中国东部新生代玄武岩的地球化学：Ⅰ.主元素和微量元素组成：岩石成因…

所研究的玄武岩包括拉斑玄武岩、碱性玄武岩、苦橄粗玄岩和钾质玄武岩。主元素和微量元素的组成变化表明，中国东部玄武岩既是不同深度地幔部分熔融的产物，又经历了岩浆结晶分层作用。强不相容元素比值的变化特征显然与岩石圈地幔交代作用有关。软流圈地幔的上涌并导致上覆不均一的岩石圈地幔的部分熔融是形成中国东部新生代玄武岩的主要机制。     

中国东部新生代玄武岩的地球化学──Ⅰ．主元素和微量元素组成：岩石成因及源区特征

所研究的玄武岩包括拉斑玄武岩、碱性玄武岩、苦橄粗玄岩和钾质玄武岩。主元素和微量元素的组成变化表明，中国东部玄武岩既是不同深度地幔部分熔融的产物，又经历了岩浆结晶分异作用。强不相容元素比值的变化特征显然与岩石圈地幔交代作用有关。软流圈地幔的上涌并导致上覆不均一的岩石圈地幔的部分熔融是形成中国东部新生代玄武岩的主要机制。     

山东临朐玄武岩微量元素地球化学特征

本文测定了山东临朐一带新生代玄武岩的稀土和某些微量元素含量。玄武岩的稀土元素含量较高,特别是轻稀土富集,同时可能存在微弱的铕正异常。在不相容元素丰度图形上,其特点和洋岛碱性玄武岩接近,和大陆裂谷玄武岩有一定差别。根据稀土元素和不相容元素含量特点,认为玄武岩是地幔部分熔融产物。根据作者提出的采用简单二元组分混合、锶同位素混合和部分熔融方程的共同制约及有关参数,计算了岩石形成时两种典型的地幔源区即MORB源和Plume源的可能混合比例。     

黔西地区峨眉山玄武岩（东岩区）铂族元素地球化学特征

利用同位素稀释-等离子体质谱(ICP-MS)方法测定了黔西水域、威宁等地的东岩区峨眉山玄武岩的铂族元素含量。结果表明，相对于原始地幔，东岩区峨眉山玄武岩的铂族元素发生了较强的分异作用，Os、Ir、Ru、Rh亏损，Pd、Pt发生富集，相对配分模式为Pd-Pt富集型；经球粒陨石及原始地幔标准化的铂族元素配分模式为向左陡倾斜型，具有陡的正斜率，Pd／Ir显著高于原始地幔、球粒陨石、原始上地幔等，而与地幔低度熔融形成的N-MORB、大陆拉斑玄武岩等接近，表明峨眉山玄武岩的物质来源为上地幔熔融程度偏低的玄武岩浆。     

滇西澜沧老厂地区玄武岩岩石成因与构造意义

对滇西澜沧老厂地区玄武岩进行了系统的主微量元素和Nd-Pb同位素地球化学研究,结果表明该玄武岩为典型的洋岛玄武岩(OIB)。Nd-Pb同位素研究表明,玄武岩浆含富集地幔组分。老厂地区玄武岩浆活动可能与地幔热柱有关,玄武岩可能为地幔热柱(软流圈)熔融产生的岩浆与富集的岩石圈地幔岩浆混合的产物。     

湘东南玄武质岩石地球化学特征及构造环境

湖南东南部是我国大规模钨，锡，锑及铅锌，稀有，稀土元素矿床集中区，其控矿构造环境倍受人们关注。幔源暗色岩系是深构造环境的产物，其地球化学特征是了解构造环境的有效途径。湘东南玄武质岩石包括碱性玄武岩和拉斑玄武岩两个系列，以碱性玄武岩系列为主。玄武质岩石稀土元素总量较高，无负铕异常，为轻稀土富集的右倾型。稀土元素反映岩浆形成主要受部分熔融作用控制。岩石形成于大陆拉张构造环境。微量元素具有明显OIB型分布特征，地壳混染程度很低，具有富集地幔特征。岩石地球化学，同位素地球化学和地球物理研究表明，软流圈地幔上涌并交代岩石圈地幔，形成以宁远－道县为中心的热地幔柱构造。该热幔柱构造控制该区的成岩，成矿作用。     

