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1.
大渡河金矿田是扬子地台西南缘一个重要的金成矿集中区.对其中自金台子和三雕两个金矿床含金石英脉的石英进行了40Ar/39Ar快中子活化法同位素年龄测试,获得坪年龄分别为25.4土0.2 Ma和24.7±0.3Ma,相应的等时线年龄分别为24.1±0.1 Ma和22.9士0.1 Ma,反等时线年龄分别为23.8士0.1 Ma和23.0±0.1Ma.这些年龄数据不仅有力地证明了大渡河金矿形成于喜马拉雅构造期,也为更好地认识扬子地台西南缘金矿形成的地质构造背景、矿床成因及成矿规律,进而指导区域找矿提供了依据. 相似文献
2.
云南东川播卡-拖布卡地区含金石英脉的^40Ar／^39Ar年龄及其地质意义 总被引：4，自引：0，他引：4
东川播卡-拖布卡地区金矿是云南中部"康滇地轴"中、新元古界昆阳群岩石中发现的第一个金矿,位于接近三江褶皱带的扬子地块西缘.原生金矿化为含金黄铁矿石英脉、细脉、网脉和浸染状石英黄铁矿.四个不同产状的典型含金石英脉的石英的阶段加热40Ar/39Ar年龄谱为马鞍形,坪年龄值范围为59.93±0.21～42.38±0.32 Ma,最小视年龄范围59.30±4.30～41.90±1.8 Ma,与计算坪年龄加热阶段相应数据的40Ar-39Ar等时线年龄范围59.34±0.17～41.25±0.10 Ma,三者基本一致.等时线年龄计算的相关系数大于0.998,40Ar/3 6Ar初始值范围为293.17±1.40～295.2±0.43,与尼尔值一致.石英形成后没有受到后期地质作用.石英样品的坪年龄没有受到过剩氩和氩丢失的影响,可以作为石英和金矿的年龄.金矿形成于新生代第三纪古新世和始新世初的陆内拉张地质构造环境中. 相似文献
3.
阿克塔斯金矿床位于新疆阿尔泰造山带南缘,矿体赋存于黑云母花岗岩与中泥盆统北塔山组中性火山岩接触带,矿石类型主要为石英脉型和蚀变岩型。矿区中酸性侵入岩体的岩石类型为二长花岗岩、黑云母花岗岩。近矿的黑云母花岗岩LA-ICP-MS锆石U-Pb年龄为(329.5±1.8)Ma,成岩时代为早石炭世;主成矿期的金-黄铁矿-石英细脉中的绢云母~(40)Ar/~(39)Ar坪年龄为(247.7±1.3) Ma、等时线年龄为(245.1±1.4)Ma,成矿时代为早三叠世。研究表明,阿克塔斯金矿成岩与成矿时代相距80 Ma,为碰撞造山和后碰撞造山不同地质作用的产物。该矿床具有造山型金矿的特点,额尔齐斯断裂带的右形剪切走滑作用控制金矿成矿过程。 相似文献
4.
图古日格金矿床是位于兴蒙造山带西端的一个大型金矿床, 矿床的矿石主要有石英脉型和蚀变岩型两种, 矿床的成矿年龄尚存在争议。本文对矿床蚀变岩型矿石中热液成矿阶段的绢云母进行了40Ar-39Ar同位素定年研究, 获得坪年龄为(258.9±1.6) Ma(MSWD=0.69), 等时线年龄为(259.2±2.9) Ma(MSWD=5.4), 与前人获得的黄铁矿Re-Os等时线年龄((268±15) Ma)在误差范围内完全一致。结合矿区地质事实及前人研究结果, 认为该矿床的成矿年龄可以限定在268~259 Ma。图古日格金矿床与矿区内的似斑状花岗岩(265 Ma)具有紧密的成因关系, 属于与花岗质岩浆活动有关的石英脉型金矿床。兴蒙造山带乃至整个中亚造山带, 可能在二叠纪时期发育有一次与伸展背景下花岗质岩浆活动有关的金成矿事件, 找矿潜力巨大。 相似文献
5.
