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1.
香加南山花岗岩基位于东昆仑造山带东段,岩基主要岩石类型为花岗闪长岩。千瓦大桥-加鲁河一带花岗岩体为香加南山岩基的重要组成部分。香加南山花岗岩基含大量暗色微粒包体,包体中捕掳晶丰富。千瓦大桥-加鲁河一带花岗岩体寄主岩中斜长石和暗色微粒包体中捕掳晶斜长石具正常环带,An值震荡变化,角闪石和黑云母Mg O含量和Mg#值较低,具壳源特征;暗色微粒包体中基质斜长石具核边结构,核部和边部An值存在间断,角闪石和黑云母Mg O含量和Mg#值较高,具幔源特征。LA-ICP-MS锆石U-Pb同位素定年结果显示千瓦大桥花岗闪长岩、暗色微粒包体和加鲁河辉长岩的结晶年龄分别为251.0±1.9Ma、252.8±3.0Ma和221.4±3.3Ma。千瓦大桥花岗闪长岩和加鲁河花岗闪长岩富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损高场强元素(HFSE),具较低的Mg#和Nb/Ta比值;从千瓦大桥到加鲁河花岗闪长岩呈现出由准铝质中钾钙碱性系列向准铝-弱过铝质中钾-高钾钙碱性系列演化;暗色微粒包体和加鲁河辉长岩轻重稀土元素分异程度相对较低,具较高的Mg#和Nb/Ta比值。千瓦大桥花岗闪长岩和加鲁河花岗闪长岩分别为古特提斯演化俯冲阶段和后碰撞阶段幔源岩浆底侵新生地壳使其部分熔融产物。镁铁质岩浆注入长英质岩浆的混合作用形成了暗色微粒包体。岩浆混合过程中,如果岩浆不完全混合,混合岩浆中混入物质除了长英质岩浆的残留岩浆和捕掳晶,还应该有镁铁质岩浆与长英质岩浆之间的元素梯度差导致的物质扩散;如果岩浆为近完全混合,混合岩浆近似为镁铁质岩浆和长英质岩浆以一定比例二元混合。东昆仑东段晚古生代-早中生代幔源岩浆对花岗质岩浆的影响是一个持续的过程,从俯冲阶段早期流体交代地幔熔融,到俯冲阶段后期板片断离,然后同碰撞阶段板片断离的持续影响,再到后碰撞阶段加厚地壳的拆沉作用,由于地球动力学体制不同,导致幔源岩浆影响的大小和特征不同。 相似文献
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斜长石作为主要造岩矿物,是研究岩石成因、示踪岩浆演化和岩浆混合过程的有效工具.对冈底斯带曲水岩基始新世花岗闪长岩、二长花岗岩、闪长岩脉和暗色包体中的斜长石进行了阴极发光图像结构特征、电子探针主量元素和LA-ICP-MS微量元素成分的分析,揭示了斜长石复杂环带的成因和相关的岩浆过程.该区斜长石的阴极发光图像呈现出多种颜色且与其An值相对应,随着An值降低依次为绿色、蓝色和暗灰色或暗红色等,并发育补丁状环带、筛状环带、韵律环带等.花岗闪长岩、二长花岗岩中斜长石的An值具有相似的变化范围(20~55),而闪长岩脉和暗色包体中An值的变化范围较大(25~85),表明曲水岩基经历了复杂的开放过程.微量元素结果表明:花岗闪长岩与闪长岩脉和暗色微粒包体具有相同的Sr含量范围(600×10^-6~1 100×10^-6);而二长花岗岩的Sr含量(1 000×10^-6~2 400×10^-6)整体高于前者.以上研究表明,花岗闪长岩中阴极发光呈现绿色的核部或幔部是偏中性岩浆注入寄主岩岩浆混合的结果;具有高Sr含量的二长花岗岩认为是高Sr含量的岩浆结晶形成的;闪长岩脉和暗色微粒包体中的筛状结构斜长石为寄主岩捕掳晶. 相似文献
3.
