Northwest Africa 4797: A strongly shocked ultramafic poikilitic shergottite related to compositionally intermediate Martian meteorites

Abstract– Northwest Africa (NWA) 4797 is an ultramafic Martian meteorite composed of olivine (40.3 vol%), pigeonite (22.2%), augite (11.9%), plagioclase (9.1%), vesicles (1.6%), and a shock vein (10.3%). Minor phases include chromite (3.4%), merrillite (0.8%), and magmatic inclusions (0.4%). Olivine and pyroxene compositions range from Fo_66–72,En_58–74Fs_19–28Wo_6–15, and En_46–60Fs_14–22Wo_34–40, respectively. The rock is texturally similar to “lherzolitic” shergottites. The oxygen fugacity was QFM?2.9 near the liquidus, increasing to QFM?1.7 as crystallization proceeded. Shock effects in olivine and pyroxene include strong mosaicism, grain boundary melting, local recrystallization, and pervasive fracturing. Shock heating has completely melted and vesiculated igneous plagioclase, which upon cooling has quench‐crystallized plagioclase microlites in glass. A mm‐size shock melt vein transects the rock, containing phosphoran olivine (Fo_69–79), pyroxene (En_44–51Fs_14–18Wo_30–42), and chromite in a groundmass of alkali‐rich glass containing iron sulfide spheres. Trace element analysis reveals that (1) REE in plagioclase and the shock melt vein mimics the whole rock pattern; and (2) the reconstructed NWA 4797 whole rock is slightly enriched in LREE relative to other intermediate ultramafic shergottites, attributable to local mobilization of melt by shock. The shock melt vein represents bulk melting of NWA 4797 injected during pressure release. Calculated oxygen fugacity for NWA 4797 indicates that oxygen fugacity is decoupled from incompatible element concentrations. This is attributed to subsolidus re‐equilibration. We propose an alternative nomenclature for “lherzolitic” shergottites that removes genetic connotations. NWA 4797 is classified as an ultramafic poikilitic shergottite with intermediate trace element characteristics.     

The basaltic shergottite Northwest Africa 856: Petrology and chemistry

Abstract— We report on the discovery of a new shergottite from South Morocco. This single stone weighing 320 g is referenced as Northwest Africa (NWA) 856 with Djel Ibone as a synonymous name. It is a fresh, fine‐grained basaltic rock consisting mainly of two pyroxenes (total ?68 vol%: 45% pigeonite, En_61‐16Wo_9–22Fs_26–68; 23% augite, En_46‐26Wo_34‐29Fs_21–43) and plagioclase converted to maskelynite (?23 vol%, Ab_43–57Or_1–5An_54‐36). Accessory minerals include merrillite, Cl‐apatite, pyrrhotite, ilmenite, ulvöspinel, silica (stishovite and glass), amorphous K‐feldspar and baddeleyite. Amorphous mixtures of maskelynite and silica occur most commonly as median layers inside maskelynite laths. In addition, melt pockets (?2 vol%) were recognized with relics of maskelynite, pyroxene and both dense silica glass and stishovite occurring as both grains and submicrometer needles. The compositions of the melt pockets are consistent with mixtures of maskelynite and pyroxenes with an average of ?50 vol% maskelynite. The meteorite is highly fractured at all scales. The bulk composition of NWA 856 has been measured for 44 elements. It is an Al‐poor ferroan basaltic rock which strongly resembles Shergotty and Zagami in its major and trace element composition. The nearly flat rare earth element (REE) pattern (La/Lu)_n = 0.9, is similar to that of Shergotty or Zagami and differs significantly from NWA 480, another Moroccan shergottite recently described. According to the U, Ba and Sr abundances, NWA 856 is not significantly weathered. The oxygen isotopes (δ18O = +5.03%, δ17O = +3.09%, and Δ17O = +0.47%) are in agreement with the martian origin of this meteorite. On the basis of grain size, pyroxene zoning and composition, abundance of silica inclusions associated with maskelynite, trace element abundances, REE pattern and oxygen isotopes, pairing with NWA 480 is excluded. The similarity with Shergotty and Zagami is striking. The only significant differences are a larger grain size, a greater abundance of silica and melt pockets, a slightly more restricted range of pyroxene compositions and the absence of significant mesostasis.     

