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Petrogenesis of a new type of intrusive shergottite: olivine-gabbro Northwest Africa 13227.
- Source :
-
Geochimica et Cosmochimica Acta . Apr2024, Vol. 370, p41-65. 25p. - Publication Year :
- 2024
-
Abstract
- Petrologic investigations of martian meteorite Northwest Africa (NWA) 13227 indicate it is an olivine-gabbroic shergottite, a relatively new shergottite group, which differs from previously described gabbroic shergottites due to relatively high quantities of olivine. NWA 13227 is comprised of phenocrystic, oscillatory-zoned pyroxene and olivine, set in a matrix of maskelynite, Fe-Cr-Ti oxides, phosphates, and sulfides. It displays gabbroic and poikilitic textures in 2D from back-scattered electron images, and in 3D from X-ray Computed Tomography (XCT) imaging, suggesting affinities to both poikilitic and gabbroic shergottites. Measured εHf and εNd values of bulk rock (-19.7 and −5.9, respectively) and its chondrite-normalized La/Yb ratio of 1.13 indicate the specimen is derived from a mantle reservoir relatively enriched in incompatible trace elements and is similar to that which produced most 'enriched shergottites.' Based on the Ti/Al ratio of pyroxene, phosphorous zoning in olivine, and minor components in phosphates and oxides, we infer that NWA 13227 began crystallizing under reducing conditions of QFM–2.6 and temperatures of ∼ 1100 °C, consistent with conditions in Mars' lower crust/upper mantle. The sample finished crystallizing at or near the surface under redox conditions between QFM–0.5 to QFM–0.1 and temperatures of ∼ 850 °C. The volatile element compositions in apatite indicate that NWA 13227 experienced degassing during the last stages of crystallization. The timing of crystallization is estimated at 225 Ma ± 50 Ma using a Lu-Hf and Sm-Nd source versus age model. [ABSTRACT FROM AUTHOR]
- Subjects :
- *OLIVINE
*COMPUTED tomography
*MARTIAN meteorites
*YTTERBIUM
*PETROGENESIS
*PYROXENE
Subjects
Details
- Language :
- English
- ISSN :
- 00167037
- Volume :
- 370
- Database :
- Academic Search Index
- Journal :
- Geochimica et Cosmochimica Acta
- Publication Type :
- Academic Journal
- Accession number :
- 176149975
- Full Text :
- https://doi.org/10.1016/j.gca.2024.02.004