青海南山构造带西段黑马河花岗杂岩体锆石U-Pb年代学、地球化学特征及其地质意义 总被引：2，自引：0，他引：2
本文对青海南山构造带西段黑马河花岗杂岩体中的石英闪长岩和花岗闪长岩以及花岗闪长岩中的暗色微粒包体进行了详细的岩石学、岩石地球化学和LA-ICP-MS锆石U-Pb年代学研究。结果表明,花岗闪长岩及暗色微粒包体的结晶年龄分别为244.4±1.1 Ma和243.0±1.2 Ma,表明岩体形成于中三叠世早期。石英闪长岩和花岗闪长岩为准铝质高钾钙碱性系列,暗色微粒包体为高钾钙碱性—钾玄岩系列,稀土元素配分曲线均具有轻重稀土明显分异的右倾特征,具弱负Eu异常(δEu=0.65~0.83),富集大离子亲石元素(Cs、Rb、Th、K)和Pb,亏损高场强元素(Nb、Ta、Ti)和P、Ba负异常。岩相学和岩石地球化学特征指示黑马河花岗杂岩体具壳幔岩浆混合特征,形成于活动大陆边缘的俯冲环境,石英闪长岩为受俯冲流体交代的地幔楔部分熔融产生的基性岩浆演化的产物,花岗闪长岩则源自壳源岩浆与少量幔源岩浆的混合。黑马河花岗杂岩体是中三叠世早期宗务隆洋向南俯冲消减的岩浆记录。 相似文献
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义敦岛弧形成于晚三叠世大规模俯冲造山作用过程中,位于松潘甘孜地体和羌塘地体之间。稻城边部岩体是义敦岛弧带内规模巨大的复式花岗质岩体,由花岗岩、花岗闪长岩和钾长花岗岩组成。大量暗色镁铁质微粒包体发育于花岗闪长岩和钾长花岗岩中,且其与寄主岩石的接触界线明显。暗色镁铁质微粒包体具有细粒结构,发育石英眼构造、针状磷灰石和具环带结构的斜长石斑晶。文中以稻城岩体寄主岩石和暗色微粒包体中斜长石、黑云母和角闪石为研究对象,开展岩相学和电子探针原位化学成分分析,厘定了矿物形成的物理化学条件,探讨了岩浆混合作用过程及其形成的构造环境。研究表明：花岗闪长岩和暗色微粒包体中的斜长石主要为中长石,其核部呈浑圆状;前者核部的An值(21~50)显著高于幔部(21~34);后者则发育典型的突变环带,An值(29~44)呈波状变化且相对集中。暗色微粒包体与寄主花岗闪长岩中斜长石的An值部分重叠表明二者形成过程中存在含量的岩浆混合作用。斜长石环带中的An值随Al2O3、FeO、MgO和CaO含量的升高而升高,但随SiO2、Na2O和K2O含量的升高而降低。寄主岩石和暗色微粒包体中角闪石富镁铁,阳离子特征为：CaB=1.56~1.75,Ti=0.08~0.13,属于钙质角闪石,具壳源特征,其结晶温度分别为697~725 ℃和680~705 ℃。花岗闪长岩中黑云母的Mg/(Mg+Fe2+)为0.37~0.45,显示出富Fe贫Ca、Mg,属于典型的岩浆成因黑云母。黑云母TiO2含量变化范围为3.54%~4.62%,Al2O3含量变化范围为13.89%~15.15%;黑云母的氧化系数为0.08~0.11,Mg#为0.39~0.46,MF值为0.36~0.44,单位分子中阳离子数AlⅥ为0.03~0.11,以单位分子中Ti和Al阳离子数计算的黑云母结晶温度为584~624 ℃,表明其结晶温度较高,具壳幔混源特征。稻城岩体是以壳源为主的壳幔混源成因的I型花岗岩,暗色微粒包体是由镁铁质岩浆与长英质岩浆不同程度的混合作用形成的。 相似文献
5.
