Collisional excitation of interstellar cyclopropenylidene

Theoretical rotational excitation rates were computed for C3H2 in collisions with He atoms at temperatures from 30 to 120 K. The intermolecular forces were obtained from accurate self-consistent field and perturbation theory calculations, and collision dynamics were treated within the infinite-order sudden approximation. The accuracy of the latter was examined by comparing with the more exact coupled states approximation.     

关于青藏高原冈底斯带岩浆作用的进一步研究

岩浆岩及其所携带的深源岩石包体的研究与地质学与地球物理学研究相结合,发挥着深部"探针"和"窗口"作用.青藏高原岩浆岩的研究,始终围绕着高原形成演化过程中壳幔各圈层物质与能量的交换-调整-再分配(方式、时限、通量)这一中心科学问题.     

The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

The abundance and 13C/12C ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 degrees C and 600-650 degrees C is interpreted to be secondary, and only the carbon recovered during a final combustion step at approximately 1200 degrees C is thought to be indigenous to the samples. For carbon released at approximately 1200 degrees C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta 13C values of -4.8 to -9.3%, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta 13C values of -6.1 to -9.2%. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta 13C ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta 13C values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.     

西藏林周盆地林子宗火山岩研究近况

在过去工作的基础上 ,于 2 0 0 1年 7— 8月对西藏林周盆地进行了 1∶5万火山地质填图 ,取得了一些新的发现和进展。(1)地层方面 :在盆地西部凯布乡一带的典中组底部发现了厚层酸性火山碎屑岩 ,其成分和厚度都有一定程度的变化 ,向上与厚层安山岩直接接触 ;在白定乡西山发现典中组安山岩自西向东尖灭 ,其流动构造显示向北东 30°方向流动 ;在典中村东的典中组安山岩及凝灰岩中发现湖相火山质沉积夹层 ,火山物质以酸性为主 ,其厚度 10余米 ;在强嘎乡至冲嘎村一带的典中组顶部发现具有红色泥岩沉积 ,以安山质火山岩呈互层状产出 ,其厚度向西增…     

西秦岭大店沟金矿成矿流体演化及矿床成因

大店沟金矿是西秦岭成矿带近年来新发现的中型金矿床,金矿体赋存在下古生界丹凤群木其滩组绢云绿泥石英片岩中,叠加在北东东向脆韧性剪切带中的脆性构造为成矿结构面。在总结控矿地质特征的基础上,通过开展系统的流体包裹体、稳定同位素地球化学研究及成矿流体演化、矿床成因探讨,认为成矿期共分半自形黄铁矿、它形粒状黄铁矿、石英多金属硫化物和碳酸盐-黄铁矿4个成矿阶段,其中它形黄铁矿阶段和石英多金属硫化物阶段为最主要成矿阶段。流体包裹体类型以水溶液包裹体、CO₂三相包裹体和纯CO₂包裹体为主,成矿温度集中在120~256 ℃之间,成矿流体盐度为4.03%~15.27%。H-O同位素研究显示成矿热液主要为变质水混合大气降水,S同位素组成特征表明成矿物质来自深源;流体不混溶和沸腾作用是金沉淀的主要机制,矿床成因类型为造山型金矿。通过成矿结构面舒缓波状特征规律总结,判断成矿流体沿成矿结构面自南西深部向北东浅部运移、沉淀,形成分段富集矿化。     

澜沧江南带三叠纪火山岩岩石学、地球化学特征、Ar-Ar年代学研究及其构造意义

滇西三江地区澜沧江南带广泛发育三叠纪火山岩。在北部云县一带,中晚三叠世火山岩出露齐全,自下而上可划分为中三叠统忙怀组(T₂m),上三叠统小定西组(T₃x)和上三叠统芒汇河组(T₃mh)。忙怀组以酸性火山岩为主,为一套流纹岩夹火山碎屑岩组合;小定西组发育为中基性火山熔岩夹火山碎屑岩;芒汇河组具有流纹质火山碎屑岩与玄武岩共存的"双峰式"火山岩特征。地球化学特征表明,南澜沧江带三叠纪火山岩具有弧火山岩与大陆板内火山岩的双重属性,推测其形成环境为过渡型的大陆边缘造山带环境。对南澜沧江带南部景洪附近采集到的石英安山岩样品进行Ar-Ar年龄测试,得到的坪年龄为236.7±2.2Ma,为中三叠世。结合火山岩年代学结果,推测澜沧江洋主碰撞期为早三叠世,中三叠世与晚三叠世早期分别为碰撞后的应力松弛阶段与洋盆继续俯冲期,到晚三叠世末期,俯冲作用结束,澜沧江洋关闭。     

太行山南段教场闪长岩矿物学特征及其地质意义

太行山南段中生代杂岩体的成因与演化是近几十年来探索的热点话题之一.基于野外调研和电子探针分析,对教场闪长岩的矿物学特征及其意义进行了研究.该闪长岩主要由斜长石、普通角闪石、黑云母、少量单斜辉石和橄榄石组成.SiO₂含量为52.91%~53.39%,具有高Mg#[100×Mg/（Mg+Fe2+）]值（60.28~62.39）、富Na（Na₂O/K₂O=1.18~1.40）特征.斜长石An介于36~60,属于中长石和拉长石,具正环带结构,含量约50%.角闪石具有高CaO（>10%）、MgO（>18%）特征,属富镁普通角闪石,含量约30%.黑云母Mg#[Mg/（Mg+Fe2++Fe3++Mn）]值为0.564~0.582,属镁质黑云母,含量约12%.单斜辉石均属Ca-Mg-Fe辉石族,含量约5%,为幔源岩浆在由深部向浅部运移过程中逐步结晶的产物.橄榄石Fo在76~91,为贵橄榄石和镁橄榄石,含量约2%,属地幔捕虏晶.通过单斜辉石温压计计算获得其岩浆结晶温度为1 060~1 094℃,压力为0.24~0.55 GPa.结果表明,岩浆源区壳幔混源特征,在岩浆上升侵位过程中,发生了弱结晶分异作用.教场闪长岩体现古太平洋板块俯冲及华北克拉通内部伸展的叠加构造背景.      

