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The concentration profiles of 13 trace elements (Li, Na, Al, P, Ca, So, Ti, V, Cr, Mn, Co, Ni, and Y) were determined in a natural mantle olivine xenocryst included in a hybridized hydrous dioritic magma during cooling from ~1000[degrees]C, which allow trace-element chemical diffusion coefficients to be evaluated relative to Mg-Fe interdiffusion under conditions that are difficult to access in the laboratory. The effective diffusion coefficients of many elements (Li, Ca, Sc, Mn, Co, Ni, and Y) fell within a factor of three of the corresponding Mg-Fe interdiffusion coefficient, in agreement with results from laboratory experiments at higher temperatures. By contrast, the concentration profiles for Na, Ti, and V implied much faster diffusion rates, while P showed no discernible diffusion. The Al and Cr profiles, which were well correlated with each other, were complex and variable on a small length scale due to local precipitation of spinel. These data show that the diffusion coefficients of cations in olivine are not simple functions of ionic charge or ionic radius, but they are likely controlled by the availability of suitable diffusion pathways. doi: 10.1130/G30788.1

Single-crystal X-ray diffraction has been used to measure the thermal expansion coefficients of forsterite, wadsleyite, ringwoodite, and their hydrous forms at ambient pressure, from temperatures as low as 133 K to as high as 919 K. Second-order polynomial fitting to ln(V/[V.sub.0]) vs. T was applied to derive the expansion coefficients in the form of [alpha] = [a.sub.l] x T + [a.sub.0]. The single crystal of anhydrous wadsleyite persisted up to 859 K. Hydrous forsterite was observed to dehydrate at 919 K, whereas hydrous wadsleyite started to dehydrate at 655 K. The crystal of ringwoodite with 0.20 wt% broke down at 911 K, and the two ringwoodite samples with 0.74 and 2.4 wt% [H.sub.2]O, were observed to break down with an irreversible unit-cell expansion at 808 and 606 K, respectively. From room temperature to high temperatures in this study, the mean thermal volume expansion coefficients are 36.4(5) and 38.1 (9) x [10.sup.-6] [K.sup.-1], respectively, for anhydrous and hydrous forsterite; 28.5(5) and 35.8(8) x [10.sup.-6] [K .sup.-1], respectively, for the anhydrous and hydrous wadsleyite; 30.6(9), 35.2(15), and 34.9(7) x [10.sup.-6] [K.sup.-1] for the samples ofringwoodite with 0.2, 0.74, and 2.4 wt% [H.sub.2]O, respectively. Thus, forsterite, wadsleyite, and ringwoodite all have larger thermal expansion coefficients in their hydrous forms than in their anhydrous forms. Keywords: Thermal expansion, forsterite, wadsleyite, ringwoodite, single crystal

The temperature dependence of the partitioning of [Al.sub.2][O.sub.3] between forsterite-rich olivine and Cr-rich spinels has been experimentally calibrated at 100 kPa between 1250 and 1450 [degrees]C under reducing conditions. For spinel with values of [Y.sub.Cr] between 0.07 and 0.69, and containing T([degrees]C) = 10 000/0.512 + 0.873[Y.sub.cr] - 0.91 ln([K.sub.D]) - 273 where [Y.sub.Cr] = Cr/(Cr + Al) in spinel in atomic proportions and [K.sub.D] = [Al.sub.2][O.sup.ol.sub.3]/[Al.sub.2][O.sup.sp.sub.3] in wt%. This equation reproduces the temperature of the experiment for the calibration data set within [+ or -] 22[degrees]C. Empirical tests suggest that this geothermometer has little pressure dependence within the range of pressures encountered in the crust and upper mantle. Keywords: Olivine, spinel, aluminum, thermometer, experiment

Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned ([Fa.sub.24-26]) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range ([Fa.sub.6]-[Fa.sub.10]) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite ([Fa.sub.28]-[Fa.sub.38]) belt. The wadsleyite-ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ringwoodite belt consist of granoblastic-like intergrowth of polygonal crystallites of both ringwoodite and wadsleyite, with wadsleyite crystallites dominating in the core and ringwoodite crystallites dominating in the belt. Texture and compositions of both high-pressure polymorphs are strongly suggestive of formation by a fractional crystallization of the olivine melt of a narrow composition ([Fa.sub.24-26]), starting with Mg-rich wadsleyite followed by the Mg-poor ringwoodite from a shock-induced melt of olivine composition ([Fa.sub.24-26]). Our findings could erase the possibility of the resulting unrealistic time scales of the high-pressure regime reported recently from other shocked L-6 chondrites. focused ion beam | transmission electron microscopy | shocked chondrite | high-pressure mineral