本次研究以东昆仑西段开木棋河东地区的花岗闪长岩及其闪长质微粒包体为研究对象,开展年代学和地球化学研究,探究其成因机制和构造背景.岩石学研究发现,花岗闪长岩与微粒包体具有相似的矿物组成,但微粒包体发育石英和长石斑晶,具有明显的岩浆混合印记.LA-ICP-MS锆石U-Pb年代学分析揭示,花岗闪长岩的结晶年龄为240.1±1.5 Ma,属中三叠世早期.暗色微粒包体w(SiO2) 54.89％～56.08％,平均55.66％,MgO相对较低;寄主花岗闪长岩与暗色包体LaN/YbN分别为6.77～13.41和5.01～7.79,δEu均＜1或接近1;二者均富集为大离子亲石元素Rb,K和不相容元素U,Th;寄主花岗闪长岩Nb/Ta均值为10.98,与地壳Nb/Ta平均值相近,Sr均值为334×10-6,Yb均值为1.63×10-6,表现为低Sr低Yb型,推测寄主花岗闪长岩起源于含角闪石—石榴石—辉石的高压麻粒岩熔融.暗色微粒包体Nb/Ta值为13.87～16.19,均值为14.8,Rb/Sr值为0.22～0.34,具有壳幔混源特征.综合区域地质资料,本次研究认为开木棋河东地区含暗色微粒包体的花岗闪长岩形成于俯冲—碰撞转换阶段,即中三叠世早期阿尼玛卿古特提斯洋俯冲闭合和巴颜喀拉与昆仑陆块发生碰撞的构造转换阶段. 相似文献
6.
西秦岭金厂石英闪长岩的岩浆混合成因：岩相学和锆石U-Pb年代学证据及其构造意义 总被引：7，自引：0，他引：7
位于西秦岭南部的金厂石英闪长岩岩体内含有大量镁铁质暗色微粒包体,包体大多呈浑圆状和水滴状,部分呈不规则拉长状,与寄主岩的接触界线截然或呈渐变过渡关系。石英闪长岩中的磷灰石呈短柱状,而包体中的磷灰石则呈细长针状,反映基性岩浆的快速冷凝结晶。石英闪长岩中的斜长石发育振荡环带,核部的斜长石An低,而边部斜长石An先急剧上升,复又下降;核部与边部之间存在明显的间断,同时斜长石边部包裹有暗色矿物,指示其形成时可能有更基性的岩浆注入。寄主岩中的角闪石大多为普通角闪石和镁普通角闪石,属SiO2饱和型,而包体中角闪石一部分为镁普通角闪石,属SiO2饱和型,一部分为韭闪石、韭闪石质普通角闪石,属SiO2不饱和类型。包体中的角闪石自核部到边部,Al2O3与TiO2含量急剧下降,说明核部和幔部相对于边部形成于更高温的环境。寄主岩中黑云母部分为铁质黑云母,部分为镁质黑云母,而包体中黑云母均为镁质黑云母,在∑FeO/(∑FeO+MgO)对MgO图解上寄主岩与包体中黑云母均落入壳-幔混源区。寄主岩和包体中的锆石均为典型的岩浆锆石,LA-ICP-MS锆石U-Pb定年表明它们的形成年龄分别为212±2Ma及215±1Ma(2σ),在误差范围内基本一致,证明二者同时形成。综合以上岩相学和年代学证据认为,金厂石英闪长岩和镁铁质暗色微粒包体是幔源基性岩浆和壳源酸性岩浆混合作用的产物,形成于秦岭造山带中三叠世造山后伸展环境。结合区域上的研究结果认为,中—晚三叠世时期的幔源岩浆底侵和下地壳部分熔融在西秦岭广泛存在。 相似文献
7.
