Siberian Large Igneous Province Research Articles

Are Late Permian carbon isotope excursions of local or of global significance?

Abstract We present a new, biostratigraphically calibrated organic and inorganic C-isotope record spanning the basal Late Permian to earliest Triassic from southern Guizhou (Nanpanjiang basin, South China). After fluctuations of a likely diagenetic overprint are removed, three negative carbon isotope excursions (CIEs) persist. These include a short-lived CIE during the early Wuchiapingian, a protracted CIE ending shortly after the Wuchiapingian–Changhsingian Boundary, and a third CIE straddling the Permian–Triassic boundary. Comparison of our new C-isotope record with others from the same basin suggests that influences of local bathymetry and of the amount of buried terrestrial organic matter are of importance. Comparison with other coeval time series outside of South China also highlights that only the negative CIE at the Permian–Triassic boundary is a global signal. These differences can be explained by the different volumes of erupted basalts between the Late Permian Emeishan and the younger Siberian large igneous provinces and their distinct eruptive modalities. Emeishan volcanism was largely submarine, implying that sea water was an efficient buffer against atmospheric propagation of volatiles. The equatorial position of Emeishan was also an additional obstacle for volatiles to reach the stratosphere and benefit from an efficient global distribution. Consequently, the local significance of these CIEs calls into question global correlations based on C-isotope chemostratigraphy during the Late Permian. The timing of the Late Permian Chinese CIEs is also not reflected in changes in species diversity or ecology, unlike the sudden and global Permian–Triassic boundary crisis and subsequent Early Triassic upheavals.

Petrology of alkaline silicate rocks and carbonatites of the Chuktukon massif, Chadobets upland, Russia: Sources, evolution and relation to the Triassic Siberian LIP

The petrogenesis of temporally and spatially associated carbonatitic and deeply derived carbonated alkaline silicate magmas provides an opportunity to gain insights into the nature of the deepest lithospheric mantle. The Chuktukon massif, which is part of the Chadobets alkaline ultramafic carbonatite complex (Chadobets upland, Siberian craton) is a carbonatite-melilitite-damtjernite intrusion, whose emplacement was coeval with the Siberian Traps large igneous province (LIP). In this study, the sources of the primary melts are examined, the petrogenetic evolution of the complex is reconstructed and the relationship with the Siberian LIP is also discussed. Isotopic and geochemical information indicate that the source for the Chuktukon primary melts was isotopically moderately depleted and the primary melts were formed by low degree partial melting of garnet carbonated peridotite. Hydrothermal processes caused 18O- and 13C- enrichment. The weathering process was accompanied by trace element re-distribution and enrichment of the weathering crust in Zn, Th, U, Nb, Pb and REE, relative to the Chuktukon rocks and a change in radiogenic (Sr, Nd) isotope compositions.

End-Permian extinction amplified by plume-induced release of recycled lithospheric volatiles

Magmatic volatile release to the atmosphere can lead to climatic changes and substantial environmental degradation including the production of acid rain, ocean acidification and ozone depletion, potentially resulting in the collapse of the biosphere. The largest recorded mass extinction in Earth’s history occurred at the end of the Permian, coinciding with the emplacement of the Siberian large igneous province, suggesting that large-scale magmatism is a key driver of global environmental change. However, the source and nature of volatiles in the Siberian large igneous province remain contentious. Here we present halogen compositions of sub-continental lithospheric mantle xenoliths emplaced before and after the eruption of the Siberian flood basalts. We show that the Siberian lithosphere is massively enriched in halogens from the infiltration of subducted seawater-derived volatiles and that a considerable amount (up to 70%) of lithospheric halogens are assimilated into the plume and released to the atmosphere during emplacement. Plume–lithosphere interaction is therefore a key process controlling the volatile content of large igneous provinces and thus the extent of environmental crises, leading to mass extinctions during their emplacement. Halogens in Siberian xenoliths show that plume–lithosphere interaction controls the volatile content of large igneous provinces. The seawater-derived volatiles, implicated in the end-Permian mass extinction, infiltrated the lithosphere during subduction.

Identification of anhydrous CaCl2 and KCaCl3 in natural inclusions by Raman spectroscopy

