共查询到20条相似文献，搜索用时 259 毫秒
1.
花岗岩的源区、温压条件及与其他岩石的共生组合的研究可以限定其形成构造背景,了解其形成的深部动力学过程。本文对浙江中部中生代芙蓉山花岗斑岩及其暗色包体开展了全岩主微量元素、锆石U-Pb年代学和Hf同位素、Ti温度计和全岩Sr-Nd同位素研究,探讨芙蓉山花岗斑岩的成因类型、源区特征及其与镁铁质包体之间的关系,并进一步限定其构造背景。锆石U-Pb定年结果显示芙蓉山花岗斑岩加权平均年龄为133.6±1.6 Ma (MSWD = 2.1,2σ),镁铁质包体加权平均年龄为130.3±4.2 Ma (MSWD = 5.8,2σ),其成岩年龄基本一致,形成于早白垩世。全岩地球化学表明芙蓉山花岗斑岩属于亚碱性系列,同时具有低的Ga/Al(<2.6),高的Na2O含量(2.75%-4.5%,平均3.78%),较高的全碱含量(Na2O + K2O = 7.93%-8.75%),以及较低的锆石Ti饱和温度特征（631-690℃）,这些特征显示芙蓉山花岗斑岩为I型花岗岩,而非A型花岗岩。芙蓉山花岗斑岩中锆石Hf同位素有比较大的范围[εHf(t)=-10.9~-1.1],全岩[n(87Sr)/ n(86Sr)]i = 0.7062-0.7078,相对富集的εNd(t)=-5.6 ~ -4.7值;而包体表现为均一的[n(87Sr)/ n(86Sr)]i=0.7071-0.7079和弱富集的εNd(t)=-3.8 ~-2.8特征。野外及岩相学和元素地球化学特征显示典型的岩浆混合特征。镁铁质包体源区可能来自于俯冲交代地幔,芙蓉山花岗斑岩则形成于古老富钾地壳熔体和交代地幔熔体混合后的结晶分异。混合模型计算表明混合比例为：~80%的地幔端元和~ 20%地壳端元。浙江中部芙蓉山富钾I型花岗斑岩与镁铁质包体共生可能指示其形成于古太平洋板块俯冲后撤初始弱伸展拉张的构造背景。 相似文献
2.
完达山地区位于中国东北部陆缘,区内已发现多个金、金铜矿床(点),集中形成于早白垩世。为确定区内早白垩世金铜成矿作用的类型、时代、构造背景及物质源区,选取258高地、358高地和跃进山等代表性矿床,在矿床学研究基础上,开展了主要成矿岩体的地质特征、地球化学特征和同位素年代学研究。结果表明,完达山地区发育矽卡岩型铜金矿(跃进山)、斑岩型铜矿(跃进山花岗斑岩体)、浅成低温热液型金矿(258高地)和中温热液脉型金矿(358高地)等四种类型金铜矿床;258高地闪长玢岩、358高地闪长玢岩和跃进山花岗斑岩的锆石U-Pb年龄分别为1107±10Ma、1084±09 Ma和1019±11Ma;258高地闪长玢岩与358高地闪长玢岩锆石ε_(Hf)(t)值(分别为+04～+103和+22～+71)、Hf二阶模式年龄(分别为051～115Ga和072～102Ga)及岩石地球化学特征显示其属于埃达克(质)岩石,形成于洋壳俯冲的构造背景;跃进山矿床花岗斑岩的锆石ε_(Hf)(t)介于22～683,二阶段模式年龄t_(DM2)介于725～1021Ma,具有典型Ⅰ型花岗岩地球化学特征,形成于古太平洋俯冲的构造背景下;岩石Sr-Nd-Pb同位素组成表明,随258高地闪长玢岩、358高地闪长玢岩和跃进山花岗斑岩的年龄变新,岩浆源区可能具有幔源向壳源过渡的趋势。结合区域构造背景演化认为,完达山地区早白垩世金铜成矿作用与古太平洋板块俯冲作用的演化过程具有明显的耦合关系。 相似文献
3.
马厂箐岩体属于滇西富碱侵入岩带上的一个典型代表,岩体中发现大量暗色微粒包体。对暗色微粒包体及其寄主岩进行系统岩石学、岩石化学和Sr、Nd、Pb同位素研究,认为马厂箐岩体为一岩浆混合成因岩体,形成于新生代陆壳加厚的构造背景下,暗色微粒包体来源于富集地幔岩浆,寄主岩花岗斑岩来源于大陆地壳的长英质岩浆,是幔源岩浆底侵作用诱发其上的陆壳岩石熔融所形成的混合岩浆上侵定位的结果。幔源岩浆对于斑岩型铜钼矿成矿具有重要作用,提供了成矿的物质和流体,暗色微粒包体对于斑岩型铜钼矿地质找矿具有指示意义。 相似文献
4.