砂宝斯金矿床是大兴安岭北部唯一一个大型岩金矿床。本文应用石英真空击碎和阶段加热40Ar/39Ar定年技术,首次获得了砂宝斯金矿床的成矿年龄。石英真空击碎40Ar/39Ar定年方法获得了石英脉中原生包裹体等时线年龄为130.1±1.3 Ma;石英粉末阶段加热40Ar/39Ar定年方法获得石英脉中钾长石微晶的等时线年龄为133.1±3.5 Ma。石英脉中原生包裹体和钾长石微晶的年龄较吻合,~130 Ma代表了含金石英脉的形成年龄。砂宝斯金矿床的成矿时代为早白垩世,形成于蒙古-鄂霍茨克造山带后碰撞阶段的挤压向伸展转换期。 相似文献
6.
安徽凤阳和张八岭地区含金石英脉的40Ar/39Ar年龄及其地质意义 总被引：3，自引：1，他引：3
用快中子活化法测定了安徽凤阳和张八岭地区朱顶、毛山和上成3个金矿床第一阶段晚期和第二阶段的含金石英脉,石英的阶段加热40Ar/39Ar坪年龄值域为(116.1±0.6～118.3±0.5)Ma,分别与其最小视年龄和等时线年龄接近.坪年龄、最小视年龄和等时线年龄3种年龄值域为(113.4±0.4～118.3±0.5)Ma,可以作为石英的形成年龄域. 根据含金石英脉和围岩的空间关系,该年龄值域作为石英脉金矿的形成年龄是合理可靠的.金矿床形成于早白垩世阿普特期,与此时郯庐断裂带略带右行走滑正断层活动一致. 相似文献
7.
西藏弄如日金矿是冈底斯成矿带发现的第一个浅成低温热液型金矿床。为确定金矿床的成矿时代,对该矿床与金矿化有关的蚀变花岗斑岩中绢云母进行了40Ar-39Ar年龄测试,获得绢云母的加权平均年龄和等时线年龄分别为19.87±0.96Ma和19.70±0.30Ma。结果表明,弄如日金矿床金矿化的主要成矿时代为中新世。该成果的获得对于进一步认识弄如日金矿成因机制、地球动力学背景以及区域找金突破具有重要意义。 相似文献
8.
河南桐柏围山城地区主要金银矿床的成矿年代学研究 总被引：2，自引：0，他引：2
河南省桐柏县围山城地区是秦岭-大别造山带上一个重要的金银矿集区,主要有破山大型银矿床、银洞坡大型金矿床和银洞岭大型银矿床.文章对围山城地区主要金银矿床内的蚀变矿物开展了40Ar/39Ar年代学研究,其中在破山银矿床内蚀变云斜煌岩的黑云母里获得的40Ar/39Ar坪年龄为(129.0±1.1)Ma,等时线年龄为(128.4±3.5)Ma(2σ),MSWD＝0.12,40Ar/36Ar初始比值为(304±84)(2σ);银洞坡金矿床含金石英脉中绢云母的40Ar/39Ar坪年龄为(373.8±3.2)Ma,等时线年龄为(373±13)Ma(2σ),MSWD＝0.073,40Ar/36Ar初始比值为(301±320)(2σ);银洞岭银矿床矿化蚀变岩中绢云母的40Ar/39Ar坪年龄为(377.4±2.6)Ma,等时线年龄为(377.8±5.7)Ma(2σ),MSWD＝0.70,40Ar/36Ar初始比值为(312±55)(2σ),这些年龄基本上代表了矿床的形成时代.研究结果表明,围山城地区主要金银矿床(包括银洞坡金矿床、银洞岭银矿床和破山银矿床)的形成与二郎坪弧后盆地闭合导致的碰撞与挤压变质作用有关,均属于造山型金银矿床.由于受后期梁湾岩体燕山期岩浆活动的影响,破山银矿床可能遭受了改造,故在矿区蚀变云斜煌岩的黑云母里记录下了这期较晚的成矿事件. 相似文献
9.
