印尼西爪哇Pongkor矿床:上新世浅成低温热液型Au-Ag-(Mn)矿床

Pongkor矿床属于浅成低温热液 Au- Ag矿床 ,金储量至少为 98t,平均品位为 16 .4× 10 -6;银储量10 2 6 t,平均品位 171.2× 10 -6.它是印尼新近发现的规模较大的 Au- Ag矿床 .冰长石 4 0 Ar/3 9Ar成矿年龄值为 2 .0 5± 0 .5Ma.矿床属于低硫化物浅成低温热液型 ,含有 4条主要的石英脉矿体 .石英脉主要位于火山构造凹陷 (破火山口 )的内缘 ,形成于爆破溶结凝灰岩的喷发 .该喷发产生了火山碎屑熔岩、火山砾及少量碎屑岩夹层 ,构成区内火山岩组合 ,不整合覆盖于中新世安山岩之上 .矿床矿体厚度较大 ,平均厚度为 4 .2 m,陡倾斜 ,由石英、方…     

中国岩石风化作用所致的碳汇能力估算

岩石的风化作用同时参与了短时间尺度和长时间尺度的全球碳循环 ,对碳酸盐岩而言 ,它的风化作用在短时间尺度上对大气二氧化碳循环具有重要影响 ,但在长时间尺度上不产生净碳汇 ;而硅酸盐岩等其他类型岩石的风化过程由于反应速率较慢 ,在短时间尺度上对全球碳循环及其变化反应不灵敏 ,但它所产生的净碳汇是遗漏汇的组成之一 .为了准确估计我国岩石风化所致的碳汇能力 ,简要评价了现有的各种模型和方法 ,并基于GEM -CO2 模型进行了计算 .计算结果表明 ,我国岩石每年因溶蚀、风化作用共消耗的CO2 约为 4 .72× 10 7t,折合成C为 1.4 1× 10 7t,其中由碳酸盐类岩石风化消耗的碳量最多 ,约为 0 .74× 10 7t/a ,占总量的 5 2 .6 5 % .硅酸盐岩及其他类型岩石风化消耗的碳量约为 0 .6 7× 10 7t/a ,占总量的 4 7.35 % .岩石风化所致碳汇能力的空间分布首先取决于岩石类型 ,其次受地区的气候条件控制 .     

宁芜向山式硫铁矿地质及矿床成因新探

宁芜具有高地热场的火山断陷盆地 ,形成于晚侏罗世 ,消亡于晚白垩世。该盆地火山活动形成的龙王山、大王山、姑山和娘娘山 4个喷发旋回 ,堆积了厚约 2 5 0 0m的陆相中基性酸性碱性火山岩系 ,在晚侏罗世沉积了硬石膏、硫铁矿层。硫铁矿在沉积特征上具有热水沉积的由稀粗转为细密的条纹—条带状构造及喷发角砾岩和硅质岩特征。电子探针所测之黄铁矿中铁的平均含量 4 5 .85 % ,硫的平均含量 5 3 .5 9% ,具有富S特征 ;稀土元素总量平均 2 .2 0× 10 -6 ～ 17.3 9× 10 -6 ,平均为 7.2 9× 10 -6 ,具有明显的负铈异常 (δCe:0 .4 9～ 0 .93 )。硫同位素组成δ34 S常见值为 10‰～ 2 3‰ ,以富重硫为特征。通过对硅质岩、硬石膏岩等常量与微量、稀土元素和稳定同位素分析结果来看 ,均表现出热水沉积的特点 ,热水沉积在向山式高品位优质硫铁矿矿床形成过程中 ,占据重要的地位。     

宁芜云台山黄铁矿矿床中黄铁矿矿物的初步研究

宁芜云台山黄铁矿矿床中黄铁矿矿物以自形晶为主 ,次为他形粒状 ;黄铁矿晶胞参数为 5 .415 2 3～ 5 .41843× 10 -10 m ,晶体化学式为 (Fe0 .9968Co0 .0 0 0 6Ni0 .0 0 2 6) 1.0 0 0 0 S2 .0 597;黄铁矿红外吸收光谱主吸收峰值为 34 8cm-1,最小透过率为 30 .0 0 %～ 48.80 % ,透过率极差为 31.13～ 47.5 1;黄铁矿中Fe平均含量为 45 .44 % ,S平均含量 5 3.91% ,具有富S特征 ;Co/Ni平均值为 0 .2 1;稀土元素总量平均为2 1.84× 10 -6,具有明显负铈异常 (δCe :0 .76～ 0 .93)和负铕异常 (δEu :0 .72～ 0 .90 ) ;硫同位素组成δ3 4S为 7.0 0‰～ 2 3.0 0‰ ,黄铁矿是含矿热液以堆积、充填和交代方式形成 ,黄铁矿床为火山热水沉积矿床。     

