Meteoritics & Planetary Science, Volume 38, Number 8 (2003)http://hdl.handle.net/10150/6412972024-03-29T08:16:32Z2024-03-29T08:16:32ZBook Review: Phosphates: Geochemical, Geobiological, and Materials Importance, M. J. Kohn, J. Rakovan, J. M. Hughes (Eds.)Quade, J.http://hdl.handle.net/10150/6557412021-02-20T01:14:17Z2003-01-01T00:00:00ZBook Review: Phosphates: Geochemical, Geobiological, and Materials Importance, M. J. Kohn, J. Rakovan, J. M. Hughes (Eds.)
Quade, J.
Book Review: Phosphates: Geochemical, Geobiological, and Materials Importance, M. J. Kohn, J. Rakovan, J. M. Hughes (Eds.). Mineralogical Society of America and Geochemical Society, Washington, D.C., USA (2002).
2003-01-01T00:00:00ZMinor element zoning and trace element geochemistry of pallasitesHsu, W.http://hdl.handle.net/10150/6557362021-02-20T01:13:03Z2003-01-01T00:00:00ZMinor element zoning and trace element geochemistry of pallasites
Hsu, W.
I report here on an ion probe study of minor element spatial distributions and trace element concentrations in six pallasites. Pallasite olivines exhibit ubiquitous minor element zoning that is independent of grain size, morphology, and adjacent phases. Ca, Cr, Ti, V, and Ni concentrations decrease from center to rim by factors of up to 10, while Mn is generally unzoned or increases slightly at the very edge of some olivine grains. The maximum concentrations of these elements at the center of olivine vary from grain to grain within the same meteorite and among the pallasites studied. These zoning profiles are consistent with thermal diffusion during rapid cooling. The inferred cooling rates at high temperature regimes are orders of magnitude faster than the low-temperature metallographic cooling rates (~0.5 to 2 deg degrees C/Ma). This suggests that pallasites, like mesosiderites, have experienced rather complicated thermal histories, i.e., cooling rapidly at high temperatures and slowly at low temperatures. Pallasite olivines are essentially free of REEs. However, the phosphates display a wide range of REE abundances (0.001 to 100 x CI) with distinct patterns. REEs are generally homogeneous within a given grain but vary significantly from grain to grain by a factor of up to 100. Albin and Imilac whitlockite are highly enriched in HREEs (~50 x CI) but are relatively depleted in LREEs (~0.1 to 1 x CI). Eagle Station whitlockite has a very unusual REE pattern: flat LREEs at a 0.1 x CI level, a large positive Eu anomaly, and a sharp increase from Gd (0.1 x CI) to Lu (70 x CI). Eagle Station stanfieldite has a similar REE pattern to that of whitlockite but with much lower REEs by a factor of 10 to 100. Springwater farringtonite has relatively low REE concentrations (0.001 to 1 x CI) with a highly fractionated HREE-enriched pattern (CI-normalized Lu/La ~100). Postulating any igneous processes that could have fractionated REEs in these phosphates is difficult. Possibly, phosphates were incorporated into pallasites during mixing of olivine and IIIAB-like molten Fe. These phosphates preserve characteristics of a previous history. Pallasites have not necessarily formed at the mantle-core boundary of their parent bodies. The pallasite thermal histories suggest that pallasites may have formed at a shallow depth and were subsequently buried deep under a regolith blanket.
2003-01-01T00:00:00ZNoble gases and mineralogy of meteorites from China and the Grove Mountains, Antarctica: A 0.05 Ma cosmic ray exposure age of GRV 98004Lorenzetti, S.Lin, Y.Wang, D.Eugster, O.http://hdl.handle.net/10150/6557372021-02-20T01:13:16Z2003-01-01T00:00:00ZNoble gases and mineralogy of meteorites from China and the Grove Mountains, Antarctica: A 0.05 Ma cosmic ray exposure age of GRV 98004
Lorenzetti, S.; Lin, Y.; Wang, D.; Eugster, O.
We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 +/- 10.0 Ma, 3.8 +/- 0.6 Ma, and 17.0 +/- 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body-Earth transfer time of 0.052 +/- 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth-crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages less than or equal to 0.1 Ma.
2003-01-01T00:00:00ZPartitioning of Ca and Al between forsterite and silicate melt in dynamic systems with implications for the origin of Ca, Al-rich forsterites in primitive meteoritesPack, A.Palme, H.http://hdl.handle.net/10150/6557392021-02-20T01:13:47Z2003-01-01T00:00:00ZPartitioning of Ca and Al between forsterite and silicate melt in dynamic systems with implications for the origin of Ca, Al-rich forsterites in primitive meteorites
Pack, A.; Palme, H.
We report the results of dynamic crystallization experiments that were specifically designed to study the dependence of Ca and Al partitioning between forsterite and melt in rapidly cooling Ca- and Al-rich melts. The partitioning of Ca between olivine and silicate melt is found to be independent of the cooling rate within the range of 1.5 to 1000 degrees C/hr and at CaO contents of up to 25 wt%. Within analytical uncertainty, our data plot on the equilibrium partitioning curve obtained by Libourel (1999). The partitioning behavior of Al at high cooling rates is more complex. Aluminum is much more heterogenously distributed in the olivine and the co-existing melt than Ca. But, no systematic trend of Al partition coefficient with cooling rate is observed. We apply the results of the experiments to the formation of meteoritic forsterites with relatively high contents of Ca and Al. Although these forsterites are found frequently inside chondrules, the Ca contents of their host chondrules are far too low to crystallize these high Ca-forsterites. This is also true for very rapid cooling of chondrule melts. The parental melt of these forsterites requires CaO contents above 20 wt%.
2003-01-01T00:00:00Z