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1.
石宝沟花岗岩体位于华北陆块南缘,主要由似斑状二长花岗岩和中细粒二长花岗岩组成,发育岩浆暗色包体。LA-ICPMS锆石U-Pb定年结果显示,似斑状二长花岗岩和中细粒二长花岗岩的成岩年龄分别为(156±1)Ma(N=15,MSWD=0.34)和(157±1)Ma(N=17,MSWD=0.10)。这些花岗岩的A/CNK=0.82~1.02,Na2O+K2O=7.61%~8.91%,K2O/Na2O=1.02~1.48,属于高钾钙碱性、准铝质-弱过铝质I型花岗岩。稀土和微量元素特征显示其富集LREE、Rb、Ba、K、Pb等大离子亲石元素,亏损HREE、P、Ti等高场强元素,具有弱的负铕异常,个别样品具有正铕异常(δEu=0.81~1.12)。似斑状二长花岗岩的锆石εHf(t)为-22.6~-8.3,tDM2为2.64~1.73Ga;中细粒二长花岗岩εHf(t)为-26.9~-12.4,tDM2为2.91~1.99Ga。岩石地球化学和锆石Hf同位素组成特征表明,石宝沟花岗岩体的源区物质以壳源物质为主,可能为太古宙太华群,但也有年轻幔源组分的参与。  相似文献   

2.
段友强  张正伟  杨晓勇 《岩石学报》2015,31(7):1995-2008
张士英岩体位于华北克拉通南缘,岩体主要由石英正长岩组成。石英正长岩的LA-ICP-MS锆石U-Pb年龄为122.8±1.5Ma。其Si O2含量为66.04%~67.80%,Na2O+K2O=9.03%~10.97%,K2O=4.40%~6.37%,K2O/Na2O1属于钾质长英质岩石。A/CNK=1.26~1.58,A/NK=1.63~1.79属于过铝质岩石系列。石英正长岩的Mg#变化范围在12.9~39.4。富集LREE亏损HREE,轻重稀土分异明显,(La/Yb)N=15.48~21.12,Eu呈弱的负异常(δEu=0.54~0.99)。富集Rb、K、Th、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素。张士英石英正长岩岩浆锆石εHf(t)集中在-17.6~-13.9,Hf两阶段模式年龄tDM2集中在1.7~1.9Ga。石英正长岩的岩浆Zr饱和温度高(936~998℃)。地球化学及同位素显示张士英石英正长岩源区主要为古老的壳源物质,并有少量年轻组分加入,这种年轻组分是幔源物质。岩体形成于拉张性构造环境下,拉张性的环境导致了幔源物质的上涌,底侵下地壳使其发生部分熔融。形成时代正好位于华北克拉通破坏峰期,张士英石英正长岩正是这一地质事件的响应。  相似文献   

3.
《地质论评》2012,58(3)
本文报道了华北克拉通南缘豫西鲁山下汤地区古元古代片麻状花岗岩和黑云角闪斜长片麻岩的全岩地球化学和锆石SHRIMP U-Pb年龄和Hf同位素组成.岩石呈包体形式存在于中元古代花岗岩中.片麻状花岗岩具深熔特征,岩浆锆石年龄为2.30 Ga;岩石高SiO2和K2O,低∑FeO、MgO和CaO,具稀土总量较高(∑REE=165.8×10-6)、轻重稀土分离较强[(La/Yb)n=37.8]及弱负铕异常(Eu/Eu(*)=0.76)的稀土模式;εNd(t)(t=2.30 Ga)=-0.75; tDM(Nd) =2.66 Ga.黑云角闪斜长片麻岩变质原岩为辉长闪长岩,捕获锆石年龄为2.25 Ga;岩石低SiO2 和MgO,高Al2O3和P2O5,具稀土总量高(∑REE=373.4×10-6)、轻重稀土分离不强[ (La/Yb)n=9.4]及较强负铕异常( Eu/Eu*=0.44)的稀土模式;εNd(t)(t=2.25 Ga)=-1.21;tDM(Nd) =2.75 Ga.片麻状花岗岩和黑云角闪斜长片麻岩都记录了1.94 Ga变质锆石年龄.片麻状花岗岩的岩浆锆石组成域的εHf(t)(t=2.30 Ga)=-6.71~0.38,tDMI(Hf) =2627 ~2910 Ma,tDM2(CC)(Hf)=2823 ~ 3255 Ma.黑云角闪斜长片麻岩的捕获锆石组成域的εHf(t)(t=2.25 Ga)=-19.58~ -1.73,tDM1 (Hf) =2664~3360 Ma,tDM2(CC)(Hf)=2968 ~4011 Ma.结合前人资料,得出如下结论:华北克拉通南缘豫陕晋结合部地区存在—规模较大的约2.3 Ga地质体分布区;华北克拉通南缘很可能存在规模巨大的>2.7 Ga基底;中部造山带与孔兹岩带具有类似的古元古代晚期构造热事件演化历史.  相似文献   

