东乌旗中铁陨石硅酸盐地球化学特征及对成因的启示

东乌旗中铁陨石为1995年在内蒙发现的、为数不多的降落型中铁陨石,由金属—硫化物和硅酸盐相紧密混合而成。硅酸盐相由角砾部分（主要为角砾状橄榄石和辉长岩岩屑）和非角砾部分组成。岩相学特征、主量元素成分及REE地球化学特征表明角砾状橄榄石、非角砾橄榄石和辉长质硅酸盐（辉长岩岩屑和除橄榄石外的非角砾部分）三者可能分别结晶自不同的岩浆源区。进一步的分析表明Mg含量非常高的角砾状橄榄石可能来自一个分异小行星的橄榄岩质地幔,非角砾橄榄石和辉长质硅酸盐可能和HED陨石具有相同的母体Vesta小行星。冲击碰撞导致两个小行星的物质发生了混合。冲击作用产生的高温（约1200℃—1450℃）使得被撞击小行星表壳玄武质和辉长质岩石发生混合重熔,熔体结晶后形成中铁陨石的辉长质硅酸盐。该温度下非角砾橄榄石和角砾状橄榄石均未发生重熔。该模型较好地解释了角砾状橄榄石、非角砾橄榄石和辉长质硅酸盐三者之间的不平衡现象。     

夏日哈木超大型镍矿I号岩体地幔源区性质和硫化物熔离过程：来自橄榄石成分、亲铜元素和硫同位素的约束

夏日哈木超大型镍矿I号岩体的地幔源区目前仍存在软流圈、大陆下岩石圈地幔和辉石岩地幔三种不同认识。本次研究通过对该岩体西段新近发现的隐伏矿体ZK3109钻孔中斜方辉石岩和浸染状矿石中的橄榄石进行原位成分分析,识别地幔源区性质,并结合硫化物原位S同位素和全岩亲铜元素组成,探讨硫化物熔离过程。样品中橄榄石均具有较低的Mn/Zn比值(基本小于13.5),而且斜方辉石岩中橄榄石具有较低的100×Mn/Fe比值(基本小于1.35),指示岩体源区有辉石岩地幔组分加入,与前人根据硫化物矿体富Ni特征的推测一致。橄榄石低Ca(小于300.00×10^-6)、高Li(平均9.83×10^-6)以及Sc与Ni正相关指示辉石岩地幔组分可能是俯冲洋壳物质交代大陆下岩石圈地幔的产物。另一方面,斜方辉石岩中橄榄石Ni、Fo值均与Co负相关且全岩S和铂族元素(PGE)相关性不明显,说明浅部岩浆房硫化物熔离发生在斜方辉石岩形成之后。浸染状矿石中橄榄石Co和Ni正相关且全岩S和PGE正相关,暗示橄榄石成分受控于硫化物熔离。样品中镍黄铁矿、磁黄铁矿和黄铜矿δ³⁴...     

钙长辉长无球粒陨石NWA 11592的岩石矿物学特征及富铁橄榄石脉成因研究

灶神星是太阳系最大的硅酸盐质小行星,它的岩石样品(HED族陨石)是目前太阳系最古老的岩浆岩之一,很有可能记录了类地行星最早期地质流体活动的重要信息。本次工作首次在一块非角砾岩平衡型的Eucrite NWA 11592中发现了较粗长的富铁橄榄石脉。通过对NWA 11592陨石进行详细的岩相学和地球化学特征研究,将NWA 11592陨石划为玄武质非角砾岩型Eucrite,冲击变质程度至少为S4,热变质程度为6型。NWA 11592中富铁橄榄石脉最有可能为含H₂O流体沿裂隙的沉淀产物,反应系统应是开放且较为氧化的(f_O2达IW+0.9),且应发生在灶神星浅层地壳> 4 km的埋藏深度。含H₂O流体渗透作用除更多地发生在灶神星表面或近地表外,还有可能发生在灶神星内部的浅层地壳中。     