Anhydrous chlorides - CaCl2, and KCaCl3 (chlorocalcite) were identified as mineral inclusions in halite from the Siberian Large Igneous Province at the contact of magmatic intrusions and evaporates. Chlorocalcite was also found as daughter mineral in polyphase hypersaline inclusions. While Raman spectra of KCaCl3 (chlorocalcite) in natural inclusions are similar to spectra of synthetic analogue, the Raman spectra of natural CaCl2 do not correspond to the published Raman spectra of synthetic CaCl2. Simulations of Raman spectra using ab initio density-functional theory (DFT) allowed us to calculate the spectra of individual polymorphs of CaCl2 and to discriminate anhydrous CaCl2 phases in natural inclusions and synthetic CaCl2. In the spectrum of the Pbcn polymorph of CaCl2 twelve different peaks could be identified at 74, 95, 99, 107, 124, 158, 164, 179, 212, 236, 244, 256 cm−1 in contrast to five peaks in the spectrum of the Pnnm polymorph of CaCl2 at 115, 157, 160, 211 and 252 cm−1. Naturally occurring CaCl2 in inclusions in halite consist of Pbcn polymorph only, which probably results from a mechanical stress on cooling from magmatic to ambient temperatures. However, the Raman spectra of the synthetic CaCl2 corresponds to the Pnnm phase with small contributions of the Pbcn phase.Raman spectra of synthetic KCaCl3 with main peaks at 58, 67, 90, 97, 133, 139, 147, 193 cm−1 agrees well with the spectra of chlorocalcite in the natural inclusions. Positions of each atom in the KCaCl3 structure were refined using the density-functional theory. There are no imaginary phonon modes for the optimized structure, indicating that the structure of KCaCl3 is stable. Calculated Raman spectrum is in a good agreement with the Raman spectrum of synthetic and natural KCaCl3 samples.

The Central European, Tarim and Siberian Large Igneous Provinces, Late Palaeozoic orogeny and coeval metallogeny

The formation of the Central European and Tarim Large Igneous Provinces (LIPs) in the Early Permian coincided with the demise of the Variscan and the Southern Tianshan orogens, respectively. The Early Triassic Si- berian LIP was formed in the wake of the Western Altaid orogeny in the Late Permian. These processes coincided with the development of the majority of known Late Palaeozoic and Early Mesozoic hydrothermal and magmatic ore deposits in the corresponding orogenic domains. Nickel-copper(-PGE) deposits followed directly from the evo- lution of the (ultra-)mafi c melts which make up the LIPs. In Western Siberia, the diverse assemblage of associated noble and base metals in the Noril'sk-Talnakh Ni-Cu(-PGE) deposits suggests these metals also had their source in the mantle domain from which the (ultra-)mafi c melts were generated. The same metals variably found their way into the hydrothermal ore deposits in the defunct Variscan and Southern Tianshan orogenic domains. These ore de- posits have traditionally been viewed as a result of orogenic processes. However, their ages, together with the timing and nature of their by then intracontinental tectonic control cause uncertainty concerning the role of the orogens. In view of their mantle sources in their association with the Siberian LIP, the mantle contribution to these Late Palaeo- zoic hydrothermal ore deposits in the orogenic belts may have been more signifi cant than previously thought. An orogenic contribution to melting of mantle complexes and to mineralisation may have resided in the earlier modifi - cation of subcontinental mantle domains by subduction of oceanic lithosphere. In all three cases, the controlling tectonic setting of orogenic cessation, LIP formation and mineralisation was dominated by translithospheric strike- slip deformation, possibly in combination with orogenic collapse and lithosphere delamination. In view of their re- currence, the orogen-lip sequences were probably not fortuitous. The controlling strike-slip faults were principal elements of the lithosphere-scale dynamic framework that led to the amalgamation of Pangaea. At this scale, the exceptionally large volume of the Siberian LIP may, in addition to the strike-slip dissection of the lithosphere, have been related to extension in the continental lithosphere of the margin of the Supercontinent (cf. Gutierrez-Alonso et al. 2008). The peripheral extension was associated with compression in its centre. The explanation of these Large Igneous Provinces does not require the concept of an active mantle plume because deep-reaching strike-slip defor- mation, orogenic collapse and lithosphere delamination involved in the destruction of the orogenic edifi ces can have caused decompression melting in large domains of the subcontinental mantle.

First direct evidence for natural occurrence of colloidal silica in chalcedony-hosted vacuoles and implications for ore-forming processes

Abstract Different forms of abundant silica (e.g., quartz and chalcedony) are closely associated with many types of ore deposits in igneous, metamorphic, and sedimentary environments. Occurrence of quartz and metal-bearing minerals together strongly indicates that silica is an important component in hydrothermal fluids transporting and concentrating economic metals to the ore grade, however chemical and physical characteristics of such ore-forming media remain debated. Understanding of the environment in which chalcedony forms is largely hampered by the lack of chalcedony-hosted fluid inclusions. Our study reports for the first time fortuitously preserved, large-sized (up to 150 μm) fluid inclusions in chalcedony from the Gonchak deposit of optical calcite in the Early Triassic basalts belonging to the Siberian large igneous province. The application of microthermometric methods, scanning electron microscopy with cathodoluminescence, and laser Raman spectroscopy to the fluid inclusions and their host chalcedony recognized the formation of chalcedony from a colloidal suspension. The fluid inclusions represent a gel-like saline aqueous fluid that is residual after precipitation of spherulitic chalcedony aggregates with numerous H2O-bearing and H2O-poor layers. We propose that the colloidal nature of fluids forming chalcedony lends strong support to the natural existence of experimentally predicted “silicothermal fluids”. Such fluids can be instrumental in mobilizing and transporting large quantities of both silica and nano- and micro-particles of ore minerals, followed by efficient separation of the latter from coagulating silica gel into ore-rich zones and bodies.

