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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
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新疆铁木尔特铅锌铜矿床锆石U-Pb和黑云母40Ar/39Ar年代学及其矿床成因意义 总被引：4，自引：4，他引：0
新疆铁木尔特铅锌铜矿床位于阿尔泰造山带南缘克兰盆地内,矿体呈脉状产于康布铁堡组火山岩地层中.为准确厘定其成岩成矿时代,作者分别对矿区赋矿火山岩和含矿石英脉中的云母进行了年龄测定,获得2件火山岩样品的锆石LA-ICP-MS U-Pb年龄分别为396±5Ma和405±5Ma,2件黑云母样品的40 Ar/39 Ar坪年龄分别为240±2Ma和235±2Ma,相应的39Ar/36Ar-40Ar/36Ar等时线年龄分别为238±3Ma和233±3Ma,与坪年龄在误差范围内一致.据此,认为矿区内康布铁堡组火山岩形成于396～405 Ma,成矿作用发生于235～240Ma;成岩年龄早于成矿年龄约165Ma.因此,铁木尔特铅锌铜矿为典型的后生矿床,而不可能是同生VMS型矿床.考虑到成矿年龄稍晚于区域大规模变质作用(约250Ma),推测成矿作用与阿尔泰造山带碰撞造山作用有关.结合矿床地质特征和流体包裹体特征,认为铁木尔特铅锌铜矿为典型的陆陆碰撞体制下形成的造山型矿床. 相似文献
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江西冷水坑斑岩型铅锌银矿床地质特征、热液蚀变与成矿时限 总被引：14，自引：1，他引：13
江西冷水坑铅锌银矿床是我国重要的铅锌银矿床之一,也是世界上少有的斑岩型铅锌银矿床.冷水坑斑岩型铅锌银矿床位于中国东部中生代月凤山火山盆地边缘,含矿斑岩为燕山中期碱性花岗斑岩,侵位于上侏罗统火山岩地层内,斑岩体边部发育大量的隐爆角砾岩.矿区发育两种矿化类型,即斑岩型矿化与层状改造型矿化,此两种均与碱性花岗斑岩有关.矿化以Pb、Zn、Ag为主,伴生少量的Cu、Au.斑岩型的铅锌银矿化发生在斑岩体内以及接触带中,具有面型矿化特点并显示出明显的矿化分带性.层状改造型以铁锰银铅锌矿化为主,矿体均为隐伏状分布于碱性花岗斑岩附近的火山岩含铁锰地层中,产状与火山岩地层一致.铁锰碳酸盐铅锌银矿体在靠近斑岩体时,银铅锌矿化相应逐渐增强,而远离花岗斑岩体,矿化明显较弱.围岩蚀变作用明显,主要为绢云母化、绿泥石化、碳酸盐化、硅化和黄铁矿化.矿化蚀变特征、蚀变类型与典型的斑岩型铜(钼)矿床不同,缺少斑岩铜(钼)矿床早期蚀变的钾交代作用(黑云母化与钾长石化),发育大量铁锰碳酸盐蚀变.矿田矿化蚀变具有一定的分带性,由岩体内向外蚀变可以分为三个带:绿泥石绢云母化带、绢云母化碳酸盐化硅化黄铁矿化带和碳酸盐化绢云母化带.斑岩型矿床的铅锌银矿化与绢云母化和绿泥石化蚀变密切相关.通过对蚀变矿物绢云母的~(40)Ar/~(39)Ar同位素测定,获得冷水坑斑岩型铅锌银矿化年龄为162.8 ±1.6Ma,与含矿斑岩形成时间一致,说明冷水坑斑岩型铅锌银成矿作用发生于中国东部燕山中期陆内环境. 相似文献
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湖南芙蓉锡矿床40Ar/39Ar 同位素年龄及地质意义 总被引：28，自引：3，他引：28
文章以金云母、角闪石和白云母为测试对象,利用40Ar/39Ar同位素定年的方法,精确厘定了芙蓉超大型锡矿床的形成时间。研究结果表明,白腊水矿区3个金云母样品的40Ar/39Ar坪年龄分别为(150.6±1.0)Ma、(157.3±1.0)Ma和(154.7±1.1)Ma;热液成因角闪石的坪年龄为(156.9±1.1)Ma。淘锡窝矿区云英岩中2个白云母样品的40Ar/39Ar坪年龄为(159.9±0.5)Ma和(154.8±0.6)Ma;因此芙蓉矿床的形成时间为151～160Ma,这与骑田岭主体花岗岩的侵入时间(151～162Ma)相吻合。湘南地区的柿竹园超大型W-Sn-Mo-Bi-F矿床、新田岭大型W矿床、瑶岗仙W矿床和黄沙坪Pb-Zn多金属矿床的形成时间亦集中在150～160Ma之间,因此,湘南有色金属矿化集中区可能主要集中在150～160Ma发生成矿,这种大规模成矿作用可能与中生代华南岩石圈的拉张、伸展作用密切相关。 相似文献
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吉松脉状铅锌多金属矿位于特提斯喜马拉雅东段中部,是该带内新近发现的铅锌矿床。吉松铅锌矿矿脉产于数条北东向断裂之中,以石英-方解石-硫化物脉形式充填断裂破碎带。本文采用Ar-Ar同位素年代学方法对石英-硫化物脉中的绢云母进行了测试分析,在760～860℃温度区间获得绢云母的坪年龄为(16.61±0.30)Ma,对应的等时线年龄为(16.64±0.30)Ma。两组年龄在误差范围内相等,能够代表绢云母的形成时间。该Ar-Ar年龄指示了吉松铅锌矿形成于17 Ma左右。特提斯喜马拉雅成矿带在主碰撞成矿阶段发育一期金(银)矿化事件(59～49 Ma),而以吉松为代表的铅锌矿化事件则集中于后碰撞阶段(21～12 Ma)。由于吉松铅锌矿与错那洞淡色花岗岩体密切的时空关系,结合二者相似的铅同位素关系,暗示错那洞淡色花岗岩为吉松铅锌成矿提供了物源和热驱动力。 相似文献
