首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Four overbank profiles from the three terraces of different age were sampled in 10 to 20 cm intervals for the bulk content of major and minor (Ca, Mg, Fe, Ti, Al, Na, K and P) and trace (Mo, Cu, Pb, Zn, Ni, Co, Mn, As, U, Th, Sr, Cd, Sb, V, La, Cr, Ba, W, Zr, Ce, Sn, Y, Nb, Ta, Sc, Li, Rb and Hf) elements in the minus 0.125 mm fraction. Univariate statistics together with analysis of variance discriminated between the lower-lying carbonate (CA) population dominantly composed of carbonates and the overlying silicate (SI) population being dominantly of silicate mineralogy. This stratified pattern resulted from the intensive erosive action of melting glaciers exerted on limestones and dolomites in the alpine region, followed by local inputs mainly of silicate composition. Elements exhibiting the greatest between-population variability are Ca and Mg being enriched in the CA population and Fe, Mn, P, Sr, Al, Na, K, Li, Rb, Y, Zr, Ni, Cr and Ti being enriched in the SI population. Anomalously high Hg, Pb and Ba concentrations (maximum values: 6,500±2,860 ppb, 225±13 ppm and 1,519±91 ppm, respectively) in the lowermost part of the profile S7, which is nearest to the Croatian-Slovenian border, derive from the mineralized Slovenian catchment area. This profile also contains trimodal frequency distributions of Fe, Mn and P whose highest concentrations coincide with increased values of Zn and Cu which are bimodally distributed. Geochemical patterns of majority of elements in all four profiles consistently reflect the average compositions of the upstream drainage basins.  相似文献   

2.
The Rb-Sr and U-Pb systematics are studied in carbonate deposits of the Satka and Suran formations corresponding to middle horizons of the Lower Riphean Burzyan Group in the Taratash and Yamantau anticlinoria, respectively, the southern Urals. The least altered rock samples retaining the 87Sr/86Sr ratio of sedimentation basin have been selected for analysis using the original method of leaching the secondary carbonate phases and based on strict geochemical criteria of the retentivity (Mn/Sr < 0.2, Fe/Sr < 5 and Mg/Ca < 0.024). The stepwise dissolution in 0.5 N HBr has been used to enrich samples in the primary carbonate phase before the Pb-Pb dating. Three (L-4 to L-6) of seven consecutive carbonate fractions obtained by the step-wise leaching are most enriched in the primary carbonate (in terms of the U-Pb systematics). In the 206Pb/204Pb-207Pb/204Pb diagram, data points of these fractions plot along an isochron determining age of 1550 ± 30 Ma (MSWD = 0.7) for the upper member of the Satka Formation. The initial 87Sr/86Sr ratio in the least altered limestones of this formation is within the range of 0.70460–0.70480. Generalization of the Sr isotopic data published for the Riphean carbonates from different continents showed that 1650–1350 Ma ago the 87Sr/86Sr ratio in the world ocean was low, slightly ranging from 0.70456 to 0.70494 and suggesting the prevalent impact of mantle flux.  相似文献   

3.
Frequent sampling during an annual cycle of dissolved(<0.45 m) and suspended (>0.45 m) elementshas been conducted in the Kafue River at Raglan'sFarm, upstream from the mining activities within theCopperbelt Province, Zambia. Additional sampling ofsediment and interstitial pore water was conductedduring low water discharge. The presence of carbonateswithin the drainage basin naturally gives rise to highelement concentrations in the dissolved phase(Ca = 626, Mg = 494, Na = 360 and K = 24 mmol l-1).During the rainy season the relative composition ofthe dissolved elements indicated a wash out ofaccumulated weathering products and mineralisedorganic material from the unsaturated zone of the soilprofile. High concentrations of dissolved Al, Fe andMn were measured during high water discharge. At lowwater discharge the sediment was a major source of Fe,Mn and associated Co and Cu to the water column.Enhanced concentrations of dissolved and suspended S,Co and Cu during the rainy season indicated thatatmospheric deposited particles from the mining areawere washed out into the river. Autochthonousformation of particles rich in Si indicated diatomproduction during low water discharge.  相似文献   

