Blood iPhones?

In the late ‘90’s and early 2000’s, there was a serious push in the west to stop the financing of rogue African militia by controlling “Blood Diamonds”. I’ve long been cynical of this approach. At the time, I was working in diamond research, and I saw far too many people leap on the blood diamond bandwagon as a way of getting additional research funding to direct to their pet projects. The fact that the program was eventually taken over by DeBeers as a marketing tool for solidifying their monopoly didn’t help either. And most importantly, I felt that diamond consumers were looking at the bloodless diamonds as a way of washing their hands of African problems and turning their backs on the continent.

Well, a decade on, and things are looking up for the diamond-producing parts of Africa. The civil wars in Angola, Liberia, and Sierra Leone are over. Botswana, Namibia, and South Africa are developing, and the latter country will be hosting the World Cup this year. But outside the cratonic cores of the continent, atrocities continue.

Yesterday, New York Times blogger columnist Nicolas Kristof wrote a heartbreaking story about the mass killings and rapes that are still occurring in the Democratic Republic of Congo. Among the various proposals he listed for stopping the violence was, “we need a U.S.-brokered effort to monitor the minerals trade from Congo so that warlords can no longer buy guns by exporting gold, tin or coltan.”

So, what on earth is “coltan”? It’s a industry term for columbite-tantalum concentrate. Columbite is the ore of niobium, which is used in steels and high strength alloys. Tantalum, which is geochemically similar and thus found in the same deposits, is used mostly in capacitors for compact electronic devices such as personal computers and mobile phones. So the purchase of the device you are using to read this blog may have financed rape, mutilation, and genocide in central Africa.

From a technical point of view, identifying blood tantalite and niobate minerals should be much easier than dealing with diamonds. These minerals generally have enough uranium to allow uranium-lead geochronology, and are far more chemically complex than diamond. The main suppliers of tantalum (Brazil and Australia) are not Machiavellian DeBeers-like monopolists. Instead, they work using long-term, fixed-price contracts that should make identifying buys from the spot market relatively easy compared to the Byzantine marketing of diamonds. So the problem is tractable.

As it turns out, there are groups working to address this problem. http://www.enoughproject.org/conflict-minerals has links to proposed legislation currently in front of congress, as well as letters to the manufacturers of various electronic devices asking the companies to buy fair-trade HFSE’s. Just about the only thing they don’t have is a clever viral phone app to spread the word. But if any of you readers are clever programmers, why not spend the evening fighting genocide instead of reading blogs?

Naughty Geology

A few months back, I blogged about the client with a spam filter so tight that it embargoed emails about single young zircon dating. After conferring with said clients, it turns out that they’ve had other issues as well. In its animatronic zeal to rid the internet of pornography, this filter also blocks image files that it suspects are explicit. What sort of images? Well, anything containing a lot of pink, as it turns out. So, rose quartz, rhodocrosite, Mg-rich garnets, and other titillating mineral images have been known to disappear into the computer program’s private locker. Luckily they ship geologic maps as GIS files instead of images, or I’m sure they’d be targeted as well.

This got me thinking. How common are explicit geologic formations? You’d think that will all the zillions of folded, rounded, curved, or protruding structures on this planet, at least a few would be shaped like something that would constrict the coronary arteries of a shrill old censor. So, this is my challenge to the blogosphere: Find juiciest, most risqué geologic image that you feel comfortable posting, and put it out on the internet. Your traffic in tragically maladjusted lapidarians will expand tremendously, I guarantee.

Sadly, all I can offer in this department is this backscattered electron image of a rutile. To most people, it is simple igneous compositional zoning of Nb, Sn and W, which reflect electrons more efficiently than titanium and therefore appear bright. But to the dirty regolithic mind, this only needs legs, arms, and a head to become a swimsuit model. And no, I don’t need to leave the lab more often.


Figure 1. Detrital Phanerozoic rutile believed to be of pegmatitic origin See Birch et al. 2007 for geochronology and trace element characteristics.

