Chemical characteristics of chromian spinel in plutonic rocks: Implications for deep magma processes and discrimination of tectonic setting

We summarize chemical characteristics of chromian spinels from ultramafic to mafic plutonic rocks (lherzolites, harzburgites, dunites, wehrlites, troctolites, olivine gabbros) with regard to three tectonic settings (mid‐ocean ridge, arc, oceanic hotspot). The chemical range of spinels is distinguishable between the three settings in terms of Cr# (= Cr/(Cr + Al) atomic ratio) and Ti content. The relationships are almost parallel with those of chromian spinels in volcanic rocks, but the Ti content is slightly lower in plutonics than in volcanics at a given tectonic environment. The Cr# of spinels in plutonic rocks is highly diverse; its ranges overlap between the three settings, but extend to higher values (up to 0.8) in arc and oceanic hotspot environments. The Ti content of spinels in plutonics increases, for a given lithology, from the arc to oceanic hotspot settings by mid‐ocean ridge on average. This chemical diversity is consistent with that of erupted magmas from the three settings. If we systematically know the chemistry of chromian spinels from a series of plutonic rocks, we can estimate their tectonic environments of formation. The spinel chemistry is especially useful in dunitic rocks, in which chromian spinel is the only discriminating mineral. Applying this, discordant dunites cutting mantle peridotites were possibly precipitated from arc‐related magmas in the Oman ophiolite, and from an intraplate tholeiite in the Lizard ophiolite, Cornwall.     

Bioaccumulation of nitroarenes in bivalves at Osaka Bay, Japan

This paper reports for the first time the detection and occurrence of nitroarenes (NPAHs) in marine organisms. Mussels and oysters collected from Osaka Bay, Japan, had total NPAHs concentrations that ranged from 2380 to 24,688 pg/g dry and 2672 to 25,961 pg/g dry, respectively. Relatively higher concentrations were detected in sampling sites located near the central district and suburbs of Osaka City implying that the most probable sources of NPAHs in the two bivalves are exhaust gases and smokes emitted by automobiles and industrial plants. Bivalves had relatively higher residues of 1-nitronaphthalene, 2-nitronaphthalene, 3-nitrophenanthrene, and 9-nitrophenanthrenes. Residues of 2-nitrofluorene, 1-nitropyrene, 4-nitropyrenes, and 6-nitrochrysene were much lower compared to nitronaphthalenes and nitrophenanthrenes. Inter-species differences was only observed for 2-nitronaphthalene with oysters exhibiting significantly higher residues than mussels.     

Scoria cone formation through a violent Strombolian eruption: Irao Volcano, SW Japan

Scoria cones are common volcanic features and are thought to most commonly develop through the deposition of ballistics produced by gentle Strombolian eruptions and the outward sliding of talus. However, some historic scoria cones have been observed to form with phases of more energetic violent Strombolian eruptions (e.g., the 1943–1952 eruption of Parícutin, central Mexico; the 1975 eruption of Tolbachik, Kamchatka), maintaining volcanic plumes several kilometers in height, sometimes simultaneous with active effusive lava flows. Geologic evidence shows that violent Strombolian eruptions during cone formation may be more common than is generally perceived, and therefore it is important to obtain additional insights about such eruptions to better assess volcanic hazards. We studied Irao Volcano, the largest basaltic monogenetic volcano in the Abu Monogenetic Volcano Group, SW Japan. The geologic features of this volcano are consistent with a violent Strombolian eruption, including voluminous ash and fine lapilli beds (on order of 10^?1 km³ DRE) with simultaneous scoria cone formation and lava effusion from the base of the cone. The characteristics of the volcanic products suggest that the rate of magma ascent decreased gradually throughout the eruption and that less explosive Strombolian eruptions increased in frequency during the later stages of activity. During the eruption sequence, the chemical composition of the magma became more differentiated. A new K–Ar age determination for phlogopite crystallized within basalt dates the formation of Irao Volcano at 0.4?±?0.05 Ma.     

The paleobiogeographical significance of the Silurian and Devonian trilobites of Japan

Six major groups of trilobites from the Silurian and Devonian of Japan are evaluated for their paleobiogeographical signature. Silurian illaenids and scutelluids show four generic‐level and at least two species‐level links with the Australian segment of the Gondwana paleocontinent; encrinurids also indicate two generic‐level links with Australia and also the South China paleocontinent; whilst Devonian phacopids, and possibly proetids, suggest at least two generic‐level links with the North China paleocontinent. These different patterns may reflect the fragmentary biostratigraphical record of Japanese trilobites, but they also appear to reflect paleoenvironmental parameters associated with lithofacies, and paleoecology. Thus, Japanese assemblages of proetids and phacopids occurring in deep‐water clastic lithofacies have counterparts in similar settings in North China, and Japanese scutelluids and illaenids are strongly associated with shallow marine carbonate lithofacies that are similar to those of their occurrences in Australia. Japanese encrinurids occur in carbonate rocks indicative of shallow marine settings in the Kurosegawa Terrane, and they demonstrate a consistent paleobiogeographical affinity with Australia and South China. Larval ecology cannot be directly assessed for Japanese trilobite groups. However, proetids have consistently been shown to have planktonic protaspides, whereas illaenids, scutelluids, and encrinurids have benthic protaspides. Planktonic protaspides would have a greater propensity for distribution in ocean currents than benthic ones, and therefore may be of more limited paleobiogeographical utility. The combined data from the six different groups indicates that the complex paleobiogeographical patterns of the Japanese trilobite assemblages need to be interpreted with caution, and similarity of taxa does not necessarily denote paleogeographical proximity to other regions.     

