安徽宣城荞麦山矿床成矿岩体及其暗色包体成因与成矿意义:锆石U-Pb年代学、地球化学、Sr-Nd-Hf-O同位素制约

宣城矿集区是长江中下游成矿带内新提出的矿集区,近年来取得了重大的找矿突破,尤其是大型斑岩型铜金矿的发现使宣城矿集区逐渐成为研究热点。宣城矿集区一系列的斑岩-矽卡岩矿床均与早白垩世侵入体密切相关。荞麦山铜钨矿床是区内典型的矽卡岩矿床,矿床形成与花岗闪长斑岩密切相关,且花岗闪长斑岩发育较多的暗色包体。确定暗色包体的成因有助于深入理解含矿岩体的岩浆演化过程及成矿意义。本次工作以荞麦山矿床花岗闪长斑岩和暗色包体作为研究对象进行U-Pb同位素年代学、岩石及矿物地球化学、全岩Sr-Nd、锆石Hf-O同位素地球化学分析,探讨暗色包体及成矿岩体的源区、岩浆演化过程及其对成矿的意义。暗色包体的形成时代为141Ma（MSWD=0.8）,（⁸⁷Sr/⁸⁶Sr）_i值为0.7059~0.7069,ε_Nd（t）值为-6.0~-9.2,ε_Hf（t）值为-12.7~-5.8,δ¹⁸O值为5.8‰~7.7‰;寄主岩石形成时代为140Ma（MSWD=0.3）,（⁸⁷Sr/⁸⁶Sr）_i值为0.7061~0.7064,ε_Nd（t）值为-8.7~-7.7,ε_Hf（t）值为-12.1~-8.1,δ¹⁸O值为5.6‰~7.4‰。此外,暗色包体与寄主岩石主要氧化物含量与SiO₂含量呈线性负相关趋势、微量元素特征相似和寄主岩石斜长石斑晶的不平衡结构及捕掳晶的发现指示荞麦山暗色包体为岩浆混合成因,花岗闪长斑岩为起源于富集地幔的岩浆与壳源岩浆混合成的母岩浆侵位而来,同时幔源岩浆和壳源岩浆的混合也分别提供了成矿金属元素铜和钨,最终形成了铜钨共生的荞麦山矿床。     

皖南旌德花岗闪长岩与暗色包体的成因: 地球化学、锆石U-Pb年代学与Hf同位素制约

旌德复式岩体位于安徽南部,主体相花岗闪长岩中发育暗色包体。本文对花岗闪长岩与暗色包体进行了岩相学观察、全岩主微量元素分析、锆石U-Pb定年与Hf同位素测试。岩相学观察发现暗色包体为典型岩浆岩结构,且发育针状磷灰石。主量元素分析数据表明花岗闪长岩的SiO₂含量为66.04%~67.80%;暗色包体的SiO₂含量为54.63%~54.77%,为二长闪长岩。花岗闪长岩的Mg^#=38~40;暗色包体的Mg^#=44~45。微量元素分析数据表明花岗闪长岩与暗色包体的REE球粒陨石标准化图呈右倾型,Eu负异常;大离子亲石元素富集,高场强元素亏损。锆石U-Pb年代学与Hf同位素研究表明,花岗闪长岩与暗色包体的年龄分别为139.7±1.3Ma和142.3±1.7Ma,在误差范围内一致。花岗闪长岩锆石的ε_Hf(t)为-2.5~0.4,地壳模式年龄(t_DM^C)为1170~1350Ma;暗色包体锆石的ε_Hf(t)为-5.2~1.8,地壳模式年龄(t_DM^C)为1090~1530Ma。两者的t_DM^C峰值都在1.2~1.3Ga。这些数据表明花岗闪长岩中的暗色包体为同源岩浆混合成因,源区为年轻地壳,有可能为中新元古代古华南洋壳俯冲扬子板块形成的火山岛弧。旌德花岗闪长岩在Pearce et al.(1984)的构造判别图上落在岛弧花岗岩区。在Sr/Y-Y图解上落在经典岛弧岩浆岩区。花岗闪长岩的岩浆Zr饱和温度低(630~680℃),与锆石钛温度计(630~720℃)给出的结果基本一致。锆石的Ce(Ⅳ)/Ce(Ⅲ)高(240~530),指示岩浆具有高的氧逸度。旌德岩体的低温与高氧逸度特征说明岩体的源区物质受到过洋壳俯冲的影响。旌德岩体的成因可能与太平洋板块后撤诱发的地壳部分熔融有关。     

