Program News

This newsletter reports 418 new meteorites from the 2004 and 2006 ANSMET seasons from the Cumulus Hills (CMS), LaPaz Ice Field (LAP), Graves Nunataks (GRA), Grosvenor Mountains (GRO), Larkman Nunatak (LAR), MacAlpine Hills (MAC), Miller Range (MIL), Roberts Massif (RBT), and Scott Glacier (SCO). These new samples include one iron, 1 eucrite, 1 mesosiderite, 6 CK chondrites (2 with pairing), 2 CV3 chondrites, 1 CM1, 7 CM2 (4 with pairing), 3 CR2 (2 with pairing), and one each of a type 3 L and H chondrites. The CK6 chondrites (LAR 06869, 06872, 06873) are unusual in that they have no discernable chondrules, extremely fine-grained texture, and are full of veins. This newsletter represents a break from recent newsletters in which we have announced many unusual and popular samples, including new lunar and martian meteorites, an unusual achondrite (GRA 06128 and 06129 – the topic of a special session at this years LPSC).

Last fall we received the third highest number of requests for samples since the start of the program in 1977 (73), yet we also continue to announce >300 new meteorites in newsletters. This combined level of activity from the field teams, Smithsonian and NASA-JSC has resulted in the allocation of >600 samples to 87 PI's, including thin sections, since last year at this time. With such a high load of samples, there can be temporary delays, and we appreciate everyone's patience during these busy periods.

This newsletter also marks the completion of characterization and announcement of the 2004 season samples. To see a summary of the seasons finds, you can search "2004" in our Classification database online.

During the recently completed 2007-2008 ANSMET field season the field team recovered a specimen (presumably a meteorite) fully enclosed within blue ice. Although specimens partially enclosed in ice have been recovered and studied before, the 2007 specimen is unique in two important ways. First, it is fully enclosed by ice and thus potentially sealed off from any anthropogenic contamination; second, it is larger than any previously discovered "in-ice" specimen (4-5 cm in longest dimension), making it easier to work with. The block of ice (roughly 30x45x60 cm) containing the new specimen is currently en route to the Meteorite Processing Laboratory at JSC, sealed in a double set of nylon bags and kept frozen since recovery. It should arrive at JSC in early April.

The Meteorite Working Group would like to receive proposals from researchers interested in joining a consortium that will extract this specimen from the ice and conduct in situ sampling of the ice or the meteorite specimen at the moment of extraction. The following ground rules apply:

All participation must be self-funded; The MWG can offer no monetary support to aid participation in these activities.
We are currently searching for a clean, ice-capable lab where we can saw the ice block to within a few mm of the specimen to allow extraction while also preserving ice structure. Participants may need to travel to this lab to participate (depending on what you propose).
All proposed sampling must take place under cleanroom conditions, at a level appropriate for ice core studies.
Currently we expect to saw the ice to within a cm of the enclosed rock using a lubricant-free steel bandsaw, and then applying gentle pressure to release the sample. Your proposed studies should take this into account.
We do not anticipate storing or making available ice samples beyond this immediate opportunity; but requests for ice samples that can be gathered during the initial extraction will be considered.
Proposals for sampling of the enclosing ice are welcome; please specify the minimum and optimum volumes you hope to collect.
Proposals for sampling of the enclosed specimen should be limited to scrapings or swabbings if possible.
After extraction and initial examination, the specimen will go to JSC for processing using normal antarctic meteorite procedures, and larger samples can be requested at that time.

If you would like to be involved in the extraction of this meteorite, please prepare a short (1 page) proposal describing exactly what you’d like to do (sample or direct measurement needs, samples sizes, etc) and your willingness to participate. Proposals should be sent to Ralph Harvey via email (rph@case.edu) no later than March 21, 2008. The Meteorite Working Group will review these proposals in late March and the consortium will be formed shortly thereafter. We anticipate extracting the meteorite in mid- to late-summer.

Antarctic Meteorite Workshop - July 26-27, 2008 at Matsue Meteoritical Society

At the upcoming Meteoritical Society meeting in Matsue, Japan (July 28 - August 1, 2008), there will be a pre-meeting Antarctic Meteorite Workshop hosted by the NIPR and MetSoc. The purpose of the workshop is to gather meteoriticists to discuss issues relating to these collections, and how to allow these new discoveries to have the largest impact on our field. The workshop format will allow discussion of topics not usually covered during the regular sessions of the Meteoritical Society meeting. Specifically, the topics of interest will include the search, recovery, classification, weathering and curation of Antarctic Meteorites. Information about the workshop will be distributed soon.