Mineralogy and petrology of the Dar al Gani 476 martian meteorite: Implications for its cooling history and relationship to other shergottites

Abstract— Dar al Gani 476, the 13th martian meteorite, was recovered from the Sahara in 1998. It is a basaltic shergottitic rock composed of olivine megacrysts reaching 5 mm (24 vol%) set in a finegrained groundmass of pyroxene (59 vol%) and maskelynitized plagioclase (12 vol%) with minor amounts of accessory phases (spinel, merrillite, ilmenite). Dar al Gani 476 is similar to lithology A of Elephant Moraine A79001 (EETA79001) in petrography and mineralogy, but is distinct in several aspects. Low‐Ca pyroxenes in the Dar al Gani 476 groundmass are more magnesian (En₇₆Fs₂₁ Wo₃～En₅₈Fs₃₀Wo₁₂) than those in lithology A of EETA79001 (En₇₃Fs₂₂Wo₅～En₄₅Fs₄₃Wo₁₂), rather similar to pyroxenes in lherzolitic martian meteorites (En₇₆Fs₂₁ Wo₃～En₆₃Fs₂₂Wo₁₅). Dar al Gani 476 olivine is less magnesian and shows a narrower compositional range (Fo_76‐58) than EETA79001 olivine (Fo_81‐53), and is also similar to olivines in lherzolitic martian meteorites (Fo_74‐65). The orthopyroxene‐olivine‐chromite xenolith typical in the lithology A of EETA79001 is absent in Dar al Gani 476. It seems that Dar al Gani 476 crystallized from a slightly more primitive mafic magma than lithology A of EETA79001 and several phases (olivine, pyroxene, chromite, and ilmenite) in Dar al Gani 476 may have petrogenetic similarities to those of lherzolitic martian meteorites. Olivine megacrysts in Dar al Gani 476 are in disequilibrium with the bulk composition. The presence of fractured olivine grains in which the most Mg‐rich parts are in contact with the groundmass suggests that little diffusive modification of original olivine compositions occurred during cooling. This observation enabled us to estimate the cooling rates of Dar al Gani 476 and EETA79001 olivines, giving similar cooling rates of 0.03‐3 °C/h for Dar al Gani 476 and 0.05‐5 °C/h for EETA79001. This suggests that they were cooled near the surface (burial depth shallower than about 3 m at most), probably in lava flows during crystallization of groundmass. As is proposed for lithology A of EETA79001, it may be possible to consider that Dar al Gani 476 has an impact melt origin, a mixture of martian lherzolite and other martian rock (Queen Alexandra Range 94201, nakhlites?).     

Petrogenesis of Grove Mountains 020090: An enriched “lherzolitic” shergottite

Grove Mountains (GRV) 020090 is a “lherzolitic” shergottite found in the Grove Mountains, Antarctica. It exhibits two distinct textures: poikilitic and nonpoikilitic. In poikilitic areas, large pyroxene oikocrysts enclose subhedral olivine and chromite chadacrysts. Pyroxene oikocrysts are zoned from pigeonite cores to augite rims. In nonpoikilitic areas, olivine, pyroxene, and interstitial maskelynite occur as major phases, and minor phases include chromite and merrillite. Compared with typical “lherzolitic” shergottites, GRV 020090 contains a distinctly higher abundance of maskelynite (19 vol%). Olivine and pyroxene are more ferroan (Fa_28–40, En_57–72Fs_24–31Wo_4–14 and En_46–53Fs_17–21Wo_26–35), and maskelynite is more alkali‐rich (Ab_43–65Or_2–7). The major phases, whole‐rock (estimated) and fusion crust of GRV 020090, are relatively enriched in light rare earth elements (LREE), similar to those of the geochemically enriched basaltic shergottites, but distinct from those of LREE‐depleted “lherzolitic” shergottites. Combined with a high oxygen fugacity of log fO₂ = QFM ? 1.41 ± 0.04 (relative to the quartz‐fayalite‐magnetite buffer), it is clear that GRV 020090 sampled from an oxidized and enriched mantle reservoir similar to those of other enriched shergottites. The calculated REE abundances and patterns of the melts in equilibrium with the cores of major phases are parallel to but higher than that of the whole rock, suggesting that GRV 020090 originated from a single parent magma and experienced progressive fractional crystallization in a closed system. The crystallization age recorded by baddeleyite is 192 ± 10 (2σ) Ma, consistent with the young internal isochron ages of enriched shergottites. Baddeleyite dating results further demonstrated that the young ages, rather than ancient ages (>4 Ga), appear to represent the crystallization of Martian surface lava flow. GRV 020090 shares many similarities with Roberts Massif (RBT) 04261/2, the first enriched “lherzolitic” shergottite. Detailed comparisons suggest that these two rocks are petrologically and geochemically closely related, and probably launch paired.     