粤北白沙地区晚侏罗世高分异I型细粒花岗岩年代学、地球化学特征及其地质意义

受东西向佛冈-丰良断裂控制的佛冈复式岩体形成于多期次和不同来源的岩浆侵入作用。白沙地区细粒黑云母二长花岗岩体位于佛冈岩体北缘,是佛冈岩体的一部分,成因目前还不明确。文章以该岩体细粒黑云母二长花岗岩为研究对象,进行了岩石学、锆石U-Pb年代学、地球化学和Hf同位素组成研究。研究结果显示,白沙地区细粒黑云母二长花岗岩LA-ICP-MS锆石U-Pb加权平均年龄为155.6~157.1 Ma,表明其侵位于晚侏罗世。岩体具高硅（w（SiO₂）=70.74%~77.47%）、富碱（w（Na₂O+K₂O）=5.78%~8.62%）、低磷（w（P₂O₅）=0~0.10）等特征,富集Rb、Th、U、K、Pb、Nd、Zr和Hf等元素,亏损Ba、Nb、La、Ce、Sr、P、Eu和Ti等元素。岩石总体上明显富集轻稀土元素（（La/Yb）_N=0.94~54.69,1个为0.94）,具明显的负Eu异常（δEu=0.07~0.57,n=6）,个别正Eu异常（1.00~1.16,n=3）。岩体地球化学特征指示,细粒黑云母二长花岗岩为高分异I型花岗岩。岩体形成于古太平洋板块（库拉板块）与欧亚板块俯冲作用和菲律宾地块与南中国-印支地块的岩石圈消减作用下,岩石圈伸展-减薄,导致地幔物质上涌,在高温条件热流作用下幔源物质诱导下地壳中-元古代物质部分熔融形成。     

川西松林口岩体锆石U-Pb定年及其地球化学特征

松林口岩体位于松潘—甘孜造山带中东部,为确定岩体的侵位时代和地球化学特征,通过镜下薄片观察、主微量元素分析以及锆石U-Pb测年,对松林口岩体进行了研究。结果表明,松林口岩体由二长花岗岩体和花岗闪长岩体组成,花岗闪长岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（212.4±0.9） Ma （MSWD=0.66）,二长花岗岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（222.4±1.1） Ma （MSWD=0.39）,形成于晚三叠世,由两期次岩浆作用形成;岩石的SiO₂含量56.56%~61.97%;铝饱和指数A/CNK=0.93~1.05,全碱含量3.78~5.38,K₂O/Na₂O=1.02~1.68,里特曼指数σ=1.194~1.612,样品属于准铝质中—高钾钙碱性岩系列。岩石轻重稀土比值LREE/HREE=5.22~7.13,La_N/Yb_N比值为6.93~8.96,轻、重稀土分异较明显,具较强的负Eu异常。岩石Mg^#值较高（50.97~61.27）,w（Rb）/w（Sr）为0.12~0.25,Rb-（Y+Nb）图解显示为后碰撞环境。因此,松林口二长花岗岩—花岗闪长岩属后碰撞准铝质中—高钾钙碱性I型花岗岩类。     