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近年来,南秦岭镇安西部地区发现了棋盘沟、核桃坪、东阳等大中型钨多金属矿床。其中棋盘沟大型钨矿床以石英脉型为主,深部可见矽卡岩型矿化,前人仅对其中的石英脉型钨矿进行了年龄测试,深部的矽卡岩型钨矿尚未开展年代学研究工作。本文以棋盘沟钨矿床为研究对象,选取两类矿石中与白钨矿、辉钼矿密切共生的金云母进行39Ar-40Ar同位素测年。结果显示,矽卡岩型矿石中金云母坪年龄为190.1±0.6Ma(MSWD=1.28),石英脉型矿石中金云母坪年龄为188.6±0.6 Ma(MSWD=1.42),均为早侏罗世成矿,且石英脉型钨矿成矿时间略晚于矽卡岩型钨矿。该成矿期处于南秦岭成矿带陆内碰撞造山向伸展转变的转折期,代表着一期重要的、尚未被广泛关注的印支末期的岩浆热液钨钼成矿事件,应在今后的找矿工作中予以重视。 相似文献
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豫西银家沟硫铁多金属矿床Re-Os和40Ar-39Ar年龄及其地质意义 总被引：4，自引：1，他引：3
河南省银家沟硫铁多金属矿床位于华北克拉通南缘的华熊地块内,是东秦岭地区最大的硫铁多金属矿床,以其硫铁矿储量大及共、伴生元素复杂区别于东秦岭其他以钼为主的矿床.矿化在空间上呈规律性的带状分布,从岩体内向外,依次出现斑岩型钼矿体→斑岩型硫铁矿体→矽卡岩型铁矿体、钼矿体→矽卡岩型硫铁、铜、锌、金矿体→脉型铅、锌、银矿体.选取5件接触带矽卡岩型钼矿体中的辉钼矿样品进行Re-Os同位素定年,获得(142.9±2.1) Ma～(143.7±2.3) Ma的模式年龄,加权平均值为(143.4±0.9) Ma(MSWD=0.071),等时线年龄为(140.0±18.0) Ma(2σ,MSWD=0.095),将(143.4±0.9) Ma认作辉钼矿的结晶年龄,表明银家沟矿床矽卡岩型矿体形成于约143 Ma前;选取1件硅化、绢云母化、黄铁矿化、辉钼矿化钾长花岗斑岩中的绢云母样品定年,获得40Ar-39Ar坪年龄为(143.6±1.4) Ma,相应的39 Ar/36 Ar-40 Ar/39Ar等时线年龄为(143.0±2.0) Ma(MSWD=0.13),将(143.0±2.0)Ma认作绢云母的Ar封闭年龄,表明银家沟矿床斑岩型矿化亦发生在约143Ma前.本次辉钼矿Re-Os和绢云母40Ar-39A定年结果表明,银家沟矽卡岩型和斑岩型矿体均形成于早白垩世初期.银家沟矿床辉钼矿的ω(Re)在38.5×10-6～43.2×10-6之间,成矿物质主要来自由火成物质组成的宽坪群和二郎坪群,成矿与矿区内的钾长花岗斑岩有关.结合前人对东秦岭造山带中生代期间地球动力学背景的研究成果,笔者认为银家沟矿床形成于EW向构造体制向NNE向构造体制大转换阶段,即形成于挤压体制向伸展体制转换的背景. 相似文献
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内蒙古甲乌拉大型铅锌银矿位于大兴安岭成矿带北段,为一与火山-次火山作用有关的浅成低温热液型矿床。该矿床绢云母的矿物学特征方面研究程度较低,绢云母的年龄还未见报道。本次研究拟从绢云母入手,利用电子探针和~(40)Ar/~(39)Ar同位素年龄测定,研究其矿物学特征,测定其年龄,进一步探究该矿区热液事件的发生和地球动力学背景,增进对该矿床成矿机制的理解。甲乌拉矿床绢云母~(40)Ar/~(39)Ar坪年龄为133. 27±0. 66 Ma,等时线年龄为131. 88±0. 83 Ma。研究认为,甲乌拉矿床绢云母可能代表了发生于矿化后的另外一期热液事件。该热液事件发生于古太平洋板块俯冲方向改变之后,可能与碰撞后的伸展背景有关。 相似文献
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望峰金矿床位于中天山北缘冰达坂韧性剪切带内,成矿单元划分属于博罗科努多金属成矿带内天格尔-可可乃克次级成矿带,矿体主要赋存于糜棱岩化花岗岩中,主要矿石类型为石英脉型和蚀变糜棱岩型矿石。对两种类型矿石中的绢云母进行~(40)Ar/~(39)Ar测年,获得坪年龄分别为(250.9±3.0)Ma、(255.8±3.0)Ma,两个样品正反等时线年龄与坪年龄在误差范围内一致,表明坪年龄结果可信,可以代表成矿年龄,说明望峰金矿床的主成矿期时代为晚二叠世末期,且蚀变糜棱岩型矿石的形成时代比石英脉型矿石略早。结合矿区地质情况及前人的研究结果,认为望峰金矿床是剪切带型金矿床,冰达坂韧性剪切带控制了望峰金矿的成矿过程。 相似文献
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辽西义县组火山岩40Ar/39Ar、K-Ar法年龄测定 总被引：35，自引：3，他引：35
