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桂东南富钾岩浆岩岩的Nd同位素组成：华南中生代地幔物质上涌事件 总被引：16，自引：9，他引：16
广西东南部罗容杂岩体由辉长岩－闪长岩－二长岩－正长岩组成，马山由碱性辉长岩－正长岩－花岗闪长岩－花岗岩组成。它们富K、富大离子亲石元素（LIL），无Nb、Ta负异常等特征表明它们是形成于板内环境的钾玄质侵入岩。罗容杂岩体的各种岩石和马山的基性岩的εNd(T)稍低，为－0．6，此岩石单元是由幔源岩浆加热地壳使之熔融的壳源岩浆形成的，并伴有幔源岩浆的混合或交换。此二杂岩体形成于拉张构造环境。地幔物质上涌导致了中生代华南地壳张裂以及华南大规模花岗岩和相关矿床的形成。 相似文献
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福州复式岩体I-A型复合花岗岩的岩石成因与源区性质目前尚未得到很好认识。本文对福州复式岩体花岗岩进行了岩石学、锆石U-Pb年代学、主量和微量元素地球化学及锆石Hf同位素研究。该复式岩体花岗岩可分为钙碱性和碱性系列。LA-ICP-MS锆石U-Pb定年结果表明,钙碱性系列花岗岩形成年龄为111～101Ma,是早白垩世多期次岩浆活动作用的产物;碱性系列花岗岩形成的年龄为95～93Ma,是晚白垩世岩浆活动的产物。两类岩石均具有Eu负异常、LREE富集和HREE亏损的特征,并且Rb、Th、U、K、Pb等大离子亲石元素相对富集,Ba、Sr以及高场强元素Nb、Ta、P、Ti相对亏损。其中,钙碱性系列花岗岩的轻重稀土分馏程度较之碱性系列花岗岩明显,而碱性系列花岗岩的负铕异常比钙碱性系列花岗岩明显。锆石Hf同位素组成表明,钙碱性系列花岗岩的ε_(Hf)(t)值为-3.9～0.2,地壳模式年龄表明花岗质岩浆源岩来自于新元古代古老地壳的部分熔融,并有少量的地幔组分卷入。碱性系列花岗岩的ε_(Hf)(t)值为0.04～4.8,地壳模式年龄指示花岗质岩浆源岩来自于新元古代古老地壳的部分熔融,并有大量幔源组分的混入。综合分析表明,福州复式岩体I-A型复合花岗岩具有相同的源区,其形成的差异主要是构造环境的变迁、幔源岩浆的加入以及岩浆分异演化等多种因素综合作用的结果。 相似文献
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胶东早白垩世高镁闪长岩类的发现及其构造背景 总被引：3，自引：2，他引：1
胶东地区发育大规模早白垩世壳幔混合源花岗岩类，但一直未发现与花岗岩类相关的独立的幔源侵入体，给深入理解早白垩世壳幔演化带来了困惑。胶东的柳林庄和夏河城岩体以往被认为是三叠纪闪长岩类，本文在详细的野外地质工作基础上，通过年代学、岩石地球化学、同位素地球化学分析，发现这2个岩体为早白垩世高镁闪长岩。样品的SiO2含量在53.29%~62.54%之间，MgO含量为3.60%~8.10%，Mg#主要介于0.47~0.68之间；富集Ba、Rb、K等大离子亲石元素，亏损Nb、Ta、Zr等高场强元素；初始87Sr/86Sr值为0.7082~0.7083，与地幔平均值接近；εNd（t=113Ma）值很低（-20.5~-16.8），与胶东地区的基性脉岩同位素组成一致。2个岩体相比而言，柳林庄岩体富K2O、Fe2O3T，REE、LILE、HFSE含量较高，而MgO、Ni和Cr含量偏低。3件样品的锆石LA-ICP-MS U-Pb同位素加权平均年龄值分别为120.1±1.6Ma、118.3±1.7Ma和122.3±4.0Ma，与壳幔混合源的伟德山型花岗岩及胶东金矿的成岩、成矿时代一致，指示他们形成于统一的地球动力学背景。高镁闪长岩的地球化学特征介于高镁埃达克岩与赞岐岩及埃达克岩与Piip型高镁安山岩之间，指示其形成于古太平洋板块俯冲的地幔楔环境，为富集岩石圈地幔部分熔融的产物。夏河城岩体的岩浆直接来源于含角闪石的富集岩石圈地幔源区，而柳林庄岩体岩浆源区为含金云母的岩石圈地幔并且在岩浆上侵过程中混染了部分地壳物质。 相似文献
