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Fissure monazite-(Ce) (hereafter called monazite) commonly crystallizes during deformation at low metamorphic grade and offers the possibility to date protracted deformation over several millions of years and to identify distinct deformation phases. We performed Th-Pb geochronology at the microscale on 10 samples of fissure monazite from two Alpine crystalline massifs (Aar Massif and Gotthard Nappe). Ion microprobe ages show that the earliest stage of crystallization recorded by fissure monazite domain ages occurred around 15.9 Ma in the Gotthard Nappe and about 1 My later in the Aar Massif, with the latest crystallization event recorded at 6 Ma. Protracted monazite crystallization in fissures indicates that deformation datable with fissure monazite lasted about 10 Ma. Comparison of Th-Pb crystallization ages of fissure monazite to existing thermochronological data shows that early monazite crystallization coincide with zircon fission track ages, whereas the youngest monazite crystallization overlaps with apatite fission track ages. Monazite also grows contemporaneous with muscovite/illite crystallization (K-Ar ages) in fault gouges. As monazite can grow during dissolution/precipitation cycles induced by tectonic activity, their chronology allows to further constrain in the Aar Massif the final Handegg phase at 12–11.5 Ma, and the coeval activity of the Pfaffenchopf (11.5–9 Ma), and the Oberaar and Rhone-Simplon phases (11.5 and 6 Ma). In the Gotthard Nappe, monazite crystallization constrains a major portion of the Chiera backfolding phase at 14–13 Ma, and confirms that the south-western termination of the nappe was affected by the Rhone-Simplon phase.

Ureilites are the second largest group of achondrite meteorites but consensus is still lacking on the nature of their precursors, melting processes, and the genetic relationship between monomict ureilites and brecciated ureilites. The recently found ureilite Ramlat as Sahmah 517 is of special interest in this context. This meteorite lacks shock features in its primary silicates and belongs to a rare augite- and chromite-bearing subset of the monomict ferroan ureilites. It hosts abundant intergranular glass veinlets speckled with pyroxene and metal globules. Detailed petrographic investigations show that the Si-Al-rich glass represents quenched anatectic melt that was present prior to formation of the reduced olivine rims by incomplete low-pressure equilibration (smelting) of carbon and silicates. The melt facilitated smelting which, along with rapid crystallization of secondary pyroxene, modified the originally trachyandesitic melt. Melt-silicate equilibrium preceding these events is constrained by modelling using MELTS and the first reported in-situ measurements of LREE-enriched glass that is largely complementary to the depleted mafic silicates in monomict ureilites. The inferred major element composition of the partial melt that formed in RaS 517 is similar to that of trachyandesite in Almahata Sitta but RaS 517 lacks phosphates which are abundant in the Almahata Sitta trachyandesite and in alkali-rich feldspathic clasts in polymict ureilites. The LREE-depletion in the dominant monomict ferroan ureilite population can be explained by the formation of melt fractions similar to the glass in RaS 517 after initial rapid melting of phosphates. These finds provide evidence for a genetic relationship between ferroan ureilites and lithologies similar to the Almahata Sitta trachyandesite and further suggest that these ureilites formed by partial melting of P- and alkali-rich precursors with trace element concentrations similar to equilibrated ordinary chondrites. Quenched Si-Al-rich glass also occurs in magnesian ureilites but has lower concentrations of alkalis and LREE-depleted trace element signatures which can reflect more depleted compositions at the onset of partial melting. The evidence presented here favors a scenario in which the primary ureilite differentiation was driven by gradual heating from radioactive decay with resulting temperatures (>1100 °C) being maintained until disruption of the ureilite parent asteroid.

Meteorite searches in Saudi Arabia between 2008 and 2014 yielded 46 meteorites from the Yabrin area (23°N 49°E), 35 meteorites from the Rub’ al-Khali sand desert (19°–20°N, 48°–51°E), and 1 meteorite from Al Haddar. No meteorites were found near Hafar al Batin (29°N 45°E). The 82 new meteorites represent ~57 falls comprising 43 ordinary chondrites, 4 carbonaceous chondrites, 2 enstatite chondrites, 3 ureilites, 3 eucrites, 1 acapulcoite, and 1 lunar meteorite. The median of 31 14C terrestrial ages is 6.2 ka, significantly younger than the Oman population (19.5 ka, n = 128). A further assessment of terrestrial 14C contamination is advised by a 11–15 ka 14C terrestrial age of heavily weathered meteorite Khawr al Fazra 014, geology indicating a terrestrial age >100 ka. Find densities of 0.4–2.8 km-2 for Yabrin and the western Rub’ al-Khali are similar to ~0.5 km-2 observed in Oman. Higher find densities of ~135 km-2 (29 km-2 for masses >10 g) exist on small Pleistocene outcrops in blowouts in the south-central Rub’ al-Khali: 21 unpaired meteorites (four >10 g) were found in 11 blowouts with a combined area of 0.14 km2. The Rub’ al-Khali meteorites show a relatively high degree of weathering (median W 3.6; 2.5 for Yabrin), low median mass (4.3/138 g), and a high H/L ratio (2.3/1.1). The high density of small meteorites is explained by prolonged sand protection and recent deflation. The high meteorite density and relatively high proportion of rare meteorite types render the Rub’ al-Khali blowouts an interesting target for future exploration.

