Franz Brandstatter

Petrology and geochemistry of Antarctic micrometeorites

Abstract The petrology and geochemistry of twentythree chondritic dust particles with masses of 1–47 μg (sizes 100–400 μm) were recovered from blue ice near Cap Prudhomme, Antarctica, and studied by INAA, ASEM, EMPA, and optical microscopy. Sample selection criteria were irregular shape and (for a subsample) black color, with the aim of studying as many unmelted micrometeorites (MMs) as possible. Of thirteen unmelted MMs, six were phyllosilicate-dominated MMs, and seven were coarsegrained crystalline MMs consisting mainly of olivine and pyroxene. The remaining ten particles were largely melted and consisted of a foamy melt with variable amounts of relic phases (scoriaceous MMs). Thus, of the black particles selected, an astonishing portion, 40% (by number), consisted of largely unmelted MMs. Although unmelted, most phyllosilicate MMs have been thermally metamorphosed to a degree that most of the phyllosilicates were destroyed, but not melted. The original preterrestrial mineralogy is occasionally preserved and consists of serpentine-like phyllosilicates with variable amounts of cronstedtite, tochilinite-like oxides, olivine, and pyroxene. The crystalline MMs consist of olivine, low-Ca pyroxene, tochilinite-like oxides, and occasional Ni-poor metal. Relics in scoriaceous MMs consist of the same phases. Mineral compositions and the coexistence of phyllosilicates with anhydrous phases are typical of CM and CR-type carbonaceous chondrites. However, the olivine/pyroxene ratio (~ 1) and the lack of carbonates, sulfates, and of very Fe-poor, refractory element-rich olivines and pyroxenes sets the MMs apart from CM and CR chondrites. The bulk chemistry of the phyllosilicate MMs is similar to that of CM chondrites. However, several elements are either depleted (Ca, Ni, S, less commonly Na, Mg, and Mn) or enriched (K, Fe, As, Br, Rb, Sb, and Au) in MMs as compared to CM chondrites. Similar depletions and enrichments are also found in the scoriaceous MMs. We suggest that the depletions are probably due to terrestrial leaching of sulfates and carbonates from unmelted MMs. The overabundance of some elements may also be due to processes acting during atmospheric passage such as the recondensation of meteoric vapors in the high atmosphere. Most MMs are coated by magnetite of platy or octahedral habit, which is rich in Mg, Al, Si, Mn, and Ni. We interpret the magnetites to be products of recondensation processes in the high (>90 km) atmosphere, which are, therefore, probably the first refractory aerominerals identified.

Structural and chemical response to varying [4]B content in zoned Fe-bearing olenite from Koralpe, Austria

Abstract Tourmaline has recently been shown to incorporate large amounts of substituent B at the tetrahedral site. To characterize the response of the tourmaline atomic arrangement to differing amounts of substitution of B for Si, five samples were separated from a core-to-rim (∼3 mm) section of an Fe-bearing olenite with a dark green core and a nearly colorless rim from Koralpe, Austria. Crystal structures of the five samples were refined to R values <0.018 using three-dimensional X-ray methods, and the compositions of the crystals were determined by electron microprobe, secondary ion mass spectrometric, and Mössbauer analyses. From core to rim, [4]B increases monotonically from 0.35 to 0.65 apfu, whereas the mean T-O distance decreases from 1.621 to 1.610 Å. Optimized formulae using chemical and structural data range from X(Na0.632Ca0.145⃞0.223) Y(Al1.320Fe2+1.202Li0.190Mg0.086Ti0.028Mn2+0.024⃞0.150) ZAl6.00 B3.00T(Si5.525B0.333Al0.130Be0.012) O27 [(OH)3.19O0.81] (core composition) to X(Na0.408Ca0.290K0.002⃞0.300) Y(Al2.338Li0.365Fe2+0.084Mn2+0.009Mg0.005Ti0.005⃞0.194) ZAl6.00 B3.00T(Si4.989B0.615Al0.362Be0.034) O27 [(OH)3.41O0.59] (rim composition). The variation of chemistry and structure, coupled with short-range order constraints, demonstrates that (1) the average tetrahedral bond length () reflects the substitution of [4]B, (2) tourmaline samples with relatively high Fe2+ contents (ca. 1 apfu Fe2+) and distances up to 1.621 Å can contain significant amounts of [4]B (up to ca. 0.3 apfu), (3) the presence of substantial [4]B is limited to, or more common in Al-rich tourmalines, (4) the presence of [4]B substituents favors OH at the O3 site, (5) the presence of Ca or Na at the X site is not simply correlated with occupancy of [4]B in the adjacent tetrahedral ring, and (6) no two B-substituted tetrahedra will link through bridging O atoms.

