Re-Os isotope systematics and fractionation of siderophile elements in metal phases from CBa chondrites

We report Os isotope compositions of metal grains in two CB_a chondrites (Bencubbin and Gujba) determined using a micromilling sampling coupled with thermal ionization mass spectrometry, together with the abundances of major and trace siderophile elements obtained by electron probe microanalysis and femtosecond laser ablation inductively coupled plasma–mass spectrometry. The CB_a metal grains presented ¹⁸⁷Os/¹⁸⁸Os ratios akin to carbonaceous chondrites with limited variations (0.1257–0.1270). Most of the CB_a metal grains were scattered along a ¹⁸⁷Re-¹⁸⁷Os reference isochron of IIIAB iron meteorites, indicating that the CB_a metals experienced limited Re-Os fractionation at the time of their formation. The Re/Os ratios of sampling spots for the CB_a metals, recast from the observed ¹⁸⁷Os/¹⁸⁸Os ratios, had a positive correlation with their Os/Ir ratios. In addition, the metal grains showed a positive correlation in a Pd/Fe versus Ni/Fe diagram. These correlations suggest that the CB_a metal grains have formed via equilibrium condensation or evaporation from a gaseous reservoir at ~10⁻⁴ bar with enhanced metal abundances. Compared to the Bencubbin metals, the Gujba metals are characterized by having systematically lower Pd/Fe and Ni/Fe ratios that span subchondritic values. Such a difference was most likely induced by the compositionally heterogeneous impact plume from which the metals were condensed.     

Outflow channel sources, reactivation, and chaos formation, Xanthe Terra, Mars

The undulating, warped, and densely fractured surfaces of highland regions east of Valles Marineris (located north of the eastern Aureum Chaos, east of the Hydraotes Chaos, and south of the Hydaspis Chaos) resulted from extensional surface warping related to ground subsidence, caused when pressurized water confined in subterranean caverns was released to the surface. Water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of Ares, Tiu, and Simud Valles of the eastern part of the circum-Chryse outflow channel system. Progressive surface subsidence and associated reduction of the subsurface cavernous volume, and/or episodes of magmatic-driven activity, led to increases of the hydrostatic pressure, resulting in reactivation of both catastrophic and non-catastrophic outflow activity. Ancient cratered highland and basin materials that underwent large-scale subsidence grade into densely fractured terrains. Collapse of rock materials in these regions resulted in the formation of chaotic terrains, which occur in and near the headwaters of the eastern circum-Chryse outflow channels. The deepest chaotic terrain in the Hydaspis Chaos region resulted from the collapse of pre-existing outflow channel floors. The release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow. Basal warming related to dike intrusions, thermokarst activity involving wet sediments and/or dissected ice-enriched country rock, permafrost exposed to the atmosphere by extensional tectonism and channel incision, and/or the injection of water into porous floor material, may have enhanced outflow channel floor instability and subsequent collapse. In addition to the possible genetic linkage to outflow channel development dating back to at least the Late Noachian, clear disruption of impact craters with pristine ejecta blankets and rims, as well as preservation of fine tectonic fabrics, suggest that plateau subsidence and chaos formation may have continued well into the Amazonian Period. The geologic and paleohydrologic histories presented here have important implications, as new mechanisms for outflow channel formation and other fluvial activity are described, and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding. Detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation, and thus chaotic terrains mark prime locations for future geologic, hydrologic, and possible astrobiologic exploration.     

Numerical Simulation of Residual Circulation due to Bottom Rouglmess Variability Under Tidal Flows in A Semi-Enclosed Bay

Nowadays there are some chronic serious environmental problems, such as eutrophication, blue tide and so on, in a complicated coastal zone or a semi-enclosed bay, because the water exchanges between an inner bay and an outer sea is weak compared with the supply of contaminant. Under this situation, a method to improve the water quality by 3-dimensional small unsymmetrical structures has been proposed by Komatsu et al. In this paper, several numerical simulations of the tidal current and concentration for various arrangements of bottom roughness in a semi-enclosed model bay are carfled out with a depth-averaged 2-D numerical model. The model is solved by the hybrid finite analytic method with nonstaggered grid. And the SIMPLES algorithm with Rhie and Chow＇ s momentum interpolation technique is used for the simulation. The effect of Komatsu＇ s method for water purification is examined by numerical simulation. The result of numerical experiment indicates that it is possible to generate a new tidal residual current and to activate a tidal exchange by bottom roughness arrangement only.     