义县组为辽西地区广泛分布的陆相火山-沉积地层,义县火山旋回分为 4个亚旋回.含珍稀化石的湖相沉积层与第二亚旋回火山岩伴生.运用激光微区 40Ar/39Ar法、常规 40Ar/39Ar阶段升温测年法和 K- Ar法,对义县旋回火山岩进行了系统的年龄测定,结果表明,直接覆盖义县组底砾岩的义县旋回第一亚旋回第一小旋回玄武岩的 K- Ar年龄为 (133.3± 2.6) Ma、 (133.6± 2.6) Ma,激光微区 40Ar/39Ar法给出的相关性很好的 Ar- Ar等时线年龄为 (132.9± 4.5) Ma,第三、第四小旋回玄武岩样品 40Ar/39Ar阶段升温获得平坦的年龄谱线,坪年龄分别为 (130.6± 0.5) Ma、 (127.7± 0.2) Ma;第二亚旋回玄武岩和流纹质凝灰岩样品 Ar- Ar等时线年龄为 (126.1± 1.7) Ma、 (127.4± 1.3) Ma,第三亚旋回火山岩全岩 K- Ar年龄为 (124.4± 2.4)～ (124.9± 2.4) Ma.义县火山旋回发生的时间大致介于 120～ 135 Ma之间, 义县组的时代应为早白垩世. 相似文献
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风化壳是不同地质历史时期风化作用的环境和物质记录,其组成、厚度、成熟度、保存程度等是古气候条件、区域构造活动性及地貌演化的直接反映。风化壳的形成年代是风化壳研究的关键内容,精确的风化壳年龄数据是查明一系列区域甚至全球事件的重要途径。风化壳中次生矿物（主要是钡硬锰矿族矿物和明矾石族矿物）的40Ar/39Ar年代学研究首次实现了对风化壳和风化作用的直接和精确定年,所获得的年龄数据为风化壳的形成演化、区域古气候古环境恢复、化学风化历史与矿床次生富集过程及新构造运动和山脉隆升历史等一系列重大地质问题的解决提供了重要途径。然而,风化壳中次生矿物定年存在的潜在问题及风化壳剖面取样的不完整性,有可能使风化壳的年龄分布变得相当复杂,导致对化学风化历史、风化壳形成过程和形成环境等的认识出现困难。为此,必须开展对风化壳的详细野外地质研究和精细取样,并综合采用多种先进测试手段,才能获得可靠的风化壳年龄数据。在对风化壳年龄数据进行解释时,还需要系统分析多种地质、环境资料（如古生物、盆地沉积物等）,才可能获得有意义的地貌、构造和古气候信息。我国华南地区广泛分布的红色风化壳中含有丰富的钡硬锰矿族矿物,是研究该区新生代以来化学风化、大规模次生富集成矿及古气候古环境演变的理想对象。 相似文献
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The geochronology and genesis of the Qingyang batholith were investigated using40Ar/39Ar and Rb-Sr isotopic techniques. The Qingyang is a composite batholith consisting of two major rock types granodiorite and granite in the Yangtze fold belt.40Ar/39Ar spectra for biotite and amphibole separates are internally concordant. The concordance of the minerals and spectra indicate no thermal disturbance of the ages, and rapid cooling of the rocks. The granodiorite has an age of 137.6±1.4 m.y. and the granite 122.7±1.2 m.y. Whole-rock Rb-Sr analysis yields ages consistent with the40Ar/39Ar dates. Thus, the Qingyang batholith was formed in two major stages in the late Jurassic and early Cretaceous. The batholith is not Triassic as was previously proposed. Special40Ar/39Ar analysis of two granodiorite samples has precisely documented a 1.0 m.y. apparent age difference between these samples. Several factors could account for this difference, but different emplacement times seem most convincible. The granodiorite and granite show little variation in initial87Sr/86Sr ratio (about 0.7085). The high initial Sr ratios suggest that the magmas were formed by anatexis of older crustal materials. 相似文献
