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Northwest Africa 11745
Basic information Name: Northwest Africa 11745
     This is an OFFICIAL meteorite name.
Abbreviation: NWA 11745
Observed fall: No
Year found: 2004
Country: (Northwest Africa)
Mass:help 554 g
Recommended:  L5    [explanation]

This is 1 of 6498 approved meteorites (plus 3 unapproved names) classified as L5.   [show all]
Search for other: L chondrites, L chondrites (type 4-7), Ordinary chondrites, and Ordinary chondrites (type 4-7)
Comments: Approved 7 Apr 2018
Writeup from MB 107:

Northwest Africa 11745 (NWA 11745)

(Northwest Africa)

Purchased: 2004

Classification: Ordinary chondrite (L5)

History: sample was purchased in Morocco from a meteorite collector by Dr Mahesh Anand (OU) some years ago. In July 2016, thin sections of the sample were passed to Craig Walton (UStA) for preliminary classification work.

Physical characteristics: One large piece is present in the collection (554.16). Sample predominantly has a light color, but has a dark fusion crust on one side. Sample contains abundant complex shock features - mainly micro-fault shear textures, associated with melt pools.

Petrography: (Craig Walton, UStA) Overall, sample has a chondritic brecciated texture. Main phases are olivine and pyroxene with opaque metal + troilite. Porphyritic olivine, radial pyroxene, barred olivine and porphyritic olivine pyroxene chondrule types are all common, along with rare cryptocrystalline and glassy chondrules. Chondrule average diameter is 0.56 mm, ranging from 1.25 mm to 0.25 mm. Chondrules comprise ~ 70% of the sample. Opaque phases are metal (Fe, Ni _ in exsolution as kamacite and taenite) and sulfide (troilite). A recrystallized and shock-darkened matrix of fine-grained lithic fragments comprises ~ 20 % of the sample area. Some isolated euhedral olivine grains (up to ~ 1mm) occur embedded in this matrix. Olivine contains planar deformation features and has undulose extinction. Planes across which shear displacement has occurred (microfaults) crosscut chondrule and brecciated matrix textures. Fine-grained silicate melt-pools bearing globules of immiscible metal and sulfide are hosted within some sections of these microfaults. Microfault textures crosscut chondrules, matrix and metal, with individual faults running along the length of the slide. Offset on the faults is on the order of 500 μm. ~50 μm-wide shock-melt pools/veins occur within the faults.

Geochemistry: Mineral compositions and geochemistry: (Craig Walton, UStA; Mahesh Anand, Sam Hammond, Richard Greenwood, OU) Microprobe (Cameca SX100 EMPA) Olivine (n=15): MgO = 38.4, MnO = 0.5, FeO = 23.4, SiO = 38.3 P2O5 = 0.1 Pyroxene (n=7): MgO = 28.7, CaO = 0.9, MnO = 0.5, FeO = 14.5, Al2O3 = 0.2, Cr2O3 = 0.1, SiO2 = 55.7, TiO2 = 0.2. Plagioclase: Na2O = 10.7, K2O = 1.1, CaO = 2.3, FeO = 0.8, Al2O3 = 22.1, SiO2 = 65.8 ; Plagioclase Ab76.1Or7.71An16.2 (N=11).. Oxygen Isotopes (Laser fluorination CO2 laser, Thermo Scientific MAT 253 gas source mass spectrometer) δ18O = 4.931, δ17O = 3.693, Δ17O = 1.129, Δ17O linear = 1.105 (all ‰).

Classification: L5. Shock stage is S4/5 as evidenced by shear microfault textures, associated shock-melt veins, shock darkening of matrix and undulose extinction and planar deformation features in olivine. Oxygen isotopes are indiscriminate between L and LL, however Fs (PX) and Fa (Ol) data indicate an L chondrite. Potentially paired with NWA 11744.

Specimens: Main mass at OU

Data from:
  Table 0
  Line 0:
Place of purchase:Morocco
Date:P 2004
Mass (g):554.16
Shock stage:S4/5
Weathering grade:W1
Fayalite (mol%):25.5±0.8 (N=15)
Ferrosilite (mol%):22.2±0.7
Wollastonite (mol%):1.7±0.2
Classifier:C. Walton, UStA, OU
Type spec mass (g):554.16
Type spec location:OU
Main mass:OU
Comments:work name M15.; submitted by Craig Walton
Plots: O isotopes:  
   and collections
OU: Planetary and Space Sciences Department of Physical Sciences The Open University Walton Hall Milton Keynes MK7 6AA United Kingdom, United Kingdom (institutional address; updated 8 Dec 2011)
SAM: Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia; Website (institutional address; updated 18 Oct 2011)
UStA: University of St Andrews College Gate St Andrews KY16 9AJ Fife, Scotland, United Kingdom (institutional address; updated 7 Apr 2018)
References: Published in Meteoritical Bulletin, no. 107, in preparation (2018)
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Public domain photographs:
Craig Walton   

     This is 1 of 6752 approved meteorites from (Northwest Africa) (plus 2052 unapproved names)

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