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1.
A. B. Vrevskii 《Petrology》2016,24(6):527-542
New data are reported on U-Pb (SHRIMP-II) age (2662 ± 7 Ma), isotope (Sm-Nd) and geochemical compositions of the anorthosites of the Patchemvarek Massif and “ovoidal” anorthosite sills of the Neoarchean Kolmozero-Voron’ya greenstone belt. Mesoarchean (2938 ± 8 Ma) zircons found in the Patchemvarek anorthosite have low Th/U ratio, are overgrown by a thin rim, and may be interpreted as xenogenic crystals assimilated by primary melts of the gabbro-anorthosite massifs from host Mesoarchean tonalites during crystallization in a magmatic chamber. The “ovoidal” anorthosite sills are dated at 2730–2740 Ma on the basis of U-Pb local zircon isotope analysis. The sills of the “ovoidal” anorthosites in the Kolmozero-Voron’ya GSB represent the older (2730–2740 Ma) rock group, which differs from the Patchemvarek anorthosites in strongly depleted Nd isotope composition and some geochemical features. In terms of age and Sm-Nd isotope characteristics, the “ovoidal” anorthosites are close to the komatiites of the lower volcanogenic sequence (εNd(Т) + 3.0–3.2), and metaandesites (2778 ± 5.4 Ma, U-Pb TIMS, εNdТ + 3.5) and metatholeiites of the upper volcanogenic sequence (εNd(Т) + 3.5–3.7) of the supracrustal complex of the Kolmozero-Voron’ya GSB. 相似文献
2.
朝鲜半岛平南盆地中元古代岩浆事件 总被引：4，自引：2，他引：2
朝鲜平南盆地翁津地区发育中元古代黄海群和同时期(称之为瓮津期)花岗岩,花岗岩体侵入于黄海群。本文采用锆石原位微区U-Pb定年技术,对黄海群中的酸性火山岩及花岗岩进行了年龄测试。获得的数据表明,黄海群中下部层位及上部层位的酸性火山岩分别在1235±5Ma和1203±7Ma喷发,由此说明黄海群的沉积时代应为中元古代,而不是传统上认为的古元古代;两个翁津期花岗岩体(翁津和黄衣山岩体)的侵位年龄分别为1251±22Ma和1248±13Ma,为中元古代花岗质岩浆活动的产物。上述1251~1203Ma年龄的获得,表明朝鲜半岛发育中元古代岩浆作用,从而明确朝鲜黄海裂谷与华北东缘裂谷在时间上具有同期性,同时也表明中国华北与朝鲜在中元古代具有类似的发展历史。 相似文献
3.
Metabasites (amphibolites, garnet amphibolites, and basic crystalline schists) compose numerous sheeted bodies (often highly boudined) from a few to 100 meters thick in the plagiogneisses and migmatites of the Kolpakov Group. Chemically, they are reconstructed as basalts and picrites that were metamorphosed, as host terrigenous rocks, under the kyanite-sillimanite subfacies of the amphibolite facies (t = 620–650°C, P s = 5.9–6.9 kbar). Metabasites are dominated by amphibolites and basic crystalline schists distributed throughout the entire section of the Kolpakov Group, whereas garnet amphibolites are more typical of the upper parts of the group, where they are intercalated with amphibolites, basic crystalline schists, plagiogneisses, and quartzites. Metaultrabasites (plagioclase-free amphibolites) occur much more rarely as small boudins up to few meters in size. According to U-Pb SHRIMP zircon dating, the plagiogneiss protolith age corresponds to the end of the Early-Late Cretaceous (90–100 Ma), which is similar in age to the weakly metamorphosed terrigenous deposits of the Kikhchik Group of the Sredinny Range. This allows us to consider the terrigenous rocks of these groups as isofacial sedimentary rocks. The same age (Early-Late Cretaceous boundary) was taken for protoliths of metabasites forming interbeds among metaterrigenous deposits of the Kolpakov Group. The interval of 100?90 Ma coincides with the beginning of the formation of the Okhotsk-Chukotka volcanogenic marginal-continental belt in East Asia. It is shown that the Kolpakov Group possesses the geochemical features of tholeiitic basalts of different geodynamic settings and comprises both typically island arc (low-Ti) and oceanic (moderate to high-Ti) tholeiites associated with ultrabasic volcanic rocks—picrites. Such a chemical peculiarity of basic rocks is typical of the marginal-continental extension zones (pull-apart basin) that were initiated on the sialic crust. It is obvious that similar geodynamic setting of the basite magmatism existed for the Sredinny Range of Kamchatka. The ascent of the mantle matter beneath the extension zone of the continental crust of the sedimentary basin and its intersection by faults that formed simultaneously with the Okhotsk-Chukotka volcanogenic belt served as the beginning of the basite volcanism in the sedimentary basin. They provided an intense fluid effect and a temperature increase in the crust with subsequent granitization and metamorphism of volcanogenic-terrigenous deposits and, finally, the development of the modern structure of the Sredinny Kamchatka Massif. The intense Late Cretaceous basite volcanism and associated granitoid magmatism in Kamchatka were presumably caused by the ascent of mantle plumes bearing hydrogen fluids. 相似文献
4.
