花垣铅锌矿床包裹体气相组份研究--MVT矿床有机成矿作用研究(Ⅱ)

矿床包裹体中气液相组份,是矿床成因的重要的直接物质证据,它直接参与了成矿作用,与矿床的沉淀机制密切有关。本文研究了湖南花垣地区,产于下寒武统清虚洞组藻灰岩和鲕粒灰岩中的密西西比河谷型(MVT)铅锌矿床中,18个矿物包裹体的气相组份、气态烃组份以及气相组份的碳同位素特征。这些包裹体由水和大量的CO₂(平均5.0mol%),气态烃(平均1.1mol%)和少量的CO、H₂组成,气态烃中CH₂的含量为89.54%,而δ13C_CH4=-27.08‰,δ13C_CO2=-17.28‰(PDB)。包体气相组份的这些特征表明:包体气相组份中,确有烃类存在,包体中气态烃和CO₂是有机成因的;气态烃可能有多个来源层,而矿床的沉淀机制可能与流体在矿床就位位置上和早已存在的古油气藏的混合作用有关。     

自动确定煤岩参数的数据处理技术

介绍了根据HY-3型全自动显微光度测定系统以煤反射率自动测定结果确定显微煤岩组分,鉴别混煤与确定混煤比例,确定煤中活惰性组分比例等采用的数据处理技术。      

Dunite channels within a harzburgite layer from the Horoman peridotite complex,Japan: Possible pathway for magmas

Two discordant dunite channels in a polished slab were collected from a harzburgite layer in the Horoman orogenic lherzolite massif, Hokkaido, Japan. The dunite channels show extreme grain‐size variations, and include very large olivine megacrysts up to 1.6 m long. Spinel‐rich pyroxenite veins or veinlets occasionally cross‐cut the olivine megacrysts. Mineral compositions differ between channels, and the mineral compositions and textures of the dunite channels and the host harzburgite suggest a replacive origin for the dunites. The Sr and Nd isotopic ratios of clinopyroxene separates from the pyroxenite veins in two dunite channels are different, but these ratios are generally similar to those of mid‐ocean ridge basalts. Assuming the channels formed by the through‐flow of melts, then the trace element compositions of the melts estimated from the clinopyroxenes are broadly similar. The melts have similar features such as enriched in incompatible elements and depleted in heavy rare earth elements, but there are differences in the depletions in Ti and Ba, indicating melts that were different but of similar origins. A Rb–Sr crystallization age (~ 52 Ma) was obtained for clinopyroxene–orthopyroxene pairs in a dunite channel and its host harzburgite. The distinctive dunite channels with megacrysts formed as a result of the through‐flow of mafic magma(s), and those magmas had trace and minor element contents that are indicative of contributions of a melt derived from subducted oceanic lithosphere.     

舟山潮差带海相沉积物的物理和化学特征

为舟山潮差带海相沉积物固结机理的深入研究提供物质基础,采用激光粒度仪分析了海相沉积物的粒度组成,并测试了海相沉积物的化学元素、化合物种类及其相对含量,还使用X-射线衍射技术分析了海相沉物的矿物组成。结果表明:海相沉积物含水率高、初始孔隙比大、呈流塑状,为低液限粉质黏土;活性指数为12.4,属于活动黏性土,矿物的亲水性较好;全盐含量高达9～11.2 g/kg,阳离子交换能力不强,有机质含量(5.82～12.7 g/kg)较高;pH值为7.35～8.36,呈弱碱性,加上孔隙水中K^+,Na^+,Ca²⁺,Mg²⁺的存在,使得高岭石常不稳定,有向伊利石、蒙脱石或绿泥石转化的趋势。     