大别造山带研子岗碱性岩体成因及其构造意义：锆石U-Pb年龄和地球化学制约

出露于大别造山带西南部的研子岗碱性杂岩体侵位于元古代和新太古代随县群中,本文采用锆石LA-ICPMS U-Pb定年方法,获得岩体的主体岩性角闪正长岩的岩浆锆石年龄为133± 1Ma,代表岩体的结晶年龄,这一年龄也是大别造山带中已知形成时代最早的早白垩世碱性岩体的结晶年龄（单颗粒锆石U-Pb法）。研子岗碱性杂岩体具有碱性岩典型的富碱（K₂O＋Na₂O＝8.38%~11.26%）、低硅（SiO₂＝63.41%~66.51%）的特点。主要矿物为微斜条纹长石,暗色矿物主要为镁角闪石。地球化学特征表明,全部岩石均具有高Ba-Sr花岗岩类高Ba（1230× 10^-6~4865× 10^-6）、高Sr（583× 10^-6~2088× 10^-6）和无负Eu异常（Eu/Eu^*＝0.97~1.12）等特征,并具有A型花岗岩的部分地球化学特征。岩石的Y/Nb比（0.46~1.09）较低,具洋岛玄武岩的部分地球化学特征,(⁸⁷Sr/⁸⁶Sr) _i初始比值（0.70513~0.70543）较低,表明岩体的物源主要来源于幔源。Nd二阶段模式年龄(t_2DM=1859~1942Ma)和锆石Hf二阶段模式年龄(t_DM2=2130~2330Ma）较老,ε_Nd(133)值(-12.5~-11.4）和ε_Hf(133)值(-18.2~-15.4）较低。综合分析表明,岩体主要为古老的富集岩石圈地幔物质低程度部分熔融和随后地壳物质轻度AFC（混染和分离结晶作用）过程的产物,源岩熔融的热量主要来源于软流圈物质的上涌底侵作用提供。研子岗岩体形成于碰撞后构造环境,岩体的形成预示着大别造山带早白垩世造山过程的即将结束,板内时期的即将来临。     

广西镇龙山地区花岗斑岩岩石地球化学及年代学研究

广西镇龙山地区发育大量脉状铅、锌、银多金属矿体，同时出露多个花岗斑岩和石英斑岩岩体，岩体和矿体受近东西向羊角山-长帽岭断裂控制。为研究岩体与矿体的关系，文章在详实野外地质工作的基础上，对研究区典型的岩体开展了岩石学、地球化学及锆石年代学研究。主量、微量元素组成显示，知府山花岗斑岩的w(SiO₂)为63.59%~68.78%，w(K²O)为4.5%~5.68%，w(MgO)为1.07%~1.77%；长帽岭花岗斑岩的w(SiO₂)为66.67%~69.75%，w(MgO)为0.71%~2%，w(K²O)为1.54%~3.91%。2个岩体均具有高硅、富钾、低镁的特征，A/CNK>1.1，均显示过铝质岩石特征。2个岩体均富集Rb、K、Ba、Th、U等大离子亲石元素，而亏损Nb、Sr、P、Ti等高场强元素，稀土元素总量（∑REE）平均值为187.94×10^-6，稀土元素配分模式呈轻稀土元素相对富集的右倾型，明显的Eu负异常。岩石地球化学特征及岩相学特征显示，该区花岗斑岩为高钾钙碱性过铝质S型花岗岩，岩体经历了较高程度的结晶分异。锆石U-Pb年龄结果显示，知府山、长帽岭花岗斑岩、洗马塘石英斑岩成岩年龄为92~95 Ma，形成于碰撞后伸展环境。成岩物质主要来自于上地壳物质的部分熔融，并有少量幔源物质加入。镇龙山地区多金属矿床在平面上围绕岩体显示高温到低温的矿化分带现象，成岩成矿时代在时间上具有一致性，表明岩浆活动与成矿作用之间存在成因联系，说明区内脉状铅锌银矿床属于岩浆热液矿床。晚白垩世岩浆热液成矿事件是华南地区燕山晚期成岩成矿事件的一部分，其构造背景与华南在晚白垩世受太平洋板块俯冲影响所致。     

