首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 156 毫秒
1.
薛家石梁-黑山寨岩浆杂岩体出露于北京市昌平区东部,由上庄辉长岩、薛家石梁闪长岩、黑山寨石英二长岩、湖门二长岩和黑熊山花岗岩组成。结合薛家石梁-黑山寨杂岩体的地质产状、各类岩性的空间分布和接触关系以及侵位深度的估算结果,我们认为该杂岩体是一个被剥露出来的掀斜岩浆房。根据岩石学特征和地球化学分析结果,可将杂岩体的岩石归为5大类:(1)堆晶成因的含钒钛磁铁矿辉长岩;(2)低Ti辉长岩;(3)高Ti闪长岩;(4)高Sr低Y中酸性岩(低Ti闪长岩、二长岩、石英二长岩)和(5)黑熊山铁质花岗岩。其岩浆活动分为3批次:第1批次的原始幔源岩浆经AFC过程演化形成该杂岩体所包含的堆晶辉长岩、低Ti辉长岩、低Ti闪长岩、石英二长岩和二长岩;在岩浆房未固结时第2批次的高Ti闪长岩浆注入其中;然后是第3批次的壳源铁质花岗岩浆注入岩浆房上部。岩浆固结后该岩浆房经历了大角度掀斜,是云蒙山变质核杂岩下盘在拆离运动过程中发生背形穹弯变形的结果。该杂岩体所含的高Ti闪长岩的地球化学和Sr-Nd-Pb同位素特征指示当时存在亏损放射性Pb同位素的岩石圈地幔,不支持岩石圈拆沉的动力学模式。薛家石梁-黑山寨杂岩体是燕山造山带挤压变形导致的地壳增厚和增温所引起的重力崩塌过程的岩浆事件响应。  相似文献   

2.
云南个旧碱性杂岩体由边缘相碱长正长岩和中心相霞石正长岩组成。全岩地球化学分析表明,该碱性杂岩体具有高碱、富钾、富铁、低镁、高分异的碱性-过碱性岩石特征,晚期更富集碱金属元素; LREE/HREE值为20~59,(La/Sm)N=8~50,(Sm/Yb)N=1.2~5.0,富集轻稀土元素,轻稀土元素较重稀土元素分馏程度高,具Eu负异常,亏损Ti、Nb、P、K、Sr等元素,富集Zr、Hf、Th、La、Ce、Nd、U、Rb等元素,岩浆来源与幔源物质有关;碱长正长岩和霞石正长岩具有相似的微量元素和稀土元素特征,具有同源岩浆分异演化的特点; Rb/Sr、Nb/Ta、Zr/Hf等比值均高于或接近于原始地幔的相应值; CIPW标准矿物计算结果表明边缘相碱长正长岩中出现紫苏辉石、锥辉石、橄榄石,中心相霞石正长岩中出现橄榄石。结合(Th/Nb)N和Nb/La值特征以及前人Sr-Nd同位素研究成果,认为个旧碱性杂岩体的岩浆来源于遭受交代作用的富集地幔部分熔融,同时受有限的地壳混染作用而成,形成于后碰撞的伸展环境。碱性岩浆演化晚期更加富碱、经历了更高程度的结晶分异作用是稀土元素、Nb、Ga和Zr元素超常富集的重要原因。  相似文献   

3.
太行山南段中生代杂岩体成因及其演化分析   总被引:1,自引:0,他引:1  
平顺-符山-武安-洪山杂岩体主要由橄榄辉长辉绿岩、角闪闪长岩,经闪长岩、二长闪长岩、正长岩、花岗岩一系列岩石组成,其地球化学性质相似,CaO、FeO、MgO和TiO与SiO2呈线性正相关,富集大离子亲石元素(如Sr、Ba、K)和LREE,亏损高场强元素(如Nb、Ta、Ti)和HREE,具有微弱的正Eu异常。符山杂岩体的εNd=-12.3~-16.9,ISr=0.705 6~0.707 1,武安杂岩体εNd=-13.8~-18,ISr=0.705 9~0.707 6,相比之下,洪山杂岩体具有比符山-武安杂岩体明显高但相对均一的εNd值(-8.2~-11)和变化较大的ISr(0.705 2~0.710 2)。平顺杂岩体Pb同位素比值较高,(206Pb/204Pb)i=17.859~18.474,(207Pb/204Pb)i=15.429~15.612,(208 Pb/204 Pb)i=37.374~38.641。而符山杂岩体(16.92~17.3,15.32~15.42,37.16~37.63)、武安岩体(16.63~17.4,15.28~15.44,36.78~37.3)和洪山杂岩体(17.28~17.74,15.40~15.48,37.01~38.12)变化连续。平顺-符山-武安杂岩体可能是同一期岩浆演化的产物,起源于EMI型富集地幔的部分熔融,但在上升过程中受到不同程度的下地壳物质混染。洪山岩体也来源于EMI型富集地幔的部分熔融,但属于不同岩浆热事件,仅受轻微下地壳混染。太行山南段中生代广泛的岩浆活动可能与邯邢地幔柱上涌有关。  相似文献   

