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1.
二叠纪海相碳酸盐的锶同位素演化及其意义 总被引：4，自引：0，他引：4
本文从沫阳和熊家场剖面二叠纪海相碳酸盐和玄武岩的锶同位素变化出发,讨论了碳酸盐的锶同位素组成与峨嵋山玄武岩喷发之间的关系,以及玄武岩中海相碳酸盐的锶同位素贫化原因,指出海相碳酸盐的锶同位素组成可作为了解地球构造演化的工具。 相似文献
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碳酸盐成岩作用是沉积学最为活跃的领域之一,与之有关的研究成果会直接影响人们对碳酸盐油气储层形成机制和层控矿床形成机制的理解。近年来,碳酸盐成岩作用在多个领域取得了令人瞩目的研究成果,主要包括以下几个方面:(1)实验室沉淀白云石获得成功:人们模拟海水(泻湖)条件下的细菌硫酸盐还原环境,在常温下沉淀出具有序反射的白云石。(2)热液白云化作为新的主流模式成为关注的热点:人们已认识到热液白云岩储层、沉积-喷流型铅锌矿床和Mississippi河谷型铅锌矿床具有共同的形成机制,它们均受构造(伸展、走滑构造)和热流体流动的强烈控制。(3)深埋藏条件下封闭系统的白云化作用受到关注:一些对油气储集空间和层控矿床有较大意义的白云化作用主要是在相对封闭条件下发生的,在对岩石储集空间的变化的贡献上以及在相应的地球化学指标上不同于开放条件下的白云化作用。(4)混合水白云化模式受到质疑:人们重新研究了作为混合水白云化典型地点的美国威斯康星弧碳酸盐的成岩作用,根据流体包裹体分析、阴极发光分析、偏光显微镜观察及稳定同位素分析等方法并结合有机物成熟度的数据,得出威斯康星弧与白云化有关的水-岩相互作用是由与温度升高有关的浓卤水导致的,白云化作用是热水成岩作用的结果。(5)淡水环境的成岩机制受到挑战:新近研究证明,大范围的低位体系域中可以没有具化学活性的淡水透镜体,海水环境同样可以产生成熟的石灰岩,细菌硫酸盐还原作用可以引起海水对碳酸盐的不饱和。(6)锶同位素在海相碳酸盐研究中的广泛应用:由于锶同位素不像氧、碳同位素那样因温度、压力和微生物作用而分馏,矿物可直接反映流体的同位素组成,地质历史中海水锶同位素组成也具有独特的长期变化趋势,这使得海相碳酸盐的锶同位素组成在沉积期后流体示踪中得到广泛应用。(7)硫酸盐还原作用对碳酸盐成岩作用的影响受到重视:如BSR和TSR可减小SO42-对白云石沉淀(或白云化)的动力学屏障,其产物H2S和CO2可在不同条件下对碳酸盐储层产生影响,BSR和TSR可提高成岩流体锶含量,甚至在形成天青石矿床中也具极大的潜在价值。 相似文献
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锶同位素地层学在碎屑岩成岩研究中的应用 总被引：15，自引：0，他引：15
基于同一地质历史时期海水的锶同位素组成为一定值的锶同位素地层学基本原理,可将锶同位素地层学用于碎屑岩成岩作用研究,以评价海相和非海相对成岩作用的影响.三个不同类型的研究实例说明:1)海相碎屑岩成岩流体的锶同位素组成的演化途径有较好的规律性,陆相影响随成岩作用的进行而增加,相对晚期的碳酸盐胶结物的87Sr/86Sr比值通常高于相对早期的碳酸盐胶结物,变化的本底值即为同期海水的锶同位素组成,该数值为一定值;2)有沉积期深源锶和非同期海相影响的陆相碎屑岩中,碳酸盐胶结物的锶同位素比值可能低于大陆淡水,但埋藏成岩过程中相对晚期的碳酸盐胶结物的87Sr/86Sr比值仍高于相对早期的碳酸盐胶结物;3)当深部流体影响碎屑岩的整个成岩过程时,深源锶的烙印可以抹掉或减少不同成岩阶段不同程度陆相影响造成的各种碳酸盐胶结物之间锶同位素组成的差别,使各种碳酸盐胶结物都具有很低的87Sr/86Sr比值,因而缺乏其它沉积盆地中常见的相对晚期碳酸盐胶结物87Sr/86Sr比值高于早期胶结物的一般模式。 相似文献
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四川东部华蓥山海相二叠/三叠系界线附近的锶同位素组成 总被引：1，自引：0，他引：1
二叠/三叠系界线附近的地球化学记录在地球环境重大变革研究中有着重要的意义。根据锶同位素地层学的基本原理, 本文对四川东部华蓥山海相二叠/三叠系界线附近碳酸盐岩样品进行显微组构观察、化学成分分析及其对同期海水代表性评估的基础上, 测试了这些样品的锶同位素组成。结果表明, 这些样品的原始沉积组构保存较好、Sr含量较高, 可以认为其只遭受过较低程度的成岩蚀变改造, 并保留了较多的海水原始信息, 锶同位素比值分布范围在0.707158～0.707334之间, 与前人公布的同期海水值吻合较好, 体现了全球地质事件对海水锶同位素组成控制的一致性。四川东部华蓥山二叠/三叠系界线附近较为系统的锶同位素演化研究, 可望为我国南方海相二叠/三叠系界线附近化学地层学及其对比研究提供一些有价值的基础资料。 相似文献
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锶是自然界广泛分布的微量元素,在生物、化学及地质过程中不易发生分馏作用,具有很好的地球化学指示意义.尤其在水文地球化学研究中,由于不同岩石锶含量不同,大气降水降落在地面后流经不同岩石,致使地表水中锶元素浓度和同位素比值不同.因此,通过研究河水中锶元素的地球化学行为,可以帮助我们探究河流集水处矿物化学风化速率、气候变化、上地壳化学特征、同位素组成以及陆地-河流-海洋之间的营养元素循环等等[1,2]. 相似文献
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石炭纪海相碳酸盐岩的锶同位素演化及其意义 总被引：4，自引：0，他引：4
本文从马角坝剖面石炭系海相碳酸盐岩和腕足化石的锶同位素变化出发,讨论了锶同位素地层曲线的地质意义,并且指出海相碳酸盐岩和腕足化石的锶同位素组成可作为了解地球构造演化的工具。 相似文献
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在地质历史时期中,海相碳酸盐的锶同位素组成具有全球基本一致的演化规律,并且海水锶同位素组成受锶的来源控制,其比值与海平面的变化有内在的联系。西藏岗巴地区晚白垩世—古近纪早期地层发育良好,笔者对宗山、宗浦两个剖面中未经蚀变的26个海相碳酸盐样品进行锶同位素测试,根据得出的数据绘制演化曲线与全球锶同位素曲线有较好的可对比性。曲线的负偏极值与地层界线较为一致,宗山剖面曲线的负向峰值（0.707612）与上/下白垩统界线相对应,宗浦剖面中,锶同位素曲线的负偏值（0.707761）与古新统/始新统界线相对应,晚白垩世—古近纪锶同位素演化曲线也与海平面变化相一致。另外,还讨论了岗巴地区锶同位素变化的原因。 相似文献
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青藏高原的隆起与海洋锶同位素组成的演化 总被引：5，自引：2，他引：3
近年来,随着构造隆升驱动气候变化假说的提出,青藏高原的隆起受到越来越多的关注,并将之与大陆化学风化速率及海洋锶同位素的演化紧密联系。围绕青藏高原的隆升及其环境与气候效应,对海洋锶同位素组成的演化特征及其影响因素的较为全面而详细的论述表明:将青藏高原的隆升与全球气候变化、大陆化学风化速率及海洋锶同位素组成的演化相联系,也许是解决目前关于海洋锶同位素组成的演化及其物源问题的重要手段,根据海洋锶同位素的演化历史来研究全球气候变化规律及青藏高原的构造演化历史将是本研究领域的重点。 相似文献
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青藏高原的隆起与海洋锶同位素组成的演化 总被引：3，自引：1，他引：2