东天山哈尔里克山区二叠纪高钾钙碱性花岗岩成因及地质意义

本文从岩石学、地球化学和同位素等方面讨论东天山克拉麦里-哈尔里克岛弧东段八大石和小铺东两个岩体的特征和成因。八大石岩体和小铺东岩体主要为二长花岗岩,SiO₂含量分别为61.92%~74.40%和69.17%~74.92%,K₂O+Na₂O的含量分别为6.50%~8.32%和7.74%~8.14%,绝大部分岩石具有高钾钙碱性花岗岩特征;∑REE分别为105×10^-6~210×10^-6和100×10^-6~172×10^-6,(La/Yb)_CN分别为4.1~8.9和9.1~15.3,配分模式右倾,δEu分别为0.40~0.93和0.59~0.80,为中-低负异常;两个岩体均富Rb、Ba等大离子亲石元素和Th、U、Hf、Zr等高场强元素,而贫Ta、Nb、Sr、Ti等。通过LA-ICP-MS分析得到八大石岩体中锆石²⁰⁶Pb/²³⁸U加权平均年龄为298±2Ma,表明岩体形成于早二叠纪,计算得到八大石和小铺东岩体的模式年龄t_DM分别为944Ma和648Ma;八大石和小铺东岩体的ε_Nd(t)u分别为+3.06和+4.47,(⁸⁷Sr/⁸⁶Sr) _i分别为0.70475和0.70384,表现出高ε_Nd(t)u 低(⁸⁷Sr/⁸⁶Sr) _i。综上所述,认为哈尔里克高钾钙碱性花岗岩可能为碰撞后挤压-伸展转折阶段的产物,主要由来自新生地壳的中钾钙碱性岩浆经过结晶分异作用而成。     

辽北西丰地区晚侏罗世营厂岩体LA-ICP-MS锆石U-Pb年龄及岩石地球化学特征

营厂岩体分布于辽北西丰县和隆镇境内，研究结果表明，该岩体主要为似斑状二长花岗岩，锆石²⁰⁶Pb/²³⁸U年龄加权平均值为156.1 Ma±1.5 Ma，形成时代为晚侏罗世。营厂岩体w（Na₂O）/w（K₂O）平均值为1.07，属高钾钙碱性系列；里特曼指数σ平均值为2.15，属钙碱系列；铝饱和指数A/CNK平均值为1.16，A/CN平均值为1.99，属过铝型；Rb、Sr、Ba、Th、Hf含量偏高，Cr、Ni、Co、V、Rb、Zr、Nb等元素含量低，为"S"型花岗岩特征。稀土元素总量平均值为w（ΣREE）＝82.80×10^-6，w（LREE）/w（HREE）=15.76，w（La）_N/w（Yb）_N=24.32，表明其轻稀土相对富集，重稀土相对亏损，稀土配分曲线右倾。δEu=0.80，铕弱负异常，说明成因与板块运动有关，w（Sm）/w（Nd）=0.20，w（Ba）/w（Sr）=1.60，w（K）/w（Rb）=249.15，表明具有壳源性质。营厂岩体具有埃达克岩的特点，其属于受太平洋板块向欧亚板块俯冲作用的影响，在挤压环境下加厚下地壳部分熔融，从而形成活动陆缘型花岗岩。     

新疆准噶尔北东缘乌图布拉克岩体形成时代、地球化学特征及地质意义

乌图布拉克岩体位于准噶尔北东缘,额尔齐斯-玛因鄂博构造带南侧。岩体主要由花岗闪长岩和二长花岗岩组成,有少量石英闪长岩和钾长花岗岩。岩体的锆石SHRIMP U-Pb年龄为360.1±3.6Ma。岩石的K₂O+Na₂O=7.05%~9.48%,A/NKC=0.91~1.04,属准铝-过铝质“I”型花岗岩。岩石稀土总量低,∑REE为72×10^-6~184×10^-6,轻稀土富集,(La/Yb)_N=5~13。石英闪长岩、花岗闪长岩、二长花岗岩具弱的铕负异常或无明显异常（δEu=0.72~0.98）;钾长花岗岩铕负异常明显（δEu=0.15~0.21）。在微量元素配分模式中,具有Sr、Ba、P、Ti的亏损,而Nb、Ta亏损不明显。岩石有低的Sr初始值（0.70165~0.70462）和高的ε_Nd(t)u（+4.7~+6.9）。2个样品的Nd模式年龄分别为758Ma和551Ma。上述特征表明,岩浆可能具有较复杂的来源,推测该岩体岩浆可能来源于年轻的玄武质地壳,并有幔源物质的加入。综合本文资料及区域地质特征分析,阿尔泰造山带后碰撞时限可能为360~290Ma,即泥盆纪末-石炭纪末。     

