Lithium isotopic disequilibrium of minerals in the spinel lherzolite xenoliths from Boeun,Korea

Spinel lherzolite xenoliths found in Boeun, Korea, have protogranular to porphyroclastic textures and are enclosed in a Miocene alkali basalt. The lithium concentration and isotopic compositions of olivine, clinopyroxene, and orthopyroxene separates from the spinel lherzolite, and whole rocks of the spinel lherzolites and alkali basalt were determined by inductively coupled plasma mass spectrometry (ICP-MS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The lithium concentrations of the olivines and orthopyroxenes range from 2.2 to 5.0 ppm and from 2.1 to 6.4 ppm, respectively. In contrast, the clinopyroxenes have larger lithium concentrations, from 2.0 to 8.4 ppm, which reflect their preferential lithium enrichment. The lithium isotopic compositions (δ⁷Li) of olivines (-5.4 to + 3.5‰), orthopyroxenes (-11.4 to -0.1‰), and clinopyroxenes (-14.4 to -4.7‰) range far beyond the average mantle composition of + 4 ± 2‰. The lithium isotopic composition of the host rock, alkali basalt (3.4‰), is within the range of the intraplate and oceanic island basalts. The spinel lherzolites from Boeun exhibits strong elemental and isotopic disequilibria due to the different lithium and lithium isotope diffusion velocities in the olivine, orthopyroxene, and clinopyroxene minerals after eruption and magma cooling.     

兴蒙造山带橄榄岩捕掳体中石榴石次变边对地幔组成转变的启示

地幔橄榄岩捕虏体中石榴石次变边的形成过程对理解地幔的构造演化和转变具有非常重要的意义。兴蒙造山带锡林浩特地区新生代玄武岩携带的石榴石橄榄岩捕虏体中的石榴石普遍发育冠冕状次变边结构。本文通过对石榴石及其次变边进行详细的岩相学和电子探针分析,探讨石榴石次变边的成因及其揭示的岩石圈地幔经历的深部过程。根据次变边矿物组成的不同,将其分为原始的次变边（R1和R2）和交代的次变边（MR1和MR2）。原始的次变边中,新鲜的石榴石由内向外依次被放射状且矿物颗粒较细的R1和粒状且矿物颗粒较粗的R2包围,且R1通常比R2宽。R1主要组成矿物为Opx+Sp+Melt1/Pl±Cpx,R2主要组成矿物为Opx+Sp+Cpx。与R2及橄榄岩捕虏体相比,R1的斜方辉石和单斜辉石具有较高的Al₂O₃含量和较低Mg^#值及SiO₂含量。与橄榄岩捕虏体相比,R1和R2中的尖晶石均具有较低的Cr^#值和较高的Mg^#值。R1的斜长石为钙长石,熔体成分与斜长石相比具有偏高的MgO和FeO含量。计算的R1的全岩成分与新鲜的石榴石一致,是石榴石等化学分解的产物。R2的全岩成分比新鲜的石榴石具有偏高的MgO和偏低的SiO₂及Al₂O₃含量,是石榴石和橄榄石反应的产物。交代的次变边是由原始的次变边受到部分或完全的交代作用形成的。完全交代的次变边仍然保留原始次变边的双圈层结构,而未完全交代的次变边则仅在原始次变边的局部出现。交代的次变边中,矿物颗粒较细的核部（MR1）和矿物颗粒较粗的边部（MR2）主要矿物组成一致,皆为Ol+Cpx+Sp+Melt2。与原始的次变边相比,MR1和MR2中的橄榄石和单斜辉石均具有较高的Mg^#值,单斜辉石同时具有较高Ca/Al比值（>8）,尖晶石具有较高的Cr^#值和较低的Mg^#值,熔体较富SiO₂、Na₂O和K₂O含量。这些现象说明交代的次变边可能是碳酸盐熔/流体交代原始的次变边消耗斜方辉石生成橄榄石和单斜辉石形成的,这与岩相学观察到的单斜辉石中包裹斜方辉石残余体一致。此外,同一样品中R1的平衡温度略高于R2的平衡温度,且二者均高于橄榄岩的平衡温度。因此,锡林浩特地区石榴石橄榄岩至少经历了两阶段的退变质作用：第一阶段为橄榄岩自石榴石相抬升至尖晶石相,且受到地幔上涌的加热作用,导致石榴石和橄榄石进行缓慢的反应形成R2;第二阶段是在连续减压且加热的背景下,第一阶段残余的石榴石发生快速等化学分解反应,形成R1。退变质作用之后,石榴石原始的次变边又经历了碳酸盐熔/流体的交代作用形成MR1和MR2,最终被寄主玄武岩携带至地表。所以,石榴石次变边的形成记录了新生代时期兴蒙造山带经历的广泛的地幔上涌和多次的地幔隆升,以及地幔交代作用,为研究深部地幔过程提供了重要证据。华北克拉通晚中生代时期经历了强烈的岩石圈伸展运动并伴随着软流圈的上涌,这些过程同样会造成岩石圈地幔的减压和加热,从而导致石榴石相橄榄岩向尖晶石相转变,这可能也是华北克拉通岩石圈地幔转变的机制之一。

