昌宁-孟连杂岩带澜沧岩群的岩石学、地球化学和变质演化及其对古特提斯构造演化的启示

云南三江地区昌宁-孟连杂岩带中的澜沧岩群内出露多种类型变沉积岩,主要包括含十字蓝晶石榴云母片岩、石榴云母片岩、硬绿泥石白云母片岩和绿泥蓝闪钠长片岩等。系统的岩相学观察、矿物化学和相平衡模拟研究结果表明,不同类型的变沉积岩保存了不同的变质演化历史。含十字蓝晶石榴云母片岩记录了自中温榴辉岩相降温降压至角闪岩相的退变质过程,峰期矿物组合为石榴子石+蓝晶石+多硅白云母+硬玉,变质温压条件为600～750℃和19～30kbar。通过石榴子石的X_(Prp)和X_(Grs),和多硅白云母的Si值限定石榴云母片岩的峰期矿物组合包括石榴子石+多硅白云母+绿辉石+硬柱石+钠云母,峰期温压条件为430～475℃和17～19.5kbar。硬绿泥石白云母片岩矿物组成包括硬绿泥石+多硅白云母+钠云母,然而峰期矿物组合则以多硅白云母+钠云母+纤柱石为特征,通过多硅白云母的Si值限定峰期温压条件约为300～330℃和17～19kbar。石榴云母片岩和硬绿泥石白云母片岩较为一致地记录了从峰期硬柱石蓝片岩相升温降压至绿帘石蓝片岩相的退变质过程。绿泥蓝闪钠长片岩主要通过变质反应和成因矿物学特征大致估算其温压条件约为430～520℃和9～11kbar。岩石地球化学性质研究结果表明,这些变沉积岩的平均化学成分与大陆岛弧、活动大陆边缘和上地壳沉积物成分较为接近,其原岩主要为一套成熟度较差的泥砂质岩类和少量的中基性火山岩。该泥砂质原岩的沉积物源以中酸性岩浆岩为主,存在不同程度古老沉积物的加入。构造判别图解表明,研究区样品主要形成于大陆岛弧或活动大陆边缘的构造背景。变质作用特征和原岩地球化学属性综合分析表明,昌宁-孟连杂岩带内大面积分布的澜沧岩群均发生不同程度的俯冲-消减过程,表现出多样的变质演化P-T轨迹的特征,表明澜沧岩群经历了多期/多阶段复杂的构造演化历史。     

中国蓝闪片岩相的变质作用

本文论述了中国蓝闪片岩的分布、变质条件及其构造位置。中国的蓝闪片岩从中晚元古代开始,各变质期均有出现。根据矿物组合,可分为两类:第一类蓝闪片岩常含有高压矿物,如硬柱石、硬玉和文石以及蓝闪石、绿纤石、黑硬绿泥石、多硅白云母、红帘石等,属高压亚绿片岩相,称蓝闪—硬柱石片岩相,形成温度约250—350℃,压力大于500—800MPa,甚至可达1200MPa。此类蓝闪—硬柱石片岩相多代表海洋板块古消减带。第二类蓝闪片岩的常见矿物为蓝闪石、青铝闪石或镁钠闪石、黑硬绿泥石、红帘石和绿片岩相中的绿帘石、阳起石、绿泥石、白云母、有时还有黑云母、铁铝榴石和钠质辉石。形成温度约350—450℃,压力500—800MPa。此类蓝闪绿片岩相虽处于活动带,但与板块构造没有直接关系。我国西藏南部和内蒙温都尔庙属第一类,但大部分蓝闪片岩带属第二类。     

新疆西天山高压变质带的变质矿物与变质作用演化

新疆西天山高压变质带主要由石榴石，角闪石，绿辉石，多硅白云母，钠云母，绿帘石，绿泥石，钠长石，石英，榍石和金红石等组成，石榴石主要含铁铝榴石组份，角闪石有蓝闪石，亚铁蓝闪石，青铝闪石，冻蓝闪石等类型，变质矿物组合显示高压变质带经历了由硬柱石蓝片岩相，榴辉岩相，绿帘蓝片岩相至绿片岩相的变质作用演化进程。     

