东秦岭松树沟超镁铁质岩中辉石巨晶的成因和^40Ar—^39Ar定年及其地质意义

对东秦岭松树沟蛇绿岩残片中超镁铁质岩中的辉石巨晶化学成分的系统研究 ,表明其具有高压变质成因的特点 ;采用 4 0 Ar/ 39Ar快中子活化法得其高温坪年龄为 833.8± 4 Ma,等时线年龄为 84 8.2± 4 Ma。考虑到辉石对 Ar的封闭温度(6 2 0℃ )明显低于该岩片早期塑性变形变质温度 (≥ 80 0℃ ) ,因此该年龄不代表形成辉石巨晶的峰期高压变质时代 ,而代表了该岩体变质后初始抬升的冷却事件。这一年龄值与区内蛇绿岩中的镁铁质变质岩获得的变质年龄 (983± 14 0 Ma)在误差范围内大体一致 ,暗示松树沟蛇绿岩片可能整体经历了俯冲至下地壳深度遭受高压变质后再抬升的地质演化过程     

Tracing Lithosphere Evolution through the Analysis of Heterogeneous G9-G10 Garnets in Peridotite Xenoliths, II: REE Chemistry

Following previous publication of major–minor elementdata, this paper presents rare earth element (REE) data forheterogeneous (chemically zoned) garnets belonging to the peridotitesuite of mantle xenoliths from the Jagersfontein kimberlitepipe, South Africa. The rim compositions of the garnets in thehighest temperature–pressure (deepest) deformed peridotitesshow a typical megacryst-like pattern, of very low light REE(LREE) increasing through the middle REE (MREE) to a plateauof heavy REE (HREE) at c. 20 times chondrite; these compositionswould be in equilibrium with small-volume melts of the mid-oceanridge basalt (MORB) source (asthenosphere). With decreasingdepth the garnet rims show increasing LREE and decreasing HREE,eventually resulting in humped relative abundance patterns.A set of compositions is calculated for melts that would bein equilibrium with the garnet rims at different depths. Theseshow decreasing relative abundance of each REE from La to Lu,and the La/Lu ratio of the melts increases with decreasing depthof formation. Modelling of the effects of crystal fractionationshows that this process could largely generate the sequenceof garnet rim and melt compositions found with decreasing depth,including the humped REE patterns in high-level garnets. Consideringthe behaviour of major–minor elements as well as REE,a process of percolative fractional crystallization is advocatedin which megacryst source melts percolate upwards through peridotitesand undergo fractionation in conjunction with exchange withthe peridotite minerals. The initial megacryst melt probablyincludes melt of lithospheric origin as well as melt from theMORB source, and it is suggested that the process of percolativefractional crystallization may form a variety of metasomaticand kimberlitic melts from initial megacryst melts. Repeatedmetasomatism of the lower lithosphere by such differentiatingmelts is suggested by consideration of garnet core compositions.Such metasomatism would progressively convert harzburgites tolherzolites by increasing their CaO content, and this may accountfor the fact that the Cr-rich diamond–garnet harzburgiteparagenesis is commonly preserved only where it has been encapsulatedin diamonds. KEY WORDS: cratonic lithosphere; garnet zoning; mantle xenoliths; megacryst magma; metasomatic melt     

花岗岩中的钾长石巨晶:以南岭佛冈花岗质杂岩体中微斜长石巨晶为例

野外地质观察和岩石显微结构研究表明，佛冈花岗质杂岩体中微斜长石巨晶是岩浆结晶的产物，不是交代斑晶，也不是变斑晶，它们与基质中的微斜长石构成双峰式粒径，反映了岩浆的两阶段结晶历史，由于微斜长石是钾长石的低温变体，因此一种可能的机制是佛冈花岗质杂岩岩浆在侵位和基本固结后，冷却缓慢，使早结晶的正长石转变为微斜长石，此外，在新近的研究中，还发现了罕见的，但在佛冈花岗杂岩体中为数不少的“十字”贯穿式双晶微斜长石，以及微斜长石巨晶的“环斑”和“珠边”结构。     

Sequential high-pressure transformations of FeGeO3 high-P clinopyroxene (C 2 /c) at temperatures up to 365 ¯C

 In order to elucidate high-pressure transformations of high-P clinopyroxene (C2/c) at kinetically low temperature where atoms are not thermally activated, the transformation processes of FeGeO₃ clinopyroxene (C2/c) have been investigated at pressures up to 20 GPa and 365 °C by powder X-ray diffraction using a synchrotron radiation source and TEM observation. With increasing pressure up to 20 GPa at room temperature, FeGeO₃ high-P clinopyroxene (C2/c) reversibly transforms into a new high-pressure phase, FeGeO₃(II). On increasing the temperature up to 365 °C, this phase rapidly transforms into FeGeO₃ ilmenite within about 2 h. Intensity analysis of the X-ray diffraction pattern reveals that the high-pressure phase of FeGeO₃(II) has an intermediate structure between clinopyroxene and ilmenite: the cation arrangement is similar to that of clinopyroxene and the oxygen arrangement is similar to that of ilmenite. The comparison of the crystal structures of these polymorphs suggests that clinopyroxene to FeGeO₃(II) and FeGeO₃(II) to ilmenite transformations are performed by the slight deformation of the oxygen packing and the short-range movement of cations, respectively. It is shown that this high-P clinopyroxene transforms into ilmenite through a low-activation energy path under the low-temperature condition. Received: 30 August 2000 / Accepted: 10 February 2001     

