over 1100 meteorites. It has some iconic samples (e.g., the main masses of Madoc, Abee, and St-Robert). Other collections include: the University of Calgary (Tagish Lake and Buzzard Coulee falls); Planétarium de Montréal; University of Western Ontario; and smaller collections at the University of British Columbia, Queens and elsewhere. The evolution of meteorite research in Canada since 1950 has proceeded in part via a number of small, very modestlyfunded academic groupings with a soupcon of government 7 cachet, under various acronyms such as ACOM, MIAC, and ADWG. The Associate Committee on Meteorites, and its successors the Meteorites and Impacts Advisory Committee (to the Canadian Space Agency) and Astromaterials Discipline Working Group, have all benefitted from a range of scientific expertise, in fields of physics and astronomy, mineralogy, geology and geochemistry (e.g., Millman and McKinley 1967). Peter Millman suggested establishing an archive of mainly-Canadian fireball events at the first ACOM meeting in 1960. The archive recounts 2129 Canadian fireballs reported from 1962 to 1989, plus 410 US and six other fireball reports (Beech 2005, 2006). Another product of ACOM was the MORP (Meteorite Observation and Recovery Project from 1971 to 1985) that focused on the three Prairie provinces and recorded 795 fireball events. Based on MORP data, ACOM undertook some epic adventures, notably recovery of the Innisfree fall of 1977 (Halliday et al. 1978, 1996). Within its modest financial bounds, MIAC also sponsored unsuccessful attempts to locate meteorites in sub-Arctic and Arctic settings such as Devon and Baffin islands. A much greater degree of success with finds has attended the Prairie Meteorite Search initiative, run by the University of Calgary, Campion College at the University of Regina, and the University of Western Ontario, which has sent summer students into communities to solicit samples from the public. The initiative brought to light substantial additional material from the Red Deer Hill find, and as many as 13 previously unknown finds, although most of these have yet to reach official status in the Meteoritical Bulletin. Notable orbital information has been reconstructed after the fact for a number of documented falls in Canada, including Shelburne (van Drongelen et al. 2010), Dresden (McCausland et al. 2006), Abee (Marti 1983), and St-Robert (Brown et al. 1996). Detailed contemporaneous follow-up analyses of public photographic and video records from fireball events have allowed for the determination of useful orbits for Tagish Lake (Brown et al. 2000) and Buzzard Coulee (Milley et al. 2010; Brown et al. 2011). Increasingly sophisticated dedicated camera networks have permitted orbital reconstructions with minimal observer error (Halliday et al. 1996; Weryk et al. 2008). Canadian fireball network meteorite recoveries so far include Innisfree (Halliday et al. 1978, 1981) and Grimsby (Brown et al. 2011). Worldwide, several fireball camera networks, along with the careful analysis of fortuitously recorded meteorite-dropping fireball events, have to date led to the reliable reconstruction of just 14 pre-atmospheric meteoroid orbits (Brown et al. 2011), of which four are from Canadian falls. Recently highlighted Canadian meteorites Here is a quick chronological survey of a dozen selected Canadian meteorites, including some of the most extensively-researched examples, with emphasis on the subjects of recent research in Canada. This is a vade mecum, a basic introduction, and much more could be said. Indeed, Whyte (2009) has provided an excellent historical overview of 14 of the meteorites recovered in the province of Alberta, plus notes on two more recent finds. Shelburne (1904 fall) provides a classic case of a fireball event, witnessed on a summer evening, with numerous observers and the rapid recovery of two multi-kilogram fragPublished by NRC Research Press Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. 