首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 125 毫秒
1.
青海泽多桌肉地区花岗闪长岩中发育大量暗色闪长质包体。通过对花岗闪长岩(寄主岩石)与暗色包体的地球化学研究发现,花岗闪长岩(寄主岩石)的SiO_2含量为w(SiO_2)=61.61%~68.80%,A/CNK=0.91~0.99,属于偏铝质钙碱性花岗岩特征;暗色包体中发育针状磷灰石,暗色包体的SiO_2含量为w(SiO_2)=52.66%~66.99%,碱度率AR=2.08~2.26(大于1),里特曼指数σ=1.89~8.67,固结指数SI=16~24.74,属过铝质钙碱性花岗岩。稀土元素分析显示,花岗闪长岩稀土总量w(ΣREE)=117.44×10~(-6)~265.68×10~(-6);暗色包体稀土总量w(ΣREE)=184.05×10~(-6)~342.11×10~(-6),总量高于寄主岩石;暗色包体和寄主花岗岩有着相似的稀土元素配分模式,显示轻稀土富集,重稀土亏损,轻重稀土元素分馏明显的特征。微量元素分析显示,暗色包体微量元素的分布型式与寄主岩微量元素特征基本一致,大离子亲石元素K、Rb、Ba相对富集,高场强元素Nb、Ta、Zr、Hf相对亏损,反映了岩浆混合作用的特征。在花岗闪长岩中获得LA-ICP-MS锆石U-Pb年龄为202.49 Ma±0.63 Ma,属晚三叠世。表明泽多桌肉花岗闪长岩属于晚三叠世以来的造山带伸展崩塌造成岩石圈较快速减薄以及幔源岩浆底侵作用的发生,并导致地壳岩石接近熔融温度产生壳源岩浆而成岩。  相似文献   

2.
德乌鲁岩体位于西秦岭地区,其主体岩性为花岗闪长岩,在岩体内及其接触带发育有多处金、铜矿床。LA-ICP-MS 锆石U-Pb定年表明该岩体侵位于印支早期,年龄为(250±1.8) Ma,该岩体为准铝质,其铝饱和指数ASI为0.9~1.0。所有样品具有高的K2O含量(2.95%~3.52%)、K2O/Na2O比值(0.97~1.10)、Mg#(0.57~0.61)和相容元素含量(w(Cr)=(88~132)×10-6)。因此,我们认为德乌鲁寄主岩形成于壳幔岩浆的混合作用。在该岩体中广泛分布有镁铁质岩浆包体,这些包体即是镁铁质岩浆注入中酸性岩浆中时迅速降温形成的。德乌鲁包体具有中性的成分,其SiO2含量为56.17%~60.95%,岩性主要为辉长闪长岩和闪长岩。相对于寄主岩,包体有着更高的Mg#(0.65~0.67)和低的TiO2含量(0.57%~0.62%)。它们也有着高的钾含量(1.74%~2.43%),属于高钾钙碱性系列岩石。所有样品具有高的相容元素含量,如Cr((212~419)×10-6)和Ni((46~111)×10-6)。相对于重稀土元素,样品中轻稀土元素相对富集,并且具有中等的Eu负异常。在原始地幔标准化的微量元素蛛网图上,所有包体具有明显的Nb-Ta负异常。德乌鲁暗色包体可能形成于曾受俯冲作用改造过的富钾的岩石圈地幔源区部分熔融过程,并伴随有后期镁铁质矿物的分异。本区的印支早期岩浆作用及与其有关的矿床很可能形成于活动大陆边缘环境。  相似文献   

3.
西秦岭教场坝岩体岩浆混合成因的新认识   总被引:3,自引:0,他引:3  
教场坝岩体是一岩浆多次脉动形成的复式深成岩体,由3个单元组成,它是岩浆混合作用形成的混合花岗岩,在混染较强的花岗闪长岩中分布有大量的镁铁质包体.寄主岩化学成份贫SiO2,富FeO* Mgo,铝饱和度(A/CNK)>1.0,岩石为过铝质类型,KzO/Na2O>1.0;镁铁质包体(MME)富SiO2,贫FeO* MgO,铝饱和度(A/CNK)<1.0,K2O/Na2O<1.0,二者均为钙碱性系列,两者间有明显的物质交换.包体与寄主岩石微量元素均富集大离子亲石元素Ba,Sr,Rb,Sm,Be及高场强元素Nb,Th等,亲铁元素Co,Cr,Ni也相对富集,但二者演化规律不同;稀土元素总量寄主岩相对较低(REE=254.78×10-6),稀土配分模式发育明显的铕负异常,δEu值较低(平均0.48);镁铁质包体稀土总量相时较高(REE=298.75×10-6),配分模式发育极微弱的铕负异常,δEu值较高(平均0.78).研究表明:镁铁质包体具幔源型花岗岩类特征,而寄主岩石二长花岗岩具壳源型花岗岩特征,包体与寄主岩石具不同的岩浆来源.氧同素显示镁铁质包体中有大量地壳物质的加入,教场坝岩体的形成与岩浆混合作用有关,是酸性岩浆与基性岩浆混合的产物.  相似文献   

