A model study on the decay of volcanic aerosol layer and verification with Pinatubo and El Chichon data     

S. Ramachandran  A. Jayaraman  B. R. Sitaram 《Journal of Earth System Science》1997,106(3):157-167

The time evolution of stratospheric aerosol layer formed after a volcanic eruption is studied taking into account the aerosol microphysical processes of growth, coagulation and sedimentation. Using a simple model we could explain the observed evolution of the Pinatubo volcanic layer which decayed in about 3 years. The experimental data obtained by Nd:YAG backscatter lidar over Ahmedabad further supports this finding. The data obtained after the El Chichon volcanic eruption also showed that the El Chichon aerosol layer decayed in about 3 years time. Thus, though the amount of SO₂ injected has been higher, in the case of Pinatubo, about two to three times more than El Chichon, it has resulted in the production of larger aerosol particles due to faster growth and coagulation processes, and subsequently a faster removal rate, to give more or less a similar background aerosol amount at the stratosphere in about 3 years time.  相似文献   

The color of pumice: case study on a trachytic fall deposit, Meidob volcanic field, Sudan   总被引：1，自引：0，他引：1  

H. Paulick  G. Franz 《Bulletin of Volcanology》1997,59(3):171-185

 This paper examines the cause of color variations of trachytic pumices which are essentially uniform in chemical composition and proposes a geological model for their formation. A pyroclastic sequence of distinct subunits with brown, buff, and black pumices was deposited during the 5000-B.P. eruption of a tuff ring in the central Meidob volcanic field (Sudan). Subunits of buff pumices locally contain minor amounts of streaky pumice with pale-gray and dark-gray domains. The combined evidence of petrographic studies, chemical analyses of whole pumices and groundmass separates, electron microprobe analyses, optical spectroscopy, transmission electron microscopy, and magnetic susceptibility measurements show that color variations of the pumice clasts are related to the size and distribution of Fe³⁺-rich oxide microcrysts. Buff pumice and light-gray domains of streaky pumice have a colorless, transparent groundmass with very few microcrysts. Dark-gray domains of streaky pumice contain abundant hematite and/or magnetite microcrysts visible in thin section within a transparent, colorless glass groundmass. The groundmass of the black pumice clasts is brown in thin section which is most likely caused by submicroscopic magnetite microcrysts. Brown pumice clasts have a mixed groundmass consisting of brown domains and domains with opaque microcrysts in transparent glass. Variations in the eruption dynamics have been inferred from lithological observations. Subunits of black pumices are related to eruption pulses with low magma discharge and high water/magma mass ratio, whereas subunits of buff pumice were deposited during eruption pulses with high magma discharge and low water/magma mass ratio. Brown pumices represent the top part of the magma body, and the initial stage of the eruption probably had a low magma discharge. Streaky pumices are interpreted as the product of syn-eruptive mixing of Fe³⁺-rich oxide microcryst-bearing magma and microcryst-free magma. Received: 3 February 1997 / Accepted: 28 July 1997  相似文献   

陆相渐新统划分中的问题及新进展   总被引：18，自引：1，他引：18  

王伴月 《地层学杂志》1997,21(2):81-90

近年来国际上关于始新世－渐新世界线的研究取得了重大进展，其同位素年龄被确认为３４Ｍａ，北美哺乳动物年代表已据此重新厘定。通过对哺乳动物群的分析和对比，论证了我国原认为是早渐新世的乌兰戈楚期和呼尔井期的时代应改归晚始新世，原认为是中渐新世的三达河期的时代应为早渐新世。在亚洲始新世－渐新世的界线不是在乌兰戈楚期之末，而是在呼尔井期与三达河期之间。  相似文献   

福建沙县地区早白垩世火山岩成因及构造环境分析   总被引：1，自引：0，他引：1  

何文兴  马金清 《福建地质》1997,16(1):21-31

本文着重阐述了沙县地区早白垩世火山岩地球化学特征，论证了中性与酸性火山岩的成因及物质来源，认为二者为不同源岩浆演化的产物，其岩浆物质来源于壳幔混源区，为省内双峰式火两端员岩石间成因关系的分析研究提供了新的例征。  相似文献   

太白维山中生代火山岩特征及其与成矿的关系     

张连营  李兆龙  樊秉鸿  唐耀林  马丽华 《地质与资源》1997,6(2):101-113

晋北太白维山火山岩属钾质碱性玄武岩系列,产于板块内部活化带,来源于上地幔或下部地壳,被上部地壳物质混染,为壳幔源型或同熔型火山岩.火山岩与Ag(Pb、Zn)矿化关系密切,是成矿热液和矿质的主要来源之一.  相似文献   

