Petrogenesis of Lunar Poikilitic Impact Melt Meteorite Oued ...Petrogenesis of Lunar Poikilitic...
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Petrogenesis of Lunar Poikilitic Impact Melt Meteorite Oued Awlitis 001 Axel Wittmann 1 , Randy L. Korotev 1 , Bradley L. Jolliff 1 , and Anthony J. Irving 2 1 Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, [email protected]. 2 Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195. Oued Awlitis (OA) 001 • a lunar meteorite with a preserved fusion crust (fig. a–b). • found in 2014 in Morocco/Western Sahara [1–2]. • main 382 g piece excavated from shallow depth. Study Objective: Unravel Petrogenesis from Petrography and Chemistry. Petrography • Plagioclase clasts and phenocrysts poikilitically enclosed in olivine or pyroxene (fig. c), minor FeS, FeNi, SiO 2 , FeTiO 3 , chromite. • Pockets of glassy shock melt occur (fig. d); planar deformation features (PDF) in plagioclase (fig. e) indicate shock pressures of >10 to <24 GPa [3–4] • Plagioclase is the only clast component observed. • Texturally and compositionally similar: NWA (Northwest Africa) 482 [5–6] and clasts in PCA (Pecora Escarpment) 2007 [7] and Shişr 161 [8] (fig. f–g). 50 μm Ol Px Pl 50 μm 100 μm Ol Pl Px Chemistry • highly feldspathic bulk rock composition with low concentrations of incompatible elements (fig. g). • low siderophile element enrichment and FeNi composition suggests small meteoritic component (figs. h–j). SiO 2 shock melt Provenance and Petrogenesis • Bulk rock composition points to origin in the Feldspathic Highlands Terrane [15]. • Poikilitic texture suggests formation in an impact melt volume ~100 m thick [8]. • 100 m thick impact melt sheets form in 50 km Ø craters on the Moon [16]. • A >500 m Ø impact crater is required to excavate poikilitic impact melt from the center of a 100 m thick melt sheet [17] such as Tycho’s (fig. k). Conclusions • Oued Awlitis 001 may have crystallized in a >100 m thick melt sheet of a >50 km Ø impact crater in the Feldspathic Highlands Terrane and was excavated by an impact that produced a >500 m Ø crater. Acknowledgments: Zaid Oussaid & Mohamed Aid for recovering Oued Awlitis 001, Hasnaa Chennaoui-Aoudjehane (Hassan II University Casablanca) for documentation of the find site, Paul Carpenter (Washington University St. Louis) & Scott Kuehner (University of Washington Seattle) for electron microprobe analysis support, funding from NASA. a b a) Find site of Oued Awlitis 001. b) Sample specimen of Oued Awlitis 001, note homogenous texture and fusion crust. c d e c) Poikilitic texture of olivine (Ol) and pyroxene (Px) enclosing plagioclase, back-scattered electron image. Photo: M. Aid d) Shock melt pocket associated with olivine (Ol); plagioclase (Pl) and pyroxene (Px), back-scattered electron image. e) Plagioclase clast with faint PDF (arrows), linear polarized light micrograph. j f f) Pyroxene (top) and olivine (bottom) EMP (electron microprobe) data in mole %. g) Bulk rock INAA (instrumental neutron activation analysis) data; diagram after [8]. h) Bulk rock INAA data with CM chondrite mixing lines; diagram after [9]. j) EMP data for FeNi particles, diagram modified after [10] with data from [12–14]. high Ni metal clasts in Apollo 15 soils Chondritic Ni:Co ratio References: [1] Wittmann A. et al. (2014) Met. Soc. 77: Abstract # 5352. [2] Korotev R. L. & Irving A. J. (2015) LPSC 46: Abstract # 1942. [3] Ostertag R. (1983) Proc. LPSC 14: B364–B376. [4] Fritz J. et al. (2011) LPSC 42: Abstract # 1196. [5] Daubar I. J. et al. (2002) MAPS 37: 1797–1813. [6] Warren P. H. et al. (2005) MAPS 40: 989–1014. [7] Korotev R. L. et al. (2006) GCA 70: 5935– 5956. [8] Wittmann A. et al. (2014) Am. Min. 99: 1626– 1647. [9] Korotev R. L. (2012) MAPS 47: 1365–1402. [10] Ryder G. (1980) Proc. LPSC 11: 471–479. [11] Reid A. M. et al. (1970) EPSL 9: 1–5. [12] Goldstein J. I. & Yakowitz H. (1971) Proc. LSC 2: 177–191. [13] Axon H. J & Goldstein J. I. (1973) EPSL 18: 173–180. [14] Rubin A. E. (1990) GCA 54: 1217–1232. [15] Jolliff B. L. et al. (2000) JGR 105: 4197–4216. [16] Cintala M. J. & Grieve R. A. F. (1998) MAPS 33: 889–912. [17] Melosh H. J. (1989) Impact Cratering, Oxford University Press: 244 p. k) 86 km Ø Tycho crater’s central uplift peeks through a ~150 m thick (partly poikilitic?) impact melt sheet. k Photo: M. Aid g h
Transcript of Petrogenesis of Lunar Poikilitic Impact Melt Meteorite Oued ...Petrogenesis of Lunar Poikilitic...