4.
通过青海东昆仑东部沟里地区阿斯哈岩体中寄主闪长岩和暗色微粒包体的岩相学、全岩地球化学研究,确定了岩石成因及其构造属性。阿斯哈岩体中暗色包体广泛分布,包体岩性主要为角闪辉长岩。包体具有岩浆结构,部分包体具有塑性流变特征,包体中可见寄主岩石矿物的捕掳晶和针状磷灰石,表现出岩浆混合的岩相学特征。主岩及暗色包体同属准铝质、高钾钙碱性-钾玄岩系列过渡岩石,主量元素在Harker图解及Al2O3/K2O-CaO/K2O和SiO2/CaO-K2O/CaO的共分母协变图上具良好的线性关系,反映两者成分的变化与岩浆混合作用有关。两者的稀土元素配分模式总体一致,显示二者密切的成因联系。两者都富含大离子亲石元素(Rb、K),相对亏损高场强元素(Nb、Ta、P、Ti)。暗色包体具有贫硅(w(SiO2)=50.70%~53.88%)和富镁、铁、钙的地球化学特征,其Mg#值较高(Mg#=0.52~0.59),暗示其来源于俯冲带流体交代地幔楔的部分熔融。主岩的Rb/Sr值为0.22~0.27,接近地壳平均值,Nb/Ta值为14.5~15.2,介于地幔平均值与地壳平均值之间,表明寄主岩石岩浆具有壳源岩浆的性质并经历了幔源岩浆的混合作用。结合区域构造演化及构造判别,认为阿斯哈岩体形成于安第斯型活动大陆边缘的构造环境。早三叠世,阿尼玛卿洋向北俯冲,俯冲带流体交代地幔楔,导致其部分熔融形成基性岩浆,底侵的幔源基性岩浆诱发下地壳部分熔融并与之发生混合形成本区闪长岩,而其中的暗色包体为幔源岩浆混合不彻底的产物。  相似文献   

5.
浙江沐尘石英二长岩体的岩石地球化学特征及构造意义   总被引:5,自引:0,他引:5  
卢成忠 《地球化学》2007,36(5):457-466
出露于江山-绍兴断裂带西南段东南侧的沐尘岩体,以发育暗色包体和环斑长石为特征,具有显著的岩浆混合作用.寄主岩为二长岩-石英二长岩组合,包体岩石为二长闪长岩.二长岩组合.造岩矿物有钾长石、斜长石、石英、普通角闪石和黑云母.岩石富碱(Na2O K2O=6.58%~10.42%,平均8.41%)、高钾(K2O/Na2O=0.72~1.45,平均1.16)、贫钛(TiO2=0.37%~1.22%,平均0.76%)、富集大离子亲石元素和轻稀土元素,具有钾玄质系列的岩石地球化学特征.该岩体侵位于后碰撞弧构造环境,是早白垩世早期该区重要的构造.岩浆热事件的产物.  相似文献   