Th-Pb age dating of zoned hydrothermal monazite from alpine-type fissures/clefts is a powerful tool for constraining polyphase deformation at temperatures below 350°C and presents an alternative to K/Ar and 40Ar/39Ar dating techniques for dating brittle tectonics. This study considers the relationship between cleft orientations in ductile shear zones and cleft mineral crystallization during subsequent brittle overprinting. In the Grimsel area, located in the Aar Massif of the Central Alps, horizontal clefts formed during a primary thrust dominated deformation, while younger and vertically oriented clefts developed during secondary strike-slip movements. The change is due to a switch in orientation between the principal stress axes σ2 and σ3. The transition is associated with monazite crystallization and chloritization of biotite at around 11.5 Ma. Quartz fluid inclusion data allow a link between deformation stages and temperatures to be established and indicate that primary monazite crystallization occurred in both cleft systems at 300–350°C. While cleft monazite crystallization ceases at ~11 Ma in inactive shear zones, monazite growth, and/or dissolution-reprecipitation continues under brittle deformation conditions in vertical clefts during later deformation until ~7 Ma. This younger shear zone activity occurs in association with dextral strike-slip movement of the Rhone-Simplon fault system. With the exception of varying Th/U values correlated with the degree of oxidation, there is only limited compositional variation in the studied cleft monazites.

Abar al' Uj (AaU) 012 is a clast-rich, vesicular impact-melt (IM) breccia, composed of lithic and mineral clasts set in a very fine-grained and well-crystallized matrix. It is a typical feldspathic lunar meteorite, most likely originating from the lunar farside. Bulk composition (31.0 wt% Al2O3, 3.85wt% FeO) is close to the mean of feldspathic lunar meteorites and Apollo FAN-suite rocks. The low concentration of incompatible trace elements (0.39ppmTh, 0.13ppm U) reflects the absence of a significant KREEP component. Plagioclase is highly anorthitic with a mean of An(96.9)Ab(3.0)Or(0.1). Bulk rock Mg# is 63 and molar FeO/MnO is 76. The terrestrial age of the meteorite is 33.4 +/- 5.2kyr. AaU 012 contains a similar to 1.4x1.5mm(2) exotic clast different from the lithic clast population which is dominated by clasts of anorthosite breccias. Bulk composition and presence of relatively large vesicles indicate that the clast was most probably formed by an impact into a precursor having nonmare igneous origin most likely related to the rare alkali-suite rocks. The IM clast is mainly composed of clinopyroxenes, contains a significant amount of cristobalite (9.0 vol%), and has a microcrystalline mesostasis. Although the clast shows similarities in texture and modal mineral abundances with some Apollo pigeonite basalts, it has lower FeO and higher SiO2 than any mare basalt. It also has higher FeO and lower Al2O3 than rocks from the FAN- or Mg-suite. Its lower Mg# (59) compared to Mg-suite rocks also excludes a relationship with these types of lunar material.

Hundred-micrometer-sized calcium-aluminum-silicates (CAS) inclusions occur in moissanite-4 H , moissanite-15 R , and moissanite-6 H from Turkey. These inclusions commonly consist of tabular exsolution lamellae of two different minerals. By combined electron microprobe and Raman spectroscopy analysis, at least eight different, essentially Mg- and Fe-free Ca-Al-silicate or Al-silicate phases have been discerned. The most common phase is dmisteinbergite, a hexagonal modification of CaAl2Si2O8, occurring in association with lamellae of Cax(Al,Si)1−xO3 or Ca1−x(Al,Si)2+xO5 compositions. All three phases contain significant amounts of BaO (up to 2 mol% of celsiane component in dmisteinbergite), SrO, SO3, and light rare earth elements (LREE). In particular, Ca1−x(Al,Si)2+xO5 contains up to 2.1 wt% of LREE, 3.9 wt% of F, and significant traces of Cl, while it is also associated to osbornite (TiN). Pure ghelenite, Ca2Al2SiO7, and three additional compositions, namely CaAl4−xSixO7, Ca1−x(Al,Si)3+xO6, and Ca3−x(Al,Si)6+xO14 have been found, either occurring as single grains or forming exsolution lamellae. They also contain significant amounts of BaO, SrO, SO3, and LREE. One last intriguing phase is composed in average of 65.9 wt% SiO2, 17.4% Al2O3, 3.0% alkalis, 6.0% BaO, 2.0% CaO+MgO, 0.9% ZrO2, and up to 0.5% LREE. Dmisteinbergite and ghelenite show Raman peaks in very good agreement with literature data, Cax(Al,Si)1−xO3 shows main Raman modes at 416 and 1009 cm−1, Ca1−x(Al,Si)3+xO6 at 531 and 1579 cm−1 while Ca3−x(Al,Si)6+xO14 has a strong peak at 553 cm−1. CaAl4−xSixO7 shows a weak Raman pattern, while Ca1−x(Al,Si)2+xO5 has no detectable Raman modes. Since the association moissanite-CAS is thermodynamically not stable at ambient pressure and moissanite crystals hosting the CAS phases have δ13C values typical of deep-mantle origin, we interpret the CAS inclusions as partially retrogressed HP minerals. Striking analogies exist between observed CAS compositions and experimentally obtained HP-HT mineralogy. For instance, Cax(Al,Si)1−xO3 contains up to 25 mol% of Al2O3, which is considered as the upper limit of alumina solubility in Ca-perovskite. The study confirms that CAS phases are an important mantle depository for large ion lithophile elements (LILE) and LREE.