4.
Fifteen new K–Ar ages in the range of 79–31 Ma are partially confirmed by three 40Ar/39Ar plateaus and isochron data of 64.9±0.4, 55.5±0.1 and 52.8±0.6 Ma. The new geochronological data reveal a much more detailed picture of the subduction imprint in the Hurd Peninsula. Using cutting relationships, the dyke emplacement history is divided into four episodes. The Late Cretaceous–Paleocene dykes in the range of 80–60 Ma are related to the main magmatism in Livingston Island and most likely reflect the final stages of subduction of the proto-Pacific oceanic crust. The Early Eocene dykes (56–52 Ma) fill the gap in volcanic activity 70–50 Ma ago. They are the only magmatic event manifested at this time in the region. The 45–42 Ma dykes may be related to the intrusion of the Barnard Point tonalite. Three samples of Oligocene age appear to represent the last igneous activities on the Hurd Peninsula prior to the opening of the Bransfield Strait.  相似文献   

5.
Supergene Mn-oxide deposits are widely distributed in Guangxi, Guangdong, Yunnan, and Hunan Provinces, South China, accounting for 18% of the total Mn reserves in the country. Direct dating of supergene Mn enrichment, however, is lacking. In this paper, we present high-resolution 40Ar/39Ar ages of Mn oxides from the Xinrong Mn deposit, western Guangdong, to place numerical constraints on the timing and duration of supergene Mn enrichment. A total of ten cryptomelane samples, spanning a vertical extent of 67 m, were dated using the 40Ar/39Ar laser incremental heating technique, with seven samples yielding well-defined plateau or pseudo-plateau ages ranging from 23.48 ± 0.91 to 2.06 ± 0.05 Ma (2σ). One sample yields a staircase spectrum that does not reach a plateau; the spectrum, however, indicates the presence of two or more generations of Mn oxides in the sample, whose ages are best estimated at 22.34 ± 0.31 and 10.2 ± 0.86 Ma, respectively. The remaining two samples gave meaningless or uninterpretable results due to significant 39Ar recoil and contamination by old phases. The 40Ar/39Ar data thus reveal a protracted history of weathering and supergene Mn enrichment that started at least in the end of the Oligocene or beginning of Miocene and extending into the latest Pliocene. Staircase-apparent age spectra, resulting from banded or botryoidal samples, yield an average growth rate of Mn oxides at 0.6–0.7 × 10−3 mm kyr−1. The values indicate that a 1-mm grain of Mn oxides may host minerals precipitated during a time span of ca. 1.5 m.y., and accumulation of Mn oxides to form economic deposits under weathering environments may take millions of years. The distribution of weathering ages shows that the oldest Mn oxides occur on the top of the profile, whereas the youngest minerals are found at the bottom, suggesting downward propagation of weathering fronts. However, two samples located at the intermediate depths of the profile yield ages comparable with those occurring at the highest elevations. Such a complexity of age distribution is interpreted in terms of preferential penetration of Mn-rich weathering solutions along more permeable fault zones, or as a result of multi stages of dissolution and re-precipitation of Mn oxides. A synthesis of geochronological and geological data suggests that formation of the Xinrong deposit was a consequence of a combination of favorable lithological, climatic, and structural conditions. Because the climatic and structural conditions are similar among the provinces of South China during the Cenozoic, the geochronological results obtained at Xinrong may also have implications for the timing of supergene Mn enrichment throughout South China.  相似文献   