Some substantial changes and additions have been made to our webpage recently, including an updated sample request form, addition of an updated master list and spreadsheet for all samples in the US Antarctic meteorite collection (cross-checked against the Meteoritical Bulletin announcements), and a summary of bandsawing at NASA-JSC and the Smithsonian Institution. Also, augmentation of photographic information available about the US Antarctic meteorite collection continues on our webpage. You will notice many new photos of achondrites announced in pre-1996 newsletters. These photos will be added for all classes of meteorites over the next few months, so please watch for updates. There are some beautiful photos taken of samples from the period 1977 to 1995 that have only been available in hard copy through JSC. Now many of these will be available electronically on our webpage in the "Classification Database" section.

NASA-JSC scientist, Mark Cintala received four ~400 g bandsawed pieces of the large LL6 chondrite LAP 02200 in May 2007 for shock experiments in his lab at JSC. After sandblasting the fusion crust off of the samples, which is customary for these shock experiments, Cintala observed what looks like a pre-existing impact crater and spallation zone in this chondrite sample. In order to preserve this feature for study by other researchers, he has traded two pieces with these features for two different pieces of LAP 02200. Below are several photos of this sample, before and after sandblasting, and then after one shock experiment, showing the artificial crater as well as the potential natural crater. If you are interested in studying these samples, please contact us through the normal request channel, but it may be beneficial to speak with the curator in advance of such a request to discuss sample dimensions, sampling needs, etc.

This newsletter announces the end of the classification of the 04’s and continues working through the 06’s. It also marks a significant transition at the Smithsonian. The staff of the Div. of Meteorites is growing and changing. LuElla Speakman has joined our staff as a Collections Technician and will assume responsibility for samples that are permanently transferred to the Smithsonian. Also joining our staff as a trust-funded Geologist is Cari Corrigan, who has twice traveled to Antarctica to collect meteorites and previously worked as a postdoctoral fellow with us. She joins us in what we anticipate to be an ongoing position funded in part by an endowment generously provided by former curator Ed Henderson. Cari will assume the day-to-day responsibilities in the classification of Antarctic meteorites and will serve as the Smithsonian’s representative to the Meteorite Working Group. Linda Welzenbach continues as Collection Manager and serves as the Fall Secretary for the Meteorite Working Group. Finally, I am moving from the MWG, where I have served for a decade, to the Meteorite Steering Group, replacing Glenn MacPherson who served on the Steering Group. We are extremely pleased to welcome LuElla and Cari and will continue to make sure the high level of service you have come to expect from the Smithsonian continues.

Sometimes it starts with just one little find. Back in 1985 the US Antarctic Research Program established a remote helicopter camp on the Bowden Névé (Beardmore South Camp), an effort designed to promote field explorations in the mid-Transantarctic Mountains. It worked, at least for us; with a bit of helicopter support and some snowmobile traversing, during that season my predecessor (Bill Cassidy) and his team discovered the meteorite concentrations near Lewis Cliff, the Queen Alexandra Range, the Grosvenor Mountains, the Geologists Range, and the Miller Range. More than 8000 LEW, QUE, GRO, GEO and MIL meteorites have been recovered over the past 22 years as a result, and there are more to come.

During that prodigal season, Bill and company found only a single meteorite on ice near the Miller Range; that find took a back seat to the dense concentrations found at Lewis Cliff and nearby areas. But that lone H5 wasn’t forgotten. In 1999 we sent a two person team back to the Miller Range, where 30 meteorites found in a day and vast extents of blue ice revealed enormous potential. A four-person team found another 100 or so meteorites in 2003, and in 2005 a full 8-person, 6-week and weather-confounded expedition found about 170 more. The Miller Range icefields yielded many meteorites of unique interest as a result of these efforts, including lunar and martian specimens; so while the numbers weren't huge, the potential of the Miller Range icefields continued to grow.

The just-completed 2007-2008 field season was the first to really exploit that potential. Good weather and lighter snow cover allowed more than 700 meteorites to be recovered, including a good number of non-OC specimens. Our efforts were concentrated on the informally-named Middle Icefields, sitting (rather obviously) between the North icefields partially searched in 2005, and the as-yet unsearched South icefields. Searching conditions were interesting, to say the least. Around the north and east ends of the Middle Icefield are myriad separate patches of exposed ice and hard firn, with both meteorites and terrestrial rocks unevenly scattered on their surfaces. We set ourselves to search all the potential stranding surfaces, not just the convenient ones, and meteorites were found in some very unexpected settings, including the steep slopes of local nunataks. We also used special techniques to recover several "ultraclean" meteorite samples to support detailed chemical and biological investigations; these will be fully described and made available in a future newsletter. Another meteorite (at least we think it's a meteorite) was found while still fully submerged in the ice. The block of ice containing this specimen was collected; look elsewhere in this newsletter for a description of what we hope to do with this sample.

My thanks to the field team, which consisted of Les Bleamaster III, Marc Caffee, Marc Fries, Marie Keiding, Lucy McFadden, John Schutt, Tim Swindle, Dejun Tan and me. Several future seasons will be required to complete the harvest of meteorites from the Miller Range and I think they'll all agree it's something to look forward to.