     

Hf isotope compositions and HREE variations in off-craton garnet and spinel peridotite xenoliths from central Asia

Garnet-facies continental mantle is poorly understood because the vast majority of mantle xenoliths in continental basalts are spinel peridotite. Peridotite xenoliths from Vitim (southern Siberia) and Mongolia provide some of the best samples of garnet and garnet-spinel facies off-craton lithospheric mantle. Garnets in those fertile to moderately depleted lherzolites show a surprisingly broad range of HREE abundances, which poorly correlate with modal and major oxide compositions. Some garnets are zoned and have Lu-rich cores. We argue that these features indicate HREE redistribution after the partial melting, possibly related to spinel-garnet phase transition on isobaric cooling. Most peridotites from Vitim have depleted to ultra-depleted Hf isotope compositions (calculated from mineral analyses: ε_Hf(0) = +17 to +45). HREE-rich garnets have the most radiogenic ε_Hf values and plot above the mantle Hf-Nd isotope array while xenoliths with normal HREE abundances usually fall within or near the depleted end of the MORB field. Model Hf isotope ages for the normal peridotites indicate an origin by ancient partial melt extraction from primitive mantle, most likely in the Proterozoic. By contrast, an HREE-rich peridotite yields a Phanerozoic model age, possibly reflecting overprinting of the ancient partial melting record with that related to a recent enrichment in Lu. Clinopyroxene-garnet Lu-Hf isochron ages (31-84 Ma) are higher than the likely eruption age of the host volcanic rocks (∼16 Ma). Garnet-controlled HREE migration during spinel-garnet and garnet-spinel phase transitions may be one explanation for extremely radiogenic ¹⁷⁶Hf/¹⁷⁷Hf reported for some mantle peridotites; it may also contribute to Hf isotope variations in sub-lithospheric source regions of mantle-derived magmas.     

Petrology and geochemistry of spinel peridotite xenoliths from Hannuoba and Qixia, North China craton

We report mineralogical and chemical compositions of spinel peridotite xenoliths from two Tertiary alkali basalt localities on the Archean North China craton (Hannuoba, located in the central orogenic block, and Qixia, in the eastern block). The two peridotite suites have major element compositions that are indistinguishable from each other and reflect variable degrees (0–25%) of melt extraction from a primitive mantle source. Their compositions are markedly different from typical cratonic lithosphere, consistent with previous suggestions for removal of the Archean mantle lithosphere beneath this craton. Our previously published Os isotopic results for these samples [Earth Planet. Sci. Lett. 198 (2002) 307] show that lithosphere replacement occurred in the Paleoproterozoic beneath Hannuoba, but in the Phanerozoic beneath Qixia. Thus, we see no evidence for a compositional distinction between Proterozoic and Phanerozoic continental lithospheric mantle. The Hannuoba xenoliths equilibrated over a more extensive temperature (hence depth) interval than the Qixia xenoliths. Neither suite shows a correlation between equilibration temperature and major element composition, indicating that the lithosphere is not chemically stratified in either area. Trace element and Sr and Nd isotopic compositions of the Hannuoba xenoliths reflect recent metasomatic overprinting that is not related to the Tertiary magmatism in this area.     

