Intensified mid-Holocene Asian monsoon recorded in corals from Kikai Island, subtropical northwestern Pacific

Coupled records of Sr/Ca and oxygen isotope ratios (δ¹⁸O) of coral skeletons have been used to produce quantitative estimates of paleo-sea surface temperature (SST) and δ¹⁸O of surface seawater that can in some cases be converted to sea surface salinity (SSS). Two fossil corals from Kikai Island in the subtropical northwestern Pacific, a location affected by East Asian summer and winter monsoons, were analyzed to investigate differences between mid-Holocene and present-day SST and SSS. At 6180 cal yr BP, SSTs were roughly the same as today, both in summer and winter; δ¹⁸O_seawater and SSS values were higher both in summer (+ 0.5‰, +1.1 psu) and in winter (+ 0.2‰, + 0.6 psu) than modern values. At 7010 cal yr BP, SSTs were slightly cooler both in summer and winter (−0.8 and −0.6 °C), whereas δ¹⁸O_seawater and SSS had higher values in summer (+ 0.3‰, + 0.6 psu) and in winter (+ 0.8‰, + 1.9 psu) than present-day values. These results are consistent with other marine records for the mid-Holocene of the low and midlatitudes in the northwestern Pacific. Such regional conditions indicate that the East Asian summer and winter monsoons were more intense in the mid-Holocene, which was likely a function of the mid-Holocene insolation regime.     

Oxygen isotopic distribution in an amoeboid olivine aggregate from the Allende CV chondrite: Primary and secondary processes

The oxygen isotopic distribution in an amoeboid olivine aggregate (AOA), TTA1-02, from the Allende CV3 chondrite has been determined by secondary ion mass spectrometry. The irregular shaped TTA1- 02 (5×3mm) consists mostly of olivine grains of ca. 5μm in diameter. Olivine grains of Mg-rich (Fo₉₅) and Fe-rich (Fo₆₀) composition are in direct contact with each other, with a sharp compositional boundary. Oxygen isotopic compositions of Fe-rich olivine grains are ¹⁶O-poor (Δ¹⁷O ≅ −5‰), whereas Mg-rich olivine is ¹⁶O-rich (Δ¹⁷O ≅ −25‰). Several Al-rich inclusions (<ca. 500 μm in diameter) are enclosed by olivine grains in the AOA. Oxygen isotopic compositions of spinel and fassaite in Al-rich inclusions are ¹⁶O-rich (Δ¹⁷O ≅ −20‰), whereas those of anorthite, nepheline and phyllosilicate are ¹⁶O-poor (Δ¹⁷O ≅ −5‰). We propose the following sequence of events during the formation of AOAs in the Allende meteorite: 1) Formation of Al-rich inclusions with ¹⁶O-rich oxygen isotopic composition; 2) Accretion of Mg-rich olivine grains with ¹⁶O-rich oxygen isotopic composition around Al-rich inclusions; 3) Accretion into parent body; and 4) Aqueous alteration in the parent body, which led to crystallization of ¹⁶O-poor minerals, Fe-rich olivine, anorthite, nepheline, and phyllosilicate. This is reflecting reactions among primary ¹⁶O-rich AOA minerals and aqueous fluid having ¹⁶O-poor oxygen isotopic composition. Fe-rich olivine grains precipitated from aqueous fluids, which partially dissolved pre-existing Mg-rich olivine grains. Sintering and Mg-Fe diffusion occurred during thermal metamorphism. Anorthite, nepheline and phyllosilicate in Al-rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage.     

Sulfur Isotope Study and Re-examination of Ore Mineral Assemblage of the Hol Kol and the Tul Mi Chung Skarn-type Copper–Gold Deposits of the Suan Mining District, Korean Peninsula

