共查询到20条相似文献，搜索用时 125 毫秒
1.
2.
闪锌矿铷-锶同位素等时线讨论 总被引：3，自引：0，他引：3
通过对闪锌矿铷-锶同位素等时线形成机制的讨论,若为同源、同期、待测同位素封闭的体系,因混合形成的直线为等时线具有定年意义,但若非同源、非同期或非封闭的体系亦可因混合形成直线,但该直线为无年代学意义的混合线.作为铷-锶同位素定年矿物,闪锌矿可能仪充当"容器"的角色,因此利用闪锌矿进行定年时,必须进行细致的物相研究.闪锌矿中的碳酸盐、硅酸盐等矿物微粒可能对铷-锶定年产生极大的影响,如不能对其进行成因鉴别或配合其他同化素定年方法加以系统研究,闪锌矿铷-锶法直线拟合结果很难反映成矿时间. 相似文献
3.
河北寿王坟铜矿黄铜矿铷锶同位素年龄测定及其成矿意义 总被引：9，自引：3，他引：6
本文以黄铜矿及其共生矿物为定年对象,采用亚样品取样和铷锶等时线定年方法测定了寿王坟铜矿的成矿时代.分析测试获得黄铜矿 黄铁矿单矿物组合的等时线年龄113.6Ma,黄铜矿 夕卡岩组合的等时线年龄112.3Ma和黄铜矿 黄铁矿 夕卡岩组合的等时线年龄115.0Ma.对比同一矿石亚样品,认为河北寿王坟夕卡岩型铜矿成矿时代为111.0Ma.实验表明,采用矿石亚样品取样方法和直接测定金属硫化物单矿物铷-锶同位素年龄可以有效地确定矿床成矿时代. 相似文献
4.
5.
6.
本文讨论了在沉积过程中伊利石的铷锶地球化学行为,论证了1md和1m型伊利石在沉积过程和成岩阶段初期是可以与其环境介质达到锶同位素平衡的,不同粒径的伊利石具有不同的铷含量。通过从地质作用的机理上考虑锶同位素均一和铷元素分异的两种地球化学过程,建立了一种新的沉积岩定年方法——伊利石Rb-Sr粒级等时线定年模式。另外,本文还将该定年模式应用到豫西前寒武纪未变质的沉积岩地层上,获得了与地质事实十分吻合的结果。 相似文献
7.
用铷—锶等时线法测定沉积岩的年龄,许多研究者已做了大量工作,取得了很大成绩。但也还存在不少问题,值得我们进一步讨论。我就某些问题谈一点自己的看法。 一、从理论上讲,用铷—锶全岩等时线法可以测定沉积来源物质的年龄,沉积时间,成岩以及变质作用的时间。沉积岩中通常含有大量他生或碎屑矿物。细粒的碎屑沉积岩,如粉砂岩,页岩以及粘土类岩石,它们的Rb_(87)/Sr_(86)和Sr_(87)/Sr_(86)比值可以构成等时线。 相似文献
8.
岩石或矿物中铷和锶的含量可以用X射线荧光光谱、原子吸收光谱、光学发射光谱、质谱、中子活化分析等分析方法进行测定。Flanagan(1976)统计了用各种分析方法测定8个USGS岩石标准样品中铷锶含量的平均值,结果表明,X射线荧光光谱的分析结果,其准确度和精密度虽不及质谱同位素稀释法,但高于光学发射光谱和原子吸收光谱分析法。1976年美国地质调查局(USGS)发行了8个新的岩石标准样品(Flanagan,1976),它们是玄武岩BHVO-1、海洋泥质岩MAG-1、石英安粗岩QLO-1、流纹岩RGM-1、页岩 相似文献
9.
10.
利用RbSr衰变系列对结晶岩进行地质年龄测定是一种广泛应用且十分成功的同位素测年技术[1]。而风化作用往往使岩石和矿物的铷锶含量及同位素比值发生变化,无法再进行RbSr同位素计年。但许多风化岩石的87Sr86Sr与87Rb86Sr之间仍存在类似等时线的线性相关关系,有时甚至形成一条非常理想的“RbSr等时线”[1]。迄今为止,仍少有研究仔细探讨这种“等时线”的具体形成机制,明确其实际意义。本文以江西南部黑云母花岗岩、花岗斑岩和片岩风化壳为例,通过对风化过程中主要矿物、铷锶含量及同位素变化规律的研究,探讨风化条件下RbSr假等时线的具体成因和意义。研究显示 相似文献
11.