8 ments in farmland in southern Ontario (see recent synthesis by McCausland and Plotkin 2009; van Drongelen et al. 2010). It illustrates the vastly greater likelihood of meteorite recovery in the well-tended farmlands and populous areas of Canada, as in the Prairie provinces and southern Ontario and Quebec, versus the sparsely settled regions of the western mountains, boreal forest, and sub-Arctic to Arctic regions. Shelburne is a veined and brecciated L5 chondrite, a fine representative of one of the most abundant meteorite classes, well-distributed in public and private meteorite collections worldwide (McCausland and Plotkin 2009). Springwater (1931 find) was the first (Nininger 1932) and by far the largest of three pallasite finds in Canada in the 20th century. Recent searching has yielded more material, and the main mass (53 kg) is now in the collection of the Royal Ontario Museum. It is the fourth-most-cited Canadian meteorite, in part because pallasites are an uncommon class, with less than 100 representatives, and because the original find was substantial (67.6 kg). Besides olivine and kamacite (a relatively Ni-poor Ni–Fe alloy), Springwater is notable for its content of phosphate minerals. Like Brenham, an historic Kansas find, Springwater is famed for its rounded olivine grains (Fig. 1). See Yang et al. (2010) for a recent synthesis of ideas on pallasite petrogenesis. Dresden (Ontario) (1939 fall), like Shelburne before it, is a fine example of the fall and recovery of an ordinary chondrite. The fascinating human history of the meteorite is recounted by Plotkin (2006). This historic stone (Fig. 2) is affirmed as a brecciated H6 (S2) chondrite by a recent reexamination of the 40 kg main mass and several other small individuals, with a measured bulk specific gravity (3.48) and aspects of mineral chemistry and bulk composition (total Fe content is 28.0% and elemental abundances are quintessential H-chondrite, except for low S, with 1.90 wt.% Ni, 0.36 wt.% Cr, and 0.10 wt.% Co; McCausland et al. 2006). Abee (1952 fall) is an enstatite chondrite, a grouping that includes some of the most chemically reduced stony meteorites. It has seen a level of research unrivalled until the arrival of the Tagish Lake carbonaceous chondrite, 48 years later, being described in ∼130 articles. The single large mass, an impressive 107 kg egg-shaped body, was retrieved from a deep hole in a farmer’s field following a widely observed evening twilight fireball (Dawson et al. 1960; Whyte 2009). The metal- and enstatite-dominated, dense and brecciated meteorite is the largest enstatite chondrite known, and so came to be widely distributed and the subject of a multidisciplinary consortium effort (Marti 1983 and references therein). The mineralogy is very exotic by terrestrial standards, including graphite and diamond, and other reduced phases scarcely ever found on Earth, such as the sulphides oldhamite, niningerite, and keilite (Shimizu et al. 2002). Bruderheim (1960 fall) remains, at 303 kg, the largest documented fall or find on Canadian soil (Folinsbee and Bayrock 1961; Whyte 2009). An L6 chondrite, it was recovered rapidly from a very productive strewnfield 50 km northeast of Edmonton (Folinsbee and Bayrock 1961), and was distributed widely for research. Bruderheim has thus been well studied as a freshly-recovered representative of an abundant class of stony meteorite. Rare gases, halogens, rare-earth elements, the light elements Li and B, and radionuclides such as 14C are all well-documented in the case of Bruderheim Can. J. Earth Sci., Vol. 50, 2013 (Jull et al. 2000), making the meteorite an oft-used reference standard. The 1960 Bruderheim fall was seminal for Canadian meteoritics, being instrumental in the growth of the University of Alberta’s diverse meteorite collection (by trades) and in the establishment of the National Research Council’s Associate Committee on Meteorites (ACOM) as a coordinating scientific body for the study of fireball reports and meteorite falls in Canada (Millman and McKinley 1967; Whyte 2009). Peace River (1963 fall) is an L6 chondrite with shock melt veins, and rare achondritic clasts (see Herd 2012). It is especially noted for its evidence of high-pressure extraterrestrial shock events (Price et al. 1983), generating high-pressure polymorphs of otherwise familiar silicate