位于西秦岭南部的金厂石英闪长岩岩体内含有大量镁铁质暗色微粒包体,包体大多呈浑圆状和水滴状,部分呈不规则拉长状,与寄主岩的接触界线截然或呈渐变过渡关系.石英闪长岩中的磷灰石呈短柱状,而包体中的磷灰石则呈细长针状,反映基性岩浆的快速冷凝结晶.石英闪长岩中的斜长石发育振荡环带,核部的斜长石An低,而边部斜长石An先急剧上升,复又下降;核部与边部之间存在明显的间断,同时斜长石边部包裹有暗色矿物,指示其形成时可能有更基性的岩浆注入.寄主岩中的角闪石大多为普通角闪石和镁普通角闪石,属SiO2饱和型,而包体中角闪石一部分为镁普通角闪石,属SiO2饱和型,一部分为韭闪石、韭闪石质普通角闪石,属SiO2不饱和类型.包体中的角闪石自核部到边部,Al2O3与TiO2含量急剧下降,说明核部和幔部相对于边部形成于更高温的环境.寄主岩中黑云母部分为铁质黑云母,部分为镁质黑云母,而包体中黑云母均为镁质黑云母,在∑FeO/(∑FeO+MgO)对MgO图解上寄主岩与包体中黑云母均落入壳-幔混源区.寄主岩和包体中的锆石均为典型的岩浆锆石,LA-ICP- MS锆石U- Pb定年表明它们的形成年龄分别为212±2 Ma及215±1Ma(2σ),在误差范围内基本一致,证明二者同时形成.综合以上岩相学和年代学证据认为,金厂石英闪长岩和镁铁质暗色微粒包体是幔源基性岩浆和壳源酸性岩浆混合作用的产物,形成于秦岭造山带中三叠世造山后伸展环境.结合区域上的研究结果认为,中—晚三叠世时期的幔源岩浆底侵和下地壳部分熔融在西秦岭广泛存在. 相似文献
8.
西藏曲水碰撞花岗岩的混合成因：来自成因矿物学证据 总被引：5，自引：3，他引：5
西藏曲水碰撞花岗岩地处冈底斯构造-岩浆带中部,呈东西向平行雅鲁藏布缝合带分布.该岩体以花岗闪长岩、石英闪长岩为主,其次为石英二长闪长岩.岩体内普遍发育微粒镁铁质包体.对花岗闪长岩、石英闪长岩及微粒镁铁质包体的成因矿物学研究结果显示：（1）斜长石发育环带且边缘和核部偏基性,幔部酸性;（2）斜长石斑晶边缘常含有角闪石、黑云母等暗色矿物包体;（3）钾长石X射线结构分析显示自核部向边缘温度呈现逐渐升高的特点;（4）长石矿物中普遍含有较高的Cr、Ni、Co元素,明显不同于壳熔花岗岩;（5）角闪石、黑云母矿物MgO含量高于典型壳熔花岗岩;（6）包体中发育针状磷灰石和角闪石,显示为岩浆淬冷的结果.上述特征不可能用正常岩浆分异作用来解释,而更可能是壳-幔岩浆混合作用的结果.采用矿物温压计所得到的结果也符合混合后的岩浆演化特征. 相似文献
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阿翁错地区早白垩世花岗闪长岩位于班公湖-怒江成矿带西段,广泛发育暗色微粒包体,是研究岩浆混合作用的理想对象。本文从地质学、岩相学和矿物化学等方面对花岗闪长岩开展了详细研究。包体形态多样,与寄主岩呈渐变或截然型接触关系,包体与寄主岩之间相互穿插,接触带发育冷凝边,包体从寄主岩中捕获了大量捕虏晶矿物,包体和寄主岩中均见针状磷灰石。电子探针结果显示:具正环带特征的寄主岩斜长石An值变化范围不大,在48.16～59.05之间,具致密韵律环带特征,可能代表镁铁质岩浆注入长英质岩浆房前结晶的斜长石;具反环带特征斜长石的An值变化范围较大,核部An值为29.86,往外An值陡增至51.09,整体呈逐渐增大趋势,暗示存在富钙基性岩浆的加入;具正-反环带特征的寄主岩斜长石核部至中间区域An值变化相对复杂,具稀疏韵律环带结构特征,反映斜长石结晶过程中因岩浆混合作用岩浆房环境发生突变,随着混合作用持续进行,岩浆逐渐冷却,斜长石在静态环境下继续结晶形成干净的正环带边部;包体斜长石虽然存在正环带,但其An值变化范围较大,在28.63～62.40之间,核部An值高,边部An值骤然降低,可能是镁铁质岩浆与长英质岩浆... 相似文献
10.
青海南山沟后岩浆杂岩体锆石U-Pb年代学、岩石成因及其地质意义 总被引：1，自引：0，他引：1
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
11.