4.
本文报道了内蒙古大青山地区早前寒武纪变质岩石的锆石Hf同位素和稀土组成。两个古元古代晚期(1.9~2.1 Ga)变质碎屑沉积岩样品中碎屑锆石的(n(176Hf)/n(177Hf))c、tDM1(Hf)和tDM2(Hf)分别为0.281079~0.281502、2548~3000 Ma、2612~3153 Ma和0.280916~0.281451、2533~2717 Ma、2600~3404 Ma; 一个古元古代早期(2.37 Ga)变质辉长岩样品中岩浆锆石的εHf(t)和tDM1(Hf)分别为1.50~6.68和2449~2647 Ma,表明大青山及邻区在新太古代晚期—古元古代早期存在强烈的构造岩浆热事件,既有地幔添加又有壳内再循环作用。三个样品的边部变质锆石εHf(t)、tDM1(Hf)和tDM2(Hf)分别为-9.49~3.91、2201~2686 Ma、2285~2887 Ma;-7.29~-2.42、2350~2540 Ma、2499~2740 Ma和-5.46~-0.53、2319~2507 Ma、2443~2687 Ma,Th/U比值普遍小于01。与核部锆石相比,边部变质锆石tDM2(Hf)变小,Th/U比值和稀土含量降低,但稀土模式十分类似。研究表明,变质锆石增生边的形成及其Hf同位素、稀土和U—Th组成受核部锆石和变质作用的双重制约。变质增生边的形成至少部分与核部锆石溶解以后的再结晶有关,变质流体起了重要作用。  相似文献   

5.
本文报道了华北克拉通南缘豫西鲁山下汤地区古元古代片麻状花岗岩和黑云角闪斜长片麻岩的全岩地球化学和锆石SHRIMP U-Pb年龄和Hf同位素组成。岩石呈包体形式存在于中元古代花岗岩中。片麻状花岗岩具深熔特征,岩浆锆石年龄为2.30Ga;岩石高SiO2和K2O,低ΣFeO、MgO和CaO,具稀土总量较高(ΣREE=165.8×10-6)、轻重稀土分离较强[(La/Yb)n=37.8]及弱负铕异常(Eu/Eu*=0.76)的稀土模式;εNd(t)(t=2.30Ga)=-0.75;tDM(Nd)=2.66Ga。黑云角闪斜长片麻岩变质原岩为辉长闪长岩,捕获锆石年龄为2.25Ga;岩石低SiO2和MgO,高Al2O3和P2O5,具稀土总量高(ΣREE=373.4×10-6)、轻重稀土分离不强[(La/Yb)n=9.4]及较强负铕异常(Eu/Eu*=0.44)的稀土模式;εNd(t)(t=2.25Ga)=-1.21;tDM(Nd)=2.75Ga。片麻状花岗岩和黑云角闪斜长片麻岩都记录了1.94Ga变质锆石年龄。片麻状花岗岩的岩浆锆石组成域的εHf(t)(t=2.30Ga)=-6.71~0.38,tDM1(Hf)=2627~2910Ma,tDM2(CC)(Hf)=2823~3255Ma。黑云角闪斜长片麻岩的捕获锆石组成域的εHf(t)(t=2.25Ga)=-19.58~-1.73,tDM1(Hf)=2664~3360Ma,tDM2(CC)(Hf)=2968~4011Ma。结合前人资料,得出如下结论:华北克拉通南缘豫陕晋结合部地区存在一规模较大的约2.3Ga地质体分布区;华北克拉通南缘很可能存在规模巨大的>2.7Ga基底;中部造山带与孔兹岩带具有类似的古元古代晚期构造热事件演化历史。  相似文献   