近年来,随着构造隆升驱动气候变化假说的提出,青藏高原的隆起受到越来越多的关注,并将之与大陆化学风化速率及海洋锶同位素的演化紧密联系.围绕青藏高原的隆升及其环境与气候效应,对海洋锶同位素组成的演化特征及其影响因素的较为全面而详细的论述表明:将青藏高原的隆升与全球气候变化、大陆化学风化速率及海洋锶同位素组成的演化相联系,也许是解决目前关于海洋锶同位素组成的演化及其物源问题的重要手段,根据海洋锶同位素的演化历史来研究全球气候变化规律及青藏高原的构造演化历史将是本研究领域的重点. 相似文献
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中国南方二叠纪古海洋锶同位素演化 总被引：17，自引：3，他引：17
本文以贵州罗甸沫阳二叠系剖面为研究对象，通过对海相碳酸盐岩的锶同位素组成变化的研究，探讨了中国南方二叠纪古海洋锶同位素组成特点、演化及其地质意义。 相似文献
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Elemental and isotopic variations in subduction related basalts: evidence for a three component model 总被引：18，自引：0，他引：18
Subduction related basalts display wide ranges in large ion lithophile element ratios (e.g., Rb/Ba and Rb/ Sr) which are unlikely to result from mixing, but suggest a role for small degree partial melting of a relatively Rb-poor mantle wedge source. However, these variations do not correlate with other trace element criteria, such as the depletions of high field strength elements (HFSE) and light rare earth elements (LREE) relative to the LILE, which characterise subduction related magmatism. Integration of radiogenic isotope and trace element data demonstrates that the elemental enrichment cannot be simply related to two component mixtures inferred from isotopic variations. Thus a minimum of three components is required to describe the geochemistry of subduction zone basalts. Two are subduction related: high Sr/Nd material is derived from the dehydration of subducted basaltic ocean crust, and a low Sr/Nd component is thought to be from subducted terrigenous sediment. The third component is in the mantle wedge, it is usually similar to the source of MORB, particularly in its isotopic composition. However, in some cases, notably continental areas, more enriched mantle wedge material with relatively high 87Sr/86Sr, low 143Nd/144Nd and elevated incompatible trace element contents may be involved Mixing of these three components is capable of producing both the entire range of Sr, Nd and Pb isotope signatures observed in destructive margin basalts, and their distinctive trace element compositions. The isotope differences between Atlantic and Pacific island arc basalts are attributed to the isotope compositions of sediments in the two oceans. 相似文献
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Mineralogy and Petrology - This study presents data of in-situ mineral major and trace element chemistry, whole-rock major and trace element and Sr–Nd isotope geochemistry, as well as zircon... 相似文献
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山东蓬莱、临朐新生代碱性玄武岩的钕、锶同位素组成 总被引：16，自引：0，他引：16
本文报道了鲁东和鲁西新生代碱性玄武岩13个样品的Nd、Sr同位素组成,~(143)Nd/~(144)Nd=0.512967—0.512744,~(87)Sr/(86)Sr=0.70349—0.70450。它们在地质剖面上呈现规律性变化,可能与其地幔源区同位素组成的层状分带有关。鲁西地幔源区具有较鲁东更加亏损的组份。两地地幔源区在演化中都曾发生过地幔交代(或富集)作用,根据玄武岩Nd同位素模式年龄估计地幔交代作用发生的时间为0.45Ga。 相似文献
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Application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis 总被引：18，自引：0，他引：18
JAY. L. BANNER 《Sedimentology》1995,42(5):805-824