Mineralogy of Antarctic basaltic shergottite Queen Alexandra Range 94201: Similarities to Elephant Moraine A79001 (Lithology B) martian meteorite

Abstract— Antarctic meteorite QUE 94201 is a new basaltic shergottite that is mainly composed of subequal amounts of maskelynite and pyroxenes (pigeonite and augite) plus abundant merrillite and accessory phases. It also contains impact melt. Complex zoning patterns in QUE 94201 pyroxenes revealed by elemental map analyses using an electron microprobe suggest a crystallization sequence from Mg-rich pigeonite (En₆₂Fss₃₀Wo_g) to extremely Fe-rich pigeonite (En₅Fs₈₁Wo₁₄) via {110} Mg-rich augite bands (En₄₄Fs₂₀Wo₃₆) in a single crystal. These textures, along with the abundant plagioclase (maskelynite), indicates single-stage rapid cooling (>5 °C/year) of this rock from a supercooled magma. Transition from Mg-rich augite to Fe-rich pigeonite reflects the onset of plagioclase crystallization. Enrichment of late-stage phases in QUE 94201 implies crystallization from an evolved magma and suggests a different parent magma composition from the other basaltic shergottites. Lithology B of EETA79001 basaltic shergottite contains pyroxenes that show complex zoning with augite bands similar to those in QUE 94201 pyroxene, which suggests similar one-stage rapid cooling. Lithology B of EETA79001 also resembles QUE 94201 in its coarse-grained texture of silicates and its high abundance of maskelynite, although QUE 94201 probably crystallized from a more fractionated magma. We also note that some Apollo lunar mare basalts (e.g., 12020 and 12021) have similar mineralogy and petrology to QUE 94201, especially in pyroxene zoning. All these basaltic rocks with complex pyroxene zoning suggest rapid metastable crystallization from supercooled magmas.     

The Loxton meteorite: A new olivine-bronzite chondrite from South Australia

Abstract— The Loxton meteorite is a single stone of 22 g found in South Australia in 1968. It has been classified as an L5 chondrite, shock facies ‘a,’ and contains olivine (Fa₂₄), orthopyroxene (Fs_21–22), clinopyroxene (Wo_44.7En_45.9Fs_9.4), nickel-iron, troilite, chromite and chlorapatite.     