The Zhoukoudian pluton in the North China craton is a circular granodiorite intrusion containing porphyritic diorite dykes (PDDs), porphyritic granodiorite dykes (PGDs) and abundant mafic microgranular enclaves (MMEs), which provide an excellent opportunity to study fractional crystallization and magma mixing. The PDDs and PGDs are located in the western part of the pluton with the PDDs intruded by the PGDs. The dykes have similar mineral assemblages although plagioclase in the PDDs has higher anorthite content than the PGDs. Linear relationships between the SiO2 and most major and trace element contents, as well as a positive trend of initial 87Sr/86Sr ratios and a negative trend of epsilon Nd values with increasing SiO2 contents for the dykes suggest that both types were formed by assimilation and fractional crystallization of a common parental magma. Major oxide mass balance and trace element Rayleigh fractionation modeling points to early separation of garnet (11 %), clinopyroxene (27 %), orthopyroxene (16 %), plagioclase (25 %), biotite (19 %), and apatite (2 %) and late fractionation of hornblende (25 %), plagioclase (46 %), biotite (25 %), apatite (1 %), and magnetite (3 %). Most MMEs occur within the transitional granodiorite of the Zhoukoudian pluton. Zoned MMEs, dyke-like MME swarms, local presence of concave margins, veins and enclaves of host granodiorite within some MMEs, and several MMEs surrounded by the biotite-rich granodiorite support their formation by multiple magma mixing events, which finally resulted in different whole-rock major oxides and compatible elements, but homogeneous mineral major oxides (except zoned plagioclase), whole-rock incompatible elements and Sr-Nd isotopes between the MMEs and their host granodiorite. We suggest that multiple magma mixing events might also cause complexly zoned plagioclase in the Zhoukoudian pluton. Relative calcic, irregular or patchy cores and dusty zoned mantles from the zoned plagioclase crystals and their relatively low anorthite content indicate multiple mixing events between mafic/intermediate and felsic magmas. The mafic/intermediate end-members could be represented by the diabase dykes and the PDDs. Therefore, the dykes and MMEs in the Zhoukoudian pluton are genetically linked. 相似文献
12.
大兴安岭南段林西地区中生代酸性岩类岩浆的混染作用 总被引：2，自引：3，他引：2
大兴安岭南段林西地区广泛出露以海相玄武安山岩、安山岩为主的晚古生代火山．沉积岩。中生代火山-侵入杂岩也广泛分布其中。花岗岩体的边部普遍二长花岗岩化和花岗闪长岩化(甚至出现闪长岩)，并含有丰富的以玄武质-安山质为主的岩石包体。侵入体-围岩接触带附近为围岩被岩浆侵蚀的港湾状交代反应过渡带。英安岩-粗面英安岩也含有相同的岩石包体，并且与流纹岩密切共生。岩石包体周缘的寄主岩常见淬冷边，聚集针状磷灰石，表明它被捕获时已是冷却的岩石，而非热的玄武岩浆团；它们的Nb／Ta、Zr／Hf比值、弱交代者的化学成分与晚古生代火山-沉积岩一致，Rb-Sr同位素比值散布在晚古生代火山-沉积岩等时线附近，其含量、未交代程度、尖棱状程度、刚性程度在侵入体中从内部到边部增多(强)，且较新鲜者结构构造与围岩相同，表明它们来自晚古生代火山-沉积岩组成的围岩；其含量与岩体边部的位置及二长花岗岩、花岗闪长岩、(粗面)英安岩的成分变化有关，表明包体成分已加入到这些岩石当中。这些岩石的环带状斜长石有两种内核：一种较富钙；另一种较贫钙。两种内核的斜长石外环成分趋同，强交代岩石包体成分和富含岩石包体的酸性岩成分趋同。两者皆记录了两种来源的物质成分同化的过程。同一岩体边部(或火山岩中)酸度较低的岩石化学成分、高场强元素在Harker图解和Nb／Ta(和Zr／Hf)-SiO2及Nb／Ta-Zr／Hf图解中具有中生代花岗或流纹岩浆与晚古生代火山-沉积岩物质混合的特征。这些事实证明林西地区中生代酸性岩浆被较基性的晚古生代火山物质混染，并生成酸度较低的混染岩浆。较基性的火山物质是在低绿片岩相变质的基础上，经钠化交代反应被酸性岩浆同化的。 相似文献
13.
