Sealevel history recorded in the Pleistocene carbonate sequence in IODP Hole 310‐M0005D,off Tahiti

Material cored during the Integrated Ocean Drilling Program (IODP) Expedition 310 ‘Tahiti Sea Level’ revealed that the fossil reef systems around Tahiti are composed of two major stratigraphic sequences: (i) a last deglacial sequence; and (ii) an older Pleistocene sequence. The older Pleistocene carbonate sequence is composed of reef deposits associated with volcaniclastic sediments and was preserved in Hole 310‐M0005D drilled off Maraa. Within an approximately 70‐m‐thick older Pleistocene sequence (33.22–101.93 m below seafloor; 92.85–161.56 m below present sealevel) in this hole, 11 depositional units are defined by lithological changes, sedimentological features, and paleontological characteristics and are numbered sequentially from the top of the hole downward (Subunits P1–P11). Paleowater depths inferred from nongeniculate coralline algae, combined with those determined by using corals and larger foraminifers, suggest two major sealevel rises during the deposition of the older Pleistocene sequence. Of these, the second sealevel rise is associated with an intervening sealevel drop. It is likely that the second sealevel rise corresponds to that during Termination II (TII, the penultimate deglaciation, from Marine Isotope Stages 6 to 5e). Therefore, the intervening sealevel drop can be correlated with that known as the ‘sealevel reversal’ during TII. Because there are limited data on the Pleistocene reef systems in the tropical South Pacific Ocean, this study provides important information about Pleistocene sealevel history, the evolution of coral reef ecosystems, and the responses of coral reefs to Quaternary climate changes.     

Rapid decrease of mass balance observed in the Xiao (Lesser) Dongkemadi Glacier,in the central Tibetan Plateau

The mass balance of the Xiao (Lesser) Dongkemadi Glacier located in the Tanggula Mountains, of the central Qinghai‐Tibetan Plateau has been monitored since 1989. The results show that the mass balance of the glacier has recently shown a deficit trend, and that the glacial terminus was also retreating. Positive mass balance of the glacier was dominant during the period 1989–1993, and the accumulated mass balance reached 970 mm. However, negative mass balance of the glacier has occurred since 1994, except for the large positive mass balance year 1997. The mass balance was ? 701 mm in 1998, an extremely negative glacier mass balance year. The equilibrium line altitude showed a significant increasing trend. The mass balance of the glacier has changed from a significantly positive mass balance to a strongly negative mass balance since 1994. Meteorological data suggest that the rapid decrease in the mass balance is related to summer season warming. Copyright © 2007 John Wiley & Sons, Ltd.     

Recycling of suspended particulates by the interaction of sea-land breeze circulation and complex coastal terrain

Summary The dispersion of recycled particulates in the complex coastal terrain surrounding Kangnung city, Korea was investigated using a three-dimensional non-hydrostatic numerical model and lagrangian particle model (or random walk model). The results show that particulates at the surface of the city that float to the top of thermal internal boundary layer (TIBL) are then transported along the eastern slope of the mountains with the sea breeze passage and nearly reach the top of the mountains. Those particulates then disperse eastward at this upper level over the coastal sea and finally spread out over the open sea. Total suspended particulate (TSP) concentration near the surface of Kangnung city is very low. At night, synoptic scale westerly winds intensify due to the combined effect of the synoptic scale wind and land breeze descending the eastern slope of the mountains toward the coast and further seaward. This increase in speed causes development of internal gravity waves and a hydraulic jump up to a height of about 1km above the surface over the city. Particulate matter near the top of the mountains also descends the eastern slope of the mountains during the day, reaching the central city area and merges near the surface inside the nocturnal surface inversion layer (NSIL) with a maximum ground level concentration of TSP occurring at 0300 LST. Some particulates are dispersed following the propagation area of internal gravity waves and others in the NSIL are transported eastward to the coastal sea surface, aided by the land breeze. The following morning, particulates dispersed over the coastal sea from the previous night, tend to return to the coastal city of Kangnung with the sea breeze, developing a recycling process and combine with emitted surface particulates during the morning. These processes result in much higher TSP concentration. In the late morning, those particulates float to the top of the TIBL by the intrusion of the sea breeze and the ground level TSP concentration in the city subsequently decreases.     