Tetrahedrally coordinated boron in tourmalines from the liddicoatite-elbaite series from Madagascar: Structure, chemistry, and infrared spectroscopic studies

Abstract Four colorless tourmalines of the liddicoatite-elbaite series from pegmatites from Anjanabonoina, Madagascar, have been characterized by crystal-structure determination and by chemical analyses. Optimized formulae range from X(Ca0.57Na0.29□0.14) Y(Al1.41Li1.33Mn2+0.07□0.19) ZAl6T(Si5.86B0.14)O18 (BO3)3V(OH)3.00W[F0.76(OH)0.24] [a = 15.8322(3), c = 7.1034(3) Å] to X(Na0.46Ca0.30□0.24) Y(Al1.82Li0.89Fe2+0.01 Mn2+0.01□0.27) ZAl6T(Si5.56B0.44)O18 (BO3)3V(OH)3.00W[(OH)0.50F0.50] [a = 15.8095(9), c = 7.0941(8) Å] (R = 1.3.1.7%). There is a high negative correlation (r2 = 0.984) between the bond-lengths (~1.618.1.614 Å) and the amount of IVB (from the optimized formulae). Similar to the olenites (from Koralpe, Austria) the liddicoatite-elbaite samples show a positive correlation between the Al occupancy at the Y site and IVB (r2 = 0.988). Short-range order configurations show that the presence of IVB is coupled with the occupancy of (Al2Li) and (Al2□) at the Y site. The structural formulae of the Al-rich tourmalines from Anjanabonoina, Madagascar, show ~ ⃞0.2 (vacancies) on the Y site. We believe that short-range order configurations with Y(Al2□) are responsible for these vacancies. Hence, an oft-used calculation of the Li content by difference on the Y site may be problematic for Al-rich tourmalines (olenite, elbaite, rossmanite). Fourier transform infrared (FTIR) spectra were recorded from the most IVB-rich tourmaline sample. The bands around 5195 and 5380 cm-1 can be assigned to H2O. Because these bands still could be observed in FTIR spectra at temperatures from -150 to +600 °C, it seems unlikely that they result from H2O in fluid inclusions. Interestingly, another FTIR spectrum from a dravite in which the X site is filled completely with Na, does not show bands at ~5200 and ~5400 cm-1. Although not definitive, the resulting spectra are consistent with small amounts of H2O at the X site of the elbaite. The rare-earth element (REE) pattern of the B-rich elbaite (ΣREE: ~150 ppm) demonstrates that this sample is strongly enriched in LREEs compared to HREEs and exhibits a negative Eu anomaly. This sample shows the strongest enrichment of LREEs and a high LaN/YbN ratio of ~351, which seems to confirm an important role of the fractional crystallization process.

