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21.
一种可能的棕闪煌斑岩变异新种—棕闪钠煌岩 总被引：2，自引：0，他引：2
浏阳县蕉溪岭岩体中发现富钠煌斑岩,Na_2O为4.05％,主要矿物钠长石为32—51％,棕闪石为25—37％,其他矿物钾长石2—8％,单斜辉石1—10％,黑云母0.5—10％,钛铁矿1—5％,可能是已知棕闪煌斑岩的一个变异新种棕闪钠煌岩。它与花岗岩体有空间上的共生关系,可能属蕉溪岭花岗岩熔离分异或结晶分异演化过程的产物。 相似文献
22.
穿地壳岩浆系统理念的提出为认知岩浆岩的形成机制提供了一个新的窗口。在穿地壳岩浆系统内,深层次岩浆储库结晶的矿物(例如辉石、角闪石、斜长石等)可通过通道向上运移至浅层次的岩浆储库,该过程可导致这些矿物的熔蚀、流体交代或再生长。上述矿物属于再循环晶,它们保留的成分环带信息可忠实地记录岩浆环境的变化。本文以华北克拉通东南缘胶北早白垩世丛家岩体(-127Ma)内产出的闪斜-拉辉煌斑岩为主要研究对象。这些钙碱性煌斑岩中常见不同结构和成分特征的单斜辉石再循环晶,它们保存了多级岩浆储库的相关信息。丛家煌斑岩包括一系列中基性煌斑岩,形成一个煌斑岩岩石组合具有轻重稀土元素分异明显((La/Yb)_N=14.2～28.1)的特征。在原始地幔标准化微量元素蜘蛛图上丛家煌斑岩表现出亏损Nb、Ta、P和Ti,而富集Ba、Pb、Sr和Nd等元素的特征。本文在丛家煌斑岩中识别出了两类单斜辉石"再循环晶"即正环带单斜辉石和振荡环带单斜辉石。正环带辉石核部Mg~#值为86.0～94.9,稀土元素总含量偏低,亏损HREE;部分核部具筛状结构,筛孔填充物富集大离子亲石元素,并表现出Cr-Ni元素的解耦,显示与流体交代作用有关。正环带辉石边部具振荡环带特征,反映了晶体在震荡环境中的再生长。再生长辉石环带的Mg~#值为78.9～89.1稀土元素总含量较高,但其分配趋势与核部相似,富集Th等元素,亏损Nb、Pb、P。振荡环带辉石的Mg~#值为82.3～89.4,化学成分特征与正环带辉石边部相近。丛家煌斑岩中的角闪石可分为低硅角闪石和高硅角闪石。低硅角闪石的SiO_2含量偏低(38.2%～40.1%),Mg~#值为72.0～82.4,结晶于较高的温压环境(976±22℃～1024+22℃,5.72～10.9kbar)。高硅角闪石的SiO_2含量较高(40.3%～44.3%)Mg~#值为70.9～83.0,结晶于相对低的温压环境(872±22℃～947±22℃,3.06～4.43kbar)。本研究认为,丛家煌斑岩中的单斜辉石再循环晶在不同层次岩浆储库内发生了熔蚀、流体交代或再生长,指示了深部岩浆系统是由多级岩浆储库构成的。 相似文献
23.
Origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in Beiya area, western Yunnan, China 总被引：6，自引：0，他引：6
Lamprophyres consisting mainly of diopside, phlogopite and K-feldspar formed in the early Tertiary around 60 Ma in the Beiya area and are characterized by low SiO2 ± 46–50 wt.%), Rb (31–45 ppm) and Sr (225–262 ppm), high Al2O3, (11.2–13.1 wt.%), CaO (8.0–8.7 wt.%), MgO (11.5–12.1 wt.%), K2O(4.9–5.5 wt.%), TiO2 (2.9–3.3 wt.%) and REE (174–177 ppm), and compatible elements (e.g. Sc, Cr and Ni) and HSF elements (e.g. Th, U, Zr, Nb, Ta, Ti and Y), and low 143Nd/144Nd 0.512372–0.512536, middle 87Sr/86Sr 0.707322–0.707395, middle 206Pb/204Pb 18.50–18.59, 207Pb/204Pb 15.60–15.65 and 208Pb/204Pb 38.75–38.8. These rocks developed peculiar quartz megacrysts with poly-layer reaction zones, melt inclusions, and partial melted K-feldspar and plagioclase inclusions, and plastic shapes. Important features of these rocks include: (1) hybrid composition of elements, (2) abrupt increase of SiO2 content of the melt, recorded by zoned diopside, (3) development of sanidine and aegirine-augite reaction zones, (4) alkaline melt and partial melted K-feldspar and plagioclase inclusions, (5) deformed quartz inclusions associated with quartz megacrysts, (6) the presence of quartz megacrysts in plastic shape with their parent melts, (7) the occurrence of olivine, high-MgO ilmenite and spinel inclusions within earlier formed diopside, phlogopite and magnetite. Median 87Sr/86Sr values between Tertiary alkaline porphyries in the Beiya area and the western Yunnan and Tertiary basalt in the western Yunnan indicate that the Beiya lamprophyre melts were derivative and resulted from the mixing between basic melts that were related to the partial melting of phenocrysts of spinel iherzolite from a mantle source. The alkaline melts originated from partial melting along the Jinshajiang subduction ductile shear zone at the contact between the buried Palaeo-Tethyan oceanic lithosphere and the upper mantle lithosphere. The alkaline melts are composed of 65% sanidine (Or70Ab28An2) and 35% SiO2. The melt mixing occurred in magma chambers in the middle-shallow crust at 8–10 km before the derivative lamprophyre melts intruded into the shallow cover in Beiya area. This mixing of basic and alkaline melts might represent a general process for the formation of lamprophyre in the western Yunnan. 相似文献
24.