马厂箐岩体属于滇西富碱侵入岩带上的一个典型代表,岩体中发现大量暗色微粒包体。对暗色微粒包体及其寄主岩进行系统岩石学、岩石化学和Sr、Nd、Pb同位素研究,认为马厂箐岩体为一岩浆混合成因岩体,形成于新生代陆壳加厚的构造背景下,暗色微粒包体来源于富集地幔岩浆,寄主岩花岗斑岩来源于大陆地壳的长英质岩浆,是幔源岩浆底侵作用诱发其上的陆壳岩石熔融所形成的混合岩浆上侵定位的结果。幔源岩浆对于斑岩型铜钼矿成矿具有重要作用,提供了成矿的物质和流体,暗色微粒包体对于斑岩型铜钼矿地质找矿具有指示意义。 相似文献
5.
德兴斑岩铜矿成矿热液来源及其演化——花岗闪长斑岩的氧同位素制约 总被引：8，自引：0，他引：8
作者研究了德兴铜厂花岗闪长斑岩的氧同位素组成特征在垂直方向上的变化规律,及蚀变作用对花岗闪长斑岩全岩和单矿物氧同位素组成的影响。结果表明,从地表到深部,花岗闪长斑岩全岩和长石单矿物的δ＾１８Ｏ值总体上有逐渐降低的趋势,反映花岗闪长斑岩受到已演化的大气降水水－岩氧同位素交换作用的影响。水－岩交换作用对花岗闪长斑岩氧同位素组成的影响在浅部和深部是不同的,这主要受控于水－岩交换温度和交换水的初始氧同位素组成等因素。石英的氧同位素组成及变化特征不同于全岩和长石,其值与岩石的蚀变作用有关从花岗闪长斑岩的氧同位煮组成及其变化规律可以推论,由大气降水演化为德兴斑岩铜矿成矿热液是可能的。 相似文献
6.
滇西新生代富碱斑岩及其深源包体的岩石学和地球化学特征 总被引：22，自引：6，他引：22
滇西地区沿金沙江—哀牢山断裂带产出了一套第三纪富碱斑岩 ,其中包含有多种类型的深源包体 ,它们对于了解滇西地区的地幔组成与演化及壳幔相互作用有重要意义。介绍了鹤庆六合、剑川新华、甸心和石鼓小桥头等地的富碱斑岩及其深源包体的岩石类型和岩相学特征 ;通过对寄主岩及其包体的主量元素、微量元素、稀土元素和Pb、Sr、Nd同位素的分析 ,运用多种地球化学判别图解并结合实验岩石学和相平衡的研究结果 ,认为研究区的富碱斑岩属于钾玄岩系列的岩石 ,主要形成于后碰撞弧环境 ;富碱斑岩起源于滇西加厚地壳的下部 (约 5 5km处 ) ,源区岩石应是榴辉岩相的岩石 ;富碱斑岩的源区具有EMⅡ型富集地幔的地球化学特征 ,其成因可能和下地壳岩石与具有俯冲残留洋壳特征的地幔的混合作用有关 相似文献
7.
宁镇地区成矿斑岩与铁镁质包体铜同位素研究 总被引：1，自引：0，他引：1
长江中下游地区成矿斑岩的成因及铜矿中铜的来源一直受到争议。寻找斑岩铜矿中铜的来源归根结底是限定其寄主岩的成因。本文拟通过测定宁镇地区一系列中生代岩体的成矿斑岩及其铁镁质包体的Cu同位素组成,来探究成矿斑岩中Cu的来源。测定结果显示,安基山闪长斑岩δ65Cu值为-0.13‰~+0.36‰;其辉长岩包体δ65Cu的值为+0.14‰~+0.19‰。铜山成矿斑岩δ65Cu值为+0.03‰~+0.36‰;其辉长岩包体δ65Cu的值为+0.10‰~+0.20‰。象山花岗闪长岩δ65Cu为+0.20‰±0.06‰;其辉长岩包体δ65Cu为+0.16‰±0.06‰。三个岩体成矿斑岩δ65Cu值为-0.13‰~+0.36‰,变化范围较大;而辉长岩包体δ65Cu值均在+0.1‰~+0.2‰之间,平均δ65Cu为+0.15‰±0.05‰,与地幔δ65Cu值(+0.07‰±0.10‰)吻合。结合前人对研究区成矿斑岩高Mg O、Mg#值,低放射性成因Pb同位素组成,以及古老下地壳来源的岩石具有较大的Cu同位素组成变化的认识,我们认为宁镇地区成矿斑岩及成矿物质主要为幔源岩浆和古老下地壳部分熔融岩浆混合成因。 相似文献
8.