4.
赵磊  吴泰然  罗红玲 《岩石学报》2011,27(10):3071-3082
内蒙古乌拉特中旗温更地区北七哥陶辉长岩岩体由橄榄辉长岩和角闪辉长岩组成,主要造岩矿物为橄榄石、辉石、斜长石及角闪石等.锆石SHRIMP U-Pb同位素定年结果表明,橄榄辉长岩形成于269±8Ma,为晚古生代华北板块北缘岩浆活动的产物.橄榄辉长岩和角闪辉长岩具有相似的稀土元素、微量元素以及同位素特征,即:轻稀土元素( LREE)富集的右倾平滑配分模式;大离子亲石元素(LILE)K、Sr、Ba明显富集,高场强元素(HFSE) Nb、Ta、U、Th相对亏损,但Zr-Hf不亏损;87Sr/86Sr(t)平均值分别为0.706776和0.706960,εNd(t)平均值分别为-8.8和-8.9,206pb/204Pb、207pb/204Pb、208Pb/204Pb比值的平均值分别为17.2019和17.2277、15.4252和15.4524、37.3082和37.4724,在s7 Sr/86Sr(t)-143Nd/144 Nd (t)图解上,北七哥陶辉长岩都落在了EMI型富集地幔附近.根据以上事实,结合区域资料表明,橄榄辉长岩和角闪辉长岩产于后碰撞的构造环境,并且来自相同的岩浆源区,主要继承了华北陆块内部EMI型富集地幔,可能受到了古亚洲洋俯冲消减过程中再循环下地壳组分对岩石圈地幔的改造.  相似文献   

5.
西天山哈拉达拉镁铁-超镁铁杂岩为一CuNi-VTiFe复合型矿化岩体,主要由橄长岩、橄榄辉长岩、角闪辉长岩、辉长岩和辉绿岩组成。获得岩体中橄榄辉长岩SHRIMP锆石U-Pb年龄为308.8±1.9Ma,辉长岩SHRIMP锆石U-Pb年龄307.3±8.2Ma。岩石具堆晶结构、辉长-辉绿结构,岩体韵律层发育;各类岩石稀土和微量元素配分曲线模式相似,多具Eu,Sr正异常,它们可能为同一岩浆结晶分异演化的产物;Sr-Nd同位素特征(87Sr/86Sr初始比值=0.703913~0.705259,εNd(t)=4.00~8.42)表明原始岩浆来自于亏损地幔源区。推测哈拉达拉岩体形成于后碰撞造山早期伸展环境、叠加近同期地幔柱活动的特殊地质背景中。  相似文献   