6.
西南三江普朗铜矿岩浆混合作用:矿物学和地球化学证据   总被引:3,自引:2,他引:1  
刘欢  张长青  贾福东  周云满  娄德波 《岩石学报》2015,31(11):3189-3202
岩浆混合作用是近年来岩石学研究中的热点与难点,其研究对揭示壳幔相互作用,探讨成岩成矿过程具有重要意义。普朗铜矿位于西南三江义敦岛弧南段,是我国近年来发现的超大型斑岩铜矿床。矿体产于复式岩体中,复式岩体内发育大量暗色微粒包体。包体粒度较细,多呈椭圆形,其内可见具暗色矿物镶边的眼球状石英、针状磷灰石以及具有结构与成分不平衡现象的斜长石斑晶;与寄主岩相比,包体富集黑云母、角闪石等暗色矿物。主量元素组成上,包体相对于寄主岩Si O2(53.67%~61.50%)含量较低,Mg O(3.12%~5.40%)和Fe2OT3(3.38%~9.00%)含量较高。微量元素结果显示,包体与寄主岩具有相似的微量元素组成与稀土元素配分模式,均表现为富集大离子亲石元素(K、Rb、Ba、Sr),亏损高场强元素(Nb、Hf、P、Ti),无明显的δCe异常,轻稀土元素富集,重稀土元素亏损;但与寄主岩相比,包体具有较高的稀土元素总量(119.0×10-6~308.9×10-6)与较明显的Eu负异常(δEu=0.56~0.95)。以上结果表明,包体为岩浆混合作用的产物。文章进一步采用多重分形理论解析了包体中Mg、Fe、Ca、Al、K、Ti、P及Ba等元素的分布特征,定量刻画了岩浆混合作用的程度。结果表明,元素分布的多重分形谱越宽,关联维越小,则岩浆混合程度越高。  相似文献   

7.
南岭中段的锡田岩体燕山期岩石以斑状黑云母二长花岗岩为主,岩体中广泛发育暗色微粒包体?暗色微粒包体为岩浆结构,大多数具有塑性外形,发育淬冷边?反向脉,存在多种不平衡结构和矿物组合,如钾长石环斑?石英眼斑?针状磷灰石等,显示岩浆混合特征?岩石地球化学方面,暗色微粒包体具有比寄主岩贫硅?贫碱,富K?Fe?Mg?Ca?Ti 特征;暗色微粒包体及寄主岩富集轻稀土元素(LREE/HREE=2.6~8.8),具有中-强的铕负异常(δEu=0.09~0.74)以及具有相似的稀土元素配分曲线和微量元素蛛网图;在主要氧化物含量Harker 图解中投点多呈直线变异趋势,反映了两者具有密切的亲缘关系,利用共分母和不共分母图解进行判别,暗色微粒包体与寄主岩具岩浆混合特征,在MgO-TFeO判别图解中也指示包体为岩浆混合成因?上述岩相学和元素地球化学特征表明暗色微粒包体是基性岩浆侵入到酸性岩浆中淬冷形成的,指示锡田岩体存在两种岩浆的混合作用?通过LA-ICP-MS锆石U-Pb 定年,得到寄主岩形成年龄(150.04±0.52)Ma,暗色包体形成年龄(145.09±0.63)Ma,二者年龄在测试误差范围内一致,显示岩浆混合作用发生的时间大致为晚侏罗世?  相似文献   

8.
高精度SHRIMP锆石U-Pb定年结果表明,二台北花岗闪长岩的形成时代为299.3±8.7Ma,代表了岩浆侵入到上地壳的年龄;其中所含的暗色微粒包体形成时代为301.5±6.6Ma,与寄主岩石的时代在误差范围内完全相同。结合野外、岩相学和主量、微量元素地球化学特征分析,偏基性的暗色微粒闪长质包体与寄主花岗闪长质岩浆并非有直接成因联系,包体可能是由过冷的镁铁质岩浆混入到花岗闪长质岩浆中发生快速冷凝,然后被花岗闪长质岩浆携带、侵入到上地壳中形成的。因此,花岗闪长岩及其包体才能够具有相同的SHRIMP锆石U-Pb年龄。二台北岩体与东准噶尔广泛分布的以碱性花岗岩为代表的后碰撞花岗岩具有相同的形成时代,乌伦古-斋桑泊断裂北侧的花岗闪长岩、石英闪长岩等和断裂南侧的碱性花岗岩、钾长花岗岩等的形成时代非常相近,应该是同一期岩浆活动的产物,无法区分出先后顺序。而这些岩体普遍具有低的~(87)Sr/~(86)Sr初始比值和正的ε_(Nd)(t)值,表明它们都是新疆北部晚古生代幔源岩浆活动的产物,它们的形成和演化提供了准噶尔地区后碰撞幔源岩浆底侵作用导致大陆地壳垂向生长过程的信息。  相似文献   

