共查询到20条相似文献，搜索用时 195 毫秒
1.
华北地台东部金伯利岩源区反演及其不均一性探讨 总被引：1，自引：0，他引：1
华北地台东部有６个后利岩岩区，它们分布于古陆核的中心、北缘及西缘元古代裂陷带。本文在不相容元素，同位素源区约束讨论的基础上，选择代表性的后夺进行源区地球化学定量反演，进而讨论了源区的不均一性，金伯利岩产出的构造部位及由此所反映的岩石圈厚度，地幔流体活动强度的差异，不仅影响金伯利岩含金刚石性，而且也是地幔源区不均一性的影响因素。 相似文献
2.
华北地台金伯利岩岩浆活动时代讨论 总被引：13，自引：0，他引：13
华北地台金伯利岩岩浆活动可分为三个时期：（１）中元古代金伯利岩和钾镁煌斑岩岩浆活动期，以鄂尔多斯陆核边缘山西阳高岩区为代表（１６４９～１８１１Ｍａ）；（２）古生代金伯利岩岩浆活动，以冀鲁辽陆核边缘的铁岭岩区、中部的复县和蒙阴岩区为代表（含矿金伯利岩，４５７～４６２Ｍａ）；（３）中～新生代金伯利岩岩浆活动时期，以鹤壁和涉县岩区为代表（１１７～５２Ｍａ）。含矿金伯利岩岩浆活动与华北地台中奥陶世晚期的造陆抬升作用有关。这类岩浆形成时必须处于克拉通岩石圈底部有小的热扰动以及流体作用的条件，而过高的地温梯度反而起到破坏金刚石保存的作用。 相似文献
3.
新疆巴楚地区金伯利质角砾橄榄岩物质组成及含矿性研究 总被引：2，自引：0，他引：2
本文讨论出露于新疆巴楚瓦吉里塔格地区的一种角砾状超镁铁岩,其结构、成分复杂,由超镁铁岩包体、斑晶（或捕晶）及基质三部分构成。超镁铁岩包体常见单辉辉石岩、纯橄岩,其次有少量橄榄辉石岩。研究表明均属基性岩浆结晶岩,本次研究未见幔源橄榄岩包体;斑晶主要为橄榄石,次为金云母,基质由微晶（10~40μm）单斜辉石、钙铁榴石、钙钛矿、磁铁矿（或含钛磁铁矿）、蛇纹石、碳酸盐及金属硫化物等组成;捕晶包括单斜辉石、褐色角闪石、磷灰石、含钛磁铁矿等。多种地球化学判别图均指示其属金伯利岩类,但低MgO和低Mg#比值、高TFe2O3和CaO等区别于世界典型金伯利岩。与典型金伯利岩有相似之处,该类岩石均具有向右陡倾的REE配分型式,但（La/Yb）n比值略偏低;微量元素蛛网图也与典型金伯利岩基本一致,仅显示更加富集不相容元素,具有更显著K, Ti负异常,且部分样品出现Rb, Zr, P负异常,指示其源区地幔交代程度偏低。鉴于岩石的产状、结构构造、矿物组合和地球化学性质近似于金伯利岩,但缺少高铬铬铁矿、镁铝榴石、镁钛铁矿等金伯利岩指示矿物,故不属典型的金伯利岩,可称之为金伯利质角砾橄榄岩。就少量研究样品所示信息,该类岩石不具有寻找金刚石的潜在远景,但鉴于巴楚及邻区尚有许多角砾状超镁铁岩岩墙和岩脉出露,该区金刚石成矿条件有待更进一步的研究。 相似文献
4.
委内瑞拉、圭亚那和巴西的圭亚那地盾的冲积金刚石的原始来源，已争论了很长时间。根据可靠证据认为，圭亚那地盾的金刚石至少有两个源区。第一个源区是该区大于200m厚的元古宙碎屑沉积层，称罗赖马群（Roraima）。但构成罗赖马群的金刚石原生来源和碎屑物质源尚不清楚。圭亚那地后金刚石的第二个源区是委内瑞拉西部的瓜尼亚莫（Guaniamo）地区含金刚石冲积矿床。金伯利岩指示矿物镁铝榴石（Pvrone）和石榴石、镁钛铁矿（Mgilmenite）出现在这些冲积物中。最近发现了原生的元古宙金伯利型源岩。但瓜尼亚莫金刚石的特征在整体上不同于罗赖… 相似文献
5.
