共查询到19条相似文献，搜索用时 125 毫秒
1.
白云鄂博陆缘裂谷系沉积物源与超大型稀土矿床含矿白云岩的成因探讨 总被引：3，自引：0，他引：3
白云鄂博群尖山组H4岩性段石英砂岩中的碎屑锆石年龄纪录了华北克拉通北缘两期重要的构造岩浆事件,一组年龄集中在新太古代—古元古代初期(2379～2596Ma),另一组年龄集中在古元古代晚期(1761～1946Ma),该结果与白云鄂博地区基底岩石的锆石年龄相吻合。白云鄂博群沉积碳酸盐岩的全岩207Pb-206Pb等时线年龄1649±45Ma,代表了白云鄂博群的沉积时代。白云鄂博地区沉积灰岩、白云岩与含矿白云岩的Pb同位素组成存在非常大的差异,在Pb同位素组成和构造图解中,含矿白云岩都集中在地幔演化线附近,靠近亏损地幔端元[(206Pb/204Pb)i=15.04～16.49,(207Pb/204Pb)i=15.17～15.28,(208Pb/204Pb)i=31.20～36.40],而白云鄂博群中的灰岩、白云岩则位于造山带演化线附近,靠近深海沉积物端元[(206Pb/204Pb)i=17.28～19.35,(207Pb/204Pb)i=15.47～15.69,(208Pb/204Pb)i=36.62～37.12]。 相似文献
2.
北京十三陵地区中—新元古界碳酸盐岩Pb—Pb年龄研究 总被引：8，自引：0，他引：8
对北京十三陵地区中一新元古界碳酸盐岩进行了系统地采样和207pb/204pb-206Pb/204Pb年龄测定.共测定了63个样品(大部分样品采取两种溶解方式),得到中元古界雾迷山组第三段的207Pb/204pb-206Pb/204pb等时线年龄为1373±92Ma(95%置信度误差,下同,MSWD＝4.7),杨庄组为1488±55Ma(MSWD＝14),高于庄组第三段为1608±74Ma(MSWD＝8.1).这些年龄数据与目前已有地质记录相吻合.串岭沟组的碳酸盐相的206Pb/204Pb-207Pb/204Pb未构成等时线,但全岩的206Pb/204pb-207Pb/204Pb比碳酸盐相具有更明显的线性趋势,其原因尚待进一步研究.另外,根据同一个样品用稀盐酸溶解和用氢氟酸加硝酸混合酸溶解的铅同位素比值的接近的现象,显示碳酸盐岩中的硅质没有陆源的特征,是沉积盆地中的产物. 相似文献
3.
滇东南白牛厂多金属矿床铅同位素组成及铅来源新认识 总被引：1，自引：0，他引：1
白牛厂矿床位于滇东南锡多金属成矿带中部,是一个Ag、Pb、Zn、Sn等共生的多金属矿床,但成因争议较大.前人引用早期矿床矿石矿物铅同位素数据得出矿石铅主要来源于基底岩石淋滤,矿床经历了热水沉积+岩浆热液叠加两个成矿阶段的结论.本文采用最新铅同位素数据系统研究了白牛厂矿床的铅同位素组成,其中,白牛厂矿床矿石矿物的铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为17.264～18.537、14.843～15.862和38.481～39.424;薄竹山花岗岩长石铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.301～18.387、15.611～15.670和38.677～38.904;薄竹山岩体接触带型矿床(点)矿石矿物铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.302～18.417、15.603～15.692和38.596～38.868;区域地层及矿区地层钻孔样品铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.307～19.206、15.622～15.809和38.436～39.932.对比四者铅同位素组成特征,白牛厂矿床矿石矿物、薄竹山花岗岩长石、薄竹山岩体接触带型矿床(点)矿石矿物具有一致的铅同位素组成,与地层铅同位素组成相差甚远,表明白牛厂矿床铅主要来自岩浆作用,在侵入的过程中可能受到了地层的轻度混染.矿床地质特征及近期地球化学和年代学研究成果表明,白牛厂矿床的形成主要受岩浆作用影响,沉积成矿作用在白牛厂矿床很可能是不存在的. 相似文献
4.