phases, such as wadsleyite and ringwoodite (after olivine) and majorite (after orthopyroxene). The mineral wadsleyite was first discovered in a Peace River shock vein (Price et al. 1983). Brief optical study reveals that other Canadian meteorites like Red Deer Hill (L6, Fig. 3) may show similar textural or mineralogical evidence of impact events. St-Robert (1994 fall) arrived in spectacular style, northeast of Montreal, depositing fragments of crusted H5 chondrite across an 8 km × 3.5 km strewnfield (Brown et al. 1996; Hildebrand et al. 1997). Several fragments of St-Robert were studied for noble gas isotopic ratios and short-lived cosmogenic radionuclides, formed by cosmic ray irradiation of the parent meteoroid during its journey to Earth (Leya et al. 2001). From these data, St-Robert is ascertained to have had a relatively simple cosmic ray exposure (CRE) history, having been liberated as a ∼90 cm diameter meteoroid from a larger body at 7.8 Ma, a common CRE age amongst H chondrites that likely represents a H chondrite small body breakup event (Leya et al. 2001). Poirier et al. (2004) reported a precise Pb–Pb age of 4566 ± 7 Ma (2s) for St-Robert chondrules, and a mineral–whole-rock Pb–Pb age of 4565 ± 23 Ma (2s), indicating that the Pb–Pb system was undisturbed in the early history of the H chondrite parent body. St-Robert is a particularly useful example of a ‘typical’ H5 chondrite with a relatively simple, well known history from its early history on the H chondrite parent body through its delivery to the Earth. There is sufficient St-Robert in Canadian collections to permit fresh study and re-evaluations, such as of physical properties, density, and porosity (McCausland et al. 2011). Tagish Lake (2000 fall) is a C2 ungrouped carbonaceous chondrite that appears to be unique; within 12 years it has become arguably the most-researched Canadian meteorite. Its recovery is a remarkable story of the arrival of friable primitive material that landed fortuitously on the frozen surface of Tagish Lake in northern British Columbia (Brown et al. 2000; Hildebrand et al. 2006). Its recovery is eerily similar to that of the 1965 Revelstoke meteorite, the smallest known Canadian fall, also a fragile primitive carbonaceous chondrite (CI1). Revelstoke was discovered some two weeks after its fall, when two beaver trappers, crossing a frozen lake on snowshoes, noted blackened snow (Folinsbee et al. 1967). Multiple, pristine frozen fragments of Tagish Lake were found on its eponymous, frozen lake (Fig. 4) ten days after a brilliant fireball was witnessed over a huge region. Later dedicated searching of the ice surface before the spring 2000 breakup defined a strewnfield at least 16 km long, consisting Published by NRC Research Press Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Wilson and McCausland of more than 420 fall locations (Brown et al. 2000; Hildebrand et al. 2006). The remarkable fall was soon awarded its own consortium study (Brown et al. 2002 and references therein). Tagish Lake ranks among the most primitive and friable meteorites ever studied, a heterogeneous accretionary breccia with high microporosity of ∼40% and a bulk specific gravity of just 1.66, a large range of unequilibrated olivine compositions (Fo71–100), magnetite, carbonates, and organic compounds (Zolensky et al. 2002; Izawa et al. 2010a, 2010b). Tagish Lake is a repository of prebiotic organic matter with origins in the solar nebula as well as from parent body aqueous alteration processes, and has become a signature pristine planetary material for developing sample handling protocols (Zolensky et al. 2002; Herd et al. 2011). Infrared reflectance spectra of Tagish Lake (which contains 4%–5% carbon and has been subject to aqueous alteration on its parent body) are consistent with its derivation from an outer main belt D-type asteroidal parent body (Hiroi et al. 2001; Izawa et al. 2010a), possibly representing material more primitive than is found in other classes of meteorite. Southampton (2001 find) is the most recent Canadian pallasite find, discovered by an observant passer-by on a beach on the shore of Lake Huron, west of Owen Sound. The main