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1.
1 Introduction The Kuda ophiolite occurred in the western Kunlun Mountains, which lies about the intersection of longitude 77°10′ E and latitude 36°45′ N (Figs. 1, 2). The upper portion of the ophiolite mainly consists of a thick layer of basaltic pillow lavas, which was well exposed along the high way from Xinjiang Uygur Autonomous Region to the western Tibetan Plateau, and the middle-lower part, the mafic-ultramafic cumulates and upper mantle rocks occur at the top of the mountain n…  相似文献   

2.
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   

3.
Summary Zircon typology and ages together with petrological data suggest similarities in the origin of the K–Mg-rich granitoids of the Mecsek Mountains (Mórágy Unit, Tisia Terrane, S Hungary) and the durbachitic to K–Mg-rich rocks of the South and Central Bohemian Batholiths. Our investigations evidence a characteristic bimodal distribution of zircon types and ages. Zircons of normal magmatic habit and a typology around S24 show an age of 354±5Ma. Zircons of tabular habit of subtype S4 indicate a possibly younger age of 339±10Ma. The ages and typology of zircons from plutonic rocks in the Mecsek Mountains strongly resemble those from the Rastenberg granodiorite in the South Bohemian Batholith (Austria). This, as well as Rb/Sr and Sm/Nd isotope systematics, support the assumption of simultaneous formation and close spatial relationship between the Mecsek Mountain granitoids and the Rastenberg granodiorite. Thus, the Mecsek Mountains granitoids likely formed in a Late Palaeozoic palaeo-position S or SSW of the Rastenberg granodiorite. Having experienced a similar metamorphic and magmatic evolution during the Carboniferous, at least the northernmost part of the Tisia Terrane, the Mórágy Unit, is therefore considered to represent a former part of the Helvetic-Moldanubian zone.  相似文献   

4.
International Journal of Earth Sciences - The Tisza Megaunit in the Southern Pannonian Basin formed part of the southern margin of the European Plate in the Early Mesozoic era. Its exact...  相似文献   

5.
Detailed zircon analyses were carried out on samples from the Bálvány North section, which contains the Permian–Triassic boundary. A fine-grained sandstone bed within the “boundary shale” contains a significant amount of zircon crystals. Pupin morphological, scanning electron microscopy [secondary electron, back-scattered electron, cathodoluminescence (CL)] and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) investigations were done in selected single grains to combine morphological information with radiometric ages, and infer the provenance of zircons. Three populations are distinguished on the basis of Pupin morphology. Their centres of gravity are S17, S2 and P1. The LA-ICP-MS radiometric ages reveal three main age groups and a smaller one, apart from a few scattered old ages. The largest group, comprising ca. 50% of the measured grains, has an age of 470–440 Ma. The two other main groups, which together represent ca. 25% of the measured grains, are around 280 and 600 Ma. The 280 Ma group contains slightly more grains than the 600 Ma group. A small group has an age of 370–340 Ma. In addition, there are some older grains with ages of 850, 969, 1,050 and 2,150 Ma. Based on the zircon morphology no clear separation of the different age groups could be made. Both the 280 Ma and the 470–440 Ma age groups tend to show zircon crystals derived from three types of sources: crustal granites, calc-alkaline granitoids and alkali granites and/or their volcanic equivalents. Zircons in the 450 Ma group have a magmatic rim around their altered, relict core, as revealed by CL images. Post-magmatic processes also affected the rim. The age of the core is possibly reset during the formation of the magmatic rim. This suggestion is supported by the LA-ICP-MS data, because no difference was seen between the core and the rim. The different roundness of the zircons, the well-sorted crystals and the at least five different source rocks indicate previous concentration of the grains, before their transportation into the “boundary shale”. Austroalpine and Southern Alpine rocks could be the sources of the zircon crystals, which fit well into the paleogeographical model of the area, which suggests that the Bükk Mts. was located in the foreground of the Alpine units.  相似文献   