Some features of jump in water temperature in aSargassum forest

To clarify the influence of aSargassum forest on water temperature distributions observations were made inside and outside aSargassum forest off the Nagata Shore on the northern Saiki Bay open to the Bungo Channel on the Pacific side of Kyushu, Japan. About sixty thermistor probes were deployed at 0.5 m depth intervals from the bottom to the sea surface at seven stations spaced at 50–80 m distances along two transects: one inside the forest and the other outside. Water temperature was measured at five minutes intervals from 6 to 9 August 1987 with thermistor probes. The spatial standing crop distribution of theSargassum forest along the transects was investigated. A water temperature jump of about 2°C, recorded during the observation, is probably caused by an intrusion of a warm water mass from the central Bungo Channel to Saiki Bay. The water temperature jump under theSargassum forest on the rough bottom with stones occurred one to two hours behind that outside the forest (sandy bed) although the distance between the transects inside and outside the forest was only 50–80 m. It is suggested that theSargassum forest and the rough bottom would prevent intruding warm water from smoothly replacing cold water due to resistance of theSargassum species and the bottom to a current.     

Upwelling of Deep-seated Fluid in the Sikhote-Alin Region,Far East of the Eurasian Plate

Aquatic Geochemistry - Spring waters with high-pCO2 content are widely distributed in the Sikhote-Alin region in Russia. Mukhen spa is one such spring located in the northern Sikhote-Alin region....     

A simple model to estimate monthly forest evapotranspiration in Japan from monthly temperature

The estimation of evapotranspiration (E) in forested areas is required for various practical purposes (e.g. evaluation of drought risks) in Japan. This study developed a model that estimates monthly forest E in Japan with the input of monthly temperature (T). The model is based on the assumptions that E equals the equilibrium evaporation rate (E_eq) and that E_eq is approximated by a function of T. The model formulates E as E (mm month⁻¹) = 3·48 T ( °C) + 32·3. The accuracy of the model was examined using monthly E data derived using short‐term water balance (WB) and micrometeorological (M) methods for 15 forest sites in Japan. The model estimated monthly E more accurately than did the Thornthwaite and Hamon equations according to regression analysis of the estimated E and E derived using the WB and M methods. Although the model tended to overestimate monthly E, the overestimation could be reduced by considering the effect of precipitation on E. As T data are commonly available all over Japan, the model would be a useful tool to estimate forest E in Japan. Copyright © 2010 John Wiley & Sons, Ltd.     

Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan

Abstract : The Hidaka metamorphic belt consists of an island-arc assembly of lower to upper crustal rocks formed during early to middle Paleogene time and exhumed during middle Paleogene to Miocene time. The tectonic evolution of the belt is divided into four stages, D₀rs, D₁, D₂rs, and D₃, based on their characteristic deformation, metamorphism, and igneous activity. The premetamorphic and igneous stage (D₀) involves tectonic thickening of an uppermost Cretaceous and earliest Tertiary accretionary complex, including oceanic materials in the lower part of the complex. D₁ is the stage of prograde metamorphism with increasing temperatures at a constant pressure during an early phase, and with a slight decrease of pressure at the peak metamorphic phase, accompanying flattening of metamorphic rocks and intrusions of mafic to intermediate igneous rocks. At the peak, incipient partial melting of pelitic and psammitic gneisses took place in the amphibolite–granulite facies transition zone, the melt and residuals cutting the foliations formed by flattening. In the deep crust, large amounts of S-type tonalite magma formed by crustal anatexis, intruded into the granulite facies gneiss zone and also into the upper levels of the metamorphic sequence during the subsequent stage. During D₁ stage, mafic and intermediate magmas supplied and transported heat to form the arc-type crust and at the same time, the magmatic underplating caused extensional doming of the crust, giving rise to flattening and vertical uplifting of the crustal rocks. D₂ stage is characterized by subhorizontal top-to-the-south displacement and thrusting of lower to upper crustal rocks, forming a basal detachment surface (décollement) and duplex structures associated with intrusions of S-type tonalite. Deformation structures and textures of high-temperature mylonites formed along the décollement, as well as the duplex structures, show that the D₂ stage movement occurred under a N-S trending compressional tectonic regime. The depth of intra-crustal décollement in the Hidaka belt was defined by the effect of multiplication of two factors, the fraction of partial melt which increases downward, and the fluid flux which decreases downward. The crustal décollement, however, might have extended to the crust-mantle boundary and/or to the lithosphere and asthenosphere boundary. The subhorizontal movement was transitional to a dextral-reverse-slip (dextral transpression) movement accompanied by low-temperature mylonitization with retrograde metamorphism, the stage defined as D₃. The crustal rocks from the basal décollement to the upper were tilted eastward on the N–S axis and exhumed during the D₃ stage. During D₂ and D₃ stages, the intrusion of crustal acidic magmas enhanced the crustal deformation and exhumation in the compressional and subsequent transpressional tectonic regime.     