In this study, rare earth element (REE) distribution has been investigated in a weathering profile from central Madagascar. Combination of bulk rock geochemical data (elements and isotopes) with mineral characterization reveals a remarkable evolution of the REE abundances and REE-minerals in the vertical weathering profile. In the fresh tonalite (bedrock), REE + Y concentrations are typical of granitoids (299–363 ppm) and the main REE-minerals are allanite and chevkinite. In the C-horizon (saprolite), primary REE-minerals disappear and REEs are transported via fluid to precipitate rhabdophane group minerals in cracks and pores. The presence of sulfate ligands, produced by sulfide oxidation, may be responsible for the REE speciation, as suggested by the composition of the secondary REE-minerals. Rhabdophane group minerals contain up to 9 wt% SO 3 and 7 wt% CaO, indicating a mixture between rhabdophane sensu stricto, (REE)PO 4 ·H 2 O, and tristamite, (Ca,U,Fe (III) )(PO 4 ,SO 4 )·2H 2 O. Due to intense Ca-leaching, rhabdophane disappears and Al-phosphates (alunite–jarosite group) are found in the soil. Cerianite (Ce (IV) O 2 ) also precipitates in the B-horizon of the soil. Mass transfer calculations based on immobile Ti indicate significant REE leaching in A-horizon with preferential leaching of the heavy REE. REEs accumulate partly in the B-horizon. The uniform Nd isotope compositions and the constant proportion of immobile elements do not reveal external input. In the B-horizon, total REE + Y reach 2194 ppm with high Ce concentrations (1638 ppm; 9 * Ce bedrock ) compared to other REE (3–4 * REE bedrock ). Tetravalent Ce state is dominant in the B-horizon and requires oxidizing conditions that likely account for the accumulation of redox-sensitive elements in B-horizon (e.g., Mn, Fe, Co). Under oxidizing conditions, cerianite precipitation causes a Ce fractionation from other trivalent REE. In comparison to the ion adsorption clay of southern China, preferential heavy REE enrichment was not observed in the weathering profile. Another remarkable peculiarity of the studied profile is the occurrence of Gd 2 SO 6 grains. The discovery of this new mineral demonstrates that a natural process exists that that can fractionate REE to such an extent to produce a pure gadolinium end-member mineral. An understanding of such a mechanisms is crucial for the REE geochemistry of low temperature alteration processes as well as for the formation of REE ore deposits or industrial processing.

The common appearance of hygroscopic brine ("sweating") on ordinary chondrites (OCs) from Oman during storage under room conditions initiated a study on the role of water-soluble salts on the weathering of OCs. Analyses of leachates from OCs and soils, combined with petrography of alteration features and a 11-month record of in situ meteorite and soil temperatures, are used to evaluate the role of salts in OC weathering. Main soluble ions in soils are Ca 2+ ,S O4 2� ,H CO3 � ,N a + , and Cl � , while OC leachates are dominated by Mg 2+ (from meteoritic olivine), Ca 2+ (from soil), Cl � (from soil), SO4 2� (from meteoritic troilite and soil), and iron (meteoritic). "Sweating meteorites" mainly contain Mg 2+ and Cl � . The median Na/Cl mass ratio of leachates changes from 0.65 in soils to 0.07 in meteorites, indicating the precipitation of a Na-rich phase or loss of an efflorescent Na-salt. The total concentrations of water-soluble ions in bulk OCs ranges from 600 to 9000 l gg � 1 (median 2500 l gg � 1 ) as compared to 187-14140 l gg � 1 in soils (median 1148 l gg � 1 ). Soil salts dissolved by rain water are soaked up by meteorites by capillary forces. Daily heating (up to 66.3 °C) and cooling of the meteorites cause a pumping effect, resulting in a strong concentration of soluble ions in meteorites over time. The concentrations of water-soluble ions in meteorites, which are complex mixtures of ions from the soil and from oxidation and hydrolysis of meteoritic material, depend on the degree of weathering and are highest at W3. Input of soil contaminants generally dominates over the ions mobilized from meteorites. Silicate hydrolysis preferentially affects olivine and is enhanced by sulfide oxidation, producing local acidic conditions as evidenced by jarosite. Plagioclase weathering is negligible. After completion of troilite oxidation, the rate of chemical weathering slows down with continuing Ca-sulfate contamination.