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南秦岭地体东江口花岗岩及其基性包体的锆石U-Pb年龄和Hf同位素组成 总被引：12，自引：10，他引：2
东江口花岗岩体位于商丹与勉略缝合带之间的南秦岭中部,其中存在大量基性暗色微粒包体.锆石的LA-MCICPMS联机U-Pb年代学分析表明,东江口岩体的形成年龄为223Ma,其包体锆石的结晶年龄为222Ma,与寄主岩体大致同时形成,指示秦岭造山带印支晚期岩石圈构造体制属性从挤压.伸展转变发生在220Ma左右.锆石的Lu-Hf同位素原位分析结果表明,南秦岭晚三叠纪花岗岩是壳幔混合作用的产物,亏损的幔源岩浆与南秦岭(或扬子)的基底地壳物质可能为南秦岭地区晚三叠纪花岗岩的源区物质,它们的形成起因于秦岭造山带在主造山期后发生的岩石圈拆沉作用.大约220Ma开始,南秦岭岩石圈构造应力性质从挤压向伸展构造体制转变,岩石圈发生拆沉作用,地幔软流圈物质上涌并底侵于下地壳,诱发下地壳物质的部分熔融,当岩浆沿构造薄弱带上升过程中,幔源岩浆与寄主岩浆发生成份的交换,两种岩浆混合过程中不完全混溶,最终形成寄主岩体和暗色基性微粒包体. 相似文献
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位于南祁连化隆地区的鲁满山花岗岩体,岩石类型主体为黑云二长花岗岩。LA-ICP-MS锆石U-Pb定年测得其成岩年龄为(452.9±1.8)Ma,属于加里东期岩浆活动的产物。化学组成上,岩体具有高硅、富碱的特征,属于弱过铝质高钾钙碱性系列。微量和稀土元素组成上,岩体富集大离子亲石元素Rb、U、Th、K和Pb,亏损Ba、Sr、Ta、Nb、P、Ti,具明显轻稀土富集,重稀土亏损特征,显示较强烈的负Eu异常(δEu=0.06~0.55,平均0.31),综合地质地球化学资料指示该岩体应属于高分异的Ⅰ型花岗岩。锆石Hf同位素分析结果显示,岩体的εHf(t)为-7.4~0.1,二阶段模式年龄介于1425~1930 Ma,指示成岩过程中应有亏损地幔组分参与,其壳源源区很可能包括化隆岩群。结合区域构造演化,认为鲁满山花岗岩体形成于柴北缘洋壳与中南祁连陆壳俯冲碰撞的地球动力学背景下,由幔源岩浆与其诱发的地壳物质熔融产生的长英质岩浆在地壳深部混合后再经历分异演化形成。 相似文献
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镁铁-超镁铁质层状杂岩体被认为是岩石圈伸展的重要标志之一,携带有丰富的地幔信息,是研究地幔物质组成、深部地质作用的绝佳对象。西南天山乌什县北巴勒的尔喀克沟地区新发现的镁铁-超镁铁质岩体具有层状杂岩特征,获得辉长岩锆石U-Pb年龄为224±4 Ma,属于晚三叠世。岩石地球化学分析显示富水、富碱、轻稀土富集、重稀土亏损以及明显富集Th、U、Nb、Ta、La、Ce不相容元素等特征,指示其源自于含水的富集型地幔源区,是石榴石二辉橄榄岩较低程度部分熔融的产物。其原生岩浆可能为富铁、钛的高镁玄武质岩浆,岩石系列主要受分离结晶作用控制,同化混染作用影响小。该期岩浆活动于南天山洋盆闭合、板块的碰撞造山活动之后的陆内造山阶段,代表了板块拉伸背景下幔源岩浆演化的产物,指示西南天山地区在三叠纪末可能存在一期岩石圈伸展事件。 相似文献
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湘东北中生代基性岩脉微量元素地球化学特征及岩石成因 总被引：7，自引：0，他引：7