江南古陆南缘四堡群同位素地质年代学研究 总被引：11，自引：0，他引：11
四堡群浅变质火山-沉积岩系主要出露于桂九万大山地区，是华南最古老的地层单元之一。对坛地区罗布山枕状玄武岩中细粒原生锆石进行单颗粒锆石蒸节-沉积法年龄测定，两组锆石样品获得207Pb/206Pb年龄分别为1374±20（2σ）Ma和1863±7（2σ）Ma。对宝坛地区基性和超基性火山岩进行了Sm-Nd同位素研究，获等时线年龄为1782±820（2σ）Ma，与锆石单颗粒207Pb/206Pb年龄一致，充分说明四堡群形成于中元古代早期。火山岩的εNd（t）为0.6，表明基性-超基性岩浆源自于亏损地幔。这套岩石的 相似文献
5.
湘南宝山铅锌矿床硫、铅、碳、氧同位素特征及成矿物质来源 总被引：3，自引：1，他引：2
宝山铅锌矿床是湘南地区代表性矿床之一。宝山铅锌矿床的成矿作用与156~158 Ma的宝山花岗闪长斑岩密切相关。花岗闪长斑岩主要由古老地壳部分熔融而成。为确定成矿物质来源,文章系统研究了宝山铅锌矿床的硫、铅、碳、氧同位素组成特征。矿床中硫化物黄铁矿、闪锌矿、方铅矿的δ34S值呈狭窄的塔式分布,变化在-2.17‰~6.46‰之间,平均值为3.13‰。δ34S值总体表现为δ34S黄铁矿δ34S闪锌矿δ34S方铅矿,表明硫同位素分馏基本达到了平衡。矿石、花岗闪长斑岩和赋矿地层硫同位素对比研究表明,矿石中的硫主要由岩浆分异演化而来,岩浆中的硫主要来自古老地壳。矿石206Pb/204Pb、207Pb/204Pb和208Pb/204Pb比值分别为18.188~18.844、15.661~15.843和38.562~39.912,赋矿地层206Pb/204Pb、207Pb/204Pb和208Pb/204Pb比值分别为18.268~19.166、15.620~5.721和38.364~39.952。矿石铅同位素组成比地层中的更富放射性成因铅,矿石中部分铅来自宝山花岗闪长质岩浆,在成矿流体运移过程中有部分地层铅参与了成矿,岩浆中的铅主要来自古老地壳。热液方解石的碳、氧同位素组成介于岩浆和赋矿碳酸盐岩的碳、氧同位素之间,主要是由于岩浆流体和碳酸盐岩不同比例的水岩反应所致,测水组有机碳的加入造成了部分热液方解石δ13CPDB值偏低。 相似文献
6.
五台地区滹沱群时代与地层划分新认识:地质学与锆石年代学证据 总被引：7，自引：7，他引：0
本文从五台地区滹沱群豆村亚群四集庄组、东冶亚群纹山组和郭家寨亚群西河里组地层中共采集了5件浅变质砂岩样品,并对其进行了La-MC-ICPMS锆石U-Pb年龄测定。分析结果显示,四集庄组2件砂岩样品碎屑锆石207Pb/206Pb年龄主要集中于~2.5Ga和2.1~2.2Ga两个峰值,其中~2.5Ga碎屑锆石来自新太古代五台群和五台地区花岗质杂岩;2.1~2.2Ga碎屑锆石获得207Pb/206Pb加权平均年龄2134±5Ma,限定了四集庄组砂岩沉积下限为2134Ma。结合四集庄组火山岩形成时代(2140±10Ma)和四集庄组底部发育厚层砾岩,我们认为滹沱群初始形成时代为~2.2Ga,即早元古代中期。东冶亚群纹山组底部砂岩中碎屑锆石207Pb/206Pb年龄主要集中于2050~2122Ma之间,其中64粒相对年轻的锆石获得207Pb/206Pb加权平均年龄2068±3Ma,代表了东冶亚群形成时代下限为2070Ma左右。综合豆村亚群青石村组火山岩形成时代2087±9Ma,我们认为东冶亚群初始形成于2070Ma左右。郭家寨亚群中最年轻碎屑锆石207Pb/206Pb年龄为1958±10Ma,表明郭家寨亚群开始沉积时代小于1.95Ga,为早元古代晚期/末期。区域上,早元古代末期是华北最终克拉通阶段,而郭家寨亚群与东冶亚群呈明显的角度不整合接触关系,两者记录了明显不同的地质过程。因此,我们建议郭家寨亚群应从滹沱群中解体出来并独立命名为郭家寨群,且郭家寨群可能沉积于华北克拉通化过程中/之后,开始沉积的时代为1.9~1.8Ga。 相似文献
7.
