UV photolysis, organic molecules in young disks, and the origin of meteoritic amino acids

The origin of complex organic molecules such as amino acids and their precursors found in meteorites and comets is unknown. Previous studies have accounted for the complex organic inventory of the Solar System by aqueous chemistry on warm meteoritic parent bodies, or by accretion of organics formed in the interstellar medium. This paper proposes a third possibility: that complex organics were created in situ by ultraviolet light from nearby O/B stars irradiating ices already in the Sun’s protoplanetary disk. If the Sun was born in a dense cluster near UV-bright stars, the flux hitting the disk from external stars could be many orders of magnitude higher than that from the Sun alone. Such photolysis of ices in the laboratory can rapidly produce amino acid precursors and other complex organic molecules. I present a simple model coupling grain growth and UV exposure in a young circumstellar disk. It is shown that the production may be sufficient to create the Solar System’s entire complex organic inventory within 10⁶ yr. Subsequent aqueous alteration on meteoritic parent bodies is not ruled out.     

湄洲湾海域表层沉积物重金属含量的分布特征及潜在生态风险评价

根据2012年福建湄洲湾海域表层沉积物样品测定的7种重金属（Cr、Co、Ni、Cu、Zn、As、Pb）含量数据,研究重金属在沉积物中的含量和空间分布特征,然后运用主成分分析法分析各重金属的主要来源,最后采用潜在生态危害指数法评价其污染程度和潜在生态危害.结果表明,相对第一类海洋沉积物标准,Cu、Zn、As和Pb含量均未超标,Cr超标21.2%.大部分重金属含量平面分布总体呈现东北往西南递减的趋势,体现陆源输入的影响,As、Zn及Pb在7号站位、Cu在8号站位出现高值区可能更多地联系于研究区域本身的背景特征.Cr、Co、Ni和Zn含量之间相关性显著,且Co、As和Zn含量也两两表现出显著正相关.主成分分析表明岩石的自然风化和侵蚀是Cr、Co、Ni、Cu、Zn和As元素在研究区域表层沉积物的主要来源,Pb可能更多来源于海上交通航运和海水养殖.研究区域综合潜在生态危害为中等生态危害程度.     

Effects of land use on water chemistry in a river draining karst terrain,southwest China

Abstract

The effects of land use on river water chemistry in a typical karst watershed (Wujiang River) of southwest China have been evaluated. Dissolved major ions and Sr isotopic compositions were determined in 11 independent sub-watersheds of the Wujiang River to investigate the spatio-temporal variations in river water chemistry and their relationship to land use. The results show significant spatial variability in pH, major ions, total dissolved solids (TDS), and Sr isotopic compositions throughout the basin. Correlation analysis indicates that nitrogen content is significantly related to forest coverage. Nitrogen and potassium generally have higher values in the rainy season, and the percentage of agricultural land controlled NO₃^- levels, which originate from anthropogenic sources. Forest cover, which varies between 35% and 71%, has no statistically significant impact on river solute concentrations, but the TDS flux is low in sub-watersheds with greater forest cover. Geological sources have a significant influence on pH and Sr isotopic compositions in river water throughout the basin.

Editor D. Koutsoyiannis

Citation Han, G., Li, F., and Tan, Q., 2014. Effects of land use on water chemistry in a river draining karst terrain, southwest China. Hydrological Sciences Journal, 59 (5), 1063–1073.     

黑龙江省金厂金矿石英闪长玢岩固结温压条件及其深部预测

黑龙江东宁县金厂金矿位于兴蒙造山带松嫩地块之东端,是吉黑岩浆成矿域的重要组成部分。其围岩蚀变和流体包裹体研究均显示具典型斑岩Au-Cu矿体特征,与燕山晚期花岗斑岩、石英闪长玢岩密切相关。通过矿物温压计对矿区中部18号矿体下部出露的石英闪长玢岩固结温压条件进行分析表明,岩体固结温度约735℃～700℃,压力约0.63MPa～1.3MPa,侵位深度大致约2km～4km,与流体包裹体获得的成矿深度(2.1km～3.2km)接近。研究结果显示目前出露的矿体属于斑岩矿床成矿体系的中部,而深部斑岩体仍未大规模出露。因此,该矿区深部仍有很大的找矿潜力。     