应用云母Rb Sr等时线法对大别山高级变质岩的后期改造历史进行了初步的探讨。采用重液变温技术将云母按比重的区别 ,分成若干组分 ,然后用常规的Rb Sr方法测定。应用这种技术对大别山黄土岭太古代麻粒岩相岩石中的黑云母和产于超高压变质带内的石马含石榴石片麻岩的白云母进行了Rb Sr等时线年龄测定。黄土岭太古代麻粒岩相片麻岩中的黑云母 全岩Rb Sr等时线年龄为 12 7± 9Ma ,与该区片麻岩中的角闪石的K Ar和Ar Ar年龄 ,及燕山期花岗岩的Rb Sr年龄一致 ,说明这一太古代下地壳岩石受到了燕山期深熔 岩浆事件的影响 ;大别山东南部石马含石榴石片麻岩 (榴辉岩相 )中的白云母Rb Sr等时线年龄为 191± 10Ma ,反映了印支 早燕山期区域性低级变质事件的时代。研究表明 ,大别山区的不同构造单元中产出的不同类型的高级变质岩自中生代以来有不同的后期演化历史。 相似文献
12.
《International Geology Review》2012,54(7):883-889
Distribution of the specific gravity of oil and the yield of fractions up to 300° is considered as a function of hypsometric position of the samples with respect to the pool outline. Relationship is determined between the difference in specific gravity of edge- and crest oils and the carbon dioxide ion content in edgewaters; it is explained by oxidation of oil by the waters. It is demonstrated by means of graphs for Ekhabi and Tungor oil fields that oxidation is more important than the force of gravity, in the distribution of the properties of oil throughout the deposit. The flushing effect of waters on the light petroleum fractions proves to be less significant that the oxidation effect. Calculation shows that the loss of oil by oxidation is small at depths below 600 m; losses by water flushing are even smaller, but rise rapidly at shallower depths. -- Author. 相似文献
13.
花岗岩锆石U-Pb年龄与全岩Rb-Sr等时线年龄对比研究及其地球化学意义 总被引：5，自引：0，他引：5
对国内外32个花岗岩体的锆石U-Pb年龄与全岩Rb-Sr等时线年龄之间差值（Δt）进行的频数统计分析表明：Δt呈对称正态分布（偏度系数CSK=0.36；峰度系数CKU=2.99）；年龄差（Δt）既呈正值又有负值，其均值为2.08Ma；相对年龄差（Rt）小于5%。采用最小二乘法计算，花岗岩体锆石U-Pb年龄（tZr）对全岩Rb-Sr等时线年龄（tRb）拟合出相关系数很高（r=0.998），回归系数接近l（α=1.003）的线性回归方程（tRb =1.003tZr +1.258）。这些统计特征表明，从总体来看，花岗岩体的Rb-Sr等时线定年测定结果与锆石U-Pb定年测定结果是一致的，花岗岩全岩Rb-Sr等时线定年方法是成熟、可信的，同时也为花岗岩锆石U-Pb年龄代表结晶年龄而不代表花岗岩侵位年龄提供了依据。 相似文献
14.
Rb-sr dating of epithermal vein mineralization stages in the eastern Harz Mountains (Germany) by paleomixing lines 总被引：1，自引：0，他引：1
A method is evaluated that enables the dating of binary isotopic paleomixing in hydrothermal alteration assemblages by iterative reconstruction and regression of corresponding two-component mixing lines from conventional Rb-Sr data. The model has been applied to illite-bearing granulometric fractions of hydrothermally altered sedimentary rocks associated with epithermal vein mineralization in the eastern Harz Mountains, Germany. These veins are characterized by a principal quartz-sulfide stage containing quartz, base metal sulfides, and siderite and a subsequent dominant calcite-fluorite-quartz stage. Rb-Sr analyses were performed on untreated granulometric fractions, HCl-treated residues, corresponding HCl leachates, and cogenetic vein minerals obtained from two silicified rock samples related to the quartz-sulfide and the calcite-fluorite-quartz mineralization, respectively.Neither the untreated nor the HCl-leached fractions of these rock samples yield statistically robust and geochronologically meaningful isochrons. When applying the binary mixing model, however, two well-defined paleomixing lines can be reconstructed for the HCl-treated fractions of the rock samples and associated vein minerals at model ages of 226 ± 1 Ma (quartz-sulfide alteration) and 209 ± 2 Ma (calcite-fluorite-quartz alteration). We examine the significance and reliability of these model ages and the corresponding paleomixing lines by means of statistical and geological criteria and discuss the effects of leaching experiments performed on the granulometric fractions using 1 N HCl as well as the nature and origin of the components dissolved in the acid leachates.Our results suggest that the mixing model provides a successful dating concept for isotopic disequilibrium processes during low-temperature hydrothermal events that produce binary mixtures among newly formed alteration phases. 相似文献
15.
