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1.
蟒岭岩体位于北秦岭构造带北部,岩石类型主要为似斑状黑云母二长花岗岩、中粗粒黑云母二长花岗岩、中细粒二长花岗岩、含辉石黑云角闪闪长岩和黑云母钾长花岗岩。依据LA-ICPMS锆石U-Pb定年结果,结合前人测试的年龄,将蟒岭岩体的岩浆演化划分为晚侏罗世早期、晚侏罗世晚期—早白垩世早期和早白垩世中期3期。第一期为含辉石黑云角闪闪长岩,其LA-ICPMS锆石U-Pb年龄为(157±1)Ma,该期岩石SiO2质量分数较低,富碱,属于准铝质,钾玄岩-高钾钙碱性系列;第二期二长花岗岩,侵位年龄为(148±1)Ma~(144±1)Ma,具有高硅、富碱的特征,属于准铝质-弱过铝质,钾玄岩-高钾钙碱性I-A过渡型花岗岩;第三期黑云母钾长花岗岩,侵位年龄为(124±2)Ma,具高硅、富碱、低镁、铝饱和指数偏高的特征,属过铝质,高钾钙碱性I-A过渡型花岗岩。组成蟒岭岩体的花岗岩从早到晚,SiO2质量分数逐渐升高,而Al2O3、TiO2、MgO、CaO、P2O5、TFe2O3质量分数逐渐降低;稀土元素总量具有由高到低的变化趋势,第一期和第二期岩石的稀土元素配分曲线为轻稀土元素相对富集的右倾型,而第三期的稀土元素配分曲线呈两边高中间低的不对称弧形,整体上负铕异常不明显或呈微弱正铕异常;微量元素上,这3期岩石均富集K、Rb、Ba、Sr等大离子亲石元素,而相对亏损P、Nb、Ta、Ti等高场强元素。与区域上同时代成矿花岗岩体对比,两者均具有高硅、富碱的特征,稀土元素球粒陨石标准化曲线呈轻稀土元素富集的右倾斜型,但蟒岭岩体中二长花岗岩没有明显的Eu异常,且Ba、P、Ti亏损及Ta、Nb富集没有含矿花岗岩明显。  相似文献   

2.
老牛山杂岩体位于华北地块南缘。野外侵入关系和锆石LA-ICP-MS U-Pb定年显示,其由晚三叠世(印支期)和晚侏罗(燕山期)花岗质岩石组成。印支期岩石类型为石英二长岩、石英闪长岩和粗粒黑云母二长花岗岩,年龄分别为223±1Ma、222±1Ma和214±1Ma; 燕山期为中粒-中粗粒黑云母二长花岗岩和细粒-中细粒黑云母二长花岗岩,年龄分别为152±1Ma和146±1Ma。印支期石英闪长岩、石英二长岩的SiO2相对含量低、富碱、高铝,为钾玄系列,准铝质Ⅰ型花岗岩;印支期粗粒黑云母二长花岗岩具富硅、碱、高铝、低镁的特点,属于高钾钙碱性系列,为准铝质-过铝质Ⅰ型花岗岩;燕山期黑云母二长花岗岩具高硅和铝、富碱,低镁的特点,为高钾钙碱性系列,准铝质Ⅰ型花岗岩。组成老牛山杂岩体的花岗岩从早到晚SiO2含量由低变高,MgO、CaO和Na2O由高变低。各期次岩石均表现出稀土元素总量较高,轻稀土元素明显富集,轻、重稀土元素分馏明显,具有较弱的铕异常。两期花岗质岩石均富集大离子亲石元素(K、Rb、Ba、Sr),而相对亏损高场强元素(Nb、Ta、P)。印支期花岗质岩石的全岩εNd(t)为-11.3~-14.87,tDM为1.7~1.9Ga,锆石的εHf(t)为-9.57~-25.11,tDM2为1863~2841Ma;燕山期花岗岩的全岩εNd(t)为-13.32~-16.83,tDM为 1.7~1.9Ga,锆石的εHf(t)为-18.28~-24.79,tDM2 为2360~2767Ma,表明该杂岩体的源区物质以壳源物质为主,可能与太古宙太华群相似,印支期有年轻地幔物质贡献。  相似文献   