MAC88105—A regolith breccia from the lunar highlands: Mineralogical, petrological, and geochemical studies☆

Abstract The new large lunar meteorite MAC88105 is a dense breccia, with lithic and mineral clasts and fragments set into a welded matrix. It is a regolith breccia which shows some recrystallization and evidence for a late shock event during which anorthositic glass veins were formed. Shock effects (most probably due to the impact ejection from the moon) are present throughout the sample and require a shock pressure of about 25–30 GPa, in agreement with observations made on other lunar meteorites. Some components of MAC88105 have been subjected to a shock pressure of about 40–45 GPa as evident from melt pockets in a clast. The population of lithic clasts in MAC88105 is similar to other lunar highland breccias. Vitric breccias are more abundant than granulitic breccias and plutonic rock fragments. The presence of devitrified glass (spheres and shards) supports a regolith origin. Most common are metameltbreccias consisting of abundant anorthitic plagioclase clasts and a dense, fine-grained matrix. Some fine-grained hornfelsic to granulitic metabreccias are also present. Lithic clast compositions are predominantly anorthositic noritic (or noritic anorthositic), and anorthositic troctolitic. Spinel-bearing rocks are present, but do not belong to the spinel-troctolite group. A spinel-bearing clast in MAC88105 consists of anorthite + pigeonite + spinel and indicates a different heritage, possibly similar to spinel cataclasites described from Apollo 17. The pyroxenes in MAC88105 have somewhat unusual compositions; orthopyroxenes and augites appear to be rare. Most lithologies (breccias and igneous rocks) contain solely pigeonite. We have found one igneous mafic rock, a gabbro, which has a low mg-number and is possibly of mare origin. A metal grain of a composition similar to metal in H chondrites supports the interpretation of MAC88105 as a regolith breccia. The bulk composition of MAC88105 is similar to the other lunar highland meteorites. The REE contents are slightly higher than for the other anorthositic meteorites, with a smaller positive Eu anomaly. This is in agreement with a possible KREEP contribution, possibly introduced from glasses. MACS 8105 is a mixture of rocks with a predominant contribution from the anorthosite suite and small admixtures from other rock types (mare basalt, Mg suite), which becomes obvious in plots of molar mg or Sm content vs. the Ti Sm ratio. The siderophile element abundances in MAC88105 are similar to other highland meteorites and show the characteristic Co excess and a Au Ir ratio similar to the other anorthositic meteorites and lower than the hyperchondritic ratio in Apollo 16 rocks, thus support the notion that the lunar meteorites are a more representative sample of the lunar highlands than the Apollo samples. The chemistry and mineralogy of MAC88105 is different from that of the other lunar meteorites and suggests a different source, which is supported by cosmic-ray and noble gas data. At this time it seems likely that about four individual impact events have been responsible for delivering the seven highland meteorites. MAC88105 and other lunar meteorites are important as they are probably random samples from the lunar surface and may thus be more representative than the Apollo and Luna rocks which come from only a small area of the moon.

Chemical Composition of Lunar Meteorites and the Lunar Crust

The paper presents the first analyses of major and trace elements in 19 lunar meteorites newly found in Oman. These and literature data were used to assay the composition of highland, mare, and transitional (highland-mare interface) regions of the lunar surface. The databank used in the research comprises data on 44 meteorites weighing 11 kg in total, which likely represent 26 individual falls. Our data demonstrate that the lunar highland crust should be richer in Ca and Al but poorer in mafic and incompatible elements than it was thought based on studying lunar samples and the first orbital data. The Ir concentration in the highland crust and the analysis of lunar crater population suggest that most lunar impactites were formed by a single major impact event, which predetermined the geochemical characteristics of these rocks. Lunar mare regions should be dominated by low-Ti basalts, which are, however, enriched in LREEs compared to those sampled by lunar missions. The typical material of mare-highland interface zones can contain KREEP and magnesian VLT basalts. The composition of the lunar highland crust deduced from the chemistry of lunar meteorites does not contradict the model of the lunar magma ocean, but the average composition of lunar mare meteorites is inconsistent with this concept and suggests assimilation of KREEP material by basaltic magmas. The newly obtained evaluations of the composition of the highland crust confirm that the Moon can be enriched in refractory elements and depleted in volatile and siderophile elements.