南海双船地震勘探介绍

双船地震法包括ESP和SAP法是研究地壳深部结构和构造的有效方法.本文介绍了这两种方法资料处理的主要问题和步骤.预处理工作主要是解决在海洋动态环境下,两船和两套系统同时工作带来的一系列与定位、计时和地震系统有关的问题.着重介绍了用ESP的τ-p记录及x-t域记录进行速度分析的各种方法,它们大都不受反射波时距曲线是双曲线假设的限制.各种方法有各自的特点和限制,用户可根据实际工作的条件和需要选用.SAP的资料处理按四个子系统分别进行,处理方法与一般水平叠加剖面的常规处理相同,获得高质量剖面的关键是求准各层速度得到符合实际情况的叠加速度文件.仔细对比四个子剖面,反复进行处理,最后再有条件地将四个子剖面合成浅、中、深都清晰的合成排列剖面.在资料处理和解释过程中,两种方法相互配合、互为补充.     

1991年大同—阳高5.8级地震的序列

对1991年3月大同—阳高5.8级地震的震源特点、序列特征及震前序列活动进行了分析研究,得出这次5.8级地震是1989年大同—阳高地震的晚期强余震、地震子序列为主余震型序列的结论。从1989年以来大同老震区的弱震活动分析表明,其弱震的几个起伏是大同及其周围应力场加强的信号,可作为今后地震监测预报的窗口。     

Quantitative evaluation of the rainfall influence on streamflow in an inland mountainous river basin within Central Asia

Stable isotopes of water have been widely used in understanding the hydrological functions of alpine inland catchments. This study identifies dominant runoff generation mechanisms based on isotopic data (δ¹⁸O and δ²H) of 487 rainwater and river-water samples from three tributaries in the Tarim River Basin in China for the period May–September 2013. The isotope hydrograph separation results provide a comprehensive overview of the rainfall influence on hydrological processes. Stream water and groundwater have varied responses to different intensities of rainfall events. Only a small proportion of rainfall is directly transported to the stream during such events. An inconsistent temporal trend of event water contribution is observed in the three catchments. The average fractional contributions of rainfall for the Tizinafu, Kumalak and Huangshuigou rivers are 10.3% (±1.1%), 9.7% (±2.9%) and 8.7% (±2.4%), respectively.     

新元古代微生物成锰作用——来自扬子北缘城口地区陡山沱组锰质叠层石的证据

叠层石菱锰矿被认为是生物成锰的证据,但少见相关报道.扬子北缘城口地区陡山沱组菱锰矿层中叠层石十分发育,但研究程度较低,其生长机制不明确,其是否是叠层石或者是附枝藻(Epiphyton)仍具有争议.从岩心描述与薄片观察出发,详细描述了研究区锰质叠层石的宏观和微观特征,根据其发育规模及形态特征将其划分为6种类型:微型分叉柱状叠层石、微型指状叠层石、指状叠层石、层状叠层石、柱状叠层石及层—柱状叠层石.研究表明,研究区柱状锰质叠层石直径一般小于l cm,具同步生长特征,与假裸枝叠层石(Pseudogymnosolenaceae)特征相似.研究区微小型、宏体型叠层石基本层常呈有立柱结构的板状,这种基本层由树形石及微型叠层石组成,而不是附枝藻.叠层石与核形石、鲕粒共生,形成于碳酸盐岩台地边缘礁滩及滩后泻湖环境.研究区锰质叠层石垂向演化从指状向层状演化为主,指示陡山沱组沉积末期水体逐渐变浅.锰质叠层石微观结构以凝块结构为主,具有丝状、球状和放射状等微生物岩显微结构.锰质叠层石记录了碳酸锰精美的原始沉积结构,暗示微生物参与了锰元素的沉积成矿作用.     

Possible europium-normal rare-earth abundances estimated from the lunar samples,and the terrestrial analogue

From the mathematical analysis of the rare-earth data on some of the Apollo 12 samples studied by Hubbard et al. (1971), the possible europium-normal primitive rare-earth pattern, in which europium is normal with respect to the adjacent rare-earth elements, has been estimated. A fact that the igneous rocks (Japanese geosynclinal basalts) appearing to reflect the analogous effect occur locally on the earth enhances our interests in the pattern resulting from the above estimation.