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22.
河南内乡板厂矿床通过近年来的勘查工作,为一大型斑岩-热液型银铜铅锌(钼)矿床.本文对该矿床斑岩型铜矿石中钾长石进行了Ar-Ar定年,获得两个年龄坪:900～1150℃年龄坪包括了43.4%的39Ar,坪年龄为(148.1±1.6)Ma,反等时线年龄为(145.7±2.3)Ma;1200～1450℃年龄坪包括了48.8%的39Ar,坪年龄为(161.0±1.6)Ma,反等时线年龄(159.0±14.0)Ma.前者代表了该矿床的成矿年龄,后者代表了含矿斑岩的成岩年龄.该二阶段年龄谱特征反映了板厂矿床成岩成矿的阶段性.在我国不少矿区的Ar-Ar法年龄谱上均有多坪显示,这与我国许多矿区成矿作用和构造事件的多期多阶段特征一致. 相似文献
23.
西藏拉萨地体西北部革吉地区两期早白垩世岩浆作用——锆石U-Pb年龄、Hf同位素和地球化学特征 总被引：2，自引：1，他引：1
邦巴岩体位于拉萨地块西部革吉地区,由主体花岗岩、花岗闪长岩、闪长质包体及一系列近平行、南北向展布的花岗斑岩脉体组成。野外地质调查和LA-MC-ICP-MS锆石U-Pb定年表明,革吉地区白垩纪的两期岩浆活动分别发生在131~132Ma和127Ma。早期岩浆作用形成主体花岗岩、花岗闪长岩及闪长质包体,具有以下特征:(1)明显富集K、Cs等大离子亲石元素,亏损Nb、Ti、Zr等高场强元素;(2)具有明显的负Eu异常(Eu/Eu*=0.49~0.61)及负Ce异常;(3)具负εHf(t)值(-3.2~-0.3)及古老的地壳模式年龄(1.210~1.399Ga);(4)初始Sr同位素比值为0.70424~0.71472,εHf(t)值为-5.70~-5.54。晚期岩浆作用形成花岗斑岩脉体,具有以下特征:(1)富集K、Cs等大离子亲石元素,强烈亏损Nb、Ta、Ti等高场强元素;(2)基本不具有负Eu异常或具有轻微的负Eu异常(Eu/Eu*=0.74~0.87);(3)具有更老的Hf同位素地壳模式年龄(1.226~1.576Ga)及更负的大范围变化的εHf(t)值(-6.1~-0.7)。晚期岩浆作用锆饱和温度(777~796℃)及轻稀土元素不饱和温度(794~812℃)均高于早期岩浆的锆饱和温度(661~762℃)及轻稀土元素不饱和温度(750~769℃)。上述特征表明,两期岩浆作用均为中拉萨地块古老基底部分与地幔物质混染部分熔融的产物,随着岩浆作用的持续进行,岩浆中的古老地壳组分增加,熔体温度也增加,可能与南向俯冲的班公-怒江洋壳回转驱动的地幔岩浆活动向北迁移有关。 相似文献
24.
