Ordinary chondritic micrometeorites from the Indian Ocean

Extraterrestrial particulate materials on the Earth can originate in the form of collisional debris from the asteroid belt, cometary material, or as meteoroid ablation spherules. Signatures that link them to their parent bodies become obliterated if the frictional heating is severe during atmospheric entry. We investigated 481 micrometeorites isolated from ~300 kg of deep sea sediment, out of which 15 spherules appear to have retained signatures of their provenance, based on their textures, bulk chemical compositions, and relict grain compositions. Seven of these 15 spherules contain chromite grains whose compositions help in distinguishing subgroups within the ordinary chondrite sources. There are seven other spherules which comprise either entirely of dusty olivines or contain dusty olivines as relict grains. Two of these spherules appear to be chondrules from an unequilibrated ordinary chondrite. In addition, a porphyritic olivine pyroxene (POP) chondrule‐like spherule is also recovered. The bulk chemical composition of all the spherules, in combination with trace elements, the chromite composition, and presence of dusty olivines suggest an ordinary chondritic source. These micrometeorites have undergone minimal frictional heating during their passage through the atmosphere and have retained these features. These micrometeorites therefore also imply there is a significant contribution from ordinary chondritic sources to the micrometeorite flux on the Earth.     

Origin of ~2.5 Ga potassic granite from the Nellore Schist Belt,SE India: textural,cathodoluminescence, and SHRIMP U–Pb data

In a geochemical and geochronological investigation of Archean and Proterozoic magmatism in the Nellore Schist Belt, we conducted SHRIMP U–Pb analyses of zircons from two cospatial granitic bodies at Guramkonda and Vendodu. The former is a Ba- and Sr-rich hornblende-bearing tonalite, whereas the latter is a Rb-, Zr-, Pb-, Th-, U-, and REE-rich biotite-bearing leucogranite. The Guramkonda tonalite displays a restitic texture with remnants of trapped granitic melt, whereas the Vendodu leucogranite contains residual/partially melted plagioclase grains. Both rock types contain two generations of zircon: tonalite contains a group of euhedral zoned zircons enclosed within plagioclase and a group of subhedral patchy zircons associated with trapped melt (quartz + feldspar matrix), and leucogranite also contains a group of doubly terminated euhedral zircons included within orthoclase as well as a group of zircons with visible cores mantled by later rim growth. Cathodoluminescence images also clearly document two distinctly textured varieties of zircon: the tonalite contains a population characterized by narrowly spaced uninterrupted oscillatory zoning and a second population lacking zoning but exhibiting a random distribution of dark (U-rich) and light (U-poor) regions; the leucogranite contains U-rich zoned zircons and U-poor zircon cores mantled by U-rich rims. The REE chemistry of zircon cores from the Vendodu leucogranite is very similar to the REE of zoned zircons from the Guramkonda tonalite. Zircon ages from both plutons exhibit bimodal distributions in U–Pb concordia diagrams. The tonalite defines an age of 2,521 Ma ± 5 Ma for zoned magmatic zircons and 2,485 Ma ± 5 Ma for unzoned newly precipitated zircons, whereas the leucogranite has an age of 2,518 Ma ± 5 Ma for U-poor zircon cores (relics of the tonalite pluton) and 2,483 Ma ± 3 Ma for U-rich zoned magmatic zircons. The trace element geochemistry of the ~2,520 Ma zircons is distinctly different from the ~2,485 Ma zircons, irrespective of the host rock. Our textural, CL image, and SHRIMP U–Pb analyses document the origin of the leucogranite by partial melting of the tonalite. High alkalis (Na₂O + K₂O), Rb, Nb, HREE, FeO^t/MgO and low Ca, Al, Ba, Sr, and large negative Eu anomalies characterize the leucogranite as a thermal minimum melt, whereas the very low K and Rb of the tonalite attests to its residual nature. We suggest that the leucogranite formed by high-T (900–950°C), moderate-pressure (<10 kbar) dehydration partial melting of the tonalite under reducing conditions. The calculated source compositions of the leucogranite melt and the tonalite residue show strong similarities to melts that are considered to have been produced in a subduction-zone environment. The leucogranite probably formed in a post-collisional realm immediately after accretion of the tonalitic crust.     

Toxicity of Mercury to Mudskipper,Boleophthalmus dentatus (cuv. and VAL.). Part 2: Changes in the Activity of Acid and Alkaline Phosphatases in Gills

Activities of the acid and alkaline phosphatase changes in gills of mudskipper B. dentatus have been analysed during treatment with different concentrations of mercuric chloride for different durations. The study shows a more or less linear inhibition of the activity of acid and alkaline phosphatases with increasing mercuric chloride concentrations as well as duration of treatment.     

Retrieval of cloud classification parameters using two-dimensional fast Fourier transform

A method is presented for the retrieval of classification parameters of clouds observed by satellite-borne imaging systems. It is based on a two-dimensional fast Fourier transform of cloud images and an analysis of their power spectra. The parameters retrieved provide quantitative information on mean brightness, size, shape and directional properties of clouds. The efficacy of the subdivision of the original cloud image into smaller regions and the determination of individual parameters is demonstrated by applying this procedure to some NOAA and INSAT cloud images.     

