Major, Minor and Trace Elements in Some Glasses from the NWA 1664 Howardite
Major, Minor and Trace Elements in Some Glasses from the NWA 1664 Howardite
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NWA 1664 霍华德石的一些玻璃中的主量、微量和微量元素
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发表时间：
2003
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通讯作者：
F. Brandstatter
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作者：
G. Kurat;M. Varela;E. Zinner;T. Maruoka;F. Brandstatter
前言：新芒硝石NWA1664重6.31公斤，是一种多金属角砾岩，主要由矿物碎屑和镶嵌在细粒碎屑基质中的岩屑(闪长岩和真核岩)组成。这块岩石含有丰富的玻璃碎片(可达2厘米)、玻璃小球(可达1厘米)和球粒状物体。大多数玻璃碎片都有不同程度的玻璃化，有些是玻璃斑结构，有些是完全透明的。在这里，我们介绍了这些玻璃碎片的主要和微量元素分析的结果。我们的初步结果使我们可以推测，方钠石玻璃与钠辉石(D‘Orbigny)和榴辉石(Cachari)中的玻璃具有相似的形成过程和相似的成因。方法和结果：使用ARL-SEMQ微探针和分析扫描电子显微镜JEOL 6400(NHM，维也纳)获得玻璃的主要化学成分。用圣路易斯华盛顿大学的Cameca IMS 3F离子探针对玻璃和辉石进行了微量元素分析。对四个玻璃碎片(A1af、A1b、A1d和A4A)和一个玻璃球(A1as，图1)进行了主元素和微量元素分析。1.5毫米大小的玻璃碎片A1af被完全玻璃化。球体A1As的直径为700？m，一侧表面有羽状辉石生长，纹影勾勒出逆流输送细胞。这两个物体都含有直径达50微米的圆形气泡。玻璃碎片A1b和A1d是部分非玻璃化玻璃的小物体(分别为400和200？m)。碎片A4A由部分玻璃化玻璃(大小为400？m)与400？m长的辉石(F_(47)Wo_(18)en_(35))接触而成。玻璃中含有1个SiO_2(~95wt%SiO_2)和4个斜长石(90-An~95)碎屑包裹体。所有玻璃的主要元素组成是不同的。每个物体都有自己的化学成分，在很小的范围内各有不同。只有少数元素在个体内和个体之间具有相关性：FeO和MnO呈正相关，并跨越FeO/MnO~36比值线。CaO和Al_2O_3含量与球粒陨石CaO/Al_2O_3比值曲线基本一致。Na2O含量与横跨x轴的CaO含量大致相关，CaO含量约为4wt%。在物体内部，化学成分的变化遵循几种相关性，如Cr2O3FeO(Alaf…
Introduction: The new howardite NWA 1664, 6.31 kg, is a polymict breccia consisting mainly of mineral fragments and lithic clasts (diogenitic and eucritic) embedded in a fine-grained clastic matrix. This rock has abundant glass fragments (up to 2 cm), glass spherules (up to 1 cm) and chondrule-like objects. Most of the glass fragments are devitrified to variable degrees, some have vitrophyric textures and some are fully hyaline. Here we present the results of a major and trace element analyses of these glass fragments. Our preliminary results allow us to speculate that the howardite glasses and those present in an-grites (D'Orbigny) and eucrites (Cachari) share similar formational processes and have similar origins. Methods and Results: Major chemical compositions of glasses were obtained using an ARL-SEMQ microprobe and an analytical scanning electron microscope JEOL 6400, (NHM, Vienna). Trace element analyses of glasses and pyroxenes were made with the Cameca IMS 3F ion microprobe at Washington University , St. Louis. Major and trace element analyses were performed on four glass fragments (A1af, A1b, A1d and A4a) and one glass sphere (A1as, Fig. 1). The glass fragment A1af, 1.5 mm in size, is totally devitrified. The sphere A1as, 700 ìm in diameter, has feathery pyroxenes growing from the surface at one side and schlieren outlining counter-flowing convec-tion cells. Both objects contain round bubbles up to 50 µm in diameter. Glass fragments A1b and A1d are small objects (400 and 200 ìm, respectively) of partly devitrified glass. Fragment A4a consists of partly de-vitrified glass (400 ìm in size) in contact with a 400 ìm long pyroxene (Fs 47 Wo 18 En 35 , Fig. 2). The glass has inclusions of one silica (~95 wt% SiO 2) and four plagioclase (An 90 – An 95) clasts. The major element composition of all glasses is variable. Each object has its own chemical composition that varies within mostly narrow limits. Only few elements have correlated abundances within and between individual objects: FeO and MnO are positively correlated and straddle the FeO/MnO ~ 36 ratio line. CaO and Al 2 O 3 contents follow more or less closely the chondritic CaO/Al 2 O 3 ratio line. Also, the Na 2 O content is roughly correlated with the CaO content straddling a line which intercepts the x-axis at about 4 wt% CaO. Within objects variation of chemical composition follows several correlations such as Cr 2 O 3 and FeO (A1af …