川西塔公松林口岩体LA-ICP-MS锆石U-Pb年龄与地球化学特征

松林口岩体出露于松潘—甘孜造山带东缘,紧邻甲基卡超大型稀有金属伟晶岩型锂矿床,为确定松林口岩体侵位时代与物质来源,探讨该岩体与甲基卡成矿岩体的地球化学和含矿性差异,本文对采集的11件岩体样品,采用X射线荧光光谱法、电感耦合等离子体质谱法（ICP-MS）、激光剥蚀电感耦合等离子体质谱法（LA-ICP-MS）和多接收电感耦合等离子体质谱法（MC-ICP-MS）,对岩石的主量和微量元素组成、锆石U-Pb年龄和锆石Lu-Hf同位素进行分析。结果表明：松林口岩体中富含闪长质暗色包体,SiO₂含量介于56.56%~68.99%之间,全碱含量3.78%~6.82%,K₂O/Na₂O=1.02~1.93,里特曼指数σ=1.01~1.93,Mg^#值总体为46.73~61.27,岩石属于高钾钙碱性Ⅰ型花岗岩系列,具有轻稀土富集的特点,LREE/HREE=2.67~8.31,La_N/Yb_N值为2.11~9.74,所有岩石样品均具有明显的负Eu异常;总体上松林口岩体及其包体富集LILE元素,Ta、Nb、P、Ti等HFSE元素相对亏损。松林口边部花岗闪长岩、中部二长花岗岩的锆石U-Pb年龄分别为212.6±1.0Ma（MSWD=0.55）、222.4±1.1Ma（MSWD=0.39）,岩浆侵位时代为晚三叠世;二长花岗岩锆石Lu-Hf同位素结果ε_Hf（t）介于-9.09~-6.86,二阶段模式年龄（T^C_DM）在1524.874~1666.002Ma之间,岩体物质来源是中元古代扬子克拉通基底物质部分熔融,并混有部分富集上地幔物质。甲基卡S型花岗岩为上地壳部分熔融形成的,与松林口岩体属不同的物质来源,且岩浆演化程度和成矿构造条件不同,这可能是松林口岩体不具有锂稀有金属成矿的主要原因。     

青海喀雅克登锌多金属矿床二长花岗岩锆石U-Pb定年及其地质意义

青海喀雅克登锌多金属矿床与成矿关系密切的二长花岗岩通过LA-MC-ICP-MS锆石U-Pb测年,年龄为(403.1±1.2)Ma,MSWD=0.46,属于早泥盆世;矿区的锌多金属矿体主要产于二长花岗岩与古元古代金水口岩群白沙河岩组大理岩岩段接触部位的夕卡岩中,表明喀雅克登锌多金属矿床形成于(或晚于)(403.1±1.2)Ma。二长花岗岩中w(MgO)=0.21%~0.87%,w(FeO_t)=0.93%~3.93%,Mg~#=25.5~34.66,K_2O/Na_2O=1.0~1.72,A/CNK=0.89~1.17,属高钾钙碱性、准铝质花岗岩系列,为壳源岩浆。喀雅克登锌多金属矿床形成于后碰撞阶段,受幔源岩浆底侵改造。     

