河北围场御道口盆地流纹岩锆石U-Pb年龄、地球化学特征及其地质意义     

巫建华  宋凯  牛子良  郭恒飞  刘帅 《地质通报》2019,38(7):1191-1205

对河北省围场县御道口盆地流纹岩进行SHRIMP锆石U-Pb定年,结果表明,盆地内流纹岩的锆石206Pb/238U年龄加权平均值为155.2±2.0Ma,属于晚侏罗世早期岩浆活动的产物,与辽源地块新民组和燕山陆內造山带髫髻山组的地质时代一致。流纹岩分为灰白色流纹岩和肉红色流纹岩2种,均具有较高的SiO2、K2O、Al2O3含量和低的CaO、MgO含量,属高钾钙碱性系列,肉红色流纹岩的K2O/Na2O和Fe2O3/FeO值略高于灰白色流纹岩。流纹岩的稀土元素总量较高,轻、重稀土元素分馏明显,负Eu异常明显,具右倾轻稀土元素富集型稀土元素配分曲线特征;富集大离子亲石元素Rb、Th、U、Ga、Y和高场强元素Zr、Hf、Nb、Ta,亏损大离子亲石元素Ba、Sr,具有A2型花岗岩和低Sr-Ba流纹岩的微量元素特征,具有较高的(~(87)Sr/~(86)Sr)i值(0.708606~0.711171)、较低的εNd(t)值(-9.78~-7.11)、相对年轻的TDM2(1520~1737Ma)和较低的(~(206)Pb/~(204)Pb)t、(~(207)Pb/~(204)Pb)t、(~(208)Pb/~(204)Pb)t值,在εNd(t)-(~(87)Sr/~(86)Sr)i图解上投影点位于下地壳和亏损地幔之间,在(~(207)Pb/~(204)Pb)t-(~(206)Pb/~(204)Pb)t和(~(208)Pb/~(204)Pb)t-(~(206)Pb/~(204)Pb)t图解上投影点位于下地壳和地幔之间,指示流纹岩可能是DMM型(亏损型)地幔岩浆、EMⅠ富集地幔岩浆和少量古老下地壳物质混合形成的年轻下地壳部分熔融的产物。御道口盆地流纹岩的锶-钕-铅同位素特征与内蒙古基底隆起带的长英质火山-侵入岩基本一致,也与燕山陆內造山带的长英质火山-侵入岩相似,但不同于辽源地块的长英质火山-侵入岩。  相似文献   

河南新县花岗岩岩基的岩石成因、来源及对西大别构造演化的启示   总被引：2，自引：0，他引：2  

陈伟  徐兆文  李红超  杨小男  陈进全  王浩  王少华 《地质学报》2013,87(10):1510-1524

本文对新县花岗岩岩基进行了系统的锆石U-Pb定年,全岩元素地球化学、Sr-Nd-Pb-Hf同位素测试,研究探讨其成岩年龄、岩石成因、物质来源以及地球化学动力学背景。锆石U-Pb年龄为125.5±1.5Ma,属于早白垩世产物。全岩元素地球化学成分表现为高硅、富碱,贫镁、铁和钙,富集轻稀土元素、大离子亲石元素（Rb、K、Th、U）和Pb,亏损重稀土元素、高场强元素(Nb、Ta、Ti)和Sr、Ba。全岩同位素具有中等略偏高的Sr 初始比值(87Sr/86Sr)i=0.706949~0.707086;低的放射性Pb同位素组成[ (206Pb/204Pb)i=16.611～17.152,(207Pb/204Pb)i=15.304～15.432,(208Pb/204Pb)i=37.316～37.702]; 低的Nd初始比值（εNd(t)=-13.65～-13.51）和老的Nd模式年龄（TDM2=2.12～2.13Ga）。锆石原位Hf同位素具有较低的初始比值（εHf(t)=-22.92～-19.40）和老的Hf二阶段模式年龄（TDM2=2.39~2.61 Ga）。综合以上元素地球化学特征、锆石U-Pb定年结果及Sr-Nd-Pb-Hf同位素组成,新县花岗岩岩基应属于分异的高钾钙碱性I型花岗岩,是化学成分类似于扬子板块北缘新元古代TTG型岩浆岩的扬子下地壳在非加厚下地壳（深度小于35km）环境下部分熔融的产物。  相似文献   

湖南衡阳关帝庙花岗岩岩基形成时代及物质来源探讨   总被引：4，自引：0，他引：4  

赵增霞  徐兆文  缪柏虎  左昌虎  陆建军  路睿  陈进全 《地质学报》2015,89(7):1219-1230

在详细的野外地质调查基础上,本文通过对湖南省衡阳市关帝庙花岗岩岩基的岩石地球化学、LAICP-MS锆石U-Pb定年和全岩Sr-Nd-Pb同位素地球化学等综合研究,参照前人研究成果,探讨关帝庙花岗岩岩基的岩石地球化学性质、形成时代、物质来源以及形成机制。LA-ICP-MS锆石U-Pb加权平均年龄为223.4±1.9Ma。岩石以富硅、富碱、高钾钙碱性、准铝质,轻稀土元素和大离子亲石元素(Rb、Th、U、K)富集,重稀土元素、高场强元素(Nb、Ta、Ti)和Ba、Sr等元素亏损为特征。全岩Sr-Nd-Pb同位素显示较高的Sr初始比值((87Sr/86 Sr)i=0.712005~0.713631),低的Nd初始比值(εNd(t)=-9.95~-9.59),老的二阶段模式年龄(TDM2=1.78~1.81Ga)以及相对均一的Pb同位素组成,(206Pb/204 Pb)i、(207 Pb/204 Pb)i和(208 Pb/204 Pb)i值分别介于18.161~18.316、15.686~15.743、38.622~38.772之间。印支晚期,华南地区处于造山阶段的后碰撞构造环境挤压峰期之后的伸展环境,应力减弱或挤压松弛体制之下,幔源基性岩浆底侵,诱发古元古界地壳部分熔融形成花岗质岩浆,沿着断裂构造运移侵位,形成了关帝庙花岗岩岩基。  相似文献   