雷琼地区晚新生代玄武岩地球化学：EM2成分来源及大陆岩石圈地幔的贡献

对雷琼地区21个晚新生代玄武岩样品的主量、微量元素和Sr、Nd、Pb同位素分别用湿化学法、ICP-MS和MC-ICPMS进行了测定.这些玄武岩主要为石英拉斑玄武岩,其次为橄榄拉斑玄武岩和碱性玄武岩.大多数样品的微量元素和同位素成分与洋岛玄武岩(OIBs)相似,而且随着SiO_2不饱和度增加,不相容元素含量也增加.除R4-1可能受到地壳混染外,其他样品相对均一的Nd同位素(ε_(Nd)=2.5-6.0)以及变化明显但范围有限的Sr同位素(0.703106～0.704481),可能继承了地幔源区的特征.~(87)Sr/~(86)Sr与~(206)Pb/~(204)Pb的正相关和~(143)Nd/~(144)Nd与~(206)Pb/~(204)Pb的负相关特征暗示DM(软流圈地幔)与EM2(岩石圈地幔)的混合.地幔捕虏体的同位素特征暗示EM2成分不可能存在于尖晶石橄榄岩地幔,而La/Yb和Sm/Yb系统表明岩浆由石榴石橄榄岩部分熔融产生,这意味着EM2成分可能存在于石榴石橄榄岩地幔.雷琼地区玄武岩的地球化学变化可以用软流圈地幔为主的熔体加入不同比例石榴石橄榄岩地幔不同程度熔融产生的熔体来解释:碱性玄武岩和橄榄拉斑玄武岩是软流圈熔体与石榴石橄榄岩地幔较低程度(7%～9%)熔融体混合,而石英拉斑玄武岩是软流圈熔体与石榴石橄榄岩地幔较高程度(10%～20%)熔融体的混合.     

扬子地块东段大陆岩石圈地幔的物质成分

根据苏皖地区新生代碱性玄武岩中的尖晶石二辉橄榄岩包体的化学成分，讨论了扬子地块东段大陆岩石圈地幔的物质成分。以包体的平均成分代表该区岩石圈地幔的平均成分，依照地幔地球化学演化趋势，估计了该区岩石圈地幔的原始组成。采用最近提出的二辉石地质温度计，计算了包体的平衡温度，讨论了该区岩石圈地幔物质成分在垂向上的分布和变化，上地幔橄榄岩中的玄武质组分在垂向上由上而下亏损程度逐渐减小。包体中稀土元素丰度模式反映了该区岩石圈地幔演化的多阶段性。除了程度不同的部分熔融作用外，局部地段曾有隐性地幔交代作用发生，造成了地幔橄榄岩中主量成分和稀土元素的解耦现象。     

东南沿海地区第四纪大陆岩石圈地幔的特征

东南沿海地区新生代玄武岩中的橄榄岩包体来自年轻的大陆岩石圈地幔 ,该岩石圈地幔在岩石学、矿物组成、痕量元素以及Sr Nd同位素组成等各方面具有很大差异。这些差异反映了它们来自不同的地幔过程。南海张开与地幔热柱有关 ,南海扩张后第四纪形成的火山岩携至地表的包体更多保留了地幔热柱的信息。橄榄岩包体的矿物成分与深海橄榄岩类似 ,相对贫Opx而富Ol;在痕量元素上 ,表现为强不相容元素的富集 ,其配分模式类似于其寄主岩 ;Nd同位素强烈亏损 ,显示出比MORB源区更亏损的特征。大陆岩石圈地幔经历了来自地幔深处的贫SiO2 熔体的进一步改造。     

河南信阳地区龟山岩组新元古代变质玄武岩的地球化学特征、Sr-Nd同位素组成及地质意义

对信阳地区商丹断裂带南侧龟山岩组新元古代变质玄武岩进行了岩石学、地球化学及Sr-Nd同位素研究,分析结果显示该套玄武岩为亚碱性拉斑玄武系列,分为低Ti及高Ti两种类型：低Ti型较富Mg,不相容元素富集程度及稀土分馏程度较低,具有E-MORB的微量元素地球化学特征,Sr-Nd同位素组成相对富集,可能来自地幔柱引发的岩石圈地幔的部分熔融,并受到一定程度的地壳混染;高Ti型较富Fe,强烈富集不相容元素,具有OIB的地球化学特征,Sr-Nd同位素组成较为亏损,可能来自地幔柱的部分熔融,并较少受到地壳物质的影响。综合构造判别显示该套玄武岩可能为地幔柱伸展背景下的岩浆活动产物,可能为区域上沿商丹断裂带分布的中—新元古代局部伸展背景岩浆活动产物的组成部分。     