10.
安庆铜牛井热液脉型铜、钼、金矿床石英的^40Ar—^39Ar快中子活化年龄 总被引：6，自引：2，他引：6
长江中下游成矿带中安庆铜牛井热液(充填)脉型铜、钼、金矿床主成矿阶段的石英样品的40Ar-39Ar快中子活化法坪年龄为134.77±0.70Ma,对应的等时线年龄为130.92±0.76Ma,最小视年龄为133.10±1.87Ma,三个年龄值在误差范围内十分接近,以等时线年龄(130.92±0.76Ma)代表石英的形成年龄.铜牛井热液脉型矿床与同一矿田中夕卡岩型矿床的形成时代相近,成矿与岩浆作用密切相关,可能为一连续的过程. 相似文献
11.
Marvin A. Lanphere 《Quaternary Research》2000,53(3):294
K–Ar and 40Ar/39Ar ages have been measured on nine mafic volcanic rocks younger than 1 myr from the Snake River Plain (Idaho), Mount Adams (Washington), and Crater Lake (Oregon). The K–Ar ages were calculated from Ar measurements made by isotope dilution and K2O measurements by flame photometry. The 40Ar/39Ar ages are incremental-heating experiments using a low-blank resistance-heated furnace. The results indicate that high-quality ages can be measured on young, mafic volcanic rocks using either the K–Ar or the 40Ar/39Ar technique. The precision of an 40Ar/39Ar plateau age generally is better than the precision of a K–Ar age because the plateau age is calculated by pooling the ages of several gas increments. The precision of a plateau age generally is better than the precision of an isotope correlation (isochron) age for the same sample. For one sample the intercept of the isochron yielded an 40Ar/36Ar value significantly different from the atmospheric value of 295.5. Recalculation of increment ages using the isochron intercept for the composition of nonradiogenic Ar in the sample resulted in much better agreement of ages for this sample. The results of this study also indicate that, given suitable material and modern equipment, precise K–Ar and 40Ar/39Ar ages can be measured on volcanic rocks as young as the latest Pleistocene, and perhaps even the Holocene. 相似文献
12.
K.A. Foland Jeffrey S. Linder Thomas E. Laskowski Norman K. Grant 《Chemical Geology》1984,46(3):241-264
Nine glauconite samples with relatively high K concentrations and which appear to be well crystallized using normal X-ray diffraction techniques have been studied using the method. The glauconite apparent ages exceed their KAr, RbSr and, in most cases, stratigraphic ages by substantial amounts. release spectra sometimes yield plateaus but these apparent ages have no geological significance. The results indicate that 39Ar is lost by recoil from mineral grains during neutron irradiation, consistent with previously reported observations. The amount of 39Ar loss was measured by isotope dilution for four samples and varied from 29% to 17%. In contrast, radiogenic 40Ar is quantitatively retained during irradiation. The very fine blades which make up glauconite grains yield the mineral susceptible to large amounts of 39Ar loss and unsuitable for dating. 相似文献
13.
Ar同位素体系定年矿物的封闭温度范围广,并且可以获得650℃～150℃温度段的非线性冷却历史,因此~(40)Ar/~(39)Ar热年代学成为研究地质体热演化历史过程中最有效的工具之一。但是由于矿物中Ar同位素扩散机制还有一些问题没有清楚地被认识,因此在一定程度上制约了~(40)Ar/~(39)Ar热年代学的发展。本文介绍了目前应用最广泛的两种~(40)Ar/~(39)Ar热年代学模式:多重扩散域模式和多路径扩散模式,讨论了它们的发展现状、存在的问题、可能解决的方法以及今后的发展方向。 相似文献
14.
