Meteoritic and non-meteoritic trace elements in Luna 16 samples

Two Luna 16 soils have been analyzed for Ag, Au, Bi, Br, Cd, Co, Cs, Cu, Ga, Ge, In, Ur, Ni, Rb, Re, Sb, Se, Te, Tl, and Zn. A meteoritic component similar to that in Apollo 11 and 12 soils seems to be present, corresponding to ∼1.5 to 2% Cl chondrites or equivalent. It probably consists largely of micrometeorites. Three elements show strong enrichments compared to Apollo 11 and 12 soils: Cd (5× to 200×), Ag (5× to 10×), and Bi (3×). Presumably these elements were brought in by Cd-Ag-Bi rich material, similar to that in Unit VI of Apollo core 12028.     

Isotopic fractionation of zinc in tektites

Tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the Earth's surface. The similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock. Tektites are among the driest rocks on Earth. Although volatilization at high temperature may have caused this extreme dryness, the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated. Volatilization can fractionate isotopes, therefore, comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation.For this study, we have measured the Zn isotopic composition of 20 tektites from four different strewn fields. Almost all samples are enriched in heavy isotopes of Zn compared to the upper continental crust. On average, the different groups of tektites are isotopically distinct (listed from the isotopically lightest to the heaviest): Muong-Nong type indochinites (δ^66/64Zn = 0.61 ± 0.30‰); North American bediasites (δ^66/64Zn = 1.61 ± 0.49‰); Ivory Coast tektites (δ^66/64Zn = 1.66 ± 0.18‰); the Australasian tektites (others than the Muong Nong-type indochinites) (δ^66/64Zn = 1.84 ± 0.42‰); and Central European moldavites (δ^66/64Zn = 2.04 ± 0.19‰). These results are contrasted with a narrow range of δ^66/64Zn = 0–0.7‰ for a diverse spectrum of upper continental crust materials.The elemental abundance of Zn is negatively correlated with δ^66/64Zn, which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation. Simple Rayleigh distillation predicts isotopic fractionations much larger than what is actually observed, therefore, such a model cannot account for the observed Zn isotope fractionation in tektites. We have developed a more realistic model of evaporation of Zn from a molten sphere: during its hypervelocity trajectory, the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere. This velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process. Our model, albeit parameter dependent, shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion-limited regime.     

Nitrogen in tektites and natural glasses

Nitrogen concentrations in various tektites and natural glasses have been measured using RNAA and are found to be almost constant at about 15 ppm. A terrestrial origin for tektite formation is favoured.     

Polystyrene spherules in the Bristol Channel

Small polystyrene beads are becoming a common component of the plankton in certain areas. They are derived from the effluents of polystyrene manufacturers.     

Microtektites: a chemical comparison of bottle-green microtektites,normal microtektites and tektites

Trace element abundances in Ivory Coast normal microtektites and Australasian bottle-green microtektites confirm that microtektites are genetically related to tektites in the associated strewn field. Although major and compatible trace element abundances imply that bottle-green microtektites are members of a fractional crystallization sequence, the similar rare earth element distributions in Australasian normal and bottle-green microtektites and tektites cannot be explained by a simple fractionation model. The similar REE abundances in tektites and microtektites of widely different major element composition also preclude simple models calling for sedimentary rock precursors.     

Isotopic compositions of potassium and calcium in magnetic spherules from marine sediments

Isotopic compositions of potassium and calcium in individual magnetic spherules were determined. No significant anomaly was observed for potassium within twice the statistical error (2σ), although for calcium isotopes enrichments of⁴⁶Ca,⁴⁴Ca and⁴²Ca were observed in one spherule. The relative excess of⁴⁶Ca,⁴⁴Ca and⁴²Ca in the spherule agrees with the relative yield of spallogenic calcium isotopes observed in iron meteorites. This fact indicates that the enrichment in the calcium isotopes was caused by cosmic ray irradiation of the spherule in outer space.     

Measurement of53Mn in deep-sea iron and stony spherules

Cosmic-ray-produced⁵³Mn (t_1/2 = 3.7 × 10⁶years) was measured in individual and groups of deep-sea iron and stony spherules by highly sensitive neutron activation analysis. The activities found were less than 20 dpm⁵³Mn/kg Fe (10^?5?10^?6 dpm⁵³Mn/sample) in iron spherules except one iron spherule whose activity was 241 ± 73 dpm⁵³Mn/kg Fe. These low activities may indicate evaporative loss of⁵³Mn due to heating in the earth's atmosphere. On the other hand, all stony spherules contained 200–260 dpm⁵³Mn/kg Fe which is similar to chondritic values. These spherules may be ablation debris from large objects.     

Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii: Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars

Iron-rich spherules (> 90% Fe₂O₃ from electron microprobe analyses) ∼10-100 μm in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe / Al ratio than the rim. Oxide totals less than 100% (93-99%) suggest structural H₂O and/or OH^− 1. The transmission Mössbauer spectrum of a spherule-rich separate is dominated by a hematite (α-Fe₂O₃) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al³⁺ for Fe³⁺ substitution and structural H₂O and/or OH^− 1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.     

Silicate-metallic spherules and the problem of the ignimbrite eruption mechanism: The Yakutinskaya volcanic depression

In the course of detailed mineralogical, geochemical, and petrological studies of volcanic rocks in the Yakutinskaya volcanic depression of the Eastern Sikhote-Alin volcanic belt (Primorye) silicate-metallic formations (small balls) were found to occur widely. This suggests a new approach to the evaluation of the mechanism that is responsible for the formation of specific large-volume ??hot?? explosions. The metallic nuclei (whose compositions vary from low-carbon cast iron to cohenite) are surrounded by symplectite, which consists of quartz, magnetite, and siliceous-potassic glass (without Na); thus, the entire formation can be considered as a siliceous-metallic spherule. Based on analyses of the gas phase, the spherules consist of hydrogen and methane. The calculation of oxidation reactions that involve these gases shows that the process entails a significant decrease of volume and heat release. This suggests that the mechanism of ??hot?? ignimbrite explosions consists of the collapse of the roof of the magma chamber into the explosion zone and the formation of a collapse caldera with the ejection of the melt and its subsequent dispersion on the surface. This is facilitated by significant overheating of magma and its saturation with hydrogen, which is accompanied by a sharp decrease in viscosity by several orders of magnitude, even for such highly siliceous melts.     

Size distribution of airborne magnetic ‘back spherules’ in the 1–5 μ range

Summary Airborne particulate matter was sampled at Mt. Cimone, Italy, to determine the size distribution of black spherules in the 1–5 diameter range. The magnetic fraction of airborne particulate matter was separated by forcing air through a strong magnetic sampling device, where ferromagnetic particles accumulated on microscope slides.Sizes of the black spherules were determined by counting under a microscope. Samples were dissolved and analyzed for iron content. Distribution was found to be in agreement with that of deep-sea sediment and satellite high atmosphere samples. The rate of terrestrial accretion of cosmic matter composed of black spherules appears to be approximately 10^–15 g cm^–2 sec^–1.     

Ferromanganese rock varnish in north Norway: A subglacial origin

A thin, dark brown rock varnish is described from ice-smoothed bedrock on the forefield of a glacier in North Norway. It occurs only in narrow strips (ca 100 mm or less wide) which run roughly parallel to the ice front and along the top edges of small treads of a series of bedrock steps. The varnish is hard, thin (< 10 μm) and consists of an iron/manganese deposit, greatly enriched in these elements compared with the composition of the underlying gabbroic bedrock. It is suggested that the varnish formation is due to localized changes in Eh/pH conditions in subglacial regelation ice and meltwater at the top of the bedrock steps. These changes may be due to CO₂ and/or O₂ degassing from water held at higher pressures under the ice than in cavities downstream where the ice is decoupled from the bedrock. Glacier retreat rates indicate that the varnish has remained exposed subaerially at the surface for about twenty years, and its restricted occurrence suggests that it is not of biological origin but rather is essentially authigenic. Possible subglacial origins for associated iron and silica precipitates are also suggested.     

Terrestrial chondrules,glass spherules and accretionary lapilli from the suevite,Ries Crater,Germany

Until recently, no terrestrial analogues of meteoritic and lunar chondrules were known. Only rare glass spherules from the Lonar Crater, India, and black magnetic spherules from various localities have been recorded. The impact breccia suevite of the No¨rdlinger Ries Crater, Germany, contains both chondrules and glass spherules, and in addition, accretionary lapilli, all of which are found imbedded within the fine-grained matrix of the suevite. The chondrules display many of the textural features characteristic of meteoritic and lunar chondrules. Lithic chondrules and fluid drop chondrules are present, the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite. Fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition. On the whole, fluid drop chondrules, lithic chondrules and glass spherules are rare in the suevite, with fluid drop chondrules prevailing. Detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules. Accretionary lapilli also represent material formed as a result of impact.     