《地球化学》2020,(1)
铧厂沟金矿床赋存于新元古界碧口群细碧岩和泥盆系踏坡群灰岩中。矿体受高角度逆冲断层和韧-脆性剪切带控制,呈似层状、透镜状产出,是南秦岭典型的造山型金矿床。根据赋矿围岩不同,该矿床划分为细碧岩矿带和灰岩矿带。细碧岩矿带矿石中黄铁矿的δ~(34)S值范围为-1.3‰～4.7‰,呈塔式分布,具岩浆硫特征;灰岩矿带矿石中黄铁矿的δ~(34)S值为-14.8‰～1.9‰,离散度强,具有生物成因硫和地层硫的特征。矿石黄铁矿的δ~(34)S值均落入碧口群细碧岩(2.1‰～4.7‰)和踏坡群(-22.5‰～6.6‰)的δ~(34)S值范围,指示硫源主要为碧口群和踏坡群。Pb同位素组成中,细碧岩矿带矿石中黄铁矿~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb和~(208)Pb/~(204)Pb范围分别为18.017～17.856、15.530～15.585和38.150～38.413,灰岩矿带矿石中黄铁矿~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb和~(208)Pb/~(204)Pb范围分别为18.202～18.491、15.624～15.659和38.690～39.401。细碧岩矿带矿石黄铁矿与围岩细碧岩全岩的~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb和~(208)Pb/~(204)Pb值相近,灰岩矿带矿石黄铁矿Pb同位素投影点全部落入踏坡群灰岩地层范围内。以上S和Pb同位素结果表明,铧厂沟金矿床金属物质来源于新元古代碧口群细碧岩及泥盆系踏坡群。 相似文献
8.
蓄集矿床是宗务隆构造带内发现的重要银铅矿床。蓄集银铅矿床赋存于石炭-二叠系宗务隆群果可山组灰岩夹千枚岩地层中,矿体呈脉状、透镜状、似层状,明显受近东西走向的断裂构造控制,矿体围岩蚀变主要为硅化和绢云母化,矿石矿物主要为方铅矿和银黝铜矿,脉石矿物主要为石英,矿石具有斑杂状和网脉状构造。对该矿床开展了S-Pb同位素组成分析。硫同位素分析结果表明矿石中硫化物矿物δ~(34)S值变化于5.0‰～8.4‰之间,显示硫主要为岩浆来源,有少量地层的贡献;铅同位素分析结果表明,矿石~(206)Pb/~(204) Pb=17.896～17.922,~(207)Pb/~(204) Pb=15.589～15.617,~(208) Pb/~(204) Pb=38.072～38.166,与围岩铅同位素组成(~(206) Pb/~(204) Pb=17.94～18.976,~(207)Pb/~(204) Pb=15.600～15.696,~(208) Pb/~(204) Pb=38.106～40.943)较为相似,而与蓄集峡口闪长岩铅同位素组成(~(206) Pb/~(204) Pb=18.144～18.589,~(207)Pb/~(204) Pb=15.623～15.636,~(208)Pb/~(204) Pb=38.790～39.033)相差较大,反映成矿物质主要来自围岩地层宗务隆群果可山组。综合分析认为,蓄集银铅矿床与宗务隆构造带晚二叠世岩浆活动关系密切,应属岩浆热液为主的热液充填-交代成因类型。 相似文献
9.
《古地理学报》2020,(1)
为了探讨华北板块南缘中元古代沉积地层的时代归属和物质来源、区域古地理格局和大地构造特征,对豫西灵宝福地地区的高山河群进行碎屑锆石U-Pb年代学和锆石微量元素特征研究。获得的高山河群年龄最小(年轻)的单颗碎屑锆石207Pb/206Pb年龄值为1685±39 Ma,从而限制了高山河群最早沉积年龄不早于1700 Ma。结合上覆的龙家园组年代学标定(1594±12 Ma),将高山河群的形成年代限定为1700—1600 Ma,即中元古代长城纪的中晚期,属国际地质年表的"固结纪"。高山河群中碎屑锆石207Pb/206Pb年龄范围为1685—2751 Ma,呈现1850 Ma、2150 Ma、2300 Ma和2500 Ma共4个年龄峰值,对应于华北克拉通古元古代重要的地质事件,并且高山河群以1850 Ma和2500 Ma峰值年龄段的地质体为主要的物源区。根据高山河群与云梦山组碎屑锆石年龄频率对比,推测在豫西地区西侧存在以往报道较少的年龄为2500 Ma的地质体。根据熊耳群火山岩及其对应锆石的地球化学特征和熊耳期盆地动力学性质,并结合高山河群沉积相特征和沉积盆地构造属性,认为熊耳群形成于与"岛弧"共生的拉张性质的弧后盆地地区,而其上覆的高山河群为弧后盆地靠近大陆一侧的具有被动大陆边缘性质的滨浅海沉积。 相似文献
10.
