Geochronology and geochemistry of Cretaceous Nanshanping alkaline rocks from the Zijinshan district in Fujian Province,South China: Implications for crust–mantle interaction and lithospheric extension     

《Journal of Asian Earth Sciences》2014

In situ zircon U–Pb ages and Hf isotopic data, major and trace elements, and Sr–Nd–Pb isotopic compositions are reported for Nanshanping alkaline rocks from the Zijingshan district in southwestern Fujian Province (the Interior or Western Cathaysia Block) of South China. The Nanshanping alkaline rocks, which consist of porphyritic quartz monzonite, porphyritic syenite, and syenite, revealed a Late Cretaceous age of 100–93 Ma. All of the rocks show high SiO₂, K₂O + Na₂O, and LREE but low CaO, Fe₂O₃^T, MgO, and HFSE (Nb, Ta, P, and Ti) concentrations. These rocks also exhibit uniform initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7078 to 0.7087 and ε_Nd(t) values of −4.1 to −7.2, thus falling within the compositional field of Cretaceous basalts and mafic dikes occurring in the Cathaysia Block. Additionally, these rocks display initial Pb isotopic compositions with a ²⁰⁶Pb/²⁰⁴Pb_i ratio of 18.25 to 18.45, a ²⁰⁷Pb/²⁰⁴Pb_i ratio of 15.63 to 15.67, and a ²⁰⁸Pb/²⁰⁴Pb_i ratio of 38.45 to 38.88. Combined with the zircon Hf isotopic compositions (ε_Hf(t) = −11.7 to −3.2), which are different from those of the basement rocks, we suggest that Nanshanping alkaline rocks were primarily derived from a subduction-related enriched mantle source. High Rb/Sr (0.29–0.65) and Zr/Hf (37.5–49.2) but relatively low Ba/Rb (4.4–8.1) ratios suggest that the parental magmas of these rocks were most likely formed via partial melting of a phlogopite-bearing mantle source with carbonate metasomatism. The relatively high SiO₂ (62.35–70.79 wt.%) and low Nb/Ta (10.0–15.3) ratios, positive correlation between SiO₂ and (⁸⁷Sr/⁸⁶Sr)_I, and negative correlation between SiO₂ and ε_Nd(t) of these rocks suggest that the crustal materials were also involved in formation of the Nanshanping alkaline rocks. Combined with geochemical and isotopic features, we infer magmatic processes similar to AFC (assimilation and fractional crystallization) involving early fractionation of clinopyroxene and olivine and subsequent fractionation of biotite-dominated assemblages coupled with a lesser amount of crustal contamination, thereby forming the Nanshanping alkaline rocks. The Nanshanping alkaline rocks appear to be associated with an extensional environment in the Cathaysia Block. This extensional regime could have resulted in the slab break-off and rollback of the subducting paleo-Pacific plate and the upwelling of the asthenospheric mantle, which induced partial melting of the enriched lithospheric mantle in the Cretaceous.  相似文献   

Geological characteristics and tectonic signifcance of unconformities in Mesoproterozoic successions in the northern margin of the North China Block     

Yongqiang Qu  Jianguo Pan  Shouxian Ma  Zhiping Lei  Lin Li  Guoli Wu 《地学前缘(英文版)》2014,(1)

Several stratigraphic breaks and unconformities exist in the Mesoproterozoic successions in the northern margin of the North China Block.Geologic characters and spatial distributions of fve of these unconformities,which have resulted from different geological processes,have been studied.The unconformity beneath the Dahongyu Formation is interpreted as a breakup unconformity,representing the time of transition from continental rift to passive continental margin.The unconformities beneath the Gaoyuzhuang and the Yangzhuang formations are considered to be the consequence of regional eustatic fuctuations,leading to the exposure of highlands in passive margins during low sea-level stands and transgressive deposition on coastal regions during high sea-level stands.The unconformity atop the Tieling Formation might be caused by uplift due to contractional deformation in a back-arc setting,whereas the uplift after the deposition of the Xiamaling Formation might be attributed to a continental collision event.It is assumed that the occurrences of these unconformities in the Mesoproterozoic successions in the northern margin of the North China Block had a close bearing on the assemblage and breakup of the Columbia and Rodinia supercontinents.  相似文献   