新疆西南天山含柯石英泥质片岩的岩石学特征及变质作用p-T轨迹

新疆西南天山高压-超高压变质带主要由泥质-长英质片岩组成,其中包裹榴辉岩、蓝片岩和超基性岩等透镜体。含柯石英泥质片岩具斑状/筛状变晶结构,片状构造,矿物组合为石榴石、多硅白云母、钠长石、钠云母、蓝闪石、冻蓝闪石、石英以及少量褐帘石、金红石和榍石,柯石英包裹在石榴石变斑晶内。根据岩石学特征和相平衡模拟的结果,识别出含柯石英泥质片岩经历了3期变质演化阶段:压力峰期之前的进变质阶段(Ⅰ),由石榴石核部到含柯石英区域的环带确定,特征为温度和压力同时升高,所限定的压力峰期条件为500℃、2.9 GPa,模拟的矿物组合为石榴石+蓝闪石+硬玉+纤柱石+硬柱石+金红石+多硅白云母+柯石英,与含柯石英的事实相符;压力峰期之后的升温降压至温度峰期阶段(Ⅱ),由石榴石含柯石英区域到边部的环带确定,特征为温度升高压力降低,所限定的温度峰期条件为560℃、2.35 GPa,模拟的矿物组合为石榴石+蓝闪石+硬玉+硬柱石+金红石+多硅白云母+石英,发生连续脱水反应蓝闪石+纤柱石+硬柱石=石榴石+硬玉+水,释放出岩石中约45%的水,导致柯石英转变为石英,纤柱石消失;温度峰期之后的近等温降压阶段(Ⅲ),由晚期矿物组合钠云母+钠长石+冻蓝闪石+榍石+石英的稳定温压条件确定(495~550℃、1.0~1.15 GPa),减压抬升过程中,在约2.1 GPa处,发生脱水反应硬玉+硬柱石=蓝闪石+钠云母+水,导致硬柱石消失,钠云母出现,在约1.1~1.25 GPa处,榍石取代金红石,绿辉石消失,钠长石和冻蓝闪石出现。阶段Ⅱ强烈的连续脱水过程十分利于矿物组合的再平衡,导致绝大多数压力峰期的柯石英转变为石英,仅有极少数因包裹在刚性石榴石中而得以保存。含柯石英泥质片岩及其榴辉岩透镜体经历了完全相同的俯冲折返过程。     

黑龙江依兰地区黑硬绿泥石片岩岩石学与P-T条件研究

依兰地区黑龙江杂岩中黑硬绿泥石片岩矿物组合为黑硬绿泥+绿泥石+多硅白云母+钠长石+透闪石+钾长石±黑云母.岩石矿物学研究表明黑硬绿泥石片岩形成于250～400℃,6～9kbar的变质条件下.黄褐色黑硬绿泥石呈束状、放射状集合体.黑硬绿泥石片岩形成于佳木斯地块向西与松嫩地块俯冲拼贴过程中蓝片岩变质作用的后期,压力稍有降低而温度略有升高的变质变形环境,是蓝片岩向绿片岩转变的蓝闪绿片岩相变质条件下的产物.     

早古生代北阿尔金HP/LT混杂岩片——一个“化石”俯冲隧道

北阿尔金高压/低温(HP/LT)变质岩呈构造岩片分布在俯冲-增生杂岩中，主要由强变形的变质沉积岩(泥质片岩、钙质片岩和石英片岩)和少量呈透镜状分布在变沉积岩中的蓝片岩和榴辉岩组成，与相邻的蛇绿混杂岩呈断层接触。榴辉岩主要矿物为绿辉石、石榴子石、多硅白云母、石英、冻蓝闪石，含少量蓝闪石、绿泥石、方解石、钠长石、榍石。蓝片岩主要矿物为蓝闪石、石榴子石、碳酸盐类矿物、阳起石、绿帘石、钠云母、绿泥石、钠长石和石英，偶见多硅白云母，其中在部分蓝片岩的石榴子石中有少量硬柱石和绿辉石包体。本文对蓝片岩(样品A06-16-7)和榴辉岩(样品A03-3-5.3)开展了岩石学和相平衡模拟研究，得到它们形成的压力峰期的温压条件分别是：T=～524℃、P=～2.1GPa和T=～527℃、P=～2.2GPa,并均经历了后期蓝片岩相的退变质叠加。结合区域上已有的研究表明，北阿尔金HP/LT混杂岩片中不同类型岩石可能经历了不同的变质演化历史，反映了古俯冲隧道的不均匀性，并在俯冲隧道的较浅部混杂在一起，共同经历了蓝片岩相或蓝片岩-绿片岩过渡相条件下的透入性变形作用。     