6.
陈立辉  韩宝福 《岩石学报》2006,22(5):1201-1214
阿尔泰造山带东段的乌恰沟地区发育大量镁铁质侵入岩(岩脉或小岩体),包括闪长玢岩和具堆积结构的角闪辉长岩和橄榄辉长岩。锆石SHRIMP U-Ph同位素定年结果说明这些镁铁质岩浆的侵位时间为257.4±5.3Ma,与峨眉山玄武岩相近(259±3Ma)。在微量元素原始地幔标准化图上,它们共同的特征是富集大离子亲石元素,亏损Nb和Ta,具K和Pb的正异常,LREE相对HREE富集,即具弧火山岩的地球化学特征。同时它们之间还存在互补的地球化学特征,如闪长玢岩存在Ba、Sr、Eu、P和Ti的负异常,橄榄辉长岩具有Ba、Sr、Eu、P的正异常,而角闪辉长岩具有Ti的正异常。如果扣除围岩混染和后期流体交代的影响,这些岩石的Sr-Nd-Pb同位素组成基本一致,因此闪长玢岩和两种辉长岩分别代表同源岩浆因结晶分离作用形成的演化岩浆和堆晶岩。乌恰沟晚二叠世镁铁质侵入岩和新疆北部早二叠世与铜镍矿有关的基性-超基性杂岩体都具有与弧火山岩相似的地球化学特征,反映了被俯冲改造的陆下岩石圈地幔的地球化学特征。但是与后者相比,前者的Mg~#值、ε_(Nd)(t)值和La/Nb比明显偏低,暗示存在软流圈地幔来源物质的显著贡献。综合阿尔泰乌恰沟地区镁铁质侵入岩的年代学、地球化学和同位素组成特征,我们推测该区在晚二叠世存在地幔柱与岩石圈地幔之间的相互作用。  相似文献   

7.
侯建光  苏尚国  周岱  王倩 《岩石学报》2014,30(12):3729-3740
内蒙古温根南岩体位于内蒙古中部,属于华北克拉通北缘中段,主要火成岩组合为纯橄岩-橄长岩-辉长岩,平面上呈NNE向延伸。元素地球化学分析结果显示,岩体富Mg、低碱和Ti O2,全岩氧化物含量主要受控于橄榄石、单斜辉石和斜长石的相对分配比例,微量元素含量总体较低,具Nb、Ta和Hf轻微亏损,Pb、Sr显著富集的特征。其中辉长岩表现出显著的Nb、Ta负异常和Pb、Sr正异常。辉长岩微量元素相对纯橄岩和橄长岩明显富集。辉长岩相-纯橄岩相中总稀土含量变化较大(1.41×10-6~111.6×10-6),稀土元素配分曲线表现为轻微右倾型与平坦型,岩体深部超基性岩类总稀土含量极低,随着其结晶分异程度的增大和堆晶作用的加强,岩石中稀土元素含量迅速升高,反映晶间残余熔体的比重不断升高。运用橄榄石与残余熔浆平衡方法制约母岩浆性质,结果表明温根南岩体初始岩浆MgO=11.73%,FeO=11.38%,属于高镁玄武质岩浆。温根南岩体基性-超基性岩中Sr-Nd同位素投点主要靠近EM I型富集地幔端元,推测幔源岩浆在源区或上升过程中受到了地壳物质的混染。运用Zr、Y、Th、Ta等不相容元素的比值(判别岩浆演化过程,基于Th/Nb比值(1)和低Nb/La比值(1)表明温根南岩体初始岩浆侵位过程中遭受到了地壳物质的混染。温根南岩体Ta/Th-Zr/Nb、Th/Yb-Th/Nb、Ta/Th-Th/Yb、Nb/Th-Nb构造环境判别图中主要落入板内玄武岩(WPB)范围,推测温根南基性-超基性岩体在早石炭纪形成于板内伸展构造环境。  相似文献   

8.
卓潘碱性杂岩体为"三江"地区富碱(高钾)侵入岩的重要组成部分,位于哀牢山-金沙江缝合带的中部,侵位于兰坪盆地南部的白垩系砂岩中,主要由碱性辉长岩、辉石正长岩和霞石正长岩组成。对卓潘碱性杂岩体的岩相学、岩石学、主元素和稀土微量及同位素地球化学特征的系统研究表明,该杂岩体主量元素显示低硅、富钾、高碱(K2O+Na2O为6.92%~13.43%)、低TiO 2(0.31%~1.20%)的特征,属钾质碱性系列岩石;杂岩体的各种岩石均富集Rb、Sr、Ba、Th等大离子亲石元素、亏损Nb、Ta、Ti等高场强元素,并具有轻稀土富集的右倾型稀土元素分布模式、具较高的87Sr/86Sr、206Pb/204Pb、207Pb/204Pb、208Pb/204Pb及较低的143Nd/144Nd等特征,表明源区具有较明显的EMⅡ型富集地幔特征,源区明显受到壳源物质的混染。卓潘岩体形成于印度-欧亚大陆后碰撞的剪切和拉张的构造环境,古扬子板片向西俯冲,诱发了经过陆壳交代混染了的岩石圈地幔的部分熔融。由于兰坪走滑拉分盆地东缘断裂拉伸强度大,岩浆起源的深度大,以及岩浆源区成分(特别是CO2含量)与其它部位不同,因此在卓潘地区形成一套与金沙江-哀牢山-红河断裂带其它新生代富碱斑岩完全不同的过碱性的岩石。  相似文献   