内蒙古嘎仙镍钴矿区岩浆作用与成矿

内蒙古嘎仙矿床为大兴安岭北段与岩浆作用有关的大型低品位镍钴硫化物矿床,成矿作用主要与花岗质岩浆作用有关。文章主要对矿区内矿体下盘的花岗岩类(花岗斑岩、长石斑岩、伟晶状花岗岩、黑云母花岗岩)进行了锆石LA-ICP-MS U-Pb定年,获得花岗斑岩的谐和线年龄(125.3±1.1)Ma～(127.5±4.5)Ma,长石斑岩的谐和线年龄为(128.1±2.2)Ma,伟晶状花岗岩的谐和线年龄为(127.9±2.3)Ma,黑云母花岗岩的谐和线年龄为(127.9±1.4)Ma,说明这些花岗岩类主要形成于中生代早白垩世。通过对矿化超镁铁岩、科马提岩、镁铁岩(辉绿岩、玄武岩)、长英质岩(闪长岩、长石斑岩、斜长花岗岩、花岗斑岩、伟晶状花岗岩、黑云母花岗岩)及围岩(大理岩)的主量、微量元素地球化学测试分析,结果表明,与吉峰科马提岩成分相比较,矿化超镁铁岩具有较高的w(SiO_2)(40.53%～54.96%)、w(TiO_2)(0.24%～0.86%)、w(Al_2O_3)(3.58%～10.47%)、w(FeO)(5.30%～8.80%)、w(CaO)(7.35%～13.66%)、w(Na_2O)(0.01%～0.76%)、w(K_2O)(0.02%～0.66%)和w(P_2O_5)(0.06%～0.61%);镁铁岩(包括辉绿辉长岩、玄武岩)铝含量较高,w(Al_2O_3)=16.34%～17.74%;长英质岩类也富铝质(Al_2O_3/(CaO+Na_2O+K_2O)=1.34～1.63),多数岩石属于钙碱性系列。闪长岩与镁铁岩相比,具有较高的硅、铝、钾、钠,较低的铁、镁和钙,微量元素具有大离子亲石元素富集,高场强元素相对亏损的右倾模式;稀土元素具有轻稀土元素富集,重稀土元素相对亏损特征,超镁铁岩类成分点位于N-MORB与OIB范围之间,而镁铁岩和长英质岩类成分点位于E-MORB和OIB之间。镁铁岩落入火山弧玄武岩范围,长英质岩落入火山弧花岗岩+同碰撞花岗岩范围,同属于造山后花岗岩的范围,因此镁铁质岩的形成应属于俯冲-碰撞环境,而长英质岩的形成应属于造山后伸展环境。根据各岩类所含成矿元素和亲流体元素分析,认为含矿热液来自矿区西部的深部,并且构建了嘎仙矿床的成矿模型,即超镁铁岩先期侵位,后期经历了区域的变质变形,最后发生燕山期大规模花岗质岩浆活动及成矿流体的蚀变矿化。     

巴颜喀拉北部江日嘎玛花岗侵入岩地球化学特征及锆石年龄

江日嘎玛花岗侵入岩位于巴颜喀拉-松潘-甘孜造山带北部,侵位于中三叠世甘德组三段地层中。本文通过对江日嘎玛花岗侵入岩进行岩相学、岩石地球化学及年代学研究,探讨其成因及构造环境。研究表明,江日嘎玛花岗侵入岩,具有较高的SiO₂(w(SiO₂)=69.63%~71.05%),A/CNK=1.017~1.043,铝饱和指数<1.1,属弱过铝质高钾钙碱性Ⅰ型花岗岩;岩石具有明显富集Zr、Hf、Ba,亏损Nb、U、Ta、Ti、Rb、K的特征,并且具有负Eu异常;花岗岩锆石SHRIMP U-Pb测年为222.5 Ma±1.9 Ma,表明岩浆侵位时代为中生代晚三叠世,形成于碰撞造山后期地壳减薄环境中。     

Geochronology,petrogenesis and tectonic implications of the Zhongchuan granitic pluton in the Western Qinling metallogenic belt,China