DURATION OF GRANITOID MAGMATISM IN PERIPHERAL PARTS OF LARGE IGNEOUS PROVINCES (BASED ON 40AR/39AR ISOTOPIC STUDIES OF ALTAI PERMIAN-TRIASSIC GRANITOIDS)

In large igneous provinces (LIP) of fold areas, granitoid rocks are dominant, while mantle-derivated rocks play a subordinate role in rock formation. If magma emissions are impulsive, it may take 25–30 million years for a LIP to form and take shape. In this paper, we present the results of 40 Ar/ 39 Ar isotopic studies of Permian-Triassic grani­toids in the Altai region, Russia, and clarify the evolution of this region located at the periphery of the Siberian LIP. These granitoids are very diverse and differ not only in their rock set, but also in the composition features. In the study region, the granodiorite-granite and granite-leucogranite association with the characteristics of I- and S-types as well rare metal ore-bearing leucogranites are observed along with gabbro- and syenite-granite series, including mafic and intermediate rocks with the A2-type geochemical features. The 40 Ar/ 39 Ar data obtained in our study suggest that most of the studied granitoids intruded within a short period of time, 254–247 Ma. This timeline is closely related to the formation of granitoids in theKuznetsk basin and dolerite dikes in the Terekta complex (251–248 and 255±5 Ma, respectively), as well as intrusions of lamproite and lamprophyre dikes of the Chuya complex (245–242 and 237–235 Ma). Thus, we conclude that the Altai Permian-Triassic granitoids are varied mainly due to the evolution of mafic magmatism.

Parameters of plumes of North Asia

This paper presents the thermal and hydrodynamic structure of the conduit of a thermochemical mantle plume based on the results of experimental and theoretical modeling of thermochemical plumes. The basic relations for determining the thermal power and diameter of plumes are given. Depending on the geodynamic setting of eruption, the following types of plumes are distinguished: plumes responsible for the formation of large igneous provinces (LIP); plumes with a mushroom-shaped head, responsible, in particular, for batholith formation; and plumes producing rift zones. Using geological data (extent of magmatism, age of igneous provinces, and sizes of igneous areas), we estimated the parameters of plumes in Siberia and its folded framing: mass flow rate of melt, thermal power, depth of origin, and diameters of plume conduits and heads. The plumes responsible for the formation of the Siberian LIP (relative thermal power Ka = 114.9) and the West Siberian rift system (Ka = 37.8 for each of the three plumes) originated from the core-mantle boundary and erupted in the presence of a refractory layer in the lithosphere. The Vilyui plume (Ka = 27.3) originated from the core-mantle boundary and caused the formation of a rift system in the absence of a refractory layer. The plumes that produced the Hangayn (Ka = 6.8) and Hentiyn (Ka = 5.5) batholiths were initiated at the core-mantle boundary and had mushroom-shaped heads. The plumes responsible for the formation of rift zones might have originated from the 670 km discontinuity.

Late Permian–Early Triassic traps of the Kuznetsk Basin, Russia: Geochemistry and petrogenesis in respect to an extension of the Siberian Large Igneous Province

The Late Permian–Early Triassic (~252Ma) volcanic rocks in the central part of the Kuznetsk Basin (the Altay–Sayan Folded Area) are a good example of intraplate magmatism in a plume-influenced environment within the platform framework. The Kuznetsk lavas are dominantly basaltic andesites, contain 5.3–3.4wt.% MgO and 1.4–1.9wt.% TiO2, and are enriched in LILE and LREE and depleted in Nb and Ta ((La/Yb)CN=5.2–7.7); Nb/La=0.3–0.4). The major and trace element data suggest that all lava units of the Kuznetsk Basin are moderately evolved (Mg#=34.6–46.6) through fractional crystallization and linked by a common deep-seated magma chamber. They are predominantly derived from non-contaminated magmas that have experienced potential early-stage sulfide segregation and Cr-spinel crystallization prior to fractionation. The Kuznetsk lavas originated from low degrees of partial melting of amphibole- and Fe–Ti oxide-bearing spinel lherzolite, with the involvement of pyroxenite component. Lavas are characterized by both OIB-like and subduction-like signatures and originated by melting of a subduction-modified lithospheric mantle by OIB-like asthenospheric fluid/melt additions. The Kuznetsk lavas are compared in petrology and geochemistry with the Siberian Traps basalts, especially the Nadezhdinsky suite from the Noril'sk region, and the West Siberian Basin basalts, and, in general, may be considered as more evolved varieties of the Nadezhdinsky basalts. Thus, the Kuznetsk volcanic rocks are genetically related to the Siberian LIP and the Kuznetsk Basin may be considered as a part of the Siberian Large Igneous Province.