– A petrographic and geochemical study was undertaken to characterize Jiddat al Harasis (JaH) 556, a howardite find from the Sultanate of Oman. JaH 556 is a polymict impact melt breccia containing highly shocked clasts, including mosaicized olivine and recrystallized plagioclase, set in a finely recrystallized vesicular matrix (grain diameter

We measured the concentrations and isotopic compositions of He, Ne, and Ar in 29 bulk samples from 11 different strewn field fragments of the large Jiddat al Harasis (JaH) 073 L6 chondrite shower, including 7 samples from known locations within the main mass. In addition, we measured the concentrations of cosmogenic 10Be, 26Al, 36Cl, and 41Ca in 10 samples. All fragments of this shower are characterized by low 10Be concentrations (7.6-12.8 dpm/kg), high 26Al/10Be ratios (3.55), large contributions of neutron capture 41Ca (200-1800 dpm/kgCa), low 3He/21Ne ratios (1.5-3.0), large variations in cosmogenic 21Ne (1.2-12) 10^(-8) cm^3 STP/g, and significant contributions of neutron-capture 36Ar. Stepwise heating experiments show that neutron-capture produced 36Ar is predominantly released between 1000-1200 °C. All these results are consistent with a first-stage exposure of ~65 Ma within ~20 cm of the surface of the L-chondrite parent body, followed by ejection of a 1.52 m large object, which was then delivered to Earth within about 0.5 and 0.7 Ma. The cosmogenic nuclide data in JaH 073 thus corroborate the trend that many of the large chondrites studied so far experienced a complex exposure history. The observed 3He/21Ne ratios of 2.53.0 in the most shielded samples (including those of the main mass) are lower than predicted by model calculations, but similar to the lowest values found in the large Gold Basin L-chondrite shower. The Bern plot, which gives a linear correlation for 3He/21Ne versus 22Ne/21Ne, is evidently not valid for very high shielding. Some of our measured 22Ne/21Ne ratios in JaH 073 are lower than 1.06, which is not well understood, but might be explained by loss of cosmogenic neon from shocked sodium-rich plagioclase during terrestrial weathering. The amount of trapped atmospheric argon in the JaH 073 fragments varies by almost two orders of magnitude and shows only a weak correlation with the size of the fragments, which range from 50 kg. Finally, low concentrations of radiogenic 4He and 40Ar indicate incomplete degassing

Samples of marble xenoliths, thermally metamorphosed by the igneous rocks of Mont Saint-Hilaire, Quebec, contain idiomorphic plates of phlogopite. These plates were later overgrown and to some extent topotactically replaced by sodian tainiolite, tapering in fragile fibers extending parallel to [100]. The fibers only protrude parallel to [100] of the phlogopite host. Unit-cell parameters of phlogopite and tainiolite, both 1 M polytypes (space group C 2/ m ), are so similar that the phases in the phlogopite –tainiolite intergrowth could not be distinguished by single-crystal X-ray methods. Phlogopite of composition K1.01(Mg1.96Fe0.66Li0.20Mn0.03Ti0.03Al0.04)∑2.92(Si3.28Al0.72)∑4O10[(OH)1.14F0.86]∑2 has the highest Si/Al value of natural samples of phlogopite known to us. The epitactic fibers of tainiolite, of composition K1.01(Mg2.00Fe0.01Li0.59Na0.38)∑2.98(Si3.99Al0.01)∑4O10[F1.79Cl0.01 (OH)0.20]∑2, represent to our knowledge the first example of an extended solid-solution, established by combined electron-microprobe and laser-ablation mass-spectrometry analyses, between tainiolite, K(LiMg2)Si4O10F2, and the recently described mineral shirokshinite, K(NaMg2)Si4O10F2. The latest mineral formed in the observed paragenesis is the zeolite mesolite, accompanied by an unidentified aluminosilicate with Ca/K ≈ 1.

Uruq al Hadd (UaH02) meteorite is found in the southwest of Oman close to the border with Yemen. Mossbauer spectroscopy has been used to assess the mineralogy of iron-bearing phases in this meteorite, supported by X-ray diffraction and electron-probe microanalysis (EPMA). Mossbauer spectra measured at 295 and 78 K exhibit paramagnetic doublets superimposed on magnetic sextets. The doublets are assigned to the silicate minerals olivine and pyroxene and the magnetic sextets reveal the presence of at least four magnetic phases: troilite (Fe 49.2 S 50.8 ), kamacite (Fe 92.2 Ni 7.8 ), taenite (FeNi), iron oxides and oxy-hydroxides. Both iron oxides and oxy-hydroxides are terrestrial alteration products. Weathering is not pervasive suggesting a relatively young terrestrial age. The mole percentages of fayalite in olivine and ferrosilite in pyroxene determined by EPMA, classifies the meteorite as an H3 chondrite of W1 weathering stage.