I’d like to thank the alaskademy

It looks like the generous allochthonous Alaskan who blogs as Wayfarer Scientista has given me the Brilliante award. Presumably, this is some sort of baddeleyite allotrope.

Baddeleyite, formula unit ZrO₂, is a great mineral, so it is a shame that synthetic cubic zirconia has a higher profile in the more colorful parts of non-geologic human culture. Of course, the trick to getting ZrO₂ to grow in a cubic structure is itself interesting- it seems that cubic zirconia is in fact a Zr-rich tazheranite solid solution. But growing big crystals at all is impressive when you consider that zirconia has one of the highest melting points of any known substance. But enough of this lapidarial digression.

In order to crystallize baddeleyite, two conditions must be met. Firstly, the major minerals must be saturated in Zr. Secondly, the SiO₂ activity has to be low enough that zircon doesn’t grow. This makes the mineral somewhat uncommon. Never the less, it does have a high U/Pb ratio, so it is used for geochronology for rocks that don’t have zircon.

Interestingly, metamorphic fluids are often silica rich, so in some altered rocks a zircon reaction rim will grow on a baddeleyite, allowing both the crystallization age and the alteration age to be determined. In practical terms, this means that if you want a good date, then natural, monoclinic zirconia is more reliable than its artificial, cubic allotrope.

Evidently I am supposed to pass this award along, so nominate the following blogs as being cubic zirconia-worthy:
The Planetary Society Blog
Molecule of the Day
This non-American Life
Apparent Dip
The Volcanism blog
All my faults are stress related
And if any of y'all have already been awarded, then give yourselves an allotrope instead.

Titanium as a cathodoluminescence activator in alkali feldspars

Ian Parsons, David A. Steele, Martin R. Lee, and Charles W. Magee 2008. Titanium as a cathodoluminescence activator in alkali feldspars American Mineralogist, Volume 93, pages 875–879

Abstract:
Albite patches in coarsely mesoperthitic alkali feldspars from the Klokken syenite have oscillatory zoning seen at blue wavelengths using cathodoluminescence. Using a five-spectrometer, high-resolution elemental mapping technique in an electron probe, we show a close correspondence between CL emission intensity and Ti, present at levels up to ~200 ppm. Albite patches were analyzed for major and 16 trace elements by laser-ablation inductively coupled-plasma mass spectrometry. SEM elemental maps acquired simultaneously with the CL showed that a similar zoning pattern is exhibited by Ca, but there is no correlation between CL intensity and Ca concentration. None of the trace elements analyzed correlate with Ti. We conclude that tetrahedral Ti4+ is the most likely activator of blue luminescence in these albitic alkali feldspars possibly because of a defect associated with Al-O-Ti bridges.

word cloud:

ab-rich above activator al albite albite-rich alkali analyses blue ca cl correlation data detail detection electron elements epma et feldspars fig figure images intensity klokken la-icpms lee limits luminescence major maps nm optical parsons patches phase ppm prep present range sample showed shown strong syenite ti ti4 trace wavelengths zoning

created at TagCrowd.com

This is an example of a low marginal cost paper. The main purpose of bringing the samples to the ICP lab was a different study, but Ian figured he might as well check this out while everything was in place. The main study was big, complicated, and only just recently went off to reviewers. But this was simpler and more straightforward, so got written up and published first. So it is a great example of why research needs to be structured in a way such that investigators can veer off of their predetermined path if they see the opportunity to potentially figure something out for relatively little time, effort, and cost.

92Nb in meteorite accessory phases

I must admit to being a fan of the element niobium. It is quite possibly my favorite element on the periodic table. So imagine my delight when I came across this paper on short-lived Nb chronology of meteoritic zircon and rutile.

Today, Nb is monoisotopic. But although all isotopes with a mass other than 93 are radioactive, ⁹²Nb has a half-life of several million years, and is stable enough to have still been present in the early history of the solar system. It decays into ⁹²Zr.