9.
西南天山哈拉达拉岩体的锆石SHRIMP年代学及地球化学研究   总被引:15,自引:6,他引:9  
薛云兴  朱永峰 《岩石学报》2009,25(6):1353-1363
西南天山哈拉达拉侵入体由橄长岩、橄榄辉长岩和辉长岩组成,橄长岩和橄榄辉长岩具有典型的堆晶结构,堆晶矿物以斜长石和橄榄石为主。辉石、角闪石和金云母主要为堆晶间隙矿物。辉长岩发育辉长—辉绿结构。结晶分异作用在岩浆演化过程中起重要作用。对从辉长岩中分选出来的锆石进行的SHRIMP年代学研究表明,辉长岩形成于308.3±1.8Ma (MSWD=0.86,n=15)。哈拉达拉岩体稀土元素配分模式与E-MORB相似,具有高Rb、Cs、Ba及Sr的特点,87Sr/86Sr初始比值0.7040~0.7050。这些特征表明,岩浆源区具有富集地幔的特征(古南天山洋俯冲流体交代形成了富集地幔)。根据平坦的稀土元素配分模式以及Gd、Sm、Nb、Zr等微量元素的地球化学行为判别,岩浆源区岩石为含角闪石的尖晶石二辉橄榄岩。批式熔融模拟计算显示,地幔岩10%~15%的部分熔融能够形成哈拉达拉岩体的母岩浆。母岩浆通过48%~50%的结晶分异作用则能够形成哈拉达拉岩体。早期结晶的橄榄石和斜长石通过堆晶作用形成橄长岩和橄榄辉长岩,剩余岩浆结晶形成辉长岩。  相似文献   

10.
内蒙古狼山山脉西侧分布有大面积的晚古生代岩浆岩,时代集中在早石炭世—晚二叠世,早石炭世角闪辉长岩、花岗闪长岩体出露于潮格温都尔镇西侧。角闪辉长岩体呈岩滴状产出,被花岗闪长岩体侵入,LA-ICP-MS锆石U-Pb年龄显示,角闪辉长岩的~(206)Pb/~(238)U加权平均年龄为329.0±2.3 Ma,花岗闪长岩的~(206)Pb/~(238)U加权平均年龄为331.1±0.9 Ma~330.0±4.2 Ma。花岗闪长岩暗色矿物以角闪石为主,富钠(Na2O=3.48%~4.46%),高钠钾比值(Na2O/K2O=1.03~2.39),钙碱性系列,P2O5-SiO_2之间存在较好的负相关性,岩石地球化学特征具Ⅰ型花岗岩的特点。Hf同位素及元素地球化学特征指示了角闪辉长岩及花岗闪长岩均来自于受地壳混染的亏损地幔,为同源岩浆演化的产物。角闪辉长岩及花岗闪长岩稀土元素配分型式一致,均为轻稀土元素富集,重稀土元素亏损,具弱的负Eu异常;角闪辉长岩富集Ba、Sr,亏损Nb、Ta、Zr、Hf;花岗闪长岩富集大离子亲石元素Rb、K、Pb、Sr,不同程度地亏损高场强元素Nb、Ta、P、Ti,总体反映了岩浆弧的地球化学特征。结合区域地质背景,早石炭世狼山地区侵入岩岩石组合为角闪辉长岩(闪长岩)+石英闪长岩+花岗闪长岩,认为狼山地区早石炭世处于大陆边缘弧构造背景。  相似文献   

