大别山北麓尖晶石橄榄岩中石榴辉石岩包体的成因矿物学信息

大别山北坡霍山饶拔寨等地的超基性岩中含有石榴辉石岩的包体。石榴辉石岩为草绿色致密块状 ,呈分米级的块体出现于蛇纹石化强烈的橄榄岩中。运用成因矿物学的方法 ,研究对比了石榴辉石岩的主要矿物组成石榴子石 ( Prp2 5— 3 5 )和钠质普通辉石 ( Jd1 0— 2 5 )等。岩石结构显示退变质作用有两期 :榴辉岩相退变形成的麻粒岩相矿物组合明显地被角闪岩相所切割。石榴辉石岩的寄主岩是尖晶石橄榄岩类 ,包括尖晶石方辉橄榄岩和尖晶石二辉橄榄岩。由于强烈的蛇纹石化 ,残余的橄榄石 ( Fo92— 93 )仅占 5%～ 4 0 % ,斜方辉石富镁 ( En87— 93)并有解理弯曲等韧性变形现象。采用 Ellisand Green的石榴子石单斜辉石 Fe-Mg交换平衡温度计 ,可计算出石榴辉石岩的 Fe-Mg分配系数 ( KD)为 4 .0 6～ 5.2 8。变质温度 t=84 1～ 94 3℃ ,估算压力 p=1 .5GPa,可以推测该橄榄岩体是从深度约 60 km的地幔 ,固态侵位于下地壳 ,而后与之一起隆升到地表。显然 ,此种石榴辉石岩应属 Coleman所划分的 A型榴辉岩 ,它与地幔岩浆作用有密切关系。石榴辉石岩和橄榄岩的岩石化学特征和稀土配分形式 ,说明它们的化学性质相当于地幔部分熔融所形成的玄武岩熔体及其残留体。在侧重探讨石榴辉石岩及其有关岩石中主要造岩矿物的成因矿物?     

新疆库地蛇绿岩中变质橄榄岩的结构、矿物组合及其成因——兼论地幔部分熔融及其产物的正确表述

新疆库地蛇绿岩中的变质橄榄岩具有呈网络状的二级粒序结构。第一级粒序由发育地幔塑性变形组构的粗粒橄榄石、斜方辉石及少量单斜辉石和尖晶石组成。第二级粒序由充填在第一级粒序颗粒之间的微粒矿物组成，在这种粒序中发现了四种含透闪石的矿物组合，它们是由残余地幔岩经过地幔交代作用和部分熔融作用形成的。同时还研究了铬铁矿中的矿物化学组成和成因。在此基础上，提出了上地幔岩初始熔体和部分熔融特征表述的设想。     

新疆库地蛇绿岩中变质橄榄岩的结构、矿物组合及其成因——兼论地幔部分熔融及其产物的正确表述

新疆库地蛇绿岩中的变质橄榄岩具有呈网络状的二级粒序结构。第一级粒序由发育地幔塑性变形组构的粗粒橄榄石、斜方辉石及少量单斜辉石和尖晶石组成。第二级粒序由充填在第一级粒序颗粒之间的微粒矿物组成，在这种粒序中发现了四种含透闪石的矿物组合，它们是由残余地幔岩经过地幔交代作用和部分熔融作用形成的。同时还研究了铬铁矿中的矿物化学组成和成因。在此基础上，提出了上地幔岩初始熔体和部分熔融特征表述的设想     

地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学…

在温度为１１３０－１４５０℃，压力为０．４－２．０ＧＰａ条件下，实验研究了地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演变。在部分熔融中，随熔融度的增大，橄榄石的Ｍｇ／（Ｍｇ＋Ｆｅ）＾尖晶石和斜方辉石的Ｍｇ／（Ｍｇ＋Ｆｅ）及Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；而橄榄石中的Ｃａ含量增至单斜辉石消失后逐渐降低；尖晶石中的Ｔｉ以较低的含量（ＴｉＯ２〈０．１５％）保持不变或稍有降低；斜方     