西藏青草山斑岩铜金矿含矿斑岩锆石U-Pb年代学、微量元素地球化学及地质意义 总被引：5，自引：0，他引：5
西藏青草山斑岩铜金矿是班公湖-怒江缝合带北侧、羌塘地块南缘新发现的具有超大型远景的斑岩型铜金矿床。本文首次对青草山含矿花岗岩闪长斑岩的锆石进行了 LA-ICPMS U-Pb年代学和微量元素地球化学研究,通过对含矿斑岩中锆石的13个点的U-Pb定年,得出锆石206Pb/238U加权平均年龄为114.60±1.20Ma (MSWD=1.07),此年龄与同样分布于该带上的多不杂斑岩铜矿含矿斑岩成岩年龄、波龙斑岩铜矿成矿年龄基本一致。应用锆石Ti温度计,计算出含矿斑岩中绝大部分锆石的结晶温度小于700℃,如此低的结晶温度指示含矿斑岩岩浆来源于水近饱和条件下发生的部分熔融。通过对锆石微量元素的详细研究,得出青草山含矿斑岩形成于活动大陆边缘的陆缘弧环境,这与前人研究得出的多不杂斑岩铜矿的形成构造背景一致。相近的成岩成矿年龄和一致的形成构造背景揭示以多不杂、青草山、波龙斑岩铜(金)矿床为主要组成的班公湖-怒江斑岩铜矿带的客观存在。依据青草山斑岩铜金矿和多不杂斑岩铜矿的含矿斑岩和同期火山岩的地球化学特征,并结合已有弧环境斑岩铜矿的经典成矿模型,本文提出班公湖-怒江斑岩铜矿带形成的动力学机制,即在早白垩世,班公湖-怒江洋壳向北俯冲,大洋板片向下俯冲到一定深度时,发生大规模脱水作用,释放的流体交代上覆地幔楔,诱发其部分熔融,产生的富含成矿物质的岩浆向上运移,在浅部地壳发育成与成矿相关的岩浆房,部分岩浆上升直接喷出地表,形成下白垩统美日切错组火山岩,部分浅成-超浅成侵位成斑岩体及斑岩型矿床,随着岩浆的多点多期次侵位,最终形成班公湖-怒江斑岩铜矿带。 相似文献
25.
Intracrystal microtextures formed by a process of mutual replacement in alkali feldspars record fluid–rock reactions that
have affected large volumes of the Earth’s crust. Regular, ≤1 μm-scale ‘strain-controlled’ perthitic microtextures coarsen,
by up to 103, by a dissolution–reprecipitation process, producing microporous patch or vein perthites on scales >100 μm. We have developed
earlier studies of such reactions in alkali feldspar cm-scale primocrysts in layered syenites from the Klokken intrusion,
South Greenland. We present new hyperspectral CL, SEM images, and laser ICPMS analytical data, and discuss the mechanism of
such replacement reactions. The feldspars grew as homogeneous sodic sanidines which unmixed and ordered by volume diffusion
during cooling into the microcline field at ~450°C, giving regular, fully coherent ‘braid’ cryptoperthite. At ≤450°C the crystals
reacted with a circulating post-magmatic aqueous fluid. The braid perthite behaved as a single reactant ‘phase’ which was
replaced by two product phases, incoherent subgrains of low albite and microcline, with micropores at their boundaries. The
driving force for the reactions was coherency strain energy, which was greater than the surface energy in the subgrain mosaic.
The external euhedral crystal shapes and bulk major element composition of the primocrysts were unchanged but they became
largely pseudomorphs composed of subgrains usually with the ‘pericline’ and ‘adularia’ habits (dominant {110} and subordinate
{010} morphology) characteristic of low T growth. The subgrains have an epitactic relationship with parent braid perthite. Individual subgrains show oscillatory zoning
in CL intensity, mainly at blue wavelengths, which correlates with tetrahedral Ti. Regular zoning is sometimes truncated by
irregular, discordant surfaces suggesting dissolution, followed by resumption of growth giving regular zoning. Zones can be
traced through touching subgrains, of both albite and microcline, for distances up to ~500 μm. At ≤340°C, the microcline subgrains
underwent a third stage of unmixing to give straight lamellar film perthites with periodicities of ~1 μm, which with further
cooling became semicoherent by the development of spaced misfit dislocations. Sub-grain growth occurred in fluid films that
advanced through the elastically strained braid perthite crystals, which dissolved irreversibly. Braid perthite was more soluble
than the strain-free subgrain mosaics which precipitated from the supersaturated solution. Some volumes of braid texture have
sharp surfaces that suggest rapid dissolution along planes with low surface energies. Others have complex, diffuse boundaries
that indicate a phase of coherent lamellar straightening by volume diffusion in response to strain relief close to a slowly
advancing interface. Nucleation of strain-free subgrains was the overall rate-limiting step. To minimise surface energy subgrains
grew with low energy morphologies and coarsened by grain growth, in fluid films whose trace element load (reflected in the
oscillatory zoning) was dictated by the competitive advance of subgrains over a range of a few tens of mm. The cross-cutting
dissolution surfaces suggest influxes of fresh fluid. Removal of feldspar to give 2 vol% porosity would require a feldspar:fluid
ratio of ~1:26 (by wt). The late reversion to strain-controlled exsolution in microcline subgrains is consistent with loss
of fluid above 340°C following depressurization of the intrusion. A second paper (Part II) describes trace element partitioning
between the albite and microcline subgrains, and discusses the potential of trace elements as a low-T geothermometer.
