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71.
72.
本章系统研究石源龙地区流纹质熔结凝灰岩、粒状碎斑熔岩、英安岩、星村中细粒黑云母花岗岩的铷锶同位素地质年龄,并根据锶、氧同位素和稀土元素含量讨论其地质意义 相似文献
73.
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
74.
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
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
75.
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
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
76.
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
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
77.
78.
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
79.
80.