Age and provenance of the target materials for tektites and possible impactites as inferred from Sm-Nd and Rb-Sr systematics

Sm-Nd and Rb-Sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects. Tektites have large negative ε^Nd(0) values and are uniform within each tektite group while the ε^Sr(0) are large positive values and show considerable variation within each group. Chemical, trace element, and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust. Each tektite group is characterized by a uniform Nd model age,T_CHUR^Nd, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites: (1) ～1.15 AE for Australasian tektites; (2) ～1.91 AE for Ivory Coast tektites; (3) ～0.9 AE for moldavites; (4) ～0.65 AE for North American tektites, and (5) ～0.9 AE for high-Si irghizites. Sr model ages,T_UR^Sr, are variable within each group reflecting Rb-Sr fractionation and in the favorable limit of very high Rb/Sr ratios, approach the time of sedimentation of the parent material which melted to form the tektites. Australasian tektites are derived from ～0.25 AE sediments, moldavites from ～0.0 AE sediments, Ivory Coast tektites from ～0.95 AE sediments. Possible parent sediments of other tektite groups have poorly constrained ages. Our data on moldavites and Ivory Coast tektites are consistent with derivation from the Ries and Bosumtwi craters, respectively. Irghizites are isotopically distinct from Australasian tektites and are probably not related. Sanidine spherules from a Cretaceous-Tertiary boundary clay have initial ε^Nd ～ +2; ε^Sr ～ +5 and are not derived from old continental crust or meteoritic feldspar. They may represent a mixture of basaltic oceanic crust and sediments, implying an oceanic impact. These isotopic results are also consistent with a volcanic origin for the spherules.     

The composition of spherules and other features on shatter cone surfaces from the Vredefort structure,South Africa

Minute spherules and other glassy objects have been found on the surfaces of shatter cones in the sedimentary rocks forming the collar around the Vredefort ring structure. The composition of twenty-five of these spherules was determined using an energy-dispersive X-ray analysis system attached to a scanning electron microscope. These results show that spherules can be classified into a Si-, Al-rich variety, an Fe-rich variety and an intermediate variety.At first, the origin of the spherules appeared enigmatic: we considered that they could have been of organic origin; that they may represent dust or fly ash particles due to atmospheric pollution; or that they may result from processes operating during shatter cone formation. For analytical and logical reasons, we argue that the first two possible modes of origin can be discounted. Instead, it is suggested that the spherules result from melts generated by friction on the host rock surfaces during the formation of shatter cones. The variations in composition of the individual spherules may indicate selective melting of different parts of the rock surface or that the melts may have been affected by liquid immiscibility processes. This argument is reinforced by the striking analogy between the particles discussed here and those found in lunar samples.     

Contrasting morphological trends of islands in Central Philippines: Speculation on their origin

Abstract The Palawan microcontinental block collided with the Philippine Mobile Belt in the Central Philippine region resulting in the counterclockwise rotation of Mindoro– Marinduque and clockwise rotation of Panay. The collision also brought about the clockwise rotation of north-east Negros, Cebu, north-west Masbate and Bohol (collectively called the Western Visayan block), resulting into their present-day northeast–southwest trend. This suggests a far more dramatic role of the collision than was previously recognized. Furthermore, the south-east Sulu Sea sub-basin is inferred to have also undergone collision-related clockwise rotation which can account for the observed east-west trending magnetic lineations in the basin. Aside from explaining the contrasting morphological trends of the different islands in Central Philippines, the rotation can also explain, albeit in a different way, how the belts of sedimentary basins, ophiolites and arcs in Panay and Negros can extend to Northern Luzon. Published paleomagnetic data suggest that the collision-related rotation commenced during the early to middle Miocene and had ceased by the late Miocene.     

The origin of josephinites: a new noble gas study

We performed a complete noble gas study on eight different josephinites and one oregonite. The ⁴He/³He ratios range between 100,000 and 330,000 and are probably due to a combination of a MORB He-component from the Josephinite Peridotite massif, where these nickel-iron specimens are found, and either atmospheric He or radiogenic He from the underlying continental or subcontinental basement. The ⁴⁰Ar/³⁶Ar ratios of 302 to 381 are slightly higher than the ratio of air-argon. The neon, krypton and xenon isotopic ratios are identical to the corresponding air ratios. We cannot confirm large³He and²¹Ne excesses published earlier. The observed noble gas isotopic signatures are in agreement with a formation of josephinites near the surface. The data do not favour a deep mantle origin or a formation at the mantle-core boundary as proposed before.     

Volcanic tremors at etna: a model for hydraulic origin

Spectral analysis of volcanic tremors at Etna reveals 2 characteristic features: (1) The escaping vapor and gas streams drive the magma in random turbulent motion, generating a seismic wave emission according toA ～f ^N · exp (?M ·f ^K), whereA amplitude,f frequency, N, M, K parameters. (2) Sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages. Their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena. It is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity. Furthermore, positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra.