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拉脊山口蛇绿混杂岩中辉绿岩的地球化学特征及SHRIMP锆石U-Pb年龄 总被引：8，自引：5，他引：3
拉脊山口蛇绿混杂岩是分布于中祁连和南祁连构造带之间蛇绿混杂带的重要组成部分。该混杂带中的岩石种类相对齐全,各岩性间为构造接触;其中辉绿岩以岩块和岩墙两种形式产出。辉绿岩块SiO2含量为49.80%~50.13%,MgO含量为5.43%~5.64%,FeOT为10.96%~11.52%,TiO2含量较高（2.38%~2.62%）;辉绿岩墙SiO2含量为43.41%~45.74%,MgO含量为9.04%~10.64%,FeOT为8.39%~9.96%,TiO2含量较低（0.89%~1.02%）,二者均属拉斑玄武岩系列。其中辉绿岩块ΣREE为135.4×10-6~150.9×10-6,（La/Yb）N=3.51~4.03,具有右倾型稀土配分模式,富集Rb、Ba、K、Sr等大离子亲石元素及Th、Nb、Ta、Zr、Hf、Ti等高场强元素,呈现洋岛拉斑玄武岩特征;辉绿岩墙ΣREE为36.10×10-6~43.72×10-6,（La/Yb）N=1.12~1.20,稀土配分曲线相对平坦,呈现出与洋中脊玄武岩相似的稀土和微量元素配分模式。这两类辉绿岩样品均缺乏Nb、Ta和Ti负异常,可能分别形成于洋岛/海山和洋中脊环境。SHRIMP锆石U-Pb测年结果显示,辉绿岩块形成时代为491.0±5.1Ma。这些不同构造属性的辉绿岩可能形成于原特提斯洋向北俯冲消减过程。 相似文献
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阿尔金山北缘蛇绿混杂岩中辉长岩锆石SHRIMP U-Pb定年及其地质意义 总被引：8，自引：3，他引：5
阿尔金北缘阿克赛青崖子附近蛇绿混杂岩组成岩石包括蛇纹岩和辉长岩等,呈透镜状构造岩片产出。蛇纹岩以富Mg,贫Al2O3、CaO、TiO2和∑REE为特征,与世界上典型蛇绿岩中变质橄榄岩的特征值一致。辉长岩SiO2含量为49.06%~50.70%,具有高的MgO（7.16%~10.01%）和Fe 2O3（6.36%~12.85%）含量,TiO2含量低到中等,为0.31%~1.02%,Na2O和K2O含量中等,平均分别为0.73%和0.75%,辉长岩在球粒陨石标准化稀土元素配分模式图上属平坦型或轻微富集型,无负Eu异常,与E-type洋中脊和OIB玄武岩类似。辉长岩的主量元素、微量元素特征表明其可能既保留了形成于MORB的背景信息,也记录了SSZ环境改造的结果,推测青崖子蛇绿混杂岩组合可能来自不同构造背景。蛇绿混杂岩中辉长岩的SHRIMP锆石U-Pb年龄测定,确定出青崖子附近蛇绿混杂岩所代表的洋壳形成于521±12Ma,为古生代早期。该年龄测定的结果还显示本区在472±10Ma有一次地质事件,可能代表了古生代的洋盆闭合的下限年龄。 相似文献
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龙陵-瑞丽增生杂岩带的构造属性对确定高黎贡构造带作为腾冲-保山地块的边界及班怒带南向延伸十分关键。本文在地质填图的基础上,通过岩石学、矿物学、岩石地球化学、同位素年代学和同位素示踪等方法,查明混杂岩带主要由蛇纹石化橄榄岩、玄武岩/辉长岩、硅质岩、碳酸盐岩、含放射虫层状硅质岩和锰结核的深海沉积岩等岩块呈规模不等的团块状、透镜状分布于浊积岩基质中,具有典型的俯冲增生杂岩岩石组合特征。蛇纹石化橄榄岩原岩由方辉橄榄岩和少量纯橄岩组成,具有轻稀土轻微富集、Mg#值高（88~92）,铬尖晶石Cr#、Mg#值分别在60~70和20~26区间,橄榄石Fo值为90~95。在铬尖晶石Cr#-Mg#指数图解和橄榄石Mg#-铬尖晶石Cr#图解上样品都落在弧前SSZ型橄榄岩区,说明研究区内的地幔橄榄岩是经历了高度部分熔融（>30%）和熔体抽离后的残留相,形成于弧前构造背景。玄武岩和辉长岩地球化学特征类似,具有富钛（TiO2>2.26%）、高Mg#值特征（49~57）,其稀土配分模式和微量元素蛛网图、构造环境判别图解、εNd（t）值（+2.2~+5.1）、以及岩石中含少量富钛角闪石和黑云母等,表明它们属于洋岛/海山型基性岩类,其岩浆来源于富集地幔。橄榄岩中脉状辉石岩锆石U-Pb年龄为183~185Ma,浊积岩中杂砂岩最小碎屑锆石U-Pb年龄为212~241Ma。此外,增生杂岩带中存在含早白垩世流纹岩/凝灰岩夹层的弧前/弧间沉积,并被晚白垩世陆相沉积岩不整合覆盖,这些特点说明俯冲增生杂岩带形成于晚三叠-早白垩世。研究区内混杂岩带的构造属性和时代与班怒带（拉萨-南羌塘地块间）和缅甸境内密支那蛇绿混杂岩带完全一致,是中特提斯洋演化的产物。中生代,高黎贡东南缘混杂岩带北连班怒带、南东连密支那蛇绿混杂岩带,随后,在新生代印度板块向北俯冲过程中,密支那蛇绿混杂岩带被Sagaing断裂带分支——八莫断裂带右行走滑位移到现今位置。 相似文献
