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我国南方若干锡矿床成矿物质来源的同位素证据 总被引:1,自引:0,他引:1
本文综合整理了我国南方十多个与锡矿有成因联系的花岗岩的锶、氧同位素组成,得出这些岩体初始锶同位素比值为0.780~0.718;全岩的氧同位素组成为+4.8~+17.66‰;石英的氧同位素组成为+10.7~+14.2‰,并探讨了它们形成和演化规律。 经研究锡矿床的氢、氧同位素组成有三种分布特征:δ~(18)O_(H2O)=+6.2~+10.2‰,δD_(H2O)=-47~-113‰(个旧、珊瑚和栗木);δ~(18)O_(H2O)=+11.8~十17.1‰(钦甲);δ~(18O_(H2O)=+1.8~-7.3‰(桂北、香花岭和长铺)。并建立沸腾体系氢、氧同位素分馏数学模型。 它们的硫化物硫同位素数据表明,岩浆来源的δ~(34)S_(Σs)一般在-2~~+5‰之间,硫化物的δ~(34)S一般变化较小,但可以是正或负。岩浆跟地层混合源的δ~(34)S_(Σs)一般>+12‰,硫化物的δ~(34)S一般变化较大,以正值为主。 相似文献
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冈底斯岩基东部的米林地区发育辉长质片麻岩和花岗质片麻岩近垂向相间排布的侵入杂岩体及东侧未变形闪长岩体。野外穿切关系和锆石SHRIMP U-Pb年龄结果表明:早期辉长质片麻岩(146.3±1.6Ma)被晚期花岗质片麻岩(141.7±2.0Ma)侵入,并一起经历了后期变质作用(~90Ma)和晚白垩世闪长质岩浆作用(87.8±1.1Ma)。辉长质片麻岩具有E-MORB特征,经历了富Ti矿物相的堆晶作用,母岩浆主要来源于板片流体交代上覆亏损地幔楔物质(εHf(t)=+9.9~+14.5;εNd(t)=+3.0~+4.1)。花岗质片麻岩具有岛弧型岩浆岩的地球化学特征,同时伴有Fe-Ti氧化物的分离结晶,源区物质主要为部分熔融的初生下地壳(εHf(t)=+10.9~+15.1;εNd(t)=+4.1~+4.3)。闪长岩具有弱的Eu正异常,暗示源区存在斜长石的堆晶作用,其母岩浆来源于板片流体交代上覆亏损地幔楔物质(εHf(t)=+12.2~+15.6),并在岩浆演化的过程中混入地壳物质。冈底斯岩基南缘发育晚侏罗世的辉长岩和早白垩世花岗可能是第一次新特提斯洋北向俯冲即将终止的产物。晚白垩世岩浆岩是与新特提斯洋再次俯冲引起的峰期岩浆活动的标志,可能是板块回撤引发软流圈上涌的产物。
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川东北地区下三叠统飞仙关组为浅海碳酸盐岩夹泥页岩与蒸发岩序列,而在碳酸盐岩台地边缘通常发育一些白云石化的鲕粒滩。这些鲕粒滩白云岩储集层是川东北地区主要的产气层,一些学者认为该套白云岩为大气淡水与海水的混合水白云石化成因,另外一些学者将其视为回流—渗透白云石化成因。飞仙关组鲕粒滩白云岩稳定同位素氧值一般为-6.73‰~-3.65‰(PDB),平均值为-4.89‰(PDB)(罗家寨地区为-10.81‰(PDB)),稳定同位素碳值一般为+0.57‰~+3.00‰(PDB)。对基质和孔洞中充填的鞍状白云石和亮晶白云石胶结物而言,稳定同位素87Sr/86Sr值为0.70735~0.70800。这些有关鲕粒滩白云岩的数据表明白云石化作用是在埋藏条件下进行的。在测定流体包裹体的均一化温度后,计算出白云石化流体稳定同位素氧成分(δ18O白云石-δ18O水=[3.2×106 T-2]-1.5,来自 Friedman 和 ONeil(1977)),其平均值约为+4‰(SMOW)。根据流体稳定同位素氧、碳成分与海水蒸发时流体盐度的正相关性,计算出流体δD平均值约为+25‰(SMOW)。流体包裹体盐度测定表明,白云石化流体是一种超盐度卤水,其盐度是海水的数倍,白云石化的温度为90~130℃。由于下三叠统鲕粒滩白云岩的稳定同位素氧和碳成分与上二叠统生物礁白云岩的稳定同位素氧和碳成分类似,因此,它们的白云石化流体很可能是同一来源。然而,这一结论还有待于进一步研究。 相似文献
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川西新元古代双峰式火山岩成因的微量元素和Sm-Nd同位素制约及其大地构造意义 总被引:44,自引:0,他引:44
系统的微量元素和Sm-Nd同位素分析表明,川西地区早震旦世苏雄组双峰式火山岩中的大多数玄武岩具有高的正εNd(T)值(+5~+6)、大离子亲石元素和LREE富集,与现代典型的洋岛玄武岩和大陆溢流玄武岩省中的碱性玄武岩有非常相似的地球化学和同位素组成特征。酸性火山岩的εNd(T)值较低(+1.1~+2.6),地球化学特征总体上与A2-型花岗岩相似,它们是受地壳混染的OIB型玄武质岩浆在地壳中部的一个“双扩散”岩浆房通过结晶分异形成的。苏雄组双峰式火山岩形成于典型的大陆裂谷环境,非常类似于现代与地幔柱活动有关的高火山活动型裂谷火山岩,扬子块体西缘 800Ma前的裂谷作用和火山活动应是约825Ma前的华南地幔柱活动引发的结果。 相似文献
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地球大气圈中40Ar/36Ar的现代比值被公认为295.5,在利用K-Ar法测定地球物质年龄时,它是校正大气氩混染量的重要参数。陨石中原始捕获(trapped)的(40Ar/36Ar)t比值是否和地球大气圈中氩同位素丰度相一致,这个问题不但在地质年龄测定中具有现实意义,而且对探索太阳系的形成和演化也有重要理论价值。近十几年,随着质谱分析技术的提高以及登月计划的实施,国外出现了一批有关月岩中氩同位素原始组分的资料,但至今对陨石中原始氩同位素丰度的报道很少。笔者采用40Ar/39Ar快中子活化技术和约克方程[3,4],对吉林陨石雨2号标本进行了原始捕获的(40Ar/36Ar)t比值进行了测定,并探讨了它的地质意义。 相似文献
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扎河坝蛇绿岩位于准噶尔北缘,是扎河坝—阿尔曼太蛇绿混杂岩带的一部分。通过对蛇绿混杂岩中堆晶辉长岩和凝灰岩夹层的锆石U-Pb年龄及Hf-O同位素进行研究,获得堆晶辉长岩的结晶年龄为485±4Ma,凝灰岩的喷发年龄为401±2.5Ma。辉长岩极度亏损Hf同位素,εHf(t)为13~20,δ~(18)O峰值为+5.37‰,显示其具有地幔特征。凝灰岩锆石的Hf同位素亏损程度低于堆晶辉长岩,εHf(t)为1.4~9.2。扎河坝蛇绿岩具有典型的SSZ型蛇绿岩特征,是通过俯冲增生到洋内弧弧前的蛇绿岩。 相似文献
