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1.
Doklady Earth Sciences - Dikes of intermediate and felsic composition from the area of the Vyun deposit and the Shumnyi occurrence, both of which belong to the Yano–Kolyma gold belt...  相似文献   

2.
正Columbia(Nuna)is a Paleo-Mesoproterozoic supercontinent that was assembled during global 2.0–1.8Ga collisional events,underwent long-lived,subductionrelated accretion at key continental margins in the period  相似文献   

3.
The formation of the Vilyui rift system in the eastern Siberian Craton was finished with breakdown of the continent and formation of its eastern margin. A characteristic feature of this rift system is the radial distribution of dyke swarms of basic rocks. This peculiarity allows us to relate it to the breaking processes above the mantle plume, the center of which was located in the region overlain in the modern structure by the foreland of the Verkhoyan folded–thrust belt. The Chara–Sina dyke swarm is the southern part of a large area of Middle Paleozoic basaltic magmatism in the eastern Siberian Craton. The OIB-like geochemical characteristics of dolerite allow us to suggest that the melting substrate for Middle Paleozoic basaltic magmatism was represented by a relatively homogeneous, mid-depleted mantle of the plume with geochemical parameters similar to those of OIB.  相似文献   

4.
Doklady Earth Sciences - Geochemical and isotope–geochronological evidence of Late Riphean intraplate magmatism within the Chernorechenskii massif at the western margin of the Siberian Craton...  相似文献   

5.
Doklady Earth Sciences - Data on the Early Jurassic volcanic rocks of the Kobyumé graben system, which formed at the Verkhoyansk passive margin of the Siberian Craton, are presented. The...  相似文献   

6.
Doklady Earth Sciences - A mineralogical-geochemical study of globular phyllosilicates (GPS) of the glauconite-illite series of the Dolgokta Formation from the stratigraphic well Chunkinskaya Well...  相似文献   

7.
The Indian Shield is cross-cut by a number of distinct Paleoproterozoic mafic dyke swarms. The density of dykes in the Dharwar and Bastar Cratons is amongst the highest on Earth. Globally, boninitic dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the Southern Indian Shield. Geochronology and geochemistry are used to constrain the petrogenesis and relationship of the boninitic dykes (SiO2 = 51.5 to 55.7 wt%, MgO = 5.8 to 18.7 wt%, and TiO2 = 0.30 wt% to 0.77 wt%) from the central Bastar Craton (Bhanupratappur) and the NE Dharwar Craton (Karimnagar). A single U-Pb baddeleyite age from a boninitic dyke near Bhanupratappur yielded a weighted-mean 207Pb/206Pb age of 2365.6 ± 0.9 Ma that is within error of boninitic dykes from the Dharwar Craton near Karimnagar (2368.5 ± 2.6 Ma) and farther south near Bangalore (2365.4 ± 1.0 Ma to 2368.6 ± 1.3 Ma). Rhyolite-MELTS modeling indicates that fractional crystallization is the likely cause of major element variability of the boninitic dykes from Bhanupratappur whereas trace element modeling indicates that the primary melt may be derived from a pyroxenite mantle source near the spinel-garnet transition zone. The Nd isotopes (εNd(t) = −6.4 to +4.5) of the Bhanupratappur dykes are more variable than the Karimnagar dykes (εNd(t) = −0.7 to +0.6) but they overlap. The variability of Sr-Nd isotopes may be related to crustal contamination during emplacement or is indicative of an isotopically heterogeneous mantle source. The chemical and temporal similarities of the Bhanupratappur dykes with the dykes of the Dharwar Craton (Karimnagar, Penukonda, Chennekottapalle) indicate they are members of the same giant radiating dyke swarm. Moreover, our results suggest that the Bastar and Dharwar Cratons were adjacent but likely had a different configuration at 2.37 Ga than the present day. It is possible that the 2.37Ga dyke swarm was related to a mantle plume that assisted in the break-up of an unknown or poorly constrained supercontinent.  相似文献   