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Please refer to the attachment(s) for more details 相似文献
15.
The Tso Morari Complex, which is thought to be originally the margin of the Indian continent, is composed of pelitic gneisses and schists including mafic rock lenses (eclogites and basic schists). Eclogites studied here have the mineral assemblage Grt + Omp + Ca-Amp + Zo + Phn + Pg + Qtz + Rt. They also have coesite pseudomorph in garnet and quartz rods in omphacite, suggesting a record of ultrahigh-pressure metamorphism. They occur only in the cores of meter-scale mafic rock lenses intercalated with the pelitic schists. Small mafic lenses and the rim parts of large lenses have been strongly deformed to form the foliation parallel to that of the pelitic schists and show the mineral assemblages of upper greenschist to amphibolite facies metamorphism. The garnet–omphacite thermometry and the univariant reaction relations for jadeite formation give 13–21 kbar at 600 °C and 16–18 kbar at 750 °C for the eclogite formation using the jadeite content of clinopyroxene (XJd = 0.48).
Phengites in pelitic schists show variable Si / Al and Na / K ratios among grains as well as within single grains, and give K–Ar ages of 50–87 Ma. The pelitic schist with paragonite and phengite yielded K–Ar ages of 83.5 Ma (K = 4.9 wt.%) for paragonite–phengite mixture and 85.3 Ma (K = 7.8 wt.%) for phengite and an isochron age of 91 ± 13 Ma from the two dataset. The eclogite gives a plateau age of 132 Ma in Ar/Ar step-heating analyses using single phengite grain and an inverse isochron age of 130 ± 39 Ma with an initial 40Ar / 36Ar ratio of 434 ± 90 in Ar/Ar spot analyses of phengites and paragonites. The Cretaceous isochron ages are interpreted to represent the timing of early stage of exhumation of the eclogitic rocks assuming revised high closure temperature (500 °C) for phengite K–Ar system. The phengites in pelitic schists have experienced retrograde reaction which modified their chemistry during intense deformation associated with the exhumation of these rocks with the release of significant radiogenic 40Ar from the crystals. The argon release took place in the schists that experienced the retrogression to upper greenschist facies metamorphisms from the eclogite facies conditions. 相似文献
16.