11.
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   

12.
In situ zircon U–Pb ages and Hf isotopic compositions and whole rock geochemical and Sr–Nd–Pb isotopic data are presented for the Zijinshan alkaline intrusive complex from the Shanxi Province, western North China Craton. Salic rocks dominate the complex with the monzonite occurring in the outermost and pseudoleucite phonolitic breccia in the center. The intrusion took place 127 Ma ago with the earliest emplacement of monzonite and the termination of cryptoexplosive pseudoleucite phonolitic breccia. All rocks from this complex show LREE enrichment and HFSE depletion and exhibit enriched to depleted Sr–Nd isotopic features. The presence of inherited zircons and enriched Hf isotopic compositions in zircon rims, along with the enriched whole rock Sr–Nd isotopic compositions, indicate that the monzonite was formed through the mixing of lithospheric mantle-derived magma with lower crust-derived melts. The diopside syenite and nepheline-bearing diopside syenite are more depleted than the monzonite in terms of the Sr and Nd isotopes, together with their very high concentrations of LILE, we proposed that they originated from a mixed mantle source of enriched lithospheric mantle and depleted asthenosphere. The nepheline syenite has very low concentrations of MgO, Ni, Cr, suggesting that the magma underwent significant crystal fractionation. The most depleted Sr and Nd isotopic compositions ((87Sr/86Sr)i = 0.7036–0.7042, εNd(t) = − 0.2–0.3) among all rock types indicate a great contribution of asthenosphere to the nepheline syenite. The Zijinshan complex and its related crust-mantle interaction occurred in an extensional environment which resulted in continuously asthenospheric upwelling. Such an extensional environment might have been developed during the post-orogenic stage of the Late Paleozoic amalgamation of North China Craton with Mongolian continents and subsequent Mongol–Okhotsk ocean closure.  相似文献   

13.
选择3个典型岩体,即位于西南天山东段的拜城县英买来岩体和位于西段阔克萨岭区的川乌鲁岩体、巴雷公岩体(为了对比,也选择了位于塔里木盆地西北缘的麻扎山岩体),进行了岩石学和地球化学研究。结果表明,这些岩体具有不同的特点。英买来岩体为黑云母花岗岩和二云母花岗岩,具有高的SiO2含量,弱过铝,高的Sr同位素初始值(约0.710)和负的εNd(t)值(-4~-6),属于S—A型之间的过渡类型。麻扎山岩体由正长岩组成,属于碱性岩,微量元素标准化图解和其他岩体明显不同的是没有明显的Nb和Ta的负异常。川乌鲁岩体是一个由3个不同期次岩石组成的杂岩体,主体为正长岩-二长岩,地球化学特征显示是由基性岩浆和酸性岩浆不同程度混合形成的。位于同一构造区的巴雷公岩体则与川乌鲁岩体中的花岗斑岩的地球化学特征相似。综合岩石学和地球化学特征推测,南天山东段的英买来岩体是地壳熔融的结果,没有任何地幔物质加入的地球化学信息,西段的阔克萨岭地区酸性岩浆的形成则可能是来自于幔源底侵的基性岩浆导致薄的地壳发生熔融的结果。麻扎山岩体则完全是不同构造背景的产物,有可能与发生在塔里木盆地的二叠纪大规模的岩浆活动有关。因此,二叠纪岩浆活动的性质主要受地壳成分和结构的控制。  相似文献   

14.
河南舞阳南部张士英岩体的地球化学与成因及其构造意义   总被引:4,自引:3,他引:1  
张士英岩体岩石类型以石英二长岩、石英正长岩为主。岩体属于准铝质的高钾-钾玄岩系列(Al2O3为14.8%~16.7%,A/CNK=0.77~1.02,K2O/Na2O在1.00~1.43之间),稀土元素总量在261.7~381.0μg/g之间,轻稀土元素相对富集,稀土元素球粒陨石标准化模式呈右倾平滑曲线,(La/Yb)N比值为28~50,具有轻微的Eu负异常,Eu/Eu?比值在0.73~0.87之间。微量元素组成上表现为Sr、Ba、Nb、Ta的亏损,而Th、U相对富集。(87Sr/86Sr)i初始平均值为0.709,εNd(t)值为-13.9~-19.9,Nd的模式年龄为1.48~2.10Ga。岩体锆石LA-ICP-MSU-Pb年龄为(124.2±0.5)Ma,为早白垩世岩浆作用的产物。岩体侵位的区域地质背景为华北克拉通白垩纪大规模岩石圈转型和减薄时期,岩石的微量元素及同位素特征表明,岩体主要来源于下地壳物质的部分熔融,但有年轻地幔物质的加入。反映在区域强烈伸展拉张和岩石圈减薄背景下,软流圈地幔岩浆底侵所造成的下地壳部分熔融及壳幔混合过程。  相似文献   