为精确厘定桂中地区都安-马山带煌斑岩的形成时代并探讨其源区属性、构造环境及其动力学背景,对其进行了LA-ICP-MS锆石U-Pb定年、40Ar-39Ar金云母定年、Hf同位素分析测试和全岩地球化学研究.结果表明,锆石U-Pb定年未能成功限定煌斑岩的成岩年龄,但煌斑岩中发育大量2 578~1 650 Ma的捕获锆石,指示其存在太古宙-古元古代变质基底.金云母40Ar-39Ar定年结果限定了煌斑岩的侵位年龄为100.4±0.99 Ma.Hf同位素研究表明,εHf（t）有正有负,且正值多于负值,表明岩浆源区主要以新生地壳为主,存在部分古老地壳的再循环.全岩地球化学分析显示,煌斑岩具有较低的SiO2含量（47.66%~50.93%）及高的K2O含量（4.98%~6.77%）、富集LILE和LREE而亏损HFSE（如Nb、Ta和Ti）,表现出富集地幔和俯冲流体交代作用的特征.桂中煌斑岩形成过程中,地壳混染作用十分有限,主要形成过程为:流体交代的富集地幔,在燕山晚期岩石圈的拉张-伸展背景下,部分熔融形成煌斑岩岩浆,同时NNW向的南丹-昆仑关大断裂为岩浆的侵位提供了通道.研究区煌斑岩形成于太平洋和印度板块向欧亚板块俯冲碰撞的动力学背景下. 相似文献
9.
西藏青草山Cu-Au矿床是班公湖-怒江缝合带北侧新发现的具有大型远景的斑岩型矿床,但该矿床含矿斑岩的年龄、成因及源区一直未得到有效的约束.对青草山花岗闪长岩以及含矿花岗岩闪长斑岩进行了锆石年代学、Hf同位素以及岩石地球化学研究.结果显示,花岗闪长岩与含矿花岗闪长斑岩的侵入时代分别为131.2±0.3 Ma与117.9±0.8 Ma,代表了班公湖-怒江缝合带早期的成岩作用以及斑岩Cu-Au成矿作用.二者具有相似的地球化学特征,表明二者可能具有相同的岩浆源区,是不同时期同源岩浆活动的产物.结合含矿花岗闪长斑岩锆石Hf同位素组成,认为青草山含矿斑岩形成于班公湖-怒江洋壳向北俯冲过程中,是下地壳部分熔融的产物,受到了少量地幔物质的混合. 相似文献
10.
鄂东南地区古家山岩体锆石U-Pb年龄和Hf同位素组成:对岩浆源区的指示 总被引：1，自引：0，他引：1
对扬子陆块鄂东南地区古家山花岗闪长斑岩体进行了锆石CL显微结构分析和LA-(MC)-ICP-MS法U-Pb年龄测定及Lu-Hf同位素分析.结果表明该花岗闪长斑岩中的锆石为岩浆锆石,其晶体内部多包裹有经历变质重结晶程度不同的继承锆石.岩浆锆石206pb/238U加权平均年龄为145.4±1 Ma (MSWD=1.5),表明古家山岩体形成于晚侏罗世.岩浆锆石εHf(t)值为-4.33-17.41,Hf同位素两阶段模式年龄tDM2为1470 ～ 2294 Ma.继承锆石207Pb/206Pb年龄为1746 ～ 2959 Ma,以古元古代为主;εHf(t)值为-18.2～ 2.65,表明该地区存在太古宙-古元古代基底物质再循环.综合野外地质调查与岩石化学、锆石微区原位分析结果,古家山花岗闪长斑岩为壳源花岗岩,其源区为古元古代基底.对古家山花岗闪长斑岩体的研究表明鄂东南地区确切存在太古宙-元古代基底,为研究扬子陆块前寒武纪基底演化提供了新的信息和线索. 相似文献
11.
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
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,εNd(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
12.