6.
Summary ¶Igneous quartz of the late-Variscan topaz-bearing granites from the Hub Stock (Slavkovský Les, Czech Republic) was investigated by cathodoluminescence (CL) and electron probe micro-analysis (EPMA) to demonstrate the intra-granular heterogeneity of growth patterns and trace element distribution in quartz. We show that EPMA is well suited for the in situ study of Al and Ti in zoned quartz, because of its high spatial resolution down to 5µm in conjunction with the ability to combine spot analyses with CL imaging. In the quartz phenocrysts of the topaz granites high Ti is associated with blue luminescent growth zones. High Ti (>40ppm) in quartz indicates a high crystallisation temperature and pressure. The groundmass quartz of the granites which is almost free of Ti, has higher Al than the phenocrysts which may reflect an increase of lithophile elements and water content in melt during the late magmatic stage. The occurrence of similar quartz phenocrysts in most of the late-Variscan granites and rhyolites of the Kruné Hory/Erzgebirge which intruded over a period of about 40Ma points to a similar crystallisation environment and origin of the quartz phenocrysts in the lower to middle crust.Received November 6, 2001; revised version accepted January 30, 2003 Published online June 2, 2003  相似文献   

7.
Summary The crystalline basement rocks of the Sopron Mountains are the easternmost and most isolated outcrops of the Austroalpine basement of the Eastern Alps. Ar/Ar and K/Ar dating of phengitic mica indicates that the Eoalpine high-pressure metamorphism of the area occurred between 76 and 71Ma. Short-lived metamorphism is characterised by fluid-poor conditions. Fluid circulation was mostly restricted to shear zones, thus the degree of Alpine overprint has an extreme spatial variation. In several metamorphic slices Variscan mineral assemblages have been preserved and biotite yielded Variscan and Permo-Triassic Ar ages. Different mineral and isotope thermometers (literature data) yielded temperatures of 500–600°C for the peak of Alpine metamorphism in the Sopron Mountains, but muscovite and biotite do not show complete argon resetting. Thus, we consider this crystalline area as a well constrained natural test site, which either indicates considerably high closure temperatures (around 550°C) for Ar in muscovite and biotite in a dry metamorphic environment, or which is suitable for testing the widely applied methods of temperature estimations under disequilibrium conditions.Apatite fission track results and their thermal modeling, together with structural, mineralogical and sedimentological observations, allows the identification of a post-metamorphic, Eocene hydrothermal event and Late Miocene-Pliocene sediment burial of the crystalline rocks of the Sopron Mountains.  相似文献   

8.
Upper Tithonian–Berriasian pelagic carbonates in the Central Western Carpathians, Tatra Mts (southern Poland), with well-established bio- and magnetostratigraphy, provide excellent possibilities of testing magnetic and geochemical methods as proxies of palaeoenvironmental changes in the Western Tethys at the Jurassic/Cretaceous boundary. Magnetic susceptibility (MS), field spectral gamma-ray (GRS) as well as CaCO3, total organic carbon (TOC), and elemental analyzes were performed in the Pośrednie III section. MS reveals very good negative correlation with CaCO3 content as well as positive correlation with Al, Zr, Ti and other lithogenic elements and therefore it might be interpreted as a proxy of a detrital input into the basin. Abrupt MS variations correlate well with relative sea-level changes and indicate regressive intervals (MS highs) in the upper Tithonian/lowermost Berriasian (M20r to M19n2n) and upper Berriasian (M16n) and transgressive interval (MS low) in the lower to middle Berriasian (M18r to M17r). Long-term MS variations might be linked to a palaeoclimatic-controlled enhanced continental runoff. Geochemical data (P, Th/U, Mn, Cd, Ni, Mo and TOC content) point to a productivity increase and a slight oxygen deficiency in the lower and middle Berriasian, which corresponds to MS low values and typical calpionellid limestone sedimentation. Timing of major palaeoenvironmental turnovers might be correlated also with general palaeoclimatic trends in the Western Tethys and Western Europe: cooling in the late Tithonian followed by a temperature increase throughout the Berriasian and an important humidity increase in the middle Berriasian (M17n).  相似文献   

9.
A combination of four thermochronometers [zircon fission track (ZFT), zircon (U–Th)/He (ZHe), apatite fission track (AFT) and apatite (U–Th–[Sm])/He (AHe) dating methods] applied to a valley to ridge transect is used to resolve the issues of metamorphic, exhumation and topographic evolution of the Nízke Tatry Mts. in the Western Carpathians. The ZFT ages of 132.1 ± 8.3, 155.1 ± 12.9, 146.8 ± 8.6 and 144.9 ± 11.0 Ma show that Variscan crystalline basement of the Nízke Tatry Mts. was heated to temperatures >210°C during the Mesozoic and experienced a low-grade Alpine metamorphic overprint. ZHe and AFT ages, clustering at ~55–40 and ~45–40 Ma, respectively, revealed a rapid Eocene cooling event, documenting erosional and/or tectonic exhumation related to the collapse of the Carpathian orogenic wedge. This is the first evidence that exhumation of crystalline cores in the Western Carpathians took place in the Eocene and not in the Cretaceous as traditionally believed. Bimodal AFT length distributions, Early Miocene AHe ages and thermal modelling results suggest that the samples were heated to temperatures of ~55–90°C during Oligocene–Miocene times. This thermal event may be related either to the Oligocene/Miocene sedimentary burial, or Miocene magmatic activity and increased heat flow. This finding supports the concept of thermal instability of the Carpathian crystalline bodies during the post-Eocene period.  相似文献   