T. B. Rusakova 《Russian Journal of Pacific Geology》2011,5(5):418-432
The paper deals with new data on the geology, geochronometry, and petrogeochemistry of the Upper Jurassic-Neocomian basaltic
andesites constituting the base of the Cretaceous volcanogenic section in the northern Okhotsk region. The geochronometric
data confirm the Late Jurassic-Neocomian age of these rocks (147–138 Ma, K-Ar method). Their characteristic features provide
grounds for considering these rocks as fragments of the Uda volcanic belt. The comparison of the petrogeochemical characteristics
with similar parameters of other different-age tectonic structures of the region under consideration that were formed in different
geodynamic environments (intracontiental and continental marginal volcanogenic belts, island arcs) revealed similarity between
the conditions of the formation of the Late Jurassic-Neocomian (Uda belt) and Albian-Cenomanian (Okhotsk-Chukotka belt) volcanics:
both characterize continental marginal environments. It is assumed that the Late Jurassic-Neocomian volcanism associates with
Au-Ag mineralization, which is also expected in other similar although poorly known volcanic structures. 相似文献
5.
针对泽当西郊贡巴日北坡剖面罗布莎群砾岩下部厚约15m的火山岩夹层进行锆石定年,测试结果表明,该火山岩LA-ICP-MS 锆石U-Pb年龄为18.7±0.2Ma,罗布莎群下伏花岗岩LA-ICP-MS锆石 U-Pb年龄为29.9±0.4Ma。据此认为,罗布莎群砾岩初始沉积时代约为20Ma前。火山岩的出现表明,中新世布尔迪加尔期罗布莎群发育一期火山活动,结合前人研究认为,沿雅鲁藏布江结合带的狭长范围内自西向东发育一期火山活动,代表雅鲁藏布江缝合带的一次活化,其时空分布特征与冈底斯带中新世钾质—超钾质火山活动具有显著的相似性。 相似文献
6.
江西相山铀矿田如意亭剖面火山岩的年代学格架及其地质意义 总被引：10，自引：5，他引：5
江西相山铀矿田如意亭剖面最底部的熔结凝灰岩代表了相山火山-侵入活动的开始时间,本文首次报导了该熔结凝灰岩的LA-ICP-MS锆石U-Pb定年结果,得出其形成年龄为137.3±0.9Ma,表明相山火山-侵入活动开始于早白垩世。此外,对如意亭剖面的两个流纹英安岩样品的锆石U-Pb定年结果分别是136.8±2.5Ma和136.4±1.5Ma,对采自如意亭剖面的流纹英安斑岩的锆石U-Pb定年结果是135.0±2.0Ma,对采自如意亭剖面的碎斑熔岩的定年结果是134.1±1.6Ma,这些定年结果结合前人已有的研究,得出相山火山-侵入杂岩的形成时代集中在135Ma左右（137~132Ma）,再次证实了相山火山-侵入活动始于早白垩世,是一次集中且短暂的火山-侵入活动。本文对如意亭剖面的定年结果证实相山地区打鼓顶组和鹅湖岭组的火山岩地层应属于早白垩世。然而赣杭构造带上原先所划分的打鼓顶组与鹅湖岭组火山岩形成的时间与武夷山北坡冷水坑盆地中火山岩系并不相同,因此,打鼓顶组与鹅湖岭组地层在区域上应予重新厘定。 相似文献
7.