6.
张士英岩体位于华北地台南缘,岩石类型包括钾长花岗岩、似斑状花岗岩和石英斑岩脉,其中只在钾长花岗岩中发育有暗色岩石包体,在包体和寄主岩中发育反映岩浆混合作用的岩石结构。钾长花岗岩、似斑状花岗岩和石英斑岩脉的SHRIMP锆石U-Pb年龄分别为107.3±2.4Ma、106.7±2.5Ma和101±3Ma。锆石Hf同位素分析结果显示,钾长花岗岩的锆石εHf(t)为-15.96~-20.80,单阶段模式年龄(tDM1)为1396~1643Ma,两阶段模式年龄(tDM2)为1880~2018Ma;似斑状花岗岩的锆石εHf(t)为-18.97~-22.18,tDM1为1512~1640Ma,tDM2为1925~2080Ma;除了一粒年龄为2.6Ga的锆石具有εHf(t)为-0.71、tDM1为2943Ma和tDM2为3036Ma的组成,石英斑岩的锆石εHf(t)为-23.41~-27.95,tDM1为1678~1896Ma,tDM2为2144~2330Ma。这些数据暗示,除了存在少量太古宙地壳物质的贡献外,张士英岩体的物质来源可能主要为1.9~2.3Ga期间形成的新生地壳,但也不排除古老地壳与富集地幔源混合的可能。综合分析前人研究成果表明,在太平洋板块俯冲方向发生转变的过程中,先存断裂带发生拉张。张士英岩体与中国东部同期岩浆活动一起可能形成于这种受断裂带控制的伸展环境。  相似文献   

7.
河北承德甲山正长岩成因的Sr-Nd-Pb-Hf同位素制约   总被引:1,自引:0,他引:1  
报道了华北克拉通北缘承德地区甲山正长岩的锆石U-Pb年龄及Hf同位素、主微量元素、Sr-Nd-Pb同位素组成。甲山岩体的LA-ICP-MS锆石U-Pb年龄为111~108 Ma,代表岩体的结晶年龄,表明其侵位于早白垩世晚期。岩体高Si O2、K2O+Na2O、Al2O3、LILEs(Rb、K)和LREE,低Fe2O3T、Ca O、Ti O2、Mg O和HFSE,具有板内裂谷岩浆岩的特征,属A型花岗岩。甲山岩体εNd(t)=-5.0~-0.9,tDM2(Nd)=0.98~1.31 Ga;εHf(t)=-2.7~+4.3,tDM2(Hf)=0.90~1.33 Ga;Δ8/4=84.9~91.3,Δ7/4=-6.4~-4.0,(206Pb/204Pb)i=16.63~17.10,(207Pb/204Pb)i=15.24~15.30,(208Pb/204Pb)i=36.54~37.20。根据野外地质观察、实验岩石学以及元素地球化学和Sr-Nd-PbHf同位素示踪的综合分析,认为甲山岩体可能起源于下地壳与亏损地幔的混合源区,是华北克拉通北缘岩石圈强烈减薄、地壳伸展作用的结果。早白垩世甲山岩体形成过程中亏损地幔物质的参与指示了华北克拉通北缘岩石圈减薄和软流圈地幔上涌,记录了陆内伸展环境下与软流圈底侵作用相关的岩浆事件。  相似文献   

