closure temperature - This is the temperature at which diffusion for a particular element in a particular system is negligible. It reflects the fact that diffusion proceeds faster at higher temperatures, and that when temperature becomes too low, diffusion is very sluggish. Radiometric ages strictly date the last time the closure temperature for daughter elements was obtained. For objects that cooled fast, the closure temperatures and ages obtained using different chronometers should be essentially the same, whereas if an object cooled more slowly, the closure temperatures and ages using different chronometers might not agree.
FUN inclusion - This is a type of CAI that has many isotopic anomalies of many elements, including anomalies produced by what were originally recognized as mass-fractionation (F) and unknown nucleosynthethic (UN) processes. This acronym was developed in the 1970s by the Lunatic Asylum folks in CalTech-- and we've had it ever since. I guess it's too FUN to let go.
epsilon (53Cr), epsilon (182W), and epsilon (142Nd) - These refer to the deviations from a standard of the isotopic ratios 53Cr/52Cr, 182W/180W, and 142Nd/143Nd, respectively, as in the following example:
epsilon (53Cr) = [(53Cr/52Cr)sample/(53Cr/52Cr)std - 1] x 10,000
where std = standard. Note the similarity to the del notation, except for the difference in the multiplier. The main thing to remember is that the values given by epsilon units represent very small deviations. We have to multiply these deviations by 10,000 just to avoid having to write so many zeroes.
internal isochron - This is an isochron determined by analyses of mutliple minerals within a particular sample. Examples include Fig. 1 of Lugmair & Shukolykov. If the data for various minerals lie along along a single line in an isotope plot such as Fig. 1, it is taken to be good evidence for a real age of a particular sample (e.g., the time of crystallization for individual rocks in Fig. 1). This contrasts with a model age, which involves an additional (model) assumption of some sort. For example, Fig. 2 of Lugmair & Shukolykov assumes that various whole-rock HED meteorites (e.g., the diogenites Shalka [SHA] and Johnstown [JT], and the remaining eucrites), are all related. This is probably a good assumption, but the isochron in this case is based on a model, and refers to a different event (in this case interpreted as the time when initial differentiation of the parent body to produce eucrites and diogenites occurred). Additional examples of the difference between internal (sample) and model ages are given in the pages from Prof. Cowley.
primitive achondrite - This is an achondrite that has igneous textures but more-or-less chondritic mineralogy. Examples include the acapulcoites, winonaites, lodranites, and silicate inclusions in IAB irons. Some people lump the brachinites in this category, too.
angrite - This is a type of achondrite that features
prominently in efforts to link data for short-lived to long-lived radionuclides,
as evidenced in the readings. Angrites are extraterrestrial basalts
and contain mainly plagioclase and clinopyroxene, and smaller amounts of
olivine and kirschtenite (Ca-Fe-Mg olivine). They differ from eucrites,
which are also achondrite basalts, in terms of mineral chemistry, mineralogy
(e.g., kirschtenite in angrites, silica minerals in eucrites), texture,
shock and metamorphic history, and age. The last angrite to be discovered,
D'Orbigny, has vesicles, as seen below.
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non-cumulate vs cumulate eucrite - There
are a variety of eucrite achondrites. Non-cumulate eucrites
are finer-grained and have textures which suggest they formed either as
basalt flows, dikes, sills, or possibly impact melts; cumulate eucrites
are coarser-grained and appear to have formed by crystal settling in a
magma chamber.