北祁连山硬柱石蓝片岩p-T条件相平衡计算及其岩石学意义

北祁连硬柱石蓝片岩主要分布在甘肃省肃南县九个泉一带,是目前中国唯一报道的、确切地含有硬柱石的蓝片岩。文中在详细的岩石学和矿物学研究基础上,根据矿物共生组合的不同,将北祁连低温蓝片岩进一步划分为绿纤石蓝片岩、硬柱石蓝片岩和绿帘石蓝片岩。绿纤石蓝片岩的特征变质矿物组合为蓝闪石(>40%)+绿纤石(30%)+绿泥石(10%)+钠长石(8%)+石英(5%)+硬柱石(<3%)±方解石/文石(<1%)。硬柱石蓝片岩的矿物组合为蓝闪石(35%~40%)+硬柱石(35%~40%)+绿泥石(10%)+钠长石(10%)+石榴石(1%~2%)+黝帘石/斜黝帘石(<2%)+石英(<1%),副矿物有磷灰石和榍石,总含量小于2%。绿帘石蓝片岩的矿物组合为蓝闪石(30%~35%)+黝帘石/斜黝帘石/绿帘石(~30%)+绿泥石(15%)+钠长石(15%)+石榴石(2%)+石英(<2%),副矿物有金红石、磷灰石和磁铁矿,总含量小于2%。利用矿物内部一致性热力学数据和Domino/Theriak软件计算了这三种类型的蓝片岩形成的峰期温压条件,它们分别是绿纤石蓝片岩为320~350℃,0.75~0.85GPa;硬柱石蓝片岩为335~355℃,0.8~0.95GPa;绿帘石蓝片岩为345~375℃;0.75~0.85GPa。北祁连低温蓝片岩带由硬柱石蓝片岩相到绿帘石蓝片岩相的转化代表了俯冲变质过程中的递进变质过程。     

藏北羌塘中北部红脊山地区蓝闪石＋硬柱石变质矿物组合的特征及其意义

蓝闪石 硬柱石是羌塘中北部红脊山地区首次发现的呈北西-南东走向展布的硬柱蓝闪片岩带中典型的低温高压变质矿物组合.蓝闪石呈浅蓝灰色,纤柱状;硬柱石无色,多呈团块状,较均匀地与蓝闪石混杂分布.电子探针分析表明,蓝闪石主要为铁蓝闪石和青铝闪石,硬柱石为较典型的硬柱石.硬柱蓝闪片岩呈(透镜状)构造岩块分布,与围岩呈断层接触,原岩主要为变质玄武岩及少量辉(长)绿岩、基性火山碎屑岩,围岩为变质砂岩、板岩和少量碳酸盐岩.红脊山硬柱蓝闪片岩带伴有构造混杂岩发育,二者共存构成红脊山地区北羌塘甜水河陆块与南羌塘查多岗日陆块之间的分界线.     

阿拉斯加Seward半岛区域前进高压变质作用

在Seward半岛蓝片岩相岩石构成了一个构造上连贯的岩带,其出露面积至少有15000km~2。放射性年龄数据表明,高压变质作用多伴发生在侏罗纪,而不象以前推测的古生代或前寒武纪。原岩属内陆盆地或大陆边缘类型的沉积物(Nome Group),并具有早古生代或许是晚前寒武纪的年龄。这样在年龄上就早于高压变质作用的年龄200Ma之多。蓝闪石片岩相矿物组合几乎在Nome Group的所有岩性中都有发育,在富含Fe、Ti的变质基性岩(篮闪石+铁铝榴石+绿帘石)和泥质岩(蓝闪石+硬绿泥石+多硅白云母)中,硬柱石—青铝闪石亚相在Darby山东侧发育,可能在Nome Group岩石中有所发育,半岛西南部钠长石—绿帘岩—角闪岩相组合代表Nome Group岩石的特征。岩带中部地区的变质作用从早期的硬柱石,到后来的绿帘石—铁铝榴石—篮闪石片岩亚相,局部发育有榴辉岩组合(Nome河以东)。高压变质矿物是同构造期的,并拥有中等规模的层内等斜褶皱和方向一致的压扁的叶理,隆起的开始很可能相当于在较早的钠质和阳起石质角闪石环边上有冻蓝闪石的生长,部分构造后绿片岩相的各种交代作用记录了后来的减压阶段,蛇绿岩及混杂岩不与Seward半岛的蓝片岩伴生,高压变质作用是由一个不定成因的外来体所引起的大陆板块的构造负荷所引起的,高压变质作用的P—T 条件大约是 9～11Kb,400～450℃,介于Shuksan和Franciscan岩区的P—T轨逆之间。     