Diffusion and solubility of Ar in optically clear natural and synthetic quartz crystals were examined at ∼500 to 1200 °C by treating polished specimens in pressurized Ar (1-185 MPa) and characterizing the resulting diffusive-uptake (or subsequent diffusive-loss) profiles using Rutherford backscattering spectroscopy (RBS). Analytical uncertainty leads to significant scatter in the data, but the Ar diffusivity, D, is reasonably well constrained by the following Arrhenius relationship:D = 8.2−4.2+8.8 × 10−19 exp[(−6150 ± 750)/T(K)] m2/sNo effects of crystallographic orientation or quartz structural form (α or β) are discernible.Apparent solubilities typically fall between 1000 and 3000 ppm (by mass), with large uncertainties (±50-60% 2σ), but some lower values (∼700 ppm) are observed near the low end of the Ar pressure range investigated. Occasional high-concentration outlier values fall between 5000 ppm and 3.8 wt.% Ar. These do not correlate with Ar pressure, suggesting extrinsic (non-lattice) siting of Ar in some cases. Field-emission SEM images and numerical simulations of the diffusion process document isolated nanopores as the hosts for the occasional very high concentrations of Ar (observable pores range down to ∼10 nm in diameter; indirect evidence points to smaller ones as the more common sinks for Ar). The systematics of the data suggest an actual (lattice) solubility of ∼2000 ppm at 100- to 200-MPa Ar pressure, which is equivalent to a partition coefficient of ∼0.001cm3STP/g · atm. Using either organic clathrate or fullerene as the Ar sources, 1-GPa experiments in a piston-cylinder apparatus result in similar uptake of Ar into quartz, in this case through partitioning equilibrium with C-O-H fluid (clathrate source) or amorphous carbon (fullerene source).The ability of quartz, relative to other minerals, to incorporate significant amounts of Ar may allow this ubiquitous and abundant mineral to serve as a local sink for Ar in crustal rocks lacking a free fluid phase. The diffusion data permit open-system behavior of Ar in quartz below the closure temperature of biotite and other 40Ar source minerals. 相似文献
17.
This study presents a new high-precision 40Ar/39Ar age for the Devonian hot-spring system at Rhynie. Hydrothermal K-feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock, date the hydrothermal activity, the fossilised biota, and syn - K-feldspar gold mineralization at 403.9 ± 2.1 Ma (2σ). Oxygen isotope data for the parent fluid (−4‰ to 2‰) show that the K-feldspar was precipitated from a dominantly meteoric fluid, which mixed with magmatic fluids from a degassing magma chamber.The 40Ar/39Ar age (403.9 ± 2.1 Ma [2σ]) when recalculated (407.1 ± 2.2 Ma [2σ]) with respect to the astronomically tuned age for Fish Canyon sanidine (28.201 ± 0.023 Ma [1σ]), also provides a robust marker for the polygonalis-emsiensis Spore Assemblage Biozone within the Pragian-?earliest Emsian. Furthermore, the age identifies the Devonian pull-apart volcano-sedimentary basins of the British and Irish Caledonides (and their root zones), as specific targets for future gold exploration. 相似文献
18.
采用激光阶段加热40Ar/39Ar定年技术,选取柴北缘超高压变质带鱼卡地体超高压变质岩及其围岩的6个多硅白云母进行了Ar同位素分析,获得丰富年代学数据。榴辉岩和云母斜长角闪岩多硅白云母具有高Si、高Mg含量的特征,阶段加热给出复杂的表观年龄图谱,总气体年龄（708~534 Ma）和等时年龄（681~513 Ma）都明显老于区内榴辉岩锆石U Pb年龄,暗示样品含大量外来40Ar。相比之下,围岩花岗质片麻岩和白云母石英片岩多硅白云母具有相对低Si高Fe的特征,阶段加热给出平坦的40Ar/39Ar年龄谱,对应坪年龄分别为454和418 Ma。构成年龄坪的数据点形成了线性关系良好的反等时线,并获得同坪年龄一致的等时年龄,能与区域地质年龄很好地吻合。坪年龄454 Ma解释为花岗质片麻岩冷却到约400 ℃时的时间,同时也代表了鱼卡变质岩在经历了深俯冲超高压变质作用后,从上地幔折返抬升至中上地壳深度的时限;片岩多硅白云母坪年龄418 Ma纪录的则是区内一次强韧性剪切事件发生的时代。考虑到榴辉岩和斜长角闪岩原岩为变基性玄武岩类,其主要含钾矿物角闪石的Ar封闭稳定性较高,同时在超高压变质过程中,它们处在一个相对封闭和缺乏流体活动的极端地质环境,所以认为鱼卡榴辉岩多硅白云母外来40Ar来自原岩而非后期渗入的流体,属于“继承”40Ar的范畴。 相似文献
19.
