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1.
莱芜张家洼铁矿磁铁矿LA-ICP-MS微量元素特征及其对成矿过程的制约 总被引：1，自引：0，他引：1
莱芜张家洼铁矿位于华北克拉通东缘的鲁西地区,矿石成因类型为夕卡岩型铁矿。矿体赋存在早白垩世高镁闪长岩与奥陶系马家沟组灰岩及白云岩接触带附近。本文通过对莱芜岩浆和热液磁铁矿电子探针(EPMA)以及激光剥蚀电感耦合等离子体质谱(LA ICP MS)分析,探讨磁铁矿微量元素组成及变化规律对成岩和成矿作用的指示,为揭示张家洼铁矿的矿床成因及其成矿流体演化过程提供重要制约。分析结果表明,莱芜岩浆磁铁矿与热液磁铁矿相比明显富集Ti、V、Cr等亲铁元素,相对富集Nb、Ta、Zr、Hf等高场强元素以及Sn、Ga、Ge、Sc等中等相容元素,Mg、Al、Mn、Zn、Co显著富集于热液磁铁矿中。Ti、V、Cr以及Mg、Al、Mn、Zn在岩浆和热液中具有不同的地球化学行为,Ti、V、Cr从熔体中进入磁铁矿主要受温度、分配系数以及fO2控制。Mg、Al、Mn、Zn主要受控于水岩反应和后期绿泥石+碳酸盐脉的交代,这些元素通过类质同象替换富集于热液磁铁矿中。Co在热液磁铁矿中除了受水岩相互作用和后期流体交代的影响外,硫化物的出现会导致Co含量急剧降低。Si、Ca、Na及Sr、Ba在岩浆和热液磁铁矿中的地球化学行为非常一致。Ti Ni/Cr图能够用于区分岩浆和热液磁铁矿,莱芜岩浆磁铁矿中Ti含量较高且Ni/Cr比值≤1,热液磁铁矿Ti含量较低且绝大多数Ni/Cr比值≥1。张家洼热液磁铁矿可分为早、晚两个阶段：早期阶段包括(1)早期原生粒状磁铁矿和(2)早期次生磁铁矿;晚期阶段包括(3)晚期原生磁铁矿和(4)晚期次生磁铁矿。原生磁铁矿具有典型的三联点结构特征;次生磁铁矿受后期热液交代影响表现为多空隙,通常呈不规则状、树枝状、骸晶以及交代残余结构。磁铁矿微量元素生动记录了成矿流体演化过程,从早期到晚期、从原生到次生都显示Mg、Al、Mn、Zn包括Co含量持续升高,表明成矿流体可能朝着富集这些微量元素的方向演化。后期流体的交代导致绿泥石蚀变为磁铁矿,连续水岩相互作用和后期流体的交代以及绿泥石直接蚀变是导致热液磁铁矿富集Mg、Al、Mn、Zn等元素的主要原因。热液磁铁矿晚期孔隙较为发育,孔隙度的增加促使更多的流体和磁铁矿发生反应。热液磁铁矿的微量元素不仅能够反映矿床形成的物理化学条件,而且可以反映围岩性质以及水岩相互作用过程。 相似文献
2.
K. Kullerud M. B. Stephens E. Zachrisson 《Contributions to Mineralogy and Petrology》1990,105(1):1-10
Pillow lavas containing an eclogitic mineral assemblage, locally with glaucophane/crossite, are described from the Tsäkkok Lens within the Seve Nappes, north-central Scandinavian Caledonides. Critical primary relationships to the host metasedimentary rocks which are dominated by marble and quartz-garnet-phengite schist are preserved. It is argued that these clastic rocks, and the ongoing igneous activity in the Tsäkkok Lens, are late Precambrian to Cambrian in age and that these rocks were deposited/emplaced along the outermost part of a continental margin related to the continent Baltica.Variations in the whole-rock chemistry of the eclogitic rocks within the Tsäkkok Lens suggest that most elements were mobile during post-extrusive/intrusive evolution. Only Ti, P and Y show significant magmatic trends in element vs Zr plots. Discriminant diagrams employing the elements Ti, P, Zr, Y, Nb and Cr suggest a tholeiitic protolith with a tendency towards enriched mid-ocean ridge basalt (E-MORB) affinity characterized by a relatively low Zr/Nb ratio. A similarity to metabasic rocks occurring in other Seve thrust sheets but lacking evidence for high-P metamorphism is apparent. A common origin for all these rocks is inferred. The Tsäkkok eclogites formed by in situ high-P metamorphism and provide further evidence for subduction of continental crustal material down to mantle depths. This subduction event has been related to collision of Baltica with an outboard are system during the late Cambrian to early Ordovician. 相似文献
3.
