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1.
淡色花岗岩的岩石学和地球化学特征及其成因 总被引：6，自引：0，他引：6
淡色花岗岩(leucogranite)是一类高铝高硅碱的酸性侵入岩,主要地球化学特征是:SiO2≥72%,Al2O3≥14%,Na2O+K2O~8.5%,富Rb,亏损Th、Ba、Sr,稀土总量较一般花岗岩低(∑REE=(40~120)×10-6),且表现为中等分异的轻稀土弱富集型,一般具有Eu负异常;Sr-Nd-Pb-O同位素指示其岩浆明显的陆壳来源。淡色花岗岩主要发育于陆壳(俯冲)碰撞加厚带,由逆冲折返的俯冲板片变沉积岩部分经过脱水熔融产生。淡色花岗岩可划分为三种不同的岩石类型:(1)二云母型淡色花岗岩,由变泥质岩(或变硬砂岩)在中地壳水平经黑云母(和/或白云母)脱水熔融产生;(2)电气石型淡色花岗岩,由变泥质岩在较低温度下经白云母脱水熔融产生;(3)石榴子石型淡色花岗岩,由长英质下地壳经黑云母脱水熔融产生。源区残留独居石、磷灰石等富REE矿物是淡色花岗岩亏损REE、Th等元素的原因。源岩为变泥质岩及源区残留钾长石是淡色花岗岩亏损Sr、Ba的主要原因。 相似文献
2.
骨洞坑大型萤石矿床位于华夏古板块北东端,产出于下白垩统馆头组与燕山晚期花岗岩的接触带中。本文在地质调查基础上,对浙江缙云骨洞坑萤石矿床中的萤石进行阴极发光(CL)及原位稀土元素(REE)地球化学研究,以探讨缙云骨洞坑萤石矿床REE演化过程以及成矿物质来源。结果表明,骨洞坑萤石REE配分模式包括3种类型:“V”字型、重稀土元素(HREE)富集型和轻稀土元素(LREE)富集型。扫描电镜阴极发光(SEM-CL)图像显示,骨洞坑萤石发育不同类型的条带,早期萤石被晚期萤石交代,表明骨洞坑萤石经历了复杂的演化。萤石光学显微镜阴极发光(OM-CL)图像主要呈蓝色与绿色,可能与Sm3+和Dy3+的激活作用有关。单颗粒萤石原位分析结果显示,从核心到边缘,骨洞坑萤石的REE地球化学特征存在3种情况:(1)完全相同的REE配分模式和∑REE;(2)REE配分模式相同,但∑REE递减;(3)REE配分模式和∑REE都不相同。通过对比萤石样品与围岩REE配分模式,推断萤石REE具有多种来源,其与矿区内各类围岩密切相关,成矿流体受REE稳定性及络合作用影响,表现出与围岩... 相似文献
3.
北祁连造山带内发育大量早古生代花岗质岩石,对其进行研究有助于加深对造山带构造演化的理解。本文以带内西段石包城地区的花岗岩为研究对象,对其进行锆石U-Pb年代学、Hf同位素以及地球化学方面的研究。结果表明:(1)该花岗岩形成时代为465~463Ma,地球化学数据表明其属于钙碱性系列,并具强过铝质特征;(2)该花岗岩T_(Zr)和T_(REE)平均温度分别为760℃和732℃,ε_(Hf)(t)变化于+7.6~+13.5,二阶段模式年龄变化于581~957Ma;(3)可能属I-S过渡型花岗岩,是新生基性地壳低温条件下由于角闪石脱水分解而发生部分熔融而成,并混入了少量中-新元古代沉积组分,岩浆未发生明显的分离结晶作用,残留相为石榴石、角闪石和斜长石为主的麻粒岩;(4)该花岗岩形成于北祁连洋北向俯冲的活动大陆边缘背景之下,并在侵位上升过程中加入了部分沉积物质。 相似文献
4.