U. A. Glasmacher P. Reynolds A. A. Alekseyev V. N. Puchkov K. Taylor V. Gorozhanin R. Walter 《International Journal of Earth Sciences》1999,87(4):515-525
West of the Main Uralian fault, the main suture in the southern Urals, 40Ar/39Ar apparent ages of amphibole, muscovite and potassium feldspar are interpreted as cooling ages. A fast exhumation of the metamorphic complex of Kurtinsky during Upper Carboniferous time is indicated by the small age difference (15 Ma) between cogenetic amphibole and muscovite. Differentiated movement in the footwall of the Main Uralian fault along strike is indicated by the age difference of 70 Ma between the metamorphic complexes of Kurtinsky (north) and Maksyutov (south). No Upper Paleozoic (Uralian) medium- to high-temperature event is recorded in 40Ar/39Ar data from the metamorphic complex of Beloretzk (MCB). An amphibole age of 718±5 Ma and the occurrence of mafic intrusions might signal the break-up of Rodinia and therefore indicate the rifting period followed by the separate movement of the "Beloretzk terrane". Muscovite ages of approximately 550±5 Ma, the unique pre-Ordovician tectonometamorphic evolution of the MCB and the Late Vendian sedimentary history of the western Bashkirian Megaanticlinorium (BMA) imply the existence of a Neoproterozoic orogeny at the eastern margin of Baltica. This orogeny might have been initiated by the accretion of the "Beloretzk terrane". The metamorphic grade of the overlain Silurian shales and the K/Ar microcline ages from the "Beloretzk terrane" give evidence for a new thermal event at approximately 370 Ma. A microcline age of 530–550 Ma obtained for the Vendian conglomerate in the western BMA suggests that a maximum temperature of approximately 200°C was reached in Cambrian or Vendian times. An orthoclase age (590–630 Ma) of the Vendian Zigan flysch deposits might be inherited from the eastern source area, the Cadomian orogen. An orthoclase age (910–950 Ma) from the Riphean Zilmerdak conglomerate coincides with a documented decrease in the subsidence rate of the Upper Riphean basin. 相似文献
20.
西藏林周基性岩脉的^40Ar/^39Ar年代学、地球化学及其成因 总被引：8，自引：2，他引：8
在西藏林周盆地林子宗火山岩地层中发现一套始新世钾玄质基性岩脉.测定了它们的主量元素、微量元素和稀土元素含量以及Sr-Nd-O同位素和^40Ar/^39Ar同位素地质年代.测试结果表明,岩脉以低硅（SiO2为45.42%～48.32%）、高镁（MgO为2.84%～5.35%,平均4.57%）、高钾高碱（K2O＋Na2O为4.60%～6.23%、K2O/Na2O为0.71～1.18）为特征,属于钾玄质基性岩脉;稀土和微量元素呈现陆缘火山弧的特征,即相对富集轻稀土元素、亏损重稀土元素,具有弱的Eu负异常（δEu=0.79～0.94,平均0.83）;强烈富集K、Rb、Sr、Ba、Th、Sr等大离子不相容元素,相对亏损Th、Nb、Ta、P、Zr、Hf、HREE等高场强元素,具有明显的Nb、Ta、Ti的负异常;Sr-Nd-O同位素组成上,具有相对原始的Sr、Nd同位素比值,初始^87Sr/^86Sr比值为0.70487～0.70543,143Nd/144Nd比值为0.51266～0.51273,εNd值为0.5～1.8,相对低的δ^18OV-SMOW值（4.8‰～7.6‰）;^40Ar/^39Ar角闪石单矿物年龄为52.9Ma.利用地幔地球化学示踪理论,推断林周钾玄质基性岩脉的形成与新特提斯洋岩石圈向欧亚大陆俯冲过程中的回转、断离以及由此引起的软流圈地幔的上涌等地球动力学过程有关,是软流圈地幔流体与先前被俯冲带流体交代过的上覆岩石圈地幔的部分熔融产物的混合,指示冈底斯带在古新世-始新世（55～50Ma）时期一次平行于造山带的伸展作用. 相似文献