Abundance and isotopic composition of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite

Abstract— Abundances and isotopic compositions of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite were measured. The abundance ratios of spallogenic components in metal reveal a ³He deficiency which is due to the diffusive loss of parent isotopes, that is, tritium (Tilles, 1963; Schultz, 1967). The diffusive loss likely has been induced by thermal heating by the Sun during cosmic‐ray exposure (～160 Ma; Lavielle et al, 1999). Thermal process such as impact‐induced partial loss may have affected the isotopic composition of spallogenic Ne. The ¹²⁹Xe/¹³¹Xe ratio of cosmogenic components in the metal indicates an enhanced production of epi‐thermal neutrons. The abundance ratios of spallogenic components in the graphite reveal that it contained small amounts of metal and silicates. The isotopic composition of heavy noble gases in graphite itself was obtained from graphite treated with HF/HCl. The isotopic composition of the etched graphite shows that it contains two types of primordial Xe (i.e., Q‐Xe and El Taco Xe). The isotopic heterogeneity preserved in the Bohumilitz graphite indicates that the Bohumilitz graphite did not experience any high‐temperature event and, consequently, must have been emplaced into the metal at subsolidus temperatures. This situation is incompatible with an igneous model as well as the impact melting models for the IAB‐IIICD iron meteorites as proposed by Choi et al. (1995) and Wasson et al (1980).     

Carbon isotope fractionation between graphite and diamond during shock experiments

Abstract— Carbon isotopic compositions were measured for shock‐produced diamond and shocked graphite formed at peak pressures ranging from 37 to 52 GPa. The δ¹³C values of diamonds produced in a sealed container were generally lower than that of the initial graphite. The differences in the carbon isotopic composition between initial graphite and shocked graphite/diamond may reflect kinetic isotopic fractionation during the oxidation of the graphite/diamond and/or analytical artifacts possibly induced by impurities in the samples. The pressure effect on the isotopic fractionations between graphite and diamond can be estimated from the δ¹³C values of impurity‐free diamonds produced using a vented container from which gases, including oxygen, in pore spaces escaped during or after the diamond formation (e.g., 0.039 ± 0.085‰ at a peak pressure of 52 GPa). Any isotopic fractionation induced by shock conversion of graphite to diamond is too small to be detected in natural shock‐induced diamond‐graphite systems related to terrestrial impact cratering processes.     

Early deformation fabrics of melange in the Mesozoic Waipapa Terrane, North Island, New Zealand

Abstract The Waipapa Terrane in northern North Island, New Zealand, is a Mesozoic accretion-ary complex formed along the Gondwana margin. It contains abundant melange rocks with distinctive characteristics. Precise analyses of their mesoscopic fabrics in Waiheke Island near Auckland have revealed the following sequence of deformation. The earliest phase of deformation of the sandstone/mudstone association, which is the main constituent of this terrane, originated by chaotic mixing of sand and mud due to liquidization of water-saturated, poorly consolidated sediments. The second phase was characterized by hydrofracturing and subsequent forceful injection of ductile mud into rather brittle sand. Local intrusions of sand forming dykes and sills followed these events, as well as intrusions of pelagic/hemipelagic green argillite originally underlying the sandstone/mudstone association. An abundant occurrence of these mixing and multi-stage injection/intrusion fabrics strongly suggest that the Waipapa Terrane around the study area was a site of high pore-fluid pressure. Scaly-foliated melange fabrics with monoclinic symmetry, originating from layer-parallel shearing, were then locally superimposed on the pre-existing melange fabrics. Similar scaly-foliated fabrics also developed in the chert beds originally intercalated between the green argillite and the uppermost part of the oceanic crust. These scaly fabrics might have been related to the regional stacking and juxtaposition of the accreted sediments. The sequence and variation in style of deformation forming the melange fabrics presumably reflected changes in porosity and state of compaction of accreted sediments in a shallow tectonic level.     

Revision of magnitudes of large shallow earthquakes, 1897–1912

In previous research, trace amplitudes of surface wave maxima recorded by undamped Milne seismographs were used to determine the surface-wave magnitudes M_s of large shallow earthquakes which occurred prior to 1912. For this purpose, the effective gain of these instruments was calibrated by using the surface-wave magnitudes M_s(GR) which were calculated from the unpublished worksheets for Seismicity of the Earth of Gutenberg and Richter. In this paper, the real quality of M_s(GR) is critically re-evaluated by using independent sets of data. It is found that M_s(GR) for the period 1904–1909 is considerably overestimated. The average excess from the real M_s is 0.5 units for 1904–1906, 0.4 for 1907, 0.3 for 1908–1909 and 0.0 for 1910–1912. This overestimation is so systematic and large that the previous results are all redetermined. The average effective gain of Milne instruments is revised to be 21.9; previously, the gain depended on M_s. This revision results in systematic reduction in the previously assigned magnitudes. The revised values of M_s for 264 shallow earthquakes, with M_s=6.8 and over in the period 1897–1912 inclusive, are listed. The present revision is large enough to preclude the possibility of the high activity of large shallow earthquakes around the turn of the century. The present results have a direct effect on all the magnitude catalogues of shallow earthquakes which occurred prior to 1909.     