So, the ⁹²Zr we find today is a combination of the solar systems original ⁹²Zr plus the solar system’s original ⁹²Nb, all of which has now decayed. Before the ⁹²Nb decay was complete, there would have been less ⁹²Zr around relative to the other Zr isotopes. So a phase with high Zr and low Nb (e.g. zircon) should show a ⁹²Zr deficit if it formed while ⁹²Nb was still around.

Similarly, a phase with high Nb and low Zr that formed when ⁹²Nb was still live should have a ⁹²Zr excess. Rutile is a prime example of a high Nb, moderate Zr phase.

So, armed with a multicollecter ICPMS and a laser, our intrepid authors pick meteorites with zircon and rutile in them, fire away, and observe the expected isotopic anomalies.

They then combine their results with those of other short-lived P process isotopes and attempt to constrain the nature of the supernova that created the isotopes, and the time between this supernova and the formation of the solar system.

I honestly don’t know enough about astronomy to know what an SNII-sources neutrino-driven wind is, so I can’t really comment on that unless a friendly blogging astronomer can help me out.

As for the 10 MA time period, this really depends on the exact age of the analysed phases. Amelin et al. 2002 give the age of CAI as 4567 MA, with chondrules being 2-3 Ma younger. So unless we know the age of the Chaunskij zircon relative to CAI’s, it isn’t apparent what this 10 MA means. In theory either U-Pb or Hf-W should help answer this question, but the absolute age of this zircon isn’t given. I didn’t chase up the references for the reported values for other short-lived P-process elements.

Full paper:
Yin, Q.Z., Jacobsen, S.B., McDonough, W.F., Horn, I., Petaev, M.I., Zippel, J. (2000). SUPERNOVA SOURCES AND THE 92Nb-92Zr p-PROCESS CHRONOMETER. The Astrophysical Journal,, 537, L49-L53.

Reference:
Amelin et al. 2002 Science Vol. 297. no. 5587, pp. 1678 - 1683

Paper Out

Stephan Klemme , Stefan Prowatke, Carsten Münker, Charles W. Magee, Yann Lahaye, Thomas Zack, Simone A. Kasemann, E. Joan A. Cabato and Benjamin Kaeser 2008. Synthesis and Preliminary Characterisation of New Silicate, Phosphate and Titanite Reference Glasses. Geostandards and geoanalytical research 32 32-54.

Eleven synthetic silicate and phosphate glasses were
prepared to serve as reference materials for in situ microanalysis of clinopyroxenes, apatite and titanite, and other phosphate and titanite phases. Analytical results using different micro-analytical techniques showed that the glass fragments were homogeneous in major and trace elements down to the micrometre scale. Trace element determinations using inductively coupled plasma-mass spectrometry (ICP-MS), multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) and secondary ionisation mass spectrometry (SIMS) showed good agreement for most elements (Li, Be, B, Cs, Rb, Ba, Sr, Ga, Pb, U, Th, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Tm, Yb, Lu,
Zr, Hf, Ta, Nb) studied and provide provisional recommended values.

So here’s the story: Often the limiting factor in the accuracy of in situ geochemical analyses is the quality and applicability of the reference material or standard. Stephan wasn’t happy with the standards available to the geochemical community, so he synthesized his own, and the rest of us analysed them to determine the composition.
It isn’t much of a story, really. So in order to add some substance to this post, I’ll give the backstory as well. Stephan and I both did our PhD’s on the ex-pet group at ANU- he was a couple of years ahead of me. As it turns out, he was the student whith whom I perpetrated anecdote number three ten years ago (aside- Easter 1998 was ten years ago. Holy shit! Where did the decade go?)
So, fast forward 8 years, and in August 2006 he comes back to Australia for the Goldschmidt conference. Obviously, a boozy catch-up over dinner is required, and we shoot the shit over the usual subjects of kids, life, and inevitably, geology. My poster for that conference is on standard synthesis, so Stephan and Simone (I got to meet the entire German-Edinburgh contingent) tell me about these new ion probe standards they have been analyzing. I point out that we could get values out of those glasses, and he informs me that he’d already been invited to use the lab by his PhD advisor, and asks if I want to show them the ropes and get on the paper. So 5 days later, he and Simone rock up to lab, I set up the run, and away we go.
Stephan is very much a petrologist- I suspect his main interest was seeing how little silica he could put into the phosphate glass and still get a quench- but Simone is a ion probe guru, so she was naturally skeptical of the apparent simplicity of laser ICPMS work. So we spent most of the morning looking at various what ifs that could get spurious results, shooting standards, and looking for potential interferences. At the risk of sounding naff, doing science with one’s friends is a lot of fun.
I didn’t have much to do with the interpretation or statistics done on the data, but as the native English speaker I was supposed to fix any Germanisms in the manuscript. “Supposed to” being the key phrase. These guys write so well that I had maybe one prepositional change to suggest in the draft. In fact, I just noticed that the most glaring grammatical error in the final manuscript was in the paragraph that I wrote. Go figure.