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本文对出露于佳木斯地块北部金银库组变沉积岩和侵入其中的火成岩脉体中的锆石进行了系统的LA-ICP-MS/SIMS U-Pb定年和Hf同位素研究,旨在限定金银库组的沉积时限,并揭示其物源及沉积环境。3个样品中锆石呈自形-半自形,显示典型的岩浆生长环带或条痕状吸收,暗示其岩浆成因。研究结果显示:采自金银库组绢云母片岩中的碎屑锆石72个分析点给出1 955~457 Ma的年龄区间,主要峰期年龄为814、757、568、491和463 Ma,其εHf(t)值为-13.9~-0.1,Hf同位素一阶段模式年龄TDM1和二阶段模式年龄TDM2分别为1 827~1 307 Ma和2 411~1 715 Ma。采自侵入金银库组的花岗细晶岩和辉绿岩分别给出了263和267 Ma的结晶年龄,前者的εHf(t)值为0.9~2.0,Hf同位素二阶段模式年龄TDM2为1 110~1 047 Ma;后者的εHf(t)值为-7.7~6.4,Hf同位素一阶段模式年龄TDM1为1 206~662 Ma。结合佳木斯地块及邻区约430 Ma火成岩的存在和金银库组中该期碎屑锆石的缺乏以及碎屑锆石年龄众数及其Hf同位素组成,我们认为金银库组的形成时代应为晚奥陶世至早志留世(463~430 Ma),形成于被动大陆边缘背景,沉积物源主要来自佳木斯地块及其邻区的古元古代和早古生代早期火成岩。 相似文献
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Initial Nd, Pb, and Sr isotopic data from carbonatites and associatedintrusive silica-undersaturated rocks from the early Jurassic,Chilwa Island complex, located in southern Malawi, central Africa,suggest melt derivation from a Rb/Sr- and Nd/Sm-depleted butTh/Pb- and U/Pb-enriched mantle source. Initial 143Nd/144Nd(0.512650.51270) isotope ratios from the Chilwa Islandcarbonatites are relatively constant, but their initial 87Sr/86Sr(0.703190.70361) ratios are variable. The 18Osmow (9.5314.15%0)and 13CPDB (3.27 to 1.50%0) isotope ratios ofthe carbonates are enriched relative to the range of mantlevalues, and there is a negative correlation between 18O andSr isotope ratios. The variations in Sr, C, and O isotopic ratiosfrom the carbonatites suggest secondary processes, such as interactionwith meteoric groundwater during late-stage carbonatite activity.The initial 143Nd/144Nd (0.51246 0.51269) and initial 87Sr/86Sr(0.703440.70383) isotope ratios from the intrusive silicaterocks are more variable, and the Sr more radiogenic than thosefrom the carbonatites. Most of the Pb isotope data from Chilwa Island plot to the rightof the geochron and close to the oceanic regression line definedby MORBs and OIBs. Initial Pb isotopic ratios from both carbonatites(207Pb/204Pb 15.6315.71; 206Pb/204Pb 19.1319.78)and silicate rocks (207Pb/204Pb 15.6115.72; 206Pb/204Pb18.1820.12) show pronounced variations, and form twogroups in Pb-Pb plots. The isotopic variations shown by Nd, Pb, and Sr for the ChilwaIsland carbonatites and intrusive silicates suggest that thesemelts underwent different evolutionary histories. The chemicaldata, including isotopic ratios, from the carbonatites and olivinenephelinites are consistent with magmatic differentiation ofa carbonated-nephelinite magma. A model is proposed in whichdifferentiation of the carbonatite magma was accompanied byfenitization (metasomatic alteration) of the country rocks bycarbonatite-derived fluids, and subsequent alteration of thecarbonatite by hydrothermal activity. The chemical and isotopicdata from the non-nephelinitic intrusive silicate rocks reveala more complex evolutionary history, involving either selectivebinary mixing of lower-crustal granulites and a nephelinitemagma, or incremental batch melting of a depleted source andsubsequent crustal contamination. 相似文献