3.
严翔  陈斌  王志强  段晓侠 《岩石学报》2019,35(2):558-588
西伯利亚板块和华北克拉通之间的古亚洲洋最终消减闭合的时间问题一直存在很大的争议，对区域内A型花岗岩的研究可以为该问题的解决提供有效约束。本文详细研究了华北克拉通北缘牛圈银矿区及其外围出露的海西期A型花岗岩和相关的暗色镁铁质微粒包体及辉绿岩脉的地质年代学和地球化学特征，以期解释其岩石成因并讨论构造指示意义。牛圈银矿区的花岗岩主要包括中粗粒黑云母二长花岗岩和细粒钾长花岗岩，锆石U-Pb定年结果表明中粗粒黑云母二长花岗岩和细粒钾长花岗岩分别形成于268.7±3.2Ma和254.2±2.8Ma，基性辉绿岩脉则形成于267.6±3.9Ma，与矿区早期中粗粒黑云母花岗岩几乎同时代或略晚。矿区两期花岗岩都具有弱过铝质特征，属于高钾钙碱性-钾玄岩系列岩石，均以高SiO2、富碱、高FeOT/（FeOT+MgO）和Ga/Al比值；贫CaO、MgO、TiO2、P2O5；富集Rb、Th、U、Y、F而亏损Ba、Sr、P、Ti、Eu等为特征，结合矿物学特征（半自形石英、他形铁质黑云母、出现条纹长石、缺乏碱性暗色矿物等）表明它们均为铝质A2型花岗岩。这也得到了较高的全岩锆石饱和温度（TZr）的支持，中粗粒黑云母二长花岗岩和细粒钾长花岗岩的岩浆结晶温度分别为784~822℃（平均值805℃）和843~871℃（平均值856℃）。中粗粒黑云母二长花岗岩中广泛发育镁铁质暗色包体。本文认为牛圈中粗粒黑云母二长花岗岩为古元古界红旗营子群基底杂岩中的花岗质片麻岩为主的中下地壳物质部分熔融，并与幔源基性岩浆发生岩浆混合作用形成的。年代学、主微量元素及Sr-Nd同位素数据表明，牛圈细粒钾长花岗岩与中粗粒黑云母二长花岗岩不是同一岩浆房演化的产物，而是代表两期岩浆活动，且晚期细粒钾长花岗岩形成过程中地幔物质添加相对更多。通过对牛圈银矿区两期A型花岗岩的研究，结合前人关于华北克拉通北缘中二叠世碱性岩浆岩带的研究，本文认为华北北缘在中二叠世伊始（~270Ma）就已经发生构造体制转换并进入后造山伸展环境，古亚洲洋的最终闭合可能早于270Ma。从牛圈早期中粗粒黑云母二长花岗岩到晚期细粒钾长花岗岩的相继侵位，伴随着更多的地幔物质的加入，其A型花岗岩特征愈发明显，指示华北北缘被破坏大陆边缘越来越强烈的伸展作用。  相似文献   

4.
徐家湾二长花岗岩体位于北淮阳构造带内桐柏-桐城与郯城-庐江两大断裂的交汇处,岩体呈岩株状侵入新元古界老变质岩层中。本文利用原子吸收光谱和ICP-MS法测定了岩体主量和微量元素的含量,表明岩体具SiO2和Al2O3较高、富碱、过铝质、Mg#小等特征。大离子亲石元素(LILE)Rb、Ba富集,Sr亏损;高场强元素(HFSE)Y、Th、Nb、Hf、U富集,Ta、P、Ti亏损;岩体整体亏损HFSE,富集LILE;LaN/YbN与LREEs/HREEs值均较大,具较弱的δCe负异常,显示该岩体为过铝质A型花岗。LA-ICP-MS锆石U-Pb定年获得徐家湾二长花岗岩侵位年龄在128.0±0.9~129.6±1.4 Ma之间,是早白垩世岩浆活动的产物。研究认为徐家湾二长花岗岩体形成于造山后的伸展环境,形成岩体的岩浆源于岩石圈地幔,并受到地壳物质的混染。  相似文献   