西藏措勤县德能铜多金属矿床石英闪长玢岩时代与成因：LA-ICP-MS锆石U-Pb年代学、地球化学和Sr-Nd-Pb同位素证据     

于玉帅  高原  杨竹森  田世洪  周云  张炜强 《地质学报》2018,92(7):1458-1473

为厘定德能铜多金属矿床侵入岩时代,查明岩石成因,本文利用LA-ICP-MS技术对德能铜多金属矿床石英闪长玢岩锆石进行了U-Th-Pb同位素测定,分析了岩石地球化学和Sr-Nd-Pb同位素。结果表明,石英闪长玢岩形成于早白垩世126.6±2.2~127.5±2.2Ma。岩石硅含量中等(平均58.58%),富碱(ALK平均6.53%),为高钾钙碱性花岗岩。稀土元素球粒陨石配分模式图右倾,(La/Yb)N为4.64~6.18。大离子亲石元素Rb、Th、K、Pb、Zr和Hf等富集,高场强元素Nb、Ta、P、Ti等亏损。206 Pb/204 Pb为18.629~18.771,207 Pb/204 Pb为15.690~15.738,208Pb/204 Pb为39.188~39.435。(87 Sr/86 Sr)i为0.709215~0.710463,(143 Nd/144 Nd)i为0.512044~0.512093,εNd(t)为-8.40~-7.45,TDM2为1524~1602Ma。上述分析结果表明,石英闪长玢岩为I型花岗岩,具岛弧岩浆活动特征,是向南俯冲的班公湖-怒江洋壳脱水,导致地幔楔发生熔融,幔源物质上涌引起中元古代下地壳物质发生部分熔融的产物。  相似文献   

内蒙古赤峰地区晚泥盆世双峰式火山岩地球化学特征与板内伸展事件   总被引：2，自引：0，他引：2       下载免费PDF全文

孙立新  张云  李影  张永  任邦方  张天福 《中国地质》2017,44(2):371-388

内蒙古赤峰敖汉旗一带的朝吐沟组火山岩由变玄武岩、变流纹岩组成,是一套典型的"双峰式"火山岩组合。采用LA-ICP-MS锆石U-Pb测年方法,获得了流纹岩的锆石206Pb/238U加权平均年龄分别为(359±1)Ma和(360±1)Ma,形成于晚泥盆世法门期。火山岩的Si O2含量分布在46.24%~56.6%和77.59%~85.75%,分别属于变玄武岩(玄武安山岩)和变流纹岩。变玄武岩(玄武安山岩)轻稀土元素弱富集而重稀土元素略亏损,(La/Yb)N=2.4~8.76,有弱Eu负异常,富集大离子亲石元素和高场强元素,Nb、Ta、Ti有明显负异常,87Sr/86Sr初始比值为0.705076~0.707770,具有高的正εNd(t)值(+0.51~+4.90)和年轻的模式年龄TDM(964~1090 Ma),推断其源于遭受地壳物质混染的亏损地幔;变流纹岩富硅、钾和钠,贫镁,具有轻稀土元素富集而重稀土元素略亏损,(La/Yb)N=7.07~11.07,有强烈的Eu负异常(δEu=0.12~0.43),Ti、P、Sr、Ba相对强烈亏损,Nb、Ta亏损,Rb、Th、U、K相对富集;其87Sr/86Sr初始比值为0.713757~0.739647,εNd(t)值为-1.75~+2.54),和年轻的模式年龄TDM(846~1156 Ma);多数锆石的εHf(t)为-2.3~+6.9,年轻的模式年龄TDM(707~1074 Ma),具有A型花岗岩的特征,推测其来源为新元古代时新生的年轻陆壳。综合前人区域研究成果、地球化学特征,朝吐沟组"双峰式"火山岩形成于晚泥盆世板内伸展构造背景。  相似文献   

粤北长塘盆地晚白垩世早期流纹岩的成因:地球化学和Sr-Nd-Pb-Hf-O同位素制约     

劳玉军  巫建华  徐勋胜 《岩矿测试》2016,35(5):558-567

长塘流纹岩为"大量流纹岩-少量玄武岩"构成的不对称双峰式火山岩组合的酸性端元,前人对年代学研究认为是目前华南识别的燕山期最年轻的流纹岩(SHRIMP年龄96.8 Ma),但在岩石地球化学特征及成因方面尚未深入研究。本文通过全岩主微量元素、Sr-Nd-Pb-O和锆石Hf同位素研究得到:流纹岩为亚碱性弱过铝质岩石,稀土元素富集,轻重稀土分馏明显,Eu负异常;具有较小的(~(87)Sr/~(86)Sr)_i、较高的εNd(t)和较低的(~(206)Pb/~(204)Pb)_i、(~(207)Pb/~(204)Pb)_i、(~(208)Pb/~(204)Pb)_i值;锆石的εHf(t)值较高且Hf模式年龄和全岩基本一致,均显示为新生下地壳岩浆;全岩的δ18O值较高。结合区域地质资料,本文认为长塘流纹岩是在晚白垩世早期拉张环境下,源于EMⅡ富集地幔的岩浆混染少量下地壳物质形成新元古代新生下地壳,发生熔融产生的岩浆在上升过程中经历结晶分异演化后喷出地表的产物。晚白垩世早期流纹岩成因对华南陆壳拉张减薄到正常厚度时间节点提供了证据。  相似文献   

