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应用~(40)Ar/~(39)Ar定年技术研究清原花岗岩-绿岩地体的形成时代 总被引:8,自引:1,他引:8
辽宁清原绿岩地层自下而上分为榆树底组、红透山组和南天门组。小莱河铁矿区榆树底组斜长角闪岩岩石化学性质和稀土元素分布曲线表明,该岩石的原岩属太古代亏损型(DAT)拉斑玄武岩。此斜长角闪岩中的角闪石的两个~(40)Ar/~(39)Ar年龄谱给出该岩石的变质作用发生在29.9亿年。清原绿岩地层形成时代可能在30亿年或稍早一些。全球范围绿岩地层的年龄是35—19亿年,峰值是27亿年.清原绿岩地层的早期形成年龄则大于全球绿岩的峰值年龄。 相似文献
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前言 多年来,在辽东地区的老变质岩中相继发现了铜-锌矿床和矿化点四十余处,其中,工业价值最大的为红透山铜矿。它是我国典型的深变质块状硫化物矿床,赋存于太古界鞍山群的黑云角闪斜长片麻岩中。同位素年龄为27.70亿年(Pb_(206)~Pb_(207)法)~28.84亿年(Rb~Sr法)。 红透山地区在区域变质过程中产生了两次大的褶皱。第一次形成了展布较宽的东西 相似文献
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前 言 多年来,在辽东地区的老变质岩中相继发现了铜-锌矿床和矿化点四十余处,其中,工业价值最大的为红透山铜矿。它是我国典型的深变质块状硫化物矿床,赋存于太古界鞍山群的黑云角闪斜长片麻岩中。同位素年龄为27.70亿年(Pb_(206)~Pb_(207)法)~28.84亿年(Rb~Sr法)。 相似文献
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斗南锰矿为一质量兼优的工业锰矿床.目前国内海相沉积锰矿床矿石相多为单一碳酸锰矿相,本矿床为原生氧化锰与原生碳酸锰混生的过渡型矿相.这里说的所谓过渡型矿相的概念,不仅包含沉积成因,也包括受变质成因的含义.笔者把产于中三迭统法郎组中的锰矿床暂名为"斗南式"锰矿.兹以斗南锰矿为例,叙述如下.矿床基本特征1.锰矿成矿时期及层位(1)本矿床含锰地层时代为中三迭世晚期(拉丁尼克期):①含锰岩系产于上三 相似文献
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虽然苏鲁变质带北部的超高压变质岩石的类型及其特征与大别山超高压带相似,但是要划出与大别山相对应的岩石构造单元是困难的。详细的区域地质、岩石学、同位素年代学及地球化学的研究已将超高压带的西界大致圈定在牟平断裂至米山断裂的范围内。特别需要提出的是,在荣成超高压变质岩石分布区的南北两侧,出露有3 种不同成因的麻粒岩,即榴辉岩化的麻粒岩;由超高压变质岩经高压升温变质作用生成的麻粒岩;以及未经过榴辉岩相变质的麻粒岩。它们有规律地成带分布。这些麻粒岩带以及在荣成地区出露的未经过麻粒岩相叠加变质的超高压变质带,各自都有着完全不同的变质历史,并且都以深大韧性剪切带为其边界。由此笔者将苏鲁变质带北部由南向北划分为海阳所变质地块(榴辉岩化扬子陆块基底变质单元)、荣成变质地块(超高压变质单元)、威海变质地块(麻粒岩相叠加变质的超高压构造岩片)、昆嵛山边界杂岩带。这些来源于地壳深层的结晶块体是超高压带形成和演化的产物,在后来的进一步碰撞挤压中,这些来源于深层而就位于中上地壳水平的结晶块体,有可能发生了与薄皮构造机制(thin-skin thrust)类似的构造过程。它们有如一系列的推覆体挤压叠置,使华北和华南陆块最后挤压在一起。 相似文献
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华北克拉通北部的怀安杂岩中分布着一些呈团块状、透镜状或似层状产出的含BIF岩石组合.相对于华北克拉通绿岩带,研究区内的含BIF岩石组合具有规模小、岩性复杂多样以及后期叠加强烈的变质-变形改造等特点,其研究程度较低.在野外地质填图的基础上,通过岩石学、同位素年代学、地球化学研究表明:(1)天镇-怀安地区的含BIF岩石组合主要由条带状(含辉石/角闪)磁铁石英岩、变质基性火山岩(二辉麻粒岩/含辉石斜长角闪岩/高压麻粒岩)、石榴黑云斜长片麻岩和少量石榴石英岩条带或团块组成,这些岩石彼此呈夹层或互层状伴生产出;天镇-怀安地区BIF矿体规模小、与变质火山岩密切共生等特征表明其属于Algoma型.(2)条带状(含辉石/角闪)磁铁石英岩中残留的中-基性火成岩锆石年龄(2 489±19 Ma)可代表含BIF岩石组合的形成时代,并经历了1 800~1 850 Ma变质作用叠加改造.(3)含BIF岩石组合中火山岩地球化学特征显示Rb、Ba、U、Pb等元素富集和Nb、Ta等元素亏损,结合微量元素蛛网图和稀土配分模式对比认为其产出构造背景为弧后盆地,铁矿石PAAS标准化稀土配分图解具有明显Eu正异常,表明与海底热液活动密切相关. 相似文献
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本文通过某些矿物之间的转化及成分的变化,研究变质反应的状态。将区内麻粒岩相变质作用划分为四个阶段,并依据变质作用演化过程中的温度、压力的变化推定了PT_t轨迹。 相似文献
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黄旗地区处于中朝准地台东部、胶辽台隆之营口-宽甸台拱南东端.研究区为辽东早前寒武纪地质构造分区东部,主要出露中生代岩浆杂岩和古元古代岩浆岩及地层,古元古代辽河群广泛发育.主要变质岩类型可划分为:片岩、变粒岩、浅粒岩、长石石英岩、钙硅酸岩及大理岩.研究区辽河群变质岩岩石化学特征为:1)硅酸盐类岩石SiO2平均含量为47.32%~78.6%,总体K2O>Na2;2)碳酸盐类岩石总体CaO>MgO,总的特征是富钙、镁.辽河群各类变质岩微量元素含量相似度较高,F、Rb含量高,浓度克拉克值较大.辽河群变质岩的稀土元素特征为:ΣREE平均值为205.9×10-6,LREE/HREE平均值为12.8,δEu平均值为0.56;稀土分布图谱属右缓倾斜型,轻稀土分异较重稀土分异好,属于轻稀土富集型,具负铕和弱负铈异常.结合区域内辽河群原岩建造特点,可推断在古元古代时期研究区属地槽型大地构造环境,反映了辽河群地层整体上构成了一个较完整的火山-沉积建造序列. 相似文献