Best. Abstract. Ever.

The first-order Raman spectrum of diamond has been measured in a diamond anvil cell up to 27 GPa. The fundamental phonon line varies linearly in pressure with a shift of 2.87 cm^-1/GPa. This line appears to be an excellent pressure-calibration standard as an alternate to the ruby pressure scale.

H. Boppart, J. van Straaten, I. F. Silvera. 1985. Raman spectra of diamond at high pressures. Phys. Rev. B, 32, 1423-1425.

This is what we did; this is what we got; this is what it’s good for. Three sentences. Efficient scientific writing at its best.

I signed off on a paper I’m et al. on, and finished and sent off my review today, in addition to the usual lab grind. And I didn’t even cite-nap the authors. It has been a good day.

Paper out

Birch, W. D., Barron, L. M., Magee, C. and Sutherland, F. L. , 'Gold- and diamond-bearing White Hills Gravel, St Arnaud district, Victoria: age and provenance based on U - Pb dating of zircon and rutile', Australian Journal of Earth Sciences, 54:4, 609 - 628

Abstract: Investigation of coarse (42 mm) heavy-mineral concentrates from the White Hills Gravel near St Arnaud in western Victoria provides new evidence for the age and provenance of this widespread palaeoplacer formation. A prominent zircon – sapphire – spinel assemblage is characteristic of Cenozoic basaltic-derived gemfields in eastern Australia, while a single diamond shows similar features to others found in alluvial deposits in northeastern Victoria and New South Wales. Dating of two suites of zircons by fission track and U– Pb (SHRIMP) methods gave overlapping ages between 67.4+5.2 and 74.5+6.3 Ma, indicating a maximum age of Late Cretaceous for the formation. Another suite of minerals includes tourmaline (schorl – dravite), andalusite, rutile and anatase, which are probably locally derived from contact metamorphic aureoles in Cambro-Ordovician basement metapelites intruded by Early Devonian granites. U – Pb dating of rutile grains by laser ablation ICPMS gave an age of 393+10 Ma, confirming an Early Devonian age for the regional granites and associated contact metamorphism. Other phases present include pseudorutile, metamorphic corundum of various types, maghemite and hematite, which have more equivocal source rocks. A model to explain the diverse sources of these minerals invokes recycling and mixing of the far-travelled basalt-derived suite with the less mature, locally derived metamorphic suite. Some minerals have probably been recycled from Mesozoic gravels through Early Cenozoic (Paleocene – Eocene) drainage systems during various episodes of weathering, ferruginisation and erosion. Comparison between heavy-mineral assemblages in occurrences of the White Hills Gravel may allow distinction between depositional models advocating either separate drainage networks or coalescing sheets. Such assemblages may also provide evidence for the present-day divide in the Western Uplands being the youngest expression of an old (Late Mesozoic – Early Cenozoic) stable divide separating north- and south-flowing streams or a much younger feature (ca 10 Ma) which disrupted mainly south-flowing drainage.

I did the rutile U/Pb, most of the zircon U/Pb, and the rutile trace element analysis and interpretation. So if anyone out there has hard core stratigraphy questions, I'll have to pass them on to Bill.