扬子西缘小相岭地区苏雄组古火山机构的发现及意义          下载免费PDF全文

鄢圣武  伍文湘  李小平  杨辉  马继跃  熊富浩 《中国地质调查》2014,6(3):47-55

通过详细的野外地质调查,发现扬子西缘小相岭地区苏雄组火山岩由巨厚的酸性-中酸性熔岩、火山碎屑岩和少量基性熔岩组成,在小相岭山脊两侧首次厘定4处古火山机构。其中,阳糯雪山古火山机构最壮观,是由火山颈相、溢流相、爆发相和火山沉积相构成的完整古火山机构。通过系统的地质剖面研究,发现该古火山机构存在2次喷发亚旋回和15个火山韵律,2次喷发亚旋回之间出现了1次明显的火山间歇期。小相岭地区古火山机构的发现,进一步厘定了苏雄组火山岩的喷发方式和构建特征,对进一步研究苏雄组酸性火山碎屑岩的起源及新元古代陆内裂谷作用具有重要意义。  相似文献   

Early Neoproterozoic granulite facies metamorphism of mafic dykes from the Vestfold Block,east Antarctica   总被引：2，自引：0，他引：2  

X. C. Liu  W.‐ Wang  Y. Zhao  J. Liu  B. Song 《Journal of Metamorphic Geology》2014,32(9):1041-1062

Proterozoic mafic dykes from the southwestern Vestfold Block experienced heterogeneous granulite facies metamorphism, characterized by spotted or fractured garnet‐bearing aggregates in garnet‐absent groundmass. The garnet‐absent groundmass typically preserves an ophitic texture composed of lathy plagioclase, intergranular clinopyroxene and Fe–Ti oxides. Garnet‐bearing domains consist mainly of a metamorphic assemblage of garnet, clinopyroxene, orthopyroxene, hornblende, biotite, plagioclase, K‐feldspar, quartz and Fe–Ti oxides. Chemical compositions and textural relationships suggest that these metamorphic minerals reached local equilibrium in the centre of the garnet‐bearing domains. Pseudosection calculations in the model system NCFMASHTO (Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃) yield P–T estimates of 820–870 °C and 8.4–9.7 kbar. Ion microprobe U–Pb zircon dating reveals that the NW‐ and N‐trending mafic dykes were emplaced at 1764 ± 25 and 1232 ± 12 Ma, respectively, whereas their metamorphic ages cluster between 957 ± 7 and 938 ± 9 Ma. The identification of granulite facies mineral inclusions in metamorphic zircon domains is also consistent with early Neoproterozoic metamorphism. Therefore, the southwestern margin of the Vestfold Block is inferred to have been buried to depths of ~30–35 km beneath the Rayner orogen during the late stage of the late Mesoproterozoic/early Neoproterozoic collision between the Indian craton and east Antarctica (i.e. the Lambert Terrane or the Ruker craton including the Lambert Terrane). The lack of penetrative deformation and intensive fluid–rock interaction in the rigid Vestfold Block prevented the nucleation and growth of garnet and resulted in the heterogeneous granulite facies metamorphism of the mafic dykes.  相似文献   

内蒙古库伦旗秦家沟土壤地球化学特征及找矿方向     

刘新运 《地质与勘探》2014,50(Z1):1338-1343

本文通过统计秦家沟土壤样品多元素地球化学参数,推测可能的矿源层和富集成矿作用,分析Grd数据对比图,分析各元素高值区的分布特征,根据相关系数（λ）矩阵的因子分析结果,得到了2个元素组合,推测出本区的主成矿元素和伴生元素,根据R型聚类分析谱系图的统计结果,推测出了本区可能存在的中高温元素组合类型和中低温元素组合类型,确定了本区有利的成矿元素组合类型,圈定了组合异常,通过归一化Grd数据图和组合异常对比,验证异常的合理性和有效性。通过施工地表工程,对所圈定的异常进行了查证,取得了良好的找矿效果,揭示了本区所蕴藏的成矿信息,指明了本区今后的找矿方向,为更好地指导本区下一步勘查工作提供了依据。  相似文献   