Distribution of PGE in Permo-Triassic basalts of the Siberian Large Igneous Province

We have revealed the spatio-temporal regularities of distribution of platinum group elements (PGE) in basaltoids related to the activity of the Siberian mantle plume. As objects of study, we chose rift and flood basalts from the Norilsk district (sampled from the SD-9 borehole), flood basalts from the central part of the Tunguska syneclise (Lower Tunguska), Kuznetsk Basin traps, and subalkalic basalt from the Semeitau volcanoplutonic structure in eastern Kazakhstan. Based on the PGE patterns of basaltoids related to the activity of the Permo-Triassic Siberian plume, we have shown that the rocks that formed in the central part of the Siberian Large Igneous Province (LIP) at the early rift stage have low contents of PGE, whereas picrites and tholeiitic flood basalts have high contents. The rift (Semeitau structure) and flood (Kuznetsk Basin traps) basalts from the peripheral regions are characterized by extremely low PGE contents. The high PGE contents in magmas of the plume head are responsible for the high productivity of ultramafic-mafic trap magmatism. The elevated K contents in magmas and the high PGE contents in the mantle plume head are probably due to the ascent of deep-seated material from the core-lower-mantle boundary, as follows from the thermochemical model of the Siberian plume.

Magmatic systems of large continental igneous provinces

Large igneous provinces (LIPs) formed by mantle superplume events have irreversibly changed their composition in the geological evolution of the Earth from high-Mg melts (during Archean and early Paleoproterozoic) to Phanerozoic-type geochemically enriched Fe-Ti basalts and picrites at 2.3 Ga. We propose that this upheaval could be related to the change in the source and nature of the mantle superplumes of different generations. The first generation plumes were derived from the depleted mantle, whereas the second generation (thermochemical) originated from the core-mantle boundary (CMB). This study mainly focuses on the second (Phanerozoic) type of LIPs, as exemplified by the mid-Paleoproterozoic Jatulian–Ludicovian LIP in the Fennoscandian Shield, the Permian–Triassic Siberian LIP, and the late Cenozoic flood basalts of Syria. The latter LIP contains mantle xenoliths represented by green and black series. These xenoliths are fragments of cooled upper margins of the mantle plume heads, above zones of adiabatic melting, and provide information about composition of the plume material and processes in the plume head. Based on the previous studies on the composition of the mantle xenoliths in within-plate basalts around the world, it is inferred that the heads of the mantle (thermochemical) plumes are made up of moderately depleted spinel peridotites (mainly lherzolites) and geochemically-enriched intergranular fluid/melt. Further, it is presumed that the plume heads intrude the mafic lower crust and reach up to the bottom of the upper crust at depths ∼20 km. The generation of two major types of mantle-derived magmas (alkali and tholeiitic basalts) was previously attributed to the processes related to different PT-parameters in the adiabatic melting zone whereas this study relates to the fluid regime in the plume heads. It is also suggested that a newly-formed melt can occur on different sides of a critical plane of silica undersaturation and can acquire either alkalic or tholeiitic composition depending on the concentration and composition of the fluids. The presence of melt-pockets in the peridotite matrix indicates fluid migration to the rocks of cooled upper margin of the plume head from the lower portion. This process causes secondary melting in this zone and the generation of melts of the black series and differentiated trachytic magmas.

Petrogenesis and timing of mafic magmatism, South Taimyr, Arctic Siberia: A northerly continuation of the Siberian Traps?

The Siberian large igneous province (LIP) forms the world's most extensive continental exposure of basalt and has several sub-provinces surrounding it, which may be genetically related. The Taimyr peninsula of north Siberia is one of these sub-provinces and is frequently assumed to be the northerly continuation of the basalts exposed at Noril'sk, the best-studied area of the Siberian LIP. However, the correlation is uncertain.We present new major and trace element data from 35 samples of extrusive and intrusive rocks from Taimyr, with Sr and Nd isotope data from a subset of ten. The Taimyr rocks fall into two groups with low (~7wt.%) and elevated (~9wt.%) MgO concentrations. The high-MgO rocks display a restricted range of initial 87Sr/86Sr (0.705 to 0.706) and 143Nd/144Nd (0.5122 to 0.5124) ratios, and share bulk silicate earth normalised rare earth element patterns strikingly similar to data observed in the ore-related Noril'sk intrusions. The remaining low-MgO group samples have a broader range with higher Sr and lower Nd isotope values and higher incompatible trace element ratios (e.g., Th/Ta>5.3 and La/Smn>1.7) similar to the crustally-contaminated Nadezhdinsky and Morongovsky suite basalts of the Noril'sk region. The major and trace element data for both groups are consistent with a process of fractional crystallisation coupled with small degrees of assimilation of incompatible-element-enriched lower crust involving different contaminants. Trace element model calculations indicate a process of magma formation at large degrees of partial melting and at pressures of less than 3GPa, probably within the garnet–spinel transition zone or the spinel stability field of the asthenospheric mantle. We obtained an argon plateau age of ~252 (252.7±1.5) Ma and a ~239Ma total fusion age from a Taimyr lava and intrusive sample, respectively, confirming that volcanism is only partly contemporaneous with the activity of the Siberian LIP. Although this is in agreement with previous interpretations, we argue that the age difference between both events is only ~13Ma and probably less (~5Ma) although further investigation of the relationship is required. Our data allow correlation with distinct Noril'sk members and most importantly to the ore-bearing (Ni–Cu) intrusions implying that whole rock chemistry could have value as a prospecting tool in Taimyr.