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This paper reports isotopic and geochemical studies of eclogites from the western ultrahigh pressure (UHP) and eastern high-pressure (HP) blocks of the Kokchetav subduction-collision zone. These HP and UHP eclogites exhumed in two stages: (1) The rocks of the western block metamorphosed within the field of diamond stability (e.g., Kumdy-Kol and Barchy); (2) In contrast, the metamorphic evolution of the eastern block reached the pressure peak within the stability field of coesite (e.g., Kulet, Chaglinka, Sulu-Tyube, Daulet, and Borovoe). The eclogites vary widely in the ratios of incompatible elements and in the isotope ratios of Nd (143Nd/144Nd = 0.51137-0.513180) and Sr (87Sr/86Sr = 0.703930.78447). The Sulu-Tyube eclogites display isotope-geochemical features close to N-MORB, while those from the other sites are compositionally similar to E-type MORB or island arc basalts (IAB). The model ages TNd(DM) of eclogites vary between 1.95 and 0.67 Ga. The Sulu-Tyube eclogite yields the youngest age; it has the values of εNd(T) (7.2) and 87Sr/86Sr (0.70393) close to the depleted mantle values. The crustal input to the protolith of the Kokchetav eclogites is evident on the εNd(T)-86Sr/87Sr and εNd(T)-T plots. The eclogites make up a trend from DM to country rocks. Some eclogites from the Kulet, Kumdy-Kol, and Barchy localities display signs of partial melting, such as high Sm/Nd (0.65-0.51) and low (La/Sm)N (0.34-0.58) values. The equilibrium temperatures of these eclogites are higher than 850 °C. The geochemical features of eclogites testify to the possibility of the eclogite protolith formation in the tectonic setting of passive continental rift margin subducted to depths over 120 km. 相似文献
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Continental Lithospheric Contribution to Alkaline Magmatism: Isotopic (Nd, Sr, Pb) and Geochemical (REE) Evidence from Serra de Monchique and Mount Ormonde Complexes 总被引:3,自引:1,他引:2 下载免费PDF全文
Bernard-Griffiths Jean; Gruau Gerard; Cornen Guy; Azambre Bernard; Mace Joel 《Journal of Petrology》1997,38(1):115-132
Isotopic results (Sr, Nd, Pb), as well as concentrations ofmajor and trace elements (REE) are reported for whole-rock samplesand mineral separates from the onland alkaline complex of Serrade Monchique (South Portugal) and the offshore alkali basaltvolcanic suite of Mount Ormonde (Gorringe Bank). These two geneticallyrelated alkaline complexes were emplaced at the east Atlanticcontinent–ocean boundary during the Upper Cretaceous,i.e. 66–72 m.y. ago. Taken together, Serra de Monchiqueand Mount Ormonde may be seen as one of the few examples ofwithin-plate magmatism that straddles the continent–oceanboundary. Major and trace element compositions fail to revealany significant differences between onland and offshore complexes.This is particularly true regarding less differentiated samples(mg-number 0.40) which show the same progressive and continuousenrichment of their trace element patterns, with no