Au–Ag–Te Mineralization of the Low‐Sulfidation Epithermal Aginskoe Deposit,Central Kamchatka,Russia

Mineralogic studies of major ore minerals and fluid inclusion analysis in gangue quartz were carried out for the for the two largest veins, the Aginskoe and Surprise, in the Late Miocene Aginskoe Au–Ag–Te deposit in central Kamchatka, Russia. The veins consist of quartz–adularia–calcite gangue, which are hosted by Late Miocene andesitic and basaltic rocks of the Alnei Formation. The major ore minerals in these veins are native gold, altaite, petzite, hessite, calaverite, sphalerite, and chalcopyrite. Minor and trace minerals are pyrite, galena, and acanthine. Primary gold occurs as free grains, inclusions in sulfides, and constituent in tellurides. Secondary gold is present in form of native mustard gold that usually occur in Fe‐hydroxides and accumulates on the decomposed primary Au‐bearing tellurides such as calaverite, krennerite, and sylvanite. K–Ar dating on vein adularia yielded age of mineralization 7.1–6.9 Ma. Mineralization of the deposit is divided into barren massive quartz (stage I), Au–Ag–Te mineralization occurring in quartz‐adularia‐clays banded ore (Stage II), intensive brecciation (Stage III), post‐ore coarse amethyst (Stage IV), carbonate (Stage V), and supergene stages (Stage VI). In the supergene stage various secondary minerals, including rare bilibinskite, bogdanovite, bessmertnovite metallic alloys, secondary gold, and various oxides, formed under intensely oxidized conditions. Despite heavy oxidation of the ores in the deposit, Te and S fugacities are estimated as Stage II tellurides precipitated at the log f Te₂ values ?9 and at log fS₂ ?13 based on the chemical compositions of hypogene tellurides and sphalerite. Homogenization temperature of fluid inclusions in quartz broadly ranges from 200 to 300°C. Ore texture, fluid inclusions, gangue, and vein mineral assemblages indicate that the Aginskoe deposit is a low‐sulfidation (quartz–adularia–sericite) vein system.     

Polymetallic and Au-Ag Mineralizations at the Mutnovskoe Deposit in South Kamchatka, Russia

Abstract. The Mutnovskoe deposit located in the Porozhisto‐Asachinskaya metallogenic province of South Kamchatka, Russia, is a polymetallic vein and Au‐Ag quartz vein associated type of hydrothermal deposit. The Mutnovskoe deposit is located inside a paleo‐caldera structure at the center of the Mutnovsko‐Asachinskaya geothermal field of Pliocene ‐ Quaternary age, where active gold deposition is identified in hot spring precipitate. The Mutnovskoe deposit is subdivided into the north flank, the central flank and the south flank based on the vein distributions and mineral parageneses. The mineralized vein system is oriented N‐S hosted in diorite ‐ gabbroic diorite stock, volcanic rocks and sedimentary rocks of Miocene ‐ Pleistocene age. The mineralization stage I (polymetallic vein) mainly in the central and the south flanks is Zn‐Pb‐Cu‐Au‐Ag contained in sphalerite, galena and tetrahedrite‐tennantite group mineral. The stage II (Au‐Ag quartz vein) occurs in the north and the central flanks. The stage III (Mn‐sulfide and Mn‐Ca‐carbonate vein) occurs in the whole deposit area. Stage II is the typical Au‐Ag quartz‐adularia vein of low‐sulfidation type. Stage III is alabandite‐rhodochrosite‐quartz‐calcite vein. The K‐Ar ages are 1.3±0.1 Ma for stage I sericite in alteration zone, and 0.7±0.1 Ma for the stage II adularia in mineralized vein. Based on the fluid inclusion study, range of ore forming temperature of the Mutnovskoe deposit is 200 to 260d?C (av. 230d?C). Salinities of fluid inclusions indicate 2.2 to 5.7 wt% NaCl in sphalerite and 0.8 to 3.3 wt% NaCl in quartz for the stage I. Mineral paragenesis of the polymetallic vein (stage I) is characterized by a district zoning of tennantite and Cd‐rich sphalerite in the south flank and tetrahedrite and Mn‐rich sphalerite in the central flank, which is due to the fractional crystallizations of ore‐forming fluid. Depositional condition of the low sulfidation state is inferred for the Mutnovskoe deposit, where the polymetallic vein of the south flank is in relatively higher sulfidation state than the central flank.     