尖晶石在地幔橄榄岩部分熔融和亚固相平衡过程中的化学指示——实验研究及在自然岩石中的应用

以三组不同的重组的尖晶石橄榄岩为起始成分.在压力为0.10—0.15GPa和温度为1000—1380℃条件下,进行了系统的部分熔融和亚固相平衡实验。实验结果显示,在部分熔融过程中,尖晶石的Mg＃,即Mg/(Mg+Fe),和Cr＃,即Cr/(Cr+Al),随熔融度的增大而增大;在亚固相平衡过程中,尖晶石的Mg＃随温度的升高而增大,但Cr＃在纯橄榄岩中保持不变,而在二辉和方辉橄榄岩中稍有增大。尖晶石的Mg＃—Cr＃间反相近线性代表了一种非整体平衡的等热关系。计算模拟得到同样的结果。这同时被自然橄榄岩中尖晶石的Mg＃—Cr＃间的关系所证明。由于亚固相条件下平衡的结果,尖晶石的化学成分中只有Cr＃变化不大,故能用来衡量其所在岩体曾经受的相对熔融度。即尖晶石的Cr＃越大,所在岩体经受的熔融度越大。相反,尖晶石的Mg＃和Cr＃在岩浆结晶过程中应随温度的降低而减小;因此,可用玄武岩中尖晶石的Cr＃来指示其岩浆的原始Cr_2O_3/Al_2O_3特征,及用尖晶石的环带特征来探讨岩浆的演化(冷却速度,混染情况)。     

地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演化──Ⅱ．在自然岩石中的应用

分析了全球一些有代表性的上地幔尖晶石橄榄岩和斜长石橄榄岩中各矿物的化学成分变化特征。发现在斜长石橄榄岩中，尖晶石和斜方辉石富Ｔｉ，且Ｔｉ含量随Ｃｒ／（Ｃｒ＋Ａｌ）的增大而增大；单斜辉石富Ｔｉ贫Ｎａ，其Ｔｉ含量随Ｎａ含量的增大而减少。据此，结合实验结果，可以肯定世界各地大多数斜长石二辉橄榄岩在斜长石相域内未经受部分熔融。岩体所曾经受的部分熔融只发生在尖晶石或石榴石相。它们的相对熔融度可以用下面两个指标来估计：（１）最贫Ｔｉ尖晶石的Ｃｒ／（Ｃｒ＋Ａｌ）；（２）单斜辉石的最高Ｎａ含量。对于尖晶石橄榄岩，从二辉橄榄岩、方辉橄榄岩到纯橄榄岩，其尖晶石和斜方辉石的Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大，而含量很低的Ｔｉ或Ｎａ在尖晶石、斜方辉石及单斜辉石中保持不变或趋向逐渐减小。尖晶石橄榄岩的相对熔融度可据尖晶石的Ｃｒ／（Ｃｒ＋Ａｌ）和单斜辉石的Ｎａ含量来判断。     

地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演化──Ⅰ．实验研究

在温度为ｌｌ３０─ｌ４５０℃，压力为０．４─２．０ＧＰａ条件下，实验研究了地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演变。在部分熔融中，随熔融度的增大，橄榄石的Ｍｇ／（Ｍｇ＋Ｆｅ）尖晶石和斜方辉石的Ｍｇ／（Ｍｇ＋Ｆｅ）及Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；而橄榄石中的Ｃａ含量增至单斜辉石消失后逐渐降低；尖晶石中的Ｔｉ以较低的含量（ＴｉＯ２＜０．１５％）保持不变或稍有降低；斜方辉石中的Ｔｉ含量及单斜辉石的Ｎａ和Ｔｉ含量逐渐降低，直至非常小的值。在从尖晶石橄榄岩向斜长石橄榄岩的相转变过程中，尖晶石强烈富Ｔｉ，且其Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；斜方辉石中的Ｔｉ含量和Ｃｒ／（Ｃｒ＋Ａｌ）同时逐渐增大；单斜辉石中的Ｎａ含量降低而Ｔｉ含量升高或保持不变。当斜长石橄榄岩经受了部分熔融（即使很微弱），其在相转变过程中引起的各矿物相的化学成分特征要全部消失，而表现部分熔融作用的特征。这可作为判别橄榄岩在斜长石相域内是否经历了部分熔融的标志。关键词     

