Structure and geochemical characteristics of trap rocks from the Noril’sk Trough, Northwestern Siberian craton (original) (raw)
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Magma differentiation and mineralisation in the Siberian continental flood basalts
Lithos, 1995
New major, trace element and Sr and Nd isotope data are presented for selected lavas from the three uppermost formations in the Siberian Trap, and on over 60 samples of the associated intrusive rocks. The lavas from a 1400 m section are remarkably homogeneous and, apart from four samples of basaltic andesites, SIO2=48.4-49.6%,
Geochimica et Cosmochimica Acta, 1993
We present a tightly controlled and comprehensive set of analytical data for the 250~Ma Siberian flood-basalt province. Consideration of major-and trace-element compositions, along with strontium, lead, and neodymium isotopic compositions, strongly supports earlier Russian subdivision of this magmatism into three magmatic cycles, giving rise to three assemblages of eleven basalt suites in the ascending order lvakinsky-Gudchikhinsky, Khakanchansky-Nadezhdinsky, and Morongovsky-Samoedsky. Geochemical and isotopic discontinuities of varying magnitude characterize most of the boundaries between the eleven recognized basalt suites in the Noril'sk area.
The Generation of Granitic Magmas by Intrusion of Basalt into Continental Crust
Journal of Petrology, 1988
When basalt magmas are emplaced into continental crust, melting and generation of silicic magma can be expected. The fluid dynamical and heat transfer processes at the roof of a basaltic sill in which the wall rock melts are investigated theoretically and also experimentally using waxes and aqueous solutions. At the roof, the low density melt forms a stable melt layer with negligible mixing with the underlying hot liquid. A quantitative theory for the roof melting case has been developed. When applied to basalt sills in hot crust, the theory predicts that basalt sills of thicknesses from 10 to 1500 m require only 1 to 270 y to solidify and would form voluminous overlying layers of convecting silicic magma. For example, for a 500 m sill with a crustal melting temperature of 850 °C, the thickness of the silicic magma layer generated ranges from 300 to 1000 m for country rock temperatures from 500 to 850 °C. The temperatures of the crustal melt layers at the time that the basalt solidifies are high (900-950 °C) so that the process can produce magmas representing large degrees of partial fusion of the crust. Melting occurs in the solid roof and the adjacent thermal boundary layer, while at the same time there is crystallization in the convecting interior. Thus the magmas formed can be highly porphyritic. Our calculations also indicate that such magmas can contain significant proportions of restite crystals. Much of the refractory components of the crust are dissolved and then re-precipitated to form genuine igneous phenocrysts. Normally zoned plagioclase feldspar phenocrysts with discrete calcic cores are commonly observed in many granitoids and silicic volcanic rocks. Such patterns would be expected in crustal melting, where simultaneous crystallization is an inevitable consequence of the fluid dynamics. The timescales for melting and crystallization in basalt-induced crustal melting (10 2-10 3 y) are very short compared to the lifetimes of large silicic magma systems (>10 6 y) or to the timescale for thermal relaxation of the continental crust (> 10 7 y). Several of the features of silicic igneous systems can be explained without requiring large, high-level, long-lived magma chambers. Cycles of mafic to increasingly large volumes of silicic magma with time are commonly observed in many systems. These can be interpreted as progressive heating of the crust until the source region is partially molten and basalt can no longer penetrate. Every input of basalt triggers rapid formation of silicic magma in the source region. This magma will freeze again in timescales of order 10 2-10 3 y unless it ascends to higher levels. Crystallization can occur in the source region during melting, and eruption of porphyritic magmas does not require a shallow magma chamber, although such chambers may develop as magma is intruded into high levels in the crust. For typical compositions of upper crustal rocks, the model predicts that dacitic volcanic rocks and granodiorite/tonalite plutons would be the dominant rock types and that these would ascend-from the source region and form magmas ranging from those with high temperature and low crystal content to those with high crystal content and a significant proportion of restite.
The Siberian Flood Basalt Province (SFBP) of Permo-Triassic age is one of the largest flood basalt provinces with an estimated area of exposure of 337,000 km*, average thickness of 1 km, and a magma volume of 337,000 km3. Forty-seven basaltic rocks from two main subprovinces, Norilsk (5-10% of area, thickness up to 3 km) and Putorana (90-95% of area, thickness of more than 2 km), were selected, on the basis of petrography and volcano-stratigraphic relation, for major-element analysis. Twentysix of these basalts, twelve from Norilsk and fourteen from Putorana, were analyzed for Nd-and Srisotopic compositions.