This paper and the Part II are dedicated in memory of J.V. Smith and W.L. Brown, both of whom died in 2007, in acknowledgement
of their unrivalled contributions to the study of the feldspar minerals over more than half a century. 相似文献
26.
RESIDUAL POST-IR IRSL SIGNALS OF POTASSIUM FELDSPAR FROM MODERN SAG POND DEPOSITS OF CENTRAL ALTYN TAGH FAULT: IMPLICATION FOR DATING YOUNG PALEOSEISMIC EVENTS 
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下载免费PDF全文 The Altyn Tagh Fault(ATF)is one of the most prominent active strike-slip faults in the India-Eurasia collision. Fresh features of surface ruptures, which are attributed to seismic events taking place in the last millennium, are identified at several sites along the Che'erchen River to Qingshui River section on the central part of ATF. Accurate chronology of these earthquake events would help understand the spatial-temporal relationship of the recent earthquakes. However, great difficulties are encountered. The central ATF is located in the arid area, and the vegetation cover is so limited that rare organic materials appropriate for radiocarbon dating can be found in the sediments. Luminescence dating technique may serve as an alternative to directly determine the burial ages of the earthquake related sediments. The optically stimulated luminescence(OSL)signal of quartz, which has been widely employed for luminescence dating, displays unwanted charateristics for accurate dating. Firstly, the quartz OSL signal is not sensitive to irradiation, which leads to low signal-to-noise ratio or even no measurable quartz OSL signal. Secondly, the targeted samples of the last millennium are very young, and the radiation dose received during the burial is expected to be less than 3~4Gy, which futher deteriorates the signal-to-noise ratio of the quartz OSL signal. Therefore, quartz OSL signal is not appropriate for dating the sediments relevant to the recent earthquakes on ATF.
The infrared stimulated luminescence(IRSL)signal of potassium feldspar is an alternative, and it is in usual an order of maginitude more sensitive to raidation than the quartz OSL signal. The enhanced signal-to-noise ratio makes it applicable to young samples. The post-IR IRSL signal has been successfully applied to date the sediments beyond the Holocene, however, the relatively slow bleaching of the post-IR IRSL signal poses challenges on applying it to young sediments, especially for the sediments deposited during the last millennium. In this study, we investigated the feasibility of using post-IR IRSL signal from potassium feldspar to date the earthquake events of the last millennium by employing modern sag pond deposits with different sorting and expected equivalent dose(De)of 0Gy. Choosing an appropriate measurement procedure and identifying the well bleached pottassium feldspar grains are essential for post-IR IRSL dating of young sediments. The non-fading characteristic of the post-IR IRSL170 signal measured at 170℃ following a prior IR stimulation at 110℃ was verified by employing the De plateau test with respect to the signal integration interval and IR stimulation temperature together. Reducing the amount of potassium feldspar grains mounted on an aliquot would help reveal the among grains variation of bleaching level of post-IR IRSL170 signal before depostion and identify the most sufficiently bleached grains. Therefore, the post-IR IRSL170 De values of 2mm aliquots were measured for three samples with different sedimentary textures. The median of De distribution of well sorted and stratified sag pond deposits is consistent with the minimum De value inferred from the minimum age model(MAM-3) and finite mixture model(FMM), while for the poorly sorted deposits, the median is significantly overestimated compared with the minimum De values from the MAM-3 and the FMM. The minimum De values of 0.6~0.8Gy of all three samples are consistent with the unbleachable residual dose previously reported for post-IR IRSL signals measured at similar temperature for well bleached samples. It implies that by combined use of small aliquot and statistical age models, the well-bleached potassium feldspar grains could be identified. Such an intrinsic unbleachable component needs to be properly corrected when earthquake events of last millennium are to be dated in this area. Otherwise, the post-IR IRSL170 age would be overestimated by 200~300a.