The Ksar Ghilane 002 shergottite—The 100th registered Martian meteorite fragment

We report on the discovery of a new shergottite from Tunisia, Ksar Ghilane (KG) 002. This single stone, weighing 538 g, is a coarse‐grained basaltic shergottite, mainly composed of maskelynitized plagioclase (approximately 52 vol%) and pyroxene (approximately 37 vol%). It also contains Fe‐rich olivine (approximately 4.5 vol%), large Ca‐phosphates, including both merrillites and Cl‐apatites (approximately 3.4 vol%), minor amounts of silica or SiO₂‐normative K‐rich glass, pyrrhotite, Ti‐magnetite, ilmenite, and accessory baddeleyite. The largest crystals of pyroxene and plagioclase reach sizes of approximately 4 to 5 mm. Pyroxenes (Fs_26–96En_5–50Wo_2–41). They typically range from cores of about Fs₂₉En₄₁Wo₃₀ to rims of about Fs₆₈En₁₄Wo₁₇. Maskelynite is Ab_41–49An_39–58Or_1–7 in composition, but some can be as anorthitic as An₉₃. Olivine (Fa_91–96) occurs mainly within symplectitic intergrowths, in paragenesis with ilmenite, or at neighboring areas of symplectites. KG 002 is heavily shocked (S5) as indicated by mosaic extinction of pyroxenes, maskelynitized plagioclase, the occurrence of localized shock melt glass pockets, and low radiogenic He concentration. Oxygen isotopes confirm that it is a normal member of the SNC suite. KG 002 is slightly depleted in LREE and shows a positive Eu anomaly, providing evidence for complex magma genesis and mantle processes on Mars. Noble gases with a composition thought to be characteristic for Martian interior is a dominant component. Measurements of ¹⁰Be, ²⁶Al, and ⁵³Mn and comparison with Monte Carlo calculations of production rates indicate that KG 002 has been exposed to cosmic rays most likely as a single meteoroid body of 35–65 cm radius. KG 002 strongly resembles Los Angeles and NWA 2800 basaltic shergottites in element composition, petrography, and mineral chemistry, suggesting a possible launch‐pairing. The similar CRE ages of KG 002 and Los Angeles may suggest an ejection event at approximately 3.0 Ma.     

Petrology,geochemistry, and cosmic‐ray exposure age of Iherzolitic shergottite Northwest Africa 1950

Northwest Africa (NWA) 1950 is a new member of the lherzolitic shergottite clan of the Martian meteorites recently found in the Atlas Mountains. The petrological, mineralogical, and geochemical data are very close to those of the other known lherzolitic shergottites. The meteorite has a cumulate gabbroic texture and its mineralogy consists of olivine (Fo₆₆ to Fo₇₅), low and high‐Ca pyroxenes (En₇₈Fs₁₉Wo₂‐En₆₀Fs₂₆W₁₄; En₅₃Fs₁₆Wo₃₁‐En₄₅Fs₁₄Wo₄₁), and plagioclase (An₅₇Ab₄₁Or₁ to An₄₀Ab₅₇Or₃; entirely converted into maskelynite during intense shock metamorphism). Accessory minerals include phosphates (merrillite), chromite and spinels, sulfides, and a glass rich in potassium. The oxygen isotopic values lie on the fractional line defined by the other SNC meteorites (Δ¹⁷O = 0.312 %o). The composition of NWA 1950 is very similar to the other lherzolitic shergottites and suggests an origin from the same magmatic system, or at least crystallization from a close parental melt. Cosmogenic ages indicate an ejection age similar to those of the other lherzolitic shergottites. The intensity of the shock is similar to that observed in other shergottites, as shown by the occurrence of small melt pockets containing glass interwoven with stishovite.     

Al Huwaysah 010: The most reduced brachinite,so far

Al Huwaysah 010 is an ungrouped achondrite meteorite, recently referred to as a brachinite-like meteorite. This meteorite, showing a fine-grained assemblage of low-Ca pyroxene and opaque phases, is strongly reduced in comparison to other reduced brachinites. The occurrence of some tiny plates of graphite and oldhamite in this meteorite suggests that a partial melt residue has experienced a further reduction process. Olivine, the most abundant phase, is compositionally homogeneous (Fo_83.3) as well as the clinopyroxene (En_45.5Fs_10.8Wo_43.7) and the plagioclase (Ab_69.5). Orthopyroxene (En_85.4Fs_13.9Wo_0.7) also occurs but only in a fine intergrowth. Other accessory phases are Fe metal grains (Ni-free or Cr-bearing Fe-Ni alloy), troilite, chlorapatite, pentlandite (as inclusions in chromite). The sample shows two different closure temperatures: the highest (≈900°C) is determined via the olivine–chromite intercrystalline geothermometer and the lowest temperature (≈520°C) is determined via the pyroxene-based intracrystalline geothermometer. These temperatures may represent, respectively, the closure temperature associated with the formation and a subsequent impact event excavating the sample from the parental body. The visible to near-infrared (VNIR) reflectance spectra of Al Huwaysah 010 exhibit low reflectance, consistent with the presence of darkening components, and weak absorptions indicative of olivine and pyroxene. Comparing the spectral parameters of Al Huwaysah 010 to potential parent bodies characterized by olivine–pyroxene mineralogy, we find that it falls within the field previously attributed to the SIII type asteroids. These results lead us to classify the Al Huwaysah 010 meteorite as the most reduced brachinite, whose VNIR spectral features show strong affinities with those of SIII asteroids.     

