Nanophase Fe0 in lunar soils

Back scattered electron and transmission electron imaging of lunar soil grains reveal an abundance of submicrometer-sized pure Fe⁰ globules that occur in the rinds of many soil grains and in the submillimeter sized vesicular glass-cemented grains called agglutinates. Grain rinds are amorphous silicates that were deposited on grains exposed at the lunar surface from transient vapors produced by hypervelocity micrometeorite impacts. Fe⁰ may have dissociated from Fe-compounds in a high temperature (>3000°C) vapor phase and then condensed as globules on grain surfaces. The agglutinitic glass is a quenched product of silicate melts, also produced by micrometeorite impacts on lunar soils. Reduction by solar wind hydrogen in agglutinitic melts may have produced immiscible droplets that solidified as globules. The exact mechanism of formation of such Fe⁰ globules in lunar soils remains unresolved.     

Solar Control of Martian Polar Caps?

Regression of polar caps of Mars for the period 1905–1988 shows a highly significant anticorrelation with sunspot numbers. This behaviour is abnormal since the regression exhibited a significant correlation for the period 1862–1912. Combined with such unusual behaviour of Jupiter and Neptune, reported earlier, this may imply a common cause outside the solar system, viz., variation of the density of the local interstellar medium.     

A seismic event on August 20, 1983: double explosion or a single earthquake

An interesting weak seismic event occurred on August 20, 1983 in the Caspian Sea region in southwestern U.S.S.R., which produced at Gauribidanur array two distinct seismic signals, viz. the leading P signal and a similar signal after an interval of nearly 12 s. Preliminary data corresponding to these two signals led to an initial assumption that the event was a double underground nuclear explosion. However, the focal depth of this event from P arrival-time data of 21 stations was found to be 45 km. Further processing of the Gauribidanur array seismograms confirmed that the second signal, detected exactly 11.85 s after the first arrival, was none other than the surface-reflected P pulse which lent excellent support to the source depth estimate. By using three discriminants, viz. signal complexity, third moment of frequency and relative efficiency of generation of core-reflected P, the event was objectively compared with 10 small presumed underground nuclear explosions in southwestern U.S.S.R. to conclude that the August 20, 1983 event was a shallow-focus small earthquake in the Caspian Sea area.     

Rare gases,water, and carbon in kaersutites

Kaersutites from Kakanui, New Zealand and from three localities in the southwestern United States have been analyzed for rare gases, water and carbon to investigate the volatile signature of the sub-continental mantle. This study does not confirm the high ³He/⁴He and ²¹Ne/²²Ne ratios reported by Saito et al. [1] for the Kakanui kaersutite. Instead, a ³He/⁴He ratio of 6 R_A and atmospheric ²¹Ne/²²Ne ratios were measured which are consistent with our current knowledge of the earth's mantle. A low ⁴⁰Ar/³⁶Ar of 320 and more than 10^?8 cm³/g of ³⁶Ar confirms the argon results of Saito et al. and indicates that significant quantities of ³⁶Ar reside in this portion of the mantle. Kaersutites from the southwestern United States (Arizona) have a heterogeneous helium isotope signature, ranging from 8.8 R_A at San Carlos to 0.46 at Hoover Dam. All D/H ratios for the water in kaersutites (?56‰ to ?78‰) represent typical mantle values with no apparent correlation with ³He/⁴He. The correlation of increasing carbon content (140–400 ppm) with increasing δ¹³C (?24.5‰ to ?16.7‰) may reflect differences in the proportions of oxidized and reduced carbon in these samples.     

Sm-Nd,K-Ar and petrologic study of some kimberlites from eastern United States and their implication for mantle evolution