Single-crystal X-ray study of different vesuvianite samples of known origin shows that different metamorphic grade results in different arrangements of structural rods oriented parallel to the vesuvianite c axis, interpreted as “rod polytypism.” There is a systematic dependence of space-group symmetry and rod arrangement on crystallization temperature: P 4 nc -dominant 500 °C. Partial occupancy of the T sites (B, Al, Fe3+) and increased F-content seem to stabilize rod disorder causing P 4/ nnc space-group symmetry. All studied vesuvianites in calcsilicate rocks and marbles from regional- and contact-metamorphic upper amphibolite facies have disordered rods ( P 4/ nnc symmetry). Electron-microprobe analyses of metamorphic vesuvianites from alpine and non-alpine occurrences, supported by structural investigation, showed that in addition to homo- and heterovalent substitution, partial occupancy of the commonly vacant T sites by B, Al, or Fe3+, and the (O4H4)4− → SiO44− (hydrogarnet-type) substitutions are significant in nature. With few exceptions, T-site occupancy seems to be restricted to high-grade metamorphic rocks whereas the “hydrovesuvianite” substitution is only found in vesuvianites formed at very low metamorphic grade. The cell parameters of vesuvianite with empty T sites increase with increasing Ti + Mg → 2 Al substitution, and this increase is even more pronounced with increasing “hydrovesuvianite” component. An increase in boron on T sites leads to a decrease of c but an increase in a . Fluorine incorporation and T-site substitution (B, Al, Fe3+) in vesuvianite are coupled with a decrease in hydroxyl groups. This causes vesuvianites to be stable under higher X CO2 conditions, and in an assemblage with quartz at conditions above the experimentally determined upper stability of quartz + T site vacant, F-free vesuvianite. Optically anomalous vesuvianites have ordered rods and are generally characterized by an intergrowth of P 4/ n and P 4 nc domains. In addition to B-rich vesuvianite and wiluite, P 4 nc -dominant vesuvianites are also commonly optically positive.

We report the first occurrence of moissanite (SiC) as a rock-forming mineral (8.4 vol%) in one unique specimen of a terrestrial rock. The sample has a homogeneous, porphyritic texture, and was found as a beach pebble thought to be derived from a Tertiary volcanic province of the Aegean Sea region. The matrix is bluish-colored and consists of very fine-grained brucite, calcite, and magnesite, in which macrocrysts of quartz (25.3 vol%) and moissanite are found. Other accessory phases are phlogopite -3T , magnesiochromite, an Fe-rich phase, Cl-bearing brucite, Al-rich orthopyroxene, and unidentified MgFe-silicates (4 vol%). The bulk-rock composition shows a “kimberlitic” chemistry (55.8 wt% SiO 2 , 28.5 wt% MgO, 1.4 wt% CaO, 18.1 wt% LOI). Colorless gemmy, and blue or black moissanite crystals are subhedral and display characteristic hexagonal symmetry ( 6H polytype). Most moissanite grains contain metallic Si and Fe-silicide (Fe 3 Si 7 ) inclusions, and more rarely, other Fe-silicides with varying amounts of Al (≤24.5 wt%), Ca (≤8.0 wt%), Mn (≤6.8 wt%), Ti (≤16.3 wt%), and Ni (≤2.6 wt%). The δ 13 C value of the moissanite is −28.1‰. According to available data, the f s O2 stability field of SiC is five to six log units below the iron-wustite (IW) buffer curve. Therefore, the observed Fe-bearing silicates cannot have been equilibrated with SiC under ambient pressure. Instead, our finding indicates that the rock most likely formed at the ultrahigh-pressure conditions of the upper mantle or transition zone.

Monazite-bearing Alpine clefts located in the Sonnblick region of the eastern Tauern Window, Austria, are oriented perpendicular to the foliation and lineation. Ion probe (SIMS) Th–Pb and U–Pb dating of four cleft monazites yields crystallization ages of different growth domains and aggregate regions ranging from 18.99 ± 0.51 to 15.00 ± 0.51 Ma. The crystallization ages obtained are overlapping or slightly younger than zircon fission track ages but older than zircon (U–Th)/He cooling ages from the same area. This constrains cleft monazite crystallization in this area to ~300–200 °C. LA-ICP-MS data of dated hydrothermal monazites indicate that in graphite-bearing, reduced host lithologies, cleft monazite is poor in As and has higher La/Yb values and U concentrations, whereas in oxidised host rocks opposite trends are observed. Monazites show negative Eu anomalies and variable La/Yb values ranging from 520 to 6050. The positive correlation between Ca and Sr concentration indicates dissolution of plagioclase or carbonates as the source of these elements. The data show that early exhumation and cleft formation in the Tauern is related to metamorphic dome formation caused by the collision of the Adriatic with the European plate and that monazite crystallization in the clefts occurred later. Our data also demonstrate that hydrothermal monazite ages offer great potential in helping to constrain the chronology of exhumation in collisional orogens.

