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1.
M. I. Tuchkova G. E. Bondarenko M. I. Buyakaite D. I. Golovin I. O. Galuskina E. V. Pokrovskaya 《Geotectonics》2007,41(5):403-421
This paper presents the results of structural, lithologic, and geochronological (K-Ar, Rb-Sr) studies of the Carnian terrigenous rocks in the sedimentary cover of the Chukchi microcontinent and U-Pb dating of detrital zircons. From the lithological features, three types of sections are recognized. Terrigenous sequences of the first type were deposited on the outer shelf in the distal zone of the prograding delta, sequences of the second type accumulated at the rise of continental slope, and sediments of the third type are characteristic of the pelagic zone. In mineralogy and geochemistry, sandstones are rather uniform and inherit the sialic composition of provenance. The detrital zircons comprise several populations with predominance of the varieties derived from igneous rocks. The U-Pb age of the youngest population is 236–255 Ma. The conditions of postsedimentation alteration reached those of greenschist metamorphic facies and anchimetamorphism. Several cleavage systems have been established. Sericite related to the oldest system is distinguished by elevated Ti, Mn, and Fe components. The first stage of deformation of the Carnian sedimentary rocks about 200 Ma ago resulted in the rearrangement of K-Ar and Rb-Sr isotopic systems in whole-rock samples and minerals and is clearly recorded in isotopic data. It is suggested that the deformation related to the normal faulting in Triassic rocks and the emergence of the Lesser Anyui Block were plausible causes of the first structural rearrangement. 相似文献
2.
D. G. Brookins H. W. Fairbairn P. M. Hurley W. H. Pinson 《Contributions to Mineralogy and Petrology》1969,22(2):157-168
The pegmatites of Eastern Connecticut have a mineralogy consistent with a magmatic origin yet occur in a non-igneous environment. Various theories of genesis have been investigated by the Rb-Sr geochronologic method.Rb-Sr measurements on early stage pegmatite minerals indicate an age of 258±1 m.y. with initial Sr87/Sr86=0.734±0.0096. Previously reported K-Ar and U, Th-Pb ages for pegmatite minerals are 249±8 m.y. and 260±3 m.y. respectively. Rb-Sr whole rock data for the host rocks vary between 285±10 m.y. and 472±15 m.y. in age and between 0.705±002 and 0.7167±0.0016 in initial Sr87/Sr86. A direct genetic relationship between the pegmatites and their host rocks is thus precluded. In addition, whole rock samples of the Brimfield schist taken at variable distances from the Strickland Quarry pegmatite have remained essentially closed systems with respect to Rb and Sr and thus an in situ origin for this pegmatite is unlikely. Mixing of pegmatite and country rock systems has occurred only locally, and isotopic studies of these mixed rocks yield a date of 231±4 m.y. with initial Sr87/Sr86=0.7188±0.004, an age not inconsistent with previously reported K-Ar and Rb-Sr mineral dates on host rock minerals (approximately 220 to 240 m.y.).Late stage cleavelandites are anomalously enriched in radiogenic Sr-87, the source of which was most probably other zones within the crystallizing pegmatite. This is indicated by analyses of pegmatite whole rocks which show both enrichment and depletion of radiogenic Sr-87 in local systems. The conclusion is drawn that there was widespread movement of radiogenic Sr-87 within each pegmatite system, but that pegmatite-host rock reactions were minimal. 相似文献
3.
Reported in this paper are K-Ar ages of volcanic rocks, biotite-granite and greisen from the Lianhuashan tungsten mine in Guangdong Province. The isotopic dilution method was adopted in this work. Whole-rock isochron ages of the volcanic rocks are in the range 120.4±12.1 m.y. The petrogenetic age of biotite-granite and the minero genetic age of tungsten ore are close to those of the volcanic rocks. The apparent ages of various types of rock in the mining district generally bias towards younger values, which may be attributed to the effects of late thermal events which took place in the circum-Pacific metallogenetic belt. 相似文献
4.
