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1.
Summary K–Ar and Ar–Ar whole rock and mineral ages are presented for 25 samples of metamorphic rocks from the Mid-Bosnian Schist Mts., representing one of the largest allochthonous Palaeozoic terranes incorporated within the Internal Dinarides. Four main age groups can be distinguished: 1) Variscan (343Ma), 2) post-Variscan (288–238Ma), 3) Early Cretaceous (mainly 121–92Ma), and 4) Eocene (59–35Ma) ages. Apart from this, an Oligocene (31Ma) age was obtained on Alpine vein hyalophane. The radiometric dating indicates a polyphase metamorphic evolution of the Palaeozoic formations and suggests a pre-Carboniferous age of the volcano-sedimentary protoliths, an Early Carboniferous age of Variscan metamorphism and deformation, post-Variscan volcanism, an Early Cretaceous metamorphic overprint related to out-of-sequence thrusting of the Palaeozoic complex, and an Eocene and Oligocene metamorphic overprint related to the main Alpine compressional deformation and subsequent strike-slip faulting, and uplift of the metamorphic core. Accordingly, the Mid-Bosnian Schist Mts. can be correlated in its multistage geodynamic evolution with some Palaeozoic tectonostratigraphic units from the Austroalpine domain in the Eastern Alps.Deceased  相似文献   

2.
In a reconnaissance study, we investigated the potential of γ-ray induced production of 38ArK from 39K for geochronological applications. For this purpose, various age monitors commonly in use for the established 40Ar/39Ar-method were co-irradiated for 60 h at 17.6 MeV maximum energy in the ELBE facility, Dresden-Rossendorf, Germany. Because the available energy was low, total production of 38ArK was depressed, leading to low J38-values of (2.1–4.1) × 10-6 and hence resulted in only minor 38Ar excess when compared with atmospheric 38Ar/36Ar ratios. In spite of these restrictions, ages of younger monitors could be reproduced within error, whereas older age reference materials showed discrepancies due to the low production rate. We observed Ca-derived contributions on 36Ar in analysed CaF2 reference materials, and calculated a limit for Ca-interference on 38ArCa of (38Ar/36Ar)Ca = 0.07 ± 0.03 (1s). In addition, we investigated a potential recoil redistribution of 38Ar by stepwise heating experiments, but could not quantify this further because of concurring processes. More work at higher photon energies is necessary to resolve other open issues, in particular the potential of utilising 40Ar/37Ar ratios for age determination and the possibility of 42Ar production from 44Ca, which would allow correction for Ca-interference reactions on other Ar isotopes. This would be a pre-requisite for dating extra-terrestrial rocks.  相似文献   

3.
Doklady Earth Sciences - The Ermakovo F–Be deposit, the largest Be deposit in Russia and one of the world’s largest deposits, is located in West Transbaikalia. The ores of the deposit...  相似文献   

4.
40Ar–39Ar geochronological studies carried out on the Khardung volcanics of Ladakh, India and our earlier Ar–Ar results from the volcanics of the Shyok suture along with the available geological and geochemical data provide good constraints for post-collision evolution of the Shyok suture zone. Whole-rock samples from the Shyok volcanics yielded disturbed age-spectra and we have demonstrated earlier that the youngest tectonic event in the Shyok suture zone responsible for the thermal disturbance of these samples is Karakoram fault activation at ～14 Ma. Contrastingly whole-rock samples from the Khardung volcanics, which are in tectonic contact with these Shyok volcanics, and are exposed in the form of thick rhyolitic and ignimbritic flows, yielded undisturbed age-spectra and good plateau-ages. The whole-rock plateau-ages of two rhyolite samples are 52.8 ± 0.9 and 56.4 ± 0.4 Ma. We interpret these ages to be the time and duration of emplacement of these volcanics over thickened margin of the continental crust, which appears to be coeval with the initiation of the collision between the Indian and Asian plate. The lesser extent of post-emplacement isotopic re-equilibration in these samples unlike the Shyok volcanics indicate that these samples were present in different tectonic settings, away from the Karakoram fault, at the time of deformation in the Shyok suture zone. We propose that the two volcanic belts of contrasting nature were brought together in juxtaposition by the Karakoram strike slip faulting at ～14 Ma.  相似文献   

5.
Doklady Earth Sciences - U–Pb and 40Ar/39Ar age data obtained for volcanic rocks of the Okhotsk–Chukotka Belt in the headwaters of the Malyi Anyui River (the vicinity of Kupol deposit)...  相似文献   