THE BEAVER-HARRISON,BEAVER COUNTY,UTAH L6 CHONDRITE

The Beaver-Harrison, Utah chondrite (find July 24, 1979), a single, shock-veined stone of 925 grams, consists of major olivine (Fa_25.0), low-Ca pyroxene (En_77.3Fs_21.1Wo_1.6) and metallic nickel-iron; minor troilite and plagioclase (Ab_82.6An_11.1Or_6.3), accessory high-Ca pyroxene (En_47.0Fs_8.5Wo_44.5), chromite (Cm_8.7Sp_10.6Uv_9.4Pc_0.6Hc_0.7), chlorapatite and whitlockite; and hydrous ferric oxide of terrestrial weathering origin. Mineral compositions indicate L-group classification, and homogeneity of minerals, highly recrystallized texture and presence of clear plagioclase suggest that the meteorite belongs to petrologic type 6.     

Fuc Bin–an L5 chondrite fall from Vietnam

Abstract— A stony meteorite fell near the Fuc Bin village, Vietnam, in July, 1971. Based on optical microscopy, scanning electron microscopy and electron probe microanalysis, the meteorite is classified as an L5 chondrite that contains olivine (Fa_23.6), low-Ca pyroxene (Fs_20.3 Wo_1.3), high-Ca pyroxene (Fs_7.5 Wo_44.2), plagioclase (Ab_83.8 Or₅), chlorapatite, merrillite and opaque minerals: chromite, troilite, kamacite, taenite, tetrataenite and native copper.     

THE CHEMISTRY AND MINERALOGY OF THE HOMEWOOD,MANITOBA, METEORITE

The Homewood meteorite is a slightly weathered find of 325 grams discovered in 1970 about 64 km southwest of Winnipeg, Manitoba. It consists of olivine (Fa_25.4; 43.8 normative wt. percent), orthopyroxene (Fs_23.3; 28.5 percent), kamacite and taenite (7.5 percent), troilite (5.6 percent), maskelynite (8.3 percent), chromite (1.0 percent), whitlockite (0.7 percent) and minor patchy Ca pyroxene. Bulk chemical analysis yielded Fe_total 21.60 wt. percent, Fe/SiO₂0.55, SiO₂/MgO 1.53 and Fe^O/Fe_total 0.29. Barred olivine, radiating pyroxene and porphyritic chondrules, all with ill-defined outlines, occur in the meteorite. Most chemical and mineralogical features characterize the Homewood meteorite as an L6 (hypersthene) chondrite. The presence of maskelynite, the undulatory extinction, extensive fracturing and pervasive mosaicism of olivine, and the poor definition of chondrule outlines suggest that the Homewood meteorite has been shocked in the range of 300–350 kbar.     

The Linum Chondrite

Abstract— Based on optical microscopy and electron microprobe analysis, Linum is classified as an L6b chondrite that contains olivine (Fa₂₄), orthopyroxene (Fs₂₀), clinopyroxene (Wo₄₅En₄₇Fs₈), plagioclase (An₁₀Ab₈₄Or₆), nickel-iron, troilite, chromite and accessory amounts of chlorapatite and whitlockite.     