Abstract: Ore specimens collected by the late Professor Takeo Watanabe from the Hol Kol and the Tul Mi Chung deposits, Suan mining district, Korean peninsula, were examined. In addition, measurements of sulfur isotopic ratio of ores and preliminary fluid inclusion microthermometry were carried out. Ores from the New orebody of the Hol Kol deposit consist mainly of bornite, wittichenite and chalcopyrite presently, which exhibit lamellae intergrowth texture, associated with native bismuth and electrum. Bismuthian bornite solid solution is considered to be a principal initial phases, while native bismuth was nucleated as molten bismuth melt initially. The occurrence of cubanite, miharaite, carrollite, siegenite, hessite and geikielite are recognized from the New orebody. Ores from the Eastern orebody of the Hol Kol deposit consist chiefly of chalcopyrite, occasionally associated with trace amounts of pyrrhotite, pyrite, bismuthinite and rare tellurobismuthite, while an ore specimen from the Western orebody consists mainly of sphalerite associated with chalcopyrite, pyrite and galena. Ores from the Tul Mi Chung deposit consist mainly of chalcopyrite and pyrite, occasionally associated with magnetite, sphalerite, galena and rare molybdenite. Some portions of magnetite are revealed to be silician magnetite. Sulfur fugacity is supposed to be below the stability field of bismuthinite in the New orebody. A reducing condition is suggested by the occurrence of geikielite without Fe³⁺ content. The sulfur and oxygen fugacities for the Eastern and Western orebodies of the Hol Kol deposit and for the Tul Mi Chung deposit were higher than the New orebody of the Hol Kol deposit. On the other hand, the Suan granite (porphyritic granodiorite) and the Chil Sing Dai granite (biotite granite porphyry) from the Hol Kol area can be classified as weakly magnetic magnetite‐series. Polyphase fluid inclusions are observed in gangue diopside associated with Cu ore of two specimens. The dissolution temperatures of daughter crystals are 394±26°C and 442±45°C, while the disappearing temperatures of vapor bubble were 475±25°C and > 500°C. Highly saline fluids were responsible for the mineralization at the Hol Kol deposit. The δ³⁴S values of ore sulfides of the Hol Kol and the Tul Mi Chung deposit range from +11. 5% to +16. 1%, having anomalous lower values mainly from the Tul Mi Chung deposit. Such anomalous lower 6³⁴S values can be caused by isotopic fractionation against oxidized sulfur species. The δ³⁴S value of bulk sulfur in the ore solutions responsible for the Hol Kol and the Tul Mi Chung deposit is estimated to be +13.5±2.5‰.     

Planform evolution of deltas with graded alluvial topsets: Insights from three‐dimensional tank experiments,geometric considerations and field applications

The profile of a river that conveys sediment without net deposition and net erosion is referred to as ‘graded’ with respect to vertical aggradation of the river segment. Three experimental series, designed in terms of the autostratigraphic view of alluvial grade, were conducted to clarify the diagnostic spatial behaviour of graded alluvial–deltaic rivers: an ‘R series’, which utilized a moving boundary setting with a stationary base level; an ‘F series’ in a fixed boundary setting with a stationary base level to produce ‘forced grade’; and an ‘M series’ in a moving boundary setting with constant base‐level fall to produce ‘autogenic grade.’ The results of the three experimental series, combined with geometrical modelling of the effects of basin water depth and other experimental data, suggest the following: (i) in a graded alluvial–deltaic system, lateral shifting and avulsing of active distributary channels are suppressed regardless of whether the downstream boundary of the deltaic system is fixed; (ii) in a delta with a downstream‐fixed boundary, the graded streams are stabilized within a valley that is incised in the axial part of the delta plain, whereby the alluvial plain outside the valley is abandoned and terraced; (iii) in moving boundary settings, the graded river simply extends basinward as a linearly elongated channel and lobe system without cutting a valley; and (iv) a modern forced‐graded alluvial river is most likely to be found in a valley incised into a fan delta in front of very deep water, and the stratigraphic signal of fossil autogenic‐graded rivers will be found in deltaic successions that accumulated in the outer to marginal areas of deltaic continental shelves during sea‐level falls. This renewed autostratigraphic view of alluvial grade suggests a thorough reconsideration of the conventional understanding that an alluvial river feeding a progradational delta is graded with a stationary base level.     

Determination of Total Sulfur in Thirty One Geochemical Reference Materials Using an Inductively Coupled Plasma-Atomic Emission Spectrometer Fitted with a Semiconductor Photodiode Detector

The total sulfur contents of thirty one geochemical reference materials were determined using an inductively coupled plasma-atomic emission spectrometer fitted with a semiconductor photodiode detector. Most samples were decomposed using an HF-aqua regia digestion. However, a few were incompletely decomposed by simple acid digestion, and these were decomposed by a fusion method. The agreement between the analytical results from this work and published data is generally good.     