Genesis of volcanic rocks related to subduction zones, geochemical point of view
The application of trace element geochemistry to models of the generation of volcanic rocks in orogenic areas indicates that all three rock associations - tholeiitic, calc-alkaline and shoshonitic - can be produced by anatexis of upper mantle peridotite. The island arc tholeiites are probably formed by partial melting of spinel peridotite while calc-alkaline volcanics are generated by melting of spinel or garnet peridotite overlying the Benioff zone. The contents of LILE in rocks of the two associations require, however, that the upper mantle source had already been enriched in those elements. It is suggested that the svstematic chemical variations with respect to the distance from the trench may reflect changes in the composition of partial melts due to a heterogeneous source and to a variable degree of anatexis. Shoshonitic rocks can be derived from the "normal" upper mantle garnet peridotite by a low degree of partial melting and do not appear to be related directly to the subduction zones. Such a model provides an explanation to the spatial zonation according to the distance of the trench ; it does not exclude the role of a crustal contamination.
Geochemistry International, 2018
A periodic character of the evolution of trap magmatism was inferred by many researchers from the fact that sequences of volcanic rocks consist of alternating units of lava flows and tuff. A new phase of studying magmatic rocks in the Siberian Platform was related to the possibility of apply high-precision geochemical techniques in studying trace elements and Sr, Nd, and Pb isotopic compositions. The use of these techniques made it possible not only to identify small individual cycles in the vertical sections of volcanic rocks but also to distinguish larger stages. The currently most widely acknowledged scenario of the origin of volcanic rocks involves three stages, during which oceanic-island basalts (OIB), transitional series (intermediate between OIB and WPB), and within-plate basalts (WPB) were formed. This scenario was inferred mostly from data on rocks in the western part of the Norilsk area (Kharaelakh Trough). This publication presents recently obtained data on the inner structure of the sequences of volcanic rocks and the geochemistry of basalts in the eastern part of the territory, where no rocks show transitional characteristics have ever been found. They can be classified into two types that have clearly different composition and occur in different areas. These types characterize two major stages of the origin of volcanic rocks: rift-related and trap magmatism itself. The rocks produced during these stages occur at neighboring territories.
Contributions to Mineralogy and Petrology, 2002
Phase equilibria analysis has been performed to elucidate whether ore-bearing Noril'sk-and poorly mineralized Lower Talnakh-type intrusions are co-magmatic with the extremely Ni-, Cu-and PGEs-depleted and not depleted flood basalts, respectively. The parental magma of the intrusions is classified as silica-undersaturated olivine basalt, whereas that of the flood basalts is assigned to silica-saturated tholeiite. The plutonic equivalent of the former parental magma is olivine gabbro or melagabbro, whereas the latter is gabbronorite. Phase equilibria relations clearly show that these two types of magmas cannot be co-magmatic as there is no way to derive one liquid from another by fractional crystallization. This provides no support for the current model considering the Noril'sk-type intrusions as exit conduits for a great volume of volcanic magma, which lost most of its chalcophile elements in the shallow settling chambers on its way to surface. The association of a large volume of chalcophile element-depleted basalts with the very sulfide-rich intrusions in the Noril'sk region is most likely coincidental and cannot, therefore, be used as a regional criterion when prospecting for the Noril'sktype sulfides deposits in other flood basalts provinces. and Fedorenko (1994a) that the ores were derived in large part from the Cu-, Ni-and PGE-depleted overlying basalts. They found no obvious correlation between Pb and Sr initial isotopic ratios of
The physicochemical conditions of early plume magmatism in West Siberia
Russian Geology and Geophysics, 2010
Complex petrological, geochemical, and isotope studies of igneous rocks sampled from the core of parametric Maizasskaya BH-1 showed a predominance of dolerite sills, which formed earlier (~263 ± 4 Ma) than most of basalts in the basement of the West Siberian sedimentary basin and in the Siberian Platform traps (248-251 Ma). Their formation took place during the crystallization of basaltic melt in intrusive chambers existing between layers of Silurian sedimentary rocks. The petrochemical, geochemical, mineralogical, and thermobarogeochemical data show that the sills resulted from the activity of complex magmatic systems different from typical oceanic and plateau-basalt melts and related, most likely, to the formation of rift structures under the influence of mantle plume. Study of melt inclusions provided data on the conditions of generation of primary melts from mantle substratum (≤1570 ºC, depths to 105-120 km) and crystallization parameters of dolerites-1130-1155 ºC, 1.5-2 kbar. The results obtained show that the studied basalt complexes in West Siberia are genetically related to the mantle plume activity, which led to the breakup of ancient crust and rifting. Formation of oceanic crust took place in the largest rifts; the ascending magma penetrated into the enclosing ancient strata to form sills.