The results of the K-Ar, Rb-Sr, and U-Pb (SHRIMP zircon method) dating of the Middle Paleozoic volcanogenic rocks of the Omolon
Massif are summarized. It was concluded that they are principally consistent with each other, as well as with the geological
data. The formation of the Kedon Group, which makes up the main volume of the Middle Paleozoic volcanics, began at the Early-Middle
Devonian boundary about 400 Ma ago (U-Pb dates of 400.5 ± 4.4 and 387 ± 6.4; Rb-Sr isochron age of 402 ± 6 Ma). The isotopic
age of the upper boundary of the Kedon Group remains unclear due to disagreements concerning its stratigraphic assignment.
The histogram based on the 111 K-Ar dates of the volcanic rocks from the Kedon Group gives a polymodal distribution, which
indicates that the K-Ar isotopic system was disturbed by thermal events, which occurred 310–290 (terminal Carboniferous—beginning
of the Permian) and 240–220 (Middle-beginning of the Late Triassic) Ma ago. Both thermal events were associated with mantle
(ultrabasic-basic) magmatism, which spanned a significantly wider territory than the distribution area of the Kedon Group 相似文献
5.
Abstract: K–Ar datings and oxygen isotope analyses revealed a cooling history of the Uchiyama granitic pluton, which is genetically related to the Pb-Zn deposits (Taishu mine) in the Tsushima Islands, Japan. The pluton intrudes into the Paleogene Taishu Group to form the biotite-hornfels zone, while the Taishu vein-type Pb–Zn deposits occur in fissures developed in the non-hornfels zone about 1 to 3 km westward from the contact. Amphibole and biotite K-Ar ages of the pluton have a wide range from 19 to 13 Ma. Oxygen isotopes of the biotite and coexisting quartz grains indicate that isotopic exchange reactions have occurred under subsolidus conditions, and that the K-Ar ages are affected by various cooling rates in the pluton. The mineralization age of the Taishu ore deposits is obtained for the first time to be 15.40.8 Ma by a K-Ar age of 2 M 1 –muscovite in a calcite–quartz–muscovite–chlorite veinlet of the Shintomi orebody. Whole rock K-Ar ages of biotite-hornfels near the pluton represent similar ages to the ore deposits. Using blocking temperature calculated from reported diffusivity for argon, the pluton was cooled from 560 to 350C in the period of 17 to 14 Ma. The vein formation took place after the time when temperature in wall rocks of the pluton had dropped below the brittle-plastic transition (about 400C). These results imply that the cooling of the pluton has caused injection of magmatic fluids into meteoric hydrothermal systems, and the Pb-Zn mineralization has occurred due to this mixing at the age of about 15 Ma. 相似文献
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V. I. Vinogradov M. I. Bujakaite D. I. Golovin Yu. V. Kushcheva Yu. A. Ivanov V. N. Teslenko O. I. Pashicheva 《Lithology and Mineral Resources》2009,44(2):174-182
Rb-Sr and K-Ar characteristics of Vendian and Upper Riphean sections in various structural units of the East European Platform are studied. It is shown that Neoproterozoic clayey rocks of the platform underwent postsedimentary transformations, primarily owing to processes of K accumulation (illitization). Their intensity decreases with depth and isotopic signatures of provenance rocks are partly retained in Riphean rocks. Stages of the most active transformations approximately 400 and 600 Ma ago are manifested in the Vendian clayey rocks. Events of approximately 1000 Ma ago are recorded in Riphean rocks of the East European Platform. The least altered rocks of the Pachelma aulacogen can retain ancient hydrocarbon pools. 相似文献
9.
Yu. O. Gavrilov Yu. V. Kushcheva I. V. Latysheva D. O. Gertsev 《Lithology and Mineral Resources》2012,47(6):473-490
The paper discusses changes in both mineral composition and structural-textural characteristics of the Jurassic terrigenous complex along the Avar Koisu River (Dagestan) profile that intersects rocks with significantly various types of deformation. The profile extends from the monoclinal zone to the intense deformation and cleavage development zone. The alterations are manifested in the change of clay mineral assemblages, polytype modifications of micaceous minerals and their crystallinity index, rock density, reflectance of vitrinite, and other properties. Growth of the degree of secondary alterations (primarily, cleavage intensity) is accompanied by an appreciable decrease in K-Ar age of rocks and simultaneous increase of their stratigraphic age. 相似文献
10.