5.
在扬子地块西缘出露有大量的新元古代岩浆岩,这些岩石对于重建罗迪尼亚超大陆有着重要的意义。本文对云南峨山岩体的花岗闪长岩和似斑状黑云母二长花岗岩开展了详细的岩石学、岩石地球化学和年代学研究,结果表明,似斑状黑云母二长花岗岩侵位于826.6±2.5 Ma,而花岗闪长岩有着较年轻的结晶年龄818.3±2.8 Ma,花岗闪长岩比似斑状黑云母二长花岗岩有着更低的SiO2含量,但是更高的Al2O3、MgO、Fe2O3、TiO2和P2O5含量。在稀土元素配分曲线和微量元素蛛网图上,两种岩性呈现出相似的特征,都是具有右倾的稀土元素配分样式,呈现出Eu负异常,相对于大离子亲石元素（LILEs）更亏损高场强元素（HFSEs）。似斑状黑云母二长花岗岩富集Nd同位素组分,而花岗闪长岩与之有着相似的Nd同位素值。地球化学数据显示可能的岩石学成因是变质火成岩源区在826 Ma时发生部分熔融形成了峨山似斑状黑云母二长花岗岩并且残留下来了一个麻粒岩化的源区;麻粒岩源区在818 Ma时再次发生部分熔融形成了具有A型属性的峨山花岗闪长岩。结合前人的数据和本文的研究,认为扬子西缘在新元古代时期是一个活动大陆边缘,而华南地块当时在罗迪尼亚的位置更可能是在边缘而不是中心。  相似文献   

6.
内蒙古苇莲河地区是近年来进行黑钨矿找矿勘查的区域,位于兴蒙造山带中东部,大兴安岭主脊中部。矿床类型可能为典型的石英脉型黑钨矿。黑钨矿石英脉以近于直立（75°）的平直脉体产于花岗岩内或岩体与地层的外接触带,脉体向下尖灭于岩体内部,主要的矿化蚀变类型有钾长石化、绿帘石化、绢云母化、硅化等。本文在初步研究矿床地质特征的基础上,对成矿岩体——花岗岩进行高精度LA-ICP-MS锆石U-Pb测年及地球化学分析。UPb测年结果显示,206Pb/238U谐和年龄为（145±1）Ma,加权平均年龄为（143±1）Ma。地球化学特征显示,岩体具有典型的富硅、富碱特征,SiO2平均74.13%,（Na2O+K2O）平均9.44%,Na2O/K2O平均0.95,属高钾钙碱性系列岩石;Al2O3平均为12.91%,铝饱和指数A/CNK全部靠近1.0,为准铝质到弱过铝质花岗岩类,相对贫Mg;稀土总量较低,∑REE变化于122.02×10-6~235.79×10-6,表现为右倾稀土元素配分模式,弱富集轻稀土,并具有强烈的负铕异常,高场强元素Th、U、Nd、Hf明显富集,而Ba、Sr、P、Ti、Nb显著亏损;低Sr,高Yb,Nb/Ta比值变化于12.12~13.78,强不相容元素Rb高度富集,Rb/Sr比值1.25~14.58,Ti/Y比值42.49~114.48,Ti/Zr比值5.20~8.45;总体为壳源岩浆的特征。苇莲河花岗岩侵位时代为早白垩世,属燕山期构造岩浆活动的产物,其可能的形成构造背景为古太平洋板块斜向俯冲后,后退过程中的伸展滑塌背景。  相似文献   