新疆西天山智博铁矿床蚀变矿物学、矿物化学特征及矿床成因探讨

智博铁矿床是西天山东部阿吾拉勒铁成矿带新发现的大型磁铁矿矿床之一。赋矿围岩为下石炭统大哈拉军山组火山岩及火山碎屑岩。围岩蚀变广泛发育,识别出3个阶段:第一阶段以辉石+钠长石+磁铁矿为主;第二阶段以角闪石+钾长石+绿帘石+磁铁矿+黄铁矿为主;第三阶段以绿帘石+绿泥石+方解石+石英+黄铁矿+赤铁矿±黄铜矿为主。电子探针分析表明,智博铁矿与其他岩浆-热液成因铁矿床具有类似的蚀变矿物化学成分。辉石以透辉石为主(Di=62.97%~83.56%),含少量钙铁辉石(Hd=16.44%~36.45%);火山岩中斜长石(Ab47.57-57.82An41.5-51.87Or0.56-0.68)蚀变形成钠长石(Ab77.89-99.33An0.46-2.48Or0.21-20.3);与热液作用有关的钾长石叠加改造早期蚀变矿物;角闪石主要为阳起石;晚期发育富铁绿帘石〔Fe/(Fe+Al)=0.2~0.36〕以及绿泥石蚀变矿物。与火山岩中的磁铁矿〔w(TiO2)3.08%〕相比,矿体中磁铁矿具有低w(TiO2)(0.23%)的特点,部分早期浸染状磁铁矿与火山岩中的磁铁矿w(V2O5)相当,暗示该矿化阶段的铁质部分来源于围岩。矿物学及矿物化学表明,热液交代作用对成矿具有重要的贡献。同时,智博铁矿具有一些暗示铁矿浆成因的结构特征,如块状磁铁矿与围岩呈截然接触,磁铁矿胶结围岩角砾,磁铁矿条带呈流动状分布以及板条状磁铁矿等。结合铁矿带区域地质特征,认为智博铁矿可能主要由富铁岩浆流体形成,在形成大量块状富铁矿体的同时,伴随有广泛的围岩蚀变。矿区内大量的磁铁矿矿化与晚石炭世大陆岛弧岩浆活动有密切的成因联系。     

Crustal deformation effects on the chemical evolution of geothermal systems: the intra-arc Liquiñe–Ofqui fault system,Southern Andes

A better understanding of the chemical evolution of fluids in geothermal and hydrothermal systems requires data-based knowledge regarding the interplay between active tectonics and fluid flow. The Southern Andes volcanic zone is one of the best natural laboratories to address this issue because of the occurrence of numerous geothermal areas, recent seismic activity generated by regional fault systems, and intense volcanic activity. Geothermal systems have been understudied in this area, and limited scientific information exists about the role of local kinematic conditions on fluid flow and mineralization during the development and evolution of geothermal reservoirs. In this study, we provide data for a 1:200,000 scale geological and structural map of the Villarrica–Chihuio area as a setting in which to perform a structural analysis of active geothermal areas. This structural analysis, combined with geochemical modelling of hot spring data, allows the identification of two magmatic-tectonic-geothermal domains based on fault systems, volcanic activity, and lithologies. The Liquiñe–Ofqui fault system (LOFS) domain encompasses geothermal areas located either along the master or subsidiary faults. These are favourably orientated for shear and extension, respectively. In the LOFS domain, the geochemistry of hot spring discharges is controlled by interaction with the crystalline basement, and is characterized by low B/Cl conservative element ratios and high pH. In marked contrast, the arc-oblique long-lived fault systems (ALFS) domain includes geothermal occurrences located on the flanks of volcanoes forming WNW-trending alignments; these systems are built over faults that promote the development of crustal magma reservoirs. Unlike the first domain, the fluid chemistry of these geothermal discharges is strongly controlled by volcanic host rocks, and is typified by lower pH and higher B/Cl ratios. Reaction path modelling supports our model: chemical evolution of geothermal fluids in the Villarrica–Chihuio area is strongly dependent on structurally controlled mechanisms of heat transfer. Within this framework, heat transfer by conduction is responsible for the LOFS domain, whereas magmatically enhanced advective transport dominates heat flow in the ALFS domain. Although more studies are needed to constrain the complex interplay between tectonics and fluid flow, results from this study provide new insights towards efficient exploration strategies of geothermal resources in Southern Chile.     