汉诺坝幔源橄榄岩包体的微量元素和Re-Os同位素地球化学：SCLM的性质和形成时代

本文报道了汉诺坝新生代碱性玄武岩中地幔橄榄岩包体的主量、微量元素和Re-Os同位素。14个尖晶石橄榄岩Re、Os含量分别为0.022～0.193ng/g和1.237～4.304ng/g，^187Os/^188Os比值为0.1183～0.1244，与^187Os/^188Os比值相关性不好，但与熔体亏损指标如重稀土元素Yb的含量、全岩Al2O3的百分含量有很好的线性关系，可能反映了地幔熔融后的Re或/和Os的活动。全岩Al2O3、CaO、TiO2含量均与MgO有很好的负相关性，全岩原始地幔标准化REE丰度模式呈现了LREE亏损，表明该区橄榄岩包体是由软流圈地幔经过部分熔融，亏损了玄武质组分后形成的。由Os同位素代理等时线得到该区陆下岩石圈地幔的形成年龄为1.7～2.0Ga，表明尖晶石相橄榄岩所代表的岩石圈地幔是中元古代的陆下岩石圈地幔减薄后的残留体。     

粗粒与剪切结构橄榄岩捕虏体及其单斜辉石微量元素对比

地山西栖霞具不同结构的“干”灾晶石相橄榄岩进行了全岩化学、微量元素,矿物成分和单斜辉石微量元素分析和对比。表明在橄榄岩从粗粒结构向剪切结构的转化中,随着变质变形作用的增强存在着复杂的熔／流体的加入富集和熔体的提取亏损作用;交代介质属具强渗透性的SiO2不饱和的硅酸盐碳酸岩熔体。同时发现不同结构橄榄岩中单斜辉石的REE与其全岩的REE程度有如下的关系;粗粒结构橄榄岩石中矿物与岩石的差别量大,但REE的配合分形可以反映全岩的情况;剪切结构橄榄岩中两者的差别较小。其它高度不相容微量元素可能主要赋存粒间组分或／和矿物流体包裹体中。     

Compositional variations and heterogeneity in fertile lithospheric mantle: peridotite xenoliths in basalts from Tariat,Mongolia

Clinopyroxene-rich, poorly metasomatised spinel lherzolites are rare worldwide but predominate among xenoliths in five Quaternary basaltic eruption centres in Tariat, central Mongolia. High-precision analyses of the most fertile Tariat lherzolites are used to evaluate estimates of primitive mantle compositions; they indicate Mg#_PM = 0.890 while lower Mg# in the mantle are likely related to metasomatic enrichments in iron. Within a 10 × 20 km area, and between ~45 and ≥60 km depth, the sampled xenoliths suggest that the Tariat mantle does not show km-scale chemical heterogeneities and mainly consists of residues after low-degree melt extraction at 1–3 GPa. However, accessory (<1%) amphibole and phlogopite are unevenly distributed beneath the eruption centres. Ca abundances in olivine are controlled by temperature whereas Al and Cr abundances also depend on Cr/Al in coexisting spinel. Comparisons of conventional and high-precision analyses obtained for 30 xenoliths show that high-quality data, in particular for whole-rocks and olivines, are essential to constrain the origin of mantle peridotites. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