煌斑岩与金矿成矿关系探讨 总被引：7，自引：0，他引：7
煌斑岩的同位素、微量元素及稀土元素特征表明煌斑岩是地幔部分熔融的产物。深断裂是其上侵地表的通道，部分煌斑岩可能是含金的岩类，但并不是矿床中的唯一来源。岩石中金含量变化范围虽然较大，但其含量高、低并不是形成金矿床的主要因素，即使含金高，但其规模都不大，也不足以形成矿床。此外，一些煌斑岩与金矿化在形成时间上往往有所不同，在成因上当然没有直接的关系。然而，煌斑岩出露区的后期热液蚀变、矿化作用可能使金带入 相似文献
25.
M. Moayyed M. Moazzen A.A. Calagari A. Jahangiri M. Modjarrad 《Chemie der Erde / Geochemistry》2008,68(2):141-154
Eslamy peninsula in NW of Iran is formed by a strato-volcano with collapsed calderon, which is intruded by lamprophyric dykes with minette composition. Also trachytic and microsyenitic dykes have intruded the volcanic rocks. The oldest volcanic activity includes eruption of leucite basanite, leucite tephrite, basanite and tephrite, which are associated with pyroclastic rocks. Lamprophyric dykes are distinguishable with large mica phenocrysts. Mica-clinopyroxenite xenoliths can be found in the rocks. The source magma of the rocks had a ultrapotassic to shoshonitic nature, rich in LREE and LILE. Eslamy peninsula lamprophyres are between alkaline and calc-alkaline lamprophyres in terms of REE patterns and spider diagrams for trace elements, but are closer to clac-alkaline lamprophyres. The behaviour of trace elements studied by the means of spider diagrams show that the magma, producing the lamprophyres, is generated from deep-mantle probably from a garnet-bearing source (garnet lherzolite) with high CO2/H2O content. The resulted magma had interacted with crustal materials and had formed Eslamy peninsula lamprophyres in a post-collisional tectonic setting. Geochemistry of rare elements indicate an extensive rutile-rich metasomatism in the source magma of the lamprophyres. 相似文献
26.
西昆仑库地煌斑岩的年代学及地球化学特征 总被引：14，自引：3，他引：11
在西昆仑库地发现的煌斑岩脉为钙碱性、钾质闪煌岩,侵位在加里东期的变质增生楔杂岩中,采用角闪石单矿物＾４０Ａｒ／＾３９Ａｒ同位素年代学方法确定粕斑岩的侵位年龄为４０４Ｍａ。煌斑岩的稀土元素总量较高,配分图呈轻稀土富集的右倾型式;微量元素以相对富含固离子亲石元素、亏损高场强元素为特征;结合地球化学、同位素特征和大地构造背景分析,煌斑岩来源于受原特提斯俯冲组分释放富含大离子不相容元素流体交代过的亏损地幔 相似文献
27.
海南岛戈枕含金剪切带煌斑岩与金成矿关系研究 总被引：2，自引：1，他引：1
许德如 《大地构造与成矿学》2000,24(3):258-265
在详细的矿床地质、岩石地球化学和同位素年代学综合研究基础上,结合区域构造演化的特点,着重对金矿与煌斑岩的成因关系进行了剖析,认为戈枕含金剪切带煌斑岩与金矿不仅具有生成构造环境上的联系,而且对金成矿具有重要的物源贡献,是金矿找矿标志。煌斑岩与金矿是长期的区域构造活动、岩浆活动事件耦合作用的产物。 相似文献
28.