金伯利岩型金刚石原生矿床含矿性评价是了解金刚石成矿规律和指导区域性找矿的重要依据。华北克拉通是我国重要的金刚石成矿远景区,目前已发现了两个重要的含金刚石金伯利岩岩区（山东蒙阴和辽宁瓦房店）。近年来,对岩区内不同品位金刚石典型矿床的研究表明金伯利岩中的金刚石品位取决于以下两个重要的地质过程：金伯利岩岩浆对金刚石的捕获作用和金伯利岩岩浆对金刚石的熔蚀作用。在华北克拉通下方存在一个金刚石稳定区,温度为950~1200 ℃,压力为4. 4~6. 1 GPa。山东蒙阴和辽宁瓦房店金伯利岩岩浆在上升过程中穿过该区域并捕获其中的金刚石,成为含矿岩浆;而铁岭和鹤县等金伯利岩岩浆在上升过程中不穿过该区域,成为不含矿岩浆。在穿过金刚石稳定区时,富矿的金伯利岩捕获了更多的金刚石以及金刚石的伴生指示矿物（如镁铝榴石,镁铬铁矿）;而贫矿的金伯利岩则相对捕获了少量的金刚石和指示矿物。这些指示矿物往往参加了金刚石的形成过程,有些作为缓冲剂控制了反应（岩浆或熔体）的氧化还原状态,有些则作为反应物或者生成物参与到反应中。部分指示矿物（如镁铝榴石）还进一步地记录了金刚石形成后金伯利岩岩浆对金刚石的交代作用。金伯利岩岩浆温度（T）,氧逸度（fO2）和挥发份(H2O和CO2)均会对金刚石的熔蚀作用产生影响,其中氧逸度作用最大,温度次之,而挥发份作用最弱。在华北克拉通,金伯利岩中指示矿物（镁铝榴石、镁铬铁矿）和金伯利岩岩浆特征（温度,氧逸度和挥发份）共同组成了金伯利岩型金刚石原生矿的评价指标。 相似文献
6.
黔东—湘西早古生代岩石圈热状态与高产热率HHPRM型地幔源区 总被引：1，自引：0，他引：1
岩石圈热结构和热状态的研究对于大陆裂解、变质作用及活化构造形成机制等大陆动力学问题的研究十分重要。通过地球化学、构造地质学和综合分析,以贵州省镇远地区金伯利岩-钾镁煌斑岩和黔东—湘西一带的晚元古代地层为例,研究了扬子地块东南缘早古生代岩石圈热结构与热状态。提出高放射性元素产热率的HHPRM型地幔源区,进一步讨论HHPRM型地幔源区形成与演化的大陆动力学机制。认为古富集地幔(HHPRM型地幔源区)是镇远一带的早古生代钾镁煌斑岩-金伯利岩的岩浆源区,镇远地区金伯利岩-钾镁煌斑岩岩浆源区深度(H)在208～244km,形成温度在1547～1403℃间,该温度和深度范围属软流层,具有形成金刚石矿床的地质条件。建议在贵州—湖南—广西三省交界区的金伯利岩和钾镁煌斑岩岩群中应进一步开展金刚石矿床研究与勘查工作。 相似文献
7.
8.
金伯利岩中的锆石按照颗粒大小可以分为细粒锆石（一般小于200μm）和巨晶锆石（一般大于500μm）。前人的研究结果显示在金伯利岩中粒径较大的巨晶锆石的U-Pb体系在高温的地幔中一直保持着开放状态,直到寄主金伯利岩浆的喷发才使地幔锆石的U-Pb体系封闭,因此这些巨晶锆石是确定金伯利岩年龄的重要矿物之一。然而,近年来的研究表明,金伯利岩中还存在一些时代远老于金伯利岩年龄的锆石,也具有较大的粒径（以下称古老锆石巨晶）。它们的存在无疑影响了利用锆石U-Pb方法确定金伯利岩年龄的准确性。本文以西伯利亚雅库特（Yakutia）金伯利岩省中的四颗古老锆石巨晶为研究对象,通过形态学、年代学、微量元素和Hf同位素组成,讨论古老锆石巨晶的来源。同时,我们统计和对比了全球多个金伯利岩中能够确定金伯利岩年龄的锆石和古老锆石巨晶的形态学、U、Th含量和微量元素组成、Hf-O同位素等特征。研究结果显示,金伯利岩中的古老锆石巨晶的tDM年龄和O同位素组成与可以用来确定金伯利岩年龄的锆石巨晶具有明显的差别。这些手段在未来的研究中可以用来区分可确定金伯利岩年龄的锆石巨晶和古老的锆石巨晶。 相似文献
9.