吉林东南部晚中生代中酸性火山作用成因的地球化学制约   总被引：4，自引：1，他引：3  

李超文  郭锋  赵亮  李红霞 《岩石学报》2010,26(4):1074-1088

详细的主、微量元素和Sr-Nd-Pb同位素研究结果显示,延吉地区晚中生代(早白垩世)中酸性火山岩具有岛弧型微量元素特征(富集轻稀土(LREE)、大离子亲石元素(LILE)和亏损高场强元素(HFSE)),和中等放射成因Sr、Pb及类似于硅质地球的Nd同位素组成(~(87)Sr/~(86)Sr(i)=0.70437～0.70525;~(206)Pb/~(204)Pb(i)=18.19～18.37,~(207)Pb/~(204)Pb(i)=15.54～15.57,~(208)Pb/~(204)Pb(i)=38.13～38.22;ε_(Nd)(t)=-2.75～+1.61)。其Sr-Nd-Pb同位素组成特征类似于区域同期基性火山岩和大兴安岭地区同时代火山岩。这些广泛分布于吉林南部的晚中生代中酸性火山岩是岩石圈地幔来源岩浆经分离结晶或地壳物质混染/AFC过程的产物。吉林省东南部晚中生代不同区域火山岩的Sr-Nd-Pb同位素对比结果显示,辽源-延吉与通化地区分属不同构造单元,其中辽源-延吉一带则为中亚造山带的东段,而通化地区为华北克拉通的一部分,夹皮沟-松江断裂可能是华北克拉通东北缘的边界。  相似文献   

滇东师宗-弥勒带北段基性火山岩地球化学及其对华南大陆构造格局的制约   总被引：7，自引：0，他引：7  

董云鹏  朱炳泉  常向阳  张国伟 《岩石学报》2002,18(1)

滇东地区的师宗-弥勒构造带是解决古特提斯东延问题的关键,综合研究表明,该带是以多条断层为骨架,包容不同性质构造岩块的构造带.明显分隔两侧不同岩石-构造组合、变质作用、岩浆活动.师宗-弥勒构造带北段的火山岩地球化学研究表明,其主要为碱性玄武岩,主元素以低TiO2、高Al2O3为特征,区别于高TiO2、低Al2O3特征的峨眉山大陆溢流玄武岩.高场强元素丰度类似于板内玄武岩平均丰度,Zr/Nb、Hf/Th值分别变化在5.6～13.5和0.9～1.3范围内,类似于板内玄武岩.球粒陨石标准化的稀土元素配分模式为LREE富集型,MORB标准化的微量元素配分型式为大隆起型,显示岩浆形成于板内裂谷构造环境.不活动元素协变关系也支持这一结论.同位素地球化学研究表明,岩石以低143Nd/144Nd、高87Sr/86Sr值为特征,类似于Rio Grande裂谷玄武岩的同位素组成,εNd(t) 值变化在+0.9～+3. 2之间,显示岩浆源于轻微亏损地幔,并受到富集地幔物质影响. (206Pb/204Pb)i、(207Pb/204Pb)i 和(208Pb/204Pb)i 分别变化在17.131～19.119, 15.386～15.670 和 37.780～39.266之间,(206Pb/204Pb)i 和(207Pb/204Pb)i 具有正相关关系. Δ206Pb/204Pb 和Δ207Pb/204Pb 分别变化在 5～24 和 21～61之间, 显示本次研究的玄武岩来源于DMM和 EMII混合组成的地幔,明显区别于具EMI特征的峨眉山玄武岩.地质、地球化学及年代学综合分析研究表明,滇东师宗-弥勒带北段的基性火山岩形成于晚古生代裂谷构造环境,指示华南大陆内部存在连通滇西特提斯的裂谷型深水海道.  相似文献   