7.
准噶尔板块东南缘沙尔德兰地区A型花岗岩构造环境研究   总被引：3，自引：2，他引：1  
研究区属于准噶尔板块东南缘,即传统意义上的北天山东段,分布有两类A型花岗岩,一种是钾长花岗岩,另一种是正长花岗斑岩。其中阔台克力克能厄肯钾长花岗岩产于大南湖岛弧带,白坡南钾长花岗岩和正长花岗斑岩均产于觉罗塔格岛弧带。白坡南与阔台克力克能厄肯钾长花岗岩同为弱过铝质,岩石化学属高钾钙碱性系列,稀土元素配分曲线为轻稀土富集型,具有明显的负Eu异常; 富集大离子亲石元素,显著亏损Sr、Nb、P2O5、TiO2,具有火山弧花岗岩的地球化学特征。正长花岗斑岩从准铝质过渡到弱过铝质,岩石化学从高钾钙碱性系列过渡到钾玄岩系列,轻重稀土元素分馏不明显,具有显著的负Eu异常; 富集高场强元素,亏损Ba、Sr、P2O5及TiO2,具有板内花岗岩的地球化学特征。这些钾长花岗岩和正长花岗斑岩均属于A2型花岗岩。根据前人在北疆地区获取的研究成果,可将该区域岛弧环境结束与后碰撞岩石圈伸展环境开始的分界时限厘定为320Ma。根据我们的研究,白坡南钾长花岗岩体的锆石U-Pb谐和年龄为338.3±4.3Ma,正长花岗斑岩的锆石U-Pb谐和年龄为278±2Ma。年代学与岩石地球化学研究表明,白坡南钾长花岗岩形成于B型俯冲阶段的岛弧环境,而正长花岗斑岩形成于后碰撞岩石圈伸展环境。由此证明,A型花岗岩不仅产于非造山和后碰撞伸展环境,还可以产于岛弧环境。  相似文献   

8.
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，LaN/YbN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。  相似文献   

9.
广山花岗杂岩体主体部分由中粒碱长花岗岩和侵入其内部的细粒碱长花岗岩组成,LA-MC-ICP-MS锆石U-Pb定年显示其形成年龄分别为162.4±0.9Ma和156.3±0.7Ma,表明岩体为燕山期多期次岩浆活动产物。两期岩体为高钾钙碱性系列,A/CNK值为0.95~1.05,属准铝质-弱过铝质花岗岩类;稀土含量中等,强Eu亏损,呈略右倾的海鸥型稀土配分模式,均为A2型花岗岩。锆石Hf同位素研究表明,εHf（t）变化范围主要集中在-4.35~0之间,均为负值,二阶段模式年龄tHf2（Ma）变化范围主要集中于1219~1478Ma,反映其源区物质来源于中元古代地壳物质。结合前人研究成果,本文认为华南燕山早期晚阶段A型花岗岩形成于由碰撞造山向板内（非造山）环境转换的后造山拉张阶段。  相似文献   

10.
新疆拜城县波孜果尔A型花岗岩类岩体位于塔里木地台北缘及邻区的近东西向碱性侵入岩带上,主要岩石类型为霓石钠闪石英碱长正长岩、霓石钠闪碱长花岗岩、黑云母碱长正长岩。全岩SiO2=68.97%~74.14%,Na2O+K2O=9.67%~11.19%,Al2O3=13.72%~15.26%,Fe2O3=0.18%~1.41%,FeO=0.91%~1.51%,CaO=0.35%~0.63%。稀土元素总量较高,ΣREE=298×10-6~1286×10-6,平均706×10-6,轻稀土富集,重稀土亏损,强烈的Eu负异常,呈“右倾海鸥型”的稀土元素配分模式。富Nb、Ta、Zr、Hf等高场强元素,亏损Ba、K、Sr等大离子亲石元素,Zr+Nb+Ce+Y=936×10-6~3684×10-6,平均1813×10-6。为A1型花岗岩。岩体形成于早二叠纪。锆石LA-ICP-MS U-Pb年龄为287.7~291.6Ma,平均289.8Ma,岩体形成后,在279.1~282Ma左右经历了后期热液流体的改造。锆石εHf（t）值为-6.3~9.0,两阶段模式年龄（tDM2）跨越古元古代晚期-新元古代中期,主要集中在中元古代。岩浆平均温度832~839℃,形成于非造山的板内构造环境,且具高温、无水、低氧逸度的成岩特点。该岩体具有壳幔混源的特点。  相似文献   