甲生盘铅锌硫矿床位于华北地台北缘狼山—渣尔泰山成矿带内,赋矿地层为中元古代渣尔泰山群的一套黑色岩系。铅同位素测试结果表明,甲生盘矿床铅同位素组成分为两组:A组以低放射性成因铅为特征,其同位素组成206Pb/204Pb为15.889~16.257,207Pb/204Pb为15.158~15.455,208Pb/204Pb为35.112~36.271;B组以相对高放射性成因铅为特征,其同位素组成206Pb/204Pb为17.871~18.990,207Pb/204Pb为15.509~15.672,208Pb/204Pb为37.525~38.770。矿石硫化物明显分为早期沉积的层纹状、浸染状细粒硫化物和后期脉状产出的粗粒硫化物,均含有A、B两组铅特征,前者以A组特征为主,后者以B组特征为主。根据铅构造模式图解及μ值等铅同位素参数综合分析:A组铅来自上地壳中的造山带,并且有幔源铅的补偿,成矿物质来自于古老的基底地层;B组铅主要来源于上地壳,部分受矿体北翼花岗岩侵入体的影响,成矿物质主要来自赋矿围岩;矿床铅具有多来源混合铅结构特征。 相似文献
11.
Zhijiao Song Cuihua Chen Yulong Yang Yan Zhang Li Yin Hongzhi Li 《Resource Geology》2020,70(3):273-295
The Nanmushu Zn‐Pb deposit, hosted by the Neoproterozoic Dengying Formation dolostone, is located in the eastern part of the Micangshan tectonic belt at the northern margin of the Yangtze Craton, China. This study involves a systematic field investigation, detailed mineralogical study, and Rb‐Sr and Pb isotopic analyses of the deposit. The results of Rb‐Sr isotopic dating of coexisting sphalerite and galena yield an isochron age of 486.7 ± 3.1 Ma, indicating the deposit was formed during the Late Cambrian to Early Ordovician. This mineralization age is interpreted to be related to the timing of destruction of the paleo‐oil reservoir in the Micangshan tectonic belt. All initial 87Sr/86Sr ratios of sphalerite and galena (0.70955–0.71212) fall into the range of the Mesoproterozoic Huodiya Group basement rocks (0.70877–0.71997) and Dengying Formation sandstone (0.70927–0.71282), which are significantly higher than those of Cambrian Guojiaba Formation limestone (0.70750–0.70980), Cambrian Guojiaba Formation carbonaceous slate (0.70766–0.71012), and Neoproterozoic Dengying Formation dolostone (0.70835–0.70876). Such Sr isotope signatures suggest that the ore strontium was mainly derived from a mixed source, and both of the Huodiya Group basement rocks and Dengying Formation sandstone were involved in ore formation. Both sphalerite and galena are characterized by an upper‐crustal source of lead (206Pb/204Pb = 17.849–18.022, 207Pb/204Pb = 15.604–15.809, and 208Pb/204Pb = 37.735–38.402), and their Pb isotopes are higher than, but partly overlap with, those of the Huodiya Group basement rocks, but differ from those of the Guojiaba and Dengying Formations. This suggests that the lead also originated from a mixed source, and the Huodiya Group basement rocks played a significant role. The Sr and Pb isotopic results suggest that the Huodiya Group basement rocks were one of the most important sources of metallogenic material. The geological and geochemical characteristics show that the Nanmushu Zn‐Pb deposit is similar to typical Mississippi Valley type, and the fluid mixing may be a reasonable metallogenic mechanism for Nanmushu Zn‐Pb deposit. 相似文献
12.