长白山新生代玄武岩中橄榄岩包体所揭示的岩石圈地幔特征

长白山地区位于华北克拉通东北部,广泛出露富含地幔橄榄岩包体的新生代玄武岩,为研究岩石圈地幔的性质和演化提供了优越条件。本文对长白山地区天池和龙岗新生代火山岩群中尖晶石相橄榄岩包体进行了岩石学、全岩主微量元素、矿物主量元素、单斜辉石微量元素和Sr-Nd-Hf同位素分析。研究结果表明,尖晶石相橄榄岩包体由二辉橄榄岩和少量的方辉橄榄岩组成,Mg#值为87.4~91.2,表现出新生饱满的特征,平衡温度为900~1100℃。橄榄石的Mg#值（% Fo）为85.6~91.3。单斜辉石包括四种类型：（1）轻稀土元素严重亏损型;（2）轻稀土元素亏损型;（3）向右微倾型和（4）"勺型"。单斜辉石表现出Sr同位素（87Sr/86Sr=0.702749~0.707276）整体亏损,部分样品富集的特征,单斜辉石的Nd-Hf同位素呈现出亏损特征（143Nd/144Nd=0.512886~0.51333、εHf=+17.7~+49.8）。长白山地区二辉和方辉橄榄岩分别经历了小于10%和略大于10%的部分熔融作用,并受到富水硅酸盐熔体的地幔交代作用。太平洋板块向西俯冲作用使得软流圈上涌并携带大量壳源物质进入地幔深部,与岩石圈地幔发生橄榄岩-熔体反应,形成了长白山地区不均一的岩石圈地幔,以新增生饱满地幔为主,夹有少量古老难熔岩石圈地幔碎片。     

Symplectite in spinel lherzolite xenoliths from the Little Hungarian Plain, Western Hungary: A key for understanding the complex history of the upper mantle of the Pannonian Basin

Two spinel lherzolite xenoliths from Hungary that contain pyroxene–spinel symplectites have been studied using EPMA, Laser ablation ICP-MS and universal stage. Based on their geochemical and structural characteristics, the xenoliths represent two different domains of the shallow subcontinental lithospheric mantle beneath the Pannonian Basin. The occurrence of symplectites is attributed to the former presence and subsequent breakdown of garnets due to significant pressure decrease related to lithospheric thinning. This implies that both mantle domains were once part of the garnet lherzolitic upper mantle and had a similar history during the major extension that formed the Pannonian Basin.

Garnet breakdown resulted in distinct geochemical characteristics in the adjacent clinopyroxene crystals in both xenoliths. This is manifested by enrichment in HREE, Y, Zr and Hf towards the clinopyroxene porphyroclast rims and also in the neoblasts with respect to porphyroclast core compositions. This geochemical feature, together with the development and preservation of the texturally very sensitive symplectites, enables us to determine the relative timing of mantle processes. Our results indicate that garnets had been metastable in the spinel lherzolite environment and their breakdown to pyroxene and spinel is one of the latest processes that took place within the upper mantle before the xenoliths were brought to the surface.     