Spatial-temporal and genetic relationships between gold and antimony mineralization at gold-sulfide deposits of the Ob-Zaisan folded zone

The Ob-Zaisan folded zone is a fragment of a single structure composed of Paleozoic sedimentary and volcanogenic rocks (mainly black shale), which was formed at the margin of the Siberian continent and features a common set of magmatic complexes and mineral systems. However, there are some differences that determine the specific geological and metallogenic features of the Irtysh-Zaisan and Kolyvan-Tomsk fragments of the Ob-Zaisan folded zone. In the gold deposits of the West Kalba and Kolyvan-Tomsk auriferous belt, the main gold-sulfide mineralization is controlled by zones of shearing and dynamic metamorphism in carbonaceous carbonate-terrigenous rocks. This type of mineralization was formed in tectonic blocks in a compressional setting. Antimony mineralization is characterized by brecciated textures and the vein-like morphology of ore bodies, reflecting extensional tectonics. At some deposits (Zherek, Mirazh, Dalny), Sb mineralization is spatially separated from the main gold-sulfide ores and shows cross-cutting relations to the principal ore-controlling structures. In other gold deposits, stibnite is spatially associated with disseminated gold-sulfide ores and forms mineral assemblages with Ni, Co, Au, Pb, and Fe (Alimbet, Zhanan, Legostaevskoe, Semiluzhenskoe, and Kamenskoe deposits). This study reveals no direct correlation between Au and Sb in gold-sulfide ores of these deposits. SEM analysis indicated the absence of free gold in stibnite veins. However, atomic absorption and electron microprobe analysis indicated the presence of “invisible gold” from a few ppm to several tens of ppm in the stibnite. High gold contents in the gold-sulfide ores overprinted by antimony mineralization (Suzdalskoe, Zhanan, and Legostaevskoe deposits) can be explained by the processes of regeneration and redeposition. The results of microstructural observations, isotope geochronology, studies of mineral assemblages and fluid inclusions in the ores from gold deposits of the Ob-Zaisan folded zone suggest that antimony mineralization was formed at gold-polysulfide stage, which was separated from the early ore pyrite-arsenopyrite stage by a 30 Ma time gap. It can be assumed that the essentially stibnite mineralization was formed at a separate stage and was separated from the gold-polysulfide mineralization by a 7 Ma interval of tectonic activity. Our Ar-Ar data on sericite from ore samples, combined with U-Pb data on zircons from igneous rocks and previous data from the literature show that there were two major stages of ore formation: the Early Permian (282-270 Ma) and the Early Triassic (250-240 Ma). Most researchers suggest that these stages of mineralization can be related to the epochs of intraplate magmatism that led to the formation of the Tarim (280 Ma) and Siberian (250 Ma) large igneous provinces. These global geological events are generally connected with the influence of Tarim and Siberian mantle plumes.

Petrogenises of Triassic gabbroic and basaltic rocks from Chukotka, NE Russia: Eastern end of the ‘arc–type’ Siberian LIP?

The Triassic gabbroic intrusions and associated basaltic lavas from Chukotka are mainly tholeiitic with both ocean island basalt (OIB) and island arc basalt (IAB)–type geochemical signatures. Mg–number [Mg# = 100 × Mg/(Mg + Fe2+)] is around 40 for OIB–type gabbros, ranges from 48 to 66 for IAB–type hornblende–rich gabbros, and 43 to 65 for IAB–type basaltic rocks (ankaramites, lamprophyres, pyroxene–phyric basalts and hornblende–phyric basaltic andesite). TiO2 contents of the IAB–type gabbros and basaltic rocks are low (<2 wt%), but are high in OIB–type gabbros (4.3–5.3 wt%). OIB–type gabbros are typically enriched in FeO* (16–18 wt%) as compared to IAB–type gabbros (10–14 wt%) and IAB–type lavas (ankaramites, ~ 10 wt%; lamprophyres, ~ 14; pyroxene–phyric basalt, 11 wt% and basaltic andesite, 9–10 wt. %). In the primitive mantle normalized trace element patterns, IAB–type basalts and gabbros are characterized by depletion in HFSE (Nb, Ta, Zr and Hf) and enrichment in LILE. OIB–type gabbros can be distinguished from the rests by the absence of HFSE depletion, with strong negative Sr anomaly. The positive Ti anomaly in the OIB–type gabbros can be attributed to high content of ilmenite in these rocks. Trace element characteristics of IAB–type gabbroic rocks and basalts are compatible with their magmas derived from subduction influenced melts, whereas OIB–type gabbros show within–plate geochemical characteristics. IAB–type gabbros and basaltic rocks display similar geochemical features to the low–Ti Nadezhdinsky suit (Noril’sk region) and Bel’kov dolerite (New Siberian Islands) of the Siberian large igneous province (LIP) in view of HFSE depletion and high H2O content of the magma to crystallize abundant hornblende not only in gabbros but also as phenocrysts in basalts. The Triassic gabbroic and basaltic rocks of both OIB and IAB types may as a whole represents the eastern end of the Siberian LIP.