9.
青海南山构造带是衔接宗务隆构造带、南祁连构造带和西秦岭造山带的重要结合带。沟后岩浆杂岩体位于青海南山构造带东段,主要由辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩组成。本文对沟后岩浆杂岩体进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb同位素年代学研究。结果表明,辉长岩、辉长闪长岩、石英闪长岩、花岗闪长岩及暗色微粒包体的结晶年龄分别为248.8±2.6 Ma、243.2±2.1 Ma、243.1±0.9 Ma、244.0±2.1 Ma和249±3 Ma。辉长岩富铁、镁,贫碱;辉长闪长岩高铝、富钙和钠,二者均为钙碱性岩类。石英闪长岩和花岗闪长岩为准铝-弱过铝质高钾钙碱性岩,暗色微粒包体属钙碱性-碱性岩系列。不同岩石类型均表现为富集大离子亲石元素(Cs、Rb、K)和Pb,亏损高场强元素(Nb、Ta、Ti)和P、Ba负异常;稀土元素配分曲线均具有轻重稀土分异的右倾特征,具弱-中等负Eu异常。岩相学和岩石地球化学特征表明沟后岩浆杂岩体具壳幔岩浆混合特征,暗示其可能形成于由俯冲流体交代地幔楔部分熔融的幔源岩浆底侵作用下的构造环境。辉长岩为幔源岩浆经分离结晶的产物,辉长闪长岩为幔源岩浆经分异演化并混染少量壳源岩浆的产物;中基性岩浆与壳源中酸性岩浆发生混合并经历一定的分异演化过程形成了石英闪长岩和花岗闪长岩。结合区域地质资料分析认为,沟后岩浆杂岩体可能代表了研究区早三叠世晚期-中三叠世早期宗务隆洋向南消减作用相关的构造岩浆事件。  相似文献   

10.
龙新岩体和夏郢岩体位于扬子地块与华夏地块拼合带的西南端,岩体中的Ⅰ型花岗岩成因研究对揭示桂东南地区早古生代的地球动力学背景及其构造演化具有重要的地质意义.对龙新岩体的寄主岩和其暗色微粒包体,以及夏郢岩体岩石进行了LA-ICP-MS锆石U-Pb定年、Lu-Hf同位素和全岩地球化学研究.锆石U-Pb定年结果显示,龙新岩体的寄主岩(花岗闪长岩)的年龄为440±2 Ma;龙新岩体的暗色包体(闪长岩)的年龄为441±1 Ma,寄主岩与暗色包体为同期岩浆作用的产物.夏郢岩体花岗闪长岩和二长花岗岩年龄分别为447±3 Ma和436±3 Ma,说明夏郢岩体至少发生了2期岩浆侵入事件.Hf同位素研究表明,龙新岩体寄主岩和暗色微粒包体的锆石εHf(t)值分别为-3.32~-5.83和-17.89~-1.82,二阶段模式年龄(TDM2)分别为1.62~1.76 Ga和1.57~2.54 Ga;夏郢岩体早期花岗岩闪长岩和晚期二长花岗岩的锆石εHf(t)值分别为-15.43~3.03和-4.79~6.82,TDM2分别为1.59~1.99 Ga和0.97~1.70 Ga,指示物源主要来自古-中元古代的地壳物质.地球化学特征表明龙新岩体寄主岩为准铝质高钾钙碱性Ⅰ型花岗岩,寄主岩和暗色微粒包体均富集轻稀土元素和大离子亲石元素,亏损重稀土元素及高场强元素;夏郢岩体早期的花岗闪长岩为弱过铝质高钾钙碱性Ⅰ型花岗岩,晚期的二长花岗岩则为强过铝质高钾钙碱性Ⅰ型花岗岩,主微量元素特征均与龙新岩体寄主岩相似.根据研究区花岗岩和镁铁质包体的岩相学、年代学、地球化学及Hf同位素组成特征,表明龙新岩体的暗色包体(闪长岩)为岩浆混合成因,而龙新岩体寄主岩(花岗闪长岩)和夏郢岩体(早期花岗岩闪长岩和晚期二长花岗岩)具有一致的岩石源区和岩石成因,但在后期的成岩过程中存在岩浆混合和结晶分异程度的差异.综合以往对华南地区构造背景的研究,认为龙新和夏郢岩体是在扬子地块和华夏地块陆内造山期后,岩石圈伸展减薄,热的幔源岩浆上涌底侵,中-下地壳受到地幔热影响发生部分熔融,形成的酸性岩浆在源区和基性岩浆经历了不均一且不强烈的壳-幔混合作用形成的.   相似文献   