15.
Geological studies on saturated to oversaturated and subsolvus aegirine-riebeckite syenite bodies of the Pulikonda alkaline complex and Dancherla alkaline complex were carried out. The REE distribution of the Dancherla syenite shows a high fractionation between LREE and HREE. The absence of Eu anomaly suggests source from garnet peridotite. The Pulikonda syenite shows moderate fractionation between LREE and HREE as reflected by enrichment of HREE and moderate enrichment of LREE. The negative Eu anomaly indicates role of plagioclase fractionation.Three distinct co-eval primary magmas i.e. mafic syenite-, felsic syenite- and alkali basalt magmas — all derived from low-degrees of partial melting of mantle differentiates and enriched metasomatised lower crust played a major role in the genesis and emplacement of the syenites into overlying crust along deep seated regional scale trans-lithospheric strike-slip faults and shear zones following immediately after late-Archaean calc-alkaline arc magmatism at different time-space episodes i.e. initially at craton margin and later on into the thickened interior of the Eastern Dharwar craton. The ductile sheared and folded Pulikonda alkaline complex was evolved dominantly from the magmas derived from partial melting of lower crust and minor juvenile magmas from mantle. Differentiation and fractionation by liquid immiscibility of mafic magma and commingling-mixing of intermediate and felsic magmas followed by fractionational crystallisation under extensional tectonics during waning stages of calc-alkaline arc magmatism nearer to the craton margin were attributed as the main processes for the genesis of Pulikonda syenite complex. Commingling and limited mixing of independent mantle derived mafic and felsic syenitic magmas and accompanying fractionation resulting into soda rich and potash rich syenite variants was tentatively deduced mechanism for the origin of Dancherla, Danduvaripalle, Reddypalle syenites and other bodies belonging to Dancherla alkaline complex at the craton interior. The Peddavaduguru syenite was formed by differentiation of alkali mafic magma (gabbro to diorite) and it’s simultaneous mingling with fractionated felsic syenitic magma under incipient rift. Vannedoddi and Yeguvapalli syenites were derived due to desilicification and accompanying alkali feldspar mestasomatism of younger potash rich granites along Guntakal-Gooty fault and along Singanamala shear zone respectively.  相似文献   

16.
本文对中国东南沿海不含幔源包体的中生代玄武岩和含幔源包体的新生代玄武岩进行了微量元素和Nd-Sr-Pb同位素对比研究。中生代玄武岩呈Ta、Nb和Hf负异常,低Ce/Pb、Nb/U比值和高La/Nb比值,与岛弧火山岩和陆壳岩石的微量元素特征相类似,说明在岩浆生成和上升过程中,幔源组分受到了陆壳组分的混染。新生代玄武岩呈Ta、Nb正异常和Pb负异常,高Ce/Pb、Nb/U比值和低La/Nb比值,与海岛玄武岩(OIB)相类似,Nd-Sr同位素成分与夏威夷玄武岩类似,因而它们未受明显的陆壳混染。143Nd/144Nd与206Pb/204Pb之间的负相关关系和87Sr/86Sr与206Pb/204Pb之间的正相关关系说明本区新生代玄武岩起源于中等亏损程度的软流圈地幔,并与EMII富集地幔组分发生了混合。  相似文献   

17.
贺敬博  陈斌 《地学前缘》2011,18(2):191-211
西准噶尔地区克拉玛依岩体主要由闪长岩和花岗岩组成,锆石SHRIMP法给出的岩体结晶年龄为(315.5±2.8)Ma,为晚石炭世侵入岩.克拉玛依岩体具岛弧岩石的元素地球化学特征:总体上岩石富钠.A/CNK=0.57~0.84,富集LREE,(La/Yb)N=4.7~6.1,Eu显示弱负异常(δEu=0.76~0.91),...  相似文献   