<正> 对鄂西兴神保、荆襄、宜昌三大聚磷区磷块岩稀土元素(REE)系统研究表明,磷块岩中的REE 丰度及变化具有一定的规律和独特的特征。这些特征不仅有助于磷块岩的沉积环境和物质来源的研究,而且用于区域矿层的划分对比也收到了理想的效果。区内磷块岩REE 丰度有如下特点:(1)各区磷块岩以低REE 含量为特征,有别于世界各地显生宙以来的磷块岩REE 含量;(2)轻REE 相对富集,重REE 贫乏;(3)轻、中、重REE 相对含量随磷块岩层位的提高而成有规律的变化;(4)磷块岩类型不同,REE 含量不同,团粒、藻菌粒磷块岩REE 含量高,壳粒、胶状、叠层石磷块岩REE 含量低;(5)磷块岩 相似文献
5.
IGCP-220项目是东南亚和西太平洋区域与花岗岩有关的锡钨矿床的对比和资源评价项目。1986年6月30日至7月2日在澳大利亚堪培拉澳大利亚国立大学召开了年度会议,由澳大利亚地质学会经济地质专家组主办。讨论内容如下:(1)花岗岩类定位的构造环境;(2)矿化花岗岩类的岩石学和成因;(3)成矿流体和花岗岩的相互作用;(4)金属在熔体和流体中的转移;(5)锡钨矿床和矿石沉淀机制;(6)锡钨成矿省 相似文献
6.
张景连 《华东地质学院学报》1983,(1)
关于在花岗岩地区如何评价形成沉积铀矿床的可能性花岗岩体的风化作用所提供的铀对形成沉积铀矿床的可能性通常取决于:(1)岩体中的铀含量;(2)岩体通过风化作用所迁移的铀的程度;(3)风化作用的强度。关于这个问题,斯塔克利斯等(stuckless et al.1976,1978)认为,形成沉积铀矿床的花岗岩体的条件是:(1)岩体钍含量高;(2)硅含量高;(3)碱金属含量高;(4)黑云母含量中等。最近,马克尼亚(McNeal et al)等研研了美国西部亚利桑那、加利福尼亚、内华达、 相似文献
7.
西藏班戈地区早白垩世高分异花岗岩年代学及岩石成因 总被引：1，自引：0，他引：1
高分异花岗岩因其特殊的成矿专属性而受到广泛关注,对班公湖-怒江结合带两侧发育的高分异花岗岩进行年代学和岩石地球化学特征的研究可为寻找相关类型矿床提供找矿标志。本文以北拉萨地块北部班戈地区的曲梅勒花岗岩为研究对象,对其进行锆石U-Pb年代学、Hf同位素以及岩石地球化学方面的研究。结果表明:(1)曲梅勒花岗岩形成时代为早白垩世(128Ma);地球化学数据表明其属于高钾钙碱性系列,并具强过铝质特征,稀土元素具有明显的四分组效应; T_(Zr)和T_(REE)平均温度分别为731℃和751℃;锆石Hf同位素显示其ε_(Hf)(t)为-3. 8～+2. 0,t_(DM2)变化于1. 0～1. 4Ga之间;(2)该花岗岩属高分异I型花岗岩,其岩浆来源于地壳物质的部分熔融,并且在岩浆演化过程中可能发生了以角闪石为主的部分镁铁矿物和斜长石为主的结晶分异,同时伴有部分副矿物(磷灰石、锆石、独居石和富Ti矿物等)的分离结晶过程,而石榴石以及碱性长石未发生明显的分离结晶;(3)曲梅勒花岗岩特殊的地球化学特征(如K/Rb 100,Nb/Ta 5,Sr 80×10~(-6),Ba 80×10~(-6)以及明显的负Eu异常和REE四分组效应等)表明强烈的岩浆/流体分馏过程在该岩体的形成过程中起了重要作用,与一些含矿高分异花岗岩具有一定的相似性。 相似文献
8.