11.
This paper presents new petrographic observations and geochemical and microprobe analyses for the Laomiaojishan, Xiaotongguanshan, and Tianebaodanshan intrusions in the Tongguanshan mineral district, East China. The plutons vary in composition from quartz monzonitic diorite to pyroxene monzonitic diorite, and contain gabbroic to dioritic xenoliths. The Xiaotongguanshan intrusion yields a SHRIMP zircon U–Pb age of 139.5±2.9 Ma, indicating Late Jurassic to Early Cretaceous magmatism in the Lower Yangtze River Valley. Relative to host rocks, the gabbro and diorite xenoliths are low in SiO2 (52.03–54.61 wt‐%), Al2O3 (12.87–14.43 wt‐%), and total alkalis (Na2O+K2O; 5.26–6.30 wt‐%), but high in MgO (5.41–11.66 wt‐%); the host rocks have high SiO2 (59.97–64.44 wt‐%), Al2O3 (16.43–17.59 wt‐%), and total alkalis (6.67–8.25 wt‐%), but are low in MgO (1.52–2.50 wt‐%). Concentrations of rare earth elements (REEs) in the xenoliths (165.70–190.40 ppm) are similar to those in the host rocks (166.12–185.95 ppm), although the ratio of light REEs to heavy REEs in the xenoliths (3.39–4.27) is lower than that in the host plutons (4.86–5.94). All of the analysed rocks show similar REE patterns, although the xenoliths display marked positive Eu anomalies and the host rocks show slightly negative Eu anomalies. Values of epsilon Nd (t) ranges from ?4.9 to ?9.9 in the gabbro xenoliths and from ?11.4 to ?11.9 in the host intrusives. Initial 87Sr/86Sr ratios are 0.7064–0.7073 in the xenoliths and 0.7072–0.7084 in the quartz monzonitic diorite host rocks. Crystallization temperatures of hornblende and plagioclase in the gabbro xenoliths, diorite xenoliths, and host rocks are 816, 773–790, and 664–725°C, respectively, based on an amphibole–plagioclase geothermometer. The pressures recorded by these phases indicate that they formed at depths of 26, 12–15, and 3–4 km, respectively, based on an aluminum‐in‐hornblende geobarometer. The petrological and geochemical features of the analysed intrusions and xenoliths are consistent with their derivation from basic to intermediate‐acidic magmas that possibly formed via a series of complex interactions between underplated, mantle‐derived basaltic magma and varying amounts of middle‐ to lower‐crustal material, followed by assimilation–fractional crystallization.  相似文献   

12.
安徽铜陵地区中生代岩浆活动频繁,形成了一系列与铜、金多金属成矿作用关系密切的中酸性侵入岩。在这些侵入岩中分布有大量的镁铁质团块、堆积晶和微粒闪长质包体。在这些侵入岩及其岩石包体中观察到了一定数量的硫化物-氧化物包裹体。文章对老庙基、小铜官山和小陶家岩体及其岩石包体中的硫化物-氧化物包裹体进行了详细的岩相学观察和电子探针分析。观察和分析结果显示,镁铁质团块中硫化物包裹体内的矿物主要有磁黄铁矿、黄铜矿、单硫化物固溶体和镍黄铁矿,这些硫化物相(黄铜矿除外)中的Ni、Cu平均含量(wB,下同)分别为6.91%和0.44%;微粒闪长质包体和寄主岩中硫化物包裹体内的矿物主要为磁黄铁矿和黄铜矿,这些硫化物相(黄铜矿除外)中的Ni、Cu平均含量分别为0.44%、0.07%(微粒闪长质包体)和0.09%、0.42%(寄主岩)。镁铁质团块、微粒闪长质包体和寄主岩中氧化物包裹体内的矿物分别为铬磁铁矿(Cr2O3平均含量为4.44%)、磁铁矿(Cr2O3平均含量为0.44%)和磁铁矿(Cr2O3平均含量为0.07%);散布的氧化物颗粒分别为铬磁铁矿(Cr2O3平均含量为6.58%)、磁铁矿+铬磁铁矿(Cr2O3平均含量为0.86%)...  相似文献   

