Controlled experiment in the ionosphere with a rocket-borne plasma gun

A controlled active experiment was performed by a plasma gun on-board a rocket to study the plasma stream across the magnetic field in space. A mother and daughter system was employed. An 8 kV 0.8 μF (25 J) capacitor bank on the daughter rocket was discharged every 12 s and about 10¹⁶ ion and electron pairs were ejected. A plasma signal was detected on the electron temperature probe. The propagation speed of the plasma stream is estimated to be 10⁶ cm/s, considerably lower than that obtained in the prelaunch test. The amplitude of the plasma signal decays as the inverse square of the mutual distance between the mother and daughter rockets and this decay is much slower than the free streaming. The importance of the geomagnetic field on the plasma propagation in space is discussed.     

Metallogenesis of Porphyry Cu Deposits of the Western Luzon Arc, Philippines: K-Ar ages, SO3 Contents of Microphenocrystic Apatite and Significance of Intrusive Rocks

Abstract: K–Ar ages of the following porphyry Cu deposits in the western Luzon arc are determined: Lobo-Boneng (10.50.4 Ma), Santo Niño (9.50.3 Ma), Black Mountain (2.10.1 Ma), Dizon (2.50.2 Ma) and Taysan (7.30.2 Ma). Microphenocrys-tic apatite in the late Cenozoic intermediate to silicic intrusions associated with porphyry Cu deposits in the western Luzon arc contains sulfur as SO₃ detectable by electron probe microanalyzer. Sulfur is supposed to have been accommodated dominantly as oxidized species in oxidizing hydrous magmas that generated porphyry Cu deposits. Likewise, such high SO₃ contents in microphenocrystic apatite are common characteristics of the intermediate to silicic magmatism of the western Luzon arc, from tonalitic rocks of the Luzon Central Cordillera of about 15 Ma to an active magmatism at Mount Pinatubo. Thus, the western Luzon arc has been generating porphyry Cu mineralization associated with oxidizing hydrous intermediate to silicic magmatism related to eastward subduction, since Miocene to the present day. Intermediate to silicic rocks since 15 Ma to present-day western Luzon arc generally show high whole-rock Sr/Y ratio ranging from 20 to 184. However, porphyry Cu deposit is not necessarily related to the rocks that show higher Sr/Y ratios compared to the other barren rocks in the western Luzon arc. The characteristics of the intermediate to silicic magma associated with porphyry Cu deposit are not attributed to the composition of the source material of the magma, but to the properties defined by the high activity of oxidized species of sulfur in the fluid phase that is encountered during the generation of intermediate to silicic magmas.     

新疆乌伦古富碱侵入岩成因探讨

对沿乌伦古深断裂分布的钠闪石花岗岩、钾长花岗岩、闪长岩、碱性正长岩等富碱侵入体进行了较系统的岩石化学、微量元素、稀土元素地球化学及Ｏ、Ｐｂ、Ｓｒ、Ｎｄ同位素组成研究，确认它们为一类幔源重熔分异型富碱侵入岩类。在分析其物质来源、形成构造环境和成岩条件等特征基础上，用部分熔融、多阶段分离结晶和分离结晶－地壳混染等模型探讨了其成岩机理。     

Attenuation of coda waves and Q c value beneath the Chengdu telemetered seismic network

Based on the single scattering model of coda power spectrum analysis, digital waveform data of 50 events recorded by the real-time processing system of the Chengdu telemetry network are analyzed to estimate the Q _c values of earth medium beneath the Chengdu telemetry network for several specified frequencies. It is found that the Q _c shows the frequency dependency in the form of Q _c = Q ₀ f ⁿ in the range of 1.0 to 20.0Hz. Estimated Q ₀ ranges from 60.83 to 178.05, and n is found to be 0.713 to 1.159. The average value of Q ₀ and n are 117 and 0.978 respectively. This result indicates the strong frequency dependency of the attenuation of coda waves beneath the Chengdu telemetry network. Comparing with the results obtained in other regions of the world, it is found that Q ₀ ⁻¹ value and its change with frequency are similar to those in regions with strong tectonic activity. This subject is supported by the Ministry of Personnel, China for partly sponsoring.     

Occurrence of Halogen-rich Phlogopite in Late Cenozoic Volcanic Rocks in the Japanese Arcs

Abstract. Halogen-rich phlogopite occurs in the groundmass of andesite and dacite lavas from Late Tertiary to Quaternary volcanoes associated with native sulfur and limonite deposits (Shiretoko-Iwozan, Hachimantai, Adatara, Omeshidake, Masaki) and hydrothermal ore deposits (Harukayama, Muineyama, Hishikari) in Japan. The F contents of the halogen-rich phlogopite range from 3.6 to 5.7 wt%, corresponding to atomic F/(F+C1+OH) ratios ranging from 0.45 to 0.69. On the other hand, the Cl contents of the halogen-rich phlogopite are around 0.2 wt%. The atomic Mg/(Mg+Fe) ratios range from 0.69 to 0.83.
The fluorine intercept value [IV(F)] defined by Munoz (1984) of the phlogopites ranges from 0.79 to 3.17, and the chlorine intercept value [IV(Cl)] ranges from -7.11 to -7.77. The observed IV(F) of the phlogopites broadly overlap the range of the IV(F) for biotites from porphyry copper deposits. On the other hand, the observed IV(Cl) are significantly lower than the IV(Cl) for biotites from porphyry copper deposits. Whereas the F contents of the phlogopite appear more prominent compared to the Cl contents, the calculation of halogen intercept values revealed that the phlogopites are enriched in Cl with respect to the element distribution effect of Mg-Fe substitution. Since the degree of Cl enrichment of the phlogopite is more significant compared to that of biotite in porphyry copper deposits, the phlogopites are considered to have formed under the condition of significantly high activity of halogens. Hydrothermal ore deposits may be formed in magmatic hydrothermal system associated with volcanoes where halogen-rich phlogopite is formed by hypersaline fluid.     