Chemistry of glass inclusions in olivines of the CR chondrites Renazzo, Acfer 182, and El Djouf 001

Abstract Glass inclusions in olivines of the Renazzo, El Djouf 001, and Acfer 182 CR-type chondrites are chemically divers and can be classified into Al-rich, Al-poor, and Na-rich types. The chemical properties of the glasses are independent of the occurrence of the olivine (isolated or part of an aggregate or chondrule) and its composition. The glasses are silica-saturated (Al-rich) or oversaturated (Al-poor, 24% normative quartz). All glasses have chondritic CaO/Al 2 O 3 ratios, unfractionated CI-normalized abundances of refractory trace elements and are depleted in moderately volatile and volatile elements. Thus the glasses are likely to be of a primitive condensate origin whose chemical composition has been established before chondrule formation and accretion, rather then the product of either crystal fractionation from chondrule melts or part melting of chondrules. Rare Na-rich glasses give evidence for elemental exchange between the glass and a vapor phase. Because they have Al 2 O 3 contents and trace element abundances very similar to those of the Al-rich glasses, they likely were derived from the latter by Ca exchange (for Na) with the nebula. Elemental exchange reactions also have affected practically all olivines (e.g., exchange of Mg of olivine for Fe 2+ , Mn 2+ , and Cr 3+ ). Glasses formed contemporaneously with the host olivine. As the most likely process for growing nonskeletal olivines from a vapor we consider the VLS (vapor-liquid-solid) growth process, or liquid-phase epitaxy. Glasses are the possible remnants of the liquid interface between growing crystal and the vapor. Such liquids can form stably or metastably in regions with enhanced oxygen fugacity as compared to that of a nebula of solar composition.

Cathodoluminescence, electron microscopy, and Raman spectroscopy of experimentally shock-metamorphosed zircon

Thorough understanding of the shock metamorphic signatures of zircon could be the basis for the use of this mineral as a powerful tool for the study of old, deeply eroded, and metamorphically overprinted impact structures and formations. This study of the cathodoluminescence (CL) and Raman spectroscopic signatures of experimentally (20–60 GPa) shock-metamorphosed zircon single crystals contributes to the understanding of high-pressure microdeformation in zircon. For all samples, an inverse relationship between the brightness of the backscattered electron (BSE) signal and the corresponding cathodoluminescence intensity was observed. The unshocked sample shows crosscutting, irregular fractures. The 20 GPa sample displays some kind of mosaic texture of CL brighter and darker domains, but does not exhibit any shock metamorphic features in BSE or CL images. The 40 GPa sample shows a high density of lamellar features, which might be explained by the phase transformation between zircon- and scheelite-structure phases of zircon and resulting differences in the energy levels of the activator elements. The CL spectra of unshocked and shocked (20, 40, and 60 GPa) zircon samples are dominated by narrow emission lines and broad bands in the region of visible light and in the near-UV range. The emission lines result from rare earth element activators and the broad bands might be associated with lattice defects. Raman spectra revealed that the unshocked and 20 GPa samples represent zircon-structure material, whereas the 40 GPa sample yielded additional peaks with relatively high peak intensities, which are indicative of the presence of the scheelite-type high-pressure phase. The 60 GPa sample has a Raman signature that is similar to that of an amorphous phase, in contrast to the observations of an earlier TEM study that the crystalline scheelite-structure phase is stable at this shock pressure. The 60 GPa Raman signature cannot be explained at this stage. The results show a clear dependence of the CL and Raman properties of zircon on shock pressure, which confirm the possible usage of these methods as shock indicators.

