Academic Journal
39 Ar‐ 40 Ar dating of the Zagami Martian shergottite and implications for magma origin of excess 40 Ar
| العنوان: | 39 Ar‐ 40 Ar dating of the Zagami Martian shergottite and implications for magma origin of excess 40 Ar |
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| المؤلفون: | BOGARD, Donald D., PARK, Jisun |
| المصدر: | Meteoritics & Planetary Science ; volume 43, issue 7, page 1113-1126 ; ISSN 1086-9379 1945-5100 |
| بيانات النشر: | Wiley |
| سنة النشر: | 2008 |
| المجموعة: | Wiley Online Library (Open Access Articles via Crossref) |
| الوصف: | — The Zagami shergottite experienced a complex, petrogenetic formation history (McCoy et al. 1992, 1999). Like several shergottites, Zagami contains excess 40 Ar relative to its formation age. To understand the origin of this excess 40 Ar, we made 39 Ar‐ 40 Ar analyses on plagioclase and pyroxene minerals from two phases representing different stages in the magma evolution. Surprisingly, all these separates show similar concentrations of excess 40 Ar, ˜1 × 10 −6 cm 3 /g. We present arguments against this excess 40 Ar having been introduced from the Martian atmosphere as impact glass. We also present evidence against excess 40 Ar being a partially degassed residue from a basalt that actually formed ˜4 Gyr ago. We utilize our experimental data on Ar diffusion in Zagami and evidence that it was shock‐heated to only ˜70 °C, and we assume this heating occurred during an ejection from Mars ˜3 Myr ago. With these constraints, thermal considerations necessitates either that its ejected mass was impossibly large, or that its shock‐heating temperature was an order of magnitude higher than that measured. We suggest that this excess 40 Ar was inherited from the Zagami magma, and that it was introduced into the magma either by degassing of a larger volume of material or by early assimilation of old, K‐rich crustal material. Similar concentrations of excess 40 Ar in the analyzed separates imply that this magma maintained a relatively constant 40 Ar concentration throughout its crystallization. This likely occurred through volatile degassing as the magma rose toward the surface and lithostatic pressure was released. These concepts have implications for excess 40 Ar in other shergottites. |
| نوع الوثيقة: | article in journal/newspaper |
| اللغة: | English |
| DOI: | 10.1111/j.1945-5100.2008.tb01116.x |
| الاتاحة: | http://dx.doi.org/10.1111/j.1945-5100.2008.tb01116.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1945-5100.2008.tb01116.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.2008.tb01116.x |
| Rights: | http://onlinelibrary.wiley.com/termsAndConditions#vor |
| رقم الانضمام: | edsbas.84D93035 |
| قاعدة البيانات: | BASE |
| DOI: | 10.1111/j.1945-5100.2008.tb01116.x |
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