10.
The Krkonoše-Jizera Massif in the northern part of the Variscan Bohemian Massif provides insight into the exhumation mechanisms for subducted continental crust. The studied region exposes a relatively large portion of a flat-lying subduction-related complex that extends approximately 50 km away from the paleosuture. wide extent of HP-LT metamorphism has been confirmed by new P-T estimates indicating temperatures of 400–450 °C at 14–16 kbar and 450–520 °C at 14–18 kbar for the easternmost and westernmost parts of the studied area, respectively. A detailed study of metamorphic assemblages associated with individual deformation fabrics together with analysis of quartz deformation microstructures and textures allowed characterisation of the observed deformation structures in terms of their subduction-exhumation memory. An integration of the lithostratigraphic, metamorphic and structural data documents a subduction of distal and proximal parts of the Saxothuringian passive margin to high-pressure conditions and their subsequent exhumation during two distinct stages. The initial stage of exhumation has an adiabatic character interpreted as the buoyancy driven return of continental material from the subduction channel resulting in underplating and progressive nappe stacking at the base of the Teplá-Barrandian upper plate. With the transition from continental subduction to continental collision during later stages of the convergence, the underplated high-pressure rocks were further exhumed due to shortening in the accretionary wedge. This shortening is associated with the formation of large-scale recumbent forced folds extending across the entire studied area.  相似文献   

11.
Zircon and xenotime, from two mineralogically and chemically contrasting granite suites occurring in the Kru?né Hory/Erzgebirge Mts., display extended compositional variability with respect to abundances of Zr, Hf, REE, Y, P, Th, Ca, Al, Fe and As. According to their geochemical signatures, P-rich (S-type) and P-poor (A-type) granites could be distinguished here. Both granite suites display high Ga/Al ratios (>2.6) and according to FeOtot./(FeOtot. + MgO) ratio can be classified as ferrous granites. Consequently, the both ratios cannot be used for discrimination S- and A-type granites. Both minerals are characterized by a variety of complex zircon-xenotime textures. They are usually strong hydrated and enriched in F. Zircon from P-rich granites displays a significant enrichment in P (up 0.24 apfu P), whereas zircon from P-poor granites has lower P and higher Y (up to 0.15 apfu Y). The xenotime-type substitution is the most important mechanism of isomorphic substitution in zircon in both granite suites. Zircon from both granite suites is typically enriched in Hf, especially unaltered zircon from P-rich granites (up to 8.2 wt. % HfO2). However in altered zircons the Hf/Zr ratio is higher in the P-poor granites. The Hf-rich zircon from unaltered P-rich granite crystallised from low temperature granite melt, whereas altered zircons crystallised during post-magmatic hydrothermal alteration (greisenization). Xenotime from P-poor granites displays a considerable enrichment in HREE (up to 40 mol. % HREEPO4) compared to xenotime from P-rich granites (up to 20 mol. % HREEPO4). Xenotime compositions from P-rich granites are influenced by brabantite-type substitution, whereas for xenotime from P-poor granites the huttonite-type substitution is dominant. Unusual enrichments in HREE is significant for xenotime from P-poor granites, especially in Yb (up to 0.17 apfu Yb) and Dy (up to 0.11 apfu).  相似文献   