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变质锆石成因的岩相学研究——高级变质岩U-Pb年龄解释的基本依据 总被引:50,自引:3,他引:50
岩相学在研究高级变质岩 (含深熔片麻岩 )的锆石中起着重要的作用 ,其内容主要包括锆石的形貌和表面特征 ,锆石在岩石中的赋存状态 ,与主晶的关系和内部结构等方面。基于大别山地区的一些榴辉岩相岩石、麻粒岩相岩石和片麻状花岗质岩石中锆石的研究 ,阐述了继承锆石、变质锆石、深熔锆石、变质增生、深熔增生和后期流体改造的基本岩相学特征。结合大别山地区的 4个实例 ,说明了高级变质岩中锆石的岩相学研究方法和步骤 ,并初步提出了高级变质岩锆石U -Pb年龄解释的岩相学标志。 相似文献
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Rocks of the Windmill Islands, Antarctica (Lat. 66°S, Long. 110°E) consist of a layered sequence of schists, gneisses, and migmatites (the Windmill Metamorphics) intruded by a charnockite (the Ardery Charnockite) and a porphyritic granite (the Ford Granite), and cut by two swarms of easterly‐trending dolerite dykes. The rocks have undergone four deformations. The first two produced tight isoclinal folds, the third developed broader less appressed concentric folds, and the last deformation produced gentle warps which plunge steeply southwards. The metamorphic grade of the Windmill Metamorphics ranges from (i) upper amphibolite facies (sillimanite‐biotite‐orthoclase) in the north, through (ii) biotite‐cordierite‐almandine granulite to (iii) hornblende‐orthopyroxene‐granulite in the south. The boundary between (i) and (ii) above is marked by the incoming ortho‐pyroxene and also the outgoing of sphene, and that between (ii) and (iii) by the outgoing of cordierite. Other metamorphic variations, apparent in the field are (i), the southward colour change of biotite (sepia—>red‐brown) and hornblende (blue‐green—>brown‐green) and (ii) the greater abundance of migmatites and pegmatites in the north of the area. Major‐element rock chemistry suggests that the pre‐metamorphic nature of the schists and gneisses probably consisted of acid and basic volcanics interbedded with sediments ranging from greywacke‐type sandstones to shales. Partial melting of these rocks is thought to have produced some of the more acidic gneisses of the area. The abundances of the elements K, Rb, and Th are lower than those of terrains of similar grade elsewhere. This is regarded as reflecting original rock composition. The ratios K/Rb, Th/K, and K/(Rb/Sr), however, are comparable with those from similar terrains elsewhere where K, Rb, and Th enrichment by crustal fractionation has been suggested. This suggests that the Windmill Metamorphics were not derived by retrogression from upper granulite‐facies rocks. 相似文献
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通过二道沟金矿区火山—侵入杂岩、构造、矿床的研究,认为成矿与早白垩世斑状花岗间长岩同源;矿脉与岩脉、爆破岩伴生,时空关系密切;结合矿石、矿物、测温资料,确认二道沟金矿为岩浆中温热液金矿床。 相似文献
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北秦岭造山带的早古生代多期变质作用 总被引:2,自引:13,他引:2
