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  • Wiley  (2)
  • McSween, Harry Y.  (2)
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  • Wiley  (2)
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  • 1
    Online Resource
    Online Resource
    Petrology and trace element geochemistry of Tissint, the newest shergottite fall
    Wiley ; 2015
    In:  Meteoritics & Planetary Science Vol. 50, No. 1 ( 2015-01), p. 63-85
    Details
    In: Meteoritics & Planetary Science, Wiley, Vol. 50, No. 1 ( 2015-01), p. 63-85
    Abstract: The fall and recovery of the Tissint meteorite in 2011 created a rare opportunity to examine a Martian sample with a known, short residence time on Earth. Tissint is an olivine‐phyric shergottite that accumulated olivine antecrysts within a single magmatic system. Coarse olivine grains with nearly homogeneous cores of Mg# 〉 80 suggest slow re‐equilibration. Many macroscopic features of this sample resemble those of LAR 06319, including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions. Unlike LAR 06319, however, no magmatic hydrous phases were found in the analyzed samples of Tissint. Minor and trace element compositions indicate that the meteorite is the product of closed‐system crystallization from a parent melt derived from a depleted source, with no obvious addition of a LREE‐rich (crustal?) component prior to or during crystallization. The whole‐rock REE pattern is similar to that of intermediate olivine‐phyric shergottite EETA 79001 lithology A, and could also be approximated by a more olivine‐rich version of depleted basaltic shergottite QUE 94201. Magmatic oxygen fugacities are at the low end of the shergottite range, with log f O 2 of QFM‐3.5 to ‐4.0 estimated based on early‐crystallized minerals and QFM‐2.4 estimated based on the Eu in pyroxene oxybarometer. These values are similarly comparable to other depleted shergottites, including SaU 005 and QUE 94201. Tissint occupies a previously unsampled niche in shergottite chemistry: containing olivines with Mg# 〉 80, resembling the enriched olivine‐phyric shergottite LAR 06319 in its crystallization path, and comparable to intermediate olivine‐phyric shergottite EETA 79001A, depleted olivine‐phyric shergottite DaG 476, and depleted basaltic shergottite QUE 94201 in its trace element abundances and oxygen fugacity. The apparent absence of evidence for terrestrial alteration in Tissint (particularly in trace element abundances in the whole‐rock and individual minerals) confirms that exposure to the arid desert environment results in only minimal weathering of samples, provided the exposure times are brief.
    Type of Medium: Online Resource
    ISSN: 1086-9379 , 1945-5100
    URL: Issue
    URL: Article
    DOI: 10.1111/maps.2015.50.issue-1
    DOI: 10.1111/maps.12403
    Language: English
    Publisher: Wiley
    Publication Date: 2015
    detail.hit.zdb_id: 2011097-2
    SSG: 16,12
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  • 2
    Online Resource
    Online Resource
    Lithium isotopes and light lithophile element abundances in shergottites: Evidence for both magmatic degassing and subsolidus diffusion
    Wiley ; 2016
    In:  Meteoritics & Planetary Science Vol. 51, No. 1 ( 2016-01), p. 80-104
    Details
    In: Meteoritics & Planetary Science, Wiley, Vol. 51, No. 1 ( 2016-01), p. 80-104
    Abstract: Degassed magmatic water was potentially the major source of surficial water on Mars. We measured Li, B, and Be abundances and Li isotope profiles in pyroxenes, olivines, and maskelynite from four compositionally different shergottites—Shergotty, QUE 94201, LAR 06319, and Tissint—using secondary ion mass spectrometry ( SIMS ). All three light lithophile elements ( LLE ) are incompatible: Li and B are soluble in H 2 O‐rich fluids, whereas Be is insoluble. In the analyzed shergottites, Li concentration decreases and Be concentration increases from cores to rims in pyroxenes. However, B concentrations do not vary consistently with Li and Be abundances, except in QUE 94201 pyroxenes. Additionally, abundances of these three elements in olivines show a normal igneous‐fractionation trend consistent with the crystallization of olivine before magma ascent and degassing. We expect that kinetic effects would lead to fractionation of 6 Li in the vapor phase compared to 7 Li during degassing. The Li isotope profiles, with increasing δ 7 Li from cores to rims, as well as Li and B profiles indicate possible degassing of hydrous fluids only for the depleted shergottite QUE 94201, as also supported by degassing models. Conversely, Shergotty, LAR 06319, and Tissint appear to have been affected by postcrystallization diffusion, based on their LLE and Li isotope profiles, accompanied by diffusion models. This process may represent an overlay on a degassing pattern. The LLE profiles and isotope profiles in QUE 94201 support the hypothesis that degassing of some basaltic shergottite magmas provided water to the Martian surface, although evidence may be obscured by subsolidus diffusion processes.
    Type of Medium: Online Resource
    ISSN: 1086-9379 , 1945-5100
    URL: Issue
    URL: Article
    DOI: 10.1111/maps.2016.51.issue-1
    DOI: 10.1111/maps.12582
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 2011097-2
    SSG: 16,12
    Location Call Number Limitation Availability
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    Online Resource
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