M. Yuhara T. Miyazaki J. Ishioka S. Suzuki H. Kagami N. Tsuchiya 《Gondwana Research》2002,5(4):771-779
Rb-Sr and Sm-Nd isotopic studies were carried out for metamorphic rocks in the Namaqualand Metamorphic Complex, South Africa. The metamorphic rocks give the Rb-Sr mineral isochron ages (whole-rock - biotite - felsic fractions) of 844±85 Ma and 811.6±6.6 Ma for the lower granulite zone and of 776.5±5.4 Ma for the upper granulite zone. The rocks yield the Sm-Nd mineral isochron ages of 1071±18 Ma (whole-rock - garnet - felsic fractions) and 1067±158 Ma (whole-rock - hornblende - biotite rich fraction - felsic fractions) for the lower granulite zone and of 1052.0±3.6 Ma and 1002.5±1.4 Ma (whole-rock - garnet - felsic fractions) for the upper granulite zone. These age data suggest that the granulite facies metamorphism took place at 1060-1000 Ma, and that the rocks cooled down at 850-780 Ma. The Sr and Nd isotopic compositions of metamorphic rocks are different between the lower and upper granulite zones. 相似文献
16.
S. S. Rathore A. R. Vijan M. P. Singh B. N. Prabhu Anand Sahu 《Journal of Earth System Science》2004,113(1):27-36
Precambrian granitic basement rocks obtained from well BH-36 of Bombay High Field, western offshore of India has been studied
both by Rb-Sr and K-Ar dating methods. Seven basement samples chosen from two cores have yielded whole rock Rb-Sr isochron
age of 1446 ± 67 Ma with an initial87Sr/86Sr ratio of 0.7062 ± 0.0012. This age has been interpreted as the formation/emplacement time of the granite. Two biotite fractions
of different grain size separated from a sample CC6B2T have yielded Rb-Sr mineral isochron age of 1385 ± 21 Ma. However, these
fractions when studied by K-Ar dating method have yielded slightly higher but mutually consistent ages of 1458 ± 43 Ma and
1465 ± 43 Ma, respectively.
Further, two biotites separated from additional samples CC5B9T and CC6B3B have yielded K-Ar ages of 1452 ± 42 Ma and 1425
± 40 Ma with an overall mean age of 1438 ± 19 Ma. This mean K-Ar age is indistinguishable from whole rock Rb-Sr isochron as
well as mineral isochron age within experimental error. The similarity in the whole rock and biotite ages obtained by different
isotopic methods suggests that no thermal disturbance has occurred in these rocks after their emplacement/formation around
1450 Ma ago. The present study provides the evidence for the existence of an important Middle Proterozoic magmatic event around
1400-1450 Ma on the western offshore of India which, hitherto, was thought to be mainly confined to the eastern Ghats, Satpura
and Delhi fold belt of India. This finding may have an important bearing on the reconstruction of Proterozoic crustal evolution
of western Indian shield. 相似文献
17.
The performance of float-sink coal cleaning devices customarily is characterized by a distribution curve, in which the percent of feed reporting to clean coal is plotted against specific gravity. For a given vessel and a given feed a family of distribution curves can be obtained, each having its own specific gravity of separation.This paper presents a method for combining these distribution curves at different specific gravities of separation, for a given coal cleaning vessel and a given feed, into a single, generalized distribution curve which is independent of the specific gravity of separation. This curve can be expressed in tabular form or it can be represented mathematically by an exponential type equation, known as a Weibull function.A different generalized distribution curve will be obtained for each of several different size fractions. A method is presented for utilizing these curves with feeds which encompass a broad spectrum of sizes.The well-known concepts of error area and probable error are extended to the generalized distribution curve. It is shown that the conventional probable error, and — under certain conditions — the conventional error area, are directly proportional to the specific gravity of separation for a given vessel and a given feed size. 相似文献
18.