Neoproterozoic zirconium-depleted boninite and tholeiitic series rocks from Adola, southern Ethiopia 总被引：1，自引：0，他引：1
In Adola, southern Ethiopia, mafic and ultramafic igneous rocks occur in narrow, 4–10 km wide, north-south-trending belts bounded by high-grade gneisses and migmatites. The mafic/ultramafic rocks are complexly deformed and metamorphosed in greenschist to lower amphibolite facies and are thought to be tectonically dismembered parts of an ophiolite complex. Preliminary geochemical and geochronological data highlight that the high-grade rocks in southern Ethiopia and northern Kenya include a significant portion of juvenile rocks that were accreted at the same time as ophiolitic rocks at 885-765 Ma. This is also the time of widespread oceanic magmatism and closure in the Arabian-Nubian Shield to the north.The Adola mafic rocks were previously described as island arc tholeiites and mid-ocean ridge basalts (MORB). New chemical analyses on the Megado belt rocks reveal the presence of boninites and related dacites interspersed with tholeiitic rocks. The Adola boninites are similar to the Cambrian boninites in western Tasmania in having relatively low Zr/Sm (≤32). Boninites with similarly low ratios have not been reported from elsewhere.The Adola tholeiites have high Ti/Zr (150–300). Mixing between tholeiite and boninite magmas may have resulted in elevated Ti/Zr (80–126) in some Adola boninites. Otherwise, Ti/Zr in the latter is low (20–40). Low Ti/Zr is characteristic of Tertiary boninites in the west Pacific. The fact that both Ti/Eu and Zr/Sm increase from the Adola and Tasmania type to the Tertiary boninites at constant Ti/Zr suggests that Ti might be an element that is also metasomatically added to the source of boninites and raises doubts about the role of amphibole in boninite petrogenesis. 相似文献
4.
QIN Xiaofeng WANG Zongqi ZHANG Yingli PAN Luozhong HU Guiang ZHOU Fusheng 《《地质学报》英文版》2012,86(5):1182-1199
The Napo-Qinzhou Tectonic Belt (NQTB) lies at the junction of the Yangtze, Cathaysia and Indochina (North Vietnam) Blocks, which is composed of five major lithotectonic subunits: the Qinzhou-Fangcheng Suture Zone (QFSZ), the Shiwandashan Basin (SB), the Pingxiang-Nanning Suture Zone (PNSZ), the Damingshan Block (DB) and the Babu-Lingma Suture Zone (BLSZ). On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups: (1) mafic igneous rocks (Group 1) from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; (2) mafic igneous rocks (Group 2) from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and (3) mafic igneous rocks (Group 3) from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206Pb/238U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low εNd(t) values (–2.61 to +1.10) and high initial 87Sr/86Sr isotopic ratios (0.705309–0.707434), indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province (SW China) and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian (or Yunkai) Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time. 相似文献
5.
The composition and metallogeny of igneous rocks and relevant weathering crusts of Jurassic–Cretaceous provenances of the Russian Platform are considered. It is shown that the association of metals that accumulated in the process of weathering and erosion of ancient substratum includes P, Fe, Ti, V, and Cr. This process is reflected in the formation of nodular phosphorites, Ti and Zr placers, and iron ore deposits in the Jurassic–Cretaceous seas of the platform. 相似文献
6.