全球气候变化对中国土地荒漠化的影响

当前 ,土地荒漠化正困扰着全人类的生存和发展 ,并被列为影响全球环境的十大问题之首。在不计极端干旱区的情况下 ,目前全球有 3 6× 10 9ｈｍ2 干旱区土地直接受到荒漠化的危害 ,约占全球干旱土地的 70 %,接近全球陆地面积的1/4 (宁大同等 ,1996 )。据联合国环境规划署估算 ,目前全球荒漠化每年仍以 5 0× 10 4 ～ 7 0× 10 4 ｈｍ2 的速度不断扩展(周欢水等 ,1998) ,由此造成的直接经济损失达 4 2 3× 10 1 0 美元 ,其间接经济损失是直接经济损失的 2～ 3倍 ,甚至 10倍(杨朝飞 ,1997)。中国是世界上荒漠化危害范围最广、程度最深的地区之…     

阿拉善地块南缘镁铁-超镁铁岩形成时代及地球化学特征

阿拉善地块南缘是镁铁超镁铁岩体的重要分布区 ,自北而南可分为北大山岩带、龙首山岩带和北海子岩带。北大山岩带以野芨里含长辉石橄榄岩侵入体为代表 ,Sm_Nd岩石矿物等时线年龄为 773.1± 10 .8Ma,εNd(t)=+0 .8～ +10 .8,ΣREE为 7.5 9× 10 -6～ 2 0 .34× 10 -6;龙首山岩带以金川二辉橄榄岩体和藏布台单辉橄榄岩为典型代表 ,Sm_Nd岩石矿物等时线年龄分别为 15 0 8± 31Ma和 15 11± 16 8Ma ,基本为同期幔源产物 ,金川岩体平均ΣREE为 3.33× 10 -6～ 115 .5 2× 10 -6,εNd(t) =- 1.9～ - 4 .3,藏布台εNd(t) =+2 .6～ +2 .9,差异显著 ;北海子岩带岩体分布有限 ,其中辉长岩体Sm_Nd岩石矿物等时线年龄为 14 4 0± 2 2 0Ma ,εNd(t) >0 ,ΣREE为 179.6 4× 10 -6～ 2 0 7.76× 10 -6。龙首山岩带和北海子岩带可能同为中元古代早期超地幔柱作用下地幔派生岩浆的产物 ,εNd(t)值的差异反映了各自岩体成岩过程的不同 ;野芨里岩体形成于新元古代 ,是亏损地幔的产物 ,与金川等岩体的形成环境和物质来源有显著不同。     

银川盆地中更新世以来的孢粉植物群古气候旋回探讨

利用银川地区孢粉时间序列的随机数字滤波分析的研究成果 ,应用频谱分析方法探讨银川盆地孢粉植物群气候波动特征 ,确定 0 .80MaB .P .以来存在 6 0× 10 4 a、30× 10 4 a、10 (或 6 )× 10 4 a的准周期 ,依据孢粉植物群的时空分布建立了该区多重气候旋回模型。该模型将该区 0 .80MaB .P .以来的气候划分为 1个 0 .6 0Ma的气候幕 ,3个 0 .30Ma的气候期 ,10个 0 .10 (0 .0 6 )Ma的气候段。并且讨论了模型与自然环境演变的关系 ,指出 0 .80～ 0 .5 5MaB .P .期间为冷凉旋回 ,0 .5 5～ 0 .2 0MaB .P .期间为暖温旋回 ,0 .2 0MaB .P .～今为冷凉旋回     