A Low‐Sulfidation Epithermal Mineralization in the River Reef Zone,the Poboya Prospect,Central Sulawesi,Indonesia: Vein Textures,Ore Mineralogy,and Fluid Inclusions

The Poboya Prospect lies along the North Northwest ‐ South Southeast Palu‐Koro Fault Zone in the central part of the West Sulawesi Arc. The geology of the area consists of the Palu Metamorphic Complex overlain by the Paleogene‐Neogene Tinombo Formation of volcanosedimentary rocks, the Celebes Molasse sediment, and Late Cenozoic granitic rocks. Petrography, scanning electron microscope with energy‐dispersive spectrometry (SEM‐EDS), electron probe microanalyzer (EPMA), and fluid inclusion microthermometry were carried out to examine vein textures, ore mineralogy, and characteristics of the ore‐forming fluid responsible for mineralization in the River Reef Zone, the Poboya Prospect. Textures of quartz‐carbonate veins in the River Reef Zone include massive micro‐comb, moss, colloform, crustiform, mosaic, feathery, flamboyant, lattice bladed, ghost bladed, parallel bladed, and saccharoidal textures representing primary growth, recrystallization, and replacement. The homogenization temperature and fluid salinity are 240–250°C and 0.3–0.7 wt% NaCl eq., respectively. Ore minerals precipitated in the early stage consist of electrum, naumannite‐aguilarite, chalcopyrite, pyrite, marcasite, sphalerite, and pyrrhotite. Apart from pyrrhotite, these ore minerals were also precipitated in the late stage along with selenopolybasite, freibergite, argyrodite, pyrargyrite, and galena. Selenium more preferably occurs as the crystallographic replacement of sulfur in naumannite‐aguilarite, argyrodite, pyrargyrite, selenopolybasite, and freibergite instead of as independent selenide minerals. The low‐sulfidation epithermal deposit in the River Reef Zone, the Poboya Prospect, illustrates the potential of the West Sulawesi Arc, particularly along the Palu‐Koro Fault Zone, to host epithermal gold mineralization.     

Geochemical Characteristics of Intrusive Rocks, Southeastern Mindanao, Philippines: Implication to Metallogenesis of Porphyry Copper-gold Deposits

This paper describes petrologic and geochemical characteristics of intrusive rocks associated with porphyry copper deposits in south-eastern Mindanao, the Philippines, where the Kingking deposit is located. Intrusive rocks at the Kingking deposit, are classified into biotite-bearing diorite porphyry, hornblende diorite porphyry and diorite porphyry. Intrusive rocks in other areas in south-eastern Mindanao, including Batoto, Bukal, Maragusan, Masara, Amacan and Sumlog, are hornblende diorite porphyry and hornblende quartz diorite. They are adakitic in Sr/Y-Y diagram, but not in La/Yb-Yb diagram due to relatively low REE contents. The magmas are oxidizing as suggested by the high X_Mg of mafic silicate phenocrysts and SO₃ contents of microphenocrystic apatite. An Oligocene-Miocene diorite intrusive complex formed by calc-alkaline, hydrous, oxidizing magma is considered to be associated with porphyry-type copper-gold mineralization.     

Study on hydraulic characteristics of sabo dam with a flap structure for debris flow

The front part of the flow is very important and complex in the case of debris flow where there is an accumulation of large boulders. It is important to control or dampen the energy of the frontal part of a debris flow for the safety of the downstream area because the impact pressure of debris flow is much greater than that of clear fluid. The main objective of this study is to analyze the hydraulic characteristics of the proposed dam (i.e. closed-type dam with flap). The vertical pressure distribution of this type is compared with conventional dam types. In the experiments, the total pressure associated with major debris flows was recorded in real time by a system consisting of four dynamic pressure sensors installed on different types of dam. The results from experimental data clearly show that the dam with the flap has advantages of capturing the debris flow with large boulders and controls the total pressure by flow circulation due to presence of the flap structure compared to a closed-type dam without flap. Further-more, the empirical coefficients of hydrodynamic and solid collision models were proposed and com-pared with available coefficients.     