A recalibration of the garnet-olivine geothermometer and a new geobarometer for garnet peridotites and garnet-olivine-plagioclase-bearing granulites

The garnet-olivine Fe-Mg exchange geothermometer and the garnet-olivine-plagioclase geobarometer have been simultaneously calibrated using reversed experimental data based on the model reactions and between 900 and 1500 °C at 9.1–95.0 kbar and between 4.7 and 7.0 kbar at 750–1050 °C, respectively. The resulting garnet-olivine thermometer reproduces experimental temperatures mostly within ±75 °C and the garnet-olivine-plagioclase barometer reproduces experimental pressures well within ±0.19 kbar. These new thermobarometers use the same garnet and olivine activity models and are thermodynamically consistent. Application of these thermobarometers to garnet peridotites from mantle xenoliths, orogenic garnet peridotites over the world and the Adirondack olivine-bearing metagabbros yielded reasonable P–T results. The present garnet-olivine thermometer can be used to measure medium-high-grade to ultrahigh-grade, low-pressure to ultrahigh–high-pressure garnet peridotites and metagabbros, whereas the garnet-olivine-plagioclase barometer has limited application to garnet-olivine-plagioclase-bearing granulites.     

A Textural Record of Solidification and Cooling in the Skaergaard Intrusion, East Greenland

The clinopyroxene–plagioclase–plagioclase dihedralangle, _cpp, in gabbroic cumulates records the time-integratedthermal history in the sub-solidus and provides a measure oftextural maturity. Variations in _cpp through the Layered Seriesof the Skaergaard intrusion, East Greenland, demonstrate thatthe onset of crystallization of clinopyroxene (within LZa),Fe–Ti oxides (at the base of LZc) and apatite (at thebase of UZb) as liquidus phases in the bulk magma is recordedby a stepwise increase in textural maturity, related to an increasein the contribution of latent heat to the total heat loss tothe surroundings and a reduction in the specific cooling rateat the crystallization front of the intrusion. The onset ofboth liquidus Fe–Ti oxide and apatite crystallizationis marked by a transient increase in textural maturity, probablylinked to overstepping before nucleation. Textural maturationat pyroxene–plagioclase–plagioclase triple junctionseffectively ceases in the uppermost parts of the Layered Seriesas a result of the entire pluton cooling below the closure temperaturefor dihedral angle change, which is 1075°C. Solidificationof the Layered Series of the Skaergaard intrusion occurred viathe upwards propagation of a mush zone only a few metres thick. KEY WORDS: magma; partial melting; asthenosphere; olivine; mantle     

铁橄榄石高温高压流变性的实验研究

通过高温高压实验研究了铁橄榄石集合体的流变性.首先,利用高精度的Paterson气体介质变形装置对铁橄榄石集合体Fe2SiO4进行了高温三轴压缩蠕变试验.变形试验条件为温度1273～1423K,围压300MPa,差应力10～250MPa,应变率10-7～10-4s-1,试件的最大变形量不超过20%.利用三维非线性拟合方法对蠕变试验数据进行分析,得到铁橄榄石集合体的微观变形机制为扩散域和位错域,扩散域的应力指数为1左右.位错蠕变域中,干燥铁橄榄石集合体的应力指数为5.4.活化能为781kJ/mol;含水铁橄榄石集合体的应力指数为3.4,活化能为516kJ/mol.实验结果表明,含水时铁橄榄石的流变强度比干燥时小一个数量级.将实验结果与铁橄榄石单晶的强度进行对比,发现铁橄榄石集合体的流变强度比铁橄榄石单晶的强度高.从而得到了铁橄榄石集合体高温高压流变性(强度)的初步试验结果.     