冈底斯中段林子宗火山岩岩石地球化学特征 总被引:4,自引:0,他引:4
广泛发育在冈底斯岩浆岩带中的林子宗火山岩及其与下伏地层间的区域不整合提供了印度-亚洲大陆碰撞的重要证据.谢通门地区的林子宗火山岩早期以中基性-中性岩为主,夹少量流纹质凝灰岩,晚期以流纹质火山岩为主.岩石学和地球化学研究表明,这套火山岩早期以钙碱性为主,带有较多陆缘火山岩特征,中期开始出现标志陆内活动的钾玄岩,晚期更多地显示了加厚陆壳条件下火山岩的特点,记录了由新特提斯俯冲消减末期过渡到印度-亚洲大陆碰撞的信息.中基性岩浆来源于俯冲带的地幔源区,长英质岩浆形成于加厚地壳的部分熔融.结合区域同位素年龄资料,可以认为林子宗火山岩中高钾流纹质火山岩是印度-亚洲大陆碰撞阶段陆壳缩短加压升温引起部分熔融的产物. 相似文献
11.
内蒙古月牙山一带基性火山岩的地质特征、形成时代及归属 总被引:2,自引:2,他引:0
内蒙古月牙山一带出露一条基性火山岩带,呈北西西向带状展布,由层状玄武岩、枕状玄武岩和蚀变玄武岩组成,前人对该套火山岩的归属意见不同。该套火山岩分布于月牙山蛇绿质构造混杂岩带中部,空间上与月牙山蛇绿岩套紧密共生,枕状构造较发育,显示海底火山喷发的特征;岩石化学、地球化学研究表明,该套火山岩具有典型的正常洋中脊玄武岩(NMORB)特征。因此,月牙山基性火山岩属于月牙山蛇绿岩套的组成部分。在侵入该套火山岩的辉长闪长岩中获得了530Ma左右的同位素年龄,在辉长岩、斜长花岗岩中获得了527~530Ma的同位素年龄,相当于早寒武世,说明该套基性火山岩的形成时代为早寒武世。 相似文献
12.
Hidemi Tanaka Nobuo Uehara Tetsumaru Itaya 《Contributions to Mineralogy and Petrology》1995,120(2):150-158
This paper describes K-Ar ages of cataclasites and fault gouges from the Akaishi Tectonic Line (ATL), central Japan. Petrological and mineralogical features of these rocks are also examined. Based on the results, we test the hypothesis that the K-Ar ages of these rocks represent the age of hydrothermal alteration associated with the fault movement. Intensity of deformation and alteration increase passing from host rock into cataclasite and finally into fault gouge. This increase corresponds to an increase of the value of crystallinity index (Kübler index) of the micaceous minerals contained in these rocks. Furthermore, the degree of rejuvention of K-Ar ages of the micaceous minerals increases in the same sense. A correlation of K-Ar ages (plotted on the y axis) versus Kübler index (plotted on the x axis) yields a concave curve asymptotically parallel with the x axis at approximately 15 Ma. This curve is interpreted to represent the mode of decrease of the relative amounts of inherited argon in the K-Ar system of the micaceous minerals, corresponding to an increase in the intensity of deformation and alteration. Inclination of the curve becomes zero if all the inherited argon is lost from the K-Ar system of the micaceous minerals. Thus, it is concluded that the hydrothermal alteration occurred at approximately 15 Ma. The strike-slip basin along the ATL formed the middle Miocene. The K-Ar dating of ATL gouges indicates that the ATL was active simultaneously with formation of the strike-slip basin along its trace during the middle Miocene. 相似文献
13.