11.
ABSTRACT

This paper presents geochronological, geochemical, and zircon Hf–O isotope data for late Mesozoic intrusive rocks from the northeastern North China Craton (NCC), with the aim of constraining the late Mesozoic tectonic nature of the NE Asian continental margin. U–Pb zircon data indicate that the Late Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Jurassic (161 ? 156 Ma) and Early Cretaceous (125 ? 120 Ma). Late Jurassic magmatism consists mainly of monzogranites. These monzogranites display high Sr/Y ratios and the tetrad effect in their REE, respectively, and have negative εHf(t) values (?22.6 to ?15.8). The former indicates that the primary magma was generated by partial melting of thickened NCC lower crust, the latter suggests that the monzogranites were crystallized from highly fractionated magma, with the primary magma derived from partial melting of lower continental crust. Combined with the spatial distribution and rock associations of the Late Jurassic granitoids, we conclude that the Late Jurassic magmatism in the eastern NCC formed in a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath the Eurasia. The Early Cretaceous magmatism consists mainly of granitoids and quartz diorites. The quartz diorites formed by mixing of melts derived from the mantle and lower crust. The coeval granitoids are classified as high-K calc-alkaline and metaluminous to weakly peraluminous series. Some of the granitoids are similar to A-type granites. The granitoid εHf(t) values and TDM2 range from ?14.3 to ?1.4 and 2089 to 1274 Ma, respectively. These values indicate that their primary magma was derived from partial melting of lower crustal material of the NCC, but with a contribution of mantle-derived material. We therefore conclude that Early Cretaceous magmatism in the northeastern NCC occurred in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath Eurasia.  相似文献   

12.
A-type granitoids (512 Ma) either intruded into Paleoproterozoic gneiss of the Alto Moxoto Terrane (Prata Complex and Serra da Engabelada Pluton) or into Early Neoproterozoic metavolcanic metasedimentary sequence of the Alto Pajeu Terrane (Serrote Santo Antonio Pluton), constitute a small proportion of Brasiliano (= Pan-African) granitoids in the Central Tectonic Domain of the Borborema Province, northeastern Brazil. The Prata Complex consists of syenogranites, monzogranites, mafic enclaves of diorites and norites. The felsic and mafic members are not genetically related through fractionation. Mingling and mixing were extensive processes within the Prata Complex. The granites evolution appears to have involved fractionation of alkali feldspar, biotite, apatite and sphene without significant wall-rock assimilation. The Serra da Engabelada and Serrote Santo Antonio plutons consist of biotite syenogranites, with rare mafic enclaves. The studied granitoids are dominantly metaluminous, characterized by Fe-rich biotite and Fe-hornblende. High total alkalis, Y, Nb and REE and low CaO, MgO and Sr abundances and high FeO/(FeO+MgO) ratios characterize these granitoids. Chondrite-normalized REE patterns show enriched LREE, moderate to strong negative Eu anomalies and more or less flat heavy REE.The studied granitoids and diabase from dykes and enclaves show negative eNd (512Ma) values (-14 to -10), high incompatible elements such as LILE, HFSE and REE, suggesting important contribution of Paleoproterozoic crust. The origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust. Such isotopic signature of the diabase from the dykes also reflects a Paleoproterozoic enriched lithospheric mantle in the area. The intrusion of the studied granitoids contemporary with sub-volcanic bimodal magmatism and deposition of many Cambrian "pull-apart" basins in the north and central tectonic Domain of the Borborema Province, suggest intrusion during post-tectonic relaxation of the Brasiliano orogeny following the assembly of West Gondwana.  相似文献   