白银厂矿田玄武岩地球化学特征及其形成地质环境

白银厂矿田玄武岩主要由玄武岩和碱性玄武岩组成 ,其中玄武岩属于钙碱性系列和拉斑系列 ,碱性玄武岩属于钾质碱性玄武岩系列和钠质碱性玄武岩系列。相对于N -MORB ,本区钙碱性系列和拉斑系列玄武岩明显富集Ba、Rb、Th、U ,而亏损Ti;碱性系列玄武岩高度富集K、Ba、Rb、Th、U ,而Ti、Zr、Ce相对亏损 ,表明该区玄武岩的形成与板块俯冲作用有关。钙碱性玄武岩系列和拉斑玄武岩系列玄武岩具有低的REE含量和亏损的LREE配分型式 ,表明它是由LREE亏损和HREE略有富集的地幔部分熔融形成 ;碱性系列玄武岩的REE含量和 (La/Yb) N 比值高 ,LREE和HREE的分馏程度较高 ,表明其形成于演化的岩浆 ,可能来自于富集LREE的地幔源区或地幔橄榄岩较低程度的熔融。痕量元素地球化学特征表明 ,本区玄武岩应是与板块俯冲作用有关的地幔部分熔融形成 ,成岩环境为火山弧环境 ,是岛弧向成熟岛弧转化过程中的产物。     

REE compositional characteristics of Hannuoba basalts

The Hannuoba basalts are a suite of associated rocks consisting of alkali basalts and tholeiites. The alkali basalts can be divided into the K-rich type and the Na-rich type, while the tholeiites are almost solely of the Na-rich type. These two types of basalt are characterized as being obviously rich in light rare earth elements, as is shown in the chondrite-normalized REE patterns exhibiting positive Eu anomalies. However, significant differences in (La / Yb)_N and Eu / Eu* ratios are noticed between these two types of basalt. They seem to have been derived from varying-degree partial melting of mantle rocks.     

Case studies on the origin of basalt

The simplified model of basalt genesis described in Part I of this series, equilibrium partial melting followed by Rayleigh-type fractional crystallization, is applied to a stratigraphically controlled sequence of basalt flows from Kohala volcano. Major-element compositions were determined for 52 samples and show a time-stratigraphic progression from tholeiites through transitional basalts to alkali basalts. Twenty-six of these samples were analyzed by isotope dilution for K, Rb, Cs, Sr, Ba and the REE, 13 for⁸⁷Sr/⁸⁶Sr, and 19 for Co, Cr, Ni and V by atomic absorption. After a simple, first-order correction for the effects of fractional crystallization (involving mostly olivine and aluminous clinopyroxene), the major element concentrations cluster tightly, and the incompatible trace elements show monotonic increases in concentration as a function of stratigraphic height. The process identification plot shows that all the (fractionation corrected) melt compositions can be explained by equilibrium partial melting of compositionally identical batches of source material. The REE and Sr are fractionated because of the presence of residual clinopyroxene. Garnet may also be present but in much smaller amounts. In this respect our results differ significantly from those of Leeman et al. (1980). The calculated chondrite-normalized REE patterns of the source are nearly flat to slightly convex upward. Therefore there is no need to invoke special mechanisms, such as metasomatic REE preenrichment of the source, in order to explain the petrogenesis of the suite of lavas. Specifically, Ce concentrations ranging from 20 to 250 times chondritic are all explained by the same calculated source pattern having a chondrite-normalized ratio of Ce/Sm=0.9±0.2. However, the normalized ratio Ce/Ba?2 shows that the source is not simply primitive mantle.     