湘东北中生代基性岩脉可以分为煌斑岩和辉绿岩两类，前者形成于136.61Ma，后者形成于86.18Ma,与华南中生代主要拉张时期相对应。岩石富集LREE，Eu负异常不明显，其形成主要受地幔部分熔融作用制约。早期煌斑岩类微量元素和Sr、Nd同位素总体上具有富集地幔（EMⅡ型）洋岛玄武岩（OIB）特征，富集Nd、P、Cs，而K、Rb、Sr、U、Th等富集程度不明显，Ta、Nb略有富集，具有软流圈地幔上涌地幔热柱玄武岩岩浆源区性质，表现出软流圈地幔上涌部分熔融的成岩特点。晚期辉绿岩类表现出Ta、Nb、Ti亏损，但LILE并不富集，反映地壳混染程度的增强，具有大陆拉张带（裂谷初期）形成的玄武岩岩浆源区性质，为岩石圈地幔部分熔融形成。二者具有不同的岩浆源区性质，从早期到晚期岩浆源区向上迁移并致使部分陆 物质混入，反映由热点式拉张到岩石圈伸展－减薄的作用过程。 相似文献
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冈底斯东段古新世朱拉岩体LA-ICP-MS锆石U-Pb定年和岩石地球化学特征 总被引：1，自引：0，他引：1
朱拉岩体位于冈底斯带东部,主要由黑云母二长花岗岩组成,其中发育闪长质包体,二者呈渐变过渡关系。3件寄主岩石LA-ICP-MS锆石U-Pb年龄加权平均值分别为64.6Ma±0.8Ma、64.3Ma±0.8Ma和63.9Ma±0.5Ma,含776Ma的继承岩浆锆石。1件闪长质包体样品年龄加权平均值为66.1Ma±0.3Ma。闪长质包体低Si,中Mg(Mg﹟平均41.1),属铝质高钾钙碱性系列,Nb/Ta值为22,Sr/Y值为3.69,稀土元素分馏较低,LREE/HREE平均值为1.92,Eu强烈亏损,富集大离子亲石元素(Rb、K、U、Th),亏损高场强元素(Nb、Ta、Sr、Ti),暗示岩浆成分主要为幔源。寄主岩石富Si、K,贫P,属铝质—偏铝质钙碱性—高钾钙碱性系列,Nb/Ta值15.9,富集大离子亲石元素(Rb、K、Th),亏损高场强元素(Nb、Ta、Ba、P、Ti),具有活动陆缘钙碱性岩系的微量元素分布特征。寄主岩石与闪长质包体具有密切的成生联系,闪长岩形成于富集俯冲带组分的地幔熔体,在上升过程中混染了一定量的壳源物质结晶分异产物,寄主岩石则为底侵作用产生的大量壳源熔体与少量幔源熔体混合并发生一定程度分离结晶后的产物。结合前人的研究成果,认为古新世朱拉岩体与雅鲁藏布江大洋的向北消减有关。 相似文献
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东天山黄山-镜儿泉过铝花岗岩矿物学、地球化学及年代学研究 总被引：3，自引：0，他引：3
对东天山黄山-镜儿泉一带黄山南、镜儿泉、图拉尔根沟三个过铝花岗岩作了岩相学、矿物学、地球化学、sr-Nd同位素和锆石U-Pb年代学研究.锆石U-Pb LA-ICP-MS原位定年测得黄山南岩体结晶年龄为259.9±1.4Ma(MSWD=0.86),图拉尔根沟岩体结晶年龄为275.4±8.3Ma(MSWD=29),均侵位于二叠纪碰撞后伸展环境.三个过铝花岗岩均具有低锶同位素初始比值(Isr=0.6969～0.70396)、高εNd(t)值( 5.5～ 7.2)以及年轻的亏损地幔单阶段模式年龄(tDM=0.48～0.56Ga),表明其岩浆源区均为来源于亏损地幔的新生地壳岩石.这种新生地壳岩石可能为偏酸性的火山岩.三个岩体的矿物学和地球化学可分为两类:一类以黄山南白云母花岗岩为代表,为强过铝花岗岩(A/CNK>1.1),强烈亏损Ba、sr和Ti而富集Cs、Rb和K,具有高的Rb/sr(2.03～14.5)和Al2O3/TiO2(110～1592),低的Nb/Ta(3.24～6.76)比值,其稀土元素配分曲线呈"V"字形,显示强烈铕亏损(Eu/Eu*=0.04～0.55),表明这类岩体的直接源岩以泥质岩为主.另一类以图拉尔根沟二云母花岗岩为代表,为弱过铝(1相似文献