Basic and intermediate-acidic igneous rocks were developed during the late Hercynian in North Tarim basin.The geochemistry characteristics of the rocks show that basic volcanic rock has K2O/Na2O = 0.18-0.61 < 1 and falls into a category of basalt of sodium system.The rocks contain enriched large-ion lithophile elements (LILE) (K,Rb,Ba,Th) and high-field strength elements (HFSE) (Nb,Ta,Ti,Zr,P),with the magmatic material from the upper mantle.The intermediate-acidic volcanic rocks have σ = 1.91-2.96 < 3.3,K2O/Na2O =1.25-1.59 > 1,as well as the enriched LILE and depleted HFSE (Nb,Ta,Ti,P),presenting the same trace element compositions and characteristics as in the granitic rocks of South Tianshan Mt.; they are either shoshonitic igneous rocks or high-K calc-alkaline igneous rocks,with a distinct crust-derived component feature.The comprehensive analyses on the characteristics of the trace elements,the graphic tectonic discrimination,and the distribution features of the two types of igneous rocks show that they were formed under different tectonic settings and geodynamic environments:the basalt was formed in the active rifting period when the active mantle upwelling caused the thinning of lithosphere; the intermediateacidic volcanic-intrusive rock was formed in the island arc area of the active continental margin in North Tarim; the formation is associated with the plate subduction during the course of South Tianshan Ocean closure-the subduction of Middle Tianshan Mountain toward the Tarim plate.The basic and intermediate-acidic igneous rocks reveal a tectonic regime of extension-extrusion transition,which is significant in determining the key tectonic revolution period of North Tarim basin. 相似文献
7.
Banded iron formations (BIF) are prominent in sediments older than 2 Ga. However, little is known about the absolute abundance of BIF in Archean and Early Proterozoic sediments, and the source of the Fe is still somewhat uncertain. Also unknown is the role that Fe may have played in the maintenance of low oxygen pressures in the Archean and Early Proterozoic atmosphere. An analysis of the chemical composition of Precambrian rocks provides some insight into the role of Fe in Precambrian geochemical cycles. The Fe content of igneous rocks is well correlated with their Ti content. Plots of Fe vs. Ti in Precambrian sandstones and graywackes fall very close to the igneous rock trend. Plots of Fe vs. Ti in Precambrian shales also follow this trend but show a definite scatter toward an excess of Fe. Phanerozoic shales and sandstones lie essentially on the igneous rock trend and show surprisingly little scatter. Mn/Ti relations show a stronger indication of Precambrian Mn loss, perhaps due to weathering under a less oxidizing early atmosphere. These data show that Fe was neither substantially added to nor significantly redistributed in Archean and early Proterozoic sediments. Enough hydrothermal Fe was added to these sediments to increase the average Fe content of shales by at most a factor of 2. This enrichment would probably not have greatly affected the near-surface redox cycle or atmospheric oxygen levels. Continued redistribution of Fe and mixing with weathered igneous rocks during the recycling of Precambrian sediments account for the excellent correlation of Fe with Ti in Phanerozoic shales and for the similarity between their Fe/Ti ratio and that of igneous rocks. 相似文献
8.
对大兴安岭鄂伦春地区满克头鄂博组火山岩年代学与岩石地球化学特征进行分析,锆石U-Pb测年结果表明火山岩形成时代为晚侏罗世(152.9±1.7 Ma).地球化学特征表明该组火山岩具有富硅、碱,贫钙、镁特征,且具较低Mg#值及极低的Cr、Co、Ni值的特点.微量元素相对富集大离子亲石元素(LILE) K、Rb、Ba和LREE,亏损高场强元素Nb、Ta、Ti.火山岩具有地壳源区特征,Rb/Sr值平均为0.66,远高于N-MORB (0.03)、OIB (0.047)和E-MORB (0.033),Ti/Zr值平均为13.94,与壳源岩浆的范围(<20)一致,表明该类岩石的原始岩浆起源于地壳岩石的部分熔融.根据岩石地球化学特征,结合区域已有研究资料,本区满克头鄂博组火山岩的形成应与蒙古-鄂霍次克洋向南东方向俯冲作用有关. 相似文献
9.
Aeolian soils in the Blayney district are characterised by having approximately 80% of their mass finer than 63 μm, Ti/Zr ratios of approximately 12, radioelement contents of 0.7% K, 2 ppm eU and 11 ppm eTh and a position high in the landscape. Their Ti/Zr ratio and abundant quartz content distinguishes them from soils derived from Tertiary basalts, which share some of the other characteristics. Many soils in the district have a partial aeolian contribution, which can be recognised by a Ti/Zr ratio that differs from that of the underlying rock. Abundance of an aeolian contribution suggests that airborne radiometric surveys should be very carefully interpreted. Ground studies suggest that high Th content in soils contrasted with low Th in adjacent rocks can be indicative of an aeolian contribution in soils. A substantial amount of fine material in a soil can also significantly dilute geochemical signatures if −63 μm (<80 mesh) samples are used for soil surveys during exploration. 相似文献
10.