上地幔流体的性质和作用——从女山幔源二辉橄榄岩捕虏体获得的证据

玄武岩浆从地幔深处挟带上来的超镁铁质捕虏体含有地幔流体的直接证据,它们对于阐明地幔深部地质作用(部分熔融作用、地幔交代作用)的机制十分重要。女山幔源二辉橄榄岩的研究结果表明,初始的地幔流体除富含CO_2外,尚含有H_2O和少量CO、CH_4、SO_2、C1、F。地幔中的初始流体(挥发组分)在源部是溶解于地幔橄揽岩的高压固体矿物相中,它们在地幔上隆减压时出溶,形成细小的最早期流体包裹体。这些自由流体相在一定部应聚集,使得地幔固相线(和液相线)下降,引起上地幔发生减压部分熔融。初始的部分熔融主要发生于矿物边界,以单斜辉石最易遭受,形成矿物边缘的海绵状部分熔融带。当地幔剪切流动时,初始的部分熔融体珠滴联合成大的珠滴,并开始渗透,在变形橄榄岩中相连成脉状网络,晚期含C0_2岩浆包裹体及填隙玻璃即为其代表。由于剪裂作用,熔体(和流体)压裂开上覆橄榄岩,产生岩墙状通道,并在上地幔的某些低压区聚集成岩浆库。流体和熔体均为地幔交代作用的介质。在流体参与下,上地幔低度部分熔融产生的熔体将高度富集不相容元素。这些熔体和流体与亏损地幔间的相互作用,可以带来不相容元素重大的局部富集。当流体(和熔体)中H_2O浓度低时,仅发生隐交代作用;当H_2O浓度较高时,部分熔融程度也较高,相应有含水相(如角闪石等)成核,出现矿物交代作用。     

The Evolution of Alpine Ultramafic Rocks and Partial Melting of the Upper Mantle

Ultramafic rocks of Tibet and Xinjiang are the products of partial melting of the upper mantle. The evolution of their mineral composition is marked by two parallel evolutionary series: one is the progressive increase of the 100 Mg/(Mg+Fe~(2+) ratio of silicate minerals in order of lherzolite→harzburgite→dunite, i.e. the increase in magnesium; the other is the increase of the 100 Cr/(Cr+Al) ratio of accessory chrome spinel in the same order, i. e. the increase in Chromium. The above-mentioned evolutionary trends are contrary to that of magmatic differentiation. The evolution of fabrics of ultramafic rocks is characterized by progressive variation in order of protogranular texture→melted residual texture, symplectic texture and clastophyritic texture→equigranular mosaic texture and tabular mosaic texture. Experiments of partial melting of lherzolite have convincingly shown that the evolution of Alpine ultramafic rocks resulted from the partial melting of pyrolite. Various subtypes of them represent different degrees of partial melting. The vertical zoning marked by more basic rocks in the upper part and more acid rocks in the lower actually belongs to the fusion zoning of pyrolite.     

The Evolution of Alpine Ultramafic Rocks and Partial Melting of the Upper Mantle1

Abstract Ultramafic rocks of Tibet and Xinjiang are the products of partial melting of the upper mantle. The evolution of their mineral composition is marked by two parallel evolutionary series: one is the progressive increase of the 100 Mg / (Mg+Fe²⁺) ratio of silicate minerals in order of lherzolite?harzburgite?dunite, i.e. the increase in magnesium; the other is the increase of the 100 Cr/(Cr+Al) ratio of accessory chrome spinel in the same order, i.e. the increase in Chromium. The above- mentioned evolutionary trends are contrary to that of magmatic differentiation. The evolution of fabrics of ultramafic rocks is characterized by progressive variation in order of protogranular texture? melted residual texture, symplectic texture and clastophyritic texture? equigranular mosaic texture and tabular mosaic texture. Experiments of partial melting of lherzolite have convincingly shown that the evolution of Alpine ultramafic rocks resulted from the partial melting of pyrolite. Various subtypes of them represent different degrees of partial melting. The vertical zoning marked by more basic rocks in the upper part and more acid rocks in the lower actually belongs to the fusion zoning of pyrolite.     