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内蒙古西乌旗地区出露一些石英闪长岩,其LA-ICP-MS锆石U-Pb年龄为(304.64±0.82)Ma和(309.84±0.86)Ma,表明这套岩石形成于晚石炭世。地球化学分析表明,西乌旗地区石英闪长岩属于低Ti O2和高Al2O3钙碱性玄武岩系列;富集Rb、Ba、K大离子亲石元素(LILE),亏损Nb、Ta、Ti、P等高场强元素(HFSE),具有典型弧岩浆岩的特征,显示岩浆源区曾经历过俯冲带流体的交代作用;稀土元素丰度偏低,呈LREE富集HREE亏损的右倾模式;强不相容元素比值(La/Nb、La/Ta等)及判别图解表明晚石炭世石英闪长岩类似大陆边缘弧玄武岩,岩浆来源于浅部岩石圈地幔,系石榴石+尖晶石二辉橄榄岩源区中等程度(10%~20%)部分熔融的结果。综合研究区样品的地球化学特征,结合区域地质资料及对比分析前人成果,认为早石炭世末期西乌旗地区在强烈拉张的裂谷环境下形成了有限洋盆,由于洋盆发育不成熟或边伸展边向两侧俯冲—消减,形成了西乌旗地区类似大陆边缘弧玄武岩特征的晚石炭世石英闪长岩。 相似文献
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为精确厘定桂中地区都安-马山带煌斑岩的形成时代并探讨其源区属性、构造环境及其动力学背景,对其进行了LA-ICP-MS锆石U-Pb定年、40Ar-39Ar金云母定年、Hf同位素分析测试和全岩地球化学研究.结果表明,锆石U-Pb定年未能成功限定煌斑岩的成岩年龄,但煌斑岩中发育大量2 578~1 650 Ma的捕获锆石,指示其存在太古宙-古元古代变质基底.金云母40Ar-39Ar定年结果限定了煌斑岩的侵位年龄为100.4±0.99 Ma.Hf同位素研究表明,εHf（t）有正有负,且正值多于负值,表明岩浆源区主要以新生地壳为主,存在部分古老地壳的再循环.全岩地球化学分析显示,煌斑岩具有较低的SiO2含量（47.66%~50.93%）及高的K2O含量（4.98%~6.77%）、富集LILE和LREE而亏损HFSE（如Nb、Ta和Ti）,表现出富集地幔和俯冲流体交代作用的特征.桂中煌斑岩形成过程中,地壳混染作用十分有限,主要形成过程为:流体交代的富集地幔,在燕山晚期岩石圈的拉张-伸展背景下,部分熔融形成煌斑岩岩浆,同时NNW向的南丹-昆仑关大断裂为岩浆的侵位提供了通道.研究区煌斑岩形成于太平洋和印度板块向欧亚板块俯冲碰撞的动力学背景下. 相似文献
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The 1300 Ma Fraser Complex in the Albany‐Fraser Orogen of Western Australia is a thrust stack of mainly gabbroic rocks metamorphosed to granulite facies. This package of fault‐bounded units was elevated from a deep crustal level onto the margin of the Yilgarn Craton during continental collision between the Mawson and Yilgarn Cratons. Incompatible trace‐element distributions demand at least three mantle sources. Primitive‐mantle‐normalised incompatible‐element distributions show strong negative Ta–Nb anomalies, typical of subduction‐derived