Geochemistry of lamprophyres from the Western Alps,Italy: implications for the origin of an enriched isotopic component in the Italian mantle 总被引：3，自引：0，他引：3
Jennifer Paige Owen 《Contributions to Mineralogy and Petrology》2008,155(3):341-362
Cenozoic lamprophyres (minettes, spessartites, kersantite) from the Western Alps, northern Italy, represent small volume,
mafic melts with high Mg#s and high Ni and Cr contents. All the lamprophyres show light REE enrichment, high incompatible
element contents, and Ta, Ti and Nb troughs on chondrite-normalized diagrams. Age-corrected 87Sr/86Sr isotopic ratios (assuming t = 30 Ma) are highly variable and range from 0.70590 to 0.71884; 143Nd/144Nd ratios range from 0.51203 to 0.51242. Pb isotopic ratios are: 206Pb/204Pb = 18.669–18.895, 207Pb/204Pb = 15.605–15.689 and 208Pb/204Pb = 38.224–39.134. 87Sr/86Sr ratios show a negative correlation with 143Nd/144Nd, and a positive correlation with K, Ba, and Rb as well as with Ti, Th, Ta, Nb and Zr abundances. The primitive nature of
the lamprophyres, coupled with their enriched incompatible trace element and isotopic signatures, suggest derivation from
a metasomatized upper mantle source. Linear arrays in isotope space and elemental data plots suggest mixing between two distinct
end-members in the Italian mantle; an enriched end-member that is isotopically similar to pelagic sediments, and a significantly
less enriched end-member that approaches Bulk Earth values. New isotopic data indicate that the mantle source(s) of the lamprophyres
from the Western Alps contain a very high proportion of the enriched end-member. The geochemical signature of the enriched
end-member is attributed to fluids or melts derived from pelagic sediments subducted during the closure of the Tethyan Ocean
in the late Cretaceous to early Tertiary. 相似文献
29.
中生代苏—鲁活动大陆边缘榴辉岩、煌斑岩、金矿及富集地幔间的成因联系 总被引：20，自引：2，他引：20
海西期末形成的初始欧亚板块，从三叠纪（250Ma)开始，便与古太平洋板块－太平洋板块发生强烈的挤压碰撞作用和俯冲作用，及由此引起的远距离效应使中国广大的东部地区从中生代开始成为活动大陆边缘，俯冲作用及构造环境的演化是控制胶东地体等大多数中生代榴0辉岩等变质岩类，花岗岩类，火山岩类，煌斑岩类以及金等矿床形成和使它们出露地表的重要因素，胶东地体中富钾的钙－碱性煌斑岩类的特征与其它活动大陆边缘和造山带中金矿有关的煌斑岩很相似，例如呈脉状产出，晚期侵位，强烈的自变质，富含大离子亲石元素（LILE）和挥发分，高的金含量，高的LREE／HREE和^87Sr/^86Sr比值，低的^143Nd/^144Nd比值，与花岗岩类，橄榄安粗岩，酸性脉岩以及热液金矿床的密切共生及它们这间与富集地幔楔的成因联系等，这些都表明它们与板块或板片俯冲过程中的去气，去碱，去ILE作用或壳－幔物质交换作用及由此形成的富集地幔楔有着紧密的联系。 相似文献
30.
Subsequent to high-pressure and temperature metamorphism of the axial zone of the Variscan foldbelt in central Europe at ca. 340 to 330 Ma, formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post-collisional stage of the orogeny. We report the results of 40Ar/39Ar mica dating, major and trace element data, and isotope compositions for lamprophyre and rhyodacite samples from the southern Black Forest. The chemical compositions of these rocks shed light on the upper mantle and crust at the end of the Variscan orogeny. 40Ar/39Ar plateau ages for four phlogopite–biotite separates from lamprophyres indicate emplacement at 332 to 314 Ma. This event coincides with melting of the crust as indicated by 40Ar/39Ar biotite plateau ages of ca. 332 Ma for rhyodacite dikes which are probably related to coeval undeformed granites. Incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction-modified mantle. Nd, Sr, and Pb isotope compositions indicate an enriched mantle source with Nd-values of −1.5 to −6.8 which is similar to Variscan crust. Significant contamination of the lamprophyric melts by Variscan crust can be ruled out as mantle-derived phlogopite phenocrysts have similar Nd-values as in the whole-rock samples. We propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment. The isotope compositions of Variscan lamprophyres from western Europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust, as has been invoked for the origin of post-collisional granites. The isotope compositions of Tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western Europe, implying that the enriched Variscan material was efficiently removed and mixed into the convecting mantle. 相似文献