L. K. Levsky I. M. Morozova O. A. Levchenkov V. S. Baikova E. S. Bogomolov 《Geochemistry International》2009,47(3):215-230
Several isotopic methods (U-Pb, Sm-Nd, Rb-Sr, and K-Ar) were applied to different rock-forming and accessory minerals to decipher the chronology of events in a separate segment of the Belomorian mobile belt. Enderbites intruded supracrustal rocks at 2.73 Ga and granodiorites were emplaced at 2.41 Ga. Immediately afterwrads, a permeable schistosity zone was formed along the enderbite-granodiorite contact. Isotopic data indicate that this zone served as a pathway for heat and fluid. The retrograde stage of regional metamorphism and subsequent cooling continued from 1.89 Ga till ~ 1.46 Ga.The cooling rate of the Pon’goma Island rocks is similar to that of other Precambrian complexes and amounted to ~1.50/Ma, which is consistent with previous data on the northern segment of the Belomorian belt. Based on isotopic geochronological data, two tectonometamorphic scenarios can be proposed for the evolution of the Belomorian belt. The first scenario suggests long-term regional metamorphism, i.e., lengthy residence of the Archean and Lower Proterozoic rocks at a significant depth and high temperatures. Geochronological data for different systems (U-Pb, Sm-Nd, Rb-Sr, and K-Ar) suggest Caledonian hydrothermal cryptometamorphic processes. However the rocks of this age are absent from the study area. 相似文献
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湘东南汝城盆地火山岩的元素地球化学及源区性质讨论 总被引:12,自引:4,他引:12
湘东南汝城盆地火山岩系由辉绿岩、玄武岩和玄武质火山碎屑岩组成 ,属于低钾拉斑玄武岩系。玄武岩全岩K Ar年龄为 ( 12 8 4± 4 2 )Ma ,辉绿岩全岩K Ar年龄为 ( 112 1±3 2 )Ma。元素地球化学分析表明火山岩系具有同一岩浆源区 ,其形成以部分熔融方式为主。岩石微量元素出现大离子亲石元素Rb、Ba、Th、U的富集和高场强元素Ta、Nb、Ti的亏损。强不相容元素含量的比值表明岩浆源区明显偏离原始地幔组分 ,具有富集型地幔的特征。岩浆源区主要受到地壳物质混染以及来自消减残留板片析出流体的交代改造作用。 相似文献
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西藏崩纳藏布和甲岗雪山地区花岗岩的地球化学特征及成因初探 总被引:11,自引:0,他引:11
西藏申扎县崩纳藏布和甲岗雪山两个地区出露的岩浆岩体一直被认为是两个较大的花岗岩基,但实际地质调查表明,这两个岩体中的每一个都可以分解为多个不同岩性的小岩体,K—Ar同位素年龄表明,这些岩体主要形成于燕山晚期(90.55Ma-114.67Ma)和喜山早期(58.75Ma)。对其中部分岩体开展的微量元素、稀土元素以及Rb—Sr和Sm—Nd同位素的地球化学初步研究表明,两地出露的花岗岩体虽然形成于不同时代,但具有相同的以壳幔混合带为主的源区。另一方面.痕量元素的含量及同位素的组成特征也同时表明了形成于不同时期的岩体具有含量、配分、趋势变化等方面的差异,反映其具体的成因和分异演化过程并不相同。 相似文献
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S. A. Palandzhyan 《Geotectonics》2015,49(2):135-149
The Ust-Belaya ophiolite terrane in the West Koryak Orogen, which is the largest in northeastern Asia, consists of three nappe complexes. The upper Ust-Belaya Nappe is composed of a thick (>5 km) sheet of fertile peridotites and mafic rocks (remnants of the proto-Pacific lithosphere); its upper age boundary is marked by Late Neoproterozoic plagiogranites. In the middle Tolovka-Otrozhny Nappe, the Late Precambrian lherzolite-type ophiolites are supplemented by fragments of tectonically delaminated harzburgite-type ophiolites, which make up the Tolovka rock association. The isotopic age of metadacite (K-Ar method, whole-rock sample) and zircons from plagiogranite porphyry (U-Pb method, SHRIMP) determines the upper chronological limit of the Tolovka ophiolites as 262–265 Ma ago. It is suggested that igneous rocks of these ophiolites were generated in a backarc basin during the Early Carboniferous and then incorporated into the fold-nappe structure in the Mid-Permian. This was the future basement of the Koni-Taigonos arc, where the Early Carboniferous ophiolites together with Late Neoproterozoic precursors were subject to low-temperature metamorphism and intruded by plagiogranite porphyry dikes in Permian-Triassic. The polymicte serpentinite mélange, which was formed in the accretionary complex of the Koni-Taigonos arc comprises rock blocks of the upper units of Late Precambrian ophiolites (in particular, plagiogranite), the overlying Middle to Upper Devonian and Early Carboniferous deposits, as well as Early Carboniferous (?) Tolovka ophiolites and meta-ophiolites. Mélange of this type with inclusions of Late Precambrian “oceanic” granitoids also developed in the lower Utyosiki Nappe composed of Middle Jurassic-Lower Cretaceous sedimentary and volcanic sequences, the formation of which was related to the next Uda-Murgal island-arc systems. 相似文献
18.