张家口中生代火山盆地火山喷发对古气候的影响

本文在详细地研究了张家口中生代火山盆地火山喷发物的基础上,利用岩石学及大气环境化学的基本原理,提出了一套系统估算火山喷出气体及气溶胶总量的程序与方法,并对张家口中生代火山喷出气体的种类、总量及气溶胶总量进行了估算;分析了火山硫化物气体转化为火山硫酸盐气溶胶的光化学过程及可能途径。在分别研究了本区火山喷发导致的“阳伞效应”与“温室效应”的基础上,探讨了该区火山喷发对地表温度的综合影响。初步结果表明：张家口中生代火山盆地火山喷发向当时大气圈中输送了约９．９６×１０１０ｋｇ的硫酸盐气溶胶,它们能导致当时北半球范围内太阳总幅射率降低０．８１％～３．６０％,最终造成地表温度下降约０．８１℃～３．６℃。     

黄土中碳酸盐含量变化及其古气候记录——以兰州红咀寺剖面为例

以兰州红咀寺剖面为例 ,以 2 cm的间隔采样 ,进行了碳酸盐含量的测定 ,获得数据 892个 ,与其它古气候指标 (磁化率、有机碳总量 )进行对比后揭示了该地区近 3 0× 10 3 a来气候变化的频率及突变事件。3 0× 10 3 a以来主要可以分为 4个阶段 :暖湿期(3 3× 10 3 ～ 40× 10 3 a B.P.)、凉偏干期 (3 0× 10 3 ～ 2 7× 10 3 a B.P.)、寒冷干燥期 (2 7× 10 3 ～ 10× 10 3 a B.P.)、暖湿期 (10× 10 3 ～ 3× 10 3 a B.P.) ,各阶段中气候快速变化明显     

全球火山活动分布特征

根据全球活动火山目录 ,分析研究了全球火山分布的特征 ,描述了各区的火山活动分布 ,总结了火山活动强度的时、空分布特征。全球火山活动可分为三大区 ,西太平洋火山活动区 ,主要与太平洋板块向北西西方向的俯冲活动有关 ;东太平洋火山活动区 ,主要与太平洋东面的小板块 (胡安德富卡板块、科科斯、纳斯卡板块 )向美洲板块的俯冲有关 ;大西洋火山活动区 ,与大西洋和非洲的裂开 ,以及地中海带的活动有关。不同火山区带具有各自的最大喷发等级与相应的复发周期。一条火山弧上活动强度的分布往往是不对称的 ,意味着火山弧在整体上有其动力学的控制机理。火山活动显示了随纬度成带状分布。在 - 10～ 0° ,10 2 0° ,30 4 0°,5 0 6 0°分布有高值带。火山喷发活动还与当地的重力势有关 ,重力势正异常可能与高的正压力有关 ,有利于产生特大喷发。火山活动与大角度的正面俯冲带的弧后火山活动最强 ,当板块运动方向与板块边缘走向成小角度相交时 ,缺少正面俯冲的动力 ,火山活动相对平静。     

全球变化背景下新疆地区气候跃变的可能影响因素分析

基于新疆过去50a气温和降水时间序列长期趋势的研究结果,结合对1986年及附近时段对全球气候产生重大影响的一系列事件（厄尔尼诺、火山爆发、核电站爆炸事故、温室气体增加等）的分析,探讨了1986年新疆气温和降水出现跳跃式变化的原因.具体表现为：当厄尔尼诺现象发生时,常常出现暖冬、早春,在该现象消退过程,往往降水有所增多;...     

长白山天池火山近代喷发中气象站组熔岩—碎屑岩流研究

中晚全新世以来,长白山天池火山的活动多为爆炸性喷发和形成火山碎屑流,熔岩流出较少,气象站组熔岩—碎屑岩流则是为数不多的熔岩溢流活动之一,它是天池火山一个寄生火山的喷发产物。气象站组熔岩—碎屑岩流的岩性为碱流岩质,岩浆粘度大,流动缓慢。据研究其喷发时间大约4 ka BP,应属天池火山的近代喷发产物。     

Glacier Peak,Washington: A potentially hazardous cascade volcano

Recent field studies of postglacial volcanic deposits at Glacier Peak indicate the volcano has erupted more often, more voluminously, and more recently than previously thought. These past eruptions produced pyroclastic flows, extensive lahars, and widely distributed tephra falls. Analysis of the magnitude of past eruptions and the distribution of volcanic sediments indicates that future eruptions at Glacier Peak as large as those of the last several thousand years would dramatically affect people and property downstream and downwind from the volcano. Pyroclastic flows and lateral blasts would primarily affect uninhabited valleys within a few tens of kilometers of the volcano. Lahars and floods constitute the major hazard to populated areas from future eruptions, and could affect areas at low elevation along valley floors and in the Puget lowland as far as 100 km downvalley west of the volcano. Air-fall tephra from future eruptions will probably be deposited primarily east of Glacier Peak because of prevailing westerly winds.     

