Systematic variations in xenocryst mineral composition at the province scale, Buffalo Hills kimberlites, Alberta, Canada

The Buffalo Hills kimberlites define a province of kimberlite magmatism occurring within and adjacent to Proterozoic crystalline basement termed the Buffalo Head Terrane in north-central Alberta, Canada. The kimberlites are distinguished by a diverse xenocryst suite and most contain some quantity of diamond. The xenocryst assemblage in the province is atypical for diamondiferous kimberlite, including an overall paucity of mantle indicator minerals and the near-absence of compositionally subcalcic peridotitic garnet (G10). The most diamond-rich bodies are distinguished by the presence of slightly subcalcic, chromium-rich garnet and the general absence of picroilmenite, with the majority forming a small cluster in the northwestern part of the province. Barren and near-barren pipes tend to occur to the south, with increasing proximity to the basement structure known as the Peace River Arch. Niobian picroilmenite, compositionally restricted low-to moderate-Cr peridotitic garnet, and megacrystal titanian pyrope occur in kimberlites closest to the arch. Major element data for clinopyroxene and trace element data for garnet from diamond-rich and diamond-poor kimberlites suggests that metasomatism of lithospheric peridotite within the diamond stability field may have caused destruction of diamond, and diamond source rocks proximal to the arch were the most affected.     

Chemical Indicator of Spinel During Partial Melting and Subsolidus Equilibration of Mantle Peridotite:Experimental Study and Application to Natural Rocks

Systematic experimental studies on partial melting and subsolidus equilibration of three reconstituted spinel-peridotites have been carried out at temperatures ranging from 1000 to 1380℃ and pressures of 1.0 and 1.5 GPa. The results shows (1) during partial melting, Mg# [=Mg/(Mg+Fe)]and Cr# [=Cr/(Cr-Al)]of spinel increase with an increase in degrees of melting) (2) during subsolidus equilibration, with increasing temperatures, Mg# of spinel increases but Cr# of spinel remains almost unchanged in dunite and increases slightly in Iherzolite and harzburgite. The negative and quasi-linear Mg# -Cr# correlation of spinel represents an isotherm of total non-equilibrium. The same results have been obtained by means of mathematical modelling. It is also proved by Mg# -Cr# correlation of spinel in natural peridotites. As a result of the spinel subsolidus equilibration, only variation of Cr# of spinel is limited, and then Cr# of spinel can be used to estimate the relative degree of melting undergone by host rocks     

雅鲁藏布江蛇绿岩再研究:从地质调查到矿物记录

蛇绿岩带出现于全球大多数碰撞构造带上,通常是板块缝合带的标志,西藏雅鲁藏布江缝合带蛇绿岩带对于此种概念模型是毫无争议的。根据近年来现代洋壳和蛇绿岩研究成果以及分析技术,在20世纪80年代中法合作项目研究成果基础上,笔者再次对西起日喀则拉孜、东至泽当金鲁,长约500km的雅鲁藏布江缝合带蛇绿岩进行了研究。在野外调查基础上,对雅鲁藏布江蛇绿岩中500多个尖晶石样品的地球化学特征进行了分析研究,以探讨蛇绿岩的成因及其动力学背景,提出雅鲁藏布江蛇绿岩带属于超俯冲作用(suprasubduction)的产物,与近年来其他研究成果的认识一致。     

大兴安岭诺敏河石榴石橄榄岩捕虏体的发现及其地质意义

在重力梯度带北端的大兴安岭诺敏河第四纪火山岩中发现石榴石相和尖晶石相地幔橄榄岩捕虏体,其矿物组成分别为Ol_40~55Opx_20~35Cpx_0~10Grt_5~25和Ol_45~65Opx_30~40 Cpx_0~15Sp_0~10。两种地幔相橄榄岩均以方辉橄榄岩为主,说明研究区上地幔具有难熔的特点。其高Mg^#橄榄石Fo_91~92和高Cr^#_31~47尖晶石特征与南区哈河的地幔橄榄岩特征一致。在橄榄石含量与Fo图解上,敏河橄榄岩包体落在太古代和元古代地幔区域,揭示大兴安岭地区岩石圈地幔可能保留了较多古老的残余地幔。根据石榴石橄榄岩的平衡温压条件(1114~1168℃和2.14~2.33GPa),推测来源深度为70~75km。这些数据暗示研究区具有较高的地温梯度,与中国东部新生代火山岩区的地温梯度相似。     

古特提斯多岛洋洋一陆俯冲：木孜塔格蛇绿岩的矿物学证据

前期研究认识到新疆东昆仑木孜塔格蛇绿岩形成在俯冲带环境．为了进一步研究该俯冲带的类型，对新疆东昆仑木孜塔格蛇绿岩变质橄榄岩的岩石学和矿物学特征进行了分析．薄片观察发现变质橄榄岩的橄榄石以变质残余、变质重结晶和斜方辉石熔融结晶3种结构存在，但探针分析发现它们具有稳定且低Fo值（87．8～89．5）；斜方辉石发育变质残余和熔融残余结构，En较低（88～90），Al2O3含量变化大（2．90％～5．13％）；尖晶石为他形一半自形结构，其Cr^#（=Cr／（Cr＋Al））集中分布在0．508～0．723和0．100～0．118两个范围内．根据这些来自岩石学和矿物学的证据，并结合该蛇绿岩的构造背景与时代，认识到该蛇绿岩形成在大洋向具有厚陆壳的大陆弧俯冲的俯冲带环境，为新疆东昆仑地区古特提斯多岛洋洋一陆俯冲的结果．     