magmas. Three lines of evidence indicate that the mafic magmas did not acquire these anomalies by assimilation of crustal rocks: (i) major‐element compositions do not allow appreciable contamination with felsic material; (ii) Ni contents of many mafic rocks are too high for a significant contribution from a felsic assimilant; and (iii) Sr and Nd isotopic data support a largely juvenile source for the magmas that produced the Fraser Complex. Hence, the Ta–Nb anomalies are interpreted to reflect subduction‐related magmatic sources. On multielement diagrams, depletions in Sr, Eu, P, and Ti can be explained by fractional crystallisation, whereas Th and Rb depletions in many of the Fraser Complex rocks probably reflect losses during granulite‐facies metamorphism. These results suggest that the lower crust in this region at 1300 Ma was dominantly of arc origin, and there is no evidence to support mantle plume components. The Fraser Complex is interpreted as remnants of oceanic arcs that were swept together and tectonically interleaved with the margin of the Mawson Craton just before, or during, collision with the Yilgarn Craton at 1300 Ma. 相似文献
14.
在华南东部浙闽沿海一带普遍发育有大量晚中生代花岗质岩体及其中的暗色包体,这些岩体被认为是大规模壳幔相互作用和岩浆混合作用的产物。本文对浙东天台地区白鹤岩体中的寄主花岗岩及其中发育的暗色包体分别进行了LA-ICP-MS锆石U-Pb定年和详细的岩石地球化学研究,其锆石U-Pb年龄分别为(120.4±1.2)Ma和(120.6±1.1)Ma,属浙东燕山期侵入活动集中的早白垩世中晚期产物。岩石地球化学特征显示,寄主花岗岩为高硅、富碱、弱过铝质的高钾钙碱性花岗岩,具有较强的Eu负异常,富集Rb、Th、U、K,并有Sr、Ba、P、Ti、Nb、Ta等元素的亏损,岩石成因为高分异I型花岗岩;暗色包体多为低硅、富钠、偏铝质低钾拉斑玄武系列岩石,轻稀土富集、重稀土亏损,并具有弱的Eu正异常。锆石Hf同位素组成表现出不同物质来源(壳幔混源)花岗岩类岩石的特点。综合年代学及岩石地球化学特征,认为浙东地区早白垩世I型花岗岩及其暗色包体是在燕山期弧后碰撞伸展引张的构造背景下,由底侵的幔源岩浆与其诱发熔融的深部壳源岩浆经混合后,经过一定程度的分异演化,最后定位于浅成环境的产物。 相似文献
15.