近年来古太平洋构造域的构造演化备受学者关注。本文报道的延边开山屯地区花岗闪长岩-石英闪长岩体LAICP-MS U-Pb年龄表明其形成时间为早侏罗世早期(198±1Ma),所采样品可根据Zr/Hf值分为高Zr/Hf值组花岗闪长岩和低Zr/Hf值组石英闪长岩。高Zr/Hf值组花岗闪长岩起源深度浅,富集Rb、Th、U、K等大离子亲石元素(LILEs),贫Nb、Ta、Ti等高场强元素(HFSEs),具壳源岩浆的特点。低Zr/Hf值组为壳源岩浆与来自深部的亏损地幔岩浆混合而成,岩石亏损Nb、Ta、Zr、Hf、Ti等高场强元素,具有典型的弧型岩浆地球化学特征。岩体中存在细粒闪长质包体,镜下可见针柱状磷灰石。开山屯岩体属钙碱性系列岩石,结合前人资料,认为其与该地区同时代火成岩组成北-东向分布的早侏罗世活动大陆边缘型火成岩带,而位于该带西侧的小兴安岭-张广才岭地区存在同时代弧后拉张带,两者构成典型的大陆弧与弧后拉张带模型,共同揭示了早侏罗世早期古太平洋板块对东北地区的俯冲作用。 相似文献
11.
《Journal of African Earth Sciences》2007,47(3):153-173
The lithology of Malawi is characterized by Precambrian metamorphic and igneous rocks which form part of the polyphase East African Orogen. Rift-related sedimentation and igneous activity during the late Paleozoic (Karoo System) and the late Mesozoic (Chilwa Province) have produced a great variety of rocks that underwent strong chemical weathering and erosion when the entire region received its final shape by peneplanation and fluvial incision during the Cenozoic under (sub)tropical climatic conditions. Aluminum is a dominating element in minerals (e.g., corundum, kyanite, beryl, gibbsite) in this region. Some minerals were concentrated in deposits bound to Al-enriched host rocks (zircon, pyrochlore, eudialyte, uranium minerals) with high A/CNK ratios, whereas others, e.g., asbestos, chalcedony, monazite, kaolinite, ilmenite and garnet have host rocks of a low A/CNK ratio. Aluminum was used to categorize these various mineral deposits. The abundance of aluminum and accumulations of Nb, Zr, Ti, REE, Sr and Ba point for some mineralisations to similar subcrustal carbonatite-forming systems that were operative during periods of the Precambrian and the Mesozoic in Malawi. Aluminum variation does not only reflect differentiation in the various igneous rock series but it is also visible in the sedimentary realm during transport and weathering. In context with other elements such as Ti and P, Al provides an opportunity to reveal chemical relationships between rocks and mineral deposits. Spinel and Al-enriched silicate minerals can be used as pathfinder minerals in the stream sediments to guide the exploration geologist to non-metallic deposits. 相似文献
12.