华北地台南缘霍邱安阳山地区八公山群地层时代归属（青白口纪）：来自碎屑锆石年代学的制约   总被引：2，自引：0，他引：2       下载免费PDF全文

李双应  程成  王松  彭亮  稽在飞  杨栋栋 《地质科学》2014,(2):608-617

分布于华北地台南缘,霍邱-固始交界安阳山地区的八公山群,由一套碎屑岩和碳酸盐岩组成。最近,人们在碳酸盐岩中发现、珊瑚等化石,确定灰岩时代为晚石炭世。但是,碎屑岩的地质时代仍然没有定论。碎屑岩由粉砂质泥岩、石英砂岩、粉砂岩等组成,厚度大于780 m。石英砂岩为中-厚层状,中细粒结构,成分成熟度和结构成熟度高,石英含量高达95%以上,属于滨海-陆棚沉积。应用LA-ICP-MS对石英砂岩中碎屑锆石U-Pb年代学研究表明,样品HQ2106和HQ2204最年轻的碎屑锆石U-Pb年龄分别为860±22.2 Ma（YSG）,877±22.6 Ma（YSG）,前者代表了地层的最大沉积年龄,它们也得到锆石年龄加权平均值（YC1σ和YC2σ）的支持。因此,研究区八公山群碎屑岩地层时代属于青白口纪（拉伸纪）。该研究结果将为华北地台南缘前寒武纪地层划分对比以及构造演化历史重塑提供重要依据。  相似文献   

区域地球化学推断地质体模型与应用——以花岗岩类侵入体为例     

向运川  龚庆杰  刘荣梅  杨万志 《岩石学报》2014,30(9):2609-2618

区域化探全国扫面计划获得的海量地球化学数据在基础地质和矿产勘查研究中已发挥了重要作用。全国矿产资源潜力评价化探工作组将全国陆地国土划分为5个地球化学域(古亚洲地球化学域、秦祁昆地球化学域、特提斯地球化学域、扬子地球化学域和滨太平洋地球化学域)和25个地球化学省。在全国地球化学图中位于云南西部地区的花岗岩类侵入体具有显著富K2O、Th、U、La、Y、Zr而贫Co、Ni、V、Cr、Ti、Fe2O3的特征。基于云南西部地区区域化探数据利用因子分析确定了高场强元素组合(F2)和相容元素组合(F1)两个公因子:F2=0.87Th+0.86Y+0.77U+0.77Zr+0.67La+0.61K2O+0.58Al2O3+0.53Be,F1=0.95Fe2O3+0.93V+0.93Ti+0.92Co+0.81Cr+0.80Ni。利用二者因子得分比值(F2/F1)构建了推断花岗岩类侵入体的区域地球化学综合指标和推断模型。以F2/F1为例介绍了制作地球化学图和地球化学异常图的方法技术。在F2/F1地球化学图中的高值区或在其地球化学异常图中的异常区与云南西部地区花岗岩类侵入体的地表出露范围十分吻合,从而验证了地球化学推断花岗岩类侵入体模型的可行性。基于构建的推断模型在全国近7百万平方千米的范围内进行推演并绘制F2/F1的地球化学图和地球化学异常图。选择华南中部地区进行详细分析,结果发现模型指标异常区与实测花岗岩类侵入体在空间形态和规模上十分吻合,尤其在韶关至桂林、贺州一带花岗岩类侵入体边界与F2/F1异常区边界几乎一致。这一结果不仅证实了针对花岗岩类侵入体所建立的区域地球化学推断模型的可行性,而且该模型在基础地质研究方面具有潜在应用价值。  相似文献   

西准噶尔早泥盆世马拉苏组火山岩岩石成因研究     

李平  王洪亮  徐学义  陈隽璐  过磊  奚仁刚 《岩石学报》2014,30(12):3553-3568

新疆西准噶尔北部地区的早泥盆世马拉苏组出露有少量富钠低钾的拉斑质中基性熔岩,这些分布于谢米斯台断裂北侧的玄武安山岩和玄武岩多呈夹层状断续产出于火山碎屑岩之中。马拉苏中基性熔岩的Mg#与主、微量元素协变关系及Th-Th/Nd图反映了其并非同源岩浆演化的结果。马拉苏火山岩中的玄武安山岩富集LILE、亏损HFSE,具有较高的Th含量及较低的Hf/Th和(Nb/Th)PM比值,显示出弧火山岩的地球化学特征。其中的玄武岩则具有略为平坦的稀土元素分配样式,较低的Th含量及较高的Hf/Th和(Nb/Th)PM比值,此同MORB地球化学特征极为相似;虽然其也显示有轻微的LILE富集、HFSE亏损,但是较高的La/Nb比值则暗示这同地壳或俯冲物质组分的卷入有关,且一系列构造环境判别图解也进一步印证了马拉苏组内的玄武岩应属似MORB基性熔岩。此外,两类岩石的高场强元素比值Zr/Nb、Hf/Ta同全球平均大洋中脊玄武岩的相应比值极为接近,反映了马拉苏组中基性火山岩的物质源区主体均为MORB地幔物质源区。La/Yb-Gd/Yb原始地幔标准化比值的模拟计算进一步显示了马拉苏组玄武安山岩与受改造(俯冲沉积物或地壳物质的混染)的石榴子石或尖晶石-石榴子石地幔橄榄岩物质源区的部分熔融作用有关,而似MORB型玄武岩则源自尖晶石地幔橄榄岩源区的部分熔融。结合区内同期的蛇绿岩、火山岩和碱性花岗岩的地球化学研究,我们可以进一步推断此类兼具有似MORB和弧火山岩地球化学特征的早泥盆世马拉苏火山岩应当是西准噶尔地块北部在早古生代受后期俯冲作用影响下经历弧后扩张形成的火山-岩浆地质记录。  相似文献   