黑龙江三矿沟铁铜矿床花岗闪长岩锆石U-Pb定年、岩石成因及构造意义   总被引：13，自引：4，他引：9  

褚少雄  刘建明  徐九华  魏浩  柴辉  佟匡胤 《岩石学报》2012,28(2):433-450

黑龙江三矿沟Fe-Cu矿床是中亚造山带东段大兴安岭北部裸河-多宝山-三矿沟NW向成矿带中矽卡岩型矿床的典型代表。LA-ICP-MS锆石U-Pb年代学表明,与成矿密切相关的黑云母花岗闪长岩的锆石谐和年龄和238U/206Pb加权平均年岭分别为175.9±1.6Ma和175.9±1.1Ma,二者在误差范围内具有良好的一致性,表明多宝山成矿区在早侏罗世晚期存在一期重要的岩浆-热液成矿事件。三矿沟花岗闪长岩的元素地球化学特征具有岛弧岩浆岩的地球化学亲缘性:岩石富钠(Na2O/K2O=1.39～1.59),准铝质(A/CNK=0.87～0.91),富集轻稀土元素(LREE),(La/Yb)N=8.02～10.45,Eu显示弱负异常(δEu=0.82～0.98),富集大离子亲石元素(LILE,如Rb、Ba、K)和元素地球化学性质活泼的不相容元素(U、Th、Pb),相对亏损高场强元素(HFSE,如Nb、Ta、Zr、Hf、Ti)。Sr-Nd-Pb同位素分析结果表明:三矿沟花岗闪长岩具有低的Sr同位素初始比值((87Sr/86Sr)i=0.7041～0.7045)、高的Nd同位素初始比值((143Nd/144Nd)i=0.512556～0.512576)、正的εNd(t)值(2.8～3.9)、年轻的二阶段亏损地幔模式年龄(tDM2=647～733Ma)和幔源铅同位素组成特征((206Pb/204Pb)t=18.121～18.418;(207Pb/204Pb)t=15.480～15.511;(208Pb/204Pb)t=37.628～37.713),上述同位素地球化学特征均显示花岗闪长质岩浆主要源于亏损地幔源区。结合东北地区区域构造演化和岩体微量元素及同位素组成特征反映该矿床形成于岛弧的构造背景,其形成可能与侏罗纪古太平洋板块的俯冲作用密切相关。  相似文献   

西准噶尔哈拉阿拉特山一带晚石炭世赞岐岩的发现及其地质意义     

李甘雨  李永军  王冉  杨高学  向坤鹏  刘佳  佟丽莉 《岩石学报》2017,33(1):16-30

西准噶尔哈拉阿拉特山一带广泛分布晚石炭世玄武安山岩、辉石安山岩,属钙碱性系列,岩石具有较高的SiO_2(52.88%~56.89%)、MgO(3.47%~6.88%,Mg#为48.5~63.7)、Sr(442×10~(-6)~970×10~(-6))、Ba(199×10~(-6)~796×10~(-6))含量,K/Na为0.22~0.70,P_2O_5变化范围较大(0.18%~0.52%),富集大离子亲石元素和轻稀土元素((La/Yb)N为1.88~15.9),亏损Nb、Ta、Hf等高场强元素和重稀土元素,弱负Eu异常(δEu=0.77~0.94),(87Sr/86Sr)i=0.70366~0.70409,(~(143)Nd/~(144)Nd)i=0.51247~0.512564,εNd(t)=4.41~6.19,~(206)Pb/~(204)Pb=18.220~18.405,~(207)Pb/~(204)Pb=15.482~15.522,~(208)Pb/~(204)Pb=37.991~38.296,与典型赞岐岩地球化学特征一致。该赞岐岩的厘定,为研究西准噶尔构造演化提供了新的思路,约束了本区残余洋盆的闭合时限并非前人确立的早石炭世,而应延迟至晚石炭世末期。  相似文献   

The petrogenesis of group 2 ultrapotassic kimberlites from Finsch Mine, South Africa     

K. J. Fraser  C. J. Hawkesworth   《Lithos》1992,28(3-6):327-345

Major, trace element and radiogenic isotope results are presented for a suite of hypabyssal kimberlites from a single pipe, at the Finsch Mine, South Africa. These are Group 2 kimberlites characterised by abundant phlogopite ± serpentine ± diopside; they are ultrabasic (SiO₂ < 42 wt.%%) and ultrapotassic (K₂O/Na₂O > 6.9) igneous rocks, they exhibit a wide range in major element chemistry with SiO₂ = 27.6−41.9 wt. % and MgO = 10.4−33.4 wt. %. (⁸⁷Sr/⁸⁶Sr)_i=0.7089 to 0.7106, ε_{Nd is} −6.2 to −9.7 and they have unradiogenic (²⁰⁷Pb/²⁰⁴Pb)_i contents which ensure that they plot below the Pb-ore growth curve. They have high incompatible and compatible element contents, a striking positive array between Y and Nb which indicates that garnet was not involved in the within suite differentiation processes, and a negative trend between K/Nb and Nb contents which suggests that phlogopite was involved. In addition, some elements exhibit an unexpected order of relative incompatibility for different trace elements which suggests that the intra-kimberlite variations are not primarily due to variations in the degree of partial melting. The effects of fractional crystallization are difficult to establish because for the most part they have been masked by the entrainment of 50–60% mantle peridotite. Thus, the Finsch kimberlites are interpreted as mixtures of a melt component and entrained garnet peridotite, with no evidence for significant contamination with crustal material. The melt component was characterised by high incompatible element contents, which require both very small degrees of partial melting, and source regions with higher incompatible element contents than depleted or primitive mantle. Since the melt component was the principal source of incompatible elements in the kimberlite magma, the enriched Nd, Sr and Pb isotope ratios of the kimberlite are characteristic of the melt source region. The melt fractions were therefore derived from ancient, trace elements enriched portions of the upper mantle, most probably situated within the sub-continental mantle lithosphere, and different from the low ⁸⁷Sr/⁸⁶Sr garnet peridotite xenoliths found at Finsch. Within the sub-continental mantle lithosphere old, incompatible element enriched source regions for the kimberlite melt fraction are inferred to have been overlain by depleted mantle material which became entrained in the kimberlite magma.  相似文献   