The mineral separate GA1550 biotite has become an international standard for K/Ar and 40Ar/39Ar dating studies, although it was prepared as an intralaboratory standard at ANU to monitor tracer depletion from a gas pipette. It is one of a small number of samples that has been calibrated against 38Ar tracers, some of which had been mixed with known amounts of atmospheric argon, so that a so-called primary calibration has been performed. By measuring GA1550 biotite against additional tracers from the same batch we have determined the radiogenic argon content of this sample as 1.342 (± 0.007) × 10? 9 mol/g, and together with the measured K content of 7.645 (± 0.050) weight percent, we derive a best estimate for the K/Ar age as 98.5 ± 0.5 Ma, where the error is derived from averaging the ages determined relative to the 38Ar tracer. 相似文献
15.
16.
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
17.
激光显微探针~(40)Ar/~(39)Ar同位素定年 总被引：10，自引：0，他引：10
已有 5 0年历史的K Ar定年法 ,由于过剩Ar和Ar丢失的普遍发现 ,使其最广泛的应用面临着严重挑战。40 Ar/ 3 9Ar分步加热释氩法是常规K Ar定年法的发展 ,它克服了常规K Ar定年法的一些局限 ,又可以测定岩浆构造热事件。激光显微探针40 Ar/ 3 9Ar定年法是在 2 0世纪末把聚焦激光束应用在40 Ar/ 3 9Ar分步加热释氩法中而发展起来的一种定年方法。它既具有常规K Ar定年法和40Ar/ 3 9Ar分步加热释氩法的所有优越性 ,又把定年引入微观领域。特别是在 2 0世纪的最后几年 ,以激光显微探针40 Ar/ 3 9Ar定年方法的完善和精度的提高为标志 ,把K Ar年代学研究推向了一个新的里程碑。微区微量高精度高分辨定年 ,把定年时限扩展到人类历史范畴 ,精细的分析技术拓宽了年代学的应用范围 ,使之解决的地质问题更广泛和深入 ,并且开始冲击着地球科学中的某些热点和难点课题。 相似文献
18.
The effects of deformation on radiogenic argon (40Ar∗) retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite. Cylindrical cores, ∼15 mm in length and 6.25 mm in diameter, were drilled from granite collected from the South Armorican Massif in northwestern France, loaded into gold capsules, and weld-sealed in the presence of excess water. The samples were deformed at a pressure of 10 kb and a temperature of 600 °C over a period 29 of hours within a solid medium assembly in a Griggs-type triaxial hydraulic deformation apparatus. Overall shortening in the experiments was approximately 10%. Transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking, cracking, and grain segmentation of the micas.Infrared (IR) laser (CO2) heating of individual 1.5-2.5 mm diameter grains of muscovite and biotite separated from the undeformed granite yield well-defined 40Ar/39Ar plateau ages of 311 ± 2 Ma (2σ). Identical experiments on single grains separated from the experimentally deformed granite yield results indicating 40Ar∗ loss of 0-35% in muscovite and 2-3% 40Ar∗ loss in biotite. Intragrain in situ ultraviolet (UV) laser ablation 40Ar/39Ar ages (±4-10%, 1σ) of deformed muscovites range from 309 ± 13 to 264 ± 7 Ma, consistent with 0-16% 40Ar∗ loss relative to the undeformed muscovite. The in situ UV laser ablation 40Ar/39Ar ages of deformed biotite vary from 301 to 217 Ma, consistent with up to 32% 40Ar∗ loss. No spatial correlation is observed between in situ40Ar/39Ar age and position within individual grains. Using available argon diffusion data for muscovite the observed 40Ar∗ loss in the experimentally treated muscovite can be utilized to predict average 40Ar∗ diffusion dimensions. Maximum 40Ar/39Ar ages obtained by UV laser ablation overlap those of the undeformed muscovite, indicating argon loss of <1% and an average effective grain radius for 40Ar∗ diffusion ?700 μm. The UV laser ablation and IR laser incremental 40Ar/39Ar ages indicating 40Ar∗ loss of 16% and 35%, respectively, are consistent with an average diffusion radius ?100 μm. These results support a hypothesis of grain-scale 40Ar∗ diffusion distances in undeformed mica and a heterogeneous mechanical reduction in the intragrain effective diffusion length scale for 40Ar∗ in deformed mica. Reduction in the effective diffusion length scale in naturally deformed samples occurs most probably through production of mesoscopic and submicroscopic defects such as, e.g., stacking faults. A network of interconnected defects, continuously forming and annealing during dynamic deformation likely plays an important role in controlling both 40Ar∗ retention and intragrain distribution in deformed mica. Intragrain 40Ar/39Ar ages, when combined with estimates of diffusion kinetics and distances, may provide a means of establishing thermochronological histories from individual micas. 相似文献
19.