四海龙湾玛珥湖沉积物中碱流质火山灰的来源及其意义

四海龙湾玛珥湖位于东北新生代龙岗火山区内,在玛珥湖沉积物距湖底69-70cm处分离出新鲜的火山灰。根据火山灰产出的层位、原生沉积特征、形貌和碱流质化学成分特征,属于长白山天池火山公元1199-1200年大喷发的产物。这一结果不仅表明天池火山历史时期大喷发的规模比原来估计的还要大,并且为建立千年以来四海龙湾沉积物及古气候演化的时间标尺提供了依据。     

Potential Hazards of Eruptions around the Tianchi Caldera Lake, China

Since the eruption of the Tianchi volcano about 1000 years ago, there have been at least 3 to 5 eruptions of small to moderate size. In addition, hazardous avalanches, rock falls and debris flows have occurred during periods between eruptions. A future eruption of the Tianchi volcano is likely to involve explosive interaction between magma and the caldera lake. The volume of erupted magma is almost in a range of 0.1-0.5 km3. Tephra fallout may damage agriculture in a large area near the volcano. If only 1% of the lake water were ejected during an eruption and then precipitated over an area of 200 km2, the average rainfall would be 100 mm. Moreover, lahars are likely to occur as both tephra and water ejected from the caldera lake fall onto flanks of the volcano. Rocks avalanching into the caldera lake also would bring about grave hazards because seiches would be triggered and lake water with the volume equal to that of the landslide would spill out of the existing breach in the caldera and cause flooding     

Unusual eruption of the Main Pugachevo gas-water-lithoclastic (Mud) volcano in Sakhalin during the Winter of 2005

The examination of the Main Pugachevo gas-water-lithoclastic volcano during the summer of 2005 and GPS-controlled large-scale (1: 1000) mapping revealed its regular but rather peculiar eruption. It was the largest among the eruptions investigated since 1911 and produced a very unusual lithoclastic field with an area of about 100 000 m² and a volume of about 100 000 m³. The eruption occurred from three distinct active centers and began with a vigorous explosion-like gas burst from one center followed by the noncontemporaneous discharge of a gas-and water-saturated liquid lithoclastic mass from the three centers, which produced a number of flows of different directions and sizes. The flows almost completely covered the smoothed flat open area of the volcano and even invaded the larch forest surrounding the volcano, where they bent, overturned, broke, and occasionally uprooted and dragged over some distance some large trees. The analysis and comparison with all the previously documented eruptions of the Main Pugachevo gas-water-lithoclastic volcano revealed their fairly diverse, sometimes strongly variable character with respect to many parameters: the amount of ejected lithoclastic material; the number of eruption centers; and the proportions of the erupted gaseous, liquid, and solid components. In general, the eruptions show a distinctly multirank periodic character: relatively minor or small low-rank eruptions take place once every 1–2 yr, and large eruptions of a higher rank are much less frequent (supposedly, once in 70 years).     

An estimate of the juvenile sulfur content of basalt

Sulfur analyses by X-ray fluorescence give an average content of 107 ppm for 9 samples of fresh subaerially-erupted oceanic basalt and 680 ppm for 38 samples of submarine erupted basalt. This difference is the result of retention of sulfur in basalt quenched on the sea floor and loss of sulfur in basalt by degassing at the surface. The outer glassy part of submarine erupted basalt contains 800±150 ppm sulfur, and this amount is regarded as an estimate of the juvenile sulfur content of the basalt melt from the mantle. The slower cooled interiors of basalt pillows are depleted relative to the rims owing to degassing and escape through surface fractures. Available samples of deep-sea basalts do not indicate a difference in original sulfur content between low-K tholeiite, Hawaiian tholeiite, and alkali basalt.The H₂O/S ratio of analyzed volcanic gases is generally lower than the H₂O/S ratio of gases presumed lost from surface lavas as determined by chemical differences between pillow rims and surface lavas. This enrichment of volcanic gases in sulfur relative to water may result from a greater degassing of sulfur relative to water from shallow intrusive bodies beneath the volcano.Publication authorized by the Director, U.S. Geological Survey.     