6.
柴北缘锡铁山榴辉岩退变质成因角闪石40Ar/39Ar年代学研究   总被引：2，自引：2，他引：0  
采用激光阶段加热40Ar/39Ar技术,对柴达木盆地北缘锡铁山榴辉岩退变质作用形成的榴闪岩和斜长角闪岩之角闪石进行了定年分析。09NQ44Amp来自榴闪岩,各阶段表观年龄(以现代空气氩40Ar/36Ar比值295.5扣除非放射性成因40Ar)构成了单调下降的阶梯状年龄谱。在反等时线图解上,2~4阶段数据点和5~18阶段数据点分别构成了两条等时线,等时年龄分别为427.6±10Ma和425.1±2.6Ma,对应的初始40Ar/36Ar比值则分别为435.2±6.1和705.3±13。角闪石09NQ43Amp来自榴辉岩强烈退变质作用形成的斜长角闪岩,40Ar/39Ar阶段加热分析也获得单调下降的年龄谱,在反等时线图解上其数据点3~6阶段和7~16阶段分别构成了两条等时线,等时年龄分别为418.9±2.9Ma和418.1±2.1Ma,对应的初始40Ar/36Ar比值则分别为493.7±2.8和685.8±34.3。等时线截距值高于现代大气40Ar/36Ar比值,表明角闪石中含过剩40Ar。同时,由低温和中-高温阶段加热数据点分别构成两条等时年龄基本一致,截距值却明显不同的等时线,表明在角闪石热力学性质不同的源区,存在两期明显不同且未混合的初始捕获Ar组分。等时年龄425~418Ma代表的是锡铁山榴辉岩角闪岩相退变质作用发生的时间。等时线图解法虽然有效的校正了角闪石中的过剩40Ar,但仅根据表观年龄图谱和等时线图谱还无法清晰判断过剩40Ar在角闪石中的赋存状态,有待进一步探讨。  相似文献   

7.
新疆东准噶尔贝勒库都克锡矿带锡成矿的40Ar-39Ar年龄   总被引：2，自引：2，他引：0  
位于新疆东准噶尔的贝勒库都克锡矿带是我国北方地区首次发现具独立锡矿床的锡成矿带。该成矿带自东向西发育萨惹什克、贝勒库都克、干梁子、卡姆斯特4个独立锡矿床。它们在主要矿石类型、脉石矿物组成上表现为两类。萨惹什克锡矿属于石英型,占优势的脉石矿物是石英,其次有长石,而白云母很不发育。其它3个锡矿则以云英岩型为特征,主要脉石矿物是石英和长石,次要矿物有白云母。本文报道了我们对发育白云母的卡姆斯特、干梁子、贝勒库都克锡矿床开展矿石40Ar-39Ar同位素定年的结果。3件与锡石平衡共生的白云母有很平坦的年龄谱,其40Ar/36Ar-39Ar/36Ar正等时线年龄与各自的坪年龄很一致,年龄值范围是305~315Ma。这些结果和我们已报道的萨惹什克锡矿的Re-Os等时线年龄一起,确定了全部4个锡矿床的成矿年龄,并证实它们构成一个锡成矿带。此外,锡矿石与花岗岩围岩年龄的一致性表明了研究区锡成矿与花岗岩浆作用间很可能存在成因关系。  相似文献   

8.
Four K-feldspar samples from the Yidun Arc, eastern Tibetan Plateau, were analysed by the 40Ar/39Ar method with the aim of recovering information on their thermal history using multiple diffusion domain (MDD) theory. Arrhenius plots for each of the samples reveal low retentivity early in the heating experiments, a property that is attributed to their recrystallised nature. This low argon retentivity appears to violate the MDD assumption that volume diffusion is the only mechanism for argon transport within the crystals, thus the thermal histories derived from these analyses are considered suspect. Nevertheless, the age spectra themselves suggest that the majority of samples had cooled below 200 °C prior to the Eocene collision of India with Asia. Thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the Cenozoic in samples from the high elevation, low relief areas of the Yidun Arc, while samples from the major Jinsha River valley show rapid cooling through the partial annealing zone beginning in the Miocene. These results suggest that significant Cenozoic denudation has been localised and that most parts of the Yidun Arc have experienced very little denudation during the Cenozoic.  相似文献   

9.
刘驰  穆治国 《地质科学》1995,30(4):329-337
在利用脉冲显微激光探针40Ar/39Ar定年技术测定标准样品的J值和年龄适用范围的基础上,研究了黑龙江省嫩江县北部多宝山斑岩铜矿区水热成因矿物的年代学。结果表明,高钾含量的水热蚀变矿物适合于激光探针的表面微区测定,并且可以克服水热蚀变矿物中的39Ar “反冲”丢失对年龄结果的影响。矿区的岩浆-水热事件主要有两期,分别为253-220Ma和184-162Ma,前者代表了成矿时代,后者反映出由成矿期后岩浆活动所引起的水热叠加事件。  相似文献   

