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531.
Syn-eruptive degassing of volcanoes may lead to syn-eruptive crystallization of groundmass phases. We have investigated this process using textural and compositional analysis of dome material from Merapi volcano, Central Java, Indonesia. Samples included dome lavas from the 1986–88, 1992–93, 1994 and 1995 effusive periods as well as pyroclastic material deposited by the November 1994 dome collapse. With total crystallinities commonly in excess of 70% (phenocrysts+microlites), the liquids present in Merapi andesites are highly evolved (rhyolitic) at the time of eruption. Feldspar microlites in dome rocks consist of plagioclase cores (Ab63An29Or8) surrounded by alkali feldspar rims (Ab53An5Or42), compositional pairs which are not in equilibrium. A change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition. A small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites, suggesting that the 1994 collapse event incorporated less-degassed, partially liquid magma in addition to fully solidified dome rock.As decompression drives volatile exsolution, rates of degassing and resultant microlite crystallization may be governed by magma ascent rate. Microlite crystallinity is nearly identical among the 1995 dome samples, an indication that similar microlite growth conditions (PH2O and temperature) were achieved throughout this extrusive period. However, microlite number density varied by more than a factor of four in these samples, and generally increased with distance from the vent. Low vent-ward microlite number densities and greater microlite concentrations down-flow probably reflect progressively decreasing rates of undercooling at the time of crystal nucleation during extrusion of the 1995 dome. Comparison between dome extrusion episodes indicates a correlation between lava effusion rate and microlite number density, suggesting that extrusion slowed during 1995. Crystal textures and compositions in the 1992–93 and 1994 domes share the range exhibited by the 1995 dome, suggesting that transitions in crystallization conditions (i.e., rates of undercooling determined by effusion rate) are cyclic. 相似文献
532.
笔者通过系统研究提出了定量晶体光学的概念。认为定量晶体光学是研究晶体在各种偏光装置下光学参数(亮度、颜色等)定量变化规律的一门科学。定量晶体光学的发展与摄象技术和计算技术的发展是分不开的。定量晶体光学研究有着深远意义,也有十分广阔的应用前景。 相似文献
533.
Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):585-596
This introductory paper aims at presenting the series of articles in this special issue of Comptes Rendus Geoscience devoted to the study and use of natural minerals. The research methodology that can be applied to the investigation of surface phenomena related to adsorption, exchange and retention onto the surface of natural minerals and divided solids is presented. A special focus is given to the retention of surfactant molecules, in view of their considerable importance in numerous industrial fields, such as, for instance, mineral flotation and enhanced oil recovery. Throughout this introductory paper, the relevance of this research approach to the field of geosciences is stressed by listing various applications where it can provide conclusive answers, especially for environmentally related issues. To cite this article: J.-M. Cases, C. R. Geoscience 334 (2002) 585–596. 相似文献
534.
Vapor-grown crystals intimately related to shock metamorphism of meteorites were found in the Yanzhuang (H6) chondrite which
had been heavily impacted in the space. These crystals include: (i) subhedral low-Ca pyroxene occurring on the wall of the
pores within a silicate melt pocket that experienced a shock temperature higher than 1500°C, (ii)Fe-Ni needle-whiskers (taenite)
occurring in the cracks in the partially melted chondritic facies that experienced a shock temperature of 850–1300°C, (iii)
troilite with abundant microholes occurring in the cracks in the brecciated facies and the lightly deformed chondritic facies
that experienced a shock temperature lower than 850°C. The occurrence and mineralogical features of vapor-grown crystals show
that vaporization of minerals could be produced in heavily impacted meteorites and that a small amount of crystals could be
depositedin situ from vapor phases.
Project supported by the Natural Science Foundation of Guangdong Province. 相似文献
535.
中国38亿年古陆壳锆石的成因矿物学研究 总被引:1,自引:0,他引:1
本文从锆石晶体形态,环带及晶体从核部于边缘的成分演化等特点,论述了中国最老(38亿年)两个锆石样品的岩浆成因属性,并发现它们的母岩在成因上存在差异,鞍山花岗靡棱岩是地幔或地幔来源为主的花岗质岩石,而冀东铬云母夕线石英岩中锆石的母岩则属壳源或壳幔混合型花风岩石,这些差别表明38亿年华北石陆壳岩石类型具有多样性。 相似文献
536.
本文用强功率四圆单晶衍射仪精确地修正了独居石和磷钇矿的晶体结构。独居石[Monazite-(Ce),CePO4]属单斜晶系,a=6.7843(17),b=6.9891(12),c=6.4592(10),β=103.626(16)°,Z=4,空间群为P21/n。使用1106个[F≥3σ(F)]的独立衍射点,经多轮最小二乘法修正后,最终获得偏离因子R=0.060。独居石的结构由孤立的[PO4]四面体构成,Ce位于[PO4]四面体包围之中,Ce的配位数为9,独居石的Ce—O平均键长为2.552,P—O平均键长为1.528。磷钇矿(Xenotime,YPO4)属四方晶系,其晶格常数为:a=6.8791(24),c=6.0147(19),Z=4,空间群为I4I/amd(No.141)。使用142个[F≥3σ(F)]的独立衍射点,经多轮最小二乘法修正后,最终获得偏离因子R为0.0483。磷和氧形成四面体配位,其P—O平均键长为1.543;稀土钇与氧原子相连构成八次配位,其Y—O平均键长为2.333。 相似文献
537.
林存山 《物探化探计算技术》1996,18(4):294-297
当前计算机技术在地学的许多领域中应用发展得很快,而且越来越加广泛。相比之下,它对结晶矿物学的影响似乎较小。事实上,结晶矿物学需要借助计算机技术的方面是很多的。本文介绍的矿物晶形的自动绘制方法就是一例。它超越传统的手算和手绘的方面是显而易见的。以下对Kanazawa和本文作者的成果作一简要介绍。 相似文献
538.
根据数据库管理系统原理,在矿物晶体形态计算机绘图的基础上,建立了一种适合于矿物晶体形态数据特征并具有一般数据库功能的数据输入与管理模型。该模型可以有效地管理矿物晶体形态数据(存储、查询、索引、编辑、分类等),并且可根据其有关信息计算晶体结晶要素、面角、绘晶体图等。 相似文献
539.
540.
利用快速分步傅里叶方法数值计算了孤子在光子晶体光纤中的传输。计算结果表明:光子晶体光纤中会产生较强的拉曼散射,非线性越强,孤子分裂得越快,同时分裂出更多孤子。而且,初始啁啾对光子晶体光纤中的拉曼散射有较大的影响,正初始啁啾会增大拉曼孤子的红移速度,而负初始啁啾则会减小拉曼孤子的红移速度。随着光子晶体光纤非线性加强,初始啁啾的作用减弱。 相似文献