specificanomaly (e.g. negative Nb anomaly) being present in samplesfrom the onland complex. Initial Pb and Sr isotopic compositionsalso do not allow any distinction to be made between Serra deMonchique and Mount Ormonde samples. Initial Pb isotope ratiosare moderately high (19.1 < 206Pb/204Pb < 19.8; 207Pb/204Pb= 15.6) in both cases. Moreover, once the effects of Sr contaminationby seawater are taken into account and the most contaminatedsamples discarded using data from fresh clinopyroxene separatesand results of leaching experiments, the initial Sr isotopiccompositions of Mount Ormonde samples are found to be unradiogenic(87Sr/86Sr = 0.7031±1) and identical to those obtainedat Serra de Monchique (87Sr/86Sr = 0.7032±1). In contrast,a systematic mean difference of 2 Nd units is observed betweenSerra de Monchique [Nd(T) = +4.8] and Mount Ormonde [Nd(T) =+6.6] whole-rock samples. Surprisingly, a variation is alsoobserved at Mount Ormonde between the whole-rock samples andone of the two analysed clinopyroxene separates. Whereas MountOrmonde whole-rock samples invariably yielded Nd(T) = +6.6 (meanvalue), a value of +0.5 is obtained for one clinopyroxene separate,whereas another gives +6.0. The above geochemical and isotopicresults make it possible to assign respective roles to the asthenosphere,lithosphere and crust in the petrogenesis of Serra de Monchiqueand Mount Ormonde complexes. We propose that both complexesshare a common mantle source whose isotopic characteristicsare very similar to the source of oceanic island basalts. Continentalmantle lithosphere, already characterized isotopically by studiesof peridotite massifs within the Iberian peninsula, acts asa contaminant which is evident onland on the whole-rock scale,and also present offshore as discrete clinopyroxene xenocrysts.The continental crust appears to play no role in the petrogenesisof the Serra de Monchique alkaline rocks. KEY WORDS: alkaline complexes; continental lithosphere; isotope geochemistry; passive continental margin; within-plate volcanics 相似文献
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V. N. Smirnov K. S. Ivanov Yu. L. Ronkin V. A. Koroteev P. A. Serov A. Gerdes 《Doklady Earth Sciences》2017,474(1):516-519
According to isotopic analysis of rocks of the Reft gabbro–diorite–tonalite complex (Middle Urals), gabbro and related diorite and dikes and vein-shaped bodies of plagiogranitoids, crosscutting gabbro, are similar to the depleted mantle substance in εNd(T) = 8.6–9.7 and εHf(T) = 15.9–17.9. Their model Hf ages are correlated with the time of crystallization. Here, the tonalites and quartz diorites constituting most of the Reft massif are characterized by lower values: εNd(T) = 3.7–6.0, εHf(T) = 11.1–12.7, and T DM values significantly exceeding the age datings. This is evidence that Neoproterozoic crustal rocks were a source of parental magma for these rocks. The primary 87Sr/86Sr ratio in rocks of both groups is highly variable (0.70348–0.70495). The data obtained allow us to reach the conclusion that the Reft gabbro–diorite–tonalite complex was formed as a result of nearly synchronous processes occurring in the crust and the mantle within a limited area. 相似文献