地壳俯冲与折返过程的变质作用演化:来自高压-超高压榴辉岩相平衡模拟的证据

本文以大别山双河柯石英榴辉岩为基础,在NCKMnFMASHO体系中计算了P-T、T-M(H₂O)和P-M(H₂O)一系列相图。这些相图表明在地壳冷俯冲(地热梯度约为6℃·km^-1)过程中饱和水的变质基性岩通过脱水反应导致矿物组合演化,随着P-T条件增加,约在2.2GPa(80km)处,绿泥石被滑石取代,在2.4GPa处,蓝闪石消失,在2.5GPa处,滑石消失,在2.9GPa(105km)处,硬柱石消失。相应地可出现硬柱石蓝片岩、蓝闪石-硬柱石榴辉岩、硬柱石榴辉岩和多硅白云母榴辉岩等高压-超高压组合。俯冲基性岩中即使含有很少量的水(如0.3%~0.5%),都会在超高压硬柱石榴辉岩相条件下达到饱和。因此硬柱石会广泛出现于经历冷俯冲地壳的变质基性岩中。高压-超高压榴辉岩的折返过程受折返温度及峰期矿物组合的控制。当峰期矿物组合中含有硬柱石(±蓝闪石±滑石,T=540~600℃)时,其早期折返发生在硬柱石稳定域,受脱水反应控制,难以保存峰期矿物组合;晚期折返发生在绿帘石稳定域,岩石处于流体缺失状态,有利于保存硬柱石消失后的高压矿物组合。当峰期矿物组合中含有绿泥石、硬柱石和蓝闪石时(T<540℃),其折返过程中的脱水作用仅发生在硬柱石与绿帘石共生的狭窄区域,在硬柱石稳定域的早期折返与绿帘石稳定域的晚期折返阶段,都不发生脱水作用,岩石处于流体缺失状态,因此,虽然峰期形成的硬柱石难以保存,但峰期形成的其他矿物可能仅受轻微改造。当硬柱石消失 (T>600℃) 后,多硅白云母高压-超高压榴辉岩中含有很少量水,在早期折返过程中的很大压力范围内,岩石保持水含量不变,更容易保留峰期矿物组合。高压-超高压榴辉岩在减压至1.5GPa以下时,由于外来流体注入,发生部分水化,形成含有钠钙质、钙质角闪石榴辉岩, 它们一般不是平衡矿物组合。榴辉岩中名义上的无水矿物在减压过程中释放的水有助于榴辉岩部分水化,但不足以形成水饱和的斜长角闪岩。     

膨润土作为药用赋形剂对Pb~(+2),Cd~(+2),Cr~(+6)离子的吸附研究

本文选用吉林省九台、小梨河、净月产地的膨润土为原料,测试了不同粒级的膨润土对Pb 2、Cd 2、Cr 6离子的吸附时间、吸附温度、吸附量,同时,又在模拟人胃条件下进行了试验,结果证实膨润土可以作为药用赋形剂。     

Auriacusite, Fe3+Cu2+AsO4O, the first M 3+ member of the olivenite group, from the Black Pine mine, Montana, USA