松辽盆地徐家围子断陷营城组粗面岩成因与隐爆机制     

孟凡超  刘嘉麒  崔岩 《吉林大学学报(地球科学版)》2013,43(3):704-715

松辽盆地徐家围子断陷营城组火山岩中含有粗面质岩石,是深层天然气重要储层之一。岩心、钻井及地震资料研究表明,粗面岩具有高位喷发、低位充填的特征,在火山口附近厚度大,远离火山口厚度小。粗面岩主量、微量及同位素地球化学显示其属于钾玄岩系列,富集稀土元素,强不相容元素Rb、Ba、Th、U质量分数较高。粗面岩的(⁸⁷Sr/⁸⁶Sr)_i=0.704 321~0.705 395,ε_Nd(t)为正值（3.36 ~ 3.83）,Pb同位素比值相对集中,(²⁰⁶Pb/²⁰⁴Pb)_i、(²⁰⁷Pb/²⁰⁴Pb)_i、(²⁰⁸Pb/²⁰⁴Pb)_i平均值分别为18.43、15.51和38.23。研究表明,粗面质岩浆由区域年轻地壳组分部分熔融形成,经历了一定程度的分离结晶作用,地壳混染作用不显著。粗面质岩浆多期次喷发后形成粗面岩,热液气体不断聚集发生隐蔽爆破形成角砾,未固结的角砾被岩浆期后热液“胶结”,形成隐爆角砾岩,构成了粗面质岩石重要的储层类型。  相似文献   

Geochemical and isotope data from the Acatlán Volcanic Field, western Trans-Mexican Volcanic Belt: Origin and evolution     

Guadalupe Maldonado-Snchez  Peter Schaaf 《Lithos》2005,82(3-4):455-470

The Quaternary Acatlán Volcanic Field (AVF) is located at the western edge of the Trans-Mexican Volcanic Belt (TMVB). This region is related to the subduction of the Pacific Cocos and Rivera plates beneath the North American plate since the late Miocene. AVF rocks are products of Pleistocene volcanic activity and include lava flows, domes, erupted basaltic andesite, trachyandesite, trachydacite, and rhyolite of calc–alkaline affinity. Most rocks show depletion in high field-strength elements and enrichment in large ion lithophile elements and light rare earth elements as is typical for magmas in subduction-related volcanic arcs. ⁸⁷Sr/⁸⁶Sr values range from 0.70361 to 0.70412, while Nd values vary from +2.3 to +5.2. Sr–Nd isotopic data plot along the mantle array. On the other hand, lead isotope compositions (²⁰⁶Pb/²⁰⁴Pb=18.62–18.75, ²⁰⁷Pb/²⁰⁴Pb=15.57–15.64, and ²⁰⁸Pb/²⁰⁴Pb=38.37–38.67) give evidence for combined influences of the upper mantle, fluxes derived from subducted sediments, and the upper continental crust involved in magma genesis at AVF. Additionally δ¹⁸O whole rock analyses range from +6.35‰ in black pumice to +10.9‰ in white pumice of the Acatlán Ignimbrite. A fairly good correlation is displayed between Sr as well as O isotopes and SiO₂ emphasizing the effects of crustal contamination. Compositional and isotopic data suggest that the different AVF series derived from distinct parental magmas, which were generated by partial melting of a heterogeneous mantle source.  相似文献   

Geochemical constraints on the origin of Mesozoic alkaline intrusive complexes from the North China Craton and tectonic implications   总被引：28，自引：0，他引：28  

Hong-Fu Zhang  Min Sun  Xin-Hua Zhou  Ji-Feng Ying 《Lithos》2005,81(1-4):297-317

Mesozoic alkaline intrusive complexes are widespread in the southern portion of the North China Craton and can provide some important constraints on the evolution of the Mesozoic lithosphere beneath the region. Three selected intrusive complexes (Tongshi, Hongshan, and Longbaoshan) are generally high in alkalis (K₂O+Na₂O=913 wt.%) and Al₂O₃ (1421.6 wt.%) and low in CaO and TiO₂ (<0.6 wt.%), with high and variable SiO₂ contents. Rocks from these complexes are all enriched in LREE and LILE (Cs, Rb, Ba, U, Th), depleted in Nb and Ti, have a highly positive Pb anomaly, and are characterized by lack of a clear Eu anomaly despite trace element abundances and isotopic ratios that vary greatly between complexes. The Tongshi complex has high Cs (2.68.5 ppm) and REE abundances (∑REE=112.6297 ppm, (La/Yb)_N=13.130.9) and MORB-like Sr–Nd–Pb isotopic ratios ((⁸⁷Sr/⁸⁶Sr)_i<0.704; ε_Nd>0; (²⁰⁶Pb/²⁰⁴Pb)_i>18). The Hongshan complex has low REE concentrations (∑REE=28.2118.7 ppm, (La/Yb)_N=4.614.7) and is moderately enriched as demonstrated by their Sr–Nd isotopic ratios ((⁸⁷Sr/⁸⁶Sr)_i>0.706; ε_Nd<−7). The Longbaoshan complex is extremely REE enriched (∑REE=211.3392.6 ppm, (La/Yb)_N=32.460.9) and has an EM2-like Sr–Nd isotopic character ((⁸⁷Sr/⁸⁶Sr)_i>0.7078; ε_Nd<−11). We suggest that the Tongshi complex originated from the asthenosphere and the Hongshan complex and the Longbaoshan complex were derived from the partial melting of previously subduction-modified lithospheric mantle, in response to post-collisional lithospheric extension and asthenospheric upwelling. The occurrence of these alkaline intrusive complexes demonstrates that the lithosphere beneath the region must have been considerably thinned at the time of intrusion of these complexes. This study also shed light on the temporal evolution of the Mesozoic lithosphere and the timing of the lithospheric thinning.  相似文献   