Olivine-hosted melt inclusions in Pliocene–Quaternary lavas from the Qorveh–Bijar volcanic belt,western Iran: implications for source lithology and cooling history

ABSTRACT

Silicate melt inclusions (SMIs) are small droplets of magma that become trapped in minerals during crystal growth. SMIs in olivine crystals can provide critical information on the range of melt compositions and processes that occur during melt generation, evolution, transport, and eruption. The Pliocene–Quaternary volcanic rocks in the Qorveh–Bijar volcanic belt of western Iran show porphyritic and microlithic textures, with olivine and clinopyroxene being the dominant minerals. Magnesian olivines in these volcanic rocks contain primary SMIs. The composition and characteristic of olivine-hosted SMI of these rocks are investigated to constrain the source lithology for mafic volcanism. Bulk compositions of the SMIs overlap those of their host rocks and extend to higher CaO/Al₂O₃ values. The estimated entrapment pressures and temperatures of the studied SMIs are 9.1–10.3 kbar and 1220–1355°C. The calculated mafic parental melt contains 42.36 wt.% SiO₂, low total alkalis (3.22 wt.%), and high MgO (16.1 wt.%). Exploratory calculations using pMELTS show that this parental composition underwent variable degrees of fractional crystallization, as reflected by the variable compositions of the SMIs. Several lines of evidence including pyroxene xenocrysts and high FeO/MnO, FC3MS (FeO/CaO – 3*MgO/SiO2), and Zn/Fe ratios (14–21), suggest that a metasomatized pyroxenitic source contributed to the genesis of the parental melt. Amphibole in the SMIs indicates a high volatile content in the parental melt, which we conclude was generated from a metasomatized lithospheric mantle source. The pyroxenite source also contained garnet. Our geochemical results lead us to propose a new petrogenetic model. Specifically, we infer that a dense and unstable portion of the lithosphere underwent localized laminar detachment and downward flow, i.e. lithospheric drip. This drip underwent volatile-enhanced partial melting during descent through the underlying hot asthenosphere and generated the studied volcanic rocks.     

河北平山阜平群两种岩石熔融过程中的矿物相变及成分变化

河北平山阜平群浅粒岩和黑云变粒岩－片麻岩熔融高温高压实验结果表明,在开放体系条件下两类岩石深熔作用性质有一定的独特性,主要表现为ＳｉＯ２不饱和的非均一局部熔融－再结晶效应,当实验温度为６８０℃时,黑云母与斜长石发生脱水熔融和部分熔融,转换成白云母,绿帘石,铁尖晶石,石英等物质成分,当温度为７５０～８００℃时,上述中间产物和残留黑云母及新生熔体进一步转变为夕线石,铁尖晶石,橄榄石,富Ｃａ斜长石和钛铁     

上地幔橄榄石电导率影响因素及高压相变初探

人们对上地幔标志性矿物橄榄石的认识，基本上是经历一个从直流到交流，又从交流到阻抗谱的认识过程．本文主要通过对橄榄石电导率的影响因素出发，包括温度、压力、铁镁比值、氧逸度等因素的影响和制约．用目前国际高温高压学术界公认的阻抗谱技术探讨了橄榄石在高压下的相变，并在此基础上，进一步研究地球物理学家非常关心的热点问题-冷地幔的实验室的模拟，并作了充分的论证．     

亚稳态橄榄石对俯冲带负浮力的影响及其动力学意义

利用有限元方法,计算了不同俯冲速度及热传导系数俯冲岩石层的负浮力.在h-lt;400km和h-gt;740km的深度范围,低温高密俯冲带的负浮力随深度单调增加.因为尖晶石相到后尖晶石相的相变有负的克兰帕龙斜率,俯冲带冷的物质在660km间断面以下不到100km的深度范围内仍以低密度的低压物质相存在.所以在该深度范围,俯冲带受到了周围地幔阻止其插入下地幔的浮力作用.在400km-lt;h-lt;660km深度范围,由于受橄榄石相变的影响,不同计算模型负浮力随深度的变化有明显的不同.对于可能的相变动力学模型,亚稳态橄榄石的存在使负浮力随深度的增加值减小.其作用是不利于俯冲带直接穿透660km间断面,并引起该深度范围俯冲带沿俯冲方向压应力分布的变化.