10.
D.R. Gray  D.A. Foster   《Tectonophysics》2004,385(1-4):181-210
Structural thickening of the Torlesse accretionary wedge via juxtaposition of arc-derived greywackes (Caples Terrane) and quartzo-feldspathic greywackes (Torlesse Terrane) at 120 Ma formed a belt of schist (Otago Schist) with distinct mica fabrics defining (i) schistosity, (ii) transposition layering and (iii) crenulation cleavage. Thirty-five 40Ar/39Ar step-heating experiments on these micas and whole rock micaceous fabrics from the Otago Schist have shown that the main metamorphism and deformation occurred between 160 and 140 Ma (recorded in the low grade flanks) through 120 Ma (shear zone deformation). This was followed either by very gradual cooling or no cooling until about 110 Ma, with some form of extensional (tectonic) exhumation and cooling of the high-grade metamorphic core between 109 and 100 Ma. Major shear zones separating the low-grade and high-grade parts of the schist define regions of separate and distinct apparent age groupings that underwent different thermo-tectonic histories. Apparent ages on the low-grade north flank (hanging wall to the Hyde-Macraes and Rise and Shine Shear Zones) range from 145 to 159 Ma (n=8), whereas on the low-grade south flank (hanging wall to the Remarkables Shear Zone or Caples Terrane) range from 144 to 156 Ma (n=5). Most of these samples show complex age spectra caused by mixing between radiogenic argon released from neocrystalline metamorphic mica and lesser detrital mica. Several of the hanging wall samples with ages of 144–147 Ma show no evidence for detrital contamination in thin section or in the form of the age spectra. Apparent ages from the high-grade metamorphic core (garnet–biotite–albite zone) range from 131 to 106 Ma (n=13) with a strong grouping 113–109 Ma (n=7) in the immediate footwall to the major Remarkables Shear Zone. Most of the age spectra from within the core of the schist belt yield complex age spectra that we interpret to be the result of prolonged residence within the argon partial retention interval for white mica (430–330 °C). Samples with apparent ages of about 110–109 Ma tend to give concordant plateaux suggesting more rapid cooling. The youngest and most disturbed age spectra come from within the ‘Alpine chlorite overprint’ zone where samples with strong development of crenulation cleavage gave ages 85–107 and 101 Ma, due to partial resetting during retrogression. The bounding Remarkables Shear zone shows resetting effects due to dynamic recrystallization with apparent ages of 127–122 Ma, whereas overprinting shear zones within the core of the schist show apparent ages of 112–109 and 106 Ma. These data when linked with extensional exhumation of high-grade rocks in other parts of New Zealand indicate that the East Gondwana margin underwent significant extension in the 110–90 Ma period.  相似文献   

11.
Cosmogenic nuclide concentrations measured on abandoned fan surfaces along the Mojave section of the San Andreas Fault suggest that sediment is generated, transported, and removed from the fans on the order of 30-40 kyr. We measured in situ produced cosmogenic 10Be, and in some cases 26Al, in boulders (n = 15), surface sediment (n = 15), and one depth profile (n = 9). Nuclide concentrations in surface sediments and boulders underestimate fan ages, suggesting that 10Be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages.Field observations, grain-size distribution, and cosmogenic nuclide data suggest that over time, boulders weather into grus and the bar sediments diffuse into the adjacent swales. As fans grow older the relief between bars and swales decreases, the sediment transport rate from bars to swales decreases, and the surface processes that erode the fan become uniform over the entire fan surface. The nuclide data therefore suggest that, over time, the difference in 10Be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized, resulting in a common surface lowering rate and common 10Be concentrations across the fan. During this phase, the entire fan is lowered homogeneously at a rate of 10-15 mm kyr−1.  相似文献   