北秦岭造山带的秦岭岩群以高级变质岩石为特征,主要包括少量榴辉岩、高压麻粒岩和区域上广泛分布的麻粒岩-角闪岩相变质岩石。年代学研究显示秦岭岩群中不同岩石记录了多期变质作用。已有的定年资料给出北秦岭官坡地区的榴辉岩的年龄为500Ma左右,代表榴辉岩相的变质时代。结合岩相学资料,对两个高压麻粒岩样品的SHRIMP和LA-ICPMS U-Pb测定分别获得504±7Ma 和506±3Ma的年龄,应代表高压麻粒岩相变质时代。这表明高压麻粒岩和相邻的榴辉岩有相近的变质时代,但形成在造山带中不同的构热造环境中。西峡地区的角闪二辉麻粒岩的U-Pb定年给出两组早古生代年龄,一组为440±2Ma,可能代表了中低压麻粒岩相的变质时代,另一组为426±1Ma,应代表区域角闪岩相的变质时代。桐柏山北部的石榴二辉麻粒岩的U-Pb定年数据给出436±1Ma的年龄,为中压麻粒岩相的变质时代。这些资料表明北秦岭造山带经历了早奥陶世的俯冲和地壳增厚作用,并在晚志留世遭受了广泛的巴罗式区域变质作用。 相似文献
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《China Geology》2018,1(1):137-157
The development of metamorphic petrology to metamorphic geology in China has a long history. Ancient basement metamorphic rocks are distributed primarily in the North China Craton, the Yangtze Block and Tarim Craton. They are mainly made up of plutonic gneiss and metamorphosed supercrust rock, transformed to granulite facies through Archean Paleoproterozoic. Many of the Paleoproterozoic metamorphic rocks have undergone high-pressure granulite facies metamorphism with a clockwise metamorphic evolution path. The ultrahigh temperature (UHT) granulites from the Late Paleoproterozoic are found in North China Craton. Many high-precision chronological data have allowed preliminary construction of the formation and evolutionary framework of different metamorphic basements. Primarily there are low-temperature and high-pressure blue schist, high-temperature and high-pressure granulite and ultrahigh-pressure (UHP) eclogite facies metamorphic rocks in the Phanerozoic orogenic belt. The discovery of eclogite in the Sulu orogen and a large quantity of coesite in its country rocks show that there was a deep subduction of voluminous continental materials during the collision process between the Yangtze block and the North China Craton in the Early Mesozoic phase. From the studies of, for instance, organic matter vitrinite reflectance, illite crystallinity, illite (muscovite) polytype and illite (muscovite) b dimension, the Late Paleozoic strata in the eastern region of Inner Mongolia and the north-central region of NE China have only experienced diagenesis to an extremely low-grade metamorphism. The discovery of impact-metamorphosed rocks in Xiuyan area of Liaoning province has enriched the type and category of metamorphic rocks in China. The phase equilibrium method has been widely used in the study of metamorphism of middle and high-grade metamorphic rocks. On the basis of existing geologic surveys and monographic study results, different scholars have respectively compiled 1:1500000 Metamorphic Geological Map and Specifications of Qinghai Tibet Plateau and its Adjacent Areas, 1:2500000 Metamorphic Tectonic Map of China, and the 1:5000000 Metamorphic Geological Map and Specifications of China, among others repectively, which have systematically summarized the research results of metamorphic petrology and metamorphic geology in China. 相似文献