大兴安岭诺敏河石榴石橄榄岩捕虏体的发现及其地质意义

在重力梯度带北端的大兴安岭诺敏河第四纪火山岩中发现石榴石相和尖晶石相地幔橄榄岩捕虏体,其矿物组成分别为Ol_40~55Opx_20~35Cpx_0~10Grt_5~25和Ol_45~65Opx_30~40 Cpx_0~15Sp_0~10。两种地幔相橄榄岩均以方辉橄榄岩为主,说明研究区上地幔具有难熔的特点。其高Mg^#橄榄石Fo_91~92和高Cr^#_31~47尖晶石特征与南区哈河的地幔橄榄岩特征一致。在橄榄石含量与Fo图解上,敏河橄榄岩包体落在太古代和元古代地幔区域,揭示大兴安岭地区岩石圈地幔可能保留了较多古老的残余地幔。根据石榴石橄榄岩的平衡温压条件(1114~1168℃和2.14~2.33GPa),推测来源深度为70~75km。这些数据暗示研究区具有较高的地温梯度,与中国东部新生代火山岩区的地温梯度相似。     

DMS and its oxidation products in the remote marine atmosphere: implications for climate and atmospheric chemistry

DMS emitted into the atmosphere over the global oceans has a range of effects upon atmospheric composition (mediated through various oxidation products) that may be significant with regard to issues as important as climate regulation, and the trace gas oxidation capacity of the marine atmospheric boundary layer. The roles played by DMS oxidation products within these contexts are diverse and complex, and in many instances are not well understood. Here we summarize what is known, and suspected, about the couplings between the marine atmospheric sulfur cycle, other atmospheric chemical cycles, and the dynamics and microphysics of the marine atmospheric boundary layer. This overview focuses heavily on measurements carried out in clean Southern Ocean air masses in association with the Australian Baseline Air Pollution Station located at Cape Grim (40° 40′ 56″S, 144° 41′ 18″ E), Tasmania. The data confirm that in the remote marine atmosphere, DMS is a central player in a variety of important atmospheric processes, reinforcing the need to understand quantitatively the factors that regulate DMS emissions from the ocean to the atmosphere.     

瓦里关大气降水的化学特征

利用2007—2009年瓦里关本底台降水化学观测资料,分析了瓦里关降水的pH值、电导率及Cl-、NO-3、SO2-4、NH+4、K+、Na+、Ca2+、Mg2+等离子成分的分布特征。结果表明,瓦里关pH值和电导率的年平均值分别为6.60和21.26μs/cm,2007—2009年呈逐年升高趋势。根据pH值,瓦里关降水以中性降水为主,占总降水的65.13%,其次为碱性降水,酸雨最少。离子浓度大小排序依次为Ca2+SO2-4Na+NH+4Cl-Mg2+NO-3K+,且存在明显的季节变化特征,K+、Na+、Ca2+、Mg2+有相似的来源。瓦里关降水中SO2-4/NO3-的范围为0.35~16.48,平均值为3.07;2007—2009年SO2-4/NO-3值呈逐年下降趋势;SO2-4/NO-3全年存在两个峰值,分别在4月和9—10月。     

Identification of the source caldera for the Middle Miocene ash-flow tuffs in the Kii Peninsula based on apatite trace-element composition

A large caldera cluster consisting of at least four calderas (Omine, Odai, Kumano-North and Kumano calderas) existed in the central–southern part of the Kii Peninsula approximately 14–15 Ma. On the other hand, thick Middle Miocene ash-flow tuffs, referred to as the Muro Ash-flow Tuff and the Sekibutsu Tuff Member, are distributed in the northern part of the Kii Peninsula. Although these tuffs are considered to have erupted from the caldera cluster in the central-southern Kii Peninsula, identifying the source caldera in the cluster has been controversial because of similarities in the petrological characteristics and identical radiometric ages of the volcaniclastic rocks of these calderas. We successfully discriminated the characteristics of the eruptive products of each caldera in the caldera cluster based on the apatite trace-element compositions of the pyroclastic dikes and ash-flow tuffs of the calderas. We also demonstrated that the source caldera of at least the lower main part of the Muro Ash-flow Tuff and the Sekibutsu Tuff Member was the Odai Caldera, which is located in the central Kii Peninsula. Our findings show possible correlations among the pyroclastic conduits and ash-flow tuffs of the caldera-fill and/or outflow deposits, even in cases where they have been densely welded and diagenetically altered. This method is useful for the study of deeply eroded ancient calderas.