安徽女山新生代玄武岩中橄榄岩包体矿物的含水性研究

本文对15个来自安徽女山新生代玄武岩的橄榄岩包体矿物（橄榄石、单斜辉石和斜方辉石）进行了详细的微区傅立叶变换红外光谱（Micro-FTIR）分析。结果显示,所有被测的橄榄石颗粒都没有明显的OH吸收峰,这表明橄榄石要么不舍结构水,要么结构水含量〈2ppm（H2Owt．下同）;所有的单斜辉石和斜方辉石颗粒都含有以OH形式存在的结构水。辉石矿物颗粒内部的结构水含量要么是均一的,要么表现出中心高边缘低的不均一分布。这种不均一分布的特征应该来自于包体上升过程中由于压力降低而引起的H扩散。如果用每个样品多个测定颗粒的中心部位的平均值来代表该样品的话,15个样品的单斜辉石水含量为6～356ppm,斜方辉石水含量6～139ppm。单斜辉石与斜方辉石之间水含量的比值为-2．5,和文献中报道的分配系数吻合,表明女山单斜辉石和斜方辉石之间达到了H平衡。女山的橄榄岩分成低温（〈950℃）和高温（〉1050℃）两组,所有的含角闪石的样品都在低温组。高温组的斜方辉石和单斜辉石表现出H2O含量和Al含量的正相关、和Mg含量的负相关,表明Al^3＋H^←→Si^4＋和Al^＋H^＋←→2Mg^2＋是辉石中H的主要结合机制,同时也表明这些样品有效地保存了其在源区的原始结构水含量。而低温组的辉石偏离了相关趋势,结合该组部分样品含有角闪石的特征,我们提出一个流体（本文中采用广义的概念,即包括熔体和流体）上升交代的模式来解释女山橄榄岩的特征：流体从下向上运移,与高温组（下部）橄榄岩先发生反应,由于水含量较低,既没有影响橄榄岩矿物的原始水含量,也没有能形成角闪石,在上升的过程中由于发生名义上无水矿物（橄榄石,辉石等巨晶）的结晶分离,流体中的水含量不断增加,积累到一定程度,即与低温组（上部）橄榄岩反应时。不仅影响了橄榄岩矿物的原始水含量,也在部分样品中形成了角闪石。     

碱性玄武岩中幔源岩石包体内尖晶石成分特征及其岩石学成因意义

通过对我国东部北起黑龙江省南至海南省３１个产地的新生代碱性玄武岩中橄榄岩类 （纯橄岩、方辉橄榄岩及二辉橄榄岩） 包体和辉石岩类包体中的１６０ 多个尖晶石电子探针分析数据, 论述了尖晶石的Ｃｒ－Ａｌ, Ｆｅ－Ｍｇ, Ｎｉ－Ｍｇ 主元素及有关比值和端员组分之间的关系, 分析研究了不同岩类包体中尖晶石的颜色、成分及成因之间的联系。并利用所分析的有关橄榄石、斜方辉石、单斜辉石共生矿物的电子探针分析数据, 采用新的、较合理的Ｂｒｅｙ－Ｋｏｈｌｅｒ温度计及Ｋｏｈｌｅｒ－Ｂｒｅｙ 压力计和Ｂａｌｌｈａｕｓ ｅｔａｌ． 氧逸度计算方法进行了计算, 探讨了尖晶石成分与其形成温度、压力和氧逸度状态的关系, 指出了尖晶石成分所反映的地幔亏损程度及部分熔融程度的变化规律及尖晶石 （相） 稳定的温度、压力和氧逸度范围。     

新疆西天山查岗诺尔铁矿床磁铁矿和石榴石微量元素特征及其对矿床成因的制约

查岗诺尔大型磁铁矿床位于西天山阿吾拉勒东段,赋存于下石炭统大哈拉军山组安山岩及安山质火山碎屑岩之中,主体矿底板夹透镜状的大理岩,矿体主要为层状、似层状、透镜状。根据矿石组构和矿物共生特征,可以划分为岩浆期和热液期两个成矿期,后者包括矽卡岩和石英-硫化物两个亚成矿期,进一步可以细分为6个成矿阶段。岩浆期的磁铁矿∑REE很低,稀土配分模式大致呈轻稀土、重稀土较富集而中稀土亏损的U型,富Ti、V、Cr,表明铁质可能来自安山质岩浆的结晶分异作用; 矽卡岩亚成矿期的磁铁矿∑REE极低,略微富集LREE,其它稀土元素亏损强烈,贫Ti、V,略富集Ni、Co和Cu。矽卡岩亚期的含矿和无矿矽卡岩中的石榴石的稀土配分模式类似,∑REE含量相对较高,呈HREE富集、LREE亏损、弱正Eu异常的分布型式,显示了交代成因石榴石的特征,暗示与其共生的磁铁矿也是通过热液流体与围岩地层的交代反应生成的,铁质来自围岩。结合矿床地质与微量元素地球化学,认为查岗诺尔铁矿可能是岩浆型和矽卡岩型(主要)的复合叠加矿床。     