"三江"北段昌都陆块晚三叠世钾质-超钾质火山岩成因及地质意义   总被引：1，自引：1，他引：0  

于峻川  莫宣学  喻学惠  朱弟成  李逸川  黄雄飞 《岩石学报》2014,30(11):3334-3344

昌都微陆块内部发育一套晚三叠世粗安岩.本文基于系统的野外踏勘,对具有代表性的火山岩进行岩石学、地球化学等研究.结果显示该区火山岩的SiO₂含量为51.36%~58.04%,全碱含量(Na₂O+K₂O)为5.03%~7.84%,根据岩石K₂O,MgO及K₂O/Na₂O比值判断,属钾质-超钾质火山岩,具高K、高Al、低Ti的特征.本区岩石强烈富集大离子亲石元素(LILE)和轻稀土元素(LREE),Nb、Ta、Ti的负异常明显,整体特征类似于弧火山岩.其稀土总量较高(270×10^-6~960×10^-6),轻重稀土分馏明显,重稀土分布形态较平缓.岩石具有较高的初始锶同位素比值(⁸⁷Sr/⁸⁶Sr)_i=0.7150~0.7176和较低的初始钕同位素比值(¹⁴³Nd/¹⁴⁴Nd)_i=0.51180~0.51184,ε_Nd(t)=-10.9~-10.2,二段Nd模式年龄为t_2DM=1.82~1.88Ga.本区岩石的地球化学特征显示其源区是由俯冲板片所产生的流体/熔体交代的岩石圈地幔,源区矿物组成分析结果显示,其源区以尖晶石二辉橄榄岩为主,含少量石榴石二辉橄榄岩及金云母.本区钾质-超钾质岩石虽然与西藏南部的钾质-超钾质岩石有相似的地球化学特征,但却产于碰撞后的构造背景之下.结合其所具有的弧火山岩特征及时代构造背景判断其为一种"滞后型"弧火山岩,其形成过程可以概括为三个阶段.  相似文献   

祁连东部西格拉高Sr/Y型花岗岩LA-ICP-MS锆石U-Pb定年及其地球化学特征     

秦海鹏  吴才来  王次松  李欣  雷敏  刘春花  李名则 《岩石学报》2014,30(12):3759-3771

西格拉花岗岩体位于祁连东部的米屈花岗岩带上,空间上呈NW-NWW向展布,岩体由花岗闪长岩-花岗岩-正长岩组成,主要岩性为花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明,西格拉花岗闪长岩存在两期岩浆作用,年龄分别为465.6±6.5Ma、443.2±4.8Ma,其中,前者与祁连洋俯冲极性发生转变的时限(~463Ma)相近,而后者与祁连洋闭合的时间(~445Ma)相似。早期淡色花岗闪长岩具正铕异常(δEu=2.44),晚期暗色花岗闪长岩则为弱负/正铕异常(δEu=0.94~1.32),两者均显示出高Si、Al,富Na贫K,富集Ba、Sr、LREE,高Sr/Y值,低Y、HREE含量,亏损HFSE(Nb、Ta、Ti、P)的特征,与Martin et al.(2005)划分的高硅埃达克岩(HSA)相似。其源区可能均残留石榴子石、普通角闪石及少量金红石,而斜长石则大量参与部分熔融过程,推测早期花岗闪长岩的源区深度可能超过50km;整体上,由早期→晚期反映出加厚地壳减薄、地幔组分贡献增强的趋势;两者可能均为加厚下地壳物质部分熔融的产物。  相似文献