高庄金矿床是豫西南一处重要金矿,成矿时代、物质来源以及矿床成因类型尚不清楚。本文对高庄金矿石中载金矿物磁黄铁矿进行Re-Os测年,获得(137±2) Ma成矿年龄,表明金矿床为燕山晚期成矿。分别对载金矿物磁黄铁矿、容矿地层(二郎坪群火神庙组)和侵入岩体(堂坪岩体)进行了S、Pb和REE组成分析。矿石硫化物δ34SCDT值为-3.0‰～-1.5‰,平均值为-2.24‰,深源S特征明显,矿石S可能来源于容矿的二郎坪群火神庙组基性火山岩地层。矿石硫化物206Pb/204Pb、207Pb/204Pb、208Pb/204Pb的变化范围分别为17.106～17.505、15.469～15.602、37.835～38.194。堂坪岩体206Pb/204Pb、207Pb/204Pb、208Pb/204Pb的变化范围分别为18.244 3～19.238 2、15.594 8～15.693 5、38.504 2～39.616 3,二郎坪群火山岩206Pb/204Pb、207Pb/204Pb、208Pb/204Pb变化范围分别为18.176 8～18.669 2、15.607 1～15.801 9、38.375 9～39.080 9。矿石铅同位素组成与地层和岩体的岩石铅组成相近,表明岩体和地层都提供了成矿物质。矿石与二郎坪群火神庙组地层的REE球粒陨石标准化配分曲线都为平坦型。可见,豫西南高庄金矿形成于秦岭碰撞造山之后的燕山晚期陆内构造岩浆热液过程,成矿物质主要来源于矿体周围火山岩地层。 相似文献
13.
华北串岭沟组凝灰岩锆石SHRIMP年龄及其地层学意义 总被引：2，自引：0，他引：2
华北克拉通燕辽地区是中国中新元古代沉积地层的标准剖面区。蓟县群和青白口群已经取得了很多重要的高精度定年数据,但是长城群除了顶部大红峪组有了高精度定年以外,其他组还缺乏可靠的高精度定年数据。为了准确标定华北克拉通中元古界长城群串岭沟组的年龄,对采自河北宽城地区神仙岭剖面串岭沟组顶部火山岩凝灰岩锆石进行了SHRIMP U-Pb定年。结果表明所测锆石207Pb/206Pb表面年龄加权平均值为(1 634.8±6.9) Ma(95% 置信度,MSWD=1.2,n=23)。可见长城群串岭沟组顶部的准确年龄为(1 634.8±6.9) Ma,表明长城群串岭沟组到大红峪组整体上属于中元古代地层。 相似文献
14.
A. B. Kuznetsov I. M. Gorokhov G. V. Ovchinnikova V. A. Melezhik I. M. Vasil’eva B. M. Gorokhovskii G. V. Konstantinova N. N. Mel’nikov 《Lithology and Mineral Resources》2011,46(2):151-164
The Rb-Sr and U-Pb systematics have been studied in the metasedimentary carbonate rocks from the Paleoproterozoic Kuetsjarvi
Formation. Samples were taken from the borehole drilled in the northern zone of the Pechenga Greenstone Belt in the northwestern
Kola Peninsula. The carbonate section of the formation is made up of three units (from the bottom to top): (I) dolomite (68
m), (II) calcareous-dolomite (9 m), and (III) clayey calcareous (1 m) ones. Dolomites (Mg/Ca = 0.55–0.61) from the lowermost
unit I contain 70.3–111 ppm Sr. Initial 87Sr/86Sr ratio in them varies within 0.70560–0.70623 and characterizes the primary continental-lacustrine carbonate sediments. Calcareous
dolomites (Mg/Ca = 0.39–0.59) and dolomitic limestones of units II and III (Mg/Ca = 0.02–0.36) are enriched in Sr (285–745
and 550–1750 ppm, respectively). Initial 87Sr/86Sr ratios in these rocks (0.70406–0.70486 and 0.70407–0.70431, respectively) fall within the range typical of the Jatulian
seawater, which indicates that the carbonate sediments of two upper units were formed in an open marine basin. Study of dolomites
from unit I showed that the Svecofennian metamorphism more significantly affected the U-Pb systems of carbonate rocks as compared
to their Rb-Sr systems. In the 207Pb/204Pb-206Pb/204Pb diagram, most data points corresponding to the carbonate constituent of dolomites define isochron with an age of 1900 ±
25 Ma (MSWD = 0.5). The same samples define a positive correlation in the 208Pb/204Pb-206Pb/204Pb plot. Since sedimentary carbonates usually do not contain Th, this correlation points to secondary enrichment of the studied
dolomites in Th or thorogenic 208Pb. Hence, the obtained Pb-Pb dating can be regarded as the age of the Svecofennian metamorphic event. Three samples from
dolomites of unit I lack any disturbance of the initial U-Th-Pb systematics, but their trend in the 207Pb/204Pb-206Pb/204Pb diagram deviates from the 1900 Ma isochron. Based on these samples, the model U-Pb premetamorphic age of the Kuetsjarvi
carbonate sediments is 2075–2100 Ma. This interval is consistent with the age range of the Lomagundi-Jatulian event, which
was responsible for the formation of carbonate sediments with high positive δ13C values. 相似文献
15.