基于中国地质资料和构造演化序列,作者将花岗岩石划分成三大类型和十三个亚类,它们分别是: 地槽阶段的花岗质岩石:早期(1)大洋岛弧M型花岗质岩石;晚期(2)褶皱带轴部S型花岗质岩石(褶皱变质重熔型);(3)沿造山带两侧发育的韧性剪切带S型花岗岩(断裂-变质型);(4)大陆边缘或岛弧Ⅰ型花岗质岩石;(5)造山期后沿着断裂带分布的高层位侵入型花岗岩(断裂-重熔型)和A型花岗岩。活化阶段(地洼阶段)的花岗质岩石:(1)地拱中的S型花岗质岩石;(2)地拱边缘混熔型花岗质岩石;(3)地拱内Ⅰ型花岗质岩石;(4)活化晚期阶段裂谷A型花岗质岩石。回返活化型花岗质岩石:(1)沿着韧性剪切带发育的S型花岗质岩(断裂-变质型);(2)混熔型花岗岩岩石;(3)A型花岗质岩石。 相似文献
9.
东昆仑山脉晚志留世-早侏罗世花岗类岩石中锆石微量元素地球化学特征及地质意义 总被引：1，自引：0，他引：1
为了更深入的认识东昆仑山脉岩浆作用和构造演化历史,本文采用激光剥蚀电感耦合等离子质谱仪(LA-ICP-MS)方法对东昆仑山脉中部和东部不同时代的花岗类岩石中锆石进行了系统的微量元素分析。东昆仑山脉晚志留世二长花岗岩和晚二叠世、晚三叠世、早侏罗世花岗岩中绝大多数锆石Th/U0.5,锆石的球粒陨石标准化REE配分曲线均为HREE相对于MREE和LREE富集,并且具有Ce正异常和Eu负异常,为典型的岩浆锆石。晚志留世二长花岗岩和晚二叠世、晚三叠世花岗岩锆石具有低的Ce正异常,高的Eu负异常;早侏罗世花岗岩锆石则具有高的Ce正异常,高Nb、Ta含量,低Eu负异常;晚二叠世花岗岩锆石还具有高∑REE、Y、Th、U含量;而晚三叠世花岗岩锆石则在所有样品中具有最高的Hf含量,是演化程度高的岩浆产物。除此之外,晚志留世、晚二叠世、晚三叠世和早侏罗世样品中部分锆石呈现LREE富集,说明它们在岩浆晚期可能遭受LREE富集热液的改造。根据锆石Ti温度计,计算出所有样品的结晶温度小于800℃,说明它们很有可能形成于富集流体的俯冲带环境。结合前人研究资料和所分析锆石的U-Pb年龄数据,对东昆仑山脉中古-中生代多期的构造-岩浆事件提供了新的约束:(1)晚志留世二长花岗岩的形成可能与一个小型洋盆的俯冲作用有关,其岩浆源区是地壳浅部的沉积基底;(2)晚二叠世花岗岩可能是在古特提斯洋向北俯冲过程中由于幔源岩浆使浅层地壳发生熔融形成;(3)晚三叠世-早侏罗世花岗岩在羌塘和昆仑-柴达木同碰撞过程形成。 相似文献
10.
藏南定结地区早中新世淡色花岗岩的形成机制及其构造动力学意义 总被引：13，自引：6，他引：7
定结日玛那穹窿位于高喜马拉雅带中段,由花岗片麻岩、变泥质岩、变基性岩及大量淡色花岗岩等组成,经历了角闪岩-麻粒岩相变质作用。为厘定淡色花岗岩的形成机制以及与高级变质岩的关系,我们对淡色花岗岩和高级变质岩进行了全岩元素和Sr和Nd同位素组成和SHRIMP锆石U-Pb地质年代学测试。全岩元素和Sr-Nd同位素测试结果揭示淡色花岗岩具有以下特征:(1)高SiO2 (>72%),高Al2O3 (>12%)和高A/CNK比值 (>1.0);(2)高Rb,低Sr,高Rb/Sr比值(>1.0);(3)高∑REE和明显的负Eu异常;(4)高Sr同位素初始比值(0.7621~0.8846)和低εNd(t)值(-13.0~-20.2)。淡色花岗岩的高Rb/Sr比值和Sr-Nd同位素系统特征表明其形成机制为主要为白云母脱水部分熔融作用,源区为由花岗片麻岩和变泥质岩组成的混合源区。SHRIMP锆石U-Pb年代学研究揭示出定结地区淡色花岗岩具有21.0±0.7Ma和15.8±0.1Ma 2期年龄,花岗片麻岩的锆石变质增生边年龄为22.2±1.4Ma,与该区的榴辉岩退变质年龄一致。这些数据共同表明,花岗片麻岩和 变泥质岩在22~21Ma发生高级变质和深熔作用,形成早期淡色花岗岩岩浆,在~16Ma进一步深熔,形成晚期淡色花岗岩岩浆。 相似文献
11.