普朗斑岩铜矿岩浆混合作用：岩石学及元素地球化学证据 总被引：11，自引：1，他引：10
普朗斑岩铜矿花岗闪长斑岩中存在大量的随机分布的镁铁质微粒包体,包体与寄主岩存在渐变接触关系。包体成分为闪长质,具有岩浆结构,存在针状磷灰石,显示了快速冷却结晶的特征。包体内可见具有暗色矿物镶边的眼球状石英,表明存在岩浆混合作用。寄主岩岩体规模较小,呈岩枝状产出,包体和寄主岩均为似斑状结构,说明两种岩浆侵位和发生岩浆混合作用的深度较浅。元素地球化学特征显示包体与寄主岩的之间有成分交换。包体和寄主岩强不相容元素均富集,高场强元素Nb、Ta、Ti均表现出显著的负异常,具有典型的岛弧岩浆岩的微量元素特征,包体和寄主岩Mg＃较高,在同等Si条件下比玄武岩部分熔融体富K2O和MgO,意味着源区必须有幔源岩浆的贡献。普朗斑岩铜矿蚀变矿化模式反映了其成矿环境偏基性,暗示镁铁质岩浆的加入对成矿具有贡献。 相似文献
14.
Sabah Yilmaz ahin 《Chemie der Erde / Geochemistry》2008,68(1):81-92
Rocks of the Late Cretaceous Tamdere Quartz Monzonite, constituting a part of the Eastern Pontide plutonism, include mafic microgranular enclaves (MMEs) ranging from spheroidal to ellipsoidal in shape, and from a few centimeters to decimeters in size. The MMEs are composed of diorite, monzodiorite and quartz diorite, whereas the felsic host rocks comprise mainly quartz monzonite, granodiorite and rarely monzogranite on the basis of both mineralogical and chemical compositions. The common texture of felsic host rocks is equigranular. MMEs are characterized by a microgranular texture and also reveal some special types of microscopic textures, e.g. antirapakivi, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures.
The distribution of major, trace and RE elements apparently reflect exchange between the MMEs and the felsic host rocks mainly due to thermal, mechanical and chemical interactions between coeval felsic host magma and mafic magma. The most evident major element transfer from felsic host magma to mafic magma blob is that of alkalis such as Na and K. LILEs such as Rb, Sr, Ba and some HFSEs such as Nb, Y, Zr and Th have been migrated from felsic host magma to MMEs. Apart from these major and trace elements, the other element transfer from felsic host magma to mafic one concerns REE contents. Such a transfer of REEs has evidently increased the LREE contents of MMEs. Enrichments in alkalis, LILEs, HFSEs and REEs could have been achieved by diffusional processes during the solidification of magma sources. The felsic and mafic magma sources behave as Newtonian and visco-plastic materials. In such an interaction, small MMEs behave as a closed system due to immediate rapid cooling, whereas the bigger MMEs suffer greater diffusion from the Newtonian felsic host magma due to slow cooling. 相似文献
15.