Auriacusite, ideally Fe³⁺Cu²⁺AsO₄O, is a new arsenate mineral (IMA2009–037) and the Fe³⁺ analogue of olivenite, from the Black Pine mine, 14.5 km NW of Philipsburg, Granite Co., Montana, USA. It occurs lining quartz vughs and coating quartz crystals and is associated with segnitite, brochantite, malachite, tetrahedrite and pyrite. Auriacusite forms fibrous crystals up to about 5?µm in width and up to about 100?µm in length, which are intergrown to form fibrous mats. Individual crystals are a brownish golden yellow, whilst the fibrous mats are ochreous yellow. The crystals have a silky lustre and a brownish yellow streak. Mohs hardness is about 3 (estimated). The fracture is irregular and the tenacity is brittle. Auriacusite crystals are biaxial (+), with α?=?1.830(5), β?=?1.865(5) and γ?=?1.910(5), measured using white light, and with 2V _meas.?=?83(3)º and 2V _calc. = 84.6º. Orientation: X?=?a, Y?=?c, Z?=?b. Crystals are nonpleochroic or too weakly so to be observed. The empirical formula (based on 5 O atoms) is (Fe _1.33 ³⁺ Cu_0.85Zn_0.03)_Σ2.21(As_0.51Sb_0.27Si_0.04?S_0.02Te_0.01)_Σ0.85O₅. Auriacusite is orthorhombic, space group Pnnm, a?=?8.6235(7), b?=?8.2757(7), c?=?5.9501(5) Å, V?=?424.63(6) ų, Z?=?4. The five strongest lines in the powder X-ray diffraction pattern are [d _obs in Å / (I) / hkl]: 4.884 / (100) / 101, 001; 2.991 / (92) / 220; 2.476 / (85) / 311; 2.416 / (83) / 022; 2.669 / (74) / 221. The crystal structure was solved from single-crystal X-ray diffraction data utilising synchrotron radiation and refined to R ₁?=?0.1010 on the basis of 951 unique reflections with F _o?>?4σF. Auriacusite is identified as a member of the olivenite group with Fe³⁺ replacing Zn²⁺ or Cu²⁺ in trigonal bipyramidal coordination. Evidence suggests that auriacusite is an intermediate member between olivenite and an as yet undescribed Fe³⁺Fe³⁺-dominant member. The name is derived from the Latin auri (golden yellow) and acus (needle), in reference to its colour and crystal morphology.     

A field and theoretical analysis of garnet+chlorite+chloritoid+biotite assemblages from the tri-state (MA,CT, NY) area,USA

The prograde evolution of minerals in metapelites of a Barrovian sequence from the tri-state area (Massachusetts, Connecticut, New York) of the Taconic Range involves assemblages with garnet (Ga), chlorite (Ch), chloritoid (Ct), biotite (Bi) and staurolite (St). Detailed petrologic observations, mineral compositions and chemical zoning in garnet show: (1) garnet high in Mn and Fe but low in Mg is stable with chlorite at grades below those where chloritoid+biotite is found; (2) early formed garnet reacted partially to form Ct+Bi at intermediate grades; (3) at higher grades garnet (with low Mn)+chlorite is again produced, at the expense of chloritoid+biotite, suggesting a reversal in the continuous reaction involving the phases Ga, Ch, Ct and Bi. Thermodynamic modeling of the assemblage Ga+Ch+Ct+Bi±St in the MnKFMASH system reveals: (1) in the MnKFASH system the prograde reaction is Ga+Ch=Ct+Bi whereas in the KFMASH system the prograde reaction is the opposite: Ct+Bi=Ga+Ch; (2) the Ga–Ch–Ct–Bi–St invariant point in the KFMASH system occurs twice, at approximately 6.5 kbar, 545° C and 14.8 kbar, 580° C (although one of them may be metastable in a complex phase system); the appearance of the petrogenetic grid is markedly different from that of Albee, but similar to that of Spear and Cheney; (3) as a consequence, in the KFMASH system, chloritoid+biotite are stable over a wide range of P-T conditions whereas garnet+chlorite assemblages are restricted to a narrow band of P-T conditions; (4) MnO increases the stability field of Ga+Ch relative to both Ct+Bi at low temperatures, and St+Bi at high temperatures; (5) in natural samples the occurrence of Ct+Bi is controlled more by bulk Mg–Fe(-Mn) composition than P-T conditions. Specifically, Ct+Bi is restricted to bulk compositions with Fe/(Mg+Fe+Mn)>0.6. Rocks with Fe/(Mg+Fe+Mn)<0.5 are likely to display only chlorite+biotite at low grade. These observations are consistent with Wang and Spear and Spear and Cheney.     