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Association of Late Paleozoic Adakitic Rocks and Shoshonitic Volcanic Rocks in the Western Tianshan, China 总被引:6,自引:1,他引:5
ZHAO Zhenhu XIONG Xiaolin WANG Qiang BAI Zhenghu XU Jifeng QIAO Yulou Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou Guangdong 《《地质学报》英文版》2004,78(1):68-72
The late Paleozoic adakitic rocks are closely associated with the shoshonitic volcanic rocks in the western Tianshan Mountains, China, both spatially and temporally. The magmatic rocks were formed during the period from the middle to the late Permian with isotopic ages of 248-268 Ma. The 87Sr/86Sr initial ratios of the rocks are low in a narrow variation range (-0.7050). The 143Nd/144Nd initial ratios are high (-0.51240) with positive εND(t) values (+1.28-+4.92). In the εNd(t)-(87Sr/86Sr)i diagram they fall in the first quadrant. The association of the shoshonitic and adakitic rocks can be interpreted by a two-stage model: the shoshonitic volcanic rocks were formed through long-term fractional crystallization of underplated basaltic magma, while the following partial melting of the residual phases formed the adakitic rocks. 相似文献
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Quartz diorites represent the earliest (ca. 540 Ma) and most primitive plutonic rocks in the Pan African Damara belt and they pre-date the main phase of high-T regional metamorphism. Two suites of synorogenic quartz diorites are unusual among Damaran intrusive rocks in their elemental and isotopic features. Comparison of the diorite compositions with melts from amphibolite-dehydration melting experiments points to a garnet-bearing meta-tholeiite, probably enriched in K2O, as a likely source rock. Partial melting processes generated mafic (ca. 50 wt% SiO2) quartz diorites in the deep crust at temperatures of between 1,000 and 1,100 °C, based on comparison with experimental results and similar temperature estimates based on P2O5 solubility in mafic rocks. Subsequently, the quartz diorites evolved by multistage, polybaric differentiation processes including fractional crystallization of mainly hornblende and plagioclase and assimilation of felsic basement gneisses. Although their chemical characteristics (high LILE, low HFSE) resemble those of other quartz diorites with calc-alkaline affinities, they differ in their enriched Sr (initial 87Sr/86Sr: 0.70943-0.71285), Nd (initial ) Nd: -9.1 to -15.2 ) and O ('18O: 6.8-8.1) isotope compositions. Neodymium model ages (TDM) that range from 1.7 to 2.2 Ga and large variation in 207Pb/204Pb relative to 206Pb/204Pb indicates involvement of ancient crustal material. Lead (206Pb/204Pb: 17.08-17.23, 207Pb/204Pb: 15.53-15.62, 208Pb/204Pb: 37.71-38.16) isotope compositions are strongly retarded, indicating that the source underwent a pre-Pan-African U/Pb fractionation and U depletion. It is proposed that the quartz diorites originated by synorogenic high temperature melting of mafic lower crust. This contrasts with previous suggestions favouring an origin of these rocks by melting of an enriched mantle during Pan-African times with characteristics modified by subduction of oceanic crust and sedimentary rocks. 相似文献