The Nimchak granite pluton (NGP) of Chotanagpur Granite Gneiss Complex (CGGC), Eastern India, provides ample evidence of magma interaction in a plutonic regime for the first time in this part of the Indian shield. A number of outcrop level magmatic structures reported from many mafic-felsic mixing and mingling zones worldwide, such as synplutonic dykes, mafic magmatic enclaves and hybrid rocks extensively occur in our study domain. From field observations it appears that the Nimchak pluton was a vertically zoned magma chamber that was intruded by a number of mafic dykes during the whole crystallization history of the magma chamber leading to magma mixing and mingling scenario. The lower part of the pluton is occupied by coarse-grained granodiorite (64.84–66.61?wt.% SiO2), while the upper part is occupied by fine-grained granite (69.80–70.57?wt.% SiO2). Field relationships along with textural and geochemical signatures of the pluton suggest that it is a well-exposed felsic magma chamber that was zoned due to fractional crystallization. The intruding mafic magma interacted differently with the upper and lower granitoids. The lower granodiorite is characterized by mafic feeder dykes and larger mafic magmatic enclaves, whereas the enclaves occurring in the upper granite are comparatively smaller and the feeder dykes could not be traced here, except two late-stage mafic dykes. The mafic enclaves occurring in the upper granite show higher degrees of hybridization with respect to those occurring in the lower granite. Furthermore, enclaves are widely distributed in the upper granite, whereas enclaves in the lower granite occur adjacent to the main feeder dykes.Geochemical signatures confirm that the intermediate rocks occurring in the Nimchak pluton are mixing products formed due to the mixing of mafic and felsic magmas. A number of important physical properties of magmas like temperature, viscosity, glass transition temperature and fragility have been used in magma mixing models to evaluate the process of magma mixing. A geodynamic model of pluton construction and evolution is presented that shows episodic replenishments of mafic magma into the crystallizing felsic magma chamber from below. Data are consistent with a model whereby mafic magma ponded at the crust-mantle boundary and melted the overlying crust to form felsic (granitic) magma. The mafic magma episodically rose, injected and interacted with an overlying felsic magma chamber that was undergoing fractional crystallization forming hybrid intermediate rocks. The intrusion of mafic magma continued after complete solidification of the magma chamber as indicated by the presence of two late-stage mafic dykes. 相似文献
16.
Rocks of the Late Cretaceous Dagbasi Pluton (88-83 Ma), located in the eastern Pontides, include mafic microgranular enclaves (MMEs) ranging from a few centimetres to metres in size, and from ellipsoidal to ovoid in shape. The MMEs are composed of gabbroic diorite, diorite and tonalite, whereas the felsic host rocks comprise mainly tonalite, granodiorite and monzogranite based on both mineralogical and chemical compositions. MMEs are characterized by a fine-grained, equigranular and hypidiomorphic texture. The common texture of felsic host rocks is equigranular and also reveals some special types of microscopic textures, e.g., oscillatory-zoned plagioclase, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures and rounded plagioclase megacrysts in MMEs. Compositions of plagioclases (An33-An60), hornblendes (Mg#=0.77-1.0) and biotites (Mg#=0.61-0.63) of MMEs are slightly distinct or similar to those of host rocks (An12-57; hbl Mg#=0.63-1.0; Bi Mg#=0.50-0.69), which suggest partial to complete equilibration during mafic-felsic magma interactions.The felsic host rocks have SiO2 between 60 and 76 wt% and display low to slightly medium-K tholeiitic to calc-alkaline and peraluminous to slightly metaluminous characteristics. Chondrite-normalized rare-earth element (REE) patterns are fractionated (Lacn/Lucn=1.5-7.3) with pronounced negative Eu anomalies (Eu/Eu*=0.46-1.1). Initial εNd(i) values vary between −3.1 and 1.6, initial 87Sr/86Sr values between 0.7056 and 0.7067.Compared with the host rocks, the MMEs are characterized by relatively high Mg-number of 22-52, low contents of SiO2 (53-63 wt%), low ASI (0.7-1.1) and low to medium-K tholeiitic to calc-alkaline, metaluminous to peraluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn=1.4-3.9; (Tb/Yb)cn=0.9-1.5] and show small negative Eu anomalies (Eu/Eu*=0.63-1.01). Isotope signatures of these rocks (87Sr/86Sr(i)=0.7054-0.7055; εNd(i)=-1.0 to 1.9) are largely similar to the host rocks. Gabbroic diorite enclaves have relatively low contents of SiO2, ASI; high Mg#, CaO, Al2O3, TiO2, P2O5, Sr and Nb concentrations compared to dioritic and tonalitic enclaves.The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, interacted with a crustal melt that originated from dehydration melting of the mafic lower crust at deep crustal levels. The existence of compositional and textural disequilibrium and the nature of chemical and isotopic variation in these rock types indicate that magma mixing/mingling between an evolved mafic and a granitic magma was involved in their genesis. Microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched lithospheric mantle source. Al-in-amphibole estimates the pluton emplacement at ca. 0.3-3.8 kbar, and therefore, magma mixing and mingling must have occurred at 3.8 kbar or below this level. 相似文献
17.