8.
本文对苏鲁造山带内荣成超高压地体片麻岩样品进行了锆石U-Pb年龄、Hf同位素和全岩Nd同位素分析,旨于探讨片麻岩的原岩性质及成因。3个片麻岩样品的锆石SHRIMP U-Pb年龄(770Ma和710Ma之间)表明原岩形成于晚元古代,与Rodinia超大陆裂解过程的岩浆活动时间相吻合。14个片麻岩的单阶段钕模式年龄变化在1.70Ga至2.30Ga(平均~1.93Ga),表明荣成超高压地体片麻岩平均地壳存留时间为古元古代,与扬子陆块的平均地壳形成年龄相一致,暗示具有扬子陆块属性。其锆石ε_(Hf)(t)值(t=750Ma)和模式年龄值变化范围大。2个片麻岩的锆石具有非常负的ε_(Hf)(t),平均值为-16.4,铪模式年龄为2.70Ga。6个片麻岩的锆石ε_(Hf)(t)平均值为-7.7,铪模式年龄为2.15Ga。这些结果表明荣成超高压地体部分原岩主要由太古代-古元古代地壳物质在晚元古代时重熔形成的,进一步说明荣成地区可能有扬子陆块的太古代地壳残留。另有6个片麻岩的锆石ε_(Hf)(t)变化范围为-0.56至6.6之间,其中部分锆石的两阶段Hf模式年龄为0.81Ga至0.94Ga,表明片麻岩原岩晚元古代形成时,有幔源岩浆活动和新生地壳形成,可能同时存在强烈壳-幔相互作用,上侵的幔源岩浆底侵导致上覆扬子陆块太古代-古元古代地壳物质重熔,形成花岗质岩浆。  相似文献   

9.
加吾金矿床大地构造上位于中央造山系"共和缺口"西缘,位于中央造山带多个块体交接转换的重要部位,其形成与区内印支期中酸性岩浆活动密切相关。对区内与金成矿关系密切的花岗斑岩脉中的锆石进行LA-ICP-MS U-Pb定年以及Lu-Hf同位素测试。测试结果显示,锆石206Pb/238 U加权平均年龄为233.4Ma±4.3Ma(MSWD=2.7),形成时代为中三叠世,与青海西秦岭地区其他印支中晚期中酸性岩浆岩形成时代相近;锆石εHf(t)值介于-12.35~-1.12之间,二阶段Hf模式年龄(tDM2)介于1.3Ga~2.0Ga之间,加吾金矿区内花岗斑岩的源区主要为早-中元古代地壳。相对较高的εHf(t)值的出现说明形成花岗斑岩脉的岩浆有一定幔源组分的加入。与加吾金矿成矿关系密切的花岗斑岩脉形成于陆-陆碰撞过程中挤压向伸展转换的地球动力学环境。由于俯冲陆壳板片断离,幔源岩浆上涌/底侵至下地壳底部,诱发增厚古老下地壳部分熔融产生壳-幔混合岩浆,在印支中期侵入到中下三叠统隆务河组地层中,为金矿的形成提供了热源和深部成矿流体。加吾金矿床成矿时代与花岗斑岩脉的成岩时间一致,即233.4 Ma±4.3 Ma。  相似文献   

10.
吴祥珂  孟繁聪  许虹  崔美慧 《岩石学报》2011,27(11):3380-3394
青海东昆仑祁漫塔格玛兴大坂岩体岩石类型为二长花岗岩,主要矿物组合为斜长石(30%~35%)+钾长石(25%~33%)+石英(23%~25%)+黑云母(3%~5%),全岩地球化学总体显示SiO2为68.61%~69.37%,K2O为3.95%~4.08%,P2O5为0.11%~0.12%,FeOT/MgO为4.02~4.21,A/CNK(0.96~0.99)<1,为高钾钙碱性系列准铝质花岗岩,具有Ⅰ型花岗岩的特征.其稀土元素配分图和蛛网图显示具有大陆弧花岗岩特点,富集Rb、Th等大离子亲石元素,而相对亏损Sr、P、Ti、Nb和Ta等元素;玛兴大坂二长花岗岩的143Nd/144 Nd比值为0.512326~0.512340、εNd(t)=-2.5~-3.2,指示该花岗岩具有壳幔混合Ⅰ型花岗岩的特征;锆石LA-MC-ICP-MS U-Pb年龄数据显示玛兴大坂二长花岗岩体的侵位时代为218±2Ma;锆石176Hf/177 Hf比值较低(0.28251~0.282623),εHf(t)值为-4.43~-0.62,可能为幔源物质(大的正εHf(t)值)与古老地壳物质(大的负εHf(t)值)混合后的结果.Nd同住素tDM2(1.20~1.25Ga)与Hf同位素tDM2(1.08~1.28Ga)基本一致,推测中元古代末期祁漫塔格地区存在壳幔分异作用,而玛兴大坂二长花岗岩的部分源岩为中元古代以前的物质.认为玛兴大坂二长花岗岩与祁漫塔格晚三叠世火山岩形成时代相近,响应于三叠纪末古特提斯洋的关闭.  相似文献   