I can't actually link my own paper from home, so anyone interested will have to look it up the old fashioned way.

Can’t hack fashion? Try chemistry

A recent article in The Australian has pointed out that the minimum entry score for university science courses is lower than the minimum required marks for almost any other course.

“At the University of Technology, Sydney, the entry score for a science degree was 76.9, compared with 88 for fashion and textile design, 80.25 for sport and exercise management and 84.15 for an arts degree.”

The study cites a lack of prestige, higher course fees, and boring year 11 and 12 courses as contributing factors. For those American readers out there, entry scores in Australia are demand driven, so either all the high-scoring students are choosing to pursue careers outside of science, or nobody at all is interested in science. Thus science departments are letting anyone in off the streets to fill up classes.

Usually I’d slide a snide punchline in here, but this is so depressing that I can’t think one up.

I disagree with some of the proposed solutions, though.

In a follow up article, a professional scientist spokesman is quoted as saying, "There's a view among some kids at secondary school that science is nerdy. We've got to make it sexy.

Alternatively, we could point out to them that being sexy without knowing any science will turn you into a syphilis-addled teen parent. But maybe he was looking for a more positive spin.

Apparent Dip and Green Gabbro both contain posts about how to get more people interested in geology, and what we ought to be communicating to the public. Thermochronic seems to be pushing the inspiration angle, while Yami prefers to hold San Francisco hostage.

I think the inspiration angle has its problems. Let’s be honest folks. We spend most of out time looking at rocks. Or squeezing them. Or figuring out what they are made of. This is not the sort of inspirational topic that propelled the Greeks to create one of humanity’s most enduring mythologies. There is no ancient Sumarian deity who split the feldspars from the amphiboles or chewed the primordial muck to distinguish silt from clay. The wow factor of rocks is essentially zero.

I don’t fancy the fear factor either. Most people don’t really care if their hometown will get flattened once every 400 years, and there is enough irrational fear-mongering going around already, without us spoiling the party by pointing out threats that are actually real.

I reckon the best approach is to find a way to communicate how science works. The really great thing about geology is how we connect seemingly unrelated things to put together a story. For example:
If you find me an ancient hunk of hyaloclastic basalt (or low-grade metagabbro), a geochemist can tell you whether or not the shoreline near where that basalt erupted had a serious tsunami risk. And they can do it by measuring three elements that most people can’t even find on the periodic table: lanthanum, niobium, and uranium.

The reasoning is simple:
Niobium is compatible in titanium minerals, due to the similar ionic radius and the ability to charge-balance trivalent cations.
Titanium residues in magma formation form during the hydrous melting of the mantle.
Transporting water into the deep hot mantle requires a subducting oceanic plate.
Subduction zones are the main sites of tsunami-generating magnitude 9+ megathrusts.

And if that sort of connectivity between seemingly unrelated factoids isn’t cool, then maybe you should be selling houses or balancing ledgers. Or maybe I’m just a dork.

The story behind each line in the above argument is an entire geology class. Learning how to test and verify these outlandish ideas is how we learn about the natural world.

I think the big challenge is getting people interested in appreciating the power of the scientific method, and then teaching them how to apply it to things that interest them. And finally, if their natural inclinations don’t point them towards outcrops or osmium, we could just appeal to their pocketbooks:

“Some geologists have eclipsed dentists as the highest-paid graduates in Australia, scoring rock-solid wages of more than $80,000 a year”.
-The Australian 19/12/05

Luke-warm lava

Today, after a couple of false starts, I managed to finally reduce some data that’s been hanging over my head for a few months. I generally don’t do much data reduction or interpretation- I get people set up and collecting, and leave the minor step of interpretation up to them. It is only the really strange, unusual, or perverse projects that get kicked down the chain of command into my lap. Luckily, this was a project that actually interests me, as opposed to the completely bizarre, esoteric stuff that sometimes comes up.