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红柳河-洗肠井蛇绿混杂岩带位于内蒙古北山造山带中部，呈北西西向展布，向东延伸至白云山-洗肠井蛇绿混杂岩带，向西延伸至牛圈子-红柳园蛇绿混杂岩带。在白云山地区，蛇绿混杂岩由不同类型的岩块与基质组成，基质具有分带性，南侧以砂板岩基质为主，北侧以蛇纹岩基质及绿泥钠长片岩基质为主，反映了俯冲增生杂岩的特征。其中基性熔岩大面积发育，岩性以绿泥钠长片岩及变质玄武岩为主，TAS及AFM图解显示基性熔岩具有拉斑玄武岩的特征，微量元素蛛网图中具有弱Nb-Ta负异常及弱Sr正异常，稀土元素配分曲线显示了轻重稀土基本未分馏的曲线型式，微量元素系列判别图解显示了类似于MORB-like玄武岩的地球化学特征。由此可见，白云山地区基性熔岩为MORB-like玄武岩，反映了蛇绿混杂岩形成于弧前的构造背景。此外，本次工作获得侵入基性熔岩中的斜长花岗岩锆石206Pb/238U加权平均年龄为519.8±2.1Ma，εHf（t）-t图解显示了斜长花岗岩为地幔分异的产物。微量元素蛛网图中Nb-Ta亏损、右倾的稀土配分曲线及Th/Yb-Nb/Yb图解反映了斜长花岗岩具有岛弧岩浆岩的特征。对比研究区晚寒武世岛弧钙碱性辉长岩，我们认为白云山地区早寒武世发育MORB-like玄武岩，中-晚寒武世为岛弧钙碱性辉长岩及斜长花岗岩，反映了初始俯冲-正常俯冲的岩浆作用。 相似文献
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为解释南冈底斯晚白垩世埃达克质岩石成因及其地球动力学机制,本文对西藏扎囊县札佐地区二长花岗岩开展了锆石U-Pb年代学、Hf同位素和全岩地球化学分析。札佐二长花岗岩锆石U-Pb定年为80.43±0.62 Ma,其SiO2为66.19%~66.84%,Al2O3为15.17%~15.48%,MgO为1.67%~1.91%,Mg#为47.4~51.5,K2O为3.86%~4.09%,A/CNK=0.91~1.01,属准铝质高钾钙碱性岩石。岩石轻稀土富集明显,高Sr（492×10-6~670.2×10-6）,低Y（8.27×10-6~14.99×10-6）,Yb（1.07×10-6~1.79×10-6）,高Sr/Y（35.0~81.0）,高La/Yb（17.4~21.4）,弱负Eu异常,具埃达克岩地球化学特征。相对富集大离子亲石元素（LILE）,亏损高场强元素（HFSE）和重稀土。锆石εHf（t）值为10.5~14.1,单阶段Hf模式年龄（tDM1）为184.8~326.1 Ma,平均为203.4 Ma,二阶段Hf模式年龄（tDM2）为247.2~476.0 Ma,平均为287.1 Ma,略大于侵位年龄,指示岩浆物质来源于俯冲洋壳,并可能卷入俯冲沉积物。岩石中地幔组分印记Mg#值和相容元素Ni、Cr含量较高,表明熔体在上升过程中与上覆地幔楔发生反应。研究分析表明,在新特提斯洋洋脊俯冲作用下,高温热流透过板片窗导致洋壳（及俯冲沉积物）部分熔融形成札佐埃达克质二长花岗岩。同时表明,在80 Ma左右,新特提斯洋仍处于洋脊俯冲阶段。 相似文献
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在柴北缘东段识别出早古生代埃达克岩-富Nb玄武岩的火山岩组合。埃达克岩富Na2O、贫K2O，K2O/Na2O比值介于0.14~0.43之间；高Sr（614×10-6~1043×10-6），但亏损Y（3.26×10-6~14.1×10-6）和Yb（0.33×10-6~1.46×10-6），具有高的Sr/Y比值（44~282）；富集Sr、Ba等大离子亲石元素，亏损Nb、Ta、Ti等高场强元素及Cr、Ni、Co、V等相容元素。富Nb玄武岩富Na2O、贫K2O、高TiO2，其Nb含量较高，介于16.9×10-6~17.9×10-6之间，具有高的Nb/Ta、Nb/U、（Nb/La）N比值，同时富集高场强元素。埃达克岩锆石U-Pb定年得到453±4Ma和457±4Ma的结晶年龄。锆石εHf（t）范围较大，介于3.40~13.23之间，对应的二阶段模式年龄tDM2介于1059~566Ma之间，显示以新生物质为主的特征。综合研究表明柴北缘东段埃达克岩可能为岛弧环境下俯冲的南祁连大洋板片部分熔融的产物。板片来源的埃达克质熔体交代或与上覆地幔楔橄榄岩反应，导致被交代的地幔橄榄岩部分熔融而形成富Nb玄武质岩浆。柴北缘东段埃达克岩-富Nb玄武岩火山岩组合的厘定表明南祁连洋可能直到~455Ma之前并未完全闭合，同时表明俯冲大洋板片的部分熔融可能是柴北缘早古生代地壳增生的一种重要方式。 相似文献