金伯利岩和金刚石的形成机制 总被引：2，自引：0，他引：2
本文对金伯利岩和金刚石形成机制进行了初步探讨,并讨论了某深断裂带两侧的金伯利岩岩浆活动特点,为寻找金伯利岩供参考。一、我国金伯利岩的某些特征金伯利岩通常受稳定地台及其边缘、环绕地台造山带的地堑区等构造背景控制。侵入活动主要见于稳定地台的深断裂带两侧或一侧的高角度断裂上盘地区,以及两个稳定地台相连接的边缘 相似文献
10.
《地球科学进展》2016,(7)
金伯利岩是研究地幔动力学过程、探讨岩石圈演化等深部重大科学问题的有效载体,也是揭示金刚石这一稀缺矿产资源的形成环境、成因、来源及找矿实践等最为重要的研究对象之一。长期以来,由于受到研究手段、研究思路等的限制,对金伯利岩相关研究的核心与瓶颈性关键基础科学问题,即"金伯利岩的初始岩浆组成"、"金伯利岩的演化过程及其意义"、"金伯利岩的金刚石含矿性评价"等知之甚少,这极大地制约了人们对金伯利岩及其相关深部过程意义等方面的深入了解。例如,基于高压熔体模拟实验、基质矿物、细小同源包裹体及金伯利岩筒边部隐晶质物质的研究,可以有效分析金伯利质岩浆的初始组成特征,但却难于有效甄别金伯利质岩浆的源区特征,难于有效区分地幔同化/混染作用、流体分异以及就位期间的脱玻化作用等对岩浆的影响等;由于缺乏再结晶及(或)再生长矿物在微成分、微结构方面的系统研究报道,难于有效精准分析金伯利质岩浆组成的变化规律及脱气作用的影响,揭示金伯利质岩浆的演化过程;尽管根据共生矿物组合、橄榄石的含水性等可用于评估金伯利岩的金刚石含矿性,但存在指标体系过于简单、数据积累少等方面问题。理论上,从微区(微米级、纳米级)的角度,对金伯利岩各组成结构单元中矿物等的微成份、微结构进行系统研究,可以更为精准地提取金伯利质初始岩浆组成、演化过程等方面的信息,因此对含金刚石与不含金刚石的金伯利岩的微组构进行精细研究,可以为有效重建金伯利质岩浆的演化机制、深入揭示其对深部过程的响应等奠定科学基础。同时,也可以在对已知金刚石矿区研究的基础上,建立用于金刚石初始品位预测和保存潜力分析的模型,以实现有效评价未知金伯利岩区的含矿性的目的。 相似文献
11.
《Russian Geology and Geophysics》2007,48(3):272-290
Using the ICP-MS method we have studied the isotope systematics of Sr and Nd as well as trace element composition of a representative collection of kimberlites and related rocks from the Siberian Platform. The summarized literature and our own data suggest that the kimberlites developed within the platform can be divided into several petrochemical and geochemical types, whose origin is related to different mantle sources. The petrochemical classification of kimberlites is based on persistent differences of their composition in mg# and in contents of indicator oxides such as FeOtot, TiO2, and K2O. The recognized geochemical types of kimberlites differ from one another in the level of concentration of incompatible elements as well as in their ratios.Most of isotope characteristics of kimberlites and related rocks of the Siberian Platform correspond to the earlier studied Type 1 basaltoid kimberlites from different provinces of the world: Points of isotopic compositions are in the field of primitive and weakly depleted mantle. An exception is one sample of the rocks from veins of the Ingashi field (Sayan area), which is characterized by the Sr and Nd isotopic composition corresponding to Type 2 micaceous kimberlites (orangeites).The most important feature of distribution of isotopic and trace-element compositions (incompatible elements) is their independence of the chemical rock composition. It is shown that the kimberlite formation is connected with, at least, two independent sources, fluid and melt, responsible for the trace-element and chemical compositions of the rock. It is supposed that, when rising through the heterogeneous lithosphere of the mantle, a powerful flow of an asthenosphere-derived fluid provoked the formation of local kimberlite chambers there. Thus, the partial melting of the lithosphere mantle led to the formation of contrasting petrochemical types of kimberlites, while the geochemical specialization of kimberlites is due to the mantle fluid of asthenosphere origin, which drastically dominated in the rare-metal balance of a hybrid magma of the chamber. 相似文献
12.