So, I finally finished my crunching, fed the geochemistry into a geothermometer to get a crystallization temperature, and scratched my chin over the answer. 90 degrees. Not 900 degrees, 90. The temperature of a cup of coffee. Trouble was, this was not a sugar crystal. So the implications were somewhat interesting.

Let’s just assume that both my measurements and the thermometer (calibrated for a completely different range) were correct. Imagine, if you will, what a world we would live in if magmatic temperatures were below the boiling point. Better yet, imagine a world in which volcanoes simply erupted coffee. Some key advantages:
-Hawaiians would be more edgy, less laid back.
-The people of Martinique would still be alive today, as the 1902 eruption would have simply covered St. Pierre in a dollop of foamy milk, instead of destroying the city with a nuée ardente.
-The mud pots of New Zealand and Yellowstone wouldn’t need a separate coffee store.
-Seattle could still be the retail coffee capital of the world.
-My data might actually make sense.

This might seem like a bit of a stretch, but remember, it is the season of forgiveness. Imagine a better world, a kinder world, where natural disasters are after-dinner beverages. The sugarplum fairies could transform the bushfire embers into snowflakes and candycanes. We could have joy for all, and peace on earth. And if you can’t imagine that for Christmas, then what future is there? A role in a Dr. Suess book? Or perhaps the life of a Dickensian mench, cruelly ignoring the crippling influence of ignorance and want. So Merry Christmas everyone, and have a happy New Year.

Google simply doesn’t give a shit about woman scientists’ publication records

Back in September, I wrote about how academic indices are incapable of realizing that a woman researcher who changes her name is still the same person. As a test name, I used my grad school colleague Helen (she has published under both names, and when I asked her, she said she didn’t mind me performing this experiment). In September’s typically bombastic, tongue-and-cheek post, I gave a couple of rather snide hypotheses which I could pretend to address with symbolic examples instead of rigorous testing.

I would like to revise those hypotheses, at least with respect to Google Scholar.

I now suggest that Google Scholar does not realize that Helen Degeling and Helen Tomkins is the same researcher because:

Hypothesis 1: The google search technology is not sufficiently savvy to determine that she is one person who changed her name.

Hypothesis 2: They have the technology, they just can’t be bothered to apply it to this particular issue (e.g. they don’t give a shit).

Hypothesis one is testable. All we need to do is to determine if any of the scientific literature accessible via Google Scholar turns up evidence connecting these two Helens. If no such evidence exists, then it would be fair to state that Google Scholar, as currently programmed, simply doesn’t know that Degeling became Tomkins.

The easiest way to do this is to search for “nee Degeling.” Here are the results.

Those of you with journal access can see that “Helen Tomkins (neé Degeling)” is listed in the acknowledgements, and that Google scholar is smart enough to have found it there (which is why Watson et al. turned up in this search).

Thus hypothesis 1 is refuted. Of the hundreds of articles published in Helen's field this year, Google Scholar unerringly picked out the one that connects her maiden and married names. It just doesn’t bother to use this information when asked to compile her publications. Thus hypothesis 2 becomes our best working hypothesis, given the available data.

Suppositions as to why Google doesn’t give a shit are left as an exercise to the reader.

A zircon that predates the universe 2

So, in the first episode, I decided to investigate the dread option two. It really doesn’t make sense. This is science, how could anything possibly go wrong? The whole point of SHRIMP is to make U/Pb geochronology simple enough for a trained monkey to perform. So what could the problem be?

Well, in theory, the zircon could contain common Pb, in addition to the radiogenic Pb that was measured. So, what happens to the results when I apply a common Pb correction? The date of 15.2 Ga drops to 15.1 Ga. And the error increases from 0.3 to 0.4. Next?

What else could happen? Well, the first rule of analysis is this: always make sure that the thing you’re measuring is actually what you think it is. For Th, there is no question. But what about Pb?

Pb is a trickier matter. Zirconium and Hafnium are so similar in chemistry that it took science 99 years to isolate Hf from Zr and identify it as a separate element. As a result, Zircon contains substantial Hf- generally 1-2%. Because SIMS creates numerous molecular species, it is worth investigating the possibility of a molecular interference, such as ¹⁷⁴Hf¹⁶O₂ on ²⁰⁶Pb, or ¹⁷⁶Hf¹⁶O₂ on ²⁰⁸Pb.