8.
Baltica was one of continents formed as a result of Rodinia break-up 850-550 Ma. It was separated from Amazonia(?) by the Tornquist Ocean, the opening of which was preceded by Neoproterozoic extension in a network of continental rifts. Some of these rifts were subsequently aborted whereas the Tornquist Rift gave rise to splitting of Rodinia and formation of the Tornquist Ocean. The results of 1-D subsidence analysis at the fossil passive margin of Baltica provided insight in the timing and kinematics of continental rifting that led to break-up of Rodinia. Rifting was associated with Neoproterozoic syn-rift subsidence accompanied by deposition of continental coarse-grained sediments and emplacement of continental basalts.Transition from a syn-rift to post-rift phase in the latest Ediacaran to earliest early Cambrian was concomitant with deposition of continental conglomerates and arkoses, laterally passing into mudstones. An extensional scenario of the break-up of Rodinia along the Tornquist Rift is based on the character of tectonic subsidence curves, evolution of syn-rift and post-rift depocenters in time, as well as geochemistry and geochronology of the syn-rift volcanics. It is additionally reinforced by the high-quality deep seismic reflection data from SE Poland, located above the SW edge of the East European Craton. The seismic data allowed for identification of a deeply buried(11-18 km), well-preserved extensional half-graben, developed in the Palaeoproterozoic crystalline basement and filled with a Neoproterozoic syn-rift volcano-sedimentary succession. The results of depth-to-basement study based on integration of seismic and gravity data show the distribution of local NE-SW elongated Neoproterozoic depocenters within the SW slope of the East European Craton. Furthermore,they document the rapid south-eastwards thickness increase of the Neoproterozoic succession towards the NW-SE oriented craton margin. This provides evidence for extensive crustal thinning occurring prior to the break-up of Rodinia and formation of the Tornquist Ocean.  相似文献   

9.
正Ophiolites represent fragments of ancient oceanic lithosphere,tectonically incorporated into continental margins during plate subduction or remained in the subduction–collisional orogenic belt.They provide  相似文献   

10.
We present results of study of mineral assemblages and PT-conditions of metamorphism of mafic garnet–two-pyroxene and two-pyroxene granulites in the Early Precambrian metamorphic complex of the Angara–Kan terrane as well as the U–Pb age and trace-element and Lu–Hf isotope compositions of zircon from these rocks and the zircon/garnet REE distribution coefficients. The temperatures of metamorphism of two-pyroxene granulites are estimated as 800–870 to ~ 900 °C. Mafic garnet–two-pyroxene granulites contain garnet coronas formed at 750–860 °C and 8–9.5 kbar. The formation of the garnet coronas proceeded probably at the retrograde stage during cooling and was controlled by the rock composition. The age (1.92–1.94 Ga) of zircon cores, which retain the REE pattern typical of magmatic zircon, can be taken as the minimum age of protolith for the mafic granulites. The metamorphic zircon generation in the mafic granulites is represented by multifaceted or soccerball crystals and rims depleted in Y, MREE, and HREE compared to the cores. The age of metamorphic zircon in the garnet–two-pyroxene (~ 1.77 Ga) and two-pyroxene granulites (~ 1.85 and 1.78 Ga) indicates two episodes of high-temperature metamorphism. The presence of one generation (1.77 Ga) of metamorphic zircon in the garnet–two-pyroxene granulites and, on the contrary, the predominance of 1.85 Ga zircon in the two-pyroxene granulites with single garnet grains suggest that the formation of the garnet coronas proceeded at the second stage of metamorphism. The agreement between the zircon/garnet HREE distribution coefficients and the experimentally determined values at 800 °C suggests the simultaneous formation of ~ 1.77 Ga metamorphic zircon and garnet. Zircon formation by dissolution/reprecipitation or recrystallization in a closed system without exchange with the rock matrix is confirmed by the close ranges of 176Hf/177Hf values for the core and rims. The positive εHf values (up to + 6.2) for the zircon cores suggest that the protolith of mafic granulites are derived from depleted-mantle source. The first stage of metamorphism of the mafic granulites and paragneisses of the Kan complex (1.85–1.89 Ga) ended with the formation of collisional granitoids (1.84 Ga). The second stage (~ 1.77 Ga) corresponds to the intrusion of the second phase of subalkalic leucogranites of the Taraka pluton and charnockites (1.73–1.75 Ga).  相似文献   

11.
Doklady Earth Sciences - The results of isotope U–Pb dating of zircons from lherzolite and vein olivine orthopyroxenite composing the Roseta ultramafic massif are presented. The zircons...  相似文献   

12.
International Journal of Earth Sciences - Early Neoproterozoic metaigneous rocks occur in the central part of the Kaoko–Dom Feliciano–Gariep orogenic system along the coasts of the...  相似文献   