N. V. Chalapathi Rao Rajesh K. Srivastava 《Contributions to Mineralogy and Petrology》2009,157(2):245-265
The petrology and geochemistry of some new occurrences of Mesoproterozoic diamondiferous hypabyssal-facies kimberlites from
the Chigicherla, Wajrakarur-Lattavaram and Kalyandurg clusters of the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton
(EDC), southern India, are reported. The kimberlites contain two generations of olivine, and multiple groundmass phases including
phlogopite, spinel, calcite, dolomite, apatite, perovskite, apatite and rare titanite, and xenocrysts of eclogitic garnet
and picro-ilmenite. Since many of the silicate minerals in these kimberlites have been subjected to carbonisation and alteration,
the compositions of the groundmass oxide minerals play a crucial role in their characterisation and in understanding melt
compositions. While there is no evidence for significant crustal contamination in these kimberlites, some limited effects
of ilmenite entrainment are evident in samples from the Kalyandurg cluster. Geochemical studies reveal that the WKF kimberlites
are less differentiated and more primitive than those from the Narayanpet kimberlite field (NKF), Eastern Dharwar craton.
Highly fractionated (La/Yb = 108–145) chondrite-normalised distribution patterns with La abundances of 500–1,000 × chondrite
and low heavy rare earth elements (HREE) abundances of 5–10 × chondrite are characteristic of these rocks. Metasomatism by
percolating melts from the convecting mantle, rather than by subduction-related processes, is inferred to have occurred in
their source regions based on incompatible element signatures. While the majority of the Eastern Dharwar craton kimberlites
are similar to the Group I kimberlites of southern Africa in terms of petrology, geochemistry and Sr–Nd isotope systematics,
others show the geochemical traits of Group II kimberlites or an overlap between Group I and II kimberlites. Rare earth element
(REE)-based semi-quantitative forward modelling of batch melting of southern African Group I and II kimberlite source compositions
involving a metasomatised garnet lherzolite and very low degrees of partial melting demonstrate that (1) WKF and NKF kimberlites
display a relatively far greater range in the degree of melting than those from the on-craton occurrences from southern Africa
and are similar to that of world-wide melilitites, (2) different degrees of partial melting of a common source cannot account
for the genesis of all the EDC kimberlites, (3) multiple and highly heterogeneous kimberlite sources involve in the sub-continental
lithospheric mantle (SCLM) in the Eastern Dharwar craton and (4) WKF and NKF kimberlites generation is a resultant of complex
interplay between the heterogeneous sources and their different degrees of partial melting. These observations are consistent
with the recent results obtained from inversion modelling of REE concentrations from EDC kimberlites in that both the forward
as wells as inverse melting models necessitate a dominantly lithospheric, and not asthenospheric, mantle source regions. The
invading metasomatic (enriching) melts percolating from the convecting (asthenosphere) mantle impart an OIB-like isotopic
signature to the final melt products. 相似文献
13.
Ilmenite is one of the common kimberlitic indicator minerals recovered during diamond exploration, and its distinction from non-kimberlitic rock types is important. This is particularly true for regions where these minerals are present in relatively low abundance, and they are the dominant kimberlitic indicator mineral recovered. Difficulty in visually differentiating kimberlitic from non-kimberlitic ilmenite in exploration concentrates is also an issue, and distinguishing kimberlitic ilmenite from those derive from other similar rocks, such as ultramafic lamprophyres, is practically impossible. Ilmenite is also the indicator mineral whose compositional variety has the most potential to resolve provenance issues related to mineral dispersions with contributions from multiple kimberlite sources.