Sayh al Uhaymir 094 is a 223.3 g, partially crusted, strongly to very strongly shocked melanocratic olivine-porphyric rock of the shergottite group showing a microgabbroic texture. The rock consists of pyroxene (52.0 - 58.2 vol%) - dominantly prismatic pigeonite (En60-68Fs20-27Wo7-9) associated with minor augite (En46-49Fs15-16Wo28-31) - brown (shock-oxidized) olivine (Fo65-69; 22.1 - 31%), completely isotropic interstitial plagioclase glass (maskelynite; An50-64Or0.3-0.9, 8.6 - 13.0%), chromite and titanian magnesian chromite (0.9 - 1.0%), traces of ilmenite (Ilm80-86), pyrrhotite (Fe92-100; 0.1 - 0.2%), merrillite (<< 0.1%), and pockets (4.8 - 6.7%) consisting of green basaltic to basaltic andesitic shock glass that is partially devitrified into a brown to black product along boundaries with the primary minerals. The average maximum dimensions of minerals are: olivine (1.5 mm), pyroxene (0.3 mm) and maskelynite (0.3 mm). Primary melt inclusions in olivine and chromite are common and account for 0.1 - 0.6% of the rock. X-ray tomography revealed that the specimen contains approximately 0.4 vol% of shock-melt associated vesicles, up to 3 mm in size, which show a preferred orientation. Fluidization of the maskelynite, melting and recrystallization of pyroxene, olivine and pyrrhotite indicate shock stage S6. Minor terrestrial weathering resulted in calcite-veining and minor oxidation of sulfides. The meteorite is interpreted as paired with SaU 005/008/051. The modal composition is similar to Dar al Gani 476/489/670/735/876, with the exception that neither mesostasis nor titanomagnetite nor apatite are present and that all phases show little zonation. The restricted mineral composition, predominance of chromite among the oxides, and abundance of olivine indicate affinities to the lherzolitic shergottites.

The new minerals manganvesuviante and tweddillite, both formed by hydrothermal alteration of primary manganese ores, are described from the Kalahari manganese fields (Republic of South Africa). In addition, single-crystal X-ray structure refinements of both new minerals are presented.Manganvesuvianite is a tetragonal vesuvianite mineral with the simplified formula Ca19Mn3+(Al,Mn3+,Fe3+)10(Mg,Mn2+)2Si18O69(OH)9, characterized by Mn3+ occupying the five-coordinated position (square pyramid). The crystals simple prismatic forms: {100}, {110} terminated by {101} and exhibit deep maroon red colour. With polarized light the crystals are strongly pleochroic, yellowish parallel to E and dark red to lilac parallel to O.Tweddillite is an epidote-group mineral (space group P21/m, a = 8.932(5), b = 5.698(4), c = 10.310(5) Å, β = 114.56(4), V = 477.3(8) Å3) with the simplified formula CaSr(Mn3+,Fe3+)2Al[Si3O12](OH), closely related to strontiopiemontite. The difference between strontiopiemontite and tweddillite is the concentration of octahedral Mn3+. Strontiopiemontite has Mn3+ mainly on the M3 site whereas tweddillite has Mn3+ with minor Fe3+ on M3 and M1. Tweddillite forms aggregates of very thin dark red {001} blades characterized by striking pleochroism. The crystals appear dark red parallel to b and orange-yellow parallel to a. Perpendicular to (001) the blades appear magenta to red.

Low-temperature vesuvianites crystallize in the two space groups P 4/ n or P 4 nc due to different arrangements of Ca-dodecahedra and M 2+,3+ square pyramids that form strings along the fourfold axes. Long-range ordered vesuvianites of acentric P 4 nc symmetry may have the same diffraction symmetry as centrosymmetric disordered P 4/ nnc vesuvianites. In contrast, P 4/ n long-range ordered vesuvianites exhibit glide plane violating reflections and can easily be identified. We report the first successful X-ray single-crystal structure refinement of a P 4 nc vesuvianite, a = 15.487(2), c = 11.764(2) A from the N’chwaning II mine of the Kalahari manganese fields (RSA). This untwinned crystal has Cu 2+ and Mn 2+ , Mn 3+ forming the square pyramid and exhibits an acentric ordering pattern with 85% string A and 15% string B. This is compared to a reinvestigation of the structure of a P 4/ n vesuvianite from Asbestos Quebec (Canada), a = 15.531(2), c = 11.817(2) A. The crystal is composed of a merohedral (110) twin with a close to 1:1 twin ratio and has mainly Fe 3+ in square pyramidal coordination. In this centric structure, string A is 84% and string B is 16% occupied. Criteria to determine the symmetry of low-temperature vesuvianites, studied by diffraction experiments, are discussed.

Recent thermochronology and thermobarometry place new constraints on the tectonic evolution of the Samail ophiolite. Zircon and radiolarian ages indicate formation of the Samail ophiolite crust at 97-94 Ma. Hornblende ages demonstrate that the metamorphic sole beneath the ophiolite formed and, only 1–4 m.y. later, cooled to 550°C. Thermobarometry dictates that the sole formed at peak temperatures of 775–875°C and unexpectedly high pressures of 1.1 GPa. These data imply extremely rapid (∼200 km/m.y.) subduction beneath a very young ophiolite for a few m.y. to depths of 30–40 km, followed by equally rapid subduction of cold lithosphere beneath the ophiolite. High-pressure rocks beneath the ophiolite show subduction of the Arabian continental margin to depths as great as 70–80 km, but the temporal and genetic relationships between the metamorphic sole and the high-pressure rocks are poorly known. Key questions remaining are the magnitude, style, and age of extension of the ophiolite, and the timing of high-pressure metamorphic event(s).