Paleomagnetism of trap intrusions, East Siberia: Implications to flood basalt emplacement and the Permo–Triassic crisis of biosphere

Despite decades of concentrated studies, large igneous provinces (LIPs) are still among the most enigmatic phenomena of the Earth evolution. Among the myriad questions facing researchers, the duration of eruptive magmatic activity and its distribution through time are probably the most mysterious ones. Although the accuracy of modern dating techniques offers relatively high resolution, it is impossible to discriminate whether magmatic activity was more or less uniform or concentrated in few powerful outbursts. Consequently, many “trap-related” questions, from their origin to possible impact on the biosphere, still cannot be answered. Some of the above questions can be addressed with paleomagnetic data as have been effectively done in the case of the end-Cretaceous Deccan traps. The Siberian traps are one of the largest LIPs in the Phanerozoic and are thought, by some, to be the triggering event for the end-Permian mass extinction. We conducted a paleomagnetic study of trap intrusions along two long profiles in the eastern part of the province and found that most site-mean directions are grouped several times tighter than is common for the data on thick lava series and dyke swarms; similar over-grouping is found in other parts of the Siberian trap province too. We argue that this phenomenon is the most likely related to nearly simultaneous emplacement of trap intrusions over areas of several ten to few hundred kilometers in dimension for few millenniums or even faster. Moreover, such brief events account for all, or nearly all, magmatism in each area; how such events correlate over the entire Siberian LIP, however, remains an open question. Still, our data together with paleomagnetic results on thick lava series in Siberia strongly indicate that magmatic activity consisted of a number of brief pulses. In comparison to the other LIPs, the Siberian one is underlain by the thickest succession of carbonates, evaporites and coal-bearing clastics that are capable of producing huge amount of green-house and poisonous gases. We hypothesize that these very fast injections of magma into thick underlying sediments and the unique geological setting of the Siberian LIP are the major reasons for the Permo–Triassic mass extinction being the strongest in Earth history.

F, Cl, and S concentrations in olivine-hosted melt inclusions from mafic dikes in NW Namibia and implications for the environmental impact of the Paraná–Etendeka Large Igneous Province

Large Igneous Provinces (LIPs) have been proposed to trigger mass-extinction events by the release of large quantities of volcanic gases which results in major climatic perturbations causing worldwide ecological stress and collapse. A prerequisite for understanding the proposed link between LIP volcanism and biological crisis is reliable information about the total gas emissions during these events. In this paper we present the first estimations of total F, Cl and S emissions from the Paraná–Etendeka LIP in the South Atlantic. Data from this province are of special interest because it is among the world's largest LIPs but is not associated with a mass extinction event. We have determined pre-eruption concentrations of F, Cl and S by in situ analysis of melt inclusions preserved in olivine phenocrysts from basaltic dikes in the Etendeka province of NW Namibia. The melt inclusions have Mg-rich basaltic bulk compositions with about 8 to 18 wt.% MgO, overlapping the compositional range of the host rocks. A major feature of the melt inclusions is their wide variation in major and minor element concentrations, including F, Cl and S. This is attributed to trapping of variably-mixed melt fractions during crystallization of olivine in the roots of the dike system. Fluorine concentrations vary from about 190 to 450 μg/g, Cl from <10 to 125 μg/g and S from <30 to 1100 μg/g. All inclusions were re-homogenized in heating experiments and the lowest concentrations may be due to partial leakage of S and halogens. Therefore, the maximum values are considered best estimates of the true melt concentrations.These melt inclusion data are combined with the volume of extruded magma in the province (2.2 to 2.35×106 km3) and with published degassing efficiencies to calculate total emissions from the Paraná–Etendeka LIP of 600–1200 Gt fluorine, 70–470 Gt chlorine and 3100–5400 Gt sulfur. The estimated sulfur emissions are similar to those from the similar-sized Deccan and Siberian LIPs, both of which are related to mass extinctions, but the Paraná–Etendeka LIP produced much lower emission of halogens. This may help explaining the smaller ecological impact of the Paraná–Etendeka magmatism. These results support the proposal that massive halogen emissions related to LIP volcanism may be an important factor for extinction scenarios because of global destruction of the ozone layer.