mass of this beautiful meteorite has been preserved at the Royal Ontario Museum, and the pallasite has been the subject of recent research (see Kissin et al. 2012). At the time of its discovery it was just the 52nd pallasite known to science. Whitecourt (2007 find) is a IIIAB iron meteorite that has the distinction of being one of very few meteorites in the world known to be associated with its own impact crater, some 36 m wide and 6 m deep in glacial till (Herd et al. 2008; Kofman et al. 2010). Whitecourt was discovered by hunters who were curious about the closed bowl structure and explored the local ground with metal detectors, correctly suspecting it to be an impact crater. A follow-up systematic study found innumerable mostly small (<5 cm) shrapnel-like shards, similar to fragments from a minority of other irons, such as Sikhote-Alin and Gebel Kamil (Kofman et al. 2010). The “total known mass” recovered is necessarily an approximation. The structure, and thus the impact of the iron meteoroid, is established to be less than 1100 years old, and it represents a size of impactor that is usually missed in the terrestrial impact record (Herd et al. 2008). Buzzard Coulee (2008 fall) arrived as the climax to a spectacular (magnitude –20) fireball event on 20 November 2008. The meteoroid, estimated mass 10 tonnes, entered the atmosphere at a low velocity of 14 km s–1 (an average velocity would be 20 km s–1), enabling it to penetrate to an altitude of just 12 km above surface before shattering to produce a fine meteorite shower of black crusted fragments, the largest found to date weighing 13 kg (Hildebrand et al. 2009). Initial classification of Buzzard Coulee is H4 (S2, W0). More than 40 kg (>130 fragments) were recovered before the first serious seasonal snow cover interfered with recovery on December 6th (Kulyk 2009; Weisberg et al. 2009) and there are most likely some thousands of fragments, TKW (total known weight) >200 kg. Grimsby (2009 fall) is an H5 chondrite (McCausland et al. 2010), the 14th meteorite fall with an instrumentally measured pre-atmospheric orbit indicating an origin in the main 9 belt asteroids (Brown et al. 2011). This fall event is notably the first to incorporate Doppler weather radar as an essential scientific component in the analysis of the behaviour of falling meteorite fragments. Grimsby is a fall with small recovered mass (215 g recovered from 13 fragments as of early 2012) in a mixed urban and agricultural area at the west end of Lake Ontario (Fig. 5). Grimsby made headline news for human interest as a “hammer” that struck, amongst other anthropogenic targets, a vehicle windshield and a garage (McCausland et al. 2010). Conclusions Vast by land mass but small by population, the recovery rate per square kilometre in Canada is very low (Beech 2003), yet some very special falls and finds have been recovered. With such a small number of meteorite recoveries, it is not surprising that some of the rarer meteorite classes, including all the achondrites (a broad chemical and textural variety of primary igneous and derived brecciated lithologies) are not, as yet, represented (Appendix A Table A1). Future meteoritical research in Canada will likely include some advanced projects as well as some inevitable associated spadework. The advanced programs will include continued optimization of fireball tracking networks to aid in impactor flux determination and possible meteorite recovery (Weryk et al. 2008; Brown et al. 2011), and additional advances in techniques for materials characterization of the payloads of sample-return missions (Herd et al. 2011; McCausland et al. 2011). The lessons learned on meteorites will in the next generation be applied, in all probability, to newly recovered samples from the moon, Mars, asteroids, and comets. Less glamourous, but nevertheless of great educational importance, the spadework includes public interaction, a feature of the Canadian meteorite community since ACOM days. Public education via presentations, Web sites and social media, museum displays, and field visits to current and historical meteorite strewnfields are all important (Plotkin 2006; McCausland