The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone), II. Geochronology and isotope geochemistry 总被引：1，自引：0，他引：1
Meihua Lu Albrecht W. Hofmann Maurizio Mazzucchelli Giorgio Rivalenti 《Chemical Geology》1997,140(3-4):223-235
Whole-rock Nd and Sr isotopic compositions of the mafic-ultramafic complex near Finero demonstrate that the magma was derived from a depleted, perhaps MORB-type mantle reservoir. The Sm-Nd data for the Amphibole Peridotite unit can be interpreted as an isochron with an apparent age of 533 ± 20 Ma, which is consistent with a 207Pb/206Pb evaporation age of 549 ± 12 Ma of a single zircon grain from the Internal Gabbro unit. However, the interpretation of these apparent ages remains open to question. We therefore retain the alternative hypotheses that the intrusion occurred either about 533 or 270 Ma ago, the latter being the most likely age of emplacement of the much larger magma body near Balmuccia (Val Sesia). The implication of the older emplacement age (if correct) would be that the igneous complex may be related to the numerous amphibolite units, which are intercalated with the metapelites of the overlying Kinzigite Formation, and together with them may constitute an accretionary complex. In this case, the mafic-ultramafic complex itself might also be part of such an accretionary complex (as has been proposed for the Balmuccia peridotite).
Internal Sm-Nd isochrons involving grt, cpx, plag and amph from the Internal Gabbro unit yield concordant ages of 231 ± 23, 226 ± 7, 223 ± 10, 214 ± 17, and 203 ± 13 Ma. These results confirm published evidence for a separate, regional heating event about 215 ± 15 Ma ago.
Initial Nd(533) values average +6.3 ± 0.4 for six samples of the Amphibole Peridotite unit and +6.0 ± 1.2 for ten samples of the External Gabbro unit. 87Sr/86Sr ratios require little or no age correction and range from 0.7026 to 0.7047 (with two outliers at 0.7053 and 0.7071). Strong correlations between 87Sr/86Sr and K2O and weaker correlations between initial Nd and K2O imply a comparatively minor (≤ 10%) contamination of the External Gabbro magma by crustal material and a later alteration by a crustal or seawater-derived fluid. These results contrast sharply with the isotopic composition (negative Nd and high 87Sr/86Sr values) of the associated mantle rocks, the Phlogopite Peridotite unit, which has been pervasively metasomatized by crustal fluids. This type of metasomatism and its isotopic signature are never seen in the magmatic complex. This evidence rules out any direct genetic relationship between the igneous complex and the mantle peridotite. The crust-mantle interaction is the opposite of that seen at Balmuccia, where the mantle peridotite is essentially ‘pristine’ and the magmatic body has been extensively contaminated by assimilation of crustal rocks. 相似文献
13.
文章报道了江西蔡江花岗质岩体中发现暗色微粒包体,以及这些包体的地质、岩相学、LA-ICP-MS锆石U-Pb年代学和元素地球化学特征。包体多呈椭圆状,显示淬冷边和反向脉,具有典型的岩浆结构并含有针状磷灰石,有的包体含有长石捕虏晶。包体具有相对较低的SiO2（低至57.05 wt%）和较高的MgO+Fe2O3（高达14.21 wt%）含量。LA-ICP-MS锆石U-Pb定年数据表明,包体形成于晚三叠世（224 Ma）,与寄主花岗岩（230~228 Ma）在误差范围内基本一致。上述特征表明,包体是离散的幔源偏基性岩浆团或者是幔源与寄主岩浆混合的产物。原始包体岩浆属于超钾质岩浆,可能是通过岩石圈地幔中交代成因的金云母辉石岩脉发生部分熔融而形成的。暗色微粒包体的发现为幔源岩浆底侵提供了直接证据,从而为蔡江花岗质岩石形成于较高温度提供佐证。该研究对于进一步探讨华南印支期花岗岩形成的热源机制具有意义。 相似文献
14.
豆世勇 《吉林大学学报(地球科学版)》2020,50(6):1752-1765
研究区位于华北克拉通北缘东段、华北克拉通与兴蒙造山带的交接部位。本文通过对辽北开原地区房木花岗斑岩的岩石学、年代学和地球化学研究，探讨了其形成时代、岩石成因和构造环境，并进一步探讨了华北克拉通东部岩石圈减薄的起始时间。用LA-ICP-MS技术测定了花岗斑岩的锆石U-Pb同位素，获得其锆石206Pb/238U加权平均年龄为（117±1）Ma，表明花岗斑岩形成于早白垩世。花岗斑岩具有高硅、富碱、贫镁和钙的特征，富集大离子亲石元素（K、Rb）和高场强元素（Th、Ta、Nb），亏损Sr、Ba、P、Ti元素，稀土配分曲线均呈现右倾海鸥型，具有明显的负Eu异常；显示研究区花岗斑岩为A型（A1亚型）花岗岩，形成于古太平洋俯冲的后造山伸展环境，其岩浆源于地幔物质上涌而导致的地壳物质重熔。研究区在（156±1）Ma之前，属于挤压造山环境，表明研究区岩石圈减薄时间应处于156~117 Ma之间。 相似文献
15.