掺锂、钠、钾的萤石色心激光晶体生长

近几年来,碱卤化合物类和碱土金属氟化物类色心激光晶体研究发展很快。色心晶体的研制促进了可调谐色心激光的飞跃发展,它已成为可调谐激光晶体中的一个重要组成部分。     

Equilibria within the mineral assemblage quartz + muscovite + biotite + garnet + plagioclase,and implications for the mixing properties of octahedrally-coordinated cations in muscovite and biotite

Interaction parameters derived using empirical calibration methods indicate strong non-ideality in the mixing of octahedrally-coordinated cations in muscovite and biotite. The data set used for calibration comprises mineral compositions from 49 samples containing quartz, muscovite, biotite, garnet, plagioclase and Al₂SiO₅ (kyanite or sillimanite). Pressures and temperatures in the data set were determined through the simultaneous application of geothermometry based on the garnet-biotite FeMg₁ exchange equilibrium and geobarometry based on the anorthite-breakdown equilibrium. Two equilibria yielded simple expressions from which binary interaction parameters for octahedrally-coordinated cations in biotite could be directly determined. A four-component (Fe²⁺, Mg, Al, Ti) regular symmetric mixing model was assumed for biotite. One equilibrium yielded a simple expression from which an interaction parameter for the mixing of the MgAl-celadonite component in muscovite could be directly determined. Two sets of calculations were performed utilizing different calibrations of the garnet-biotite geothermometer and the anothite-breakdown geobarometer and different garnet activity models. Both placed samples within or near the stability field of the Al₂SiO₅ phase present in each sample and both yielded similar values for the interaction parameters within narrow uncertainties, indicating that the values are insensitive to differences in the underlying methods. Using the derived interaction parameters, activity models were formulated for the annite, phlogopite, eastonite, and siderophyllite components of biotite, and for the MgAl-celadonite component of muscovite. These were utilized for the empirical calibration of 45 fluid-independent equilibria involving unique combinations of phase components from the mineral assemblage garnet + plagioclase±biotite±muscovite±quartz. Forty-three of the equilibria may be applied as geobarometers to equilibrium assemblages of quartz + muscovite + biotite + garnet + plagioclase when care is taken to insure that applications are restricted to valid compositional ranges. For these, the calibrations yielded multiple correlation coefficients ranging from 0.953 to 0.998 and standard deviations of the residuals ranging from 597 to 118 bars.     

Mg,Fe2+ site occupancies in coexisting pyroxenes

The separate distributions for MgSiO₃ and FeSiO₃ in coexisting pyroxenes from the Skaergaard and Bushveld intrusions and charnockites, which were introduced in an earlier communication, indicate directly that significant amounts of both Fe²⁺ and Mg were present in the M(2) site of the Ca-rich pyroxene at the temperature of final intercrystalline equilibration. The calculated Fe²⁺ M(2) site occupancy in the Ca-rich pyroxene increases markedly with decrease in total MgSiO₃ content but the corresponding Mg site occupancy appears largely independent of MgSiO₃. The mean value of the distribution constant for intracrystalline exchange in the Ca-rich pyroxene decreases, away from unity, with decreasing temperature of equilibration. Occupancy of Mg and Fe²⁺ in the M (2) site of the Ca-rich pyroxene effectively compensates for the expected variation in K _D with composition resulting from intracrystalline partition in Ca-poor pyroxene, and this largely accounts for the difference in K _D between igneous and metamorphic pyroxenes. The variation of the augite limb of the pyroxene solvus within the pyroxene quadrilateral is developed as a possible geothermometer.     

Phase transitions in langbeinites I: Crystal chemistry and structures of K-double sulfates of the langbeinite type M 2 + + K2(SO4)3, M + +=Mg,Ni, Co,Zn, Ca

The crystal structures of the langbeinite type M ₂ ^{+ +} K₂(SO₄)₃ with M ^{+ +}=Mg, Ni, Co, Zn, Ca in their cubic phase (P 2 ₁ 3) and Ca₂K₂(SO₄)₃ in its orthorhombic phase (P 2 ₁ 2 ₁ 2 ₁) are determined. Whereas the SO₄-tetrahedra in these compounds are almost undistorted, the two symmetry-independent coordination polyhedra of M ^{+ +} are highly distorted octahedra with trigonal site symmetry in P 2 ₁ 3. The deformation of the oxygen octahedra and the off-centering of M ^{+ +} along the trigonal axis show systematic dependences on the ionic radii and the electronegativities of the M ^{+ +}-ions. The correlations are remarkably different for the two symmetry-independent M ^{+ +}-ions indicating different M ^{+ +} — O bonding. The octahedral deformations show also linear correlations with the phase transition temperatures (P 2 ₁ 3 — P 2 ₁ 2 ₁ 2 ₁) of the different compounds. This observation leads to a new model for the phase transition mechanism which is based on thermal instabilities of the M ^{+ +} — O and K — O polyhedral distortions. The cubic high temperature phase is characterized by high symmetric oxygen coordinations around M ^{+ +} which distort with decreasing temperature. At T _c the trigonal site symmetry is broken in such a way that the K — O coordination becomes denser at the expense of a wider and less symmetric M ^{+ +} — O coordination.     