Multimethod analyses of several size fractions of clays were used to reconstruct the diagenetic history of the shallow buried claystones within the Paris Basin. A systematic decrease occurred in K-Ar dates relative to the decrease in size of the clay fractions, signifying higher amounts of newly formed clay material in the finer fractions. We suggest that the authigenic clay minerals occurring in the fine fractions had an Al-montmorillonite composition. By assuming that the isotopic K-Ar and Rb-Sr dates obtained on a bentonite layer in the sedimentary sequence stand for pure, authigenic clay minerals, one may interpret all K-Ar dates as mixtures of one authigenic and two detrital end-members. The results imply that a period of low sea level favoured diagenetic smectite-type clay formation about 10-15 million years after deposition of the sediments. Signatures of limited-scale chemical and isotopic homogenisation mean that the rock volumes affected by the diagenetic modifications had to be quite limited. The study of clay minerals extracted from some stylolites further suggests that any overpressure related to the origin of stylolites had no effect on clay authigenesis. 相似文献
19.
On the basis of U-Pb, Rb-Sr and K-Ar isotope analyses of Proterozoic rocks and minerals, a chronology has been established for the tectonic, intrusive and metamorphic evolution of the Svecokarelian orogeny 1750–1950 Ma ago in the Uppsala Region, Eastern Sweden. It is suggested that when synkinematic granitoids intruded the orogenic belt, at a stage of general subsidence and at medium metamorphic conditions (600°C and 3.5–4 kbar), the U-Pb isotope system in zircons closed earlier than the Rb-Sr whole-rock system. The zircon age (1886 Ma) reflects the intrusion and crystallization of the rock melt and the Rb-Sr whole-rock age (1830 Ma) the time when the temperature had decreased below the threshold for 87Sr migration. The Rb-Sr whole rock age (1898 Ma) determined for metaandesites and metadacites reflects a recrystallization related to the intrusion of the granitoids. On the contrary, the more silicic metarhyodacitic volcanic rocks have a Rb-Sr whole rock age (1830 Ma) reflecting the cessation of the synkinematic metamorphism. The difference in the way the Rb-Sr isotope system responds in subsilicic or silicic metavolcanics is probably dependent on the amount of radiogenic 87Sr and on the fixation of 87Sr in Ca-rich minerals. Subsequent, late-kinematic, low amphibolite facies metamorphism has not altered the Rb-Sr ages of the granitoids and the recrystallized metavolcanics. 相似文献
20.
The metamorphic sequence in the Nababeep district of Namaqualandis considered in terms of major recumbent folding accompaniedby hornblende granulite subfacies metamorphism. Rb-Sr isotopicdata are presented for thirty-one whole-rock samples of metamorphicrocks and associated intrusives, together with U-Pb isotopicdata for nineteen fractions of the constituent zircon and apatite.The metamorphic suite has yielded a Rb-Sr whole-rock isochronage of 1213?22 m.y., with an initial Sr87/Sr88 ratio (Ro) of0?7191?0?0021 suggesting reworking of pre-existing crustal rocks;data from certain distinctive rock-types indicate that Sr-isotopichomogenization was incomplete during this event. Cross-cuttinggranites and related rocks give a Rb-Sr isochron age of 1166?26m.y. (Ro, 0?708?0?001). These events were post-dated by theintrusion of largely dioritic bodies of the cupriferous NoritoidSuite; zircon recrystallization 1070 m.y. ago is interpretedas the age of emplacement of these bodies. On Sr-isotopic andchemical grounds, a source-bed model is tentatively suggestedfor the Noritoid Suite, involving derivation from gneisses andgranulites of intermediate-basic composition within the metamorphicsuccession. Isotopic events at 1000 and 900 m.y. ago, recordedby zircon and apatite, are believed to reflect the imprint ofregional pegmatite emplacement. 相似文献