6.
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7.
Doklady Earth Sciences - The first data of U/Pb and 40Ar/39Ar dating of volcanogenic rocks of the Pre-Dzhugdzhur volcano-tectonic trough (PDVT) of the Okhotsk–Chukotka volcanogenic belt...  相似文献   

8.
Many studies have examined the Japan Sea basalts recovered during Ocean Drilling Program (ODP) Leg127/128. Of these, the 40Ar–39Ar dating undertaken is important in constraining the timing of the formation of the Japan Sea; however, the implications of their results do not appear to be fully appreciated by the geological community. In this paper, I reassess the 40Ar–39Ar age data of the basalts with reference to Nd–Sr isotopic data. The 40Ar–39Ar dating was performed on basalts somewhat enriched in large-ion lithophile elements and recovered from ODP Sites 794, 795 and the lower part of 797, yielding the plateau ages of 21.2–17.7 Ma. These basalts show the Nd–Sr isotopic signature of a moderately depleted mantle source (εNd: 0.6–6.9). In contrast, the basalts from the upper part of Site 797 have yet to be dated due to their low K content, although their Nd isotopic compositions are similar to that of MORB (εNd: 8.4–10.4). By analogy to the secular Nd–Sr isotopic trends reported for Sikhote-Alin and northeast Japan, the age of the upper basalts at Site 797 may be inferred to be younger than the lower basalts, probably around 16 Ma. The Nd–Sr isotopic compositions of the Japan Sea basalts have been interpreted in terms of eastward asthenospheric flow, as have the lavas of the Sikhote-Alin and northeastern Japan. The timing of volcanic activity in the Japan Sea region (i.e., from 21.2 to 14.86 Ma) is consistent with the timing of rotational crustal movements inferred from paleomagnetic studies of the Japanese Islands (i.e., 14.8–4.2 Ma for southwest Japan and 16.5–14.4 Ma for northeast Japan).  相似文献   

9.
Doklady Earth Sciences - Our investigations have made it possible to estimate the age of hydrothermal ore metasomatic rocks at the Burinda Au–Ag deposit, one of the best known in East Asia,...  相似文献   

10.
Doklady Earth Sciences - A first set of K–Ar isotopic ages obtained, which allowed to estimate the age of the largest volcanoes of the Anaunsky Dol (3.2, 2.2 and 1.9 Ma) and eruptive centers...  相似文献   

11.
Doklady Earth Sciences - An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X22340013  相似文献   

12.
Four samples of plagioclase and biotite from the Shaxi porphyry in the lower part of the Yangtze metallogenic belt were analyzed for age determination with the 40Ar/39Ar method. The results yield reproducible ages of 126 Ma to 135 Ma with a high level of confidence according to the agreement between isochron and plateau ages. The four Ar-Ar ages are relatively consistent within the analytical error. These ages are also consistent with, but more precise than, previous K-Ar and Rb-Sr ages and thus provide better constraints on the time of porphyry formation and associated Cu-Au mineralization along the middle to lower part of the Yangtze metaliogenic belt. The ages of 126 to 135 Ma are interpreted to represent the intrusive time of the Shaxi porphyry, so that the Cu-Au mineralization should have occurred later due to the post-magmatic hydrothermal event.  相似文献   

13.

40Ar‐39Ar age spectra on minerals from granitic, metamorphic and hydrothermal rocks confirm that the Early Proterozoic Tennant Creek Block was affected by two thermal events during its evolution. Although extensive alteration of biotite and feldspar within the granites precludes the direct determination of their cooling history, 40Ar‐39Ar analyses for hydrothermal muscovite from several nearby gold‐copper deposits indicate that regional cooling to below ～ 300°C was not prolonged. Flat, uniform muscovite age spectra were obtained from gold deposits east of the Tennant Creek town site and indicate a minimum age of 1825–1830 Ma for their formation. These ages are within error of those for the felsic volcanism of the Flynn Subgroup, and a genetic relationship between the two may exist. Samples from gold deposits elsewhere in the area indicate disturbance of the K‐Ar isotope system. The second thermal event to affect the region occurred at around 1700 Ma, and is confirmed by the 40Ar‐39Ar muscovite ages for the ‘Warrego’ granite (1677 ± 4 Ma) and for the metamorphism of the Wundirgi Formation (1696 ± 4 Ma).  相似文献   