A new martian meteorite from the Sahara: The shergottite Dar al Gani 489

Abstract— Dar al Gani 489 (DaG 489) is a meteorite fragment of 2146 g found in the Libyan Sahara by a meteorite finder during one of his search campaigns in 1997–98. It is a porphyritic rock with millimetersized olivine crystals (Fo_79–59) set in a fine‐grained groundmass (average grain size 0.1 mm) consisting of pigeonite (En_75–57 Wo_5–15) crystals and interstitial feldspathic glass (An_67–56 Or_0–1). Minor phases include enstatite (En_82–71 Wo_2–4), augite (En_48–52 Wo_29–32), chromite, Ti‐chromite, ilmenite, pyrrhotite, merrillite, and secondary calcite and iron oxides. On the basis of mineralogical, petrographic, bulk chemical, O‐isotopic, and noble gas data, DaG 489 can be classified as a highly shocked martian meteorite (e.g., Fe/Mn_(bulk) = 42.1, Ni/Mg_(bulk) = 0.002; δ¹⁷O = 2.89, δ¹⁸O = 4.98, and Δ¹⁷O = 0.305), belonging to the basaltic shergottite subgroup. The texture and modal composition of DaG 489 are indeed those of basalts; nonetheless, the bulk chemistry, the abundance of large olivine and chromite crystals, and enstatitic pyroxene suggest some relationship with lherzolitic shergottites. As such, DaG 489 is similar to the hybrid shergottite Elephant Moraine (EET) A79001 lithology A; however, there are some relevant differences including a higher olivine content (20 vol%), the lack of orthopyroxene megacrysts, a higher molar Mg/(Mg + Fe)_(molar) = 0.68, and a lower rare earth element content in the bulk sample. Therefore, DaG 489 has the potential of providing us with a further petrogenetic link between the basaltic and lherzolitic shergottites. Noble gases data show that DaG 489 has an ejection age of ～1.3 Ma. This young age lends support to the requirement of several ejection events to produce the current population of shergottites, nakhlites, and chassignites (SNC) meteorites. In terms of texture, mineral and bulk compositions, shock level, and weathering features, DaG 489 is essentially identical to DaG 476, another basaltic shergottite independently found ～25 km due northnortheast of DaG 489. Because DaG 489 also has the same exposure history as DaG 476, it is very likely that both meteorites are fragments of the same fall. In addition to the existing hypotheses on the petrogenesis of the similar EETA79001 lithology A and the identical DaG 476, we propose that DaG 489 could have formed through high‐degree partial melting of a lherzolite‐like material.     

ALH84001, a cumulate orthopyroxenite member of the martian meteorite clan

Abstract— ALH84001, originally classified as a diogenite, is a coarse-grained, cataclastic, orthopyroxenite meteorite related to the martian (SNC) meteorites. The orthopyroxene is relatively uniform in composition, with a mean composition of Wo_3.3En_69.4Fs_27.3. Minor phases are euhedral to subhedral chromite and interstitial maskelynite, An_31.1Ab_63.2Or_5.7, with accessory augite, Wo_42.2En_45.1Fs_12.7, apatite, pyrite and carbonates, Cc_11.5Mg_58.0Sd_29.4Rd_1.1. The pyroxenes and chromites in ALH84001 are similar in composition to these phases in EETA79001 lithology A megacrysts but are more homogeneous. Maskelynite is similar in composition to feldspars in the nakhlites and Chassigny. Two generations of carbonates are present, early (pre-shock) strongly zoned carbonates and late (post-shock) carbonates. The high Ca content of both types of carbonates indicates that they were formed at moderately high temperature, possibly ～700 °C. ALH84001 has a slightly LREE-depleted pattern with La 0.67x and Lu 1.85x CI abundances and with a negative Eu anomaly (Eu/Sm 0.56x CI). The uniform pyroxene composition is unusual for martian meteorites, and suggests that ALH84001 cooled more slowly than did the shergottites, nakhlites or Chassigny. The nearly monomineralic composition, coarse-grain size, homogenous orthopyroxene and chromite compositions, the interstitial maskelynite and apatite, and the REE pattern suggest that ALH84001 is a cumulate orthopyroxenite containing minor trapped, intercumulus material.     