13.
The Pleasant Bay layered gabbro–diorite intrusion, locatedon the coast of Maine between Bar Harbor and Machias, is roughlyoval in plan, measuring 12 km by 20 km. Gravity data, contactrelations, and internal layering suggest that it is basinformin structure with a maximum thickness of {small tilde}3 km.Its roof and upper parts have been lost through erosion. Whereit is in contact with underlying granite, the base of the intrusiontypically consists of strongly chilled gabbro with convex-downwardlobate forms, suggesting that the granite was incompletely solidifiedwhen the gabbro was emplaced. Roughly 90% of the exposed rocksare weakly layered gabbro and mafic diorite, both of which varywidely in grain-size and texture. Layers and lenses of medium-grainedleucocratic diorite to granodiorite are widely intercalatedwith the chilled mafic rocks and commonly contain partly digestedmafic inclusions; they also commonly contain zones of pillow-likebodies of gabbro chilled on all margins. The dioritic rocksare consistently topped by gabbroic layers with chilled lobatebases and commonly appear to feed granitic pipes and diapirsinto overlying gabbro. Much of the intrusion can be subdividedinto hundreds of macrorhythmic units (from 1 to 100 m thick)consisting of basally chilled gabbro that grades upward to dioriteor highly evolved leucocratic silicic cumulates. Basaltic dikesare abundant both in the underlying granite and in the layeredgabbro–diorites; they have appropriate compositions tobe feeders for chilled gabbroic layers in the Pleasant Bay intrusion. The layered rocks of the Pleasant Bay intrusion record hundredsof basaltic injections into a chamber with resident silicicmagma. Small injections produced chilled gabbroic layers andpillows within silicic cumulates. Larger infusions of basalticmagma produced temporary compositional stratification and episodesof double-diffusive convection within the chamber. Althoughfractional crystallization produced compositional variationin much of the gabbro, units that grade from chilled gabbroat the base to highly silicic cumulates at the top provide cumulaterecords of magma stratification and hybridization along a double-diffusiveinterface between basaltic and silicic magmas. The intrusionprovides a superb plutonic record of events that have oftenbeen inferred for silicic eruptive centers. Mafic–siliciclayered intrusions comparable with the Pleasant Bay are morewidespread than has generally been appreciated.  相似文献   

14.
Wadi El-Markh gabbro–diorite complex is composed of pyroxene hornblende gabbros, hornblende gabbros, diorites and quartz diorites. According to their bulk rock geochemistry and mineral chemistry, the gabbroic and dioritic rocks represent fractionates along a single line of descent and crystallized from a calc-alkaline mafic magma. When compared to the primitive mantle, all members of the gabbroic–dioritic rock suite are enriched in the large ion lithophile elements relative to the high field strength elements and display distinctive negative Nb and P2O5 anomalies. This signals an arc setting. Fractionation modeling involving the major elements reveals that the hornblende gabbros were generated from the parent pyroxene hornblende gabbros by 61.86% fractional crystallization. The diorites were produced from the hornblende gabbros by fractional crystallization with a 58.97% residual liquid, whereas the quartz diorites were formed from the diorites by 26.58% fractional crystallization. According to geothermobarometry based on amphibole mineral chemistry, the most primitive pyroxene hornblende gabbros crystallized at ~830 °C/~5 kbar. The crystallization conditions of the quartz diorites were estimated at ~570 °C/~2 kbar. In consequence the Wadi El-Markh gabbro–diorite complex represents a single magmatic suite of which fractionates crystallized in progressively shallower levels of an arc crust.  相似文献   

15.
The Nabar pluton with the age of Oligo-Miocene located northwest of Isfahan, the Urumieh-Dokhtar magmatic belt, is composed of gabbro, gabbro diorite, diorite, quartz diorite, tonalite, and quartz monzonite. These rocks contain plagioclase, quartz, alkali-feldspar, magnesiohornblende, actinolite, tremolite-hornblende, actinolite-hornblende, anthophyllite, biotite, and Na-poor pyroxene. Application of the Al-in-hornblende barometry indicates pressures of 2–2.15 kbar, whereas the clinopyroxene barometry shows a pressure of 5 kbar. The temperature (i.e., 750–800°C) is estimated using the amphibole-clinopyroxene thermometry in a dioritic sample. Magmatic water content was greater than 10% at the time of formation of dioritic rocks in the Nabar pluton. Based on chemistry of mafic minerals and geochemical data, the Nabar plutonic complex comprises medium-K, calc-alkaline, and I-type granitoid. The rocks are characterized by enrichment of lithophile elements (LILEs) and depletion of high-field-strength elements (HFSEs). The Nabar rocks have weak concave-upward rare earth element (REE) patterns, suggesting that amphibole played a significant role in their generation during magma segregation. Low (Al2O3/(FeO + MgO + TiO2) and (Na2O + K2O)/(FeO + MgO + TiO2) ratios, and the patterns of trace and rare earth elements suggest that these rocks formed along a destructive plate margin and were derived from a lower crustal source. The magma probably formed by partial melting of lower crustal protoliths (amphibolites). Lower crust contamination with magma derived from partial melting of the upper mantle has an important role in the formation of this intrusive body, and a fractional crystallization of melts in higher crustal levels generated this spectrum of rock types. Mantle-derived gabbroic magmas emplaced into the lower crust are the most likely heat sources for partial melting.  相似文献   