Carbonate rocks and natural waters exhibit a wide range in the concentration and isotopic composition of strontium. This wide range and the quantifiable covariation of these parameters can provide diagnostic tools for understanding processes of fluid-rock interaction. Careful consideration of the uncertainties associated with trace element partitioning, sample heterogeneity and fluid-rock interaction mechanisms is required to advance the application of the trace element and isotope geochemistry of strontium to studies of diagenesis, goundwater evolution, ancient seawater chemistry and isotope stratigraphy. A principal uncertainty involved in the application of Sr concentration variations to carbonate systems is the large range of experimental and empirical results for trace element partitioning of Sr between mineral and solution. This variation may be a function of precipitation rate, mineral stoichiometry, crystal growth mechanism, fluid composition and temperature. Calcite and dolomite in ancient limestones commonly have significantly lower Sr concentrations (20–70 p.p.m.) than would be expected from published trace element distribution coefficient values and Sr/Ca ratios of most modern sedimentary pore waters. This discrepancy probably reflects the uncertainties associated with determining distribution coefficient values. As techniques improve for the analytical measurement and theoretical modelling of Sr concentration and isotopic variations, the petrological analysis of carbonate samples becomes increasingly important. The presence of even small percentages of non-carbonate phases with high Rb concentrations and high 87 Sr86 Sr values, such as clay minerals, can have significant effects on the measured 87 Sr/86 Sr values of carbonate rocks, due to the decay of 87Rb to 87 Sr. For example, a Permian marine limestone with 50 p.p.m. Sr and 1 p.p.m. Rb will have a present-day 87 Sr/86 Sr value that is >2 × 10?4 higher than its original value. This difference is an order of magnitude greater than the analytical uncertainty, and illustrates the importance of assessing the need for and accuracy of such corrections. A quantitative evaluation of the effects of water-rock interaction on Sr concentrations and isotope compositions in carbonates strengthens the application of these geochemical tracers. Geochemical modelling that combines the use of trace elements and isotopes can be used to distinguish between different mechanisms of water-rock interaction, including diffusive and advective transport of diagenetic constituents in meteoric pore fluids during the recrystallization of carbonate minerals. Quantitative modelling may also be used to construct diagnostic fluid-rock interaction trends that are independent of distribution coefficient values, and to distinguish between mixing of mineral end-members and fluid-rock interaction. 相似文献
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A conceptual isotopic/geochemical model is presented to explain the variation of major, trace and rare earth element (REE)
geochemistry and Sr isotope systematics in suspended particulate matter (SPM) as a function of particle/colloid size. This
conceptual model is an extension of a previous investigation of the origin of SPM in the Murray-Darling River system (MDRS)
that utilised Sr isotope systematics to examine aspects of SPM (particle/colloid) origin, structure and mineralogy. The geochemical
processes that give rise to the often coherent trends in major, trace and REE geochemistry and Sr isotopic signature as a
function of particulate (<1 μm) and colloidal (>1 μm) size in the MDRS have been identified using an enhanced SPM size fractionation