Petrogenesis of the Northwest Africa 4898 high‐Al mare basalt

Northwest Africa (NWA) 4898 is the only low‐Ti, high‐Al basaltic lunar meteorite yet recognized. It predominantly consists of pyroxene (53.8 vol%) and plagioclase (38.6 vol%). Pyroxene has a wide range of compositions (En_12–62Fs_25–62Wo_11–36), which display a continuous trend from Mg‐rich cores toward Ca‐rich mantles and then to Fe‐rich rims. Plagioclase has relatively restricted compositions (An_87–96Or_0–1Ab_4–13), and was transformed to maskelynite. The REE zoning of all silicate minerals was not significantly modified by shock metamorphism and weathering. Relatively large (up to 1 mm) olivine phenocrysts have homogenous inner parts with Fo ~74 and sharply decrease to 64 within the thin out rims (~30 μm in width). Four types of inclusions with a variety of textures and modal mineralogy were identified in olivine phenocrysts. The contrasting morphologies of these inclusions and the chemical zoning of olivine phenocrysts suggest NWA 4898 underwent at least two stages of crystallization. The aluminous chromite in NWA 4898 reveals that its high alumina character was inherited from the parental magma, rather than by fractional crystallization. The mineral chemistry and major element compositions of NWA 4898 are different from those of 12038 and Luna 16 basalts, but resemble those of Apollo 14 high‐Al basalts. However, the trace element compositions demonstrate that NWA 4898 and Apollo 14 high‐Al basalts could not have been derived from the same mantle source. REE compositions of its parental magma indicate that NWA 4898 probably originated from a unique depleted mantle source that has not been sampled yet. Unlike Apollo 14 high‐Al basalts, which assimilated KREEPy materials during their formation, NWA 4898 could have formed by closed‐system fractional crystallization.     

Mineral and chemical composition of the Jezersko meteorite—A new chondrite from Slovenia

The Jezersko meteorite is a newly confirmed stony meteorite found in 1992 in the Karavanke mountains, Slovenia. The meteorite is moderately weathered (W2), indicating short terrestrial residence time. Chondrules in partially recrystallized matrix are clearly discernible but often fragmented and have mean diameter of 0.73 mm. The meteorite consists of homogeneous olivine (Fa_19.4) and low‐Ca pyroxenes (Fs_16.7Wo_1.2), of which 34% are monoclinic, and minor plagioclase (Ab₈₃An₁₁Or₆) and Ca‐pyroxene (Fs₆Wo_45.8). Troilite, kamacite, zoned taenite, tetrataenite, chromite, and metallic copper comprise about 16.5 vol% of the meteorite. Phosphates are represented by merrillite and minor chlorapatite. Undulatory extinction in some olivine grains and other shock indicators suggests weak shock metamorphism between stages S2 and S3. The bulk chemical composition generally corresponds to the mean H chondrite composition. Low siderophile element contents indicate the oxidized character of the Jezersko parent body. The temperatures recorded by two‐pyroxene, olivine‐chromite, and olivine‐orthopyroxene geothermometers are 854 °C, 737–787 °C, and 750 °C, respectively. Mg concentration profiles across orthopyroxenes and clinopyroxenes indicate relatively fast cooling at temperatures above 700 °C. A low cooling rate of 10 °C Myr^?1 was obtained from metallographic data. Considering physical, chemical, and mineralogical properties, meteorite Jezersko was classified as an H4 S2(3) ordinary chondrite.     

NEPHELINE AND SODALITE IN A BARRED OLIVINE CHONDRULE FROM THE ALLENDE METEORITE

Nepheline and sodalite have been found in association with glass in a barred olivine chondrule from the Allende C3V meteorite. The major minerals of the chondrule are olivine (Fo_80–88), bronzite (En₈₅Fs₁₂Wo₃), and chromite. Olivine bars are separated by glass of nearly pure plagioclase composition (An_81–99). Olivine composition is more Fe-rich than predicted by olivine-liquid equilibria (Fo₉₆). Conditions of non-equilibrium are implied from this and the presence of plagioclase glass and small amounts of subcalcic diopside (En₇₅Fs₁₂Wo₁₃) in the chondrule. The properties of this chondrule are consistent with liquid condensation, but melting of an amoeboid olivine aggregate or similar object could also have generated the chondrule-forming liquid. Nepheline and sodalite appear to have crystallized from this liquid under non-equilibrium conditions.     