华北克拉通新太古代板块俯冲作用:来自山西云中山地区变质高镁火成岩组合的证据 总被引：3，自引：3，他引：0
在华北克拉通中部的山西云中山地区,新太古代花岗闪长质片麻岩中存在一些超镁铁质岩-镁铁质岩块及由斜长角闪岩、角闪变粒岩、石英岩和石榴夕线黑云片岩等岩石类型构成的变质表壳岩残片,其中的超镁铁质-镁铁质岩、斜长角闪岩和角闪变粒岩构成一套高镁火成岩组合。超镁铁质岩已变质为橄榄绿泥阳起片岩等岩石类型,呈变余斑状结构,橄榄石斑晶仍有保存;岩石SiO_2含量为39.22%～44.99%,Al_2O_3为8.82%～13.47%,Mg O为19.24%～22.13%,Na_2O+K_2O=0.71%～1.11%,CaO为5.75%～8.42%;Al_2O_3/TiO_2=14.8～17.4,CaO/Al_2O_3=0.60～0.84;化学成分上与科马提岩有一定的相似性。与之紧密伴生的斜长角闪岩也具有高镁特征,Mg O含量为11.28%～15.09%,铝、硅和碱质均偏低,具正铕异常,显示堆晶辉长岩的特征。非高镁斜长角闪岩有相对高的铝、硅和碱质,其原岩应为钙碱性玄武岩。角闪变粒岩样品的SiO_2含量为54.21%～55.71%,Al_2O_3为14.24%～15.49%,Mg O为6.26%～8.28%,Fe OT/Mg O=1.11～1.58,高钠低钾,Na_2O+K_2O=3.7%～4.78%,Na_2O/K_2O=5.15%～13.13,Mg#=53.0～61.5,属于高镁安山岩。由超镁铁质质岩-斜长角闪岩-角闪变粒岩构成的变质高镁火山岩组合具有钙碱性系列趋势。超镁铁质岩稀土元素含量总量较低,具有轻稀土富集和重稀土亏损的稀土型式;斜长角闪岩与超镁铁质岩比较,除富集大离子亲石元素和Cr、Ni明显较低外,具有相似的微量元素图谱形态。三种岩石类型在微量元素蛛网图上均显示出Ta、Nb、Ti负异常和Pb正异常。野外产状和岩石地球化学特征表明超镁铁质岩和高镁斜长角闪岩属于阿拉斯加型杂岩体,角闪变粒岩属于赞岐岩质高镁安山岩。在Zr/Nb-Nb/Th和Nb/Y-Zr/Y构造环境判别图解上显示出与俯冲相关的演化趋势,在Hf-Th-Ta、Nb/La-(La/Sm)N和Th/Yb-Nb/Yb图解上也落在岛弧钙碱性岩石区域。以上特征表明高镁火成岩组合形成于与板块俯冲相关的岛弧构造背景。野外地质关系和锆石U-Pb年龄限定高镁火成岩组合形成时代在～2.5Ga。云中山地区阿拉斯加型镁铁质-超镁铁质杂岩与赞岐岩质高镁安山岩共生,表明该地区存在新太古代的板块俯冲作用,为太古宙存在板块构造机制提供了新证据。 相似文献
13.
A late-stage rift-related tholeiite-alkalic suite of igneous intrusions cut the Deccan Traps lavas at the western Indian continental margin. The suite comprises intrusives that can be grouped into ten lithotypes on the basis of their mutual relationships. Tholeiitic types predate the alkaline rocks and greatly predominate, however, the alkaline members exhibit more diversity in mineralogy and chemistry, and are amongst the rare magmatic rocks from the Deccan that host both mantle and lower crustal xenoliths. The mineralogy of most rock types is dominated by clinopyroxene. The diversity of the alkaline rocks could be mainly accounted for by fractional crystallization and mixing between evolved and primitive melts under varying P-T conditions. Sodic and potassic lamprophyres are amongst the most primitive samples with high Mg #, FeO/MgO < 1, high Cr and also with relatively high Ba, Sr, Zr and Nb. They are the most deeply derived magmas within the Deccan Traps as is evident from the mantle and lower crustal xenoliths entrained by them. They possibly represent low degree melts of incompatible element-enriched mantle source rocks. The nephelinites are strongly porphyritic and despite their high Mg #s can be regarded as evolved magmas that have been responsible for the formation of the tephriphonolite daughter. The nephelinites have undergone contamination by lower crustal granulites. The composite intrusions of microdiorites with their complexly zoned mineralogy dominated by plagioclase and amphiboles/micas represent hybrid rocks that have resulted from mixing between tholeiitic and trachytic melts partly at depth and partly at shallow crustal levels. 相似文献
14.