Hydrothermal Gold Mineralization at the Rodnikovoe Deposit in South Kamchatka, Russia

Abstract. The Rodnikovoe gold deposit situated in a presently active hydrothermal system located north of the Mutnovsko-Asachinskaya geothermal area in southern Kamchatka, Far Eastern Russia, consists of typical low-sulfidation quartz-adularia veins in a host rock of diorite. The age of the mineralization was dated by the K-Ar method as 0.9 to 1.1 Ma based on adular-ia collected from the veins. Representative ore minerals in the deposit are electrum, argentite, aguilarite, polybasite, pearceite and lenaite. Dominant alteration minerals are adularia, α-cristobalite, chlorite, illite and kaolinite. Hydrothermal solutions of neutral pH were responsible for the mineralization, which is divided into six stages defined by tectonic boundaries. Gold mineralization occurred in stages I and III. Hydrothermal brecciation occurred during stages III, IV and VI. Stages II, IV, V and VI were barren. The estimated ore formation temperature based on a fluid inclusion study is 150 to 250 °C at a depth of approximately 170 m below the paleo-water table. Boiling of hydrothermal fluids is hypothesized as the cause of the intermittent deposition of gold ore. The sulfur and oxygen fugacities during the deposition of anhydrite prior to the hydrothermal brecciation were higher than those during the gold mineralization stages. The occurrence in the hydrothermal breccia of fragments of high grade Au-Ag and polymetallic ores suggests that higher grade mineralization of these metal ores might have occurred in a deeper portion of the deposit.     

Observational features of field line resonances excited by solar wind pressure variations on 4 September 1984

In the course of the magnetic storm of 4 September 1984, after an inverse sudden impulse (SI), geomagnetic pulsations in the Pc5-frequency range were observed at magnetometer stations in the local evening sector. They occurred at L-values of 6, and lasted for several hours, their period increasing from about 320 to 550 s. In this study, two events of enhanced activity are discussed in some detail. During the 16:00 U.T. event, a favourable position of the AMPTE/IRM spacecraft allows conjugate observations in the Northern and Southern Hemispheres and in the magnetosphere. This constellation permits a precise determination of the wave mode. During a later intensification around 18:00 U.T., the AMPTE/CCE spacecraft near local noon monitored poloidal waves, obviously driving the pulsations on the ground. Generally, the observations are consistent with the theory of field line resonance. They are interpreted as being excited by pressure variations in the solar wind. The hydromagnetic cavity mode is assumed to link the magnetopause surface motions to the field line resonances.     

A magnetodynamic mechanism for loop flares

Loop flares are given a new magnetodynamic interpretation. In this model, the top of the magnetic loop is heated up by a collision of magnetic twist-wave packets (non-linear torsional Alfven wave) which are produced in the process of the loop emergence, and stored and released from the footpoints of the loop with some retardation. The appearance of the blueshifted component in CaXIX and FeXXV lines a minute or so before the impulsive phase, and the so-called instantaneous acceleration of ions deduced from the nearly simultaneous (with a delay of seconds) occurrence of -ray line emission with the impulsive hard X rays, are very naturally explained in the present model which originally aims at providing an explanation of the source of energy, a blackbox located at the top of the loop in the loop flare theories discussed thus far.