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对钦杭结合带西南段大瑶山东南缘的中晚侏罗世埃达克质花岗岩（165~153 Ma）进行了岩石学、地球化学研究,并探讨了埃达克质和TTG岩类的特征属性。岩石SiO2含量63.76%~72.13%,总体具高Al2O3（Al2O3≥15%）、低MgO （<3%）,亏损重稀土元素（HREE）、正Eu异常或弱的负Eu异常,低Y （≤18×10-6）和Yb （≤1.9×10-6）,高Sr （>300×10-6）和Sr/Y值（>20）等埃达克岩独特的地球化学特征。结合区域构造演化分析认为,该侏罗纪埃达克质花岗岩形成于陆内伸展构造背景,为大陆板内加厚（隆起区）的下地壳底部岩石部分熔融的产物,属大陆板内环境I型花岗岩。具有类似于低镁安山岩/闪长岩系列（LMA）和镁安山岩/闪长岩系列（MA）两种高压型TTG亚类的属性,为古俯冲增生带下地壳弧型岩石熔融的继承性特征,与中生代古太平洋俯冲板片熔融过程无关,属非俯冲成因的埃达克/TTG岩类。其空间上与大瑶山东南缘早古生代俯冲增生带高度重合,且与早古生代TTG侵入岩组合紧密相邻,提示它们可能源自于早古生代洋壳俯冲带或大陆边缘弧下地壳玄武质岩石的部分熔融,因而具有洋俯冲成因的特征属性。 相似文献
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中亚造山带东段内蒙古兴安盟扎赉特旗地区作为二连-贺根山断裂的东延部分,蕴含了古亚洲洋俯冲消亡过程及洋-陆转换的关键信息,然而对于该区蛇绿构造混杂岩的研究相对薄弱,成为制约古亚洲洋构造演化研究的瓶颈。本文在扎赉特旗沙巴尔吐地区发现了蛇绿构造混杂岩、与岛弧环境相关的英云闪长岩-奥长花岗岩和碱长花岗岩组合。对蛇绿构造混杂岩中超镁铁质岩和碱长花岗岩开展LA-ICP-MS锆石U-Pb测年显示其年龄分别为279.2±3.3 Ma和278.2±1.7 Ma,表明其形成于中二叠世早期。超镁铁质岩含有低的SiO_2含量(43.54%～46.38%),低Na_2O和K_2O而富MgO,Mg~#为89～94,显示亏损地幔-过渡型地幔特征,起源于约70%的石榴石二辉橄榄岩的部分熔融,属俯冲型(SSZ)蛇绿岩。英云闪长岩-奥长花岗岩属准铝质钙碱性系列,高Al_2O_3含量,相对富钠贫钾,高Sr(平均600.00×10~(-6))、低Y(平均12.50×10~(-6))和Yb(平均1.18×10~(-6)),具典型。型埃达克岩特征,是俯冲环境下低钾洋壳玄武岩部分熔融的产物。碱长花岗岩富硅和碱,低铁和镁,具有高的正εHf(t)值(平均+18.9),位于亏损地幔线之上,一阶段、二阶段模式年龄基本近于或者小于岩石结晶年龄,起源于岛弧型的新生地壳。沙巴尔吐蛇绿构造混杂岩代表中二叠世早期洋内俯冲的产物,表明古亚洲洋在中二叠世早期未闭合,仍存在持续性的俯冲活动,闭合时间至少应在中二叠世之后。 相似文献
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东准噶尔扎河坝蛇绿混杂岩中的石榴角闪岩 总被引：1，自引：0，他引：1
继报道了超高压成因的石榴辉石岩和石英菱镁岩之后,作者在扎河坝地区又发现了具有超高压成因特征的石榴角闪岩。扎河坝石榴角闪岩主要组成矿物为角闪石、石榴石、辉石和钠长石,它不但含硬玉、多硅白云母等高压变质矿物,而且还残留着具有超高压成因特征的超硅石榴石和超硅辉石。根据野外产状和矿物组成特征,扎河坝石榴角闪岩可以细分成含硬玉石榴角闪岩和含多硅白云母石榴角闪岩两类,它们的原岩为大洋玄武岩。石榴角闪岩的厘定进一步证实在扎河坝蛇绿混杂岩带内确实存在着超深俯冲后折返的洋壳,同时超深俯冲洋壳的组成也较复杂,包括沉积岩、辉长岩和大洋玄武岩等。石榴角闪岩、石英菱镁岩及石榴辉石岩等超高压变质岩的存在表明扎河坝蛇绿岩带是一条大洋板块的超深俯冲带,它可能通过克拉玛依蛇绿岩带西延出境,形成一条横贯东西准噶尔北缘的超深俯冲带。这条超深俯冲带的发现为研究新疆北部早古生代洋陆转换过程及机制提供了新的视野和思路,对深入探讨准噶尔盆地北缘及阿尔泰南缘早古生代壳幔相互作用及中亚造山带形成的动力学机制具有重要的启示。 相似文献