稀土元素的示踪作用在地质学、地球化学研究中具有重要意义,稀土参数图解可以揭示岩石的形成机理、条件和成因分类,追踪各种复杂地质作用的演化历史。利用稀土元素参数REE与SiO2、REE与LREE/HREE、δEu与LREE/HREE图解,在内蒙古拜仁达坝-维拉斯托铅锌银多金属矿区从偏基性端元向偏酸性端元演化的闪长岩类野外岩相学观察和室内测试的基础上,发现其全岩稀土参数之间的相关关系,进而结合岩石地球化学数据、稀土参数图解新方法与微量元素聚类分析,判别其闪长岩的成因和岩浆源区。结果显示,拜仁达坝赋矿的闪长岩具有高硅、富钠及较高MgO和Al2O3含量的特征,属钙碱性系列,显示地幔岩浆分异与下地壳熔融岩浆混合的特点;拜仁达坝-维拉斯托闪长岩LREE/HREE-REE和δEu-LREE/HREE曲线显示,稀土高值组端元分别呈负相关和正相关关系,负Eu异常明显,相对富集Rb、Th、U、K等大离子亲石元素,亏损Nb、Ta、Sr、P、Ti等高场强元素,而稀土低值组端元反之。上述特征表明, 拜仁达坝-维拉斯托闪长岩为一套活动大陆边缘幔源为主、壳幔混合成因的钙碱性岩浆岩系列。实例研究初步证实,提出的稀土参数图解新方法是有效的,具有较强的普适性,适合在常规的地质科研中完善并推广。 相似文献
12.
There is a positive correlation between the concentration of P2O5 in basic magmas and the concentration of the REE and also between their light: heavy ratio, represented by both Ce/Yb and
Nd/Sm. This suggests that a phosphate mineral, such as apatite or whitlockite, both of which can contain high concentrations
of REE, is present in the magma source regions. Thermodynamic calculations indicate that fluorapatite is stable over the whole
P-T range of magma generation, but at the greatest depths it may co-exist with whitlockite in the presence of fluorphlogopite.
Using published REE crystal-liquid distribution coefficients, it is evident that for P2O5-rich basic magmas with 700–1000 times chondritic abundances of LREE, garnet need not have contributed significantly to their
composition. The most convincing match of hypothetical liquid with actual basic magma is for the derivation of mid-ocean ridge
(MOR) basalts from plagioclase- or spinel-lherzolite containing 3 times chondritic REE by ∼5% partial melting. The more P2O5-rich, and hence REE-rich, basic magmas are apparently derived from crystalline sources which are progressively impoverished
in garnet and clinopyroxene, or in other words, the greater the REE concentration of basic magma, the more refractory is the
mineral assemblage of the source. There is some evidence for a compositional dependence of radiogenic neodymium and lead in
basic magma, and one way that this can be reconciled with mantle source-region evolution is to postulate that fusion is not
always accompanied by isotopic equilibrium. 相似文献
13.