Partitioning of Ni2+, Co2+, Fe2+, Mn2+ and Mg2+ between olivine and silicate melts: compositional dependence of partition coefficient

Partitioning of Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺ and Mg²⁺ between olivine and silicate melts has been determined near the join (Mg_0.5·-Fe_0.5)₂SiO₄-K₂O 4SiO₂ and for seven different basaltic compositions. The experiments were made at 1 atm total pressure, 1500-1100°C, and under moderate to reducing oxygen fugacities. The concentration factor, defined as K^MO = (MO)^ol/(MO)^liq (molar ratio), increases markedly for all the cations studied as the olivine component of the liquid decreases. Much of the increase in K^MO is considered as due to the compositional effect of the coexisting liquid: the temperature effect on K^MO is probably opposite to the compositional effect (K^MO decreases as temperature decreases).The partition coefficient K^MO-MgO = (MO/MgO)^ol/(MO/MgO)^liq for the reaction, M_ol²⁺ + Mg_liq²⁺ = M_liq²⁺ + Mg_ol²⁺. is relatively constant over a wide range of SiO₂ content of the liquid, except in the case of Ni²⁺. The partition coefficients have similar ranges both in synthetic and natural rock systems: K^NiO-MgO = 1.8–3.0, K^CoO-MgO = 0.6–0.8, K^FeO-MgO = 0.27–0.38, and K^MnO-MgO = 0.23–0.32. There is a systematic variation in the partition coefficient K^MO-MgO with the composition of liquid; K^MO-MgO increases with increasing SiO₂ content of melt. The partition coefficients for Co²⁺, Fe²⁺ and Mn²⁺ are useful to test the equilibration of olivine with magma of a wide compositional range.     

Polymerization of silicate and aluminate tetrahedra in glasses,melts and aqueous solutions—II. The network modifying effects of Mg2+ , K+, Na+, Li+, H+, OH−, F−, Cl−, H2O,CO2 and H3O+ on silicate polymers

The effect of the group IA and VIIA ions, as well as Mg²⁺, and the molecules H₂O, CO₂, H₃O⁺ and OH^? on the energy of the Si-O bond in a H₆Si₂O₇ cluster has been calculated using semiempirical molecular orbital calculations (CNDO/2). Three types of elementary processes, i.e. substitution, addition, and polymerization reactions have been used to interpret data on the dynamic viscosity, surface tension and surface charge, hydrolytic weakening, diffusivity, conductivity, freezing point depression, and degree of polymerization of silicates in melts, glasses, and aqueous solutions. As a test of our calculational procedure, observed X-ray emission spectra of binary alkali silicate glasses were compared with calculated electronic spectra. The well known bondlength variations between the bridging bond [Si-O(br)] and the non-bridging bond [Si-O(nbr)] in alkali silicates are shown to be due to the propagation of oscillating bond-energy patterns through the silica framework. A kinetic interpretation of some results of our calculations is given in terms of the Bell-Evans-Polanyi reaction principle.     

Crystal-field theory calculations for Fe2+ Ions in bronzite,augite, and olivine

Crystal-field theory was applied to Fe²⁺ ions in three types of silicates in an attempt to assign all the major absorption bands with only one parameter to adjust. Coulomb potential energy field were calculated by Fourier method based on all the actual atomic coordinates refined by X-ray diffraction studies. Perturbed d-electron splitting energies of the central Fe²⁺ ion were calculated by introducing Configuration Interaction (CI) method for the lowest energy spectral states. All the major absorption bands observed in powdered bronzite, augite, and olivine, were assigned to the transitions between those calculated energy levels by optimizing only one parameter that expresses expansion or contraction of d-electron cloud. The result of the calculations gives almost the same assignments as the other previous works for bronzites, different assignments for augites, and a possibility of the existence of the fourth band hidden in the composite 1-μm band of olivines.