11.
On the marine geochemistry of barium   总被引:6,自引:0,他引:6  
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Bismuth has been determined in 74 rocks from a differentiated tholeiitic dolerite, two calc-alkaline batholith suites and in 66 mineral separates from one of the batholiths. Average bismuth contents, weighted for rock type, of the Great Lake (Tasmania) dolerite, the Southern California batholith and the Idaho batholith are, 32, 50 and 70 ppb respectively. All three bodies demonstrate an enrichment of bismuth in residual magmas with magmatic differentiation. Bismuth is greatly enriched (relative to the host rock) in the calcium-rich accessory minerals, apatite and sphene, but other mineral analyses show that a Bi-Ca association is of little significance to the magmatic geochemistry of bismuth. Most of the bismuth, in the Southern California batholith at least, occurs in a trace mineral phase (possibly sulfides) present as inclusions in the rock-forming minerals.  相似文献   

16.
The distribution of manganese in eruptive rocks has been elaborated together with A. Berger (1965). There are systematically higher MnO-values in intrusive rocks than in the corresponding extrusives with the same SiO2-content. Thus, negative values of potential ore metal are characteristic for manganese. Therefore, Mn is strongly concentrated in magmatic residual solutions, contrary to chromium and titanium which have positive values of potential ore metal, and which are concentrated in the very early products of fractional crystallization of basaltic magmas. Under fresh water conditions with low ionconcentrations, small asbolan deposits may be formed on peridotite-serpentinites (New Caledonia Type). Rich ore concentrations may be formed in connection with lateritic weathering, above all on the southern continents (old Gondwana Shield) on the basis of primarily poor protores. Special reaction processes of two groundwater masses may lead to the Lindener Mark Type in the southern part of the Rheinisches Schiefergebirge as well as to the big ore bodies of Postmasburg in South Africa. Under marine conditions with the development of a carbonic-acid-zone, manganese may be dissolved in solutions with much higher pH- and more positive Eh-values. Thus, the separation of Mn and Fe and of both from the main mass of Si-Al-components can take place. Pure manganese ore deposits of the Tschiaturi/Nikopol Type in an expanded Black Sea could thus be built up. On the other side, the volcanic-sedimentary type with shale-chert-spilite-manganese ore formation is strictly bound to residual solutions of basaltic provenance in an eugeosynclinal realm. The different genetic types are schematically demonstrated in Fig. 2. The physicochemical conditions for the separation of Mn and Fe are elucidated in Fig. 9.
Zusammenfassung Auf der Grundlage einer umfassenden Untersuchung von A. Berger (1965) über die Lagerstättenkunde und Geochemie des Mangans werden die natürlichen Prozesse, welche von der geochemischen Verdünnung zu Konzentrationen und Lagerstättenbildungen führen können, kritisch untersucht. Der Vergleich der MnO-Gehalte der verschiedensten Typen von Eruptivgesteinen (von den ultrabasischen bis zu den sauersten) zeigt, daß die Ergußgesteine stets höhere Mangangehalte aufweisen, verglichen mit den Tiefengesteinen gleichen SiO2-Gehalts. Daher ergeben die Differenzen stets positive Werte des potentiellen Lagerstättenmetalls, was gleichzeitig für die starke Anreicherung des Mangans in hydrothermalen Restlösungen charakteristisch ist. Im Mittelpunkt der Gesamtuntersuchung steht das lagerstättenkundlich besonders wichtige Verhalten des Mangans — verglichen mit dem Fe — in kontinentalen Verwitterungslösungen und im marinen Bereich.
  相似文献   

17.
《Applied Geochemistry》2001,16(11-12):1291-1308
Land degradation and pollution caused by population pressure and economic development pose a threat to the sustainability of the earth's surface, especially in tropical regions where a long history of chemical weathering has made the surface environment particularly fragile. Systematic baseline geochemical data provide a means of monitoring the state of the environment and identifying problem areas. Regional surveys have already been carried out in some countries, and with increased national and international funding they can be extended to cover the rest of the land surface of the globe. Preparations have been made, under the auspices of the International Union of Geological Surveys (IUGS) and the International Association of Geochemistry and Cosmochemistry (IAGC) for the establishment of just such an integrated global database.  相似文献   

18.
The geochemistry of strontium   总被引:2,自引:0,他引:2  
The geochemistry of strontium has been investigated, using an emission spectrographic technique checked by isotope dilution analyses described elsewhere ( et al., in press). Hence the determinations are claimed to have good accuracy as well as precision.