The Mianning–Dechang (MD) REE belt of Sichuan, China is one of the most important REE belt in China, which includes Maoniuping, the third largest REE deposit in the world and a series of large to small REE deposits. Mineralization styles varied across the belt, as well as within different parts of the same deposit. Styles include vein-stockworks, pegmatites, breccias and disseminated REE mineralization. Based on geological, geochemical and inclusion studies, this paper proposes a new model for carbonatite hosted REE mineralization. The results show that ore-forming fluid is derived from carbonatite magma, which has high temperature, pressure and density, and is characterized by high K, Na, Ca, Sr, Ba, REE and SO4 contents. The supercritical ore fluid underwent a distinctive evolution path including phase separation, exolution of sulfate melt and unmixing between aqueous fluid and liquid CO2. Rapid geochemical evolution of a dense carbonatite fluid causes REE mineralization and associated alteration to occur within or proximal to the source carbonatite. Veins, pegmatites and carbonatite comprise a continuum of mineralization styles. Veins occur in the outer zone of the upper levels of the deposit. Pegmatites occur in the inner zone of upper levels, whereas disseminated REE ore occurs at the base of the carbonatite. High water solubility in the carbonatite magma and low water, high REE in the exsolved ore-forming fluids, imply that a giant carbonatite body and deep magma chamber are not necessary for the formation of giant REE deposits. 相似文献
14.
S.A. Drury 《Precambrian Research》1978,7(3):237-257
Seventeen rocks from the Lewisian Gneiss of the Inner Hebrides of Scotland, which represent three distinct lithological types at granulite to greenschist facies of metamorphism show rare-earth element patterns which seem not to have been disturbed by their complex metamorphic history. Some indication of their origin can be obtained by simple geochemical models.Three tonalitic pyroxene gneisses are characterized by: (1) light REE enrichment and heavy REE depletion; (2) low total REE contents; (3) moderate Eu enrichment. Their REE chemistry can be approximated by a model involving 10% partial melting of various garnet-bearing basaltic source materials. Alternatively, they may be some form of crystal cumulate, preserving their original anhydrous mineralogy, representing 30% crystallization of a parent tonalitic magma.Three tonalitic to granodioritic hornblende-biotite gneisses are characterized by: (1) light REE enrichment and heavy REE depletion; (2) significantly higher total REE contents than the pyroxene gneisses; (3) moderate Eu depletion. Their REE patterns can be approximated by a residual silicic melt in a model involving 30% fractional crystallization of solids with the modal mineralogy of the pyroxene gneisses or 40% removal of pure anorthosite from a parent dacitic magma.Two strongly metasomatised diopside-actinolite gneisses and one highly sheared epidote-chlorite gneiss have REE patterns which are not significantly different from the hornblende-biotite gneisses which were their precursors before metasomatism and late greenschist-facies shearing. This suggests that strong alteration has not enciphered the REE systematics of the gneisses.Basic gneisses of quartz tholeiite composition occurring as early dykes, which shared the same metamorphic history as the tonalitic to granodioritic gneisses, are characterised by: (1) slight enrichment in light REE relative to heavy REE; (2) variable total REE contents; (3) little difference between granulite and amphibolite facies types. Their REE patterns can be matched by models involving 5–15% partial melting of ultrabasic mantle with 3 times chondritic REE abundances, leaving a residue of olivine and orthopyroxene. 相似文献
15.