We provide new data on Sm-Nd systematics, K-Ar dating and the major element chemistry of kimberlites from the eastern United States (mostly from central New York State) and their constituent mineral phases of olivine, clinopyroxene, garnet, phlogopite and perovskite. In addition, we report Nd-isotopes in a few kimberlites from South Africa, Lesotho and from the eastern part of China. The major element compositions of the New York dike rocks and of their constituent minerals including a xenolith of eclogite are comparable with those from the Kimberley area in South Africa. The K-Ar age of emplacement of the New York dikes is further established to be 143 Ma.We have analyzed the Nd-isotopic composition of the following kimberlites and related rocks: Nine kimberlite pipes from South Africa and Lesotho, two from southern India; one from the U.S.S.R., fifteen kimberlite pipes and related dike rocks from eastern and central U.S. and two pipes from the Shandong Province of eastern China. The age of emplacement of these kimberlites ranges from 1300 million years to 90 million years. The initial Nd-isotopic compositions of these kimberlitic rocks expressed as _Nd ^I with respect to a chondritic bulk-earth growth-curve show a range between 0 and +4, with the majority of the kimberlites being in the range 0 to +2. This range is not matched by any other suite of mantle-derived igneous rocks. This result strengthens our earlier conclusion that kimberlitic liquids are derived from a relatively primeval and unique mantle reservoir with a nearly chondritic Sm/Nd ratio.     

Sm-Nd Isotopic and Geochemical Study of the Archean Tonalite-Amphibolite association from the eastern Indian Craton

We report the results of a Sm-Nd isotopic, major element and rare earth element (REE) study of the Older Metamorphic Group (OMG) tonalite-amphibolite association of the eastern Indian Craton. The Older Metamorphic Tonalite Gneisses (OMTG) have been previously dated to be 3.8 Ga using Sm-Nd isotope systematies, and 3.2–3.4 Ga by Rb-Sr and Pb-Pb dating. The results of this study indicate that the protoliths of the OMG amphibolites are 3.3 Ga isochron age=3.30±0.06 Ga, _Nd= +0.9 ± 0.7), and therefore, the OMTG, which intrude into the associated amphibolites, cannot be any older than 3.3 Ga. The amphibolites display light REE enrichment ((Ce/Yb)_N=2.2–6.7; La=30–100 x chondrite) and nearly flat heavy REE patterns ((Tb/Lu)_N=1.2–1.9); the basaltic parents of the amphibolites were probably generated by the partial melting of a spinel lherzolite mantle. Strong linear relationships between the amphibolites and tonalites in ¹⁴⁷Sm/¹⁴⁴Nd-¹⁴³Nd/¹⁴⁴Nd space (isochron age =3.29±0.04 Ga, _Nd= +0.8 ± 0.8) imply that they are genetically related. The tonalites display fractionated REE patterns (La=100–300 x chondrite) with moderate heavy REE depletions ((Tb/Lu)_N=1.9–3.4). The isotopic, major element and REE data are consistent with the derivation of the OMTG from partial melting of OMG amphibolites or equivalent rocks at amphibolegarnet stabilization depths. An initial _Nd(t) value of +0.9±0.7 for the amphibolites indicates the presence of a slightly depleted mantle source at 3.3 Ga with ¹⁴⁷Sm/¹⁴⁴Nd. between 0.20 and 0.22. It is suggested that the growth of continental crust in the eastern Indian craton occurred in response to magmatic underplating in a plume setting.     

Non-stationary seismic response of MDOF systems by wavelet transform

A wavelet-based formulation has been presented in this paper for the stochastic analysis of a linear multi-degree-of-freedom (MDOF) classically damped system subjected to earthquake ground motion. The ground motion has been modelled as a non-stationary process (both in amplitude and frequency) using wavelets. Closed-form expressions of the moments of the instantaneous Power Spectral Density Function (PSDF) of the response have been derived and used to predict the statistics of the response peak of any desired order. For illustration of the formulation, an example torsionally coupled multistoried building has been considered along with the twenty synthetically generated time-histories corresponding to an example ground motion process. © 1997 John Wiley & Sons, Ltd.     

On precursors to the Italy earthquake M.6.2 using VLF signal of NSY(45.9 kHz) received at Kiel Longwave Monitor

On August 24, 2016, an earthquake of magnitude 6.2 struck Central Italy (42.706°N and 13.223°E) at 1:36 UT. We present the results obtained from the US Navy VLF Transmitter’s NSY signal of 45.9 kHz transmitted from Niscemi, in the province of Sicily, Italy and received at the Kiel Longwave Monitor, Germany for 2016. We analysed the terminator times and their individual differences. We also analysed trends, dispersion and night time fluctuation which gave us a possible precursor the Italy earthquake. We found ionospheric perturbations in these parameters on 14th, 19th and 22nd of August, few days prior. Moreover, we filtered the possible effects due to lightning, storms and auroras if any.