新疆北部基性岩脉40Ar/39Ar年代学研究 总被引：8，自引：4，他引：4
晚古生代以来,新疆北部地区侵入了一系列的基性岩脉,成为了解该地区地壳生长过程的重要窗口.本文采用激光40Ar/39Ar年代学方法,对整个北疆地区出露的基性岩脉进行了精细年代学研究.从数据特征上分析.低本底激光加40Ar/39Ar方法能对低钾含量、极少量样品(0.1mg～5mg)进行精细定年,所以非常适合进行基性岩脉的精细定年.本文展示的基性岩脉激光40Ar/39Ar方法的高质量数据显示新疆北部基性岩脉群的活动时限跨越332～174Ma,为石炭纪-侏罗纪.由数据分析可以看出,新疆北部基性岩脉群在时间上,呈现脉动式侵位特征,在332～174Ma之间,有多达6～7次脉动式活动,时间间隔大致为20～30Ma.从基性岩脉所揭示的大地构造含义来分析,新疆北部地区从石炭纪到侏罗纪处在一个相似的地壳演化阶段.为一个陆壳垂向生长、区域构造应力场显示拉张的构造环境,并在时间、空间上具有相对统一的特征. 相似文献
20.
Steven M. Reddy Graham J. Potts Simon P. Kelley 《Contributions to Mineralogy and Petrology》2001,141(2):186-200
Detailed field and microstructural studies have been combined with high spatial resolution ultraviolet laser 40Ar/39Ar dating of naturally deformed K-feldspar to investigate the direct relationship between deformation-related microstructure and Ar isotope systematics. The sample studied is a ~1,000 Ma Torridonian arkose from Skye, Scotland, that contains detrital feldspars previously metamorphosed at amphibolite-facies conditions ~1,700 Ma. The sample was subsequently deformed ~430 Ma ago during Caledonian orogenesis. The form and distribution of deformation-induced microstructures within three different feldspar clasts has been mapped using atomic number contrast and orientation contrast imaging, at a range of scales, to identify intragrain variations in composition and lattice orientation. These variations have been related to thin section and regional structural data to provide a well-constrained deformation history for the feldspar clasts. One hundred and forty-three in-situ 40Ar/39Ar analyses measured using ultraviolet laser ablation record a range of apparent ages (317-1030 Ma). The K-feldspar showing the least strain records the greatest range of apparent ages from 420-1,030 Ma, with the oldest apparent ages being found close to the centre of the feldspar away from fractures and the detrital grain boundary. The most deformed K-feldspar yields the youngest apparent ages (317-453 Ma) but there is no spatial relationship between apparent age and the detrital grain boundary. Within this feldspar, the oldest apparent ages are recorded from orientation domain boundaries and fracture surfaces where an excess or trapped 40Ar component resides. Orientation contrast images at a similar scale to the Ar analyses illustrate a significant deformation-related microstructural difference between the feldspars and we conclude that deformation plays a significant role in controlling Ar systematics of feldspars at both the inter- and intragrain scales even at relatively low 'bulk' strains. The data show that Ar loss and trapping within the deformed K-feldspars reflects the presence of a deformation-induced population of small diffusion domains in combination with 'short-circuit' diffusion along deformation-induced defects. The complex history of microstructures induced in the K-feldspars during their cooling, alteration, erosion and sedimentation do not appear to be as significant as deformation-induced microstructures in controlling the distribution of apparent ages at the grain scale. 相似文献