and Plotkin 2009). It is a common perception that meteorites are “manna from heaven”, and every researcher soon develops a repertoire of stories concerning “meteorwrongs” and members of the public who occasionally are suspicious of any demythologizing of their precious finds. Much more frequently, finders of prospective meteorites are genuinely curious about their finds and open to learning about meteorites. We consider the best approach to be to engage the curious public, and (in most cases) explain not only that their material is not a meteorite, but what it actually is, and discuss the specific features that attracted their attention in the first place. Almost invariably, possible meteorite enquiries become excellent opportunities to educate the very people who are most curious about their surroundings. A small investment of meteorite education can pay large dividends in elevating interest in the real wonder of science and possibly lead to the recovery of future meteorites. Good illustrated reference books to have on hand are those of Norton (1994) and Norton and Chitwood (2008). Once a meteorite has been recovered, classification using standard techniques can be conducted (see, e.g., Dodd 1981; Hutchison 2004), with a view to submitting a type specimen Published by NRC Research Press 10 to a meteorite research institution as soon as possible to enable long-term availability of research sample from the meteorite, and submitting a brief descriptive report for the consideration and approval of the Nomenclature Committee of the Meteoritical Society. Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Acknowledgements We thank past and present members of the Meteorite Impact Advisory Committee (MIAC) and the Astromaterials Discipline Working Group (ADWG) for stimulating discussion, and all those sample preparators who struggle to provide excellent polished thin sections for meteorite research! Reviews by Martin Beech and Michael Higgins were most helpful in improving this work. 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Published by NRC Research Press 12 Can. J. Earth Sci., Vol. 50, 2013 Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Table A1. Canadian meteorites — approved (60) and listed in Meteoritical Bulletin. Meteorite Chondrites (32) Revelstoke Tagish Lake Blithfield Abee Beaver Creek Buzzard Couleea Redwater Skiff Wood Lake Grimsby Riverton St-Robert Wynyard Belly River De Cewsville Dresden (Ontario) Great Bear Lake Vulcan Shelburne Vilna Blaine Lake Bruderheim Catherwood Ferintosh Homewood Kinley Kitchener Peace River Red Deer Hill Holman Island Innisfree Benton Achondrites (0) Irons (25) Fillmore Mayerthorpe Midland Osseo Annaheim Bernic Lake Burstall Hagersville Lac Dodon Penouille Torontob Bruno Edmonton (Canada) Chambord Iron Creek Madoc Manitouwabing Welland Whitecourt Kinsella Thurlow Millarville Class Region Ni%Metal Fa%Oliv History Date TKW (kg) RefsMINLIB Earliest CI1 C2 ungrouped EL6 EH5 H4 H4 H4 H4 H4 H5 H5 H5 H5 H6 H6 H6 H6 H6 L5 L5 L6 L6 L6 L6 L6 L6 L6 L6 L6 LL(?) LL5 LL6 BC BC Ont Alta BC Sask Alta Alta Ont Ont Man Que Sask Alta Ont Ont NWT Alta Ont Alta Sask Alta Sask Alta Man Sask Ont Alta Sask NWT Alta NB — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — 0–29 — — 19 17.8 19 18 19 18 20 19 18 20 18 20 19 20 24 25 26 24 25 26 25 — 26 23 26 29 27 31 Fall Fall Find Fall Fall Fall Find Find Find Fall Find Fall Find Find Fall Fall Find Find Fall Fall Find Fall Find Find Find Find Fall Fall Find Find Fall Fall 1965 2000 1910 1952 1893 2008 2009 1966 2003 2009 1960 1994 1968 1943 1887 1939 1936 1962 1904 1967 1974 1960 1965 1965 1970 1965 1998 1963 1975 1951 1977 1949 0.001 11.0 1.83 107 14 200 0.230 3.54 0.35 0.215 0.103 25.4 3.479 7.9 0.340 47.7 0.04 19 18.6 0.00014 1.896 303 3.92 2.201 0.325 2.44 0.202 45.76 25.0 0.552 4.58 2.84 15 132 20 131 22 11 0 7 3 10 2 26 4 11 3 21 2 9 20 5 5 89 10 4 5 6 12 39 6 8 30 7 1967 2000 1922 1960 1963 2008 2010 1980 2004 2009 1976 1994 1980 1953 1900 1939 1963 1967 1904 1973 1978 1961 1973 1984 1976 1971 1998 1967 1978 1963 1978 1964 IA IA IA IA IA-ANOM IAB IAB IAB IAB IAB IAB IIA IIA IIIA IIIA IIIA IIIA IIIA IIIAB IIIB IIIB IVA-ANOM