16.
Cliff S.J. Shaw   《Lithos》1997,40(2-4):243-259
The Coldwell alkaline complex is a large (> 350 km2) gabbro and syenite intrusion on the north shore of Lake Superior. It was emplaced at 1108 Ma during early magmatic activity associated with the formation of the Mid-Continent Rift of North America. The eastern gabbro forms a partial ring dyke on the outer margin of the complex and consists of at least three discrete intrusions. The largest of these is the layered gabbro that comprises a 300 m thick fine- to medium-grained basal unit overlain by up to 1100 m of variably massive to layered gabbroic cumulates which vary from olivine gabbro to anorthosite. Several xenoliths of Archaean metamorphic rocks that range in size from 10's to 100's of meters are present in the central part of the intrusion. Within discrete horizons in the layered gabbro are many centimeter- to meter-scale, gabbroic xenoliths. The main cumulus minerals, in order of crystallization, are plagioclase, olivine and clinopyroxene ± Fe-Ti oxides. Biotite and Fe-Ti-oxide are the dominant intercumulus phases. Orthopyroxene occurs not as a cumulus phase but as peritectic overgrowths on cumulus olivine. A detailed petrographic and mineral chemical study of samples from two stratigraphically controlled traverses through the layered gabbro indicates that the stratigraphy cannot be correlated along the 33 km strike of the ring dyke. Mineral compositions show both normal and reversed fractionation trends. These patterns are interpreted to record at least three separate intrusions of magma into restricted dilatant zones within the ring dyke possibly associated with ongoing caldera collapse. Calculations of parental melt composition using mineral — melt equilibria show that even the most primitive gabbros crystallized from an evolved magma with mg# of 0.42-0.49. The presence of orthopyroxene overgrowths on cumulus olivine suggests rising silica activity in the melt during crystallization and implies a subalkaline parentage for the layered gabbro.  相似文献   

17.
Two types of mafic intrusions have been recognized in the north of the Bafq district, Central Iran. A number of olivine-gabbroic to gabbroic sills intruded the Rizu Formation, comprised of alternating carbonate and volcanic rocks. Mineralogical data show that olivine + pyroxene + brown amphibole (kaersutite) + calcic plagioclase + opaque comprise the olivine-gabbroic rocks, and intermediate (or sodic) plagioclase + altered pyroxene and altered amphibole to biotite + opaque minerals the gabbroic rocks. Both rock types have shown within-plate and alkaline characters and have been presumed to be related to rift formation. The mafic-alkaline magma source of the sills is proposed to have been derived from enriched mantle. Regionally, two Gabbro–Diorite intrusions have been identified in the metamorphic complexes. Mineralogical data suggest that the pyroxene + amphibole (hornblende) + plagioclase + biotite + opaque minerals formed the gabbro to diorite intrusions. These rocks have shown characteristics of calc-alkaline and volcanic arc magmatism.  相似文献   

18.
Geochemical anomaly separation using the concentration–number (C–N) method at the Haftcheshmeh porphyry system in NW Iran is the aim of this study. We used lithogeochemical data sets to explore Cu, Mo, Au and Re mineralization in gabbroic, dioritic and monzonitic units at the Haftcheshmeh Cu–Mo porphyry system. The obtained results were interpreted using a rather extensive set of information available for each mineralized area, consisting of detailed geological mapping, structural interpretation and alteration data. Threshold values of elemental anomalies for the mineralized zone were computed and compared with the statistical methods based on the data obtained from chemical analyses of samples for the lithological units. Several anomalies at local scale were identified for Cu (40 ppm), Mo (12 ppm), Au (79 ppb), and Re (0.02 ppm), and the results suggest the existence of local Cu anomalies whose magnitude generally is above 500 ppm. The log–log plots show the existence of three stages of Cu and Mo enrichment, and two enrichment stages for Au and Re. The third and most important mineralization event is responsible for presence of Cu at grades above 159 ppm. The identified anomalies in Haftcheshmeh porphyry system, and distribution of the rock types, are mainly gabbrodiorite–monzodiorite, granodiorite and monzodiorite–diorite that have special correlation with Cu–Mo and gabbroic and monzonitic rocks, especially the gabbrodiorite–monzodiorite type, which is of considerable importance. The study shows that these elemental anomalous parts have been concentrated dominantly by potassic and phyllic, argillic and propylitic alterations within the gabbroic, monzonitic and dioritic rocks especially in the gabrodioritic type in certain parts of the area. The results, which were compared with fault distribution patterns, revealed a positive correlation between mineralization in anomalous areas and the faults present in the mineralized system.  相似文献   