Comparison of the LEW88516 and ALHA77005 martian meteorites: Similar but distinct

Abstract By mineral and bulk compositions, the Lewis Cliff (LEW) 88516 meteorite is quite similar to the ALHA77005 martian meteorite. These two meteorites are not paired because their mineral compositions are distinct, they were found 500 km apart in ice fields with different sources for meteorites, and their terrestrial residence ages are different. Minerals in LEW88516 include: olivine, pyroxenes (low- and high-Ca), and maskelynite (after plagioclase); and the minor minerals chromite, whitlockite, ilmenite, and pyrrhotite. Mineral grains in LEW88516 range up to a few mm. Texturally, the meteorite is complex, with regions of olivine and chromite poikilitically enclosed in pyroxene, regions of interstitial basaltic texture, and glass-rich (shock) veinlets. Olivine compositions range from Fo₆₄ to Fo₇₀, (avg. Fo₆₇), more ferroan and with more variation than in ALHA77005 (Fo₆₉ to Fo₇₃). Pyroxene compositions fall between En₇₇Wo₄ and En₆₅Wo₁₅ and in clusters near En₆₃Wo₉ and En₅₃Wo₃₃, on average more magnesian and with more variation than in ALHA77005. Shock features in LEW88516 range from weak deformation through complete melting. Bulk chemical analyses by modal recombination of electron microprobe analyses, instrumental neutron activation, and radiochemical neutron activation confirm that LEW88516 is more closely related to ALHA77005 than to other known martian meteorites. Key element abundance ratios are typical of martian meteorites, as is its non-chondritic rare earth pattern. Differences between the chemical compositions of LEW88516 and ALHA77005 are consistent with slight differences in the proportions of their constituent minerals and not from fundamental petrogenetic differences. Noble gas abundances in LEW88516, like those in ALHA77005, show modest excesses of ⁴⁰Ar and ¹²⁹Xe from trapped (shock-implanted) gas. As with other ALHA77005 and the shergottite martian meteorites (except EETA79001), noble gas isotope abundances in LEW88516 are consistent with exposure to cosmic rays for 2.5–3 Ma. The absence of substantial effects of shielding from cosmic rays suggest LEW88516 spent this time as an object no larger than a few cm in diameter.     

A new Martian meteorite from Oman: Mineralogy,petrology, and shock metamorphism of olivine‐phyric basaltic shergottite Sayh al Uhaymir 150

Abstract— The Sayh al Uhaymir (SaU) 150 meteorite was found on a gravel plateau, 43.3 km south of Ghaba, Oman, on October 8, 2002. Oxygen isotope (δ¹⁷O 2.78; δ¹⁸O 4.74), CRE age (?1.3 Ma), and noble gas studies confirm its Martian origin. SaU 150 is classified as an olivine‐phyric basalt, having a porphyritic texture with olivine macrocrysts set in a finer‐grained matrix of pigeonite and interstitial maskelynite, with minor augite, spinel, ilmenite, merrillite, pyrrhotite, pentlandite, and secondary (terrestrial) calcite and iron oxides. The bulk rock composition, in particular mg (68) [molar Mg/(Mg + Fe) x 100], Fe/Mn (37.9), and Na/Al (0.22), are characteristic of Martian meteorites. Based on mineral compositions, cooling rates determined from crystal morphology, and crystal size distribution, it is deduced that the parent magma formed in a steady‐state growth regime (magma chamber) that cooled at <°C/hr. Subsequent eruption as a thick lava flow or hypabyssal intrusion entrained a small fraction of xenocrystic olivine and gave rise to a magmatic foliation, with slow cooling allowing for near homogenization of igneous minerals. SaU 150 experienced an equilibration shock pressure of 33–45 GPa in a single impact event. Post‐shock heat gave rise to localized melting (?11 vol%). Larger volume melts remained fluid after pressure release and crystallized dendritic olivine and pyroxene with fractal dimensions of 1.80–1.89 and 1.89–1.95, respectively, at ‐ΔT >70–365 °C. SaU 150 is essentially identical to SaU 005/094, all representing samples of the same fall that are similar to, but distinct from, the DaG shergottites.