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Zircon dating, geochemical and Nd-Sr isotopic analyses have been determined for samples from two granitic intrusions in the Talate mining district, Chinese Altay. Our data suggest that these intrusions were emplaced from 462.5 Ma to 457.8 Ma. These rocks have strong affinity to peralumious S-type granite and are characterized by prominent negative Eu anomalies(δEu=0.20–0.35), strong depletion in Ba, Sr, P, Ti, Nb, Ta and positive anomalies in Rb, Th, U, K, La, Nd, Zr, Hf. Nd-Sr isotopic compositions of the whole rock show negative εNd(t) values(-1.21 to-0.08) and Mesoproterozoic Nd model ages(T2 DM=1.20–1.30 Ga). Their precursor magmas were likely derived from the partial dehydration melting of Mesoproterozoic mica-rich pelitic sources and mixed with minor mantle-derived components, under relatively low P(≤1 kbar) and high T(746–796°C) conditions. A ridge subduction model may account for the early Paleozoic geodynamic process with mantle-derived magmas caused by Ordovician ridge subduction and the opening of a slab window underplated and/or intraplated in the middle–upper crust, which triggered extensive partial melting of the shallow crust to generate diverse igneous rocks, and provided the heat for the crustal melting and juvenile materials for crustal growth. 相似文献
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Geochemistry, U-Pb Geochronology and Sr-Nd-Hf Isotopes of the Early Cretaceous Volcanic Rocks in the Northern Da Hinggan Mountains 总被引:1,自引:0,他引:1
Whole-rock geochemical, zircon U-Pb geochronological and Sr-Nd-Hf isotopic data are presented for the Early Cretaceous volcanic rocks from the northern Da Hinggan Mountains. The volcanic rocks generally display high SiO2(73.19–77.68 wt%) and Na2O+K2O(6.53–8.98 wt%) contents, with enrichment in Rb, Th, U, Pb and LREE, and depletion in Nb, Ta, P and Ti. Three rhyolite samples, one rhyolite porphyry sample, and one volcanic breccia sample yield weighted mean 206Pb/238 U ages of 135.1±1.2 Ma, 116.5±1.1 Ma, 121.9±1.0 Ma, 118.1±0.9 Ma and 116.9±1.4 Ma, respectively. All these rocks have moderate(87Sr/86Sr)i values of 0.704912 to 0.705896, slightly negative εNd(t) values of –1.4 to –0.1, and positive εHf(t) values of 3.7 to 8. Their zircon Hf and whole-rock Nd isotopic model ages range from 594 to 1024 Ma. These results suggest that the Early Cretaceous volcanic rocks were originated from melting of subducted oceanic crust and associated sediments during the closure of the Mongol-Okhotsk Ocean. 相似文献