14.
Three metapelite samples from the Aksu blueschist terrane, Xinjiang, China, were dated by the 40Ar/39Ar method on separated phengite grains, obtaining plateau ages in the range of 741−757 Ma. In contrast, the measured Rb and Sr isotope data for the three samples yielded isochron ages ranging from 630 Ma to 900 Ma, suggesting large heterogeneity in the blueschist protolith and suppression of diffusional exchange owing to the low-temperature metamorphic conditions. Because the protolith of Aksu blueschist is composed of oceanic materials that formed 40Ar-free phengite during HP and UHP metamorphism and the apparent 40Ar/39Ar plateaus ages in this study are similar to previous K–Ar and Rb–Sr ages, the existence of excess argon in these rocks is considered to be insignificant. As a result, the 40Ar/39Ar plateau ages in this study (ca. 750 Ma) likely represent the approximate time for peak metamorphism, given the low peak metamorphic temperatures for the Aksu blueschist terrane (300−400 °C). This strongly implies that modern style, cold subduction tectonics operated along the margin of the Aksu terrane no later than 750 Ma, in Neoproterozoic time.  相似文献   

15.
Silurian, Devonian and Carboniferous geological bodies in the Mianxian-Lüeyang (Mian-Lüe) collisional belt (MLB) and its neighbouring areas, southern Qinling Mountains, China, show similar characteristics of having undergone deformation of two stages. The earlier one, which is inferred to be related to collisional orogeny between the Yangtze and Sino-Korean palaeocontinents based on previous geological data, is responsible for large-scale, north-verging recumbent folds and overthrusts, and associated with low greenschist facies metamorphism. 40Ar/39Ar dating of three muscovite samples taken from different localities yields plateau ages of 226.9(0.9 and 219.5(1.4 Ma and an apparent age of 194.5(3.0 Ma. Thus, the late Triassic collision between the Yangtze and Sino-Korean palaeocontinents has been constrained.  相似文献   

16.
Silurian, Devonian and Carboniferous geological bodies in the Mianxian-Lüeyang (Mian-Lüe) collisional belt (MLB) and its neighbouring areas, southern Qinling Mountains, China, show similar characteristics of having undergone deformation of two stages. The earlier one, which is inferred to be related to collisional orogeny between the Yangtze and Sino-Korean palaeocontinents based on previous geological data, is responsible for large-scale, north-verging recumbent folds and overthrusts, and associated with low greenschist facies metamorphism. 40Ar/39Ar dating of three muscovite samples taken from different localities yields plateau ages of 226.9(0.9 and 219.5(1.4 Ma and an apparent age of 194.5(3.0 Ma. Thus, the late Triassic collision between the Yangtze and Sino-Korean palaeocontinents has been constrained.  相似文献   

17.
Located along the southern part of the Yarlung Zangbo suture zone in southern Tibet, Bangbu is one of the largest gold deposits in Tibet. Auriferous sulfide-bearing quartz veins are controlled by second- or third-order brittle fractures associated with the regional Qusong–Cuogu–Zhemulang brittle-ductile shear zone. Fluid inclusion studies show that the auriferous quartz contains aqueous inclusions, two-phase and three-phase CO2-bearing inclusions, and pure gaseous hydrocarbon inclusions. The CO2-bearing inclusions have salinities of 2.2–9.5% NaCleq, and homogenization temperatures (Th) of 167–336 °C. The δD, δ18O, and δ13C compositions of the Bangbu ore-forming fluids are − 105.5 to − 44.4‰, 4.7 to 9.0‰ and − 5.1 to − 2.2‰, respectively, indicating that the ore-forming fluid is mainly of metamorphic origin, with also a mantle-derived contribution. The 3He/4He ratio of the ore-forming fluids is 0.174 to 1.010 Ra, and 40Ar/36Ar ranges from 311.9 to 1724.9. Calculations indicate that the percentage of mantle-derived He in fluid inclusions from Bangbu is 2.7–16.7%. These geochemical features are similar to those of most orogenic gold deposits. Dating by 40Ar/39Ar of hydrothermal sericite collected from auriferous quartz veins at Bangbu yielded a plateau age of 44.8 ± 1.0 Ma, with normal and inverse isochronal ages of 43.6 ± 3.2 Ma and 44 ± 3 Ma, respectively. This indicates that the gold mineralization was contemporaneous with the main collisional stage between India and Eurasia along the Yarlung Zangbo suture, which resulted in the development of near-vertical lithospheric shear zones. A deep metamorphic fluid was channeled upward along the shear zone, mixing with a mantle fluid. The mixed fluids migrated into the brittle structures along the shear zone and precipitated gold, sulfides, and quartz because of declining temperature and pressure or fluid immiscibility. The Bangbu is a large-scale Cenozoic syn-collisional orogenic gold deposit  相似文献   