8.
伊勒呼里山中生代火山岩:锆石U-Pb年代学及其对岩浆事件的制约 总被引：3，自引：0，他引：3
伊勒呼里山地区中生代火山岩由安山岩、粗面英安岩、流纹岩、流纹质凝灰岩和流纹质玻屑凝灰岩等组成。中生代火山岩中的锆石多呈半自形-自形晶,振荡环带发育,Th/U值略高（0.30~2.56）,为岩浆成因。锆石U-Pb同位素年代学研究表明：塔木兰沟组安山岩年龄为（161.0±1.0）Ma（n=22）,形成于中侏罗世;满克头鄂博组流纹岩年龄为（157.8±2.3）Ma（n=24）,形成时代属于晚侏罗世;玛尼吐组火山岩2个样品的年龄分别为（154.0±2.0）Ma（n=23）和（151.7±1.4）Ma（n=25）,形成时代属于晚侏罗世;白音高老组火山岩2个样品的年龄分别为（124.1±1.1）Ma（n=25）和（125.1±0.7）Ma（n=23）,形成时代为早白垩世。捕获锆石的定年结果显示,本区存在前寒武纪岩浆事件（774 Ma）、加里东期岩浆事件（472 Ma）、印支期岩浆事件（214、210 Ma）,这与周边基底岩石中锆石U-Pb的定年结果相吻合。 相似文献
9.
L. F. Mishin 《Russian Journal of Pacific Geology》2013,7(1):16-25
The Sizindzha hypabyssal intrusive massif located in the Kuidusun volcanic zone of the Okhotsk-Chukotka volcanic belt has been mapped and studied in detail. The complex of textural-petrographic features indicates the in situ formation of granitoids by the successive replacement of the host sedimentary rocks of the Verkhoyansk Complex and the medium-grained diorites (more rarely, gabbro) by later granites. It was established that the oldest fine-grained intermediate rocks observed as xenoliths in all the granitoids are in situ relicts of the molten substrate. 相似文献
10.
Petrological, geochemical, and isotope geochronological aspects of the evolution of calc-alkaline magmatism were investigated
in the Western Okhotsk flank zone, the Okhotsk segment, and the Eastern Chukchi flank zone of the Okhotsk-Chukotka volcanic
belt (OCVB). The OCVB is a tectonotype of continental margin volcanic belts comprising much greater volumes of felsic ignimbritic
volcanics compared with mature island arcs (MIA, Kuril-Kamchatka and Aleutian) and the Andean continental margin. The volcanic
rocks of continental margin volcanic belts (OCVB and Andean belt) are enriched in K, Ti, and P compared with the rocks of
MIA and show a trend toward the field of high-potassium calc-alkaline series. Primitive andesite varieties (Mg# > 0.6) were
not yet found in the OCVB, but there are relatively calcic varieties unknown in Andean-type structures and a significant fraction
of moderately alkaline rocks, which are not typical of MIA. Variations in trace and major element characteristics in the basalts
and andesites of the OCVB were interpreted as reflecting the competing processes of assimilation/mixing and fractional crystallization
during the evolution of the parental basaltic magma. Significant lateral variations were established in the composition of
the mantle sources of calc-alkaline magmas along the OCVB over more than 2500 km. The initial isotopic ratios of Sr, Nd, and
Pb in the volcanics of the Okhotsk segment are relatively depleted and fall near the mixing line between PREMA and BSE. The
magma source of the Western Okhotsk flank zone is most enriched and approaches EMI, whereas that of the central and eastern
Chukchi zones contains an admixture of the EMII component. The geochronological characteristics of all the main stages of
OCVB magmatism were comprehensively studied by U-Pb SHRIMP and ID-TIMS zircon dating (86 samples) and 40Ar/39Ar analysis (73 samples). In general, a discontinuous character was established for the OCVB magmatism from the middle Albian
to the early Campanian (106–77 Ma). The volcanism is laterally asynchronous. There are several peaks of volcanism with modes
at approximately 105, 100, 96, 92.5, 87, 82, and 77 Ma. The Coniacian-Santonian peaks correspond to the most extensive stages
of the middle and late cycles of felsic volcanism. A decreases and a hiatus in magmatic activity were reconstructed for the
end of the Cenomanian and the beginning of the Turonian. The volcanism was terminated by plateau basalts with ages of 76–78
Ma, which mark a change in the geodynamic setting from frontal subduction to the regime of a transform margin with local extension
in zones normal to the slip direction. A catastrophic character of eruptions with rather narrow ranges of volcanism (<2 Myr)
were established taking into account new reliable age estimates for some individual large calderas. The accumulation rate
of volcanic materials in such structures was up to 0.15–0.36 km3/yr and even higher. 相似文献
11.