陕西西沟钼矿床辉钼矿Re-Os年代学和同位素地球化学特征及其地质意义

西沟钼矿床是东秦岭黄龙铺地区近些年新发现和勘查的碳酸岩脉型钼矿床。钼矿体主要赋存于新太古界太华群变质岩内的石英方解石碳酸岩脉中,呈脉状、似层状或透镜状产出。辉钼矿主要呈浸染状、薄膜状、团块状分布于石英方解石碳酸岩脉中,成矿有关的围岩蚀变有钾长石化、硅化、黄铁矿化、萤石化、硬石膏化等。为查明西沟钼矿床的成矿时代、成矿物质来源、成矿机制、确定矿床类型,文章开展了辉钼矿Re-Os同位素测年,同位素地球化学分析。6件辉钼矿样品Re-Os同位素测年结果,模式年龄为(222.3±3.4)Ma～(226.6±3.7)Ma;加权平均年龄为(225.1±1.4)Ma;等时线年龄为(224.6±9.1)Ma,表明该矿床形成于晚三叠世。硫化物和硫酸盐的S同位素组成、重晶石和方解石Sr-Nd同位素组成及方解石C-O同位素组成均指示:西沟钼矿的成矿物质可能主要来源于地幔。根据其与华北陆块南缘其他碳酸岩型钼矿床地质特征、成矿时代和成矿物质来源等对比,确定西沟钼矿床属碳酸岩型脉状矿床。成矿作用发生于扬子板块与华北板块碰撞造山的后碰撞伸展环境,由于软流圈物质上涌诱发富集岩石圈地幔发生低程度部分熔融,所形成的碳酸质流体携带钼等成矿物质上升,在NW-NWW向深断裂带沉淀富集成矿。     

Spatial and seasonal variations in the ecological characteristics of the free-living nematode assemblages in a large microtidal estuary

This study has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large southern hemisphere microtidal estuary change spatially and seasonally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at this time and thus when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material (%POM) in the sediment. Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum.     

天山托洋峰花岗质岩石的同位素地球化学特征

分析了西天山托木尔峰地区花岗质岩石和基底岩石的稀土元素,微量元素以及Ｏ、Ｐｂ、Ｓｒ、Ｎｄ同位素组成。本区北部伊犁地块基底岩石的Ｎｄ同位素模式年龄约为１．９Ｇａ,南部南天山褶皱带的约为０．７０５到０．７３３）表明本区花岗质岩石主要为地壳溶融产物。Ｏ、Ｐｂ、Ｓｒ、Ｎｄ同位素组成批示位于伊犁地块和南天山褶皱带的花岗岩源区岩石的Ｎｄ模式年龄都相当于伊犁地壳,但源区性质不同,前者源区δ＾１８Ｏ低,μ值低,Ｔ     

Mantle-derived magmatic gas releasing features at the Rehai area, Tengchong county, Yunnan Province, China

This paper deals with the chemical and isotopic compositions of escaped gases from the Rehai geothermal area in Tengchong county of Yunnan Province. Results indicate that there is the mantle-derived magmatic intrusion in shallow crust at this area. Modern mantle-derived magmatic volatiles are being released currently in a steady stream by way of active faults. The escaped gases are mostly composed of CO₂, together with subordinate amounts of H₂S, N₂, H₂, CH₄, SO₂, CO and He. At the studied area, the north-south directed fault is the deepest, and it may be interlinked with the deep-seated thermal reservoir that would be directly recharged by the mantle-derived magmatic volatile. The He, C isotopic evidence reveals that the modern active magma beneath Rehai area may originate from the historical mantle-derived magma which caused the latest eruptive activity of volcanoes in that region.     

Pb, Nd, and Sr isotopic constraints on the origin of Miocene basaltic rocks from northeast Hokkaido, Japan: Implications for opening of the Kurile back-arc basin

Late Miocene (7–9 Ma) basaltic rocks from the Monbetsu‐Kamishihoro graben in northeast Hokkaido have chemical affinities to certain back‐arc basin basalts (referred to herein as Hokkaido BABB). Pb‐, Nd‐ and Sr‐isotopic compositions of the Hokkaido BABB and arc‐type volcanic rocks (11–13 Ma and 4–4.5 Ma) from the nearby region indicate mixing between the depleted mantle and an EM II‐like enriched component (e.g. subducted pelagic sediment) in the magma generation. At a given ⁸⁷Sr/⁸⁶Sr, Hokkaido BABB have slightly lower ¹⁴³Nd/¹⁴⁴Nd and slightly less radiogenic ²⁰⁶Pb/²⁰⁴Pb compared with associated arc‐type lavas, but both these suites are difficult to distinguish solely on the basis of isotopic compositions. These isotopic data indicate that while generation of the Hokkaido BABB involves smaller amounts of the EM II‐like enriched component than do associated arc lavas, Hokkaido BABB are isotopically distinct from basalts produced at normal back‐arc basin spreading centers. Instead, northeast Hokkaido BABB are more similar to basalts erupted during the initial rifting stage of back‐arc basins. The Monbetsu‐Kamishihoro graben may have developed in association with extension that formed the Kurile Basin, suggesting that opening of the basin continued until late Miocene (7–9 Ma).