The obduction-related basal part of the Muslim Bagh ophiolite (Baluchistan, Pakistan) and the underlying metamorphic sequence were studied structurally which demonstrated a WSW-ENE-trending thrusting sequence for the initial obduction. 40Ar/39Ar measurements on amphiboles and plagioclase from the subophiolitic metamorphic rocks, and on plastically deformed and recrystallized dolerite samples from the base of the sheeted dyke complex give apparent ages between 70.7 ± 5.0 and 65.1 ± 4.1 Ma interpreted as cooling ages dating approximately the formation of the plastic deformation and obduction. The results indicate that the Muslim Bagh ophiolite represents a segment of ocean floor from the small and slow-spreading ocean branch of the Neo-Tethys located between the Indo-Pakistani and the Afro-Arabian plates. The WSW-ENE-oriented obduction of the Muslim Bagh ophiolite onto the Indo-Pakistani continental margin occurred with the convergence of the Neo-Tethys branch during the Late Cretaceous and before the Tertiary collision of the Indo-Pakistani plate with the Eurasian plate.

The assemblage tephroite-hausmannitess-galaxitess has been found in a granulite-facies manganese ore body associated with metabasites and quartzrich lithologies. The metamorphic rocks are located in the Khawr Fakkan massif near the northern end of the Semail Ophiolite, United Arab Emirates (U.A.E.), metamorphosed at 800–850°C and 6.5–9 kbar. The galaxite shows approximately 35% solid solution of hausmannite, similar to that reported for jacobsite and franklinite whereas the solid solution of galaxite in hausmannite is maximally 7%. The assemblage of tephroite-hausmannite and hausmannite-galaxite indicates a restricted log fO2 of-9 to-11 which is outside the stability of braunite under similar physico-chemical conditions. The modal abundance of the minerals and bulk rock chemistry indicate that the present assemblage was formed from the breakdown of Fe-poor braunitess+hausmannitess.

Granulite facies metasedimentary and metavolcanic rocks occur imbricated with the Cretaceous Semail Ophiolite in the United Arab Emirates and Oman. Peak metamorphic assemblages in highly oxidized lithologies of these rocks include sapphirine (7 : 9 : 3)-hercynitic spinel-magnetite-ilmeno-hematite-plagioclase-enstatite-quartz and sapphirine (2 : 2 : 1)-corundum-ilmeno-hematite-phlogopite-plagioclase. The observed mineral assemblages in quartzitic rocks are an example of overlapping stability of sapphirine-quartz and spinel-quartz and are therefore not diagnostic for high pressures. Both types of sapphirine occur within the stability field of Mg-rich cordierite. The common association of sapphirine and spinel with magnetite and ilmeno-hematite in quartzitic rocks suggests that sapphirine was formed by a reaction including spinel, hematite and quartz on the educt side. Metamorphic conditions estimated from associated parageneses point to temperatures of 800–850°C and pressures of 6.5–9 kbar.

The Jiddat al Harasis (JaH) 422 ureilite was found in the Sultanate of Oman; it is classified as a ureilitic impact melt breccia. The meteorite consists of rounded polycrystalline olivine clasts (35%), pores (8%), and microcrystalline matrix (57%). Clasts and matrix have oxygen isotopic values and chemical compositions (major and trace elements) characteristic of the ureilite group. The matrix contains olivine (Fo83-90), low-Ca pyroxene (En84-92Wo0-5), augite (En71-56Wo20-31), graphite, diamond, Fe-metal, sulfides, chromite, and felsic glass. Pores are partly filled by secondary Fe-oxihydroxide and desert alteration products. Pores are surrounded by strongly reduced silicates. Clasts consist of fine-grained aggregates of polygonal olivine. These clasts have an approximately 250 lm wide reaction rim, in which olivine composition evolves progressively from the core composition (Fo79-81) to the matrix composition (Fo84-87). Veins crossing the clasts comprise pyroxene, Fe-oxihydroxide, C-phases, and chromite. Clasts contain Ca-, Al-, and Cr-rich glass along olivine grain boundaries (

K−Ar ages have been determined on micas and hornblendes in the basal metamorphic sequence and in metamorphic rocks squeezed into the mantle sequence of the Semail Ophiolite. The hornblende ages of 99±0.5 and 102±0.8 Ma and the 90 Ma ages of coexisting micas from the high-grade metamorphic portion of the sequence are interpreted as cooling stages following the peak of metamorphism (T 800–850° C, P 6.5–9 kbar). The new pressure estimates are based on findings of kyanite in garnet-amphibolite and cordierite in quartzitic rocks. These data indicate a cooling rate of 10–30° C/Ma. The oldest mica ages of 95±1 Ma are observed in the lowest-grade greenschists. These also largely represent cooling ages, but might in part also include formation ages. The pattern of the muscovite ages across the metamorphic sole indicates that the cooling front moved from the low-grade metamorphic zone, through the high-grade rocks and into the base of the overlying ophiolite. Radiometric ages of hornblendes (92.3±0.5 and 94.8±0.6 Ma) indicate that the crustal gabbro sequence cooled below 500° C later than the base of the ophiolite sequence. Metamorphism of the sole rocks occurred during subduction of oceanic sediments and volcanic or gabbroic rocks as they progressively came into contact with hotter zones at the base of the overriding plate. The peak of metamorphism must have been contemporaneous with the main magmatism in the Semail Ophiolite. One of the dated muscovites yields an age of 81.3±0.8 Ma, but this is related to discrete deformation zones that were active during late-stage emplacement of the ophiolite.