11.
《地学前缘(英文版)》2022,13(2):101341
Melting of subducting oceanic lithosphere and associated melt-mantle interactions in convergent plate margins require specific geodynamic environment that allows the oceanic slab to be abnormally heated. Here we focus on the Early Mesozoic mafic rocks and granite porphyry, which provide insights into slab melting processes associated with final closure of the Paleo-Asian Ocean. The granite porphyry samples are calc-alkaline and distinguished by high Sr contents, strong depletion of heavy rare earth elements, resulting in high (La/Yb)N and Sr/Y ratios, and negligible Eu anomalies. Based on their high Na2O and MgO, low K2O contents, positive εHf(t) and εNd(t) and low (87Sr/86Sr)i values, we propose that the granite porphyry was likely derived from partial melting of subducting Paleo-Asian oceanic crust. The Nb-enriched mafic rocks are enriched in Rb, Th, U, Pb and K, and depleted in Nb, Ta, Ba, P and Ti, corroborating a subduction-related origin. Their heterogeneous Sr-Nd-Hf-O isotopic compositions and other geochemical features suggest that they were likely derived from partial melting of peridotitic mantle wedge interacted with oceanic slab-derived adakitic melts. Trace element and isotope modeling results and elevated zircon δ18O values suggest variable subducting sediments input into the mantle wedge, dominated by terrigenous sediments. Synthesizing the widely-developed bimodal rock associations, conjugated dikes, thermal metamorphism, tectonic characteristics, paleomagnetic constraints, and paleogeographical evidence along the Solonke-Changchun suture zone, we identify a slab window triggered by slab break-off, which accounts for slab melting and formation of the Nb-enriched mafic rocks and associated adakitic granite porphyry in southeastern Central Asian Orogenic Belt. 相似文献
12.