13.
This paper reports U–Pb–Hf isotopes of detrital zircons from Late Triassic–Jurassic sediments in the Ordos, Ningwu, and Jiyuan basins in the western-central North China Craton (NCC), with the aim of constraining the paleogeographic evolution of the NCC during the Late Triassic–Jurassic. The early Late Triassic samples have three groups of detrital zircons (238–363 Ma, 1.5–2.1 Ga, and 2.2–2.6 Ga), while the latest Late Triassic and Jurassic samples contain four groups of detrital zircons (154–397 Ma, 414–511 Ma, 1.6–2.0 Ga, and 2.2–2.6 Ga). The Precambrian zircons in the Late Triassic–Jurassic samples were sourced from the basement rocks and pre-Late Triassic sediments in the NCC. But the initial source for the 238–363 Ma zircons in the early Late Triassic samples is the Yinshan–Yanshan Orogenic Belt (YYOB), consistent with their negative zircon εHf(t) values (−24 to −2). For the latest Late Triassic and Jurassic samples, the initial source for the 414–511 Ma zircons with εHf(t) values of −18 to +9 is the Northern Qinling Orogen (NQO), and that for the 154–397 Ma zircons with εHf(t) values of −25 to +12 is the YYOB and the southeastern Central Asian Orogenic Belt (CAOB). In combination with previous data of late Paleozoic–Early Triassic sediments in the western-central NCC and Permian–Jurassic sediments in the eastern NCC, this study reveals two shifts in detrital source from the late Paleozoic to Jurassic. In the Late Permian–Early Triassic, the western-central NCC received detritus from the YYOB, southeastern CAOB and NQO. However, in the early Late Triassic, detritus from the CAOB and NQO were sparse in basins located in the western-central NCC, especially in the Yan’an area of the Ordos Basin. We interpret such a shift of detrital source as result of the uplift of the eastern NCC in the Late Triassic. In the latest Late Triassic–Jurassic, the southeastern CAOB and the NQO restarted to be source regions for basins in the western-central NCC, as well as for basins in the eastern NCC. The second shift in detrital source suggests elevation of the orogens surrounding the NCC and subsidence of the eastern NCC in the Jurassic, arguing against the presence of a paleo-plateau in the eastern NCC at that time. It would be subsidence rather than elevation of the eastern NCC in the Jurassic, due to roll-back of the subducted paleo-Pacific plate and consequent upwelling of asthenospheric mantle.  相似文献   

14.
On and Off the North China Craton: Where is the Archaean Keel?   总被引：67，自引：2，他引：65  
Geophysical data indicate that the lithosphere beneath the NorthChina Craton (NCC) is  相似文献   

15.
Doklady Earth Sciences - Novel data from mineralogical studies of the peridotite xenoliths from the Komsomol’skaya–Magnitnaya kimberlite pipe, Upper Muna field, Siberian craton, are...  相似文献   

16.
《Comptes Rendus Geoscience》2018,350(6):245-254
The Oulad Dlim Massif represents the northern segment of the Mauritanide belt that thrusts over the western margin of the Reguibat Shield, north of the West African Craton (WAC). This belt includes various metamorphic units of Archean, Neoproterozoic and Palaeozoic ages that were stacked and thrust eastward during the Variscan orogeny. The core of the Oulad Dlim Massif comprises the Adrar–Souttouf Metamafic Complex that represents a large tectonic unit made of high-grade mafic rocks and vast exposures of amphibolites. A characterisation of the metamorphism in these amphibolites is essential to understand the relationships of the Oulad Dlim Massif with the southern segments of the Mauritanide belt and to provide constraints on the geodynamic evolution of the western margin of the WAC. Here we determine the P–T conditions of metamorphism of two samples of garnet amphibolites collected at the northernmost end of the Adrar–Souttouf Metamafic Complex. The samples show a main mineral assemblage of garnet + low-Ti pargasite + oligoclase + phengite + epidote + quartz + rutile ± paragonite ± K-feldspar. We calculated their P–T conditions using the amphibole–plagioclase NaSi–CaAl exchange thermometer, and the garnet–amphibole–plagioclase–quartz and the amphibole–plagioclase Si–Al partitioning barometers. The thermobarometric results indicate that this mineral assemblage was formed at high-P amphibolite-facies conditions at 650–700 °C and 10–13 kbar. The observed stability of paragonite and phengite reveals fluid-absent conditions or the presence of a fluid phase with reduced H2O activity during the peak of metamorphism. We found no relicts of eclogite-facies mineral assemblage in the garnet amphibolites. This contrasts with the eclogite-facies metamorphism found due south in the Tarf Magneïna unit. This suggests that the northernmost end of the Adrar–Souttouf Metamafic Complex may have been buried to shallower depths than the units further south, probably during the Variscan orogeny. However, precise absolute radiometric dating of the high-P amphibolite-facies metamorphism is required to confirm these findings.  相似文献   