Origin of Ross Island basanitoids and limitations upon the heterogeneity of mantle sources for alkali basalts and nephelinites

Primary basanitoids from Ross Island, Antarctica have REE patterns and Pb isotope ratios similar to those for primary alkali basalts and nephelinites on ocean islands. The lead data from all volcanics on Ross Island have a spread of 4% in the 206/204 ratio and give a two-stage model lead age of 1500 m.y. The age is interpreted to be the time since the development of the chemical heterogeneity of the mantle source, presumably during an earlier melting process. Comparison of REE, K, Rb, Sr, Ba and P₂O₅ concentrations for alkali basalts and nephelinites shows that the chondrite normalized mantle source is enriched in light REE with average La/Sm=3.4, Ce/Sm=2.6, Nd/Sm=1.6. Assuming a mantle source with heavy REE abundances of three times chondrites, nephelinites require 3 to 7% partial melting of the mantle source and alkali basalts require 7 to 15% partial melting. The patterns of K, Cu, V and Ti abundances suggest that phlogopite is a residual mineral for most nephelinite, but not alkali basalt mantle sources, and that a sulfide phase and a titanium-rich mineral are in the residual mantle source for both alkali basalts and nephelinites. Small positive Eu anomalies (2–5%) in near primary alkali basalts and nephelinites suggest that the xxx of the mantle sources is 10^?6 to 10^?9 atm. The progressive enrichment of light REE and incompatible elements in the mantle sources for nephelinites and alkali basalts is proposed to result by intrusion of veins of basaltic melt due to very low percentages of melting 1 000 to 3 000 m.y. ago when this part of the deeper mantle was previously involved in convection and partial melting.     

新疆西准噶尔齐Ⅰ金矿火山岩地球化学特征

根据齐Ⅰ号玄武质火山岩的化学成分、微量元素和稀土元素丰度特征及相互关系,说明它们是地幔岩浆源直接演化的产物,推测其岩石可能是由部分熔融的亏损源和富集源组份混合而成.     

Petrogenesis of Archaean ultrabasic and basic volcanics: Evidence from rare earth elements

Rare earth element (REE) and major element data are presented on 44 Archaean samples which include spinifex textured ultramagnesian lavas (STPK) spinifex textured basalts (STB) and low MgO tholeiites. The samples come from the Yilgarn and Pilbara Blocks (W. Australia), Barberton (South Africa), Belingwe and Que Que (Rhodesia), Abitibi (Canada) and the 3.7 b.y. Isua Belt of Western Greenland. In addition REE data are given on three near primitive mid-ocean ridge basalts (MORB) and a glassy MORB-type basalt from Taiwan. We suggest that REE patterns, particularly the light REE and Eu, can be affected by metamorphism, but argue that the consistency of pattern from samples both within and between areas enables recognition of primary patterns. La/Sm ratios of 2.7 b.y. STPK are characterised by being lower than those of associated basalts. The 3.5 b.y. STPK Barberton material does not show this feature but instead displays significant heavy REE depletion. The separation of garnet from these liquids is suggested as a possible mechanism for the high CaO/Al₂O₃ ratios, (Al loss) and the heavy REE and Sc depletion. The REE data on Barberton material is equivocal on the derivation of the so-called basaltic komatiites from the peridotitic komatiites. However, REE analyses on STPK and high magnesian lavas from elsewhere suggests that crystal fractionation is not a viable mechanism to produce one from the other. We suggest instead, that varying amounts of partial melting of different sources is responsible for the spectrum of compositions. The STB appear to be an easily recognised rock type within the Archaean. They are characterised by quench (clinopyroxene) textures and a light REE enriched pattern. It is suggested that these are near primary melts and that their REE patterns mirror their mantle source. We propose a two stage model for the 2.7 b.y. mafic complexes, in which, prior to the generation of ultrabasic magmas, the source underwent a small amount of partial melting which resulted in the removal of a melt enriched in incompatible elements. The depletion process could be achieved either during mantle diapirism or by upward migration of interstitial melts into an Archaean low velocity zone. The spread of La/Sm ratios in STPK and STB is used as an argument that the Archaean mantle was chemically heterogeneous and that the degree of heterogeneity was similar to that observed in modern ocean volcanics. As a result, partial melting of the mantle under different P-T conditions produced a spectrum of magma types. The information presently available on Archaean mafic and silicic magmatism and the incompleteness of geochemical data on present day tectonic environments are two major obstacles in formulating Archaean tectonic models. In addition a comparison of present day and Archaean ultramafic and silicic rocks suggests that plate tectonic models as presently understood may not be suitable analogues for all Archaean tectonic environments.     