13.
The zircon SHRIMP dating of the Zhangtiantang granite gave an age of 159±7 Ma., which shows that the granite was produced at the early Late Jurassic. The Ar-Ar plateau ages of biotite and K-feldspar from the Zhangtiantang pluton are 153.2±1.1 Ma and 135.8±1.2 Ma, respectively. The Ar-Ar anti-isochrone ages of biotite and K-feldspar are 152.5±1.7Ma and 135.4±2.7Ma, respectively. The ages represent the isotopic closure ages of minerals in the pluton. The Zhangtiantang granites are regarded as peraluminous crust-derived type granites to possess the typical geochemical characteristics of calc-alkaline rocks on continental margin, with enriched Si, K, Al (average value of A/CNK as 1.18), HREE, Rb, U, and Th, heavily depleted V, Cr, Co, Ni, Ti, Nb-Ta, Zr, Sr, P, and Ba, strongly negative Eu and common corundum normative (average value of C as 1.84). The εNd(t) values of the Zhangtiantang granite are −5.84 to −7.79, and t 2DM values are 1.69 to 1.83 Ga, which indicates partial melting of continental-crust metamorphic sedimentary rocks during the Middle Proterozoic. The cooling history of the Zhangtiantang granitic pluton indicates that the cooling velocity of pluton was faster (about 67°C/Ma) from zircon (158 Ma) to biotite (152 Ma), and was slower (about12°C/Ma) from biotite (152.5 Ma) to K-feldspar (135.8 Ma). It can be deduced that the temporal gap (about 10 Ma) between the granite formmation and W-Sn mineralization in South China may be related to ordinary magma-hydrothermal processes by the variational cooling curve of the pluton. The Zhangtiantang pluton was formed in a compressive setting, with differentiation evolution and mineralization occurring in a relative relaxation setting.  相似文献   

14.
Haijin Xu  Changqian Ma  Kai Ye   《Chemical Geology》2007,240(3-4):238-259
Two stages of early Cretaceous post-orogenic granitoids are recognized in the Dabie orogen, eastern China, which recorded processes of extensional collapse of the orogen. The early stage granitoids ( 132 Ma) are foliated hornblende quartz monzonites and porphyritic monzogranites. They are of high-K calc-alkaline series and metaluminous to weakly peraluminous, with high K2O and low MgO contents (Mg# values: 32.0–46.0), they contain high Sr, low Y and heavy rare earth elements (HREE), and have high Sr/Y and (La/Yb)N ratios, without clear negative Eu, Sr and Ti anomalies. The early stage deformed granitoids have adakitic geochemical compositions and are equilibrated with residues rich in garnet and poor in anorthite-rich plagioclase, and thus indicate the existence of an over-thickened (> 50 km) crustal root beneath the orogen at  132 Ma. The later stage granitoids ( 128 Ma) are undeformed fine-grained monzogranites, fine-grained K-feldspar granites and coarse-grained K-feldspar granite-porphyry. They belong to a peraluminous and high-K calc-alkaline to shoshonite series, and display a flat HREE pattern and have strong negative Eu, Sr and Ti anomalies, with low Sr/Y and (La/Yb)N ratios. The late stage granitoids are equilibrated with residues rich in anorthite-rich plagioclase, hornblende, ilmenite/titanite and poor in garnet, indicating that the crust of the Dabie orogen became thinner (< 35 km) at  128 Ma. SHRIMP zircon U–Pb ages and changing compositional trends for these two stages of granitoids indicate that the over-thickened crust formed by the Triassic continental subduction/collision under the Dabie orogen remained until the early Cretaceous, and collapsed quickly in a few million years during the early Cretaceous.  相似文献   

15.
The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO2 between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated (Lacn/Lucn = 6.0?14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59–0.84). Initial ?Nd(i) values vary between ?3.1 and ?4.1, initial 87Sr/86Sr values between 0.7058 and 0.7072, and δ18O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36–38, low contents of Na2O (2.3–2.5 wt%) and SiO2 (52–55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn =  2.8–3.3; (Tb/Yb)cn =  1.2] and show small negative Eu anomalies (Eu/Eu* = 0.74–0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher 87Sr/86Sr (0.7075–0.7079) and lower ?Nd(i) (–4.5 to –5.3). The syenogranites have high SiO2 (70–74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher Lacn/Lucn (12.9) and Eu/Eu* (0.76–0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [?Nd(i) =  ?4.0 to ?3.3; 87Sr/86Sr(i) =  0.7034?0.7060; δ18 O =  + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe–Ti oxides played an important role in the evolution of Torul granitoids. The crystallization temperatures of the melts ranged from 800 to 900°C as determined from zircon and apatite saturation thermometry. All these characteristics, combined with low K2O/Na2O, low Al2O3/(FeOT + MgO + TiO2), and low (Na2O + K2O)/(FeOT + MgO + TiO2) ratios suggest an origin through dehydration melting of mafic lower crustal source rocks.  相似文献   