Martian meteorite Tissint records unique petrogenesis among the depleted shergottites

Tissint, a new unaltered piece of Martian volcanic materials, is the most silica‐poor and Mg‐Fe‐rich igneous rock among the “depleted” olivine‐phyric shergottites. Fe‐Mg zoning of olivine suggests equilibrium growth (<0.1 °C h^?1) in the range of Fo_80–56 and olivine overgrowth (Fo_55–18) through a process of rapid disequilibrium (~1.0–5.0 °C h^?1). The spatially extended (up to 600 μm) flat‐top Fe‐Mg profiles of olivine indicates that the early‐stage cooling rate of Tissint was slower than the other shergottites. The chemically metastable outer rim of olivine (55) consists of oscillatory phosphorus zoning at the impact‐induced melt domains and grew rapidly compared to the early to intermediate‐stage crystallization of the Tissint bulk. High‐Ca pyroxene to low‐Ca pyroxene and high‐Ca pyroxene to plagioclase ratios of Tissint are more comparable to the enriched basaltic and enriched olivine‐phyric shergottites. Dominance of augite over plagioclase induced augite to control the Ca‐buffer in the residual melt suppressing the plagioclase crystallization, which also caused a profound effect on the Al‐content in the late‐crystallized pyroxenes. Mineral chemical stability, phase‐assemblage saturation, and pressure–temperature path of evolution indicates that the parent magma entered the solidus and left the liquidus field at a depth of 40–80 km in the upper mantle. Petrogenesis of Tissint appears to be similar to LAR 06319, an enriched olivine‐phyric shergottite, during the early to intermediate stage of crystallization. A severe shock‐induced deformation resulted in remelting (10–15 vol%), recrystallization (most Fe‐rich phases), and exhumation of Tissint in a time scale of 1–8 yr. Tissint possesses some distinct characteristics, e.g., impact‐induced melting and deformation, forming phosphorus‐rich recrystallization rims of olivine, and shock‐induced melt domains without relative enrichment of LREEs compared to the bulk; and shared characteristics, e.g., modal composition and magmatic evolution with the enriched basaltic shergottites, evidently reflecting unique mantle source in comparison to the clan of the depleted members.     

Major and trace element geochemistry of S‐type cosmic spherules

Micrometeorites that pass through the Earth's atmosphere undergo changes in their chemical compositions, thereby making it difficult to understand if they are sourced from the matrix, chondrules, or calcium–aluminum‐rich inclusions (CAIs). These components have the potential to provide evidence toward the understanding of the early solar nebular evolution. The variations in the major element and trace element compositions of 155 different type (scoriaceous, relict bearing, porphyritic, barred, cryptocrystalline, and glass) of S‐type cosmic spherules are investigated with the intent to decipher the parent sources using electron microprobe and laser ablation inductively coupled plasma‐mass spectrometry. The S‐type cosmic spherules appear to show a systematic depletion in volatile element contents, but have preserved their refractory trace elements. The trends in their chemical compositions suggest that the S‐type spherules comprise of components from similar parent bodies, that is, carbonaceous chondrites. Large fosteritic relict grains observed in this investigation appear to be related to the fragments of chondrules from carbonaceous chondrites. Furthermore, four spherules (two of these spherules enclose spinels and one comprised entirely of a Ca‐Al‐rich plagioclase) show enhanced trace element enrichment patterns that are drastically different from all the other 151 cosmic spherules. The information on the chemical composition and rare earth elements (REEs) on cosmic spherules suggest that the partially to fully melted ones can preserve evidences related to their parent bodies. The Ce, Eu, and Tm anomalies found in the cosmic spherules have similar behavior as that of chondrites. Distinct correlations observed between different REEs and types of cosmic spherules reflect the inherited properties of the precursors.     

Bianchi type-III bulk viscous cosmic string model in a scalar-tensor theory of gravitation

A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the presence of bulk viscous fluid containing one dimensional cosmic strings in the frame work of a scalar-tensor theory of gravity proposed by Saez and Ballester (in Phys. Lett. A 113:467, 1986). We have obtained a determinate solution of the field equations of this theory, using (i) a barotropic equation of state for the pressure and density and (ii) the bulk viscous pressure is proportional to the energy density. Some physical properties of the model are also discussed.     

Bianchi type-III bulk viscous string cosmological model in Brans-Dicke theory of gravitation

A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the framework of a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961) in the presence of bulk viscous fluid containing one dimensional cosmic strings. We have found a determinate solution of the field equations using the plausible physical conditions (i) a barotropic equation state for the pressure and density, (ii) special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B74:182, 1983), (iii) shear scalar is proportional to scalar expansion and (iv) the trace of the energy tensor of the fluid vanishes. We have also assumed that bulk viscous pressure is proportional to energy density. Some physical and kinematical properties of the model are, also, discussed.     

Evaluating Renewable Groundwater Stress with GRACE Data in Greece

Groundwater is a resilient water source and its importance is even greater in periods of drought. Areas such as the Mediterranean where adverse climate change effects are expected are bell‐weather locations for groundwater depletion and are of considerable interest. The present study evaluates renewable groundwater stress (RGS) as the ratio of groundwater use to groundwater availability, quantifying use as the trend in gravity recovery and climate experiment‐derived (GRACE) subsurface anomalies (ΔGW_trend) and renewable groundwater availability as mean annual recharge. Estimates for mean annual recharge for the various regions in Greece have been derived using numerical models. Our results highlight two RGS regimes in Greece (variable stress and unstressed) of the four characteristic stress regimes, that is, overstressed, variable stress, human‐dominated stress, and unstressed, defined as a function of the sign of use and the sign of groundwater availability (positive or negative). Variable stress areas are found in Central Greece (Thessaly region), where intensive agriculture results in negative ΔGW_trend values combined with positive mean annual recharge rates. RGS values range from ?0.05 to 0, indicating a low impact area. Within this region, adverse effects of groundwater overexploitation are already evident based on the negative GRACE anomalies; however, recharge is still positive, mitigating the effects of over‐pumping. The rest of Greek aquifers fall within the unstressed category, with RGS values from 0.02 to 0.05, indicating that the rate of use is less than the natural recharge rate.