As it turns out, the whole reason for building SHRIMP back in the 70’s was to have an ion probe with enough mass resolution to separate these peaks. Hf and O both have higher binding energies, and therefore lower mass/amu, than does Pb. Specifically, ²⁰⁶Pb has a mass defect of -27mAMU, while ¹⁶O is -5.1 and ¹⁷⁴Hf is -59.9. So the HfO2 peak should be 43.1 mAMU lighter. This is seen in figure 1, a mass scan taken on SHRIMP 1.



A few caveats about these figures. First of all, these are quick-and-dirty, low resolution mass scans, so SHRIMP-haters should not use these peak shapes as evidence that the machine is inherently imprecise. Secondly, these are all scans of the Temora standard, correctly centered on Pb, and not of the pre-universal grain. Thirdly, I know that the calibration of the X axis is off. Setting this is generally more trouble than it’s worth, as we measure peak positions relative to each other; the nominal “absolute” value is not all that important.

Anyway, as fig 1 shows, The HfO₂ and Pb peaks are clearly resolvable. Furthermore, in this grain, the ²⁰⁶Pb peak is considerably larger than the HfO₂ peak. This is not the case for the mass 208 peaks, as fig 2 shows.



There are two reasons for this. First, ¹⁷⁶Hf is 33 times more abundant than ¹⁷⁴Hf. Second, although the Th/U ratio of this zircon is greater than 0.3, Th has a much longer half-life, so relative to ²⁰⁶Pb, not much ²⁰⁸Pb has been produced in the 418 million year lifetime of this particular grain.

Thus, if the instrument was accidentally measuring HfO₂ peaks instead of Pb peaks, one would expect to find very large Th ages, accompanied by modest ²³⁸U ages. That is exactly what was observed with the “pre-universal” grain. Unfortunately, the measured Th/HfO₂ ratio is not very geologically useful.

As for how this happens, it is quite simple. The machine can be told to autocenter peaks, to allow it to correct for magnet instability. However, this centering assumes that the ²⁰⁶Pb peak will be larger than the HfO₂ peak (such as is the case in fig1). If you have a young, or low U zircon, then the HfO₂ peak may be larger. In such instances, the instrument will pick the Hf peak instead of the Pb peak, and the lab lemming who foolishly left centering on will get geologically meaningless results.

Anally observant readers will notice a discrepancy between my figures and my explanation. I won’t say what this problem is, but I will tell you this: The answer, in a single word, is:
YTTERBIUM!

Playing the name game

Tonight, I bring you the tale of two papers. The first paper, Zr budgets for metamorphic reactions, and the formation of zircon from garnet breakdown, is by H. Degeling, S. Eggins, and D. J. Ellis. The second paper, In situ U–Pb dating of zircon formed from retrograde garnet breakdown during decompression in Rogaland, SW Norway, is by H. S. Tomkins, I. S. Williams, and D. J. Ellis. Aside from the third author (and really, who cares about third authors?), the subject matter, the methodology, the samples, and the overall geologic framework, these two papers have something else in common. Something rather important, that neither Web of Science nor Google Scholar can discern (I also tried Georef, but it crashed my work comp, and I don’t have a home subscription).

Both papers are written by the same first author, who for the purposes of this blog will referred to as either Dr. Tomkins, or Helen*. As you might be able to surmise from the publication dates, Helen got married in 2003 +/-2 AD (1 permil precision is good enough for geochronologists), and changed her name. But as far as the system is concerned, she is no longer the same person. And neither index seems to list both of her papers as being written by the same person. Why is this?

I offer three hypotheses:

1. Computers are stupid, and a single person with more than one name is more than they can handle.
2. Married women aren’t worth listing because...
2a. Once they’re hitched, women have no future in scientific research.
2b. Real, hard-core science chicks are all feminist zealots who would never consider a name change.
3. The scientific indices are run by a bunch of lazy dumbasses.

Test of hypothesis 1:
Go to imdb.com, a large on-line database. Search for “Jamie-Lynn Siegler”. Then try “Jamie-Lynn DaScala”. If television database is smart enough to recognize that both names refer to the actress who plays Tony’s daughter in The Sopranos, is it really too much to ask for a scientific database to display the same level of competence? After all, the Web of Science certainly charges more for subscriptions.

Test of Hypothesis 2:
Consider the career of Marie Sklodowska. Married at the age of 28, she took her husband’s name, and first published under it three years later, with “Rayons emis par les composes de l'uranium et du thorium”. Over the next 37 years, she added to her scientific credentials with
-The discovery of polonium and radium.
-The Nobel Prize for physics, in 1903
-The Davy Medal of the Royal Society in 1903
-The Nobel Prize for chemistry, in 1911
All in all, Marie Curie didn’t do too badly.

Test of hypothesis 3:
The best way to test this is to see how long it takes the various indices to get their acts together.

Now, I’m a rogue, not a feminist, so I ain’t gonna campaign for any sort of systemic change. I will simply offer two bits of advice to Dr. Tomkins:
1. If future editors ask you for the name of a referee for future papers, why not suggest Dr. Degeling?
2. Make sure you reference her work many times, as the citation indices probably think you two are independent researchers.

* ‘cause that’s her name.

Hafnium is for lovers

Geologists who are passionate about their analytical methods will have a hard time passing up the laser-MC-ICP-MS method of hafnium isotopic analysis in zircon. All too often, geochemistry is a struggle against the inexorable drag of entropy, as columns and calibrated solutions strain to withstand the natural inclinations of the elements they seek to constrain.

Not so with Hf-La-MC-ICP-MS. The natural inclination of zircon melds perfectly with the strengths of the machine. The embrace of distribution co-efficients and analytical processes is so picturesque that the raw data from a Monastery zircon can agree with that of the most popular pulp journals to within one digit in the fifth decimal place.

Even without accommodation for aging amplifiers or the crass interference of the heavy rare-earth elements, this conjoining of HFSE enrichment and pervasive ionic excitation allows transcendent analyses of this highly evolved phase. Primitive mantle petrologists are positively molten with jealousy at the ease of working with such a refined, but compositionally dependent mineral. If only all mass spectrometry was as satisfying.

Myth Busted

So, Thursday arvo I managed to finally test my theory on the anomalous backgrounds that I was whinging about here. I did an excellent job of disproving my hypothesis. Trace HF in a solution ICP-MS does not remobilize HFS elements from laser ablation. The great thing about proving myself wrong in this case is that it means that I don’t need to worry about rejuggling the schedule. There is no point trying to shuffle people around to avoid a problem that doesn’t actually exist.

Every disaster is an opportunity.

We may have discovered a new way to cross-contaminate samples between solution and laser-ablation ICP-MS today. I’m not saying that no-one has ever done this before, although that is possible. But as far as I know, nobody has done what we did in a repeatable and predictive manner, much less published the results. More importantly, as far as I know there is no record in the literature of how to fix the problem in a simple and timely fashion.

So, on Monday, I am going to see if today’s observation can be repeated, or if it is just a Friday arvo fluke. If I can figure it out, it might even be worth turning into a short paper or a technical note, so that other people don’t have to spend all day cleaning up their machine and pulling their hair out, like today’s analyst has been doing. I don’t know if that will make up for spending all Friday night in the lab running samples that were supposed to be finished hours ago, but you always gotta look on the bright side- a paper’s a paper.

On the other hand, if my hunch about the source of this thing is wrong, then I’ll be stuck in lab all day Monday banging my head against the wall over the same flaky trace elements. At least then he’ll have someone to share the misery with. And even if it is a total write off, at least I can whinge about it to you folks. So have a good weekend, everyone- even if you’re stuck in lab at sundown with ten hours of samples left and backgrounds that are two orders of magnitude too high.