火山活动与气候变化研究进展

综述了火山活动对气候影响的研究进展。不同岩浆成分及喷发类型的火山活动对气候的影响不同：中酸性普林尼（Pl inian）式火山喷发主要造成气候变冷和臭氧层破坏，它导致气候变化的时间较短，但空间范围较大；大火成岩省造成气候变化的时空范围及程度均较大，它能够导致地表温度、海平面大幅度变化，最终引起生物灭绝；中小规模玄武质裂隙式喷发主要造成火山盆地内气候较大幅度变化，但对气候影响的持续时间较短，主要气候效应是导致附近地区温度快速下降和形成酸雨。简要阐述了第四纪火山活动的特点。     

Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr

Many years of low growth identified in a western USA regional chronology of upper forest border bristlecone pine (Pinus longaeva and Pinus aristata) over the last 5000 yr coincide with known large explosive volcanic eruptions and/or ice core signals of past eruptions. Over the last millennium the agreement between the tree-ring data and volcano/ice-core data is high: years of ring-width minima can be matched with known volcanic eruptions or ice-core volcanic signals in 86% of cases. In previous millennia, while there is substantial concurrence, the agreement decreases with increasing antiquity. Many of the bristlecone pine ring-width minima occurred at the same time as ring-width minima in high latitude trees from northwestern Siberia and/or northern Finland over the past 4000-5000 yr, suggesting climatically-effective events of at least hemispheric scale. In contrast with the ice-core records, the agreement between widely separated tree-ring records does not decrease with increasing antiquity. These data suggest specific intervals when the climate system was or was not particularly sensitive enough to volcanic forcing to affect the trees, and they augment the ice core record in a number of ways: by providing confirmation from an alternative proxy record for volcanic signals, by suggesting alternative dates for eruptions, and by adding to the list of years when volcanic events of global significance were likely, including the mid-2nd-millennium BC eruption of Thera.     

Geochemical characterization of marker tephra layers from major Holocene eruptions,Kamchatka Peninsula,Russia

Kamchatka Peninsula is one of the most active volcanic regions in the world. Many Holocene explosive eruptions have resulted in widespread dispersal of tephra-fall deposits. The largest layers have been mapped and dated by the ¹⁴C method. The tephra provide valuable stratigraphic markers that constrain the age of many geological events (e.g. volcanic eruptions, palaeotsunamis, faulting, and so on). This is the first systematic attempt to use electron microprobe (EMP) analyses of glass to characterize individual tephra deposits in Kamchatka. Eighty-nine glass samples erupted from 11 volcanoes, representing 27 well-identified Holocene key-marker tephra layers, were analysed. The glass is rhyolitic in 21 tephra, dacitic in two, and multimodal in three. Two tephra are mixed with glass compositions ranging from andesite/dacite to rhyolite. Tephra from the 11 eruptive centres are distinguished by their glass K₂O, CaO, and FeO contents. In some cases, individual tephra from volcanoes with multiple eruptions cannot be differentiated. Trace element compositions of 64 representative bulk tephra samples erupted from 10 volcanoes were analysed by instrumental neutron activation analysis (INAA) as a pilot study to further refine the geochemical characteristics; tephra from these volcanoes can be characterized using Cr and Th contents and La/Yb ratios.

Unidentified tephra collected at the islands of Karaginsky (3), Bering (11), and Attu (5) as well as Uka Bay (1) were correlated to known eruptions. Glass compositions and trace element data from bulk tephra samples show that the Karaginsky Island and Uka Bay tephra were all erupted from the Shiveluch volcano. The 11 Bering Island tephra are correlated to Kamchatka eruptions. Five tephra from Attu Island in the Aleutians are tentatively correlated with eruptions from the Avachinsky and Shiveluch volcanoes.