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O.P. Polyansky A.V. Prokop'ev A.V. Babichev S.N. Korobeynikov V.V. Reverdatto 《Russian Geology and Geophysics》2013,54(2):121-137
Results of modeling of the formation of the Vilyui sedimentary basin are presented. We combine backstripping reconstructions of sedimentation and thermal regime during the subsidence with a numerical simulation based on the deformable solid mechanics. Lithological data and stratigraphic sections were used to “strip” the sedimentary beds successively and calculate the depth of the stratigraphic units during the sedimentation. It is the first time that the evolution of sedimentation which is nonuniform over the basin area has been analyzed for the Vilyui basin. The rift origin of the basin is proven. We estimate the spatial distribution of the parameters of crustal and mantle-lithosphere extension as well as expansion due to dike intrusion. According to the reconstructions, the type of subsidence curves for the sedimentary rocks of the basin depends on the tectonic regime of sedimentation in individual basins. The backstripping analysis revealed two stages of extension (sediments 4–5 km thick) and a foreland stage (sediments > 2 km thick). With the two-layered lithosphere model, we conclude that the subcrustal layer underwent predominant extension (by a factor of 1.2–2.0 vs. 1.1–1.4 in the crust). The goal of numerical experiments is to demonstrate that deep troughs can form in the continental crust under its finite extension. Unlike the oceanic rifting models, this modeling shows no complete destruction or rupture of the continental crust during the extension. The 2D numerical simulation shows the possibility of considerable basement subsidence near the central axis and explains why mafic dikes are concentrated on the basin periphery. 相似文献
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This paper reports the results of the numerical modeling of gravitationally instable processes in the lithospheric mantle
of ancient cratons. The gravitational instability is considered as a result of melting at the lithosphere base owing to its
local heating by anomalous mantle. Modeling was based on a finite element method in 2D formulation and took into account the
geological structure and thermomechanical parameters of the lithosphere of the Siberian platform. Numerical results revealed
the main tendencies in the mantle diapirisim of the mafic and ultramafic magma ascending through the “cold” high-viscosity
lithosphere. It was shown that the shape of diapiric magmatic bodies is controlled by realistic visco-elastic-plastic rheology
of lithosphere. The ascent of diapir in lithosphere was modeled for diverse regimes differing in duration, temperature field,
and upwelling depth. It was concluded that the ascent of melt through lithosphere to the crust-mantle boundary is mainly controlled
by rheology, and conditions of oscillatory diapirism with recurrent magma replenishments were modeled. Modeling results may
shed light on some features related to the trap magmatism of the Siberian igneous province. The duration and rate of magma
upwelling as well as the parameters of periodical magma upwelling were estimated and attempt was made to explain the high-velocity
seismic anomalies that were recorded in the subcrustal regions of the Siberian platform. 相似文献
54.
Computer modeling of granite gneiss diapirism in the Earth’s crust: Controlling factors,duration, and temperature regime 总被引：1，自引：0，他引：1
This paper is devoted to the modeling the granite gneiss formation by means of diapiric upwelling. The natural examples of
granitic diapirism in the Precambrian granite-greenstone belts and complexes of metamorphic cores are described. A new approach
is proposed to describe the partial melting and development of gravity instability in the crustal granitic layer, which experienced
heat impact and melting during intrusion of basaltic melt. Rheology of partially melted material and surrounding medium is
regarded to be temperature-dependent, following either plasticity or creep (non-Newtonian viscosity) law. Modeling results
show that crustal rheology plays a significant role in the character of diapirism (shape of upwelling bodies, duration of
the process, and width of thermal aureole). The rates of upwelling within the crust behaving as elastoplastic body are orders
of magnitude higher (meters to tens meters per year) than those obtained for creep (viscous) liquid model (0.8 cm/yr). Modeling
results revealed that the limiting depth of upwelling of partially crystallized melt, with allowance for temperature dependence
of creep, corresponds to the isotherm of 400°C. 相似文献
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V. V. Reverdatto V. N. Sharapov V. G. Melamed 《Contributions to Mineralogy and Petrology》1970,29(4):310-337
At least sis or perhaps seven types of contact metamorphism may be distinguished in nature (see Table 1). They differ from each other by a set of metamorphic facies in the exocontact aureoles, also by thermodynamic conditions of metamorphism. The manifestation of some types of metamorphism depends chiefly on magma temperature and composition, on the initial temperature of the country rocks (prior to contact metamorphism) and on the depth of the intrusive formation. The movement of magma through the intrusive channel (chamber) and the kinetic peculiarities of metamorphism exert additional influence on metamorphic conditions.Since the temperature elevation with depth corresponds in a general way to the increase in the lithostatic pressure, the maximum temperature levels attained at the direct intrusive contact must differ for various pressure levels (or depths). The two series of contact metamorphic rooks may be distinguished by their pressure: 1. common hornfelsic rock low-pressure series (types of metamorphism 1–4, Table 1), and 2. thermal transformed gneissous rock series metamorphosed under moderately high pressure (types 5–6, Table 1). The initial temperature of the country rock is low