Various published data sets from selected kimberlitic (including kimberlites, lamproites, and various ultramafic lamprophyres) and non-kimberlitic rock types have been compiled and evaluated in terms of their major element compositions. Compositional fields and bounding reference lines for ilmenites derived from kimberlites (sensu stricto), ultramafic lamprophyres, and other non-kimberlitic rock types have been defined primarily on MgO–TiO2 graphs as well as MgO–Cr2O3 relationships. 相似文献
14.
Based on original data on the East European and Siberian platforms and materials on the best studied foreign objects, a comparative
analysis of kimberlites and lamproites was conducted and the criteria of their differences were formulated. Among most significant
differences are the following: (1) the high-Mg potassic rocks (kimberlites and lamproites) show major-component variations,
which are significantly wider in lamproites as compared to kimberlites. Kimberlites differ from lamproites not only in the
content of SiO2, but also in alkalis, volatiles, and some trace elements. Kimberlites are characterized by CO2-dominated regime, whereas formation of lamproites was assisted by essentially H2O fluid; (2) Kimberlites are localized within ancient cratons, while within-plate lamproites are restricted to adjacent Proterozoic
belts. Kimberlites are produced in the low-heat flow regions, whereas lamproites occur in the high-heat flow regions; (3)
Kimberlites and lamproites were formed in different time; in particular, most productive kimberlitic magmatism was observed
in the EEP and SP in the Devonian; (4) Kimberlite and lamproite bodies have different morphology: lamproites compose small
subvolcanic bodies with lava flows, while kimberlites form volcanic pipes with no lavas; (5) Kimberlites contain highly silica-undersaturated
minerals, while ultrabasic lamproites—silica-undersaturated ones; priderite and wadeite, the characteristic accessory minerals
of lamproites, are not observed in kimberlites; (6) The primary melts of kimberlites and lamproites were derived from different
types of mantle. The moderate and low-Ti kimberlites were generated from BSE or EMI type mantle. Precisely these types of
kimberlites host diamond deposits, including economic grade objects in EEP. The lamproite sources were localized only in the
enriched mantle (EMI and EMII). At the same time, these rocks share some similarities, primarily, with respect to their genesis
and classification. Diamonds are common accessory minerals of kimberlites (low-Ti and some other types), but are observed
only in only lamproite variety—olivine lamproites. 相似文献
15.
V.B. Vasilenko A.V. Tolstov V.A. Minin L.G. Kuznetsova N.V. Surkov 《Russian Geology and Geophysics》2008,49(12):894-907
The intensity of postmagmatic processes in the Botuobinskaya pipe kimberlites was estimated from the calculated content of normative secondary quartz (Q). Several simple algorithms are proposed to calculate the Q content from chemical analyses of kimberlites. Ten groups of altered kimberlites have been recognized from the Q contents. The contents of MgO, some trace elements, and LREE in the groups, the contents of Cr and Ca of crimson garnets, the diamond contents of kimberlites, and the average weight of diamonds decrease as the Q content increases. It is shown that the negative SiO2–MgO correlation is the most effective indicator of the postmagmatic alteration of kimberlites. As the degree of their secondary alteration increases, the kimberlites transform into an assemblage of quartz and clay minerals enriched in some trace elements and almost completely lacking REE and diamonds. 相似文献
16.