Petrogenetic implications of Ti,Zr, Y,and Nb variations in volcanic rocks 总被引：113，自引：0，他引：113
Data from experimental runs, coexisting phases in ultramafic rocks and phenocryst-matrix pairs in volcanic rocks have been used to compile a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions. These values have then been used to interpret variations of these elements, first in basalts and second, during fractional crystallization from basic to acid magmas. For basalts, petrogenetic modelling of Zr/Y, Zr/Ti, and Zr/Nb ratios, when used in conjunction with REE, Cr and isotopic variations, suggests that: (1) the increase in Zr/Y ratio from mid-ocean ridge to within plate basalts and the low Zr/Nb ratios of alkalic basalts are due to (fluid controlled) source heterogeneities; (2) the low Zr and Zr/Y ratio of volcanic arc basalts results from high degree of partial melting of a depleted source; and (3) the high Zr and similar Zr/Y ratio of basalts from fast spreading relative to slow spreading ridges results from open-system fractional crystallization. Modelling of fractionation trends in more evolved rocks using Y-Zr, Ti-Zr and Nb-Zr diagrams highlights in particular the change in crystallizing mafic phases from island arcs (clinopyroxene-dominated) to Andean-type arcs (amphibole±biotite-dominated). These methods can be applied to altered lavas of unknown affinities to provide additional information on their genesis and eruptive environment. 相似文献
15.
《Gondwana Research》2001,4(3):509-518
The Proterozoic Bandal mafic rocks, exposed in Kullu-Rampur window, Lesser Himalaya, Himachal Pradesh, indicate two distinct (high-Ti and low-Ti) magma types. The high-Ti basalts are characterised by high-TiO2 (> 2 wt%), Ti/Y, Ti/Zr, TiO2/K2O and low Rb/Sr ratios. They are enriched in high field strength (HFS) elements (Nb, Zr, Ti) relative to low field strength (LFS) incompatible elements (K, Rb). The low-Ti basalts are charactersied by low TiO2 (< 2 wt%), Ti/Y, Ti/Zr and high Rb/Sr and Rb/Ba ratios. Quartz-normative composition, continental tholeiite characteristics with Nb/La less than 1 are some of the common factors of the two groups of the Bandal mafic rocks. The trace element concentrations and their ratios of the two groups of the basalts indicate that they have been derived from the asthenosphere at different depths, low-Ti at shallow and high-Ti at deeper levels. Some of the chemical features like low Mg #, Cr, Ni, high incompatible element concentrations (especially Ba), light rare earth element (LREE) enriched patterns point towards assimilation and fractional crystallisation (AFC) process which may have played a significant role in the generation of these basalts.Furthermore, the Bandal mafic rocks, apart from field settings, are geochemically similar to other Proterozoic mafic bodies like the Rampur volcanics, Mandi-Darla volcanics, Garhwal volcanics and Bhimtal-Bhowlai volcanics of the Lesser Himalaya. This widespread Proterozoic continental tholeiitic magmatism over an area of 170,000 km2 in the Lesser Himalaya provides an evidence of plume activity in the region. 相似文献
16.
We report the results of LA-ICP-MS analyses of rock forming minerals in clinopyroxene-apatite-K feldspar-phlogopite (CAKP) metasomatic xenoliths and primary carbonatite melt inclusions (CMI) hosted in apatite (Ap) and K feldspar (Kfs). The xenoliths are from the Cretaceous lamprophyre dikes of the Transdanubian Central Range, Hungary. The CMI in Ap have phosphorus dolomitic composition as opposed to CMI in Kfs, which display dolomitic alkali-aluminosiliceous character. The melts found in CMI in Ap and in Kfs likely formed by liquid-liquid separation from an originally carbonate- and phosphorous-rich melt. Primitive mantle (PM) normalized trace element distributions of both Ap- and Kfs-hosted CMI (n = 60 and 20, respectively) reveal a strong negative Ti-anomaly, and an extreme enrichment in incompatible elements (U, Th, LILE and LREE) relative to HREE, Sc, V, Ni and Cr. Rarely, apatites contain unique CMI, which show major- and trace-element signature transitional to K feldspar-hosted CMI. This is due to heterogeneous entrapment of an immiscible phosphorous-bearing carbonatite melt and a carbonate-bearing alkali aluminosiliceous melt, which is a further evidence for their co-existence. CMI reveal that U, Th, Pb, Nb, Ta, P, Sr, Y and REE partitioned into the phosphorous-bearing carbonatite melt, whereas Cs, Rb, Na, K, B, Al, Zr and Hf preferred the silicate-bearing liquid.PM normalized REE pattern (high LREE/HREE), elevated Zr and Hf contents and negative Ti anomaly of clinopyroxene (Cpx) indicate that its formation is genetically linked to carbonatite metasomatism attested by CMI. Trace element partitioning between the studied Cpx and CMI is in accordance with experimentally determined trace element distributions between Cpx and carbonatite melt. Cpx, which occur in samples with high modal proportion of apatite represent mantle section, which interacted with a higher amount of “initial” carbonatite melt than Cpx from apatite-poor xenoliths. This is confirmed by higher Cr, Ni, V, Sc, Ti and lower Zr, as well as Hf concentration in Cpx from xenoliths with low modal abundance of Ap. CMI reveal that Ti, V, Ni and Cr were in lower concentration in the “initial” carbonatite melt than in PM. Contrarily, Zr and Hf were more abundant in this melt than in PM. Consequently, a continuously migrating “initial” carbonatite melt, increased Zr and Hf concentration, and decreased Ti, Sc, V, Ni and especially Cr in the clinopyroxenes. Our findings suggest that the studied CAKP rocks were formed by carbonatite melt metasomatism, which occurred in an open system in the upper mantle. 相似文献
17.