本文在研究西藏北拉萨块体中段桑心日岩体中的暗色包体时发现了一种具有特殊岩石成因的暗色包体。暗色包体呈椭球状,在暗色包体和寄主岩的接触面上通常形成一个明显的可能由风化作用造成的间隙面。暗色包体为二长玢岩-花岗闪长玢岩,寄主岩为花岗岩,暗色包体明显较寄主岩更基性,更富Na_2O、CaO、MgO和Fe_2O_3~T。暗色包体和寄主岩具有明显不同的稀土元素特征,暗色包体的稀土元素含量变化较大,最基性样品具有最高的稀土含量,随着基性程度的降低稀土元素含量明显下降。随着岩浆的进一步演化,岩浆向花岗岩方向演化,稀土含量又逐步升高。寄主岩和暗色包体具有基本一致的微量元素组成,具有典型的弧岩浆岩的特征,富集Rb、Cs、K等大离子亲石元素和Th、U,亏损Nb、Ta、Ti等高场强元素。此外,暗色包体和寄主岩具有明显的Ba、Sr的负异常。暗色包体成岩年龄为75. 6±1. 2Ma,寄主岩的成岩年龄为71. 8±0. 6Ma,暗色包体成岩年龄较寄主岩早约4Myr。两者具有一致的锆石原位Lu-Hf同位素特征。综合以上岩相学、年代学、元素地球化学和同位素地球化学证据,我们认为桑心日暗色包体和寄主岩来源于同源母岩浆,初始岩浆在母岩浆房中经历了不同程度的含钾角闪石结晶分离作用,并沿早期较弱的构造裂隙侵入到地壳的某一层位,随着构造活动进一步加剧,经过进一步分异母岩浆大规模上侵,并将早先侵位处于半塑性状态的暗色包体侵吞、裹挟至近地表。桑心日暗色包体最可能的成因模式可以解释为同源岩浆不同期次间的物理混合。 相似文献
16.
X射线衍射分析和化学成分研究表明,磷灰石为氟磷灰石,榍石成分中存在着的主要类质同象替代是(Fe~(3+)、Al)+(F,OH)~-=Ti~(4+)+O~(2-)。磷灰石和榍石是碱性辉长岩的REE、Ba、Zr等微量元素的主要载体;它们是在较高氧逸度的条件下结晶的。磷灰石的Sr同位素特征说明形成双龙桥碱性辉长杂岩的物质来源于上地幔。 相似文献
17.
Recognized in the Xianghualing region,South Hunan are three major types of granitoids,i.e.,biotite granite,zinnwaldite-albite granite and xianghuagite,which evolved form the same granitic magma,but were formed at different stages.These granitoid rocks constitute a complete magmatic evolutionary series.With the evolution of magma,REE contents and negative Eu anomalies tend to decrease progressively,and LREE become more and more enriched relative to HREE .The facts mentioned above show that the tendency of REE evolution in granitoid rocks in the region studied is different from that in other regions.Evidence indicates that the granitic magma system became more and more depleted in Si(K Na),but richer and richer in Al,Li,F and H2O^ during the process of its evolution,re-sulting in relatively weak acidity and strong alkalinity .It may be the most important factor leading to a specific REE evolutionary trend for the granitoid rocks in this region.In addition,the changing oxidation-reduction environments at different evolutionary stages of this magma system may be anoth-er important factor which should be taken into consideration. 相似文献
18.
This paper reports the results of numerical simulation for the behavior of rare earth elements (REE) during decompression
degassing of H2O- and Cl-bearing granite melts at pressures decreasing from 3 to 0.5–0.3 kbar under near isothermal conditions (800 ± 25°C).
Fluid phase in equilibrium with the melt contains mainly chloride REE complexes, and their behavior during magma degassing
is, therefore, intimately related to the behavior of chlorine. It was shown that the contents and distribution patterns of
REE in the aqueous chloride fluid phase formed during decompression vary considerably depending on (1) the contents of volatiles
(Cl and H2O) in the initial melt, (2) the redox state of the magma, and (3) the dynamics of fluid phase separation from magmas during
their ascent toward the Earth’s surface. During decompressiondriven degassing, the contents of both Cl and REE in the fluid
decrease, especially dramatically under opensystem conditions. The REE patterns of the fluid phase compared with those of
the melt are characterized by a higher degree of light to heavy REE fractionation. A weak negative Eu anomaly may be present
in the REE patterns of Cl-rich fluids formed during the early stages of degassing at relatively high pressures. At a further
decrease in pressure and Cl content in the fluid, it is transformed into a positive Eu anomaly increasing during decompression
degassing. Such an anomalous behavior of Eu during degassing is related to its occurrence in magmatic melts in two valence
states, Eu3+ and Eu2+, whereas the other REE occur in melts mainly as (REE)3+. The Eu3+/Eu2+ ratio of melt is controlled by the redox state of the magmatic system. The higher the degree of melt reduction, the more
pronounced the anomalous behavior of Eu during decompression degassing. The amount of REE extracted by fluid from melt during
various stages of degassing does not significantly influence the content and distribution patterns of REE in the melt. 相似文献
19.