19.
《International Geology Review》2012,54(14):1559-1575
The middle segment of the Yangtze River Deep Fault Belt, located in the foreland of the Dabie orogen, contains widely exposed volcanic–intrusive complexes that formed during two episodes of magmatism (post-collisional and post-orogenic), reflecting crust–mantle interactions during the Late Jurassic (J3) to Early Cretaceous (K1). This article summarizes research on the Mesozoic igneous suites and xenolith suites in the area along the Yangtze River. ‘Post-collisional magmatism’ occurred during lithospheric extension at ~145–130 Ma. Its beginning and end are marked by gabbroic xenoliths and pyroxene cumulates within intrusions at Tongling, and by alkali-rich magmatic rocks. The association includes peraluminous silicic rocks and metaluminous mafic–felsic igneous suites, ranging from medium-K to high-K calc-alkaline to shoshonitic compositions. Taking the Tongling region as an example, quartz monzodiorite yields a sensitive high resolution ion microprobe (SHRIMP) zircon U–Pb age of 139.5 ± 2.9 Ma, and granodiorite yields an age of 135.5 ± 4.4 Ma. These intrusive rocks contain 52.79–66.46 wt.% SiO2, 13.12–17.73 wt.% Al2O3, 1.37–4.62 wt.% MgO, 3.86–6.84 wt.% FeOT, and 4.71–7.87 wt.% total alkalis (Na2O?+?K2O). ACNK values range from 0.62 to 1.20, and ANK values from 1.45 to 3.48. ‘Post-orogenic magmatism’ occurred during lithospheric delamination at ~130–120 Ma. The start of magmatism was marked by the formation of gabbro containing spinel lherzolite xenoliths in the Nanjing–Wuhu Basin (NWB), and its end was marked by the generation of feldspathoid phenocryst-bearing phonolite in the NWB and the Lujiang–Zongyang Basin (LZB), respectively. The association that formed during this episode ranges from alkaline to peralkaline. Taking the Niangniangshan Formation in the NWB as an example, the Nosite phonolite yields a whole-rock monomineral Rb–Sr isochron age of 120 ± 9 Ma, and contains 49.92–60.09 wt.% SiO2, 17.67–20.65 wt.% Al2O3, 0.08–2.45 wt.% MgO, 1.32–6.62 wt.% FeOT, and 9.24–13.92 wt.% total alkalis (Na2O?+?K2O). ACNK values range from 0.72 to 1.24, and ANK values from 1.03 to 1.35.

The two magmatisms correspond to two episodes of crust–mantle interaction. The first involved intensive interaction between middle–lower crust and underplated basaltic magma derived from the upper mantle lithosphere, whereas the second involved minor interaction between the middle–lower crust and basaltic magma derived from the lower lithospheric mantle.  相似文献   

20.
Gabbro inclusions from Tindfjallajökull are divided into two types: I. Panidiomorphic gabbros of non-cumulative origin composed of plagioclase + olivine ± clinopyroxene and interstitil vesicular glass. They have formed in equilibrium with the host magma and may either represent a marginal facies or a highly solidified magma body. In the latter case the host magma or part of it could be mobilized interstitial liquid. II. Allotriomorphic-hypidiomorphic tholeiitic olivine gabbro and diorite xenoliths with scarce Ti-pargasite which have undergone less than 10% partial melting in the host magma forming melts of alkali basaltic or Hekla andesite-like compositions dependent on the original mineral assemblage. Such liquids, enriched in K2O and possibly other incompatible elements, may contaminate basaltic magmas rising slowly through a gabbroic lower crust. Large scale production of andesites by partial melting of such rocks is not possible but would need more hydrous or differentiated source rocks.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号