益阳市矿泉水的基本特征及形成机理探讨     

卜鸿鹄 《湖南地质》1997,16(3):175-181

益阳市矿泉水是一种弱酸、弱碱性、低矿化、富含偏硅酸的ＨＣＯ３－Ｃａ天然优质饮料矿泉水。它赋存于武陵期海底裂隙式喷溢形成的基性火山岩－细碧玄武岩的构造断裂和半风化层的风化裂隙之中。矿泉水水量起源于多途，化学成分形成于多因，是多因复成的产物。  相似文献   

试论层序地层学在1∶5万区调工作中的应用—以浑江地区为例   总被引：2，自引：0，他引：2  

周晓东  殷长健  陈跃军 《吉林地质》1997,(2)

通过在吉南浑江地区开展的白山市等三幅１∶５万区调工作，尝试性地运用层序地层学的理论，初步总结了不同特征的不整合面（层序界面）及凝缩段的识别标志；分析了地层序列中矿产分布特征；探讨了层序分析中以剖面岩石（岩性、组构）、相转换界面的基础研究方法。进而将浑江地区新元古代—早古生代地层划分为三个Ⅱ级沉积序列（超层序）、七个Ⅲ级沉积序列（层序）。  相似文献   

长江源雀莫错-带上二叠统那益雄组火山岩特征及其构造环境   总被引：3，自引：0，他引：3  

白云山  李莉  牛志军  姚华舟  段其发 《华南地质与矿产》2004,(1):7-10

雀莫错一带那益雄组火山岩是由玄武岩组成的基性熔岩,岩石化学表现为低TiO2(<1％)和Al2O3,Na2O>K2O,属钙碱性系列。地球化学特征表现为轻稀土富集,Eu平坦或轻微负异常,富集大离子亲石元素(Rb,Sr,Ba,K)和高强场元素Th,亏损高强场元素Nb和Ta,反映了岛弧构造环境。上二叠统那益雄组岛弧型火山岩的发现,说明长江源地区晚古生代有岛弧存在,且该岛弧应为晚古生代特提斯洋向东俯冲在中北段形成的多岛-弧盆系统的一部分。  相似文献   

内蒙古满都拉泥盆纪基性火山岩特征及其形成环境   总被引：7，自引：0，他引：7  

白立兵  李玉玺  刘俊杰 《华南地质与矿产》2004,(3):50-54

满都拉西部出露的蛇绿混杂岩中橄榄辉长岩的单颗粒锆石U-Pb年龄(385.6±1.7)Ma,显示该蛇绿岩形成于早泥盆世晚期。其中的基性火山岩岩块为一套浅变质的枕状玄武岩、橄榄玄武岩,多与超基性岩岩块伴生。玄武岩的SiO2为47.16%～51.93%,TiO2为1.44%～2.13%,Al2O314.08%～17.51%,Na2O3.42%～5.39%,K2O0.22%～0.83%;具低钾特点,显示拉斑玄武岩特征。其富集大离子亲石元素Rb,Ba,Th和U,贫高场强元素Zr,Ti,Y等,似岛弧玄武岩或岛弧-洋中脊过渡型玄武岩或弧后盆地玄武岩。ΣREE为(113.130～189.560)×10—6,LREE/HREE为0.684～1.369,配分曲线呈右缓倾、平坦型,显示岛弧、洋中脊或E-洋中脊玄武岩特征。根据岩石学、岩石地球化学特征,结合区域构造背景,认为该套火山岩或该蛇绿岩的形成环境为弧后盆地。  相似文献   

藏南特提斯喜马拉雅带中段二叠纪-白垩纪的火山活动(Ⅰ):分布特点及其意义   总被引：12，自引：1，他引：12  

朱弟成潘桂棠  莫宣学廖忠礼江新胜  王立全 《地质通报》2004,23(7):645-654

在野外实地考察和追索的基础上，详细厘定了特提斯喜马拉雅带中段晚古生代以来火山岩的分布特点和迁移规律。结果表明，在特提斯喜马拉雅带中段晚古生代以来的地层系统中，从二叠纪→三叠纪→侏罗纪→白垩纪，共有11个层位含规模不等的火山岩，它们以透镜体、薄夹层或以块状玄武岩、玄武质安山岩等形式产出于不同地层系统中；从二叠纪→早中三叠世→晚三叠世→侏罗纪和白垩纪，具有由西向东、从南→北→南→北的迁移规律。这些火山活动的发现和厘定，对填补特提斯喜马拉雅带火山岩研究的空白，了解陆下岩石圈地幔和软流圈地幔之间的相互作用和新特提斯洋盆的形成演化都具有一定的指示意义。  相似文献