Shock metamorphism of siliceous volcanic rocks of the El'gygytgyn impact crater (Chukotka, Russia)

The 18-km-diameter El’gygytgyn crater is located on the Chukotka peninsula, northeastern Russia. It represents the only currently known impact structure formed in siliceous volcanics, including tuffs. The impact melt rocks and target rocks provide an excellent opportunity to study shock metamorphism of volcanic rocks. The shockinduced changes observed in porphyritic volcanic rocks from El’gygytgyn can be applied to a general classifi cation of shock metamorphism of siliceous volcanic rocks. Strongly shocked volcanic rocks with phenocrysts converted to diaplectic quartz glass and partially melted feldspars as well as cryptocrystalline matrices are widespread in the El’gygytgyn crater. In particular, the following different stages of shock metamorphism are observed: (i) weakly to moderately shocked lavas and tuffs with phenocrysts and clasts of quartz and feldspars; (ii) moderately shocked volcanic rocks and tuffs with diaplectic glasses of quartz and feldspars; (iii) strongly shocked lavas and tuffs with phenocrysts of diaplectic quartz glass and fused glasses of feldspars in melted matrixes; and (iv) impact melt rocks and impact glasses. In addition, thin glassy coatings of voids in impact melt rocks have been observed. While the shock-induced changes of clasts of framework silicates in these volcanic rocks do not differ from respective changes in other crystalline rocks, the fi negrained matrix of porphyritic rocks is converted into fused glass at the same shock pressures as feldspar minerals. No remnants of fi ne-grained quartz are preserved in matrix converted into fused glass by shock.

Limitations of Fe2+ and Mn2+ site occupancy in tourmaline: Evidence from Fe2+- and Mn2+-rich tourmaline

Abstract Fe2+- and Mn2+-rich tourmalines were used to test whether Fe2+ and Mn2+ substitute on the Z site of tourmaline to a detectable degree. Fe-rich tourmaline from a pegmatite from Lower Austria was characterized by crystal-structure refinement, chemical analyses, and Mössbauer and optical spectroscopy. The sample has large amounts of Fe2+ (~2.3 apfu), and substantial amounts of Fe3+ (~1.0 apfu). On basis of the collected data, the structural refinement and the spectroscopic data, an initial formula was determined by assigning the entire amount of Fe3+ (no delocalized electrons) and Ti4+ to the Z site and the amount of Fe2+ and Fe3+ from delocalized electrons to the Y-Z ED doublet (delocalized electrons between Y-Z and Y-Y): X (Na0.9Ca0.1) Y(Fe2+2.0Al0.4Mn2+0.3Fe3+0.2) Z(Al4.8Fe3+0.8Fe2+0.2Ti4+0.1) T(Si5.9Al0.1)O18 (BO3)3V(OH)3W[O0.5F0.3(OH)0.2] with a = 16.039(1) and c = 7.254(1) Å. This formula is consistent with lack of Fe2+ at the Z site, apart from that occupancy connected with delocalization of a hopping electron. The formula was further modified by considering two ED doublets to yield: X(Na0.9Ca0.1) Y(Fe2+1.8Al0.5Mn2+0.3Fe3+0.3) Z(Al4.8Fe3+0.7Fe2+0.4Ti4+0.1) T(Si5.9Al0.1)O18 (BO3)3V(OH)3W[O0.5F0.3(OH)0.2]. This formula requires some Fe2+ (~0.3 apfu) at the Z site, apart from that connected with delocalization of a hopping electron. Optical spectra were recorded from this sample as well as from two other Fe2+-rich tourmalines to determine if there is any evidence for Fe2+ at Y and Z sites. If Fe2+ were to occupy two different 6-coordinated sites in significant amounts and if these polyhedra have different geometries or metal-oxygen distances, bands from each site should be observed. However, even in high-quality spectra we see no evidence for such a doubling of the bands. We conclude that there is no ultimate proof for Fe2+ at the Z site, apart from that occupancy connected with delocalization of hopping electrons involving Fe cations at the Y and Z sites. A very Mn-rich tourmaline from a pegmatite on Elba Island, Italy, was characterized by crystal-structure determination, chemical analyses, and optical spectroscopy. The optimized structural formula is X(Na0.6□0.4) Y(Mn2+1.3Al1.2Li0.5) ZAl6TSi6O18 (BO3)3V(OH)3 W[F0.5O0.5], with a = 15.951(2) and c = 7.138(1) Å. Within a 3σ error there is no evidence for Mn occupancy at the Z site by refinement of Al ↔ Mn, and, thus, no final proof for Mn2+ at the Z site, either. Oxidation of these tourmalines at 700-750 °C and 1 bar for 10-72 h converted Fe2+ to Fe3+ and Mn2+ to Mn3+ with concomitant exchange with Al of the Z site. The refined ZFe content in the Fe-rich tourmaline increased by ~40% relative to its initial occupancy. The refined YFe content was smaller and the distance was significantly reduced relative to the unoxidized sample. A similar effect was observed for the oxidized Mn2+-rich tourmaline. Simultaneously, H and F were expelled from both samples as indicated by structural refinements, and H expulsion was indicated by infrared spectroscopy. The final species after oxidizing the Fe2+-rich tourmaline is buergerite. Its color had changed from blackish to brown-red. After oxidizing the Mn2+-rich tourmaline, the previously dark yellow sample was very dark brown-red, as expected for the oxidation of Mn2+ to Mn3+. The unit-cell parameter a decreased during oxidation whereas the c parameter showed a slight increase.