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Petrogenesis of Lunar Poikilitic Impact Melt Meteorite Oued Awlitis 001
Axel Wittmann1, Randy L. Korotev1, Bradley L. Jolliff1, and Anthony J. Irving2
1Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, [email protected]. 2Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195.
Oued Awlitis (OA) 001
• a lunar meteorite with a preserved fusion crust (fig. a–b).
• found in 2014 in Morocco/Western Sahara [1–2].
• main 382 g piece excavated from shallow depth.
Study Objective: Unravel Petrogenesis from Petrography and Chemistry.
Petrography
• Plagioclase clasts and phenocrysts poikilitically enclosed in olivine or pyroxene (fig. c), minor FeS, FeNi, SiO2, FeTiO3, chromite.
• Pockets of glassy shock melt occur (fig. d); planar deformation features (PDF) in plagioclase (fig. e) indicate shock pressures of >10 to 500 m Ø impact crater is required to excavate poikilitic impact melt from the center of a 100 m thick melt sheet [17] such as Tycho’s (fig. k).
Conclusions
• Oued Awlitis 001 may have crystallized in a >100 m thick melt sheet of a >50 km Ø impact crater in the Feldspathic Highlands Terrane and was excavated by an impact that produced a >500 m Ø crater.
Acknowledgments: Zaid Oussaid & Mohamed Aid for recovering Oued Awlitis 001, Hasnaa Chennaoui-Aoudjehane (Hassan II University Casablanca) for documentation of the find site, Paul Carpenter (Washington University St. Louis) & Scott Kuehner (University of Washington Seattle) for electron microprobe analysis support, funding from NASA.
a b
a) Find site of Oued Awlitis 001. b) Sample specimen of Oued Awlitis 001, note homogenous texture and fusion crust.
c d e
c) Poikilitic texture of olivine (Ol) and pyroxene (Px) enclosing plagioclase, back-scattered electron image.
Photo: M. Aid
d) Shock melt pocket associated with olivine (Ol); plagioclase (Pl) and pyroxene (Px), back-scattered electron image.
e) Plagioclase clast with faint PDF (arrows), linear polarized light micrograph.
j f
f) Pyroxene (top) and olivine (bottom) EMP (electron microprobe) data in mole %.
g) Bulk rock INAA (instrumental neutron activation analysis) data; diagram after [8].
h) Bulk rock INAA data with CM chondrite mixing lines; diagram after [9].
j) EMP data for FeNi particles, diagram modified after [10] with data from [12–14].
high Ni metal clasts
in Apollo 15 soils
Chondritic
Ni:Co ratio
References: [1] Wittmann A. et al. (2014) Met. Soc. 77: Abstract # 5352. [2] Korotev R. L. & Irving A. J. (2015) LPSC 46: Abstract # 1942. [3] Ostertag R. (1983) Proc. LPSC 14: B364–B376. [4] Fritz J. et al. (2011) LPSC 42: Abstract # 1196. [5] Daubar I. J. et al. (2002) MAPS 37: 1797–1813. [6] Warren P. H. et al. (2005) MAPS 40: 989–1014. [7] Korotev R. L. et al. (2006) GCA 70: 5935–5956. [8] Wittmann A. et al. (2014) Am. Min. 99: 1626–1647. [9] Korotev R. L. (2012) MAPS 47: 1365–1402. [10] Ryder G. (1980) Proc. LPSC 11: 471–479. [11] Reid A. M. et al. (1970) EPSL 9: 1–5. [12] Goldstein J. I. & Yakowitz H. (1971) Proc. LSC 2: 177–191. [13] Axon H. J & Goldstein J. I. (1973) EPSL 18: 173–180. [14] Rubin A. E. (1990) GCA 54: 1217–1232. [15] Jolliff B. L. et al. (2000) JGR 105: 4197–4216. [16] Cintala M. J. & Grieve R. A. F. (1998) MAPS 33: 889–912. [17] Melosh H. J. (1989) Impact Cratering, Oxford University Press: 244 p.
k) 86 km Ø Tycho crater’s central uplift peeks through a ~150 m thick (partly poikilitic?) impact melt sheet.
k
Photo: M. Aid
g h