Magma chamber–scale liquid immiscibility in the Siberian Traps represented by melt pools in native iron

Research Article| October 01, 2013 Magma chamber–scale liquid immiscibility in the Siberian Traps represented by melt pools in native iron Vadim S. Kamenetsky; Vadim S. Kamenetsky * 1ARC Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Hobart, TAS 7001, Australia *E-mail: Dima.Kamenetsky@utas.edu.au. Search for other works by this author on: GSW Google Scholar Bernard Charlier; Bernard Charlier 2Institut für Mineralogie, Leibniz Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany Search for other works by this author on: GSW Google Scholar Liudmila Zhitova; Liudmila Zhitova 3Novosibirsk State University, Novosibirsk 630090, Russia4V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia Search for other works by this author on: GSW Google Scholar Victor Sharygin; Victor Sharygin 3Novosibirsk State University, Novosibirsk 630090, Russia4V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia Search for other works by this author on: GSW Google Scholar Paul Davidson; Paul Davidson 1ARC Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Hobart, TAS 7001, Australia Search for other works by this author on: GSW Google Scholar Sandrin Feig Sandrin Feig 5Central Science Laboratory, University of Tasmania, Hobart, TAS 7001, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Vadim S. Kamenetsky * 1ARC Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Hobart, TAS 7001, Australia Bernard Charlier 2Institut für Mineralogie, Leibniz Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany Liudmila Zhitova 3Novosibirsk State University, Novosibirsk 630090, Russia4V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia Victor Sharygin 3Novosibirsk State University, Novosibirsk 630090, Russia4V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia Paul Davidson 1ARC Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Hobart, TAS 7001, Australia Sandrin Feig 5Central Science Laboratory, University of Tasmania, Hobart, TAS 7001, Australia *E-mail: Dima.Kamenetsky@utas.edu.au. Publisher: Geological Society of America Received: 10 Apr 2013 Revision Received: 30 May 2013 Accepted: 12 Jun 2013 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2013) 41 (10): 1091–1094. https://doi.org/10.1130/G34638.1 Article history Received: 10 Apr 2013 Revision Received: 30 May 2013 Accepted: 12 Jun 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Vadim S. Kamenetsky, Bernard Charlier, Liudmila Zhitova, Victor Sharygin, Paul Davidson, Sandrin Feig; Magma chamber–scale liquid immiscibility in the Siberian Traps represented by melt pools in native iron. Geology 2013;; 41 (10): 1091–1094. doi: https://doi.org/10.1130/G34638.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Magma unmixing (i.e., separation of a homogeneous silicate melt into two or more liquids) is responsible for sudden changes in the evolution of common melts, element fractionation, and potential formation of orthomagmatic ore deposits. Although immiscible phases are a common phenomenon in the mesostasis of many tholeiitic basalts, evidence of unmixing in intrusive rocks is more difficult to record because of the transient nature of immiscibility during decompression, cooling, and crystallization. In this paper, we document a clear case of liquid immiscibility in an intrusive body of tholeiitic gabbro in the Siberian large igneous province, using textures and compositions of millimeter-sized silicate melt pools in native iron. The native iron crystallized from a metallic iron liquid, which originated as disseminated globules during reduction of the basaltic magma upon interaction with coal-bearing sedimentary rocks in the Siberian craton. The silicate melts entrapped and armored by the native iron are composed of two types of globules that represent the aluminosilicate (60–77 wt% SiO2) and silica-poor, Fe-Ti-Ca-P–rich (in wt%: SiO2, 15–46; FeO, 15–22; TiO2, 2–7; CaO, 11–27; P2O5, 5–30) conjugate liquids. Different proportions and the correlated compositions of these globules in individual melt pools suggest a continuously evolving environment of magmatic immiscibility during magma cooling. These natural immiscible melts correspond extremely well to the conjugate liquids experimentally produced in common basaltic compositions at <1025 °C. Our results show that immiscibility can occur at large scale in magma chambers and can be instrumental in generating felsic magmas and Fe-Ti-Ca-P–rich melts in the continental igneous provinces. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The chemical compositions and abundances of volatiles in the Siberian large igneous province: Constraints on magmatic CO2 and SO2 emissions into the atmosphere