12.
新华铅锌(银)矿床位于钦杭成矿带南端云开地区的六万大山隆起区,是以铅锌为主的含银热液脉型多金属矿床。矿体赋存在含堇青石黑云母花岗岩中,主要呈脉状和透镜状产出。文章利用激光阶段加热技术对与矿化密切共生的白云母进行Ar-Ar年龄测定。结果表明,新华铅锌(银)多金属矿床的~(40)Ar/~(39)Ar坪年龄为(165.3±1.6)Ma(MSWD=0.38),反等时线年龄为(165.2±1.6)Ma(MSWD=0.42),等时线年龄和坪年龄一致,代表了白云母的冷却年龄和矿床的形成年龄,表明该矿床的形成与云开地区燕山早期的岩浆活动有关,这与区域成矿事件相吻合。结合前人对华南地区地球动力学背景的研究成果,初步认为新华铅锌(银)矿床形成于中-晚侏罗世碰撞板块边缘再次活化,岩石圈伸展的构造背景。  相似文献   

13.
Rhyolitic pumices in the 26.5 ka Oruanui eruption (Taupo volcano, New Zealand) contain an average of 10 wt% crystals. About 2 wt% of the crystal population is feldspar crystals that display bluish–grey cloudy cores, the colour being imparted by exsolved needles of rutile. The volume of cloudy-cored feldspars thus amounts to ~1.0 km3 in a total magma volume of ~530 km3. The cored feldspars show great variability in detail, but in general have a rounded cloudy core bounded by a zone rich in glass and mineral inclusions, that was then overgrown by a euhedral clear rim. Sr-isotopic variations in eight representative crystals were measured on micromilled samples of selected growth zones in the cores and rims, and linked to feldspar compositions through microprobe traverses. The cloudy cores range from 87Sr/86Sr = 0.70547 to 0.70657, with compositions of An43 to An78. The overgrowth rims display wider variations: inner parts show extreme ranges in composition (maxima 87Sr/86Sr = 0.70764 and An78), while outer parts in seven of eight crystals are zoned, with outward-decreasing Sr-isotopic and An values to figures that are in accord with the bulk pumice and other, clear-feldspar values, respectively. The three parts of the crystals represent distinct regimes. The cloudy cores are inherited from an intermediate plutonic protolith that has been subjected to melting. The inner overgrowth rims were crystallised from a high temperature, relatively radiogenic melt derived from Mesozoic-Palaeozoic metasedimentary rocks (“greywacke”). The outer euhedral rims reflect mixing into and continued growth within the growing Oruanui magma body. The cloudy-cored feldspars also contain rare zircon inclusions. Twenty one zircons were recovered by HF digestion of a bulk sample of cloudy feldspars and analysed by SHRIMP for U–Th isotopes with which to calculate model ages. Eighteen of 21 crystals returned finite ages, the model-age spectrum of which is similar to the age spectra from free zircons in Oruanui pumices. Assembly of the Oruanui magma body was not only rapid (over ~40 kyr, as shown by other data) but involved a wide open system, with significant contributions from partly-melted intermediate-composition igneous intrusions (cloudy cores) and greywacke melts (inner overgrowths) being introduced into the magma body up to the point of eruption. Such open system behaviour contrasts with that proposed in models for comparably voluminous silicic magmas derived dominantly by fractionation (such as the Bishop Tuff) where the magma and its crystal cargo were better insulated thermally and chemically from country-rock interaction.  相似文献   

14.
The Precambrian/Cambrian (PC/C) boundary is one of the most important intervals for the evolution of life. However, the scarcity of well-preserved outcrops across the boundary leaves an obstacle in decoding surface environmental changes and patterns of biological evolution.In south China, strata through the PC/C boundary are almost continuously exposed and contain many fossils, suitable for study of environmental and biological change across the PC/C boundary. We undertook deep drilling at four sites in the Three Gorges area to obtain continuous and fresh samples without surface alteration and oxidation. 87Sr/86Sr ratios of the fresh carbonate rocks, selected based on microscopic observation and geochemical signatures of Mn/Sr and Rb/Sr ratios, aluminum and silica contents, and δ13C and δ18O values, were measured with multiple collector-inductively coupled plasma–mass spectrometric techniques.The chemostratigraphy of 87Sr/86Sr ratios of the drilled samples displays a smooth curve and a large positive anomaly just below the PC/C boundary between the upper part of Baimatuo Member of the Dengying Formation and the lower part of the Yanjiahe Formation. The combination of chemostratigraphies of δ13C and 87Sr/86Sr indicates that the 87Sr/86Sr excursions preceded the δ13C negative excursion, and suggests that global regression or formation of the Gondwana supercontinent, possibly together with a high atmospheric pCO2, caused biological depression.  相似文献   