西藏日喀则地区德村-昂仁蛇绿岩内基性岩的元素与Sr-Nd-Pb同位素地球化学及其揭示的特提斯地幔域特征

系统研究了西藏雅鲁藏布江蛇绿岩带中部日喀则地区德村、吉丁和昂仁蛇绿岩中基性岩石的元素与 Sr-Nd-Pb 同位素地球化学特征。这些基性岩石,包括玄武岩、辉长岩和辉绿岩,属于低钾拉斑玄武岩系列,球粒陨石标准化稀土元素分配模式为轻稀土元素亏损的 N-MORB 型,(La/Yh)_N=0.31～0.65(除样品 DC993为1.17)。在原始地幔标准化微量元素图上,亏损高度不相容元素,与 N-MORB 配分模式一致。相对于 Th,无 Nb、Ta的亏损,显示样品不是产于 SSZ 环境。经构造环境图解判别,样品落入了 N-MORB 区域内;这些元素成分特征表明样品具有洋中脊环境或成熟的弧后盆地环境属性。Sr、Nd 和 Pb同位素组成特征表明特提斯地幔源区以 DM(亏损地幔)为主,同时存在少量 EMⅡ(富集地幔类型Ⅱ)、Sr,Nd 和 Pb 同位素组成特征还表明特提斯地幔域具有印度洋 MORB 型的 Sr-Nd-Pb 同位素组成特征。本文的结果进一步支持 Zhang et al.(2005)的研究结果,现今印度洋不仅在地理位置上占据了曾经是特提斯洋的大部分,而且它的地幔域还继承了曾经特提斯的地幔域的地球化学特征。     

Preservation of biological information in thermal spring deposits: developing a strategy for the search for fossil life on Mars

Current interpretations of the early history of Mars suggest many similarities with the early Earth and therefore raise the possibility that the Archean and Proterozoic history of life on Earth could have a counterpart on Mars. Terrestrial experience suggests that, with techniques that can be employed remotely, ancient springs, including thermal springs, could well yield important information. By delivering water and various dissolved species to the sunlit surface of Mars, springs very likely created an environment suitable for life, which could have been difficult, if not impossible, to attain elsewhere. The chemical and temperature gradients associated with thermal springs sort organisms into sharply delineated, distinctive and different communities, and so diverse organisms are concentrated into relatively small areas in a predictable and informative fashion. A wide range of metabolic strategies are concentrated into small areas, thus furnishing a useful and representative sampling of the existing biota. Mineral-charged springwaters frequently deposit chemical precipitates of silica and/or carbonate which incorporate microorganisms and preserve them as fossils. The juxtaposition of stream valley headwaters with volcanoes and impact craters on Mars strongly implies that subsurface heating of groundwater created thermal springs. On Earth, thermal springs create distinctive geomorphic features and chemical signatures which can be detected by remote sensing. Spring deposits can be quite different chemically from adjacent rocks. Individual springs can be hundreds of meters wide, and complexes of springs occupy areas up to several kilometers wide. Benthic microbial mats and the resultant stromatolites occupy a large fraction of the available area. The relatively high densities of fossils and microbial mat fabrics within these deposits make them highly prospective in any search for morphological evidence of life, and there are examples of microbial fossils in spring deposits as old as 300 Myr.     

太行山木吉村斑岩铜(钼)矿床岩石地球化学、Sr-Nd-Pb同位素特征及其地质意义

木吉村斑岩铜(钼)矿床位于太行山北段涞源杂岩体的腰部,是太行山构造-岩浆-成矿带的一个重要矿床。在野外调研的基础上,对木吉村斑岩铜(钼)矿床含矿岩体进行了系统的岩石学、地球化学和Sr-Nd-Pb同位素研究。结果表明：木吉村矿床的含矿岩体闪长玢岩为高钾钙碱性I型侵入岩,具有较高的SiO₂、Al₂O₃、Sr含量和Sr/Y比值以及(La/Yb)_N,较低的Yb、Y的特征;稀土元素配分曲线呈右倾趋势,轻稀土相对富集,轻重稀土分异明显,具微弱的正Eu异常;微量元素蛛网图中富集大离子亲石元素Ba、K、U、Sr,亏损高场强元素Nb、Ta、P、Ti,总体显示出与埃达克岩相似的地球化学特征。闪长玢岩的I_Sr为0.705 386~0.706 838,ε_Nd(t)为-16.7~-14.9,²⁰⁸Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb、²⁰⁶Pb/²⁰⁴Pb的平均值分别为36.614、15.226、16.545,与木吉村矿床矿石中的硫化物铅同位素数值基本一致,Sr-Nd-Pb同位素共同表明其岩浆形成可能与有深源基性物质参与的古老下地壳部分熔融有关。结合研究区地质背景,认为木吉村含矿岩体可能主要来自古老下地壳的部分熔融,并受到幔源物质的混染作用。