The Zhongchuan district is an important component of the metallogenic belt in the Western Qinling. The Zhongchuan granite pluton occurring in the centre of the Zhongchuan metallogenic area has been poorly constrained, though the Triassic granite in Western Qinling has been well documented. In‐situ zircon U–Pb ages, Hf isotopic compositions and whole‐rock geochemical data are presented for host granite and mafic microgranular enclaves (MMES) from the Zhongchuan pluton, in order to constrain its sources, petrogenesis and tectonic setting of the pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMES and the host granitic rocks mainly due to interactions between coeval felsic host magma and mafic magma. The zircon U–Pb age of host granite (231.6 ± 1.5 to 235.8 ± 2.3 Ma) has overlapping uncertainty with that of the MMES (236.6 ± 1.3 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the MMES (ε_Hf(t) = −13.4 to 4.0) is distinct from the host granite (ε_Hf(t) = −15.7 to 0.0), indicating that both enriched subcontinental lithosphere mantle (SCLM) and crustal sources contributed to their origin. The zircons have two‐stage Hf model ages of 1064 to 1798 Ma for the host granite and 858 to 1747 Ma for the MMES. This suggests that the granitic pluton was likely derived from partial melting of a Late Mesoproterozoic crust, with subsequent interaction with the SCLM‐derived mafic magmas in tectonic affinity to the South China Block. Copyright © 2012 John Wiley & Sons, Ltd.     

Petrogenesis of granitoids in the Wulan area: Magmatic activity and tectonic evolution in the North Qaidam,NW China

Numerous granitic intrusions crop out in the eastern segment of the North Qaidam block (NQ), NW China. To evaluate their ages, petrogenesis and genetic relationships to other granitoids in the NQ, we present geochemical and geochronologic data for six intrusive bodies and review regional data. Zircon U-Pb (SHRIMP) dating yielded ages of 413 ± 3 Ma for the Hadesengou granite; 254 ± 3 Ma for the Xugeigou granite; 251 ± 1 Ma for the Qiluoshan granite; 249 ± 1 and 248 ± 2 Ma for the Chahannuo hornblende diorite and granite, respectively; 240 ± 2 Ma for the Chahanhe granite; and 250 ± 1 and 244 ± 3 Ma for the Shailekegoulei granodiorite and granite, respectively. Consequently, the Wulan plutons can be divided into two petrologic groups: Early Devonian (D₁) quartz monzonite and syenogranite, and Late Permian to Early Triassic (P₃-T₁) hornblende diorite, granodiorite, and granite. The D₁ granitic intrusions have geochemical affinities with A-type granites (A₂-type) characterized by low Ca, Sr, Ba and Nb, and high Fe, Ga, Y and Rb, consistent with derivation by partial melting of metapelitic source rocks containing a small amount of metagraywacke. The P₃-T₁ I-type granitic intrusions are geochemically typical of active continental margin rocks, consistent with derivation by partial melting of metabasalt and clay-poor metagraywacke. Combined with previous studies, we recognize five periods of granitic magmatism in the NQ: (1) 465–473 Ma; (2) 423–446 Ma; (3) 391–413 Ma; (4) 372–383 Ma; and (5) 240–271 Ma. Based on the temporal-spatial distribution of granitic intrusions in the NQ and the regional tectonic evolution, we interpret the first and second periods of granitic magmatism as related to normal plate subduction, and the third period to slab break-off and exhumation of the subducted plate. The fourth stage of granitic magmatism is attributed to large-scale lithospheric mantle delamination, involving the differential movement of orogenic blocks. The fifth period of granitic plutonism probably reflects northward subduction of the East Kunlun Paleotethys oceanic crust and southward subduction of Zongwulong oceanic crust beneath the Oulongbuluke continental block.     