Mn-rich tourmaline and fluorapatite in a Variscan pegmatite from Eibenstein an der Thaya, Bohemian massif, Lower Austria

Mn-rich tourmaline (up to 8.89 wt% MnO) and fluorapatite (up to 9.15 wt% MnO) occur in an elbaite-subtype pegmatite from the Drosendorf Complex (near Eibenstein an der Thaya, Bohemian massif, Austria). Based on geological and radiometrical data (337 ± 5 Ma from Sm/Nd garnet-albite isochron) the pegmatite might be related to the Variscan Rastenberg type granodiorites or Weinsberg type granites. Coexisting minerals with Mn-rich, pink-brown to yellow-brown tourmaline and bluish, Mn-rich fluorapatite are quartz, feldspars, Mn-rich garnet (63 mol% spessartine), pink Mn-bearing muscovite (up to ∼0.3 wt% MnO), topaz, cassiterite and rarely, beryl and bertrandite. Tourmaline composition evolves from Mn-poor (0.09 apfu ) schorl through Al-rich Mn-bearing (0.15–0.33 apfu ) schorl, Mn-rich (0.58 apfu ) Fe-bearing olenite-elbaite to Mn-rich (0.86–1.27 apfu ) olenite-elbaite, which reflects the Mn-enrichment of the pegmatite system during the late stages of its evolution. Mn-rich Li-bearing olenite has the formulae x (Na 0.71 Ca 0.01 □ 0.28 ) Y (Al 1.36 Mn 2+ 1.27 Li 0.34) Z Al 6.00 T Si 6 B 3 O 27 [(OH) 3 (F 0.44 ,OH,O)] (8.89 wt% MnO) and X (Na 0.84 Ca 0.03 K 0.01 □ 0.12 ) Y (Al 1.33 Mn 2+ 0.86 Li 0.51 Fe 2+ 0.06 Ti 0.02 □ 0.22 ) Z Al 6.00 T Al(Si 5.74 Al 0.26 ) B 3 O 27 [(OH) 3 ) (F 0.54 OH 0.37 O 0.09 ] (6.22 wt% MnO), with lattice parameters a = 15.9158(4) A, c = 7.1201(2) A ( R = 0.021). This pegmatite has two different zones: a Mn-enriched zone and a Mg-enriched zone. The younger, fine-grained, Mn-enriched zone contains the Mn-bearing minerals described above which have low Mg contents. The coarse-grained, Mg-enriched zone contains Mg-bearing muscovite, tourmaline from the dravite-schorl series, and pale-green fluorapatite but essentially contains no Mn-bearing minerals. Interestingly, albite has a pale bluish-greenish color in the Mn-enriched zone while it has a white color in the Mg-enriched zone.