Variation of Cl and SO3 Contents of Microphenocrystic Apatite in Intermediate to Silicic Igneous Rocks of Cenozoic Japanese Island Arcs: Implications for Porphyry Cu Metallogenesis in the Western Pacific Island Arcs

Abstract. Determinations of SO₃ and Cl contents of igneous accessory apatite were carried out on Late Cenozoic intermediate to silicic intrusive and volcanic rocks in the Japanese island arcs of the western Pacific rim including the southwestern Kuril arc (eastern Hokkaido), Northeast Japan arc (southwestern Hokkaido through northeastern Honshu to central Honshu), Izu‐Bonin arc, Kyushu‐Palau ridge, Southwest Japan arc (northern Kyushu) and northern Ryukyu arc (southern Kyushu). These were compared to those from the Western Luzon arc, Philippines, to better understand the metallogenesis of porphyry Cu deposits in the western Pacific island arcs. In addition, SO₃ and Cl contents of accessory apatite in the Cretaceous magnetite‐series granitic rocks in the Kitakami belt (northeastern Honshu) and the Miocene ilmenite‐series granitic rocks in the Outer Zone of Southwest Japan (southern Kyushu) were also examined. Microphenocrystic apatites in shallow intrusions associated with porphyry Cu deposits in the Western Luzon arc contain >0.1 wt% S as SO₃. Such high SO₃ contents of microphenocrystic apatite are a common characteristic of hydrous mag‐matism in the Western Luzon arc, from 15 Ma old tonalitic plutonic rocks of the Luzon Central Cordillera to present‐day volcanism at Mount Pinatubo. The accessory apatite in intrusive rocks associated with porphyry Cu deposits, especially those at the Santo Tomas II deposit, show significantly high Cl contents (>2 wt%). The SO₃ contents of microphenocrystic apatite in most of the hydrous silicic rocks along the volcanic front, in andesites related to native sulfur deposits, and in Miocene and younger shallow granitic intrusions in northeastern Honshu, are generally <0.1 wt%. On the other hand, the SO₃ contents of apatite in such rocks from eastern Hokkaido, southwestern Hokkaido, Izu, northern Kyushu and southern Kyushu are similar to those from the Western Luzon arc. The SO₃ contents of accessory apatite in the Cretaceous magnetite‐series granitic rocks in the Kitakami belt are variable, whereas those of the Miocene ilmenite‐series granitic rocks in southern Kyushu are extremely low. The Cl contents of accessory apatite in some rocks of the Northeast Japan arc, Izu‐Bonin arc and Southwest Japan arc are significantly high. In terms of the Cl and SO₃ contents of microphenocrystic apatite, Cenozoic Japanese arc magmatism show similarities with arc magmatism associated elsewhere with porphyry Cu mineralization, except for the most of northeastern Honshu of the Northeast Japan arc. Apatite commonly occurs as inclusions in other phenocrystic phases. Thus the variation in SO₃ contents of apatite is a feature of early stage magmatic differentiation. The SO₃ contents of microphenocrystic apatite are considered to reflect the redox state of the magma source region or fluids encountered during magma generation.     

Assessment of potential outburst floods from the Tsho Rolpa glacial lake in Nepal

Flood and sediment disasters caused by glacial lake outbursts have occurred frequently in recent years in the Himalayas of Nepal. Glacial lake outburst floods (GLOFs) can cause catastrophic flooding in downstream areas with serious damage to lives and property. It is thus important to investigate outburst floods from potentially dangerous glacial lakes. In this study, the characteristics of potential outburst floods from the Tsho Rolpa glacial lake due to two types of moraine dam failure caused by seepage flow or water overtopping were analyzed with various scenarios by using integrated modeling system of three numerical models: (1) the flow and bed-surface erosion model, (2) the seepage model and (3) the slope stability model. Flood inundation areas were also identified by using the numerical model of the flow and moraine dam failure and geographical information system tools. Possible threats and damages due to the potential GLOF events from the lake were also analyzed based on numerical results, flood inundation maps and field investigations.