Host rock compositional controls on zircon trace element signatures in metabasites from the Austroalpine basement 总被引：11，自引：0，他引：11
Zircon populations of Neoproterozoic and early Paleozoic age occur in metabasites of a high-pressure amphibolite-facies unit of the Austroalpine basement south of the Tauern Window. The host rocks for these zircons are eclogitic amphibolites of N-MORB-type character, hornblende gneisses with volcanic-arc basalt signature, and alkaline within-plate-basalt amphibolites. Bulk rock magmatic trace element patterns were preserved during amphibolite-facies high-pressure and subsequent high-temperature events, as well as a greenschist-facies overprint. Positive Ce and negative Eu anomalies and enrichment of HREE in normalized zircon REE patterns, as analysed by LA-ICP-MS, are typical for an igneous origin of these zircon suites. Zircon Y is well correlated to HREE, Ce, Th, U, Nb, and Ta and allows discrimination of compositional fields for each host rock type. Low Th/U ratios are correlated to low Y and HREE abundances in zircon from low bulk Th/U host rocks. This is likely a primary igneous characteristic that cannot be attributed to metamorphic recrystallization. Variations of zircon/host rock element ratios confirm that ionic radii and charges control abundances of many trace elements in zircon. The trace element ratios—presented as mineral/melt distribution coefficients—indicate a selectively inhibited substitution of Zr and Si by HREE and Y in zircon which crystallized from a N-MORB melt. Correlated host rock and zircon trace element concentrations indicate that the metabasite zircons are not xenocrysts but crystallized from mafic melts, represented by the actual host rocks. 相似文献
18.
A.A. Vorontsov G.S. Fedoseev S.V. Andryushchenko 《Russian Geology and Geophysics》2013,54(9):1001-1025
Based on geological data and the geochemical and isotopic (Sr, Nd) parameters of the Devonian volcanic associations of the Minusa basin, the main regularities of volcanism development are considered, the composition of magmatic sources is studied, and the geodynamic mechanisms of their involvement in rifting are reconstructed. The early stage of formation of the Minusa basin was characterized by intense volcanism, which resulted in differentiated and, more seldom, bimodal volcanic complexes composed of pyroclastic rocks and dolerite sills. At the late stage, only terrigenous deposits accumulated in the basin. It has been established that the basites are similar in composition and are intermediate in geochemical characteristics between intraplate rocks (OIB) and continent-marginal ones (IAB). The basites, like OIB, have high contents of all lithophile elements, which is typical of enriched mantle sources, and, like IAB, show negative anomalies of Nb, Ta, Ti, and, to a smaller extent, Rb, Th, Zr, and Hf, selective enrichment in Pb and Ba (and, sometimes, Sr), and a weak REE differentiation (7 < (La/Yb)N < 17). In contrast to the basins in other segments of the Devonian Altai–Sayan rift area, the igneous associations in the Minusa basin are characterized by a worse expressed geochemical inhomogeneity of rocks and lack of high-Ti (> 2 wt.% TiO2) basites. The Sr and Nd isotope compositions of the Minusa basites deviate from the mantle rock series toward the compositions with high radiogenic-strontium and low REE contents.This points to the melting of a mantle substratum (PREMA-type) and carbonate-rich sedimentary rocks, which were probably assimilated by basaltic magma. The correlations between the contents of trace incompatible elements in rocks with SiO2 = 53–77 wt.% testify to the assimilation of crustal substrata by parental basaltic melts and the subsequent differentiation of contaminated magmas (AFC model). We propose a model for the formation of primary melts with the simultaneous participation of magmatic sources of two types: plume and fluid-saturated suprasubductional, localized beneath the active continental margin. 相似文献
19.