Quaternary lavas of the normal island-arc basalt—andesite—dacite association in the islands of Java and Bali range from those belonging to tholeiitic series over Benioff-zone depths of ～ 150 km to high-K calc-alkaline series over Benioff-zone depths of 250 km. More abundant and diverse calc-alkaline lavas are found over intermediate Benioff-zone depths. On average, basaltic lavas become slightly more alkaline (largely due to increased K contents) with increasing depth to the Benioff zone. Levels of incompatible minor and trace elements (K, Rb, Cs, Ba, Nb, U, Th, light REE) show a corresponding increase of almost an order of magnitude.Low average Mg-numbers (～ 0.52) and Ni and Cr abundances (15–25 and 35–60 ppm, respectively) of basaltic lavas suggest that few lavas representing primary mantle-derived magma compositions are present. Calculated primary basaltic magma compositions for most tholeiitic and calc-alkaline volcanic centres are olivine tholeiites with 15–30% ol. The single high-K calc-alkaline centre considered yielded transitional alkali olivine basalt—basanite primary magma compositions. These calculated magma compositions suggest that the percentage of mantle melting decreases with increasing depth to the Benioff zone (from >25 to <10%), while the corresponding depth of magma separation increases from ～ 30 to 60 km.Calculation of REE patterns for basaltic magmas on the basis of peridotitic mantle sources with spinel lherzolite, amphibole lherzolite or garnet lherzolite mineralogy, and model REE levels of twice chondritic abundances, indicates that change in the conditions of magma genesis alone cannot explain the observed change in light-REE abundances of basaltic lavas with increasing depth to the Benioff zone. Complementary calculations of the REE levels of mantle sources required to yield the average tholeiitic, calc-alkaline and high-K calc-alkaline basaltic magma indicate that light-REE abundances must increase from 2–3 to 7–8 times chondrites with increasing depth to the Benioff zone. The percentages of mantle melting favoured on REE evidence are lower than those indicated by major-element considerations.The observed variation in incompatible element geochemistry of mantle magma sources is thought to be related directly or indirectly to dehydration and partial-melting processes affecting subducted oceanic crust. The possible nature of this relationship is discussed. 相似文献
20.
稀土元素(REE)作为"三稀资源"之一,是中国重要的战略性矿产资源,碳酸岩型稀土矿床是世界稀土的主要来源.成矿碳酸岩的岩浆演化以及稀土元素的富集和分异机理一直是碳酸岩型稀土矿床研究的热点和难点,国内外学者对碳酸岩的岩浆起源、岩浆演化过程中稀土元素富集与分异的机理进行了大量的研究与探讨,但仍存在较多的争议,限制了碳酸岩型稀土元素成矿理论的发展及国内外碳酸岩型稀土矿床的找矿勘查工作.文章重点对稀土成矿碳酸岩的起源、岩浆演化过程及在此过程中REE的富集与分异行为进行了详细的文献调研和评述,同时,基于笔者在冕宁牦牛坪稀土矿床前期的研究工作和最新发现,认为碳酸岩中普遍存在矿物学分带,它是岩浆演化过程的最佳记录,是不同成分矿物结晶分异作用的体现.对牦牛坪稀土矿床碳酸岩的矿物学分带特征及其中的熔体、熔流体和流体包裹体进行了初步描述与探讨,以期为研究碳酸岩的岩浆演化、岩浆-流体转化过程及稀土元素的富集与分异机理提供新的思路,促使对稀土碳酸岩矿物学分带及其对REE富集与分异的研究引起更多的关注和重视. 相似文献