Experimental Study of Partial Melting of Mantle Peridotite -A Discussion about the Genesis of Sih'ca-rich Fluids (Melts)

Experiments on partial melting of mantle lherzolite have been realized at 0.6 and 1.0 GPa and the chemical compositional variations of melts during different melting stages have been first discussed. The results show that the trends of variations in SiO2, CaO, Al2O3, Na2O and TiO2 are different at different melting stages. The melts produced at lower pressure are richer in SiO2 than those at higher pressure. The mantle-derived silica-rich fluids (silicate melts) are polygenetic, but the basic and intermediate-acid silicate melts in mantle peridotite xenoliths from the same host rocks, which have equivalent contents of volatile and alkali components and different contents of other components, should result from in-situ (low-degree) partial melting of mantle peridotite under different conditions (e.g. at different depths, with introduction of C-O-H fluids or in the presence of metasomatic minerals). The intermediate-acid melts may be the result of partial melting (at lower pressure) Opx + Sp + K-Na-rich f     

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     

Fluids and Melts in the Upper Mantle

This paper presents a direct study of the fluids and melts in the upper mantle by examining the fluid inclusions, melt inclusions and glasses trapped in the mantle lherzolite xenoliths entrained by Cenozoic alkali basalts (basanite, olivine-nephelinite and alkali-olivine basalt) from eastern China. The study indicates that the volatile components, which are dissolved in high-pressure solid mineral phases of mantle peridotite at depths, may be exsolved under decompressive conditions of mantle plume upwelling to produce the initial free fluid phases in the upper mantle. The free fluid phases migrating in the upper mantle may result in lowering of the mantle solidus (and liquidus), thereby initiating partial melting of the upper mantle, and in the meantime, producing metasomatic effects on the latter.     

中国东北地区上地幔组成、结构及热状态

本文通过对中国东北地区新生代玄武岩中超镁铁质包体的研究,根据地质压力计所估算的包体形成深度、玄武岩浆及辉石岩浆起源的深度等,建立了中国东北地区上地幔组成模式:1.壳幔过渡带;2.尖晶石二辉橄榄岩层;3.含有痕量硅酸盐熔体的低速层;4.尖晶石方辉橄榄岩层;5.石榴石二辉橄榄岩层。与此同时,根据地质温度计与地质压力计推算资料,作者认为中国东北地区上地幔属大洋地温。与典型克拉通地温相比,低速层位置较浅,上地幔处于过热状态,这与大陆裂谷的发育有关。     

地幔置换作用:华北两类橄榄岩及其透辉石微量元素对比证据

在华北地块东部，河南鹤壁新生代玄武岩中的耐熔橄榄岩捕虏体被认为是克拉通地幔的残留；山东山旺饱满橄榄岩捕虏体被认为是新生代玄武岩所捕获的新生地幔物质，对它们全岩的常量、微量元素，组成单矿物的常量元素和透辉石微量元素进行了对比．结果显示代表古老岩石圈的鹤壁克拉通型地幔和代表新生岩石圈的山旺“大洋型”地幔分别相当于原始地幔经历15％一25％和1％一5％熔融的产物．它们在熔融之后又都遭受了硅酸盐质碳酸岩熔体的交代改造作用，但前者明显强于后者．古老岩石圈橄榄岩的固相线温度受地幔熔／流体的长期交代而降低．由于早中生代时华北地块受扬子地块碰撞的地幔热扰动和软流圈上涌影响，促使橄榄岩熔融．所融出的基性岩浆主要垫托在地壳底部，形成壳-幔过渡带并实现大规模的壳-幔物质和热交换．第三纪以后的热沉降使抬升的软流圈物质冷却垫托在岩石圈底部构成新增生的岩石圈．因此，发生于东部的中、新生代(相对于古生代)岩石圈减薄不是软流圈抬升所引起的简单岩石圈厚度变小，而是伴随着新生地幔物质对古老地幔的置换过程．     