12.
The low-grade metavolcanic/volcanosedimentary complex of the Devonian Vrbno Group (Silesicum, NE Bohemian Massif, Czech Republic) occurs in two ~NE–SW trending belts, separated by tectonic slices of Cadomian metagranitic paraautochton. (1) The basic–intermediate lavas of the calc-alkaline Western Volcanic Belt came from a moderately depleted mantle $ \left( {\varepsilon_{\text{Nd}}^{370} \sim + 3} \right) $ . Rare rhyolites (374.0 ± 1.7 Ma: 2σ, LA–ICP–MS U–Pb Zrn) were derived most likely from immature crust or by extensive fractionation of primary basaltic melts. The rock association is interpreted as a vestige of a deeply dissected continental arc. (2) The Eastern Volcanic Belt consists mainly of (nearly) contemporaneous (371.0 ± 1.4 Ma) felsic alkaline lavas with high HFSE contents, as well as high Ga/Al and Fe/Mg ratios, typical of within-plate igneous setting. The petrology and Nd–Sr isotopic data point to a high-T anatexis of a young metagranitic crust, resembling the Cadomian (Brunovistulian) basement, in a back-arc setting. The attenuated Brunovistulian lithosphere could have partially melted by the heat provided by the upwelling asthenosphere and/or underplating basic magma. (3) Finally, the region was penetrated by numerous subalkaline, MORB/EMORB-like dolerite sheets—a hallmark of the considerable crustal thinning.  相似文献   

13.
The aims of this study were to summarize current knowledge of a large runout prehistoric landslide, critically review all of the existing data and, in particular, gather new data in order to estimate the age of the accumulation and reveal the movement mechanism. The reconstruction of a large rockslide-rock avalanche in the NW part of the Czech Republic was supported by the analysis and interpretation of 216 boreholes and by GIS analysis of the original 1950s pre-mining surface using digitized old military topographic maps. For the age estimation, we used the Schmidt hammer test. The total volume of the quaternary deposit was calculated to be between 25.4 and 27.4 mil m3, occupying an area of 778,000 m2 and consisting of six to eight generations of colluvial sediments. Three main landslide events were identified based on extensive Schmidt hammer sampling, and the approximate age was established using a regression equation assembled by Engel (2007). All three of the documented events occurred around the time of significant climate change. The oldest event occurred due to the Oldest Dryas warming, the largest event probably occurred at the end of the Younger Dryas (11,700 yBP), and the youngest of the documented events was purely of a Holocene age, with the highest landslide frequency being during the Atlantic temperature fluctuations (approximately 8200 yBP). The slope deformation occurred on a fault slope with a relative height of over 400 m and in tectonically weakened rocks. Sediments in the Most Basin were weakened from meltwater during rapid warming periods, which allowed mobilization of rockslide deposits and runout of up to 1000 m from the mountain foothills.  相似文献   

14.
Since the coexistence of the Cretaceous and Palaeocene was ascertained in the Hengyang Basin of Hunan in the middle of the 1960's, the Cretaceous and Tertiary boundary has been discussed in several papers, but it still remains controversal. The points at issue are the connotation, stratigraphical position and lateral correlation of the Dongtang (or Chejiang) Formation.  相似文献   

15.
A simple mechanical model explaining the long-period (about 100-year) variations in the Earth’s rotational velocity is proposed. This model takes into account the gravitational interaction of the mantle with the solid core of the Earth and the fact that the core rotation leads that of the mantle. Well-known Earth parameters provide estimates of the gravitational torque that support the proposed model. The mathematical problem involved reduces to the classical problem of a nonlinear oscillator exposed to a constant torque. The well-known parameters of the core-mantle system result in a stable equilibrium and a stable limiting cycle on the phase cylinder of this oscillator. This equilibrium corresponds to a single angular velocity for the mantle and solid core, with no long-period oscillations in the length of the day. The limiting cycle corresponds to the core rotation leading the mantle rotation. In this case, the ellipsoidality of the gravitationally interacting bodies provides a periodic interchange of kinetic angular momentum between the mantle and solid core that results in long-period variations in the length of the day. The proposed model does not support the formerly widespread opinion that the core rotates more slowly than the mantle.  相似文献   