In the last newsletter (AMN 30, no. 2) we announced 10 reclassifications of various chondrites and achondrites. Continuing to update our database, here are listed re-classifications of various carbonaceous, enstatite and R chondrites. These are based on either new published information or correction of terminology. Also, R chondrites were rare about a decade ago, and now we have 20 in the US collection making the subtypes more important for distinction. We anticipate more in future newsletters, and we thank Jeff Grossman for his aid in identifying many of these.

Notes and references: Many carbonaceous chondrites were initially classified as C2 in early newsletters. These are mostly CM2, based on matrix properties, chondrules abundance and sizes, and therefore all these samples have been reclassified more specifically here as CM2. References for other samples: 1) Zolensky et al., 1997, GCA 61, 5099-5115; 2) Clayton and Mayeda, 1999, GCA 63, 2089-2104; 3) Weisberg et al., 2001, MAPS 36, 401-418; 4) D.W.G.Sears et al., 1991, Proc. NIPR Symp. Ant. Met. 4, 319; 5) R.H.Jones, 1997, Workshop on Modification of Chondritic Materials, LPI Tech. Rpt. 97-02, Part 1, p.30 (abs.); 6) subtype classification, E.R.D.Scott and R.H.Jones, 1990, GCA 54, 2485; 7) TL data, petrologic type 3.4, D.W.G.Sears et al., 1991, Proc. NIPR Symp. Ant. Met. 4, 319; 8) Grossman, J.N. and Brearley, A. (2005) MaPS 40, 87-122; 9) A.E.Rubin and E.R.D.Scott, 1997, GCA 61, 425; 10) A.E.Rubin, 1997, LPSC 28, 1201; 11) A.E.Rubin et al., 1995, LPSC 26, 1197; 12) A.E.Rubin et al., 1997, GCA 61, 849; 13) Y.Zhang et al., 1995, J. Geophys. Res. 100, 9417–9438; 14) A.E.Rubin and G.W.Kallemeyn, 1989, GCA 53, 3035; 15) Rubin, A.E. and Kallemeyn, 1994, Meteoritics 29, 255-264; 16) G.W.Kallemeyn, 1998, MAPS 33, p.A80 (abs.).

Terrestrial Age Survey of Antarctic Meteorites
Kuni Nishiizumi and Kees Welten

We are continuing a terrestrial age survey of Antarctic meteorites, based on the concentration of cosmogenic ³⁶Cl (half-life = 3.01x105 yr) in the metal fraction. After separation of clean metal and chemical separation of Cl at the Space Sciences Laboratory, University of California, Berkeley, the ³⁶Cl concentrations were measured by accelerator mass spectrometry (AMS) at PRIME Lab, Purdue University (mcaffee@purdue.edu). Table 1 shows the results of ³⁶Cl concentrations and terrestrial ages in 100 Antarctic meteorites that were measured since our last report in Antarctic Meteorite Newsletter (Volume 29, Number 1, 2006). Since the ³⁶Cl saturation values in the metal phase of small to medium-sized meteorites are in a relatively narrow range of 19-25 dpm/kg (2σ), the measured ³⁶Cl concentrations yield a direct measure of the terrestrial age (Nishiizumi et al. 1989). The apparent terrestrial age, T(terr), (in kyr) can be calculated using the following equation:

where A is the measured ³⁶Cl concentration and A₀ is the average ³⁶Cl saturation value of 22.1±2.8 dpm/kg (2s) (Nishiizumi 1995). For meteorites with ³⁶Cl concentrations >22.1 dpm/kg we only report an upper limit of the terrestrial age, whereas for meteorites with ³⁶Cl concentrations between 19.3 and 22.1 dpm/kg, we report the possible range of terrestrial ages, with the age and error in Table 1 having the same value, e.g. 37±37 kyr instead of 8±57 kyr for ALHA 79016. For meteorites with ³⁶Cl concentrations <19 dpm/kg there is a small possibility that these low values are due to unusually high shielding conditions or a short exposure age, but this can only be verified by measuring additional cosmogenic nuclides.

For more information about the ³⁶Cl results, or the terrestrial ages, please contact Kees Welten (kcwelten@berkeley.edu) or Kuni Nishiizumi (kuni@ssl.berkeley.edu). This work was supported by NASA’s Cosmochemistry Program.

References
Nishiizumi K., Elmore D. and Kubik P. W. (1989) Update on terrestrial ages of Antarctic meteorites Earth Planet. Sci. Lett. 93, 299-313.
Nishiizumi K. 1995. Terrestrial ages of meteorites from cold and cold regions. In Workshop on meteorites from cold and hot deserts. (eds. L. Schultz, J. O. Annexstad and M. E. Zolensky) pp. 53-55. LPI Technical Report No. 95-02, Lunar and Planetary Institute, Houston, Texas.

Table 1. Measured ³⁶Cl concentrations (in dpm/kg-metal) and ³⁶Cl-derived terrestrial ages (in kyr) of Antarctic meteorites.