吉南天桥地区基性岩墙与其围岩TTG片麻岩的成因及构造意义 总被引：2，自引：2，他引：0
吉南地区太古宙基底中发育大量早前寒武纪基性岩墙群,是陆壳伸展的直接证据。对白山市东部天桥太古宙基底出露区内基性岩墙及其围岩进行了锆石U-Pb定年和地球化学分析,以确定该期伸展事件的形成机制及地质意义。天桥地区基性岩墙岩性为斜长角闪岩,侵位于TTG片麻岩中。英云闪长质片麻岩(TN1)中锆石具核-边结构,岩浆核的LA-ICP-MS测年结果为2500±6Ma,指示其形成于新太古代末期。天桥岩墙(TN3)中的锆石内部结构与TN1相同,酸性岩浆核的SHRIMP测年结果为2490±17Ma,与TN1在误差范围内一致,表明这些锆石不是基性岩墙原生锆石,而是岩墙侵位过程中在围岩中捕获的锆石,但根据岩墙仅侵位在太古宙基底中且变质程度高于周围古元古界老岭群,将其侵位年龄大致限制在新太古代末期-古元古代早期。地球化学特征显示,基性岩墙具有低SiO_2、Na_2O、K_2O含量,高CaO、MgO含量,A/CNK=0.56～0.59,属于准铝质的拉斑玄武岩系列岩石,∑REE低、配分曲线平坦,富集LILE(Rb、Ba和K),亏损HFSE(Th、U、Nb和Ta),具有与原始地幔相同的Nb/Ta、Zr/Hf比值及接近地壳的Nb/U、Ta/U比值,指示其岩浆可能来源于地幔且在上升过程中受到地壳混染,形成于板内伸展环境。TTG片麻岩具有中等的SiO_2和MgO含量,高Al_2O_3和Na_2O含量以及低CaO含量,A/CNK=1.00～1.14,属弱过铝质的钙碱性系列岩石,∑REE低、具有右倾的REE配分曲线,轻稀土富集、重稀土亏损,富集LILE(Rb、Ba、K和Sr),强烈亏损HFSE(U、Nb、Ta、Sm和Ti),其岩浆可能来源于变质玄武质岩石和极少量沉积岩的部分熔融,结合邻区TTG的研究成果,认为其形成于与俯冲相关的活动大陆边缘环境。前人研究表明,新太古代晚期板块构造体制可能已经启动,结合我们以往研究,认为新太古代晚期华北克拉通东北部可能发生了弧陆碰撞造山运动,天桥岩墙的侵位标志着新太古代末期至古元古代早期之间华北克拉通东北部进入造山后伸展环境,可能是对新太古代造山运动结束的响应。 相似文献
16.
Yuanyuan Zhang Jaroslav Dostal Zehui Zhao Chang Liu Zhaojie Guo 《Gondwana Research》2011,20(4):816-830
The Liuyuan mafic and ultramafic rocks are exposed in Southern Beishan, which is along the southern branch of the Central Asian Orogenic Belt (CAOB). Zircon SHRIMP U–Pb dating showed that Liuyuan gabbros intruded during the early Permian (~ 270–295 Ma) coeval with the basalts and the ultramafic rocks were emplaced at about 250 Ma. The basalts are within–plate tholeiites with slight enrichment in light rare earth elements (LREE) relative to heavy rare earths (HREE) and small negative anomalies of Nb and Ta. Gabbros including olivine gabbros, olivine gabbronorites and troctolites are grouped into two: the cumulate gabbros are depleted in LREE and show small negative Nb and Ta anomalies but distinct positive Sr and Eu anomalies; non–cumulate gabbros resemble tholeiitic basalts. Lamprophyres and cumulate ultramafic rocks are characterized by large enrichment of LREE relative to HREE with depletion in Nb and Ta. The enriched Sr–Nd isotopic trend from DM towards the EM II end member component implies that the lithospheric mantle was progressively enriched with depth by the involvement of subducted crustal material due to the delamination of thickened mantle lithosphere after collision. The digestion of subducted crustal material into the mantle resulting in the metasomatized and enriched mantle is inferred to be an important process during crust–mantle interaction. 相似文献
17.