江苏盘石山玄武岩中橄榄岩包体的氧同位素和微量元素地球化学

本文研究了8个来自江苏盘石山新生代碱性玄武岩中的橄榄岩包体，利用ICP—MS技术测定了橄榄岩中单斜辉石的微量元素组成；利用激光氟化技术系统地分析了橄榄石、单斜辉石和斜方辉石的氧同位素比值。结果显示，盘石山橄榄岩包体矿物的氧同位素比值落在“正常”地幔矿物的氧同位素变化范围之内，而且矿物之间达到了氧同位素平衡。部分单斜辉石不相容元素富集的特征表明，有些样品经历了隐性地幔交代作用（cryptical metasomatism），配合氧同位素的数据来看，影响盘石山上地幔的交代介质为来自地幔内部的熔体，不合有地壳组分。从盘石山和安徽女山（盘石山以北约100km）的对比看来，影响女山上地幔的洋壳流体可能来自于华南一华北陆陆碰撞之前的海洋板块俯冲，因此华南一华北的深部缝合带可能就在女山和盘石山之间。     

Continuation of the San Andreas fault system into the upper mantle: Evidence from spinel peridotite xenoliths in the Coyote Lake basalt, central California

The Coyote Lake basalt, located near the intersection of the Hayward and Calaveras faults in central California, contains spinel peridotite xenoliths from the mantle beneath the San Andreas fault system. Six upper mantle xenoliths were studied in detail by a combination of petrologic techniques. Temperature estimates, obtained from three two-pyroxene geothermometers and the Al-in-orthopyroxene geothermometer, indicate that the xenoliths equilibrated at 970–1100 °C. A thermal model was used to estimate the corresponding depth of equilibration for these xenoliths, resulting in depths between 38 and 43 km. The lattice preferred orientation of olivine measured in five of the xenolith samples show strong point distributions of olivine crystallographic axes suggesting that fabrics formed under high-temperature conditions. Calculated seismic anisotropy values indicate an average shear wave anisotropy of 6%, higher than the anisotropy calculated from xenoliths from other tectonic environments. Using this value, the anisotropic layer responsible for fault-parallel shear wave splitting in central California is less than 100 km thick. The strong fabric preserved in the xenoliths suggests that a mantle shear zone exists below the Calaveras fault to a depth of at least 40 km, and combining xenolith petrofabrics with shear wave splitting studies helps distinguish between different models for deformation at depth beneath the San Andrea fault system.     

大兴安岭岩石圈地幔特征——哈拉哈河-绰尔河橄榄岩捕虏体的证据

大兴安岭哈拉哈河-绰尔河第四纪火山岩中含有尖晶石相和石榴石相橄榄岩捕虏体.本文报道的尖晶石相橄榄岩包括方辉橄榄岩和二辉橄榄岩两类,前者分布数量略高于后者.方辉橄榄岩多数具有较高的平衡温度(1072～1193℃),矿物化学成分变化大,含有高Mg橄榄石和高Cr#尖晶石,这些特征一致表明是古老岩石圈地幔残余的样品.而二辉橄榄岩显示相对均一的矿物化学成分和很宽的平衡温度变化范围(636～1178℃),代表了明显受到改造的岩石圈地幔,可能反映岩石圈地幔的不同深度和局部经历了软流圈与岩石圈相互作用.通过与华北克拉通的对比,发现地处兴蒙造山带的大兴安岭岩石圈地幔中仍保留有相当量的古老岩石圈地幔残余,区别于遭受强烈改造和破坏的华北克拉通东部地区的岩石圈地幔.     