Experimental Study of Partial Melting of Mantle Peridotite--A Discussion about the Genesis of Silica-rich Fluids (Melts)

Experiments on partial melting of mantle lherzolite have been realized at 0.6 and 1.0 GPa and the chemical compositional variations of melts during different melting stages have been first discussed. The results show that the trends of variations in SiO2, CaO, Al2O3, Na2O and TiO2 are different at different melting stages. The melts produced at lower pressure are richer in SiO2 than those at higher pressure. The mantle-derived silica-rich fluids (silicate melts) are polygenetic, but the basic and intermediate-acid silicate melts in mantle peridotite xenoliths from the same host rocks, which have equivalent contents of volatile and alkali components and different contents of other components, should result from in-situ (low-degree) partial melting of mantle peridotite under different conditions (e.g. at different depths, with introduction of C-O-H fluids or in the presence of metasomatic minerals). The intermediate-acid melts may be the result of partial melting (at lower pressure) Opx + Sp + K-Na-rich fluid±(Amphi)±(Phlog)= Ol+melt.But the intermediate-acid magmas cannot be produced from the partial melting of normal mantle peridotite unless the crustal materials are introduced to some extent.     

High-pressure Partial Melting of Mafic Lithologies in the Mantle

We review experimental phase equilibria associated with partialmelting of mafic lithologies (pyroxenites) at high pressuresto reveal systematic relationships between bulk compositionsof pyroxenite and their melting relations. An important aspectof pyroxenite phase equilibria is the existence of the garnet–pyroxenethermal divide, defined by the enstatite–Ca-Tschermakspyroxene–diopside plane in CaO–MgO–Al₂O₃–SiO₂projections. This divide appears at pressures above 2 GPa inthe natural system where garnet and pyroxenes are the principalresidual phases in pyroxenites. Bulk compositions that resideon either side of the divide have distinct phase assemblagesfrom subsolidus to liquidus and produce distinct types of partialmelt ranging from strongly nepheline-normative to quartz-normativecompositions. Solidus and liquidus locations are little affectedby the location of natural pyroxenite compositions relativeto the thermal divide and are instead controlled chiefly bybulk alkali contents and Mg-numbers. Changes in phase volumesof residual minerals also influence partial melt compositions.If olivine is absent during partial melting, expansion of thephase volume of garnet relative to clinopyroxene with increasingpressure produces liquids with high Ca/Al and low MgO comparedwith garnet peridotite-derived partial melts. KEY WORDS: experimental petrology; mantle heterogeneity; partial melting; phase equilibrium; pyroxenite     

Chemical Composition of the Primitive Mantle Source of Peridotite Inclusions at Mount Lianshan, Liuhe County,Jiangsu Province

This paper presents a study of the major and trace element compositions of fresh mantle-derived spinel lherzolite and harzburgite inclusions from Cenozoic alkaline basalt in Mount Lianshan and Mount Panshi, Liuhe County, Jiangsu Province. An estimation is made of the contents of the major elements and some of the trace elements in the primitive mantle source region of the area, from which the authors have obtained MgO/Al2O3= 7.86. The contents of MgO and Al2O3 are also obtained as 37.58% and 4.78% respectively based on the correlation of MgO-Al2O3. Then, the contents of various elements in the primitive mantle are calculated using their regression equations with MgO, and the compositor) of the primitive mantle, a basic issue in geochemistry study, is discussed on that basis.