新疆北部晚古生代埃达克岩、富铌玄武岩组合：古亚洲洋板块南向俯冲的证据 总被引：50，自引：0，他引：50
地球化学研究结果表明，新疆北部富蕴县境内的晚古生代下泥盆统托让格库都克组的安山质岩石具有与埃达克岩非常相似的地球化学特征，它们具有较高的Al2O3，Na2O和Sr含量以及Sr/Y比值；明显亏损重稀土和Y，它们的MORB标准化微量元素蛛网图表现为明显的Nb，Ta负异常和Sr正异常，同时强烈亏损高场强元素。与埃达克岩共生的玄武岩的地球化学特征则与富铌玄武岩一致，表现为Si过饱和及富Na的特征，同时具有较高的Nb，TiO2和P2O5含量，并富集高场强元素。由于埃达克岩和富铌玄武岩的形成均与板块俯冲有关，因此，它们的存在表明，古亚洲洋在早-中泥盆世向南(哈萨克斯坦-准噶尔板块)发生了一次洋壳俯冲作用。 相似文献
13.
西准噶尔玛依勒地区枕状玄武岩年代学、地球化学及岩石成因 总被引：2，自引：2，他引：0
通过对造山带内洋岛玄武岩的时代及地球化学性质研究,不仅可以进行古海山/大洋高原的识别,而且还可以进行古洋盆演化及古构造格局恢复。笔者等最新在西准噶尔玛依勒山北侧识别出一套枕状玄武岩,其与火山碎屑岩、硅质岩共生。枕状玄武岩斜长石微晶普遍发育中空骸晶结构,是在水下熔岩急剧萃冷条件下迅速结晶的产物。通过LA-ICP-MS锆石U-Pb测年,获得枕状玄武岩206Pb/238U加权平均年龄为437.2±2.2Ma,该年龄的获得填补了志留纪碱性玄武岩的空白。岩石地球化学分析结果显示,玛依勒枕状玄武岩为碱性玄武岩系列,岩石具有中等Si O2(44.89%~47.81%),高Ti O2(3.28%~4.12%)及P2O5(0.50%~0.70%),低Mg O(3.49%~6.79%),轻、重稀土元素分异较为明显((La/Yb)N=5.5~7.3),无明显Eu异常(Eu/Eu*=0.96~1.06),相对富集Rb、Th、U,亏损Ba、K、Sr,没有明显Nb、Ta负异常,这些地球化学特征与洋岛玄武岩(OIB)极其相似。微量元素含量及反映源区性质的比值表明,枕状玄武岩来源于富集地幔源区,主要组成为尖晶石和石榴石二辉橄榄岩,并发生了5%±的部分熔融,其形成于大洋板内与地幔柱有关的海山/大洋岛屿环境。结合前人研究,认为西准噶尔乃至古亚洲洋在中古生代洋内俯冲的同时,大洋板内可能存在地幔柱活动。 相似文献
14.
《International Geology Review》2012,54(1):66-87
The Late Cretaceous Alihoca ophiolite in the Inner Tauride suture zone (ITSZ) of South-Central Turkey represents part of a single ophiolitic thrust sheet that originated from the Inner Tauride ocean. The ophiolite contains upper mantle peridotites, cumulate wehrlites, layered-to-isotropic gabbros, and microgabbroic-to-doleritic dikes. An ophiolitic mélange beneath the Alihoca ophiolite includes blocks of limestone, peridotite, dolerite, basalt, and deep-sea sedimentary rocks (radiolarite, chert) in a matrix comprising sheared serpentinite and mudstone. Isotropic gabbro and dolerite dike rocks show enrichment in Sr, K, Rb, Ba, and Th (LILE) and depletion of Ta, Nb, Zr, Ti, and Y (HFSE), indicating an island arc tholeiite (IAT) affinity. Relatively younger dolerite rocks display low TiO2 (<0.5 wt.%) contents, concave REE profiles with low HREE concentrations, and high LREE values, typical of boninitic affinities. The Alihoca ophiolite, hence, displays an IAT to boninitic geochemical progression in its magmatic evolution, reminiscent of many other Tethyan ophiolites in the region. It represents the remnant of a forearc oceanic crust, which developed during the early stages of subduction within the Inner Tauride ocean. Volcanic, volcano-sedimentary, and sedimentary rocks of the Uluk??la–Çamard? basin north of the ITSZ disconformably overlie the mafic-ultramafic rocks of the Alihoca ophiolite. Pillowed and massive lavas of the latest Cretaceous–Palaeocene Uluk??la Formation have alkaline basalt-to-basaltic andesite compositions, displaying relatively enriched LILE and LREE patterns with negative Nb and Ta anomalies. These geochemical features suggest that magmas of the Uluk??la–Çamard? volcanic rocks formed from partial melting of a metasomatized lithospheric mantle. This melting event was triggered by the influx of asthenospheric heat through a slab breakoff-induced window in the downgoing Tethyan oceanic lithosphere. 相似文献
15.