Kimberlites and lamproites of the East European Platform: Petrology and geochemistry 总被引：2，自引：0，他引：2
Several episodes of kimberlite magmatism occurred in the East European Province (EEP) during a long (about 1.5 Gyr) time period, from the Late Paleoproterozoic (ca. 1.8 Ga) in the Archean Ukrainian and Baltic shields to the Middle Paleozoic (ca. 0.36 Ga) mainly in the Arkhangelsk, Timan, and adjacent regions. Based on the analysis of data on 16 kimberlite occurrences and four lamproite occurrences within the EEP, five time stages can be distinguished; one of them, the Middle Paleozoic stage (Middle Ordovician and Devonian), is the most productive epoch for diamond in the northern hemisphere (EEP, Siberian Craton, and part of the China Craton). The analysis of petrological and geochemical characteristics of kimberlites (lamproites were studied less thoroughly) revealed variations in rock composition and their correlation with a number of factors, including the spatial confinement to the northern or southern Archean blocks of the craton, time of formation of the source of kimberlite melts, contents of volatiles and autoliths, etc. Three petrogeochemical types of kimberlites were distinguished: high-, medium-, and low-Ti (TiO2 > 3 wt %, 1–3 wt %, and <1 wt %, respectively). There are two time intervals of the formation of kimberlite and lamproite sources in the EEP, corresponding to TNd(DM) values of about 2 Ga (up to 2.9 Ga in the Por’ya Guba occurrence) and 1 Ga. The latter interval includes two groups of occurrences with model source ages of about 1 Ga (low-and medium-Ti kimberlites of the Zolotitsa and Verkhotina occurrences) and about 0.8 Ga (high-Ti kimberlites of the Kepino and a number of other occurrences); i.e., there seems to be an evolutionary trend in the composition of kimberlites. Concentric zoning patterns were recognized. The role of the crust in kimberlite sources is discussed; it is assumed that buried remnants of the oceanic lithosphere (megaliths) may underlie whole continents. A unique feature of the composition of low-Ti kimberlites, for instance, kimberlites of the Zolotitsa occurrence (to a smaller extent, medium-Ti kimberlites of the V. Grib pipe) is the distinct depletion of highly charged elements and pronounced negative anomalies of Ti, Zr, Th, U, Nb, and Ta in trace-element distribution patterns, which indicates a contribution of crustal material to the source of these kimberlites. It was shown that autoliths exert a significant influence on the differentiation of kimberlite material, resulting in the enrichment of rocks in the whole spectrum of incompatible elements. It was argued that geochemical criteria can be used together with traditional criteria (including those based on indicator minerals) for the assessment of diamond potential in EEP occurrences. We hope that such a combined approach will yield important outcomes in the future. 相似文献
17.
A. D. Beard H. Downes E. Hegner S. M. Sablukov V. R. Vetrin K. Balogh 《Contributions to Mineralogy and Petrology》1998,130(3-4):288-303
Minor magmatic intrusions of kimberlite, melilitite and cpx-melilitite occur in the southern part of the Kola Peninsula,
Russia, on the Terskii Coast and near the town of Kandalaksha. They yield K-Ar ages of 382 ± 14 Ma and 365 ± 16 Ma, similar
to the magmatic rocks from the Kola Alkaline Province. The Terskii Coast kimberlites have mineralogical and geochemical affinities
with group 1 kimberlites, whereas the Kandalaksha monticellite kimberlite more closely resembles calcite kimberlites. The
lower Al2O3 content in the Kola kimberlites indicates a strongly depleted harzburgitic source, while higher Al2O3 in the melilitites suggests a lherzolitic source. The Terskii Coast kimberlites are anomalously potassic and significantly
enriched in P and Ba compared to other group 1 kimberlites. In contrast, the melilitites are sodic and are anomalously depleted
in P compared to worldwide melilitites. Trace element patterns of the Kola kimberlites and melilitites indicate the presence
of K- and P-rich phases in the mantle source. To account for the K-troughs shown by both magma types, a K-rich phase such
as phlogopite is thought to be residual in their sources; however, the anomalous K-enrichment in the Terskii Coast kimberlites
may indicate that an additional metasomatic K-rich phase (e.g. K-richterite and/or a complex K-Ba-phosphate) existed in the
kimberlite source. The P-depletion in the melilitites may suggest that a phosphate phase such as apatite remained residual
in the melilititic source. However, anomalous P-enrichment in the kimberlites cannot be explained by complete melting of the
same phase because the kimberlites are a smaller degree melt; thus, it is most likely that another metasomatic phosphate mineral
existed in the source of the kimberlites. The Kola kimberlites and melilitites are all strongly LREE-enriched but the kimberlites
have a steeper REE pattern and are significantly more depleted in HREE, indicating a higher proportion of garnet in their
source. Higher Nb/Y ratios and lower SiO2 values in the kimberlites indicate that they were a smaller degree partial melt than the melilitites. The presence of diamonds
in the Terskii Coast kimberlites indicates a relatively deep origin, while the melilitites originated from shallower depth.