Geochemistry and Petrogenesis of Three Series of Cenozoic Basalts from Southeastern China

Cenozoic basaltic volcanism in southeastern China was related to the lithospheric extension and asthenospheric upwelling at the eastern Eurasian continental margin. The cenozoic basaltic rocks from this region can be grouped into three different series: tholeiitic basalts, alkali basalts, and picritic-nephelinitic basalts. Each basalt series has distinctive geochemical features and is not derived from a common source rock by different degrees of partial melting or from a common parental magma by fractional crystallization. The mineralogy, petrography, and major and trace-element geochemistry of the tholeiites are similar to oceanic island basalts, implying that the mantle source for these Chinese continental tholeiites was similar to that of the oceanic island basalts—an asthenospheric mantle. The alkali basalts and picritic-nephelinitic basalts are enriched in incompatible trace elements, and their geochemical features can be interpreted as a result of partial melting of an enriched lithospheric mantle, or the mixing products of an asthenospheric magma with a component derived from an enriched lithospheric mantle through thermal erosion at the base of the lithosphere. But the lack of a transitional rock type and continuous variational trends among these basalts suggests that the mixing between asthenospheric magmas and lithospheric magmas probably was not significant in the petrogenesis of the basalts from SE China. Low-degree partial melting of enriched lithospheric mantle alone can account for the observed geochemical data from these basalts.     

Petrogenesis of Garnet Pyroxenite and Spinel Peridotite Xenoliths of the Tell-Danun Alkali Basalt Volcano,Harrat As Shamah,Syria

A suite of samples, including kaersutite and ilmenite megacrysts, spinel peridotites, garnet pyroxenites, and the alkali basalts that host them, have been studied in an effort to better constrain the mineralogy and chemistry of the subcontinental mantle beneath the central portion of the Arabian plate. Kaersutite megacrysts are classified as Type-A high-pressure precipitates of the alkali basalt host, which transported these xenoliths to the surface and extruded them during formation of the Tell-Danun volcano, southwestern Syria. Ilmenite megacrysts are classified as Type-B megacrysts and could not have precipitated from the alkali basalts presently sampled. Instead, they were derived from a magma that was enriched in the rare-earth elements (REE) by ca. four times and depleted in Zr and Hf, compared to the alkali basalts.

Garnet pyroxenites from the Tell-Danun volcanic field yield temperatures and pressures of 946-1045° C and 8-10 kbar, respectively. These xenoliths likely were precipitated as dikes or along walls of conduits at depths of 24-30 km in the lower crust and/or upper mantle beneath the Arabian plate. Spinel peridotites last were equilibrated at temperatures of 755-1080° C and pressures from 10-20 kbar (30-60 km depth) and could represent samples of a mantle that has been depleted by a prior partial melting event. Many spinel peridotites also contain evidence (specifically in concave-upward REE patterns) of a subsequent enrichment event. However, the age and timing of this depletion, and of the subsequent enrichment event, are not known. This event could have occurred as a consequence of the entrainment of the xenoliths in the LREE- enriched alkali basalts or could have occurred prior to alkali basalt volcanism via metasomatic processes.     

四川华蓥偏岩子晚二叠世玄武岩地球化学特征及其与峨眉山大火成岩省的成因关系

四川华蓥偏岩子地区位于四川盆地中东部,新发现的晚二叠世玄武岩介于茅口组(下伏)和龙潭组(上覆)之间,可与峨眉山玄武岩进行对比.矿物学和地球化学研究表明,偏岩子玄武岩属于高钛亲碱性系列,具有OIB型的稀土元素和微量元素配分模式.偏岩子玄武岩基本未遭受地壳混染,单斜辉石的结晶温度为1405～1439℃,指示源区存在异常高温...     

华北克拉通北缘尚义地区新太古代TTG成因分析:洋壳玄武岩不同深度下熔融的产物

尚义玄武岩为尚义-赤城新太古代洋壳残片的组成端元,地球化学性质指示其源于富集地幔。根据稀土元素分配特征,尚义玄武岩可被分为TH1型(稀土元素平坦型)和TH2型(稀土元素分异型)。尚义TTG属于中钾偏铝质钙碱性岩类,其Al2O3含量与低铝型TTG相近,同时微量元素Rb、Sr、Y和REE表现出俯冲板片熔融成因的埃达克岩的性质。根据主量元素SiO2、K2O、Na2O、Al2O3和微量元素Rb、Sr、Y、REE等指标判别和微量元素平衡熔融模式计算得出,尚义TTG形成压力遍及低压—高压范围,是洋壳玄武岩(TH1型)在深度压力变化的条件下部分熔融形成的,其中的低铝型TTG形成于低压熔融。