鄂东南地区程潮大型矽卡岩型铁矿区岩体成因探讨   总被引：2，自引：0，他引：2  

李伟  谢桂青  姚磊  朱乔乔  孙洪涛  王建  王小雨 《吉林大学学报(地球科学版)》2014,44(6):1827-1855

湖北程潮铁矿是鄂东南矿集区内最大的矽卡岩型铁矿床。为了系统研究矿区内不同侵入体的成因,对程潮矿区内不同时代的侵入体进行了矿物学、地球化学和Sr-Nd-Pb同位素研究。矿区内花岗岩、石英二长斑岩、闪长岩中的黑云母成分特征暗示它们均为壳幔物质混合成因的镁质黑云母;与成矿相关的花岗岩、石英二长斑岩中原生黑云母矿物学成分显示出原始岩浆具有高氧逸度的特征,高氧逸度为磁铁矿的形成提供了有利条件。岩石地球化学特征研究表明,不同类型的岩石都具有富钾和准铝质的特征,富集Rb、Ba、K等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti等高场强元素。矿区岩石的(⁸⁷Sr/⁸⁶Sr)_i值为0.705 0~0.709 1,ε_Nd(t)值为-14.16~-6.95,²⁰⁶Pb/²⁰⁴Pb值为17.636~18.919,²⁰⁷Pb/²⁰⁴Pb值为15.451~15.613,²⁰⁸Pb/²⁰⁴Pb值为37.833~39.556。矿物学、地球化学、Sr-Nd-Pb同位素特征暗示矿区岩体为富集地幔发生部分熔融并同化混染了不同比例下地壳物质的产物,早期闪长岩（（140±1） Ma）比晚期花岗岩和石英二长斑岩（（128±1） Ma）的源区有更多的地幔成分,花岗岩和石英二长斑岩与闪长岩具有相近的锆石饱和温度（平均值分别为783、788、765℃）。  相似文献   

Geochemistry and Sr, Nd, Pb isotopic composition of the Central Atlantic Magmatic Province (CAMP) in Guyana and Guinea   总被引：2，自引：0，他引：2  

Katja Deckart  Herv Bertrand  Jean-Paul Ligeois 《Lithos》2005,82(3-4):289-314

The Central Atlantic Magmatic Province (CAMP) is one of the largest igneous provinces on Earth, extending more than 5000 km north to south, on both sides of the Atlantic Ocean. Its emplacement occurred about 200 Ma ago, at the Triassic–Jurassic boundary, and is linked to the initial breakup of Pangaea. Two areas of the province are studied here: French Guyana/Surinam (South America) and Guinea (West Africa), in order to document the petrogenesis and geodynamical significance of high-Ti and low-Ti basaltic magmas from the CAMP.

In Guyana, doleritic and gabbroic dykes are located on the edge of the Guiana Shield, and represent limited volumes of magma. They display low SiO₂ (47–50%), high TiO₂ (2.5–3.5%) and high FeO tholeiitic trends and show variably enriched trace element patterns ((La/Yb)_n=1.5–5.1). Their isotopic signature and ratios of very incompatible elements (εNd_i=+5.8 to +4.2, (⁸⁷Sr/⁸⁶Sr)_i=0.703–0.705, (²⁰⁷Pb/²⁰⁴Pb)_i=15.46–15.64) match a depleted PREMA (prevalent mantle)-like source. Their genesis can be modeled by ca. 15% partial melting of a lherzolite source, and a subsequent limited fractional crystallization (5–10%) or a slight upper crustal assimilation–fractional crystallization (AFC, r=0.1, Proterozoic contaminant). In Guinea, in contrast, huge volumes of CAMP magmas were intruded along the Rockelides suture and the West African craton, forming the Fouta Djalon sills and the Kakoulima laccolith. The laccolith is more than 1000 m thick. These features consist of gabbros, dolerites, diorites and mafic (gabbro) and ultramafic (dunite, wherlite) cumulates. Guinean tholeiites show high SiO₂ (51–58%), low TiO₂ (0.7–1.2%) and FeO trends, with high LILE/HFSE ratios and slight negative Nb–Ta anomalies. Isotopic signatures (εNd_i=+0.4 to −5.3, (⁸⁷Sr/⁸⁶Sr)_i=0.705–0.710, (²⁰⁷Pb/²⁰⁴Pb)_i=15.57–15.66) indicate a more enriched source than for Guyana as well as a higher rate of magma–upper crust interaction through an AFC process (r=0.3, Birimian crust contaminant) and, probably, an additional upper crustal contamination for the most differentiated sample.

This geochemical study supports the prevalence in Guinea, as for other low-Ti CAMP tholeiites, of a lithospheric mantle source, previously enriched during ancient subduction events, and preferentially reactivated in late Triassic times by edge-driven convection between cratonic and mobile belt domains. A larger contribution from a depleted asthenospheric source is required to generate high-Ti tholeiites in Guyana, which may reflect the development of CAMP rifting towards the initiation of the Central Atlantic oceanic crust.  相似文献   

Spinel-facies mantle xenoliths from Cerro Redondo, Argentine Patagonia: Petrographic, geochemical, and isotopic evidence of interaction between xenoliths and host basalt   总被引：1，自引：0，他引：1  

M. Schilling  R.V. Conceio  G. Mallmann  E. Koester  K. Kawashita  F. Herv  D. Morata  A. Motoki 《Lithos》2005,82(3-4):485-502