丽江玄武岩水含量：对峨眉山大火成岩省源区水含量分布特征的启示

近年来对太古宙科马提岩和显生宙大火成岩省中苦橄岩的水含量、地幔潜热、源区成分等研究表明，这些短时间内喷出巨量岩浆的地表过程都与水化的地幔柱有关。峨眉山大火成岩省位于扬子板块西部，是我国被公认的大火成岩省之一。前人从地球化学的角度将其分为西、中、东三区；并通过对西区丽江、永胜、宾川、大理苦橄岩和中区二滩玄武岩的水含量分析，发现形成峨眉山大火成岩省的地幔柱可能自喷发初期就已普遍存在强烈的水化，且该特征持续至喷发中晚期。然而前人的研究着重于苦橄岩，对作为大火成岩省主体部分的玄武岩研究甚少。本文以位于西区的仕满、大具剖面中的高Ti/Y玄武岩为研究对象，采用单斜辉石斑晶反演原始熔体水含量的方法，得到仕满、大具玄武岩原始熔体的水含量下限分别为1. 15%和0. 83%，该水含量略低于丽江苦橄岩水含量。而计算出的源区最低水含量分别为1380×10 -6和1245×10 -6，与二滩玄武岩相当。结合前人报道的数据，本次工作的结果证明了峨眉山大火成岩省的地幔柱水化现象普遍且长期存在，地幔柱内部的热化学组成是不均一的，且其热化学结构是随着时间而发生变化的。本次工作还暗示了峨眉山大火成岩省地幔柱内部的水含量可能是由轴部南端向轴部北端，由轴部向边缘呈放射状递减的，这对于进一步认识大火成岩省的形成过程有一定的启示。     

福建省新生代玄武岩中辉石巨晶的矿物学研究

本文对我国福建省三条断裂带上产出的辉石巨晶进行了成分、结构、差热及穆斯堡尔谱分析,提出辉石巨晶有黑色和绿色两种类型,每种辉石巨晶均由两个相组成,两个相的存在决定了辉石巨晶的许多特殊性质。黑色辉石巨晶与玄武岩有明显的成因联系,而绿色辉石巨晶则没有。     

中国东部新生代玄武岩中低压单斜辉石的矿物化学及岩石学意义

本文搜集了中国东部11个省区新生代玄武岩中低压单斜辉石(Cpx)—斑晶、微晶Cpx的电子探针分析结果96个,通过大量的计算与投影,研究了Cpx的矿物化学特征,包括Cpx的种属划分及其成分特点,不同种属的Cpx成分变化及Cpx中SiO_2与其它氧化物的相关方程;也分析了Cpx矿物化学的岩石学意义,包括玄武岩的碱度顺序及系列划分,斑晶与微晶Cpx的成分差异及演化方向,Cpx结晶的温、压方程及斑晶形成的条件,玄武岩产出的板块构造环境等等。     

中国东部岩石圈地幔的演化——地幔岩捕虏体微量元素的证据

对中国东部赋存于新生代玄武岩中的地幔岩捕虏体的全岩和单斜辉石等作了主元素和微量元素分析，证实了二辉橄榄岩及其单斜辉石在主元素有连续变化的趋势，反映了具部分熔融后残留相的性质。方辉橄榄岩及其中的单斜辉石的主元素，Ｎｄ／Ｙｂ，Ｔｉ／Ｚｒ和Ｓｒ／Ｚｒ值与二辉橄榄岩的同类矿物是不连续过渡。     

榴辉岩富铝单斜辉石中出溶石榴子石现象研究

本文研究了江苏孟中榴辉岩富铝单斜辉石中出溶石榴子石现象，建立了出溶母体辉石成分，提出了出溶石榴子石的矿物反应。结果表明，富铝单斜辉石首先出溶富镁石榴子石，并形成绿辉石。后二者正是榴辉岩的典型矿物组合，因此，母体辉石可能正代表了榴辉岩的母体。本文中变质成因榴辉宕中出溶现象的研究尚属少见。     

岩浆过程中影响矿物稀土元素质量分数的因素──来自女山幔源单斜辉石巨晶的启示

运用电子微探针（ＥＭＰ）和二次离子质谱（ＳＩＭＳ）对安徽女山新生代碧玄岩中的１３个单斜辉石巨晶进行了主要元素和稀土元素的分析,１３件样品表现出稀土总量与Ｎａ质量分数的正相关。根据这些数据,结合文献中的资料,我们认为不同种矿物间稀土质量分数的差异是由晶体化学性质决定的;而同种矿物在一个相对简单的地球化学过程中,它们之间的稀土质量分数变化受地球化学过程发生的程度和周围环境的控制。