富铌玄武岩：板片熔体交代的地幔楔橄榄岩部分熔融产物 总被引：4，自引：0，他引：4
富铌玄武岩是一类具有特殊地球化学特征的岛弧玄武岩。与正常岛弧玄武岩相比，它具有硅饱和并富钠的特征；同时具有相对高的Nb（一般>7×10-6）、TiO2（1%～2%）和P含量，以及低的LILE/HFSE和HREE/HFSE比值，并富集高场强元素；它的原始地幔标准化微量元素图显示了弱的Nb、Ta负异常（有时出现弱的正异常），原始地幔标准化La/Nb比值小于2（但很少小于0.7），它是由受埃达克质熔体交代过的地幔橄榄岩部分熔融形成的。由于富铌玄武岩与埃达克岩是大洋板片俯冲作用的直接产物，因此，通过对该岩石组合及与俯冲作用有关的流体和熔体的研究，不仅可以查明洋壳俯冲作用过程中的岩浆活动特征，还可以阐明洋壳俯冲及壳幔相互作用，具十分重要的地质意义。 相似文献
16.
俯冲带复杂的壳幔相互作用 总被引：15，自引：0，他引：15
俯冲带除俯冲板片脱水形成的富大离子亲石元素流体、交代地幔楔形成的岛弧钙碱性玄武岩安山岩-英安岩-流纹岩及相应侵入岩组合外，还存在由俯冲扳片熔融形成的埃达克质熔体交代地慢楔形成的埃达克岩-富铌玄武岩-富镁安山岩组合，从而构成了俯冲带的流体交代与熔体交代两大类壳慢相互作用体系及相应的岩石组合。熔体交代作用的显著特点是Mg、高场强元素Nb、Ti、P等含量增加，Nd／Sr值增高，而Si、K、Na及La／Yb降低。洋壳板片或洋脊俯冲、玄武质岩浆底侵使地壳增厚，或板片断离、撕裂等作用均可产生埃达克质熔体并随之产生熔体交代作用。流体和熔体与地幔橄揽岩的相互作用构成了俯冲带复杂的地球化学体系。 相似文献
17.
Shao-Chen Liu Qun-Ke Xia Sung Hi Choi Etienne Deloule Pei Li Jia Liu 《Contributions to Mineralogy and Petrology》2016,171(12):100
Various enriched recycled oceanic components in the source of Cenozoic intra-plate alkaline basalts from eastern China were identified by previous studies. Due to the existence of a stagnant subducted Pacific slab in the mantle transition zone beneath eastern China, it is logical to connect the stagnant slab to the recycled oceanic materials. However, the recycled oceanic materials could also result from ancient subduction events (e.g., Paleo-Tethyan, Paleo-Asian or Izanagi plate subduction) because enriched geochemical signatures of a recycled slab can be preserved in the mantle for longer than 1 Gyr. Investigating the temporal variations of the recycled oceanic materials in the mantle source is a useful way to trace the origin of the basalts. In this article, we have conducted a detailed geochemical study, including major and trace elements and Sr–Nd–Pb isotopes, on two alkaline basalt groups from Zhejiang, SE China, which erupted 26–17 Ma and after 11 Ma, respectively. In particular, we recovered the H2O content of the initial magmas based on the H2O content of the clinopyroxene (cpx) phenocrysts and the partition coefficients of H2O between cpx and basaltic melts. The H2O contents of the Zhejiang basalts range from 1.3 to 2.6 (wt.%), which fall within the range of back-arc basin or island arc basalts. The older basalts are more alkaline and have lower Si and Al contents; higher trace element concentrations; higher La/Yb, Ce/Pb and Nb/La ratios; lower H2O/Ce and Ba/Th ratios; and stronger negative K, Pb, Hf and Ti anomalies than the younger ones. The co-relationships between Ba/La, H2O/Ce, Nb/La, Ce/Pb and Ba/Th in the two groups of the Zhejiang basalts indicate that a recycled dehydrated oceanic alkaline basalt component is needed in the source of the older rocks, along with a depleted mantle component. Meanwhile, an additional recycled dehydrated sediment component was required in the source of the younger rocks. The temporal change in the recycled oceanic materials in the mantle sources of Zhejiang Cenozoic basalts demonstrates that the recycled components can only originate in the stagnant Pacific slab that is the only plate subducted since 100 Ma in this area. 相似文献
18.