17.
431 oriented samples were collected from 27 dolerite dykes at 17 sites, belonging to 2.95, 2.65, and 1.90 Ga swarms, that trend SE, E and NE, respectively from the Bushveld Igneous Complex into the eastern Kaapvaal Craton (ages determined by Olsson et al., 2010; Olsson in Söderlund et al., 2010). Samples were analyzed for paleomagnetism and also anisotropy of magnetic susceptibility (AMS). For the 2.95 Ga SE-trending dykes high temperature/coercivity ‘P’ component has unblocking temperatures up to 590 °C and coercivity 40–90 mT and demonstrate SSW declination and intermediate positive inclination. Based on positive contact and conglomerate tests we argue for a primary origin of this component. The paleopole (BAD), calculated from ‘P’ component, does not correspond to any of the previously obtained Archean–Paleoproterozoic paleopoles for the Kaapvaal Craton, and represents a new key pole for 2.95 Ga. The high-coercivity ‘H’ component for the 2.65 Ga-old E-trending dykes has a SSW declination and steep positive inclination. Paleomagnetic pole (RYK), recalculated from this component, is close to the paleopoles, obtained by Wingate (1998) and Strik et al. (2007) for 2.78 Ga Ventersdorp volcanics. The third group, NE-trending dykes of the 1.90 Ga Black Hill swarm demonstrate an ‘M’ component with dual polarity high-coercivity component with SSE-declination and negative intermediate inclination. The paleopole (BHD), calculated from this component is close to the 1.87 Ga pole of the Kaapvaal Craton obtained by Hanson et al. (2004). Overprint directions include a very well developed thermo-chemical overprint (Dec = 329° Inc = −36°), which is believed to be associated with a ∼0.18 Ga regional ‘Karoo’ thermal event.  相似文献   

18.
《International Geology Review》2012,54(16):1945-1963
The basement of the northeastern periphery of the East-European Craton (ЕЕС) is composed of volcanic-sedimentary sequences, volcanic rocks, granitoids, and rare ophiolite complexes. Geochronological data constrain their age from ca. 750 to 500 Ma, and there is a consensus that these rocks represent relicts of a late Neoproterozoic–Cambrian Pre-Uralides–Timanides orogeny. Combining new integrated isotopic (U-Pb, Lu-Hf) and trace-element data (TerraneChrone® approach) on detrital zircons from sandstones of the lower Cambrian Brusov Formation in the Mezen basin (White Sea region in the northeastern periphery of the EEC) with available studies on detrital zircons from Neoproterozoic–middle Cambrian (meta)sedimentary units of the northeastern periphery of the EEC allow us to conclude that (1) the onset of the Arctida–Baltica collision can now be constrained to the time interval between ca. 540 and 510 Ma and (2) the Ediacaran–early Cambrian Mezen sedimentary basin was a basin on the Timanian passive margin of Baltica up to 540 Ma, but was not a foreland basin of the Pre-Uralides–Timanides orogen.  相似文献   

19.
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20.
Graphite in Archaean-Palaeoproterozoic rocks has been a subject of interest since it could represent an evidence of early life on Earth. In the Palaeoproterozoic basement of the Tandilia Belt, graphite was found both in fluid inclusions (FI) hosted in the San Miguel skarn calc-silicate minerals, and as solid inclusions in calcite crystals from the protolithic marble (a13C enriched carbonate from the “Lomagundi-Jatuli event”). FI microthermometry and oxygen stable isotope ratios indicated the skarn minerals formation within the range of 630–650 °C (at ∼5 kbars) and ∼642–654 °C, respectively. Also, the characterisation of the metasomatic fluid (of a low salinity <7 wt% NaCl eq. NaClH2O/NaClKClH2O aqueous system) pointed out that the zonal crystallisation pattern shown by the skarn minerals (wollastonite-vesuvianite, grossular-diopside-calcite and diopside-calcite zones in the exoskarn, and grossular-diopside and diopside-calcic plagioclase zones in the endoskarn) responds to the increase of the involved cation activity gradients (Ca2+-Si4+-Mg2+-Fe2+/3+-Al3+) and not to significant changes in the temperature or concentration of CO2 in the system. Variation in the crystallinity degree of the graphite hosted in the skarn minerals and in marble calcite, shown by Raman spectroscopy, would indicate that the graphite could have been formed from the ripening of organic matter present in the sedimentary rocks during the metamorphic-metasomatic event (Transamazonian Orogeny). In this sense, the increase of the organic carbon productivity in the oceans during the Palaeoproterozoic, represented by the “Lomagundi-Jatuli event”, would support this graphite origin and also the possible existence of a marine sedimentary basin in the previous stages of the Río de la Plata amalgamation (Siderian-Rhyacian), in the San Miguel area of the Tandilia Belt.  相似文献   

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