15.
高锰酸盐指数(CODMn)、硝酸根(NO-3)、铵根(NH+4)是判断水体是否受到三氮污染的重要指标。对于测定这三个指标的水样保存方式和时间,地质行业标准和国内外主要国家标准间存在明显差异。地质行业标准规定地下水样品原水室温保存,CODMn和NH+4在3天内测定;NO-3在20天内测定;国家标准和美国标准推荐样品硫酸酸化,避光或冷藏保存,在2~7天内完成CODMn和NO-3和1~7天内完成NH+4测试。为了分析各类标准在样品保存要求上的差异对检测结果的影响,确保检测数据能真实地反映水体污染状况,找寻简便的保存方式,本文在广州地区采集地下水,按照地质行业标准与国家标准进行处理和保存,并在不同时间段对三个指标进行测试。分析验证结果表明:地质行业标准与国家和美国标准关于水样的保存方法均非常可靠。地质行业标准主要针对静态地下水,保存方法相对宽松;国家标准和美国标准适用范围除了地下水,还包括动态的地表水和废水,采样对象成分更为复杂,更不稳定,更容易受外界影响发生变化,故保存条件高于地质标准。在广州地区,采用原水室温避光保存水样,CODMn、NH+4保存时间可为5天,NO-3保存时间可为30天;采用酸化水室温保存水样,CODMn、NO-3和NH+4保存时间可长达30天。这两种方式均比地质行业标准和国家标准推荐的有效时间长,且原水和酸化水室温保存方式相对于冷藏保存方式更为方便。本文提出,如果采集的水样能方便、快速送达实验室,可采用原水保存;如果不能在短时间内送达实验室检测,可采用硫酸酸化保存。  相似文献   

16.
东昆仑祁漫塔格地区白干湖钨锡矿田是认识中国西北地区钨锡矿床成矿规律的重要窗口。作者对采自含矿石英脉的2个白云母样品进行40Ar/39Ar定年,获得其坪年龄分别为(422.7±4.5)Ma和(421.8±2.7)Ma。2个样品的等时线年龄与反等时线年龄也在误差范围内一致,分别为(424±15)Ma和(418±24)Ma,表明分析数据可信。获得的白云母40Ar/39Ar坪年龄指示成矿作用发生在晚志留世,与原特提斯洋闭合事件密切相关,闭合后的陆陆碰撞使富含成矿物质的变质沉积物重熔而形成花岗岩浆;花岗岩浆侵入并析出含矿热液,导致钨锡成矿。  相似文献   

17.
Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb2+, Ce3+ and Mn2+, respectively, as activators. The Pb2+ excitation band is observed at 243 nm, and the Ce3+ excitation band at 295 nm. The Pb2+ excitation band is also observed by monitoring the Ce3+ fluorescence, and the Pb2+ and Ce3+ excitation bands, in addition to six Mn2+ excitation bands, are also observed by monitoring the Mn2+ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb2+ → Ce3+, (2) Pb2+ → Mn2+, (3) Ce3+ → Mn2+ and (4) Pb2+ → Ce3+ → Mn2+.  相似文献   