Alexander Deutsch 《Contributions to Mineralogy and Petrology》1984,85(1):45-57
Fortyfive new K-Ar ages and Sr isotope data on amphiboles, biotites, clinopyroxenes and whole rock samples from subvolcanic dykes south of the Tauern Window establish, that alkalibasaltic dykes were intruded 30 m.y. ago and shoshonitic volcanism occured between 30 and 24 m.y. ago. Two calc-alkaline rocks of high-potassium composition yielded ages of 40 and 26 m.y. resp., a spread which may or may not be real. Calc-alkaline dykes with medium and low potassium contain excess argon and are hence undatable. Alkalibasaltic dykes have 87Sr/86Sr ratios of 0.7056–0.7070, shoshonitic rocks 0.7075–0.7133, potassium rich calc-alkaline dykes 0.7077–0.7100. 87Sr/86Sr of all other calc-alkaline rocks scatter between 0.7074 and 0.7150. Sr data indicate that dykes studied do not represent closed Sr systems, but that Sr characteristics result from selective strontium assimilation en route to surface. Primary Sr isotopic ratios of alkalibasaltic dykes point to an origin of these rocks in enriched sub-continental upper mantle. The source region of shoshonitic and high-potassium calcalkaline rocks could have 87Sr/86Sr around 0.707, which is assigned to the input of a component rich in alkalies, LREE and LIL elements. Genetic relationships with other Tertiary magmatites of similar geotectonic position are explained in terms of plate tectonic models of the Eastern Alps. 相似文献
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《Applied Geochemistry》2004,19(3):359-377
The Dakota aquifer of the central and eastern Great Plains of the United States is an important source of water for municipal supplies, irrigation and industrial use. Although the regional flow system can be characterized generally as east to northeasterly from the Rocky Mountains towards the Missouri River, locally the flow systems are hydrologically complex. This study uses Sr isotopic data from groundwater and leached aquifer samples to document the complex subsystems within the Dakota aquifer in Nebraska and Kansas. The interaction of groundwater with the geologic material through which it flows has created spatial patterns in the isotopic measurements that are related to: long-term water–rock interaction, during which varying degrees of isotopic equilibrium between water and rock has been achieved; and the alteration of NaCl fluids by water-rock interaction. Specifically, Sr isotopic data distinguish brines from Kansas and western Nebraska from those in eastern Nebraska: the former are interpreted to reflect interaction with Permian rocks, whereas the latter record interaction with Pennsylvanian rocks. The Sr isotopic composition of groundwater from other parts of Nebraska and Kansas are a function of the dynamic interaction between groundwater and unlithified sediments (e.g., glacial till and loess), followed by interaction with oxidized and unoxidized sediments within the Dakota Formation. This study illustrates the power of combining Sr chemistry with more conventional geochemical data to obtain a more complete understanding of groundwater flow systems within regional aquifer systems where extensive monitoring networks do not exist. 相似文献