Geochemistry, Monazite U–Pb Dating, and Li–Nd Isotopes of the Madi Rare Metal Granite in the Northeastern Part of the North China Craton

The Madi rare metal granite is a complex massif, which contains a variety of rare metals, such as Nb, Ta, Li, and Be. In this paper, the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry (MC-ICP-MS). The precise crystalline age of the granite was obtained from monazite U-Pb dating, and the source of the granite was determined using Li-Nd isotopes. The Madi rare metal granite is a high-K (calc-alkaline), peraluminous, S-type granite. The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma, which is Early Jurassic. The granite is characterized by a relatively wide range of δ7Li values (+2.99‰ to +5.83‰) and high lithium concentrations (181 ppm to 1022 ppm). The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation. An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation. The lithium isotopic composition of the granite significantly differs from that of the wall rock, but it is very similar to that of a primitive mantle peridotite xenolith (mean δ7Li value +3.5‰). The plot of Li concentration versus δ7Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas. Based on the above-described evidence, the granite was mainly derived from the crust, but it was contaminated by a deep granitic magma.     

Mantle-like Sr–Nd isotope composition of Fe–K subalkaline granites: the Peneda–Gerês Variscan massif (NW Iberian Peninsula)

The Peneda–Gerês massif is one of the most representative NW Iberian late‐ to post‐orogenic Variscan granitic plutons. It resulted essentially from the subsynchronous emplacement, at 290–296 Ma, of two granitic magmas of Fe–K subalkaline affinity, with primitive isotopic composition: Sr_i = 0.703–0.707 and εNd_i=?1.5 to ?2.4. An origin by mantle input followed by mantle–crust interactions is proposed, implying the contribution of a less enriched mantle component than that involved in the genesis of synorogenic hybrid granitoids of Mg–K subalkaline affinity. A less voluminous aluminopotassic and isotopically more evolved magma (Sr_i=0.708–0.709 and εNd_i=?3.5 to ?3.9) with little or no mantle input was also generated, suggesting the involvement of lower crust materials. Therefore, this study suggests an input of juvenile magmas in late Variscan times, the mantle‐like isotope signature of Fe–K granitic magmatism being clearly related to a geodynamic setting of extensional processes, large‐scale uplift and thinning.     

福建李家坊金矿区火成岩岩体锆石U-Pb年龄、地球化学特征及其地质意义

福建李家坊金矿为何宝山矿田近年新发现的中型金矿床,矿区内广泛发育火成岩岩体,然而,由于缺少对其岩浆活动时限及地球化学特征的研究,各类岩体与金矿化的关系尚不明确.针对这一问题,文章通过全岩主微量元素分析和LA-ICP-MS锆石U-Pb定年及微量元素测试,约束李家坊金矿床内火成岩岩体成岩年龄,并讨论了其地球化学特征.研究表...     

Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of the Late Silurian Shidonggou granite from the Wulonggou area in the Eastern Kunlun Orogen,Northwest China

ABSTRACT

The Wulonggou area in the Eastern Kunlun Orogen (EKO) in Northwest China is characterized by extensive granitic magmatism, ductile faulting, and orogenic gold mineralizations. The Shidonggou granite is located in the central part of the Wulonggou area. This study investigated the major as well as trace-element compositions, zircon U–Pb dates, and zircon Hf isotopic compositions of the Shidonggou granite. Three Shidonggou granite samples yielded an average U–Pb zircon age of 416 Ma (Late Silurian). The Late Silurian Shidonggou granite is peraluminous, with high alkali contents, high Ga/Al ratios, high (K₂O + Na₂O)/CaO ratios, and high Fe₂O₃^T/MgO ratios, suggesting an A-type granite. The Shidonggou granite samples have zircon ε_Hf(t) values ranging from ?7.1 to +4.4. The Hf isotopic data suggest that the Late Silurian granite was derived from the partial melting of Palaeo- to Mesoproterozoic juvenile mantle-derived mafic lower crust. Detailed geochronological and geochemical data suggest that the Late Silurian granite was emplaced in a post-collisional environment following the closure of the Proto-Tethys Ocean. Combining data of other A-type granitic rocks with ages of Late Early Silurian to Middle Devonian, such post-collisional setting related to the Proto-Tethys Ocean commenced at least as early as ~430 Ma (Late Early Silurian), and sustained up to ~389 Ma (Middle Devonian) in the EKO.