Approximately 700 analyses have been made on silicate rocks and over 300 on carbonate materials (a detailed analysis of the latter appearing in other papers). An attempt was made at a representative sampling of the crust of the earth.

The difference in behaviour of strontium relative to calcium in granitic rocks as compared to basaltic rocks is striking. For granitic rocks there is an increase of strontium content with an increase in calcium not only for samples from a single batholith but also when extended to a universal sampling. On the other hand, though some differentiated basaltic bodies show a covariance of strontium and calcium, it is always with the strontium content increasing as the calcium content decreases. On a worldwide basis, however, this relationship is destroyed because marked regional variations subdue any differentiation effects that might be present locally.

The crustal abundance of strontium in basaltic rocks may be estimated without difficulty by taking a simple average, but a similar procedure for granitic rocks is ruled out because of the dependence of strontium content on rock-type. The table below summarizes the abundances of strontium in the various phases of the earth's crust.  相似文献   


19.
Subduction zone geochemistry   总被引:1,自引:0,他引:1  
Crustal recycling at convergent plate boundaries is essential to mantle heterogeneity.However,crustal signatures in the mantle source of basaltic rocks above subduction zones were primarily incorporated in the form of liquid rather than solid phases.The physicochemical property of liquid phases is determined by the dehydration behavior of crustal rocks at the slab-mantle interface in subduction channels.Because of the significant fractionation in incompatible trace elements but the full inheritance in radiogenic isotopes relative to their crustal sources,the production of liquid phases is crucial to the geochemical transfer from the subducting crust into the mantle.In this process,the stability of specific minerals in subducting crustal rocks exerts a primary control on the enrichment of given trace elements in the liquid phases.For this reason,geochemically enriched oceanic basalts can be categorized into two types in terms of their trace element distribution patterns in the primitive mantle-normalized diagram.One is island arc basalts(IAB),showing enrichment in LILE,Pb and LREE but depletion in HFSE such as Nb and Ta relative to HREE,The other is ocean island basalts(OIB),exhibiting enrichment in LILE and LREE,enrichment or non-depletion in HFSE but depletion in Pb relative to HREE.In either types,these basalts show the enhanced enrichment of LILE and LREE with increasing their incompatibility relative to normal mid-ocean ridge basalts(MORB).The thermal regime of subduction zones can be categorized into two stages in both time and space,The first stage is characterized by compressional tectonism at low thermal gradients.As a consequence,metamorphic dehydration of the subducting crust prevails at forearc to subarc depths due to the breakdown of hydrous minerals such as mica and amphibole in the stability field of garnet and rutile,resulting in the liberation of aqueous solutions with the trace element composition that is considerably enriched in LILE,Pb and LREE but depleted in HFSE and HREE relative to normal MORB.This provides the crustal signature for the mantle sources of IAB.The second stage is indicated by extensional tectonism at high thermal gradients,leading to the partial melting of metamorphically dehydrated crustal rocks at subarc to postarc depths.This involves not only the breakdown of hydrous minerals such as amphibole,phengite and allanite in the stability field of garnet but also the dissolution of rutile into hydrous melts.As such,the hydrous melts can acquire the trace element composition that is significantly enriched in LILE,HFSE and LREE but depleted in Pb and HREE relative to normal MORB,providing the crustal signature for the mantle sources of OIB.In either case,these liquid phases would metasomatize the overlying mantle wedge peridotite at different depths,generating ultramafic metasomatites such as serpentinized and chloritized peridotites,and olivine-poor pyroxenites and hornblendites.As a consequence,the crustal signatures are transferred by the liquid phases from the subducting slab into the mantle.  相似文献   

20.
The geochemistry of indium   总被引:1,自引:0,他引:1  
A double-arc spectrochemical procedure was used to analyse numerous minerals and rocks for indium. The method had sensitivity of the order of 0.02 ppm In with precision of ±20%.  相似文献   

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