Cerro Redondo is an ancient cinder cone now almost completely eroded, sited over a sill that corresponds to a sub-volcanic magma chamber, in Santa Cruz province, Patagonia, Argentina. It is composed of Pliocene-Pleistocene alkaline basalt containing spinel-facies lherzolite and harzburgite mantle xenoliths. Core compositions of pyroxenes indicate temperatures of 823 °C to 1043 °C and pressures of 12.4 kb to 21.4 kb. Based on P–T estimates, petrographic, geochemical, and isotopic characteristics, we propose that Cerro Redondo xenoliths come from a thick homogeneous mantle column (36 km to 63 km depth), and present different degrees of basalt infiltration. A simple mixing model based on Sr isotopes was used to quantify the host basalt infiltration, and contamination values of 0.0%, 0.2%, 3%, and 12% were obtained for samples X-F, X-D, X-C, and X-B, respectively. For unknown reasons, samples X-G and X-E suffered selective isotopic and trace element modification, respectively, associated with 1% of basalt infiltration. Sample X-F best represents the sub-continental lithospheric mantle column, conserving primary equilibrium textures with sharp grain boundaries, and having TiO₂, CaO, Na₂O, K₂O, and P₂O₅ contents lower than average spinel lherzolite, flat chondrite-normalized REE pattern, and ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of 0.70519 and 0.51297, respectively. This sample records a decoupling of the Sr–Nd system where Sr ratios increase at constant Nd ratios, possibly caused by chromatographic processes. Its ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios are 17.987, 15.556, and 37.959, respectively. As the interaction with the host basalt increases, xenoliths show a gradual increase of disequilibrium textures such as reaction rims and exsolution lamellae in orthopyroxene and clinopyroxene, and increase of TiO₂, CaO, Al₂O₃, Na₂O, K₂O, P₂O₅, LREE, and incompatible element concentrations. The Sr–Nd system shows an unusual positive trend from the unmodified sample X-F toward the host basalt isotope composition with ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of 0.70447 and 0.51279, respectively, while ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios tend to increase toward those of the host basalt (18.424, 15.648, and 38.728, respectively) as the xenolith–basalt interaction increases. The basalt–xenolith reaction probably started during the transport of the xenoliths to the surface, and continued during the residence of xenoliths in the sub-volcanic magma chamber of Cerro Redondo.  相似文献   

浙江建德新生代玄武岩源区特征及其成因     

何叶  陈立辉  曾罡  王小均 《高校地质学报》2020,26(3):241-254

中国东南部浙江境内分布有大量新生代板内玄武岩，这些玄武岩的分布受到三条北东—南西向的断裂控制，将浙江玄武岩分为西部、中部、东部三个区域。其中，出露于浙江西部江山-绍兴断裂带的建德玄武岩是浙江境内最古老的新生代玄武岩（约40 Ma）。为进一步认识浙江境内新生代岩浆作用的本质，测定了建德玄武岩的元素组成和Sr、Nd、Hf、Pb同位素组成，并在与浙江境内其它新生代玄武岩对比的基础上，探讨它们之间的成因联系。建德玄武岩为碧玄岩，与浙江西部其它新生代玄武岩一样，碱性程度明显高于浙江中部和东部的新生代玄武岩（以弱碱性的碱性橄榄玄武岩和拉斑玄武岩为主）。这些玄武岩具有较低的SiO₂ (41.3~42.3 wt%）和Al₂O₃（9.70~12.6 wt%）含量，较高的MgO（8.90~15.6 wt%）、CaO（8.92~12.1 wt%）、TiO₂（2.78~3.18 wt%）和Fe₂O₃^T（14.1~16.2 wt%）含量以及较高的Ca/Al（1.02~1.16）比值。不相容微量元素组成上与火成碳酸岩具有亲缘性，即蛛网图上表现为明显的K、Zr、Hf、Ti的负异常（Hf/Hf*=0.74~0.77, Ti/Ti*=0.70~0.74），同时具有高的Zr/Hf比值（48.5~50.1），表明其地幔源区含有碳酸盐组分。建德玄武岩具有亏损的Sr-Nd-Hf同位素组成（⁸⁷Sr/⁸⁶Sr=0.7032~0.7034, εNd=5.85~5.95, εHf=7.78~8.56）和较高的²⁰⁶Pb/²⁰⁴Pb（18.491~18.554）、²⁰⁷Pb/²⁰⁴Pb（15.488~15.518）和²⁰⁸Pb/²⁰⁴Pb（38.387~38.523）比值。相比浙江中部和东部玄武岩，浙江西部玄武岩及建德玄武岩具有更高的碱含量、不相容微量元素含量、La/Yb比值和更明显的K、Zr、Hf、Ti负异常，表明浙江西部玄武岩是碳酸盐化地幔低程度熔融的产物。浙江新生代玄武岩的Ti/Ti*与Ba/Th、K/La比值之间较好的正相关性表明其源区存在两端元混合的特征。其中，以浙江西部玄武岩（包括建德玄武岩）为代表的地幔端元是由含碳酸盐的再循环洋壳熔融产生的碳酸盐熔体与亏损地幔反应形成的碳酸盐化地幔，以较低的Ba/Th、K/La和Ti/Ti*比值为特征。以浙江东部玄武岩为代表的地幔端元具有和碳酸盐化地幔端元互补的、较高的Ba/Th、K/La和Ti/Ti*比值，代表熔融残余的再循环洋壳。因此，浙江新生代玄武岩的地幔源区是不均一的，这种不均一性主要是由具有成因联系的两种端元组分所控制。  相似文献   

Origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in Beiya area, western Yunnan, China   总被引：6，自引：0，他引：6  

Xing-Wang Xu  Bao-Lin Zhang  Ke-Zhang Qin  Qian Mao  Xin-Ping Cai 《Lithos》2007,99(3-4):339-362

Lamprophyres consisting mainly of diopside, phlogopite and K-feldspar formed in the early Tertiary around 60 Ma in the Beiya area and are characterized by low SiO₂ ± 46–50 wt.%), Rb (31–45 ppm) and Sr (225–262 ppm), high Al₂O₃, (11.2–13.1 wt.%), CaO (8.0–8.7 wt.%), MgO (11.5–12.1 wt.%), K₂O(4.9–5.5 wt.%), TiO₂ (2.9–3.3 wt.%) and REE (174–177 ppm), and compatible elements (e.g. Sc, Cr and Ni) and HSF elements (e.g. Th, U, Zr, Nb, Ta, Ti and Y), and low ¹⁴³Nd/¹⁴⁴Nd 0.512372–0.512536, middle ⁸⁷Sr/⁸⁶Sr 0.707322–0.707395, middle ²⁰⁶Pb/²⁰⁴Pb 18.50–18.59, ²⁰⁷Pb/²⁰⁴Pb 15.60–15.65 and ²⁰⁸Pb/²⁰⁴Pb 38.75–38.8. These rocks developed peculiar quartz megacrysts with poly-layer reaction zones, melt inclusions, and partial melted K-feldspar and plagioclase inclusions, and plastic shapes. Important features of these rocks include: (1) hybrid composition of elements, (2) abrupt increase of SiO₂ content of the melt, recorded by zoned diopside, (3) development of sanidine and aegirine-augite reaction zones, (4) alkaline melt and partial melted K-feldspar and plagioclase inclusions, (5) deformed quartz inclusions associated with quartz megacrysts, (6) the presence of quartz megacrysts in plastic shape with their parent melts, (7) the occurrence of olivine, high-MgO ilmenite and spinel inclusions within earlier formed diopside, phlogopite and magnetite. Median ⁸⁷Sr/⁸⁶Sr values between Tertiary alkaline porphyries in the Beiya area and the western Yunnan and Tertiary basalt in the western Yunnan indicate that the Beiya lamprophyre melts were derivative and resulted from the mixing between basic melts that were related to the partial melting of phenocrysts of spinel iherzolite from a mantle source. The alkaline melts originated from partial melting along the Jinshajiang subduction ductile shear zone at the contact between the buried Palaeo-Tethyan oceanic lithosphere and the upper mantle lithosphere. The alkaline melts are composed of 65% sanidine (Or₇₀Ab₂₈An₂) and 35% SiO₂. The melt mixing occurred in magma chambers in the middle-shallow crust at 8–10 km before the derivative lamprophyre melts intruded into the shallow cover in Beiya area. This mixing of basic and alkaline melts might represent a general process for the formation of lamprophyre in the western Yunnan.  相似文献   

Early Cretaceous gabbroic rocks from the Taihang Mountains: Implications for a paleosubduction-related lithospheric mantle beneath the central North China Craton   总被引：20，自引：0，他引：20  

Yuejun Wang  Weiming Fan  Hongfu Zhang  Touping Peng 《Lithos》2006,86(3-4):281-302

SHRIMP zircon U–Pb ages and geochemical and Sr–Nd–Pb isotopic data are presented for the gabbroic intrusive from the southern Taihang Mountains to characterize the nature of the Mesozoic lithospheric mantle beneath the central North China Craton (NCC). The gabbroic rocks emplaced at 125 Ma and are composed of plagioclase (40–50%), amphibole (20–30%), clinopyroxene (10–15%), olivine (5–10%) and biotite (5–7%). Olivines have high MgO (Fo = 78–85) and NiO content. Clinopyroxenes are high in MgO and CaO with the dominant ones having the formula of En_42–46Wo_41–50Fs_8–13. Plagioclases are dominantly andesine–labradorite (An = 46–78%) and have normal zonation from bytownite in the core to andesine in the rim. Amphiboles are mainly magnesio and actinolitic hornblende, distinct from those in the Precambrian high-pressure granulites of the NCC. These gabbroic rocks are characterized by high MgO (9.0–11.04%) and SiO₂ (52.66–55.52%), and low Al₂O₃, FeOt and TiO₂, and could be classified as high-mg basaltic andesites. They are enriched in LILEs and LREEs, depleted in HFSEs and HREEs, and exhibit (⁸⁷Sr/⁸⁶Sr)_i = 0.70492–0.70539, ε_Nd(t) = − 12.47–15.07, (²⁰⁶Pb/²⁰⁴Pb)_i = 16.63–17.10, Δ8/4 = 70.1–107.2 and Δ7/4 = − 2.1 to − 9.4, i.e., an EMI-like isotopic signatures. Such geochemical features indicate that these early Cretaceous gabbroic rocks were originated from a refractory pyroxenitic veined-plus-peridotite source previously modified by an SiO₂-rich melt that may have been derived from Paleoproterozoic subducted crustal materials. Late Mesozoic lithospheric extension might have induced the melting of the metasomatised lithospheric mantle in response to the upwelling of the asthenosphere to generate these gabbroic rocks in the southern Taihang Mountains.  相似文献