海南岛石碌矽卡岩铁矿石中石榴子石的熔融包裹体及其意义

对石碌铁矿一块具有代表性的新鲜矽卡岩铁矿石标本进行了岩石薄片显微镜观察、电子探针和喇曼光谱分析研究.在石榴子石中发现了熔融包裹体.这些包裹体主要特点是大小悬殊和成群或成带分布,最大者达98μm×5μm,最小者为1μm×1μm,多数包裹体长约5～30μm,宽约2～7μm,也有不少呈孤立状散布在石榴子石中.其形态多样,呈纺锤形、哑铃形,串珠状,藕形,近圆形和不规则状.研究的矽卡岩主要由钙铁榴石组分高的石榴子石、磁铁矿、石英、透闪石和透辉石组成,还有呈定向和星点分布的磷灰石,少量锆石与榍石;石榴子石中的熔融包裹体捕获的熔体由含Ca、Fe、Al和挥发分(H2O和CO2)的硅酸盐熔融体组成.在熔融包裹体冷却过程中,由于温度缓慢降低,赤铁矿、钙铁榴石、石英、方解石和透辉石从上述硅酸盐熔体中析出,剩下的残余熔体不混溶,变成含有Ca和Si等杂质的铁质熔体、含si、Fe的碳酸盐熔体和含Ca、Al、Fe的硅酸盐熔体.喇曼光谱测定显示,石榴子石中熔融包裹体含有石榴子石、赤铁矿和方解石,个别含少量水蒸气.磁铁矿含有可疑的Fe、Sj熔融包裹体和Sj、Fe熔融包裹体.在透辉石-透闪石矽卡岩铁矿石的石榴子石里发现大量熔融包裹体的事实无疑.矽卡岩铁矿石石榴子石中熔融包裹体的首次发现,它可能有助于石碌铁矿床挖掘老矿潜力和拓宽找矿的新思路.     

Interaction between protokimberlite melts and mantle lithosphere: Evidence from mantle xenoliths from the Dalnyaya kimberlite pipe,Yakutia (Russia)

The Dalnyaya kimberlite pipe(Yakutia,Russia) contains mantle peridotite xenoliths(mostly Iherzolites and harzburgites) that show both sheared porphyroclastic(deformed) and coarse granular textures,together with ilmenite and clinopyroxene megacrysts.Deformed peridotites contain high-temperature Fe-rich clinopyroxenes,sometimes associated with picroilmenites,which are products of interaction of the lithospheric mantle with protokimberlite related melts.The orthopyroxene-derived geotherm for the lithospheric mantle beneath Dalnyaya is stepped similar to that beneath the Udachnaya pipe.Coarse granular xenoliths fall on a geotherm of 35 mWm-2 whereas deformed varieties yield a 45 mWm-2)geotherm in the 2-7.5 GPa pressure interval.The chemistry of the constituent minerals including garnet,olivine and clinopyroxene shows trends of increasing Fe~#(=Fe/(Fe+Mg))with decreasing pressure.This may suggest that the interaction with fractionating protokimberlite melts occurred at different levels.Two major mantle lithologies are distinguished by the trace element patterns of their constituent minerals,determined by LA-ICP-MS.Orthopyroxenes,some clinopyroxenes and rare garnets are depleted in Ba,Sr,HFSE and MREE and represent relic lithospheric mantle.Re-fertilized garnet and clinopyroxene are more enriched.The distribution of trace elements between garnet and clinopyroxene shows that the garnets dissolved primary orthopyroxene and clinopyroxene.Later high temperature clinopyroxenes related to the protokimberlite melts partially dissolved these garnets.Olivines show decreases in Ni and increases in Al,Ca and Ti from Mg-rich varieties to the more Fe-rich,deformed and refertilized ones.Minerals showing higher Fe~#(0.11-0.15) are found within intergrowths of low-Cr ilmenite-clinopyroxene-garnet related to the crystallization of protokimberlite melts in feeder channels.In P-f(O_2) diagrams,garnets and Cr-rich clinopyroxenes indicate reduced conditions at the base of the lithosphere at-5 log units below a FMQ buffer.However,Cr-poor clinopyroxenes,together with ilmenite and some Fe-Ca-rich garnets,demonstrate a more oxidized trend in the lower part of lithosphere at-2 to 0 log units relative to FMQ.Clinopyroxenes from xenoliths in most cases show conditions transitional between those determined for garnets and megacrystalline Cr-poor suite.The relatively low diamond grade of Dalnyaya kimberlites is explained by a high degree of interaction with the oxidized protokimberlite melts,which is greater at the base of the lithosphere.     