16.
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17.
The Dahongliutan granitic pluton consists of two-mica granites and is located in the eastern part of the Western Kunlun Orogen, northwestern Tibetan Plateau. Zircon separates from the pluton yield a SIMS U–Pb age of 217.5 ± 2.8 Ma. Rocks from the pluton contain relatively high and uniform SiO2 (72.32–73.48 wt%) and total alkalis (Na2O + K2O = 8.07–8.67 wt%) and are peraluminous and high-K calc-alkaline to shoshonitic in composition. The Dahongliutan granites are relatively depleted in the high-field-strength elements and the heavy rare earth elements (HREEs) and have relatively high Rb, and low Ba and Sr concentrations. They contain low total rare earth element (REE) concentrations. The light REEs are strongly enriched relative to the HREEs, with (La/Yb)N values of 28.56–37.01. The εNd(t) values range from ?10.6 to ?8.8, and (87Sr/86Sr)i = 0.7142–0.7210. Zircons from the pluton yield εHf(t) values of ?13.8 to ?1.6, and δ18O = 10.5–11.6‰. Petrographic and geochemical features of the pluton indicate that the granites are S-type and were derived from parting melting of a mixture of metasedimentary and minor metaigneous sources in the middle–lower crust. Magmatic differentiation was dominated by the fractional crystallization of plagioclase, K-feldspar, muscovite, biotite, and accessory monazite, allanite, and Fe–Ti oxides. Regional granitoids were emplaced in the Early-to-Middle Triassic. Other younger granitoids, with ages of 240–200 Ma, are mostly I-type in character and were likely derived from multiple types of source rock, suggesting the source was heterogeneous Triassic crust. Such a scenario is consistent with their formation in a post-collisional setting. Our new data, combined with other geological evidence, suggest that the collision between the Tianshuihai and southern Kunlun terranes occurred between ca. 250 and 240 Ma, resulting in the closure of the Palaeo-Tethys. Post-collisional tectono-magmatic events may have occurred between 240 and 200 Ma.  相似文献   

18.
The Dalat zone in southern Vietnam comprises a Cretaceous Andean-type magmatic arc with voluminous granitoids and contemporary volcanic rocks. On the basis of petrographical and mineralogical studies, the granitoids were subdivided into three suites: Dinhquan, Deoca and Cana. Rocks of the Dinhquan suite are hornblende–biotite diorites, granodiorites and minor granites. The Cana suite encompasses mainly leucocratic biotite-bearing granites with scarce hornblende. The Deoca suite is made up of granodiorites, monzogranites and granites. Geochemically, the granitoids are of subalkaline affinity, belong to the high-K, calc-alkaline series, and most of them display typical features of I-type granites. This paper presents the new Rb–Sr mineral and U–Pb zircon and titanite age data for the granitoids, which establish the ages of the plutonic suites as: the Dinhquan at ~112–100 Ma, Cana at ~96–93 Ma and Deoca at ~92–88 Ma. These ages are significantly different from earlier publications, and indicate that the earliest magmatism in the Dalat zone began at ~112 Ma ago, that is ~30–50 Ma later than previously thought. Our geochronological data are also support the continuation of an Andean-type arc running from SE China via southern Vietnam to SW Borneo.  相似文献   

19.
The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.  相似文献   

20.
This paper reports the first U-Pb geochronological data on the Precambrian granitoids of the Batomga block (Aldan shield). It was established that the amphibole diorites of this block have an age of 2062 ± 14 Ma, while biotite granites are dated at 2055 ± 7 Ma. These granitoids were subjected to epidote-amphibolie facies metamorphism 1920 ± 8 Ma ago.  相似文献   

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