A. B. Kuznetsov G. V. Ovchinnikova M. A. Semikhatov I. M. Gorokhov O. K. Kaurova M. T. Krupenin I. M. Vasil’eva B. M. Gorokhovskii A. V. Maslov 《Stratigraphy and Geological Correlation》2008,16(2):120-137
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
16.
G. V. Ovchinnikova A. B. Kuznetsov I. M. Vasil’eva I. M. Gorokhov M. T. Krupenin B. M. Gorokhovskii A. V. Maslov 《Doklady Earth Sciences》2013,451(2):798-802
The Pb-Pb age of phosphorite concretions of the Zigaza-Komarovo Formation, which composes the intermediate horizons of the Riphean stratotype of the South Urals, was determined in fractions resulting from the stepwise dissolution of concretions in 0.1 N, 0.5 N, and 1 N HCl. The determination of the Sr isotopic composition in phosphate fractions was favorable for rejection the fractions polluted with extraneous material. On the 207Pb/204Pb-206Pb/204Pb diagram, the isochron based on 31 points corresponds to 1330 ± 20 Ma (MSWD = 1.12), which is in agreement with the stratigraphic position of the Zigaza-Komarovo Formation. The decreased μ2 value of 9.57 for the phosphorite concretions relative to that of the average earthly lead based on the Stacey-Kramers model (9.74) is related to the rocks with an admixture of mantle lead, which occur in the run-off area of the Zigaza-Komarovo sediments. 相似文献
17.
汝阳群分布在华北克拉通西南缘,位于河南-陕西-山西交界地区,主要为一套未变质的碎屑岩及碳酸盐岩地层,不整合于熊耳群火山岩系之上,其上被洛峪群整合覆盖。长期以来,其地质时代一直存有较大的争议。本文通过对汝阳群下部白草坪组4个石英砂岩样品中的碎屑锆石进行LA-ICP-MS U-Pb年龄测定,获得的207Pb/206Pb年龄分布范围为3 000～1 800 Ma,主要集中在2 600～2 400 Ma之间(约占67%),年龄主峰值为2 550～2 500 Ma,说明其沉积物质主要来源于新太古代末以及古元古代的地质体。其中,最年轻锆石的207Pb/206Pb谐和年龄值分别为1 817±22 Ma、1 838±23 Ma、1 924±17 Ma和1 829±28 Ma,说明汝阳群沉积时代不老于1 800 Ma,与其上覆洛峪群中近期获得1 611±8 Ma的年龄相吻合,因此其形成时代应为中元古代早期。 相似文献
18.
云南武定迤纳厂铁铜矿岩浆角砾岩LA-ICP-MS
锆石U-Pb年龄及其意义 总被引：5，自引：1，他引：4
康滇地区是中国西南地区重要的元古宙铁铜成矿带.该地区元古宙昆阳群中串珠状分布岩浆角砾岩,周边分布大量铁铜矿床.选取武定迤纳厂东方红矿段穿插斜切入迤纳厂组的岩浆角砾岩,挑选胶结物中的岩浆锆石进行LA-ICP-MS测年,得到复合岩浆锆石内核207pb/206pb年龄为2193Ma±8Ma,代表深部围岩原生锆石年龄;岩浆锆石或复合岩浆锆石边缘环带207Pb/206Pb年龄为1739Ma±13Ma,代表岩浆侵位年龄;下交点年龄为980Ma±11Ma,代表变质年龄.结合相关资料判断,迤纳厂组与上昆阳群、大红山群、河口群均为1.7Ga左右昆阳板内裂谷拉张、岩浆侵位/喷发的同时异相产物.这对在滇中地区昆阳裂谷中,元古宙地层内的岩浆角砾岩周边寻找IOCG(IRON-OXIDE-COPPER-GOLD,铁氧化物-铜-金)型铁铜矿具有重要的启示. 相似文献