新疆克拉玛依地区百口泉发现尖晶石橄榄岩

新疆克拉玛依地区出露的早古生代蛇绿混杂岩带规模巨大,岩石单元出露齐全。白碱滩地区的地幔橄榄岩相对比较新鲜,单斜辉石、斜方辉石、尖晶石和橄榄石保存完好。研究表明,白碱滩蛇绿岩就位前,地幔岩发生了大于50km的快速隆升,且没有发生部分熔融。百口泉地区发现的地幔岩普遍遭受了改造,辉石多发生了强烈蚀变(透闪石化),但尖晶石和橄榄石保存较好。百口泉地区出露的地幔岩和白碱滩地幔岩的矿物组成基本一致,表明它们属于同一蛇绿混杂岩带。百口泉蛇绿岩剖面的揭露,将该蛇绿混杂岩带的范围向NE方向延伸了35km。     

High‐temperature,low‐pressure metamorphism and development of prograde symplectites,Marble Hall Fragment,Bushveld Complex (South Africa)

Metapelitic rocks from the Marble Hall Fragment, enclosed in the granites of the magmatic Bushveld Complex, record a two‐stage, low‐pressure, high‐temperature metamorphism. An early paragenesis containing chiastolitic andalusite, cordierite, biotite and quartz ± garnet crystallized in most rocks and equilibrated at 550–600 °C, 0.2 GPa. It was transformed during the second, peak event into various parageneses that commonly coexist within a single thin section. These include garnet–cordierite–biotite–K‐feldspar–quartz, sillimanite–cordierite–K‐feldspar–quartz and spectacular quartz‐undersaturated cordierite–spinel symplectites replacing the chiastolite porphyroblasts. Based on a detailed phase diagram analysis, we argue that these parageneses result from rapid heating at an approximately constant pressure to temperatures of more than about 720 °C. At these temperatures, the internally buffered activity of water was reduced by incipient water‐saturated partial melting, while only minor quantities of melt were produced. Subsequent dry conditions inhibited large‐scale equilibration and, together with local inhomogeneities in mineral distribution, led to the development of contrasting parageneses and symplectite textures. No signs of widespread fluid‐absent melting of biotite were found, and so the temperature probably did not exceed 760 °C. The peak metamorphic event is attributed to the emplacement of the hot Nebo granite, whereas the early metamorphism was probably caused by the intrusion of one of the phases of the Rustenburg Layered Suite. We infer the conditions of development of the cordierite–spinel intergrowths and we show that, although symplectites are commonly associated with retrograde processes (cooling and/or decompression), they can record a prograde metamorphic evolution. Furthermore, our contribution emphasizes the importance of the concept of reduced equilibration volume for the understanding and interpretation of some particular textures and parageneses in common rocks.     

A Mssbauer effect study of Fe3+ bearing

Three synthetic Fe3+ bearing γ-Fe2SiO4 were analyzed usingelectron probe method, and the Mssbauer spectra of the samples at 298 K, 150 K, and 95 K were measured. Each spectrum at three temperatures is composed of two doublets. These two doublets are assigned to Fe2+ in the octahedral sites and Fe3+ in the tetrahedral sites, respectively. Site occupancies were determined. The results show that Fe3+ and a small amount of Si4+ are in the tetrahedral and octahedral sites, respectively. The average bond lengths of the octahedral and tetrahedral sites were calculated according to the equations primarily given by Hill et al., O’Neill and Navrotsky and modified by the authors. Furthermore, the octahedral and tetrahedral bond lengths were used to calculate cell parameters and oxygen parameters. In addition, Fe3+ line broadening in the M?ssbauer spectra of Fe3+ bearing γ-Fe2SiO4 were interpreted by using the next nearest neighbor effects.     

宇宙尖晶石与地球尖晶石的比较

本文就宇宙尖晶石的形态，化学组成，及产状特征作了概要性论述，对它的成因机制 作了介绍；并和地球尖晶石作比较，表明它们之 间的成因和形成条件的差异，突出了宇宙尖晶石的特点，即宇宙尖晶石为陨石物质在大气氧化过程中结晶而成，无例外的都有一个较高的氧化态和高镍含量。在地质纪录中宇宙尖晶石的发现具有双重意义，它既是地外物质的标志，又反映了增生事件独特的形成环境。     

武钢镁碳砖首次用于盛钢桶衬砖的侵蚀机理研究

作者对我国武钢转炉盛钢桶镁碳砖的理化性能、使用条件,侵蚀情况等进行了详细的研究,在渣线处,它明显地优于镁砖.同时,在镁碳砖渐变带与反应带之间发现—镁铝尖晶石层,有延缓钢渣的锓蚀作用,并从热力学计算揭示了脱碳层及镁铝尖晶石层的形成,提出了增强衬砖寿命的具体改进措施,具有重要的理论和实际意义.