The non-diamondiferous Kandalaksha monticellite kimberlite has lower abundances of all incompatible trace elements, suggesting
a higher degree of partial melting and/or a less enriched and shallower source than the Terskii Coast kimberlites. The 87Sr/86Sri, 143Nd/144Ndi and Pb isotope compositions confirm that the Terskii Coast kimberlites have close affinities with group 1 kimberlites and
were derived from an asthenospheric mantle source, while the Kandalaksha monticellite kimberlite and Terskii Coast melilitites
were derived from lithospheric mantle. Impact of a Devonian asthenospheric mantle plume on the base of the Archaean-Proterozoic
lithosphere of the Kola Peninsula caused widespread emplacement of kimberlites, melilitites, ultramafic lamprophyres and other
more fractionated alkaline magmas. The nature of the mantle affected by metasomatism associated with the plume and, in particular,
the depth of melting and the stability of the metasomatic phases, gave rise to the observed differences between kimberlites
and the related melilitites and other magmas.
Received: 3 March 1997 / Accepted: 7 October 1997 相似文献
18.
The Generation of Kimberlites, Lamproites, and their Source Rocks 总被引：18，自引：8，他引：10
Measurements of rare earth element (REE) concentrations in SouthAfrican kimberlites and in the Argyle lamproite from WesternAustralia constrain the composition of the source rocks fromwhich these melts originate. To account for the concentrationsof Tm, Yb, and Lu in these magmas, their sources must firsthave been strongly depleted by 20% melting in the garnet stabilityfield, and then enriched by a metasomatic melt rich in lightREE and other incompatible elements. The calculated source compositionsclosely resemble those of coarse, low-temperature, depletedperidotite nodules that are the commonest nodules in kimberlites.Rarer nodule types have undergone either more or less depletionthan have the source regions of kimberlites and lamproites.The REE composition of the metasomatic melt calculated fromthe diopsides and garnets in the sheared nodules, from the diopsidemegacrysts, and from majorite garnet inclusions in diamonds,is in excellent agreement with that expected for a melt producedby melting 0.5% of the source region of ocean ridge basalts.The initial depletion event requires the extraction of 20% meltfrom a region in which garnet and chrome-spinel were stable.The melt distribution obtained from inversion of komatiite compositionssatisfies both these conditions. Kimberlite source rocks areshallower than the layer from which fertile nodules originate.Such nodules must therefore be transported by entrainment ofthe lower boundary of the layer that becomes unstable. Thisproposal can account for their strong fabric. 相似文献
19.
中国金伯利岩地球化学 总被引：4，自引：0，他引：4
本文利用了100多个金伯利岩的主要元素及微量元素分析结果,用Si/Mg、C.l——(SiO_2+Al_2O_3+Na_2O)/(MgO+2K_2O)、Mg/(Mg+Fe)比值及SiO_2、Al_2O_3及Na_2O含量研究了金伯利岩的混染程度。结果表明,绝大部分金伯利岩受到了混染作用的影响,它们的成分实际上不能代表形成这些岩石的岩浆的成分。金伯利岩的Al_2O_3和Na_2O的含量比其他碱性超基性及基性岩石的Al_2O_3和Na_2O含量低得多。含金刚石的金伯利岩比不含金刚石的金伯利岩的MgO、(Cr_2O_3+NiO)高,而TiO_2+Al_2O_3+Na_2O+K_2O+P_2O_5低。 我国金伯利岩中Cr-Al,Ni-Co,Ni-Cr,Ni-V,Sc-Ti,Zn-Ti,Ba-Sr,Zr-Hf,Nb-Ta,U-Th,K-Rb呈正相关关系。 相似文献
20.
A comparative geochemical investigation of kimberlites from the Middle Markha region and traditional diamond-bearing areas of Yakutia supported the division of kimberlites into two geochemical types. One of them includes kimberlites from the traditional diamond-bearing areas of Yakutia, and the other is represented by the kimberlites of the Middle Markha region and the rocks of the Zolotitsa field and V. Grib pipe of the Arkhangelsk province. The obtained representative parameters of the two kimberlite types indicate a sharp geochemical contrast between them, and the individual features of correlation relationships between the elements in the rocks of the two types suggest that these differences are related to fundamental genetic factors, which concern primarily the group of highly charged incompatible trace and radioactive elements. The presence of geochemically contrasting rocks within a rather uniform petrochemical association and the geochemically specialized occurrences of kimberlites and related rocks are consequences of repeated metasomatic transformations of mantle rocks under the influence of deep-derived fluids or volatiles released during the recycling of subneous source and subsequent derivation of geochemically specialized types of deep magmas showing signatures of individual mantle sources. 相似文献