16.
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17.
The distribution of permafrost and taliks is very complex in the Tuotuo River Basin(TRB), which is located in interior of the Qinghai-Tibet Plateau. Characterizing the spatial distribution and the thermal stability of permafrost and taliks is of great significance to community activities and engineering construction in TRB. Based on the zonation of permafrost and talik distribution around TRB conducted in the 1980s, the soil temperature and its variation process of permafrost and taliks in the south and north banks of the Tuotuo River were analyzed by using the observation data of five boreholes(N1~N5)along the Qinghai-Tibet Railway in the north bank and five boreholes(S1~S5)on the first terrace in the south bank. The results showed that, under the climate warming, permafrost and taliks in the north banks experienced significant degradation and warming process. From 2005 to 2020, the permafrost at the N1 borehole has undergone a significant down-draw degradation process, from extremely unstable and high-temperature permafrost to thawed zone. From 2005 to 2013, the annual average ground temperature of the talik at N2 increased at a rate of 0. 3~0. 4 °C·(10a)-1. At Maqutang on the south bank, permafrost prevails from the first-class terrace to the gentle slope of the Kaixinling Mountain, with both through and non-through taliks on the first-class terrace. The spatial distribution and the thermal stability of permafrost and talik in the TRB are further promoted by analyzing the changes in temperatures at boreholes in the basin. However, to meet the requirements of mapping and engineering construction of permafrost and taliks in the TRB, it is still necessary to carry out geological investigation with multiple methods and in-depth research on development mechanism of taliks in the future. © 2022 Nanjing Forestry University. All rights reserved.  相似文献   

18.
Over the past two decades development has been shifting its focus toward smaller scales and particular problems. As a result, the household has become an increasingly important institution for development, and has come under increased scrunity as development practitioners and scholars seek to better understand this institution’s functions and foundations, trying to ‘get the household right’. These efforts, rather than clarifying the character and the function of the household, have contributed to its indeterminacy by reifying the very institution they seek to analyse. Arguing that these efforts fundamentally miss the point of examining the household, this paper introduces a different framework of analysis that addresses the household not as a fixed object of research, but as a local construction that embodies flows of power and knowledge both within and transcending the local. Using the example of varying constructions of the household in two villages in Ghana’s Central Region, this article illustrates how such an approach allows us to address the various functions of the household as particular embodiments of these flows, an approach that better explains the endurance or ephemerality of these functions. Such an approach provides a stronger foundation for the consideration of how particular constructions of this institution may have troubling implications for issues like gender equity and sustainability.  相似文献   

19.
A new approach, the fluid inclusion plane technique coupled with fluid inclusion microthermometry and field measurements have been applied to demonstrate the exhumation and relative vertical displacements of an allochthonous, Permian granite intrusion (Velence Mts.) which was situated in the Middle Triassic at the western end of the Neotethys rift system. The pressure and the temperature conditions during the Permian fluid flow (>350 °C and ∼2 kbar) in the granite were considerably higher than during the Triassic fluid flow (<250 °C and ∼0.5 kbar), which indicates the exhumation of the granite intrusion in a primarily extensional tectonic stress regime. The fluid inclusion planes with NE–SW and NW–SE strike prove stress field permutation that can be explained by the exhumation of the host granite during the Middle Triassic fluid flow.It is suggested that the exhumation of the Velence Mts. along with the regional fluid flow can be connected to the passive pre-rift phase of the northern Adriatic Block, during the Middle–Late Triassic. The variations in homogenization temperatures of Triassic regional fluid inclusion assemblages between the blocks of the granite, as well as variations in the fluid inclusion plane orientations, suggest a post-Triassic vertical segmentation and relative block rotation of the granite.  相似文献   

20.
The following determinations in the Norwegian fjord Framvaren and the Black Sea have been compared: carbon-14, carbon-13, alkalinity, total dissolved inorganic carbon, sulfide, tritium (HTO), trace metals, silica, ammonium and phosphate. The historical development of the two anoxic basins is quite different. The carbon-14 age of the total inorganic dissolved carbonate in the deep water is 2000 years in the Black Sea, but only 1600 in Framvaren. The fresh water supply and composition are different. The rivers entering the Black Sea have a high alkalinity, but the river input and runoff to Framvaren has a very low alkalinity. The alkalinity, carbonate and sulfide concentrations in the anoxic waters below the chemoclines are much higher in Framvaren. This is mainly an effect of the different surface to volume ratios. The difference in carbon-13 (-8 for the Black Sea deep water, -19 in the Framvaren bottom water) is mainly due to the smaller imprint of the decomposition of organic matter on the Black Sea deep water.The concentration of trace metals in the particulate form are about the same in the deep water. About 76% of the molybdate in seawater is lost in the sulfidic water of Framvaren, and about 82–96% of the molybdate carried into the Black Sea by the Bosporus undercurrent is lost in the deep water. The relation between silica, ammonium and phosphate can be understood if part of the ammonium is being removed by denitrification, a process that most likely has been going on for thousands of years.  相似文献   

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