technique as a basis to not only obtain a broad range of particle/colloid size ranges, but also to provide sufficient material
for subsequent geochemical and isotopic analysis. The conceptual isotopic/geochemical model proposed here contains three major
components: (i) the differential weathering of micas and alkali (K-) feldspars to form the majority of the particulate (<1
μm) fractions (high 87Sr/86Sr ratio), which have a geochemical and Sr isotopic signature that closely resembles precursor
mineralogies, (ii) the differential weathering of Na, Ca-feldspars (plagioclase) which decompose to form clay minerals in
the colloidal (>1 μm) fractions (low 87Sr/86Sr ratio), with a range of geochemical signatures related to the relative proportions
of inorganic and organic constituents, and (iii) the presence of natural organic matter as coatings on the particulate (<1
μm) and colloidal (>1 μm) matter and possibly as organo-colloids which exert an increasing influence in particular on bulk
colloid geochemistry with decreasing colloid size. This conceptual isotopic/geochemical model also accounts for the distinct
variation in major, trace and REE geochemistry and Sr isotopic systematics between the particulate (<1 μm) and colloidal (>1
μm) fractions, the variation being primarily a function of the distinctly different precursor mineralogies of the SPM fractions
and geochemical fractionation during the weathering and transport. Additionally, this model explains a systematic fractionation
of REE apparent within colloidal (>1 μm) fractions. Statisitcal (hierachical cluster) analysis of two particulate and three
colloidal fractions from 23 samples from the MDRS is used as a basis to investigate geochemical and mineralogical associations
within the particulate and colloidal size fractions and to provide additional supporting evidence for the conceptual isotopic/geochemical
model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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雁林寺金矿位于雪峰弧形构造带(江南造山带湖南段)东段,是湘东北地区一个较为典型的金矿床。本文在前人研究的基础上,统计分析了矿区不同地质体Au元素含量、稀土元素地球化学、微量元素地球化学特征,对比研究了矿区含金石英的H-O同位素、Sr同位素地球化学特征及成矿流体组成特征。提出赋矿围岩冷家溪群浊积岩在沉积阶段就具有明显的金富集。矿区矿石、(矿化)蚀变围岩、未蚀变围岩稀土、微量元素地球化学特征呈现出高度相似性。含金石英的H-O同位素地球化学、Sr同位素地球化学及成矿流体成分特征表明成矿流体为变质流体。综合矿区地质特征、不同地质体金含量、稀土-微量元素地球化学特征、H-O同位素、Sr同位素及成矿流体成分特征,认为地层中的金元素为雁林寺金矿床提供了成矿物质。 相似文献
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M.H. Dodson 《Lithos》1982,15(3):215-219
A general null hypothesis for isotope geochemistry states that the isotopic composition of an element is independent of its concentration or any other geochemical property of the population. ‘Spurious’ correlations between the ratios 87Sr/86Sr and 87Rb/86Sr (orRb/Sr), due to the common denominator effect, may be ruled out because they contradict this null hypothesis. Mixing processes may be regarded as geochemical counterparts of the common denominator effect. In geochronological systems which satisfy the basic assumptions of the Rb-Sr isochron method observed correlations between Sr isotope abundance and Sr concentration must be secondary to the direct causal dependence of 87Sr/86Sr upon Rb/Sr ratios. 相似文献
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黔西二叠纪玄武岩及岩浆来源初步分析 总被引：2，自引：0，他引：2
本文以织金熊家场剖面为例进行岩石学及岩浆来源分析研究。岩性和岩石化学特征表明,区内玄武岩为碱性—钙碱性拉斑玄武岩。同位素地球化学和稀土元素分布模式研究资料表明,本区玄武岩原始岩浆来源于地壳和地幔二元组分相混合的体系。通过锶同位素组成的计算,显示了原始岩浆中的幔源和壳源二元组分的混合比例为5.4:1。 相似文献