喜马拉雅造山带中新世岩浆型石榴子石的矿物化学特征:从高Sr/Y花岗岩到淡色花岗岩

石榴子石是演化花岗岩常见的重要副矿物之一,但石榴子石地球化学特征如何随岩浆演化而变化是有待探讨的问题之一。雅拉香波片麻岩穹隆发育年龄分别为20. 3±0. 5Ma和20. 1±0. 3Ma(锆石U-Pb年龄)的高Sr/Y比二云母花岗岩(TMG)和淡色花岗岩(Grt-LG)。虽然两类花岗岩都含石榴子石,且在形成时代和Sr-Nd同位素组成上相似,但在元素地球化学特征上具有明显的差异,淡色花岗岩和二云母花岗岩分别代表演化程度较高和较原始的岩浆。在同一件样品中,在石榴子石颗粒之间,存在一定程度的微量元素地球化学特征的不均一性,反映了局部熔体地球化学特征。在两类花岗岩中,岩浆型石榴子石具有以下相似的地球化学特征:(1)从核部到边部,Mn和HREE含量降低,表现出典型的生长环带特征;(2)富集HREE,亏损LREE;和(3)显著的Eu负异常。但在关键微量元素Zn、Sc和Y上,具有明显的差异性。在花岗质岩浆演化过程中,贫Fe、Mg和Mn矿物相的分离结晶作用,导致残留熔体的Ca和Sr含量降低,Eu负异常幅度增大,Sc、Zn、Y和HREE增高,是导致淡色花岗岩石榴子石相应元素含量增高的主要原因。上述观测表明:高Sr/Y花岗岩也可以结晶石榴子石,与通常的淡色花岗岩石榴子石相比,这些石榴子石的Sc、Zn和Y含量和Eu异常幅度明显较低。但随分异程度的升高,石榴子石的元素地球化学特征与源自变沉积岩的淡色花岗岩的类似。因此,花岗岩中的石榴子石矿物化学特征变化记录了花岗岩岩浆演化的重要信息。     

Melting of crustal xenoliths within ascending basalt: Example from the Kula volcanic field,western Anatolia,Turkey

During its storage or ascent, basaltic magma inevitably interacts with the surrounding rocks. In this study, schist xenoliths incorporated within ascending basalt are examined. Heating of the xenoliths combined with decompression effect of rapid magma uprise led to dehydration melting of hydrous minerals producing hercynitic spinel, melt, sillimanite and FeTi oxides. The melt is rhyolitic, strongly peraluminous (1.77 < A/CNK < 2.35) and corundum normative. It may contain up to 8 wt%FeO_t. It occurs between the foliation planes and in the intragranular environment. Dehydration melting of micas in the schist is probably related to combined effects of heating by basaltic magma and decompression due to the rapid rise. Melting of xenoliths was a progressive process at low pressure. To cite this article: H. Bayhan et al., C. R. Geoscience 338 (2006).     

Trace element contents and correlation in surface soils in China's eastern alluvial plains

 A study investigating the contents of 13 trace elements and the correlations between these trace elements and soil parameters of the surface soils in the eastern alluvial plains of China is summarized and discussed in this paper. The results show that the contents of some elements studied differ from region to region. Close relations have been noted between all the trace element contents in the soils of the eastern alluvial plains and the relevant surface materials of erosion regions, which demonstrate the effects of parent materials, while climatic conditions and human interventions are also found to be important factors. Close relations were found between the transition elements of the Quaternary period and the chalcophile elements (except Cu). The chemical and geochemical properties of these elements are identified as beeing important inherent characteristics that affect the relations of these elements in the soils. Received: 5 June 1997 · Accepted: 2 March 1998