内蒙古二连—贺根山缝合带额很傲包图英云闪长岩体,出露于西乌旗梅劳特乌拉SSZ型蛇绿岩带北侧。为了确定该岩体的岩石成因类型,探讨其构造环境及古亚洲洋俯冲消亡过程,对该岩体进行了岩石学、地球化学和LAICP-MS锆石U-Pb年代学研究。额很傲包图英云闪长岩高硅富铝,富钠贫钾,高锶低钇,富集Rb、Ba、Sr等大离子亲石元素和LREE,亏损Nb、Ta、Ti、P等高场强元素和HREE,无明显Eu异常。岩石学和岩石地球化学特征表明,该英云闪长岩体为高Si埃达克岩(HSA),形成于岛弧环境,具有洋内俯冲洋壳+俯冲深积物部分熔融并与上覆地幔楔橄榄岩反应成因特征。锆石LA-ICP-MS U-Pb测年表明,额很傲包图英云闪长岩体的侵位年龄为(305.6±1.5)Ma,形成时代为晚石炭世。结合二连—贺根山缝合带石炭纪蛇绿岩、石炭纪—二叠纪岛弧型岩浆岩的时空分布与演化特征,认为古亚洲洋二连—贺根山洋盆在石炭纪—早二叠世处于以洋内俯冲为特征的大洋俯冲消亡过程中。 相似文献
19.
20.
High Field Strength Element Enrichment of Pliocene--Pleistocene Island Arc Basalts, Zamboanga Peninsula, Western Mindanao (Philippines) 总被引：37，自引：0，他引：37
SAJONA FERNANDO G.; MAURY REN C.; BELLON HERV; COTTEN JOSEPH; DEFANT MARC 《Journal of Petrology》1996,37(3):693-726
The Pliocene—Pleistocene magmatic activity of the Zamboangaare is linked to the southward subduction of the Oligocene—Mio-ceneSulu Sea back-are basin along the Sulu Trench. The magmaticproducts include small amounts of adakites dated from 3.8 to0.7 Ma, abundant Nb-enriched basalts and basaltic andesites(NEB) dated from 2 to 1 Ma and a lone calc-alkaline potassicbasaltic andesite dated at 0.4 Ma. Three kinds of NEB are distinguished:nearly primitive Mg-rich (MG) basalts displaying positive orno Nb anomalies with respect to adjacent incompatible elementsand more evolved low-K (LK) and calc-alkaline (CA) lavas which,despite their Nb enrichment, display negative Nb anomalies.Although the role of OIB-type mantle components has been advocatedto explain the HFSE enrichment of NEB, the spatial and temporalassociation of these rocks with adakites suggests a petrogeneticlink between them. Trace element characteristics of the NEBimply that amphibole and ilmenite might be present in theirsource. We suggest that these minerals could be added metasomaticallyto the mantle through hybridization by percolating slab melts,during which Nb and Ti are preferentially extracted from theadakitic melts. In an early stage (4–3 Ma) of the subductionof the young and hot Sulu Sea basin crust beneath the Zamboangapeninsula, adakitic liquids formed at depths of 75–85km. A few of them were emplaced at the surface but most wereconsumed through slab melt-mantle metasomatic reactions. Adakiteproduction and emplacement continued later (<2 Ma), whilethe Nb-enriched mantle was brought by convection to depths thatallowed its melting and the subsequent emplacement of NEB behindthe adakitic front of the Zamboanga are. KEY WORDS: adakite; metasomatism; Mindanao; Nb-enriched basalts; subduction
*Corresponding author. Present address: Mines and Geosciences Bureau, North Avenue, Diliman, 1100 Quezon City, Philippines 相似文献