塔里木西南缘铁克里克地区广泛发育早古生代中酸性侵入岩,本文对其中布雅岩体及其暗色包体进行系统的岩石学、年代学及岩石地球化学研究,确定了岩石成因及其构造属性。LA-MC-ICP-MS锆石U-Pb年代学研究表明,寄主石英二长闪长岩结晶年龄为432.6±2.5 Ma(MSWD=1.5),暗色包体结晶年龄为432.4±6.4 Ma(MSWD=0.031),二者形成时代相同,均为志留纪早期岩浆活动的产物。地球化学特征表明,布雅暗色包体应来源于地幔的部分熔融,而寄主岩石岩浆具有壳源岩浆的性质并经历了幔源岩浆不均匀的混合。野外及岩相学特征均显示暗色包体为铁镁质岩浆注入长英质岩浆快速冷凝形成的,是幔源岩浆底侵下地壳形成的岩浆混合作用的产物。它们是塔里木南缘早古生代碰撞造山作用晚期的岩浆记录。 相似文献
16.
The Rio Espinharas pluton, northeastern Brazil, belongs to the shoshonitic series and consists mainly of syenogranite, quartz–monzonite and porphyritic quartz–monzonite, but diorite, quartz–monzodiorite, quartz–syenite and microsyenogranite also occur containing microgranular enclaves, except for the diorite. Most variation diagrams of rocks, amphiboles, biotites and allanites show linear trends, but K, Zr, Sr and Ba of rocks display curved scattered trends. The rocks ranging from diorite to syenogranite define a pseudo-errorchron and have similar REE patterns. Syenogranite and microsyenogranite are derived from two distinct pulses of granite magma with initial 87Sr/86Sr ratio of 0.7083±0.0003 and 0.7104±0.0007, respectively. Modelling of major and trace elements shows that the syenogranite evolved by fractional crystallization of plagioclase, microcline, edenite, biotite and titanite, whereas quartz–monzonite, porphyritic quartz–monzonite, quartz–monzodiorite and quartz–syenite resulted from simple mixing between an upper mantle-derived dioritic magma and the upper crust-derived syenogranite magma. Dioritic enclaves are globules of a mafic magma from the upper mantle. 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.
Yoji Arakawa 《Lithos》1989,24(4):261-273
The Sr isotopic compositions of Late Triassic to Early Jurassic Funatsu granitic rocks in the Hida belt, Japan, were determined and variations of the compositions within single intrusions and on a regional scale were compared with previously reported data.
Relatively low and constant (or narrow range of) initial 87Sr/86Sr ratios of granitic rocks within an intrusion (0.7044-0.7055) are found mostly in the outer part of the belt, while intrusions with high and wide ranges of initial ratios (0.7056-0.7105) are situated in the inner part. This difference in initial ratios within an intrusion is due to the different degrees of mixing between the parental mafic magma from the lower crust or upper mantle and the middle to upper crustal (or crust-derived) materials. On a regional scale, a smooth and regular increase of the ratios from 0.7044 to 0.7057, from outer to inner part, is outlined by the lowest ratio in each intrusion and this almost coincides with a trend given by the ratios of mafic rocks (or mafic enclaves) in the intrusion. This suggests a gradual change of source materials in the lower crust or upper mantle. The degree of crustal contributions to the parental magma, lesser in the outer part and larger in the inner part of the Hida belt, shows close relationships to some geophysical factors, such as the emplacement depth and uplift rate of mafic magma from deeper levels and stress state (extensional or compressional) in the middle to upper crustal levels. These factors are probably due to the plate tectonic configuration in the continental margin area where the Hida belt was included. 相似文献
19.
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
20.
《International Geology Review》2012,54(10):1150-1162
Late Cretaceous calc-alkaline granites in the Gyeongsang Basin evolved through the mixing of mafic and felsic magmas. The host granites contain numerous mafic magmatic/microgranular enclaves of various shapes and sizes. New SHRIMP-RG zircon U–Pb ages of both granite and mafic magmatic/microgranular enclaves are 75.0?±?0.5 Ma and 74.9?±?0.6 Ma, respectively, suggesting that they crystallized contemporaneously after magma mixing. The time of injection of mafic melt into the felsic magma chamber can be recognized as approximately 75 Ma by field relations, petrographic features, geochemical evolution, and SHRIMP-RG zircon dating. This Late Cretaceous magma mixing event in the Korean Peninsula was probably related to the onset of subduction of the Izanagi (Kula)–Pacific ridge. 相似文献