12.
R. I. Mil’kevich T. A. Myskova V. A. Glebovitsky A. B. L’vov N. G. Berezhnaya 《Geochemistry International》2007,45(5):428-450
New geochemical data on volcanic rocks and the first U-Pb zircon ages for the Kalikorva structure made it possible to determine the time and conditions of their formation and constrain geodynamic models. The lower sequences of the Kalikorva structure is dominated by metatholeiites with high MgO, Cr, and Ni contents, high Mg#, and REE distribution patterns close to the mantle level. They contain rare komatiite interlayers and lenses of pyroxenites and peridotites and can be considered as products of the deep melting of mantle material. At the same time, the tholeiitic metabasalts bear island-arc signatures and are intercalated with metagraywackes and metadacites (adakites). This rock association could be formed under spreading conditions at the beginning of an island-arc regime. The upper sequence is dominated by metagraywackes and contains diverse rocks with both MORB (tholeiitic and komatiitic basalts) and island-arc (calc-alkaline andesite and dacites, subalkaline basalts, and picritic basalts) affinity, which is typical of back-arc basins. The U-Pb dating of zircons from the metadacites and detrital zircons from the metagraywackes of the Kalikorva structure yielded similar ages of 2785 ± 13 and 2766 ± 21 Ma, respectively. They coincide with the age of the late volcanic complex of the Hisovaara Group of the Hisovaara structure (2780 Ma). Both complexes include island-arc associations with subduction signatures and contain adakites, Nb-Ti basalts, and basaltic andesites. The metagraywackes and metadacites of the Chupa sequence of the Belomorian mobile belt are older than the similar rocks of the Kalikorva complex and have an age of 2870 ± 30 Ma. Ages of 2735 ± 20 Ma and 2720 ± 4 Ma were previously obtained for the metaandesites of the Kichany volcanogenic complex, which could be an even younger volcanic arc. 相似文献
13.
岗岔金矿是在西秦岭西段北缘发现的中型金矿床,有潜力达到大型。该金矿目前发现的5条金矿脉明显受断裂控制,赋矿围岩浅部主要是一套火山岩和火山碎屑岩。该套火山岩长期以来被认为是侏罗系郎木寺组。采用锆石U-Pb法对其中的凝灰岩进行定年测试,结果显示年龄为(245±2) Ma,说明该火山岩不是侏罗系而应该属于三叠系。矿区内与金矿脉空间关系密切的花岗闪长岩和石英闪长岩锆石U-Pb定年结果显示,二者年龄也分别为(242±2) Ma和(246±3) Ma。这说明矿区内侵入体与赋矿围岩属于近乎同时代(印支期)岩浆活动的产物。上述测年结果进一步限定了岗岔金矿形成时间为三叠纪早期,即构造岩浆活动之期后的热液期。该结论为深入认识矿床成因、总结成矿规律和指导勘查方向提供了新的依据。 相似文献
14.