Geochemistry of the Emeishan flood basalts at Yangliuping, Sichuan, SW China: implications for sulfide segregation 总被引：10，自引：0，他引：10
Xie-Yan Song Mei-Fu Zhou Reid R. Keays Zhi-Min Cao Min Sun Liang Qi 《Contributions to Mineralogy and Petrology》2006,152(1):53-74
A well-developed, 1,000 m thick basaltic sequence in the Yangliuping region, northern part of the Emeishan basalt province, includes the Lower and Middle Units of tholeiitic basalts and an Upper Unit of both tholeiites and subalkalic basalts. The basalts contain 42–55 wt% SiO2 and 4.1–8.3 wt% MgO. Most of these lavas have Gd/Yb > 2.0, Zr/Nb < 12, and ɛNd(260 Ma) values from +2.5 to +4.7. The platinum-group elements (PGE) are very mildly depleted in most of the basalts which contain 8–19 ppb Pt and 7–27 ppb Pd. However, a significant proportion of the Middle Unit basalts are strongly depleted in PGE with some samples having concentrations lower than detection limits. They have extremely high Zr/Nb ratios (up to 14.5) and low ɛNd(260 Ma) values (+3.21 to +0.65), features of extensive lower crustal contamination. Some samples in this unit have high Ni/Pd (3,965–61,198) and low Pd/Cr (410,000–3,930,000) ratios, indicating sulfide segregation and PGE depletion prior to eruption. The primary magmas were S-undersaturated and derived from partial melting at variable depths in the upper mantle. The early and late stage magmas, as represented by the Lower and Upper Units, underwent AFC processes which induced mild S-saturation and PGE depletion in some of the basalts, whereas the magmas represented by the Middle Unit experienced more extensive crustal contamination resulting in stronger S-saturation and in most cases significant PGE depletion. 相似文献
18.
Origin and Source Evolution of the Leucite Hills Lamproites: Evidence from Sr-Nd-Pb-O Isotopic Compositions 总被引：2，自引：0，他引：2
Whole-rock major and trace element and O, Sr, Nd and Pb isotopicdata are reported for 3·0–0·89 Ma lamproitesfrom the Leucite Hills, Wyoming, USA. The two main groups oflamproites, madupitic lamproites and phlogopite lamproites,are geochemically distinct and cannot be related to one anotherby either fractional crystallization or crustal contamination.It seems likely that the geochemical differences between thesetwo rock types are related to variations in source mineralogyand depth of partial melting. The high Mg-number and large ionlithophile element abundances and negative Nd values of thelamproites indicate a mantle source that has experienced stagesof both depletion and enrichment. The negative Nb, Ta and Tianomalies in mantle-normalized trace element diagrams and lowtime-integrated U/Pb, Rb/Sr and Sm/Nd ratios of both lamproitegroups and other Cenozoic igneous rocks from the Wyoming ArcheanProvince indicate an ancient metasomatic enrichment (>1·0Ga) of the mantle source associated with the subduction of carbonate-bearingsediments. Other chemical characteristics of the Leucite Hillslamproites, especially their high K2O and volatile contents,are attributed to more recent metasomatism (<100 Ma) involvinginflux from upwelling mantle during back-arc extension or plumeactivity. KEY WORDS: isotopes; lamproites; metasomatism; Leucite Hills; Wyoming 相似文献
19.
The origin of the Cretaceous gabbros in the Fujian coastal region of SE China: implications for deformation-accompanied magmatism 总被引：2，自引：0，他引：2
Zhihong Wang 《Contributions to Mineralogy and Petrology》2002,144(2):230-240
The Cretaceous gabbros in the Fujian coastal region, southeastern China, experienced different magmatic and tectonic processes associated with deformation of the Changle-Nanao shear zone. Group 1 gabbros (115 Ma) show marked LILE (e.g., Sr, Ba and K) and LREE enrichment, and HFSE (e.g., Ta, Nb, Zr and Hf) depletion, strongly suggesting an island-arc affinity. The parental magma of group 1 gabbros, arguably derived from an arc-related source mantle modified by previous subduction, rose into and interacted with the coexisting syntectonic granitic magma generated during the main stage of shear zone deformation, and produced the gabbro-diorite-granite complexes. Group 2 and 3 gabbros (106-95 Ma) possibly formed by coupling of the subduction-modified source mantle with part of undepleted mantle (e.g., Nb enrichment) in an extensional environment at the end of deformation. Their parental magmas did not undergo significant magma mixing but produced a cumulate nature. All the three groups of gabbros were contaminated by crustal material during the processes of intrusion and emplacement. 相似文献
20.