Sask Alta Ont Ont Sask Man Sask Ont Que Que Ont Sask Alta Que Alta Ont Ont Ont Alta Alta Ont Alta — — — — — — — — — — — — — — — — — — — — — — Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find Find 1916 1964 1960 1931 1916 2002 1992 1999 1993 1984 1997 1931 1939 1904 1866 1854 1962 1888 2007 1946 1888 1977 0.200 12.61 0.034 46.3 11.84 9.8 0.359 30.0 0.800 0.072 2.715 13 17.34 6.6 145.93 167.5 38.6 8.16 200 3.72 5.5 15.636 3 6 4 14 13 5 5 5 4 3 5 9 6 5 15 26 16 23 7 4 5 6 1971 1971 1971 1938 1921 2004 1998 2001 1995 1995 1997 1936 1969 1963 1886 1855 1964 1891 2008 1978 1900 1979 7.18 7.19 8.37 6.51 7.74 6.53 6.57 6.89 8.64 9.40 7.04 5.79 5.37 7.53 7.72 7.52 7.34 8.77 8.11 8.78 9.92 9.78 Published by NRC Research Press Wilson and McCausland 13 Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by UNIVERSITE QUEBEC A CHICOUTIMI on 11/25/13 For personal use only. Table A1 (concluded). Meteorite Class Region Ni%Metal Fa%Oliv History Date TKW (kg) Skookum Garden Head Gay Gulch Stony irons (3) Giroux Southampton Springwaterc IVB IRANOM IRANOM YT Sask YT 17.13 16.96 15.06 — — — Find Find Find 1905 1944 1901 15.88 1.296 0.483 19 6 8 1915 1971 1915 Pallasite Pallasite Pallasite Man Ont Sask 10.3 9.47 12.6 11 12.5 18 Find Find Find 1954 2001 1931 4.275 3.58 167.6 12 4 62 1967 2002 1932 RefsMINLIB Earliest Note: All 60 meteorites are listed in the Meteoritical Bulletin, but individual details may be drawn from the wider meteoritic literature. The various falls and finds are listed by the province or territory where they were recovered: Alberta, British Columbia, Manitoba, New Brunswick, Northwest Territories, Ontario, Quebec, Saskatchewan, and Yukon Territory. No recoveries have yet been reported for Newfoundland, Nova Scotia, Prince Edward Island, and the Territory of Nunavut. Classification: two key factors are included: the percentage of nickel in bulk metal (irons and stony irons) and the mole proportion of fayalite (100 – Mg #) in olivine. Total known weight (TKW) is reported using the best available data, but in the newer falls (e.g., Buzzard Coulee) and finds (e.g., Whitecourt) the quoted values should be taken as minima. As an indication of the extent of research and general interest, the number of records citing each meteorite in Graham C. Wilson’s unpublished MINLIB bibliographic database are quoted. Published titles on Canadian meteorites, appearing as records in the MINLIB database, may be viewed in an on-line chronological–alphabetical bibliography at http://www.turnstone.ca/canmetbib.htm a The Buzzard Coulee TKW is now believed to be in excess of the nominal 200 kg noted here, in >1000 fragments. b The Toronto iron (Fig. A1) was identified in that city and classified at the University of Toronto and Lakehead University, but the true provenance may never be known — an earlier find in rural Quebec is suspected but unverifiable. c The TKW includes the original 67.6 kg from the 1930s and a nominal 100 kg from recent finds. Fig. A1. The Toronto iron, in the uncut 2.7 kg mass, a find of uncertain but probable Quebec provenance (Kissin and Wilson 2006). Note added to proof 1. A 61st Canadian meteorite was accepted in Meteoritical Bulletin 101, on 23 August 2012: this is the Lone Island Lake IAB-sLL iron, Manitoba, 7.62% Ni in metal, a find in 2005, TKW 4.8 kg, 3 references, 2005 onwards. 2. As of Met. Bull. 101, 23 August 2012, the official world tally of approved meteorite names rose to 43 973. In judging the qualities of a meteorite display, it may be helpful to remember the approximate proportions of the major classes. In round figures, seven out of eight meteorites are the most-common, ordinary chondrites (H, L and LL, 88%); 5% are achondrites (of which 55% are in the "vestoid" HED clan); 4% are less-common to rare chondrites, primarily eight subclasses of carbonaceous chondrite, plus the enstatite chondrites; >2% are irons; and <1% are pallasite and mesosiderite stony-irons. Reference Kissin, S.A., and Wilson, G.C. 2006. Toronto, a new Canadian meteorite. Meteoritics & Planetary Science, 41(S8): A243–A246. doi:10.1111/j.1945-5100.2006.tb01001.x. 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