A. A. Sorokin A. B. Kotov E. B. Sal’nikova N. M. Kudryashov V. P. Kovach 《Stratigraphy and Geological Correlation》2007,15(3):241-257
Magmatic rocks of the Pikan and Un’ya massifs situated in eastern segment of the Mongolian-Okhotsk foldbelt are studied using isotopic-geochronological (U-Pb zircon dating) and geochemical methods. Two rock complexes different in age are recognized in the Pikan massif: the high-Al gabbro-tonalite association of the Middle Ordovician (468 ± Ma) and granodiorite-granite association of the Late Silurian-Early Devonian (415 ± 7 Ma). The Late Ordovician age (454 ± 5 Ma) is established for leucocratic granites of the Un’ya massif. As is suggested, the Pikan and Un’ya massifs are “allogenic blocks” detached from continental framework of the Mongolian-Okhotsk foldbelt and tectonically emplaced into the foldbelt structure at the last stage of its development. 相似文献
15.
三江造山带兰坪盆地东缘火山岩锆石U-Pb年代学、Hf同位素组成 总被引：5，自引：5，他引：0
青藏高原东南缘"三江"复合造山带南、北两段发育若干火山-岩浆岩带,随着火山岩年代学、地球化学数据的积累,其时空关系渐趋清晰。但由于中-新生界沉积覆盖,这些火山岩带向南常终止于兰坪盆地附近,致使火山岩时空构架不明。兰坪盆地东部弥沙地区出露盆地基底岩石,由两个构造层组成,上部为碎屑岩及生物碎屑灰岩,下部出现大量火山碎屑物质。含火山岩段出露厚约150m,可分为三个喷发-沉积韵律,由流纹质熔结凝灰岩、晶屑岩屑熔结凝灰岩组成的火山碎屑岩与紫红、灰黑色泥岩、大理岩组成的沉积岩相间组成。火山岩锆石LA-ICP-MS U-Pb数据表明,岩浆活动始于或早于258Ma,一直持续到248Ma。锆石原位Lu-Hf分析结果显示,早期岩浆包含较多幔源物质,而晚期岩浆则几乎完全由古老地壳局部熔融形成。本文提供的新数据表明,兰坪盆地东缘火山岩与三江造山带其它地区古特提斯洋俯冲阶段火山岩具有一致的年代学组成、相同的Hf同位素变化规律,可能属于发育在扬子板块西缘之上江达-维西-云县弧火山岩带。 相似文献
16.
相山火山盆地主体岩石为一套由熔结凝灰岩、流纹英安岩、流纹英安斑岩、碎斑熔岩、粗斑花岗斑岩及似斑状花岗岩组成的酸性火山-侵入杂岩体, 构成了两个完整的喷发-溢流(侵出)-侵入的岩浆活动亚旋回。本文在野外地质调查的基础上, 采用SIMS、LA-ICP-MS技术对主要岩类进行了高精度的锆石U-Pb年代学研究, 并建立了火山-侵入杂岩体的演化序列。结果表明, 打鼓顶组熔结凝灰岩代表了相山火山-侵入活动的最早期产物, 其锆石U-Pb年龄为140.7±2.7 Ma、140.1±1.8 Ma和138.2±1.6 Ma, 第一亚旋回主体流纹英安岩的锆石U-Pb年龄135.0±1.8 Ma。鹅湖岭组熔结凝灰岩代表了火山-侵入活动的第二亚旋回的开始, 其U-Pb年龄为135.6±1.2 Ma, 第二亚旋回主体碎斑熔岩的锆石U-Pb年龄133.6±1.3 Ma, 沙洲单元的粗斑花岗斑岩和似斑状花岗岩属于该亚旋回最晚期的侵入岩, 其锆石U-Pb年龄代表了相山火山-侵入活动的结束时间(分别为133.4±1.2 Ma和133.9±1.1 Ma)。相山早白垩世火山-侵入活动延续时间较短, 整体上呈现一个连续的过程, 初始时间在141 Ma附近, 结束时间在132 Ma左右。概言之, 第一亚旋回(141~135 Ma)以形成熔结凝灰岩、流纹英安岩和流纹英安斑岩为主, 第二亚旋回(135~132 Ma)以熔结凝灰岩、碎斑熔岩、粗斑花岗斑岩和似斑状花岗岩为主。岩石地球化学和野外地质特征也与两个亚旋回火山-侵入岩浆活动相吻合。 相似文献
17.