in the first series. It may apparently be discounted in certain cases. The usual non-abyssal contact low-pressure metamorphism (the proper contact metamorphism) depends essentially on magma temperature and composition, while in the second series, the initial temperature of the country rocks may be rather high. This and the effect of the intrusive heat and high lithostatic pressure results in rock transformation under conditions of the regional metamorphism of the facies (under moderately high pressure).Since superposition of the local temperature field on a regional high-temperature field in the neighbourhood of intrusives (in deep conditions) results in an increase in the thickness of the contact aureole, Ingersoll's criterion (the ratio of the thickness of the aureole to the thickness of the intrusive body) may be helpful for distinguishing abyssal from non-abyssal contact metamorphism. The values of this criterion cannot exceed 0.2–0.3 for the non-abyssal contact metamorphism. 相似文献
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I. I. Likhanov A. D. Nozhkin V. V. Reverdatto A. A. Krylov P. S. Kozlov V. V. Khiller 《Petrology》2016,24(4):392-408
This study provides the first evidence for the occurrence of ultrahigh-temperature (UHT) granulite-facies metamorphism in the Yenisei Ridge (Angara–Kan block). UHT metamorphism is documented in Fe-Al-rich metapelites on the basis of the garnet–hypersthene–sillimanite–cordierite–plagioclase–biotite–spinel–quartz–K-feldspar assemblage. Microtextural relationships and compositional data for paragneisses of the Kan complex attest to three distinct metamorphic episodes: (M1) pre-peak prograde (820?900°C/5.5–7 kbar), (M2) peak UHT (920–1000°C/7–9 kbar), and (M3) post-peak retrograde (770?900°C/5.5–7.5 kbar). The observed counterclockwise P–T evolution at a high geothermal gradient (dT/dP = 100–200°C/kbar) suggests that UHT metamorphic assemblages were formed in an overall extensional tectonic setting accompanied by underplating of mantle-derived mafic magmas, which may be sourced from ~1750 Ma giant radiating dike swarms linked to the Vilyuy mantle plume as part of the Trans-Siberian LIP. The broad synchroneity of UHT metamorphism (1744 ± 26 Ma; monazite–zircon isochron age) and rift-related endogenic activity in the region can provide an additional line of evidence for the two-stage evolution of granulite-facies metamorphism in the Angara–Kan block. The Aldan–Stanovoy, Anabar, and Baikal basement inliers of high-grade metamorphic rocks within the Siberian craton record two Paleoproterozoic peaks (1.9 and 1.75 Ga) of granulite-facies metamorphism. The synchronous sequence of tectonothermal events at the periphery of the large Precambrian Laurentian, Baltica, and Siberian cratons provide convincing evidence for their spatial proximity over a wide time interval, which is consistent with the most recent paleomagnetic reconstructions of the Proterozoic supercontinent Nuna. 相似文献
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The mineralogical, petrological, geochemical and geochronological data were used to evaluate the age and petrogenesis of compositionally contrasting metamorphic rocks at the junction between Meso-Neoproterozoic Transangarian structures and Archean-Paleoproterozoic complexes of the Angara–Kan inlier of the Yenisei Ridge. The studied metabasites and metapelites provide clues for understanding the evolution of the region. The magmatic protoliths of low-Ti metabasites were derived by melting of depleted (N-MORB) upper mantle, and their high-Ti counterparts are interpreted to have originated from an enriched mantle source (E-MORB). The petrogeochemical characteristics of protoliths of the metabasite dikes resemble those of within-plate basalts and ocean island tholeiites. The Fe- and Al-rich metapelites are redeposited and metamorphosed products of Precambrian weathering crusts of kaolinite and montmorillonite-chlorite-hydromica compositions. The Р–Т conditions of metamorphism (4.9–5.5 kbar/570–650°С for metabasites; 4.1–7.1 kbar/500–630°С for metapelites) correspond to epidote–amphibolite to amphibolite facies transition. The evolution of the Angara complex occurred in two stages. The early stage (1.18–0.85 Ga) is associated with Grenville tectonics and the late stage is correlated with accretion/collision episodes of the Valhalla orogeny, with the peaks at 810–790 and 730–720 Ma, and the final stage of the Neoproterozoic evolution of the orogen on the southwestern margin of the Siberian craton. The correlation of regional crustal processes with globalscale geological events in the Precambrian evolution of the Earth supports recent paleomagnetic reconstructions that allow a direct, long-lived (1400–600 Ma) spatial and temporal connection between Siberia, Laurentia, and Baltica, which have been parts of ancient supercontinents. 相似文献
60.
V. V. Reverdatto A. V. Babichev I. I. Likhanov O. P. Polyansky 《Doklady Earth Sciences》2018,480(2):750-752
The rate of mineral transformations in rocks near magmatic intrusions may be estimated using mathematical modeling for study of the duration of metamorphism and geological and mineralogical data. At the contacts of the Anakit trappean massif on the Nizhnyaya Tunguska River, where the temperature reached 900°C, the rate of growth of a wollastonite rim at the boundary between the limestone and the siliceous nodule was ～3 × 10–10 cm/s. The zone of “spotted” hornfels with a width of 300?400 m was formed during metamorphism of chlorite–sericite–epidote–albite–quartz schist near the Kharlov gabbro massif in the foothills of the Altai Mountains. The movement rate of the metamorphic front during the formation of rock may be estimated as ～2 × 10–8 cm/s. It is suggested that the rate of metamorphism is controlled by the temperature and rock composition. As a whole, the rates of metamorphism of rocks near magmatic intrusive bodies exceed the rates of regional metamorphism. Upon accumulation of the actual data, this may be applied for diagnostics of the types of metamorphism. 相似文献