18.
The 40Ar/39Ar dating technique is based on the knowledge of the age of neutron fluence monitors (standards). Recent investigations have improved the accuracy and precision of the ages of most of the Phanerozoic-aged standards (e.g. Fish Canyon Tuff sanidine (FCs), Alder Creek sanidine, GA1550 biotite and LP-6 biotite); however, no specific study has been undertaken on the older standards (i.e. Hb3gr hornblende and NL-25 hornblende) generally used to date Precambrian, high Ca/K, and/or meteoritic rocks.In this study, we show that Hb3gr hornblende is relatively homogenous in age, composition (Ca/K) and atmospheric contamination at the single grain level. The mean standard deviation of the 40Ar?/39ArK (F-value) derived from this study is 0.49%, comparable to the most homogeneous standards. The intercalibration factor (which allows direct comparison between standards) between Hb3gr and FCs is RFCsHb3gr = 51.945 ± 0.167. Using an age of 28.02 Ma for FCs, the age of Hb3gr derived from the R-value is 1073.6 ± 5.3 Ma (1σ; internal error only) and ± 8.8 Ma (including all sources of error). This age is indistinguishable within uncertainty from the K/Ar age previously reported at 1072 ± 11 Ma [Turner G., Huneke, J.C., Podosek, F.A., Wasserburg, G.J., 1971. 40Ar-39Ar ages and cosmic ray exposure ages of Apollo 14 samples. Earth Planet. Sci. Lett. 12, 19-35].The R-value determined in this study can also be used to intercalibrate FCs if we consider the K/Ar date of 1072 Ma as a reference age for Hb3gr. We derive an age of 27.95 ± 0.19 Ma (1σ; internal error only) for FCs which is in agreement with the previous determinations. Altogether, this shows that Hb3gr is a suitable standard for 40Ar/39Ar geochronology.  相似文献   

19.
林木森  彭松柏  乔卫涛 《岩石学报》2017,33(10):3137-3146
腾冲芒棒地区广泛发育新近纪以来的火山岩,本文首次对该区粗面安山岩进行的高精度40Ar/39Ar同位素定年,其坪年龄分别为2.1±0.1Ma和2.0±0.1Ma,代表其喷溢时代为早更新世。岩石地球化学特征研究显示,粗面安山岩属高钾钙碱性系列,富集大离子亲石元素、亏损高场强元素,具有弧火山岩与大陆板内火山岩的双重属性,推测其形成于后造山环境。综合研究表明,腾冲地块更新世火山岩的形成与印度-欧亚板块俯冲-碰撞造山隆升后的伸展垮塌、富集地幔部分熔融作用密切相关,而印支陆块向东南逃逸以及腾冲弧形走滑断裂带(龙川江断裂带、大盈江断裂带)的活化促使了该期火山岩的喷发与侵位。  相似文献   

20.
曹四夭斑岩钼矿床位于内蒙古兴和县,是华北克拉通北缘最大的钼矿床。该矿床中部发育斑岩型钼矿体,外围和上部产出热液脉型铅锌金矿体。文章选取1件与斑岩钼矿化共生的绢云母样品进行了40Ar-39Ar定年,获得40Ar-39Ar坪年龄为(144.4±1.2)Ma,相应的39Ar/36Ar-40Ar/39Ar等时线年龄为(146.4±2.2)Ma(MSWD=0.31),将等时线年龄认作绢云母的Ar封闭年龄,表明曹四夭斑岩钼矿化发生在约146 Ma前。选取14件脉型铅锌矿石中的闪锌矿、黄铁矿和磁黄铁矿样品开展了Rb-Sr定年,获得4件闪锌矿的Rb-Sr等时线年龄为(145.1±3.0)Ma(MSWD=0.63);5件黄铁矿的Rb-Sr等时线年龄为(145.2±1.3)Ma(MSWD=0.53);4件闪锌矿、5件黄铁矿和1件磁黄铁矿的Rb-Sr等时线年龄为(145.3±1.0)Ma(MSWD=0.43)。硫化物Rb-Sr定年结果表明曹四夭矿床脉型铅锌矿化形成于约145 Ma前。本次绢云母40Ar-39Ar和硫化物Rb-Sr定年结果表明,曹四夭矿床斑岩型钼矿化和脉型铅锌金矿化为同期产物,两者均形成于晚侏罗世末期,属于同一个斑岩成矿系统。曹四夭矿床硫化物的w(Rb)和w(Sr)分别为0.1867×10~(-6)~1.305×10~(-6)和0.3175×10~(-6)~6.935×10~(-6),Sr同位素初始比值(87Sr/86Sr)i介于0.709 919~0.711 951之间,平均值0.710 952,结合前人获得的辉钼矿Re含量,认为曹四夭矿床的成矿物质主要来源于地壳。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号