The post-IR IRSL170 procedure investigated in this study is not only applicable for dating the paleoearthquake events along the Altyn Tagh Fault, but also with great potential to be applied to other tectonically active area. With consideration of the potential variability in post-IR IRSL signal characteristics of potassium feldspar grains from different origins, the signal stability needs to be routinely inspected. The modern analog sample would also be informative for justifying the measurement procedure and analytical method employed. 相似文献
The infrared stimulated luminescence(IRSL)signal of potassium feldspar is an alternative, and it is in usual an order of maginitude more sensitive to raidation than the quartz OSL signal. The enhanced signal-to-noise ratio makes it applicable to young samples. The post-IR IRSL signal has been successfully applied to date the sediments beyond the Holocene, however, the relatively slow bleaching of the post-IR IRSL signal poses challenges on applying it to young sediments, especially for the sediments deposited during the last millennium. In this study, we investigated the feasibility of using post-IR IRSL signal from potassium feldspar to date the earthquake events of the last millennium by employing modern sag pond deposits with different sorting and expected equivalent dose(De)of 0Gy. Choosing an appropriate measurement procedure and identifying the well bleached pottassium feldspar grains are essential for post-IR IRSL dating of young sediments. The non-fading characteristic of the post-IR IRSL170 signal measured at 170℃ following a prior IR stimulation at 110℃ was verified by employing the De plateau test with respect to the signal integration interval and IR stimulation temperature together. Reducing the amount of potassium feldspar grains mounted on an aliquot would help reveal the among grains variation of bleaching level of post-IR IRSL170 signal before depostion and identify the most sufficiently bleached grains. Therefore, the post-IR IRSL170 De values of 2mm aliquots were measured for three samples with different sedimentary textures. The median of De distribution of well sorted and stratified sag pond deposits is consistent with the minimum De value inferred from the minimum age model(MAM-3) and finite mixture model(FMM), while for the poorly sorted deposits, the median is significantly overestimated compared with the minimum De values from the MAM-3 and the FMM. The minimum De values of 0.6~0.8Gy of all three samples are consistent with the unbleachable residual dose previously reported for post-IR IRSL signals measured at similar temperature for well bleached samples. It implies that by combined use of small aliquot and statistical age models, the well-bleached potassium feldspar grains could be identified. Such an intrinsic unbleachable component needs to be properly corrected when earthquake events of last millennium are to be dated in this area. Otherwise, the post-IR IRSL170 age would be overestimated by 200~300a.
The post-IR IRSL170 procedure investigated in this study is not only applicable for dating the paleoearthquake events along the Altyn Tagh Fault, but also with great potential to be applied to other tectonically active area. With consideration of the potential variability in post-IR IRSL signal characteristics of potassium feldspar grains from different origins, the signal stability needs to be routinely inspected. The modern analog sample would also be informative for justifying the measurement procedure and analytical method employed. 相似文献
27.