The Meteoritical Bulletin,No. 111

Meteoritical Bulletin 111 contains the 3094 meteorites approved by the Nomenclature Committee of the Meteoritical Society in 2022. It includes 11 falls (Antonin, Botohilitano, Cranfield, Golden, Great Salt Lake, Longde, Msied, Ponggo, Qiquanhu, Tiglit, Traspena), with 2533 ordinary chondrites, 165 HED, 123 carbonaceous chondrites (including 4 ungrouped), 82 lunar meteorites, 28 Rumuruti chondrites, 27 iron meteorites, 23 ureilites, 22 mesosiderites, 22 Martian meteorites, 21 primitive achondrites (one ungrouped), 17 ungrouped achondrites, 13 pallasites, 7 enstatite achondrites, 6 enstatite chondrites, and 5 angrites. Of the meteorites classified in 2022, 1787 were from Antarctica, 1078 from Africa, 180 from South America, 34 from Asia, 6 from North America, 4 from Europe, and 1 from Oceania.     

Solid‐state 13C NMR characterization of insoluble organic matter from Antarctic CM2 chondrites: Evaluation of the meteoritic alteration level

Abstract— Chemical structures of the insoluble organic matter (IOM) from the Antarctic CM2 chondrites (Yamato [Y‐] 791198, 793321; Belgica [B‐] 7904; Asuka [A‐] 881280, 881334) and the Murchison meteorite were analyzed by solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy. Different types of carbons were characterized, such as aliphatic carbon (Ali‐C), aliphatic carbon linked to hetero atom (Hetero‐Ali‐C), aromatic carbon (Aro‐C), carboxyls (COOR), and carbonyls (C=O). The spectra of the IOM from Murchison and Y‐791198 showed two major peaks: Ali‐C and Aro‐C, while the spectra from the other meteorites showed only one major peak of Aro‐C. Carbon distribution was determined both by manual integration and deconvolution. For most IOM, the Aro‐C was the most abundant (49.8–67.8%) of all carbon types. When the ratios of Ali‐C to Aro‐C (Ali/Aro) were plotted with the atomic hydrogen to carbon ratio (H/C), a correlation was observed. If we use the H/C as a parameter for the thermal alteration event on the meteorite parent body, this result shows a different extent of thermal alteration. In addition, IOM with a lower Ali/Aro showed a lower ratio of Ali‐C to COOR plus C=O (Ali / (COOR + C=O)). This result suggests that the ratio of CO moieties to aliphatic carbon in IOM might reflect chemical oxidation that was involved in hydrothermal alteration.     

Four climate regimes on a land planet with wet surface: Effects of obliquity change and implications for ancient Mars

Series of numerical experiments are performed using a general circulation model to gain insights on the hydrologic cycle on ancient Mars. Since the state of the ancient Mars atmosphere is not well constrained, we did not try to simulate an ancient Mars climate under warm and wet condition. In stead, we used an idealized model and tried to extract general features of the hydrologic cycle by modeling an ideal land planet that has no ocean on its surface. Four different climate regimes, “warm-upright,” “warm-oblique,” “frozen-upright,” and “frozen-oblique” regimes, are recognized depending on the inclination of the spin axis (obliquity) and average surface temperature. The period of active hydrologic cycle suggested from the geomorphology on Mars seems to be consistent with that at the “warm-oblique” regime, which appears at warm (above-freezing) environment with high-obliquity (higher than about 30°) condition.