Central Fujian Rift is another new and important volcanogenic massive sulfide Pb-Znpolymetallic metailogenetic belt. In order to find out the material genesis and mineralization period ofMeixian-type Pb-Zn-Ag deposits, S and Pb isotope analysis and isotope geochronology of ores and wallrocks for five major deposits are discussed. It is concluded that the composition of sulfur isotope fromsulfide ore vary slightly in different deposits and the mean value is close to zero with the δ34S rangingfrom -3.5‰ to 5.6‰ averaging at 2.0‰, which indicates that the sulfur might originate from magmaor possibly erupted directly from volcano or was leached from ore-hosted volcanic rock. The lead fromores in most deposits displays radioactive genesis character (206Pb/204Pb>18.140, 207Tb/204Pb>15.584,208Pb/204Pb>38.569) and lead isotope values of ores are higher than those of wall rocks, which indicatesthat the lead was likely leached from the ore-hosted volcanic rocks. Based on isotope data, twosignificant Pb-Zn metallogenesis are delineated, which are Mid- and Late-Proterozoic sedimentaryexhalative metallogenesis (The single zircon U-Pb, Sm-Nd isochronal and Ar-Ar dating ages of ore-hosted wall rocks are calculated to be among 933-1788 Ma.) and Yanshanian magmatic hydrothermalsuperimposed and alternated metallogenesis (intrusive SHRIMP zircon U-Pb and Rb-Sr isochronalages between 127-154 Ma). 相似文献
18.
New data on the structure and composition of the rock complexes making up the Otrozhnaya sheet of the Ust-Belaya Terrane are discussed. This sheet is currently regarded as a complete section of the Early Devonian oceanic crust. The U-Pb age of zircon (547 ± 17 Ma) from plagiogranite porphyry that cuts through the ultramafic-gabbroic complex indicates that the country rocks are much older. Basalts of volcanic complex are similar to MORB-type rocks. The contact between volcanic and volcano-sedimentary complexes is tectonic. No volcanic-cherty association of rocks typical of ophiolites has been established at the base of the sedimentary sequence. The U-Pb age of detrital zircons from the base of this section is 571 Ma. As follows from the composition of terrigenous rocks and the suprasubduction origin of andesitic lavas and tuffs, the rocks of the lower part of volcano-sedimentary complex were deposited at the marginal part of the basin near convergent boundary. The remains of conodont elements make it possible to estimate the age of the upper part of the volcano-sedimentary complex as Late Devonian. The composition of terrigenous rocks shows that the provenance has abruptly changed. Sporadic rock fragments evidence the erosion of ophiolitic sections. Silurian rocks became the main source of clastic material. This is corroborated by redeposited microfauna species and U-Pb age of detrital zircons (～432 Ma). The geochemistry of dacite pebbles from conglomerate indicates that this volcanic rock was formed in a suprasuduction setting. The Ordovician-Silurian island arc could have been a source. 相似文献
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内蒙古达茂旗花岗岩类LA—ICP—MS锆石U—Pb年龄及其地质意义 总被引：1，自引：0，他引：1
对内蒙古达茂旗北部构造单元的巴特敖包岛弧带2个花岗闪长岩岩体样品和南部构造单元一个花岗岩岩体的2件样品进行了LA—ICP-MS锆石u—Pb定年。北部构造单元采自2个花岗闪长岩岩体的样品锆石^206Pb／^238U年龄分别为468Ma±2Ma和452Ma±2Ma,代表了这2个岩体的侵位时间,表明古亚洲洋向华北克拉通之下俯冲不晚于468Ma±2Ma;南部构造单元采自同一花岗岩岩体的2件样品获得的锆石~pb／z38U年龄分别为268Ma±2Ma和264Ma±2Ma,和该单元西部岩体已有的锆石年龄相符。这为华北克拉通北缘岩浆作用研究提供了新的年代学证据。 相似文献