Numerical forecasting of the time interval between successive M8 earthquakes along the Nankai Trough,southwest Japan,using ocean bottom cable network data

One possible approach to estimating the time interval between large-scale Tōnankai (Tōkai) and Nankai earthquakes on the Japan arc is sequential assimilation of crustal deformation data. We conducted numerical modeling of sequential assimilation using surface deformation calculated from earthquake generation cycle simulations along the Nankai Trough. To account for observation noise, we used measured ocean bottom pressure gauge data, excluding tidal modulation, from a station on the ocean bottom cable network Dense Oceanfloor Network System for Earthquakes and Tsunamis in the Kumano basin. We used sequential importance sampling as our data assimilation method. We found that as the amount of data increased, the estimated time interval between the Tōnankai and Nankai earthquakes approached the “true” observed interval. In addition, the noise in the pressure gauge data was sufficiently small that simulated crustal deformation patterns could be distinguished for different time intervals.     

Bandwidth Effects in the 3G Photometric System

Bandwidth effects in the GAIA photometric system 3G are discussed. It is demonstrated that careful account for the bandwidth effects in any proposed GAIA photometric system has to be made, in order to determine the fundamental parameters of heavily reddened stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diffuse Interstellar Band at 862 nm as a Reddening Tracer for GAIA

We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations, covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σ_E(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σ _E(B-V) ≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales within the framework of the GAIA mission. This revised version was published online in July 2006 with corrections to the Cover Date.     

Primordial noble gases in a graphite‐metal inclusion from the Canyon Diablo IAB iron meteorite and their implications

Abstract— We have carried out noble gas measurements on graphite from a large graphite‐metal inclusion in Canyon Diablo. The Ne data of the low‐temperature fractions lie on the mixing line between air and the spallogenic component, but those of high temperatures seem to lie on the mixing line between Ne‐HL and the spallogenic component. The Ar isotope data indicate the presence of Q in addition to air, spallogenic component and Ar‐HL. As the elemental concentration of Ne in Q is low, we could not detect the Ne‐Q from the Ne data. On the other hand, we could not observe Xe‐HL in our Xe data. As the Xe concentration and the Xe/Ne ratio in Q is much higher than that in the HL component, it is likely that only the contribution of Q is observed in the Xe data. Xenon isotopic data can be explained as a mixture of Q, air, and “El Taco Xe.” The Canyon Diablo graphite contains both HL and Q, very much like carbonaceous chondrites, retaining the signatures of various primordial noble gas components. This indicates that the graphite was formed in a primitive nebular environment and was not heated to high, igneous temperatures. Furthermore, a large excess of ¹²⁹Xe was observed, which indicates that the graphite was formed at a very early stage of the solar system when ¹²⁹I was still present. The HL/Q ratios in the graphite in Canyon Diablo are lower than those in carbonaceous chondrites, indicating that some thermal metamorphism occurred on the former. We estimated the temperature of the thermal metamorphism to about 500–600 °C from the difference of thermal retentivities of HL and Q. It is also noted that “El Taco Xe” is commonly observed in many IAB iron meteorites, but its presence in carbonaceous chondrites has not yet been established.     

A 35 kyr record of organic matter composition and δ13C of n-alkanes in bog sediments close to Lake Baikal: Implications for paleoenvironmental studies

We characterized the compositions of organic compounds in a Cheremushka bog sediment core (deposited over the last 35 kyr), located at the eastern coast of Lake Baikal, to obtain basic information about the terrestrial organic matter (OM) which contributed to Lake Baikal sediments. The bog sediment was analyzed for the molecular composition of n-alkanes, lignin phenols and n-C₂₄ to C₃₀ alkanoic acids, as well as the carbon isotopic composition of plant wax derived n-C₂₇ to C₃₃ alkanes.Concentrations of lignin phenols [vanillyl (V) plus syringyl (S) phenols] normalized to total organic carbon (TOC) in the Holocene are twice those for the last glacial maximum (LGM), while concentrations of TOC-normalized n-C₂₄ to C₃₀ alkanoic acids do not change markedly in this period. Thus, the ratio of lignin phenols to n-C₂₄ to C₃₀ alkanoic acids increases from the LGM to the Holocene. This result is essentially consistent with pollen analysis indicating an expansion of woody plants in the Holocene and a prevailing herb-abundant environment for the LGM. The δ¹³C values of n-C₂₇ to C₃₃ alkanes (e.g. ?29‰ to ?33‰ for C₃₁) indicate the presence of C₃-dominant plants throughout the core.The contribution of terrestrial OM to Lake Baikal sediments was estimated using the biomarkers, on the assumption that the OM in the bog sediments is a representative of the terrestrial OM around the lake. Hence, the estimation using lignin phenol or n-C₂₄ to C₃₀ alkanoic acid parameters indicates that 11–24% of the TOC in the Academician Ridge sediments is land-derived for both the Holocene and the LGM, which is similar to the estimates from C/N values of bulk OM. However, the estimates for terrestrial OM using the n-C₂₇ to C₃₃ alkane parameter are generally higher than those using lignin phenol or n-C₂₄ to C₃₀ alkanoic acid parameters. The difference is thought to be associated with the difference in source and behavior of these biomarkers.