18.
In situ zircon U–Pb ages and Hf isotope data, major and trace elements and Sr–Nd–Pb isotopic compositions are reported for coeval syenite–granodiorites–dacite association in South China. The shoshonitic syenites are characterized by high K2O contents (5.9–6.1 wt.%) and K2O/Na2O ratios (1.1–1.2), negative Eu anomalies (Eu/Eu* = 0.65 to 0.77), enrichments of Rb, K, Nb, Ta, Zr and Hf, but depletion of Sr, P and Ti. The adakitic granodiorite and granodiorite porphyry intrusions are characterized by high Al2O3 contents (15.0–16.8 wt.%), enrichment in light rare earth elements (LREEs), strongly fractionated LREEs (light rare earth elements) to HREEs (heavy rare earth elements), high Sr (438–629 ppm), Sr/Y (29.2–53.6), and low Y (11.7–16.8 ppm) and HREE contents (e.g., Yb = 1.29–1.64 ppm). The calc-alkaline dacites are characterized by LREE enrichment, absence of negative Eu anomalies, and enrichment of LILEs such as Rb, Ba, Th, U and Pb, and depletion of HFSEs such as Nb, Ta, P and Ti.Geochemical and Sr–Nd–Hf isotopic compositions of the syenites suggest that the shoshonitic magmas were differentiated from parental shoshonitic melts by fractional crystallization of olivine, clinopyroxene and feldspar. The parent magmas may have originated from partial melting of the lithospheric mantle with small amount contribution from crustal materials. The adakitic granodiorite and granodiorite porphyry have Sr–Nd–Pb isotopic compositions that are comparable to that of the mafic lower crust. They have low Mg# and MgO, Ni and Cr contents, abundant inherited zircons, low εNd(t) and εHf(t) values as well as old whole-rock Nd and zircon Hf model ages. These granodiorites were likely generated by partial melting of Triassic underplated mafic lower crust. The Hf isotopic compositions of the dacites are relatively more depleted than the Cathaysia enriched mantle, suggesting those magmas were derived from the partial melting of subduction-modified mantle sources. The coeval shoshonitic, high-K calc-alkaline and calc-alkaline rocks in Middle to Late Jurassic appear to be associated with an Andean-type subduction. This subduction could have resulted in the upwelling of the asthenosphere beneath the Cathaysia Block, which induced partial melting of the mantle as well as the mafic lower crust, and formed an arc regime in the coastal South China during Middle to Late Jurassic.  相似文献   

19.
Subduction-related Quaternary volcanic rocks from Solander and Little Solander Islands, south of mainland New Zealand, are porphyritic trachyandesites and andesites (58.20–62.19 wt% SiO2) with phenocrysts of amphibole, plagioclase and biotite. The Solander and Little Solander rocks are incompatible element enriched (e.g. Sr ~931–2,270 ppm, Ba ~619–798 ppm, Th ~8.7–21.4 ppm and La ~24.3–97.2 ppm) with MORB-like Sr and Nd isotopic signatures. Isotopically similar quench-textured enclaves reflect mixing with intermediate (basaltic-andesite) magmas. The Solander rocks have geochemical affinities with adakites (e.g. high Sr/Y and low Y), whose origin is often attributed to partial melting of subducted oceanic crust. Solander sits on isotopically distinct continental crust, thus excluding partial melting of the lower crust in the genesis of the magmas. Furthermore, the incompatible element enrichments of the Solander rocks are inconsistent with partial melting of newly underplated mafic lower crust; reproduction of their major element compositions would require unrealistically high degrees of partial melting. A similar argument precludes partial melting of the subducting oceanic crust and the inability to match the observed trace element patterns in the presence of residual garnet or plagioclase. Alternatively, an enriched end member of depleted MORB mantle source is inferred from Sr, Nd and Pb isotopic compositions, trace element enrichments and εHf ? 0 CHUR in detrital zircons, sourced from the volcanics. 10Be and Sr, Nd and Pb isotopic systematics are inconsistent with significant sediment involvement in the source region. The trace element enrichments and MORB-like Sr and Nd isotopic characteristics of the Solander rocks require a strong fractionation mechanism to impart the high incompatible element concentrations and subduction-related (e.g. high LILE/HFSE) geochemical signatures of the Solander magmas. Trace element modelling shows that this can be achieved by very low degrees of melting of a peridotitic source enriched by the addition of a slab-derived melt. Subsequent open-system fractionation, involving a key role for mafic magma recharge, resulted in the evolved andesitic adakites.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号