Triaxial stress state deep in orogenic belts: an example from Turkey

A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ₁−σ₂)/(σ₁−σ₃) was calculated to be 0.64, indicating that σ₂ lies closer to the midpoint between σ₁ and σ₃ than to σ₃.     

Primary Ore Mineral Assemblage and Fluid Inclusion Study of the Batu Hijau Porphyry Cu-Au Deposit, Sumbawa, Indonesia

Abstract. The Batu Hijau porphyry Cu‐Au deposit, Sumbawa Island, Indonesia, is associated with a tonalitic intrusive complex. The temperature‐pressure condition of mineralization at the Batu Hijau deposit is discussed on the basis of fluid inclusion microthermometry. Then, the initial Cu‐Fe sulfide mineral assemblage is discussed. Bornite and chalcopyrite are major copper ore minerals associated with quartz veinlets. The quartz veinlets have been classified into ‘A’ veinlets associated with bornite, digenite, chalcocite and chalcopyrite, ‘B’ veinlets having chalcopyrite bornite along vuggy center‐line, rare ‘C’ chalcopyrite‐quartz veinlets, and late ‘D’ veinlets consisting of massive pyrite and quartz (Clode et al., 1999). Copper and gold mineralization is associated with abundant ‘A’ quartz veinlets. Abundant fluid inclusions are found in veinlet quartz consisting mainly of gas‐rich inclusions and polyphase inclusions throughout the veinlet types. The hydrothermal activity occurred in temperature‐pressure conditions of aqueous fluid immiscibility into hypersaline brine and dilute vapor. The halite dissolution (Tm[halite]) and liquid‐vapor homogenization (Th) temperatures of the polyphase inclusions in veinlet quartz range from 270 to 472d?C and from 280 to 454d?C, respectively. The estimated salinity ranges from 36 to 47 wt% (NaCl equiv.). The apparent pressures lower than 300 bars are estimated to have been along the liquid‐vapor‐halite curve for the fluid inclusions having the Th lower than the Tm that trapped the brine saturated with halite, or at slightly higher pressure relative to liquid‐vapor‐halite curve for the fluid inclusions having the Th higher than the Tm that trapped the brine unsaturated with halite. The actual temperature and pressure during the hydrothermal activity at the Batu Hijau deposit are estimated to have been around 300d?C and 50 bars. At such temperature‐pressure conditions, the principal and initial Cu‐Fe sulfide mineral assemblages are thought to be chalcopyrite + bornite solid solution (bnss) for the chalcopyrite‐bearing assemblage, and chalcocite‐digenite solid solution and bnss for the chalcopyrite‐free assemblage.     

Evolution of Hydrothermal System at the Dizon Porphyry Cu-Au Deposit, Zambales, Philippines

Abstract. Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu‐Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragen‐esis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bornite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW‐trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bornite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bornite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas‐rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360d?C to >500d?C but liquid (brine) and gas (vapor) do not homogenize at <500d?C. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500d?C. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alteration (stage 2) consist mainly of gas‐rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid‐vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid‐vapor homogenization of polyphase inclusions from 230d?C to >500d?C and from 270d?C to >500d?C, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245d?C. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas‐rich inclusions accompanied with minor liquid‐rich inclusions that homogenize at temperatures between 350d?C and 490d?C. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas‐rich inclusions with subordinate polyphase inclusions that do not homogenize below 500d?C. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid‐rich two‐phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190d?C to 300d?C (suggesting boiling) and the salinity ranges from 1.0 wt% to 3.4 wt% NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190d?C from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature‐pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture‐controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0 % to +5 %. Sulfur originated from an iso‐topically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system.     

Deep structure of the northeastern Japan arc and its implications for crustal deformation and shallow seismic activity

Seismic tomography studies in the northeastern Japan arc have revealed the existence of an inclined sheet-like seismic low-velocity and high-attenuation zone in the mantle wedge at depths shallower than about 150 km. This sheet-like low-velocity, high-attenuation zone is oriented sub-parallel to the subducted slab, and is considered to correspond to the upwelling flow portion of the subduction-induced convection. The low-velocity, high-attenuation zone reaches the Moho immediately beneath the volcanic front (or the Ou Backbone Range) running through the middle of the arc nearly parallel to the trench axis, which suggests that the volcanic front is formed by this hot upwelling flow. Aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the Backbone Range where they are expelled from solidified magma and migrate further upward. The existence of aqueous fluids may weaken the surrounding crustal rocks, resulting in local contractive deformation and uplift along the Backbone Range under the compressional stress field of the volcanic arc. A strain-rate distribution map generated from GPS data reveals a notable concentration of east–west contraction along the Backbone Range, consistent with this interpretation. Shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone. Based on these observations, a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern Japan arc.