N.V. Dmitrieva E.F. Letnikova M.M. Buslov A.I. Proshenkin H. Geng 《Russian Geology and Geophysics》2013,54(10):1164-1176
A comparative geochemical characteristics of Late Precambrian sedimentary rocks (Ust’-Kelyana and Tuluya rock units) in the Anamakit–Muya zone of the Baikal–Muya belt is given, and the conditions of their sedimentation are considered. The first results of U–Pb (LA-ICP-MS) dating of detrital zircons and Sm–Nd isotope data on the Tuluya unit deposits are presented. Petrogeochemical study showed that the studied sediments are first-cycle rocks similar in composition to terrigenous island-arc sediments. The low contents of Th, Rb, Zr, Hf, and LREE and high contents of Co, Ni, Sc, V, Cr, and Fe2O3* in the sandstones of the Ust’-Kelyana unit evidence that these rocks are similar to oceanic-arc deposits. In contrast, the enrichment of the Tuluya unit rocks in Zr, LREE, Th, Rb, and Nb indicates their similarity to deposits of continental island arcs or active continental margin. Isotope-geochronological studies of the Tuluya rock unit showed the mixing of detrital material resulted from the erosion of Neoproterozoic island-arc igneous rock associations (625–700 Ma), like those in the Karalon–Mamakan zone (Yakor’ and Karalon Formations), and more ancient associations, like the Kelyana (812–824 Ma) and/or Dzhaltuk Groups. Judging from the minimum age of detrital zircon, the lower time bound of sedimentation corresponds to 0.6 Ga. 相似文献
20.
《Chemie der Erde / Geochemistry》2019,79(2):384-398
Geochemical compositions of the Lower Cambrian Niutitang Formation shales in the southeastern Yangtze Platform margin were investigated for provenance, tectonic setting, and depositional environment. The shale samples are characterized by higher abundances of large ion lithophile elements (Cs, Ba, and Pb), lower abundances of high field strength elements (Cr, Sc, and Co) and transition elements (Th, Zr, Hf, Nb, and Ta) relative to average shale. North American shale composition (NASC) -normalized rare earth element (REE) patterns are observed, with negative Ce anomalies, negative Eu anomalies, and positive Y anomalies. The chemical index of alteration (CIA) varies from 68.67–74.93. Alkali and alkaline element contents and CIA values suggest that the source rocks have undergone moderate weathering. The index of compositional variability (ICV), Zr/Sc and Th/Sc ratios vary from 0.53 to 1.07, 5.31 to 8.18 and 0.52–1.02, respectively. ICV values and relationships between Zr/Sc and Th/Sc ratios indicate negligible sedimentary recycling. The Al2O3/TiO2 (14–26) and TiO2/Zr (56–77) ratios imply that the source rocks of the investigated shales had intermediate igneous compositions. However, Cr/V ratios and a La/Th–Hf discrimination diagram suggest that the intermediate compositional signal of the source rocks was derived from a mixture of 75% mafic and 25% felsic igneous rocks rather than intermediate igneous rocks. The major source was the Jiangnan continental island arc with bimodal igneous rocks, lying to the south of the study area, together with a contribution from granites and gneisses uplifted and eroded in the Yangtze Block. Discrimination of tectonic setting using major and trace elements indicates that the source rocks originated in a transitional setting from active continental to passive margin, consistent with the failed intracontinental rift model for the evolution of the South China plate. The Niutitang Formation shales were deposited in a rift basin setting under conditions of anoxic bottom water in a redox-stratified water column, with organic-rich shales prospective for shale-gas production being found in deep-water downslope and basin environments rather than the shallow-water shelf. 相似文献