An investigation of accessory minerals in plutonic rocks from central Madagascar reveals local very low-grade alteration of the primary REE and Th-bearing phases monazite ((LREE,Th)PO4), allanite (CaREEFe2+Al2(SiO7)(SiO4)O(OH)) and thorite (ThSiO4). All examples are found in relatively fresh looking samples, in which alteration occurs on the micron to submicron scale. The alteration occurs associated with micro-fissures and predominantly affects the accessory minerals. One type of alteration is replacement of thorite and monazite by thorogummite, (Th,U)[(SiO4)(OH)4], and rhabdophane, REEPO4·H2O. Some of these secondary phases grow topotactically on the original magmatic crystals. During development of rhabdophane, Pb and Th can be transferred from the monazite precursor to rhabdophane resulting in similar apparent ages for both phases. A second type of alteration, has been investigated in two granites where bastnasite (REECO3F) forms at the expense of allanite, which requires a fluid containing H2O, CO2 and F. In either type of alteration, mass transport of Pb is deduced from galena development in the vicinity of the altered mineral. In other examples, mass transport of REE is assumed based on REE-fractionation in secondary phases. Th-rich minerals (Th-rich monazite, thorite) are more affected by alteration than Th-poor phases. This may be due to chemical disequilibrium at low-temperatures or partial metamictization before alteration. Overlooking such alterations can lead to pitfalls during dating.

[1] Mantle xenolith-bearing alkali basalts, basanites and tephrites with 1.5–2 K2O and 4–5 wt% Na2O occur as small (

Ferrohogbomite-2 N 2 S is a polysomatic hogbomite-group mineral composed of two nolanite modules ( N ) and two spinel modules ( S ) where the spinel modules have ideally hercynite composition. Ferrohogbomite has been described in the literature for a long time but was not distinguished from magnesiohogbomite and simply named hogbomite. The revised nomenclature of hogbomite minerals required definition of ferrohogbomite polysomes as new mineral species. The sample from Ain Taiba, northwestern edge of Grand Erg Oriental in the Algerian Sahara, has the simplified composition IV (Fe 2+ 3 ZnMgAl) Σ = 6 VI (Al 14 Fe 3+ Ti 4+ ) Σ = 16 O 30 (OH) 2 . The crystal structure was refined from single-crystal X-ray data. The mineral crystallizes in the acentric space group P 6 3 mc with a = 5.712(1), c = 18.317(7) A, and shows twinning by merohedry with the inversion centre as twinning operation. This ferrohogbomite-2 N 2 S is associated with ilmenite, hematite, minor magnetite, and pseudorutile. Some of the ferrohogbomite-2 N 2 S grains are rimmed by hercynite, Fe 0.57 Zn 0.26 Mg 0.18 Al 2 O 4 , which separates them from hematite. The original assemblage probably consisted of ilmenite and Al-bearing magnetite or another Ti-bearing spinel phase. During oxidation ilmenite was replaced by ferrohogbomite on its rims and magnetite was oxidized to hematite. Finally, residual ilmenite was partly transformed along cracks and grain boundaries to pseudorutile. A HRTEM study showed homogeneous ferrohogbomite-2 N 2 S with minor planar faults increasing towards the grain boundaries. The observed orientation relation between ferrohogbomite-2 N 2 S and hematite suggests that ferrohogbomite-2 N 2 S formed topotactically from a primary spinel or magnetite phase that had been subsequently oxidized to hematite.

Strongly zoned Mn-rich vesuvianites with MnO concentrations up to 14.3 wt% from the N’chwaning II mine of the Kalahari manganese field (South Africa) crystallized at hydrothermal conditions below 450 °C. These vesuvianites are by far the most Mn-rich samples hitherto described and have either space group P 4 nc or P 4/ n due to partial long-range ordering. Most crystals are assembled of P 4 nc and P 4/ n domains yielding P 4 average symmetry. The crystal structure of one Mn-rich crystal of average composition Ca19Mn3.5Al9.5Si17.4(O,OH)78 was refined from single-crystal X-ray data (R1 = 3.85%) in space group P 4/ n ( a = 15.571(2), c = 11.789(2) A). Mn2+ and Mn3+ are concentrated on the fivefold-coordinated square pyramidal Y′ site. Additional Mn3+ was located on the octahedral sites Y2a (35%), Y1a (22%), Y2b (13%) and Y1b (8%). Electron microprobe analyses and crystal-structure refinements indicated tetrahedral vacancies in the orthosilicate tetrahedra (Z1 and Z2) but not in the disilicate units (Z3). Z1 tetrahedra with up to 17% vacancies have strongly increased Z1-O distances of 1.67 A. Structural and chemical evidence combined with the similarity of the structures of vesuvianite and garnet suggest a partial hydrogarnet-like substitution of SiO4 tetrahedra by H4O4.