青藏高原东南缘是研究构造、地貌演化和气候变化相互作用的理想场所，前人研究主要揭示了晚始新世—早中新世和晚中新世以来的快速剥蚀事件，缺乏晚白垩世—早新生代时期地貌演化过程的研究。次林错花岗岩已有的低温热年代学数据覆盖了整个新生代时期，为探索该区域新生代早期的剥露演化历史提供了重要资料。该岩体新生代早期冷却事件是岩浆冷却单一作用的结果，还是受快速剥蚀作用的影响，目前仍然存疑，需要定量研究。因此，本文结合已有的岩石地化和年代学数据，对次林错花岗岩开展了锆石饱和温度和一维岩浆冷却模拟研究。锆石饱和温度计算结果表明次林错花岗岩的岩浆结晶温度介于647~705℃之间，属低温花岗岩。一维岩浆冷却模拟结果显示岩体侵位时的最小围岩温度为160~120℃，对应深度约为3. 7~5. 0 km。结合锆石和磷灰石(U- Th)/He年代学数据，本文认为该岩体在晚白垩世—早新生代时期(67~40 Ma)经历了一期剥蚀量至少为2 km的快速剥蚀事件。已发表成果的综合分析表明，此次快速剥露事件可能是整个青藏高原地区广泛存在的构造剥蚀事件，新特提斯洋的俯冲闭合与印亚板块的初始碰撞可能是触发此次大规模区域剥蚀的主要原因 相似文献
28.
29.
采用电子探针显微分析(EMPA)和粉末X射线衍射(XRD)分析了采自乌拉山金矿床含金钾长石石英脉、石英脉以及其他类型岩石中的10 0多个钾长石样品的化学成分和结果状态,并采用R和Q模式聚类分析、Spearman等级相关分析方法对实验数据进行了统计分析。结果表明,含金矿脉、岩浆热液脉和蚀变花岗岩中的钾长石为中等到最大微斜长石,其特征为K2 O含量高,但相对而言,Na2 O、CaO和BaO的含量低。其他岩石类型中的钾长石的化学成分和结果状态变化很大,可以从透长石、正长石到微斜长石,其特征为K2 O的含量相对较低,但Na2 O、CaO和BaO的含量相对较高。含金样品中的钾长石通常更富K2 O ,表明金的成矿作用与富钾的热液流体和碱质交代作用有关。乌拉山金矿床的成矿作用分为两个阶段,主要的含金钾长石石英脉中的钾长石富K2 O ,形成温度为30 7～379℃,平均为35 3℃;第二阶段含金石英脉中的钾长石含K2 O较低,形成温度为2 6 0～318℃,平均为2 81℃。这些结果表明成矿流体与岩浆热液作用有关,流体朝温度降低、K2 O含量降低的方向演化,K2 O含量高的热液流体和2 6 0～380℃的形成温度有利于金的成矿作用。 相似文献
30.
Thermodynamic conditions of framework grain dissolution of clastic rocks and its application in Kela 2 gas field 总被引：2，自引：2，他引：2
LAI Xingyun YU Bingsong CHEN Junyuan CHEN Xiaolin LIU Jianqing MEI Mingxiang JING Weiguang & CHENG Suhua School of Earth Sciences Mineral Resources China University of Geosciences Beijing China Key Laboratory of Lithospheric Tectonics Deep-level Process Exploration of Ministry of Education Beijing China 《中国科学D辑(英文版)》2005,48(1):21-31
Feldspar and clastic debris are the most important constituent framework grains of sedimentary clastic rocks and their chemical dissolution plays an essential role in the formation and evolution of the secondary pore in the reservoir rocks. On the basis of thermodynamic phase equilibrium, this study investigates the chemical equilibrium relationships between fluid and various plagioclase and K-feldspar in diagenesis of the sediments, particularly, the impact of temperature and fluid compositions (pH, activity of K+, Na+, Ca2+ and so on) on precipitation and dissolution equilibria of feldspars. Feldspar is extremely easily dissolved in the acid pore water with a low salinity when temperature decreases. The dissolution of anorthite end-member of plagioclase is related to the Ca content of the mineral and the fluid, higher Ca either in the mineral or in the fluid, easier dissolution of the feldspar. Moreover, the dissolution of albite end-member of plagioclase is related to Na of both the mineral and fluid, 相似文献