暗色微粒包体广泛分布于湘中紫云山岩体中的似斑状角闪石黑云母花岗闪长岩中,但其研究程度较低.对具有火成结构的暗色微粒包体及其寄主岩进行了岩相学、全岩及长石、辉石、黑云母的矿物地球化学研究,探讨其岩石成因及构造意义.寄主岩的全岩主量、微粒元素较为均一,而暗色微粒包体变化较大,且后者相对贫SiO2而富Na2O,但总体上二者均具有准铝质、钙碱性、镁质的特征,均富集轻稀土和大离子亲石元素,而亏损重稀土和高场强元素.寄主岩和暗色微粒包体的斜长石、辉石和黑云母均分别属于中长石、次透辉石－低铁次透辉石和铁质黑云母的范畴,显示相似的矿物地球化学特征.详尽的岩相学和地球化学特征表明,寄主岩属于I型和ACG型花岗岩,具有明显壳幔混合的特点;而暗色微粒包体形成时处于液态并具有流动性,与寄主岩间存在明显的机械和化学混合作用,并具有早期为骤冷快速结晶、晚期缓慢结晶这两期过程.因此,紫云山岩体中出现大量暗色微粒包体,是印支晚期湘中地区在强烈挤压之后的松弛阶段,由于软流圈物质上涌,并与其诱发的壳源酸性岩浆混合作用的产物. 相似文献
18.
The Daocheng batholiths, located in the east of the Yidun arc, consist of granite, granodiorite and K-feldspar granite. Abundant massive mafic microgranular enclaves (MMEs) mainly developed within the granodiorite and K-feldspar granite, and they have clear contacts with the hosted granites. The MMEs are characterized by the quartz eye structure, quenched apatite, and plagioclases phenocrysts with obvious oscillatory zones. Petrographical studies on MMEs and host granites, zoned plagioclase and whole-rock geochemical analysis were carried out to identify the presence of magma mixing. Combined with the previous studies on the whole-rock Sr-Nd-Hf isotopic signatures, the petrogenesis of Daocheng batholith was discussed. The zoned plagioclases from MMEs have An contents varying between 29 and 44, while those from the host granites have An contents of 21~50. The compositional variations and corrosion structure of plagioclase are probably related to magma mixing. Geochemically, the MMEs have relatively low SiO2 contents (56.34~60.91wt%), high Al2O3 contents of 16.06~17.98wt%, and are enriched in magnesium and iron, belonging to metalumnious series (A/CNK=0.82~0.98). The Daocheng batholith belongs to high-K calc-alkaline series, which have high alkaline contents (Na2O+K2O=6.25~7.79wt%) and low CaO contents (1.40~3.22wt%). Furthermore, both the MMEs and hosted granites are enriched in LILEs (K, Rb and Pb) and LREEs and depleted in HFSEs (Nb, Ta, Zr, Hf, P and Ti), showing affinities of typical arc magmas. Compared with the host granites, the MMEs are characterized by lower (La/Yb)N ratios of 1.99 to 2.46, and much more obvious Eu depletions (Eu/Eu*=0.30~0.50). The host granites have Rb/Sr ratios ranging from 1.0 to 1.9, and they are consistent with the crust-derived materials (Rb/Sr>0.5). Their Zr/Hf ratios range from 27.5 to 36.9, which are close to the transitional Zr/Hf ratios between mantle-and crust-derived materials. This indicates that the formation of Daocheng batholith is genetically related to the mixing between mantle-and crust-derived materials. In addition, the relatively low silica contents and high Mg# values, and the linear patterns of MgO, Al2O3 and Fe2O3 with SiO2 contents from the MMEs and host granites, show that the formation of MMEs is genetically related to magma mixing. Overall, the parent magmas of Daocheng granites are derived from the partial melting of Late Triassic arc lower crust, with the input of minor mantle-derived materials. The MMEs are generated by the mixing of the mafic magma with felsic magma. 相似文献