18.
Doklady Earth Sciences - The original and published geochronological data and the geological position of different granitoid complexes of the Main (Kolyma) Batholith Belt of Northeast Asia have...  相似文献   

19.
K–Ar dating of mineral separates extracted from various granitoid rock units of the eastern Pontides and central Anatolia, Turkey, has provided some new insights unravelling various stages of the Neo-Tethyan convergence system, which evolved with northward subduction between the Eurasian plate (EP) to the north and the Tauride-Anatolide platform (TAP) to the south along the İzmir-Ankara-Erzincan suture (IAES) zone. Arc-related granitoid rocks are only encountered in the eastern Pontides and yield K–Ar cooling ages of both Early Cretaceous (138.5 ± 2.2 Ma) (early arc), and Late Cretaceous, ranging from 75.7 ± 0.0 to 66.5 ± 1.5 Ma (mature arc), respectively. The multi-sourced granitoids of the eastern Pontides, with a predominant mantle component and K–Ar ages between 40 and 50 Ma, are considered to be a part of post-collisional slab break-off magmatism accompanied by tectonic denudation of pre-Late Cretaceous granitoid rocks following juxtaposition of the EP and the TAP around 55–50 Ma in the eastern Pontides. The K–Ar cooling ages of collision-related S-, I- and A-type granitoids in central Anatolia reflect good synchronism between 80 and 65 Ma, suggesting a coeval genesis in a unique geodynamic setting but with derivation from various sources—namely, purely crustal, purely mantle and/or of mixed origin. This sort of simultaneous generation model for these S-I-A-type intrusives seems to be consistent with a post-collisional lithospheric detachment related geodynamic setting. I-type granodioritic to tonalitic intrusives with K–Ar cooling ages ranging from 40 to 48 Ma in east-central Anatolia are interpreted to have been derived from a post-collisional, within-plate, extension-related geodynamic setting following the amalgamation of the EP and the TAP in east-central Anatolia.  相似文献   

20.
The Awulale iron metallogenic belt (AIMB) hosts the majority of rich iron ores in Tianshan Orogen and has attracted much attention. However, a hot debate exists about the genesis of these iron deposits. Geochronological data are among the few critical evidences to solve the dispute. This study chooses the Beizhan iron deposit to carry out a geochronological research. The Beizhan magnetite deposit, with total iron ore reserves of 468 Mt at an average grade of 41% TFe, is the largest iron deposit in the AIMB. The orebodies of the Beizhan deposit are hosted in Carboniferous dacite and crystal tuff. Four stages of mineral formation can be recognized: an early skarn mineral stage, followed by the magnetite stage, the sulphide stage, and the carbonate stage in order. Pyrite separated from pyrite-rich ore samples yields an isochron age of 302.5 ± 8.2 Ma. Muscovite separated from muscovite-rich ore samples yields 40Ar/39Ar plateau ages of 304.7 ± 1.8 Ma, 304.5 ± 1.9 Ma, 308.1 ± 1.9 Ma, and 307.2 ± 1.8 Ma, and isochron ages of 306.1 ± 3.5Ma, 304.0 ± 3.0Ma, 308.2 ± 3.1Ma, and 308.7 ± 3.1Ma, respectively. These ages are consistent within the error range and are interpreted as the age of the Beizhan iron deposit. The results, combined with the other latest precise dating and geologically inferred ages, demonstrate that the iron deposits in the AIMB were formed in the Late Carboniferous. These iron deposits are considered to be iron skarn or medium–low -temperature hydrothermal origin and have genetic linkages between each other. They may be different mineralizing manifestations proximal to or distal from a pluton. The Late Carboniferous iron ores and the related magmatic rocks in the AIMB were produced when upwelling of the asthenosphere causes the partial melting of various sources and the formation of a narrow linear extension in the upper crust. The upwelling of the asthenosphere may be triggered by the detachment of an orogenic root zone.  相似文献   

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