Geochemistry, Nd Isotopic Characteristics of Metamorphic Complexes in Northern Hebei： Implications for Crustal Accretion 总被引：4，自引：0，他引：4
K. H. PARK 《《地质学报》英文版》2006,80(6):807-818
The middle segment of the northern margin of the North China Craton （NCC） consists mainly of metamorphosed Archean Dantazi Complex, Paleoproterozoic Hongqiyingzi Complex and unmetamorphosed gabbro-anorthosite-meta-alkaline granite, as well as metamorphosed Late Paleozoic mafic to granitoid rocks in the Damiao-Changshaoying area. The -2.49 Ga Dantazi Complex comprises dioritic-trondhjemitic-granodoritic-monzogranitic gneisses metamorphosed in amphibolite to granulite facies. Petrochemical characteristics reveal that most of the rocks belong to a medium- to high-potassium calc-alkaline series, and display Mg^# less than 40, right-declined REE patterns with no to obviously positive Eu anomalies, evidently negative Th, Nb, Ta and Ti anomalies in primitive mantlenormalized spider diagrams, εNd（t）=＋0.65 to -0.03, and depleted mantle model ages TDM=2.78-2.71 Ga. Study in petrogenesis indicates that the rocks were formed from magmatic mixing between mafic magma from the depleted mantle and granitoid magma from partial melting of recycled crustal mafic rocks in a continental margin setting. The 2.44-2.41 Ga Hongqiyingzi Complex is dominated by metamorphic mafic-granodioritic-monzogranitic gneisses, displaying similar petrochemical features to the Dantazi Complex, namely medium to high potassium calc-alkaline series, and the mafic rocks show evident change in LILEs, negative Th, Nb, Ta, Zr anomalies and positive P anomalies. And the other granitiod samples also exhibit negative Th, Nb, Ta, P and Ti anomalies. All rocks in the Hongqiyingzi Complex show right-declined REE patterns without Eu anomaly. The metamorphic mafic rocks with εNd（t） = -1.64 may not be an identical magmatic evolution series with granitoids that have εNd（t） values of ＋3.19 to ＋1.94 and TDM ages of 2.55-2.52 Ga. These granitic rocks originated from hybrid between mafic magma from the depleted mantle and magma from partial melting of juvenile crustal mafic rocks in an island arc setting. All the -311 Ma Late Paleozoic metamorphic mafic rocks and related granitic rocks show a medium-potassium calc-alkaline magmatic evolution series, characterized by high Mg^#, obviously negative Th, Nb, Ta anomalies and positive Sr anomalies, from no to strongly negative Ti anomalies and flat REE patterns with εNd（t） = ＋8.42, implying that the maflc magma was derived from the depleted mantle. However the other granitic rocks are characterized by right-declined REE patterns with no to evidently positive Eu anomalies, significantly low εNd（t） = -13.37 to -14.04, and TDM=1.97-1.96 Ga, revealing that the granitoid magma was derived from hybrid between maflc magma that came from -311 Ma depleted mantle and granitoid magma from Archean to Early Paleoproterozoic ancient crustal recycling. The geochemistry and Nd isotopic characteristics as well as the above geological and geochronological results indicate that the middle segment of the northern margin of the NCC mainly experienced four crustal growth episodes from Archean to Late Paleozoic, which were dominated by three continental marginal arc accretions （-2.49, -2.44 and 311 Ma）, except the 1.76-1.68 Ga episode related to post-collisional extension, revealing that the crustal accretion of this segment was chiefly generated from arc accretion and amalgamation to the NCC continental block. 相似文献