The Siberian large igneous province (SLIP) is known to be synchronous with the most severe mass extinction on the Earth at the end of Permian. The viability of the SLIP as a trigger for the mass extinction depends crucially on the total amounts of important volatiles such as CO2 and SO2 emitted from the SLIP into the atmosphere. The chemical compositions and abundances of volatiles in picrite and gabbroic rocks of the SLIP have been determined by a vacuum stepwise heating mass spectrometer system. The volatiles released at temperatures <400°C from mineral separates are interpreted to derive from secondary fluid inclusions and are therefore not included in the summation of primary volatiles which had been primarily entrapped in the minerals from magma. The primary volatiles released from different types of samples from the SLIP are characterized by dominant H2O with high contents of CO2, SO2 and H2, plus detectable He. The total amounts of primary volatiles in the picrite are 19,991mm3.STP/g (STP-standard temperature and pressure) H2O, 331 CO2, 202 H2, 28 CO, 13 SO2 and 2 H2S. The total amounts of primary volatiles in the gabbroic rocks are 2869mm3.STP/g H2O, 131 SO2, 120 H2, 85 CO2, 79 H2S and 16 CO. These data, together with other important constraints from literatures, are used to calculate the total amounts of volatiles emitted from the SLIP into the atmosphere. In our mass balance calculations we used the abundances of CO2 and SO2 in melt inclusions in olivine phenocrysts from the SLIP determined previously by other researchers to represent their initial concentrations in magma before degassing, and our new data for the SLIP picrite to represent the volatile compositions of magma (basalt) after eruption. Our results for the gabbroic rocks are used to estimate the proportions of volatiles that are still retained in the subvolcanic intrusions of the SLIP. The results reveal that the total amounts of important volatiles emitted from the SLIP are 8.5×107 Tg CO2, 4.4×106 Tg CO, 7.0×106 Tg H2S and 6.8×107 Tg SO2 (Tg, Trillion grams). These values are similar to the previous estimates using different methods by other researchers. Our data support a popular notion that the end-Permian mass extinction on the Earth was caused by the emission of enormous amounts of volatiles from the SLIP into the atmosphere.

Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Bay, Chukotka (NE Russia): Links to the Siberian LIP

In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska–Chukotka microplate prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Bay, eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments, minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U–Pb zircon age of 252 ± 4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal mafic rocks of the Kolyuchinskaya Bay region have trace elements, Sm–Nd and Rb–Sr isotope compositions identical to the tholeiitic flood basalts of the main plateau stage of the Siberian LIP, but differ from the latter in the major-element variations. We conclude that compositional variations in the hypabyssal rocks studied reflect their generation in an extensional environment that might be related to the Siberian super-plume activity at the time. Although the genetic and temporal links between intrusive mafic rocks and lavas are not well proved, compositional variations of the eruptive rocks still indicate their generation in an extensional environment.

Intracontinental strike-slip faults, associated magmatism, mineral systems and mantle dynamics: examples from NW China and Altay-Sayan (Siberia)

Abstract In the orogenic belts of the Central Asian Orogenic Belt (CAOB), many mafic and felsic plutons are temporally and spatially associated with orogen-scale strike-slip faults. The CAOB is a huge and complex orogenic collage of accreted terranes that was formed in the Early to Mid-Palaeozoic. In the CAOB, orogen-scale strike-slip faults extend for 100–1000 s of kilometres marking the boundaries of tectonic units and terranes. I use examples from southern Siberia and NW China to illustrate the important role that strike-slip faults have in localising intraplate magmatism and associated metallogeny. Cases from the Altay-Sayan in southern Siberia, the Altay and Tianshan orogens in NW China, are compelling for providing good evidence of the control that strike-slip structures exert for the emplacement of magmas and related mineral systems. These strike-slip faults controlled the emplacement of mafic-ultramafic intrusions, alkaline mafic and felsic magmatism in the period 280–240 Ma, which coincides with mantle plume(s) activity that led to the emplacement of the Tarim and Siberian large igneous provinces (LIPs). Mineral systems that are associated with these LIPs include magmatic Ni-Cu in sill-like intrusions, concentrically zoned mafic-ultramafic intrusions (e.g. Kalatongke, the second largest Ni-Cu sulphide deposit in China, after Jinchuan), epithermal systems, breccia pipes, polymetallic hydrothermal veins, granitoid-related greisen and rare earth pegmatites, as well as kimberlite fields. In the Altay-Sayan and NW China regions, orogen-scale translithospheric strike-slip faults provided the channels for the emplacement of magmas, resulting from lateral flow of mantle melts along the base of the lithosphere. This lateral flow is interpreted to have resulted from the impingement of mantle plumes to the base of the lithosphere of what was, to all intents and purposes, a stationary plate. Lateral flow from mantle plumes head was sustained or facilitated, during stages of extension and movements along orogen-scale strike-slip faults. In the Altay-Sayan and NW China, decompression melting of the mantle material produced mafic-ultramafic magmas that were emplaced along the comparatively narrow conduits of the strike-slip zones, forming concentrically zoned complexes that locally, where favourable conditions allowed it (e.g. crustal contamination), host magmatic Ni-Cu sulphides. Flow of mantle melts into translithospheric strike-slip structures also caused partial melting of a thinned and metasomatised lithosphere, resulting in alkaline magmatic products and a wide range of related mineral systems, from polymetallic veins to greisens. Partial melting of the lower crust also produced A-type granitic magmas that locally vented to the surface, forming calderas hosting epithermal and porphyry systems, as observed in NW China.