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The Emeishan flood basalts (EFB), which occur in southwestern China, are tightly associated with the Paleo-Tethyan volcanism. In order to find out relationships between the EFB and Paleo-Tethyan volcanism, a comprehensive geochemical study of EFB, MORB and IAB was carried out. Based on geochemical features, EFB can be divided into five groups, in which HM (high-Mg basalts and picrites), HT1 (high-Ti and high-HFSE basalts) and LT1 (low-Ti and high-HFSE basalts) occur in the eastern district, and LT2 (low-Ti and low-HFSE basalts) and HT2 (high-Ti and low-HFSE) occur in the western and central districts. Geochemically, the western EFB show transition features between the eastern EFB and the Paleo-Tethyan MORB-IAB in the Jinshajian-Alaoshan zones. HFSE and REE tracing indicates that HT1 flooded from an aggregate magma layer derived from fraction melting of a primitive mantle, and LT1 magmas had a major component derived from partial melting of subducted slabs. HT1, LT1 and HM with mg# varying from 82 to 32 covered an area of about 150,000 km² yield consistent Nd isotopic compositions from primitive to slight depleted mantles (ε _Nd ( T ) = 0...+3) and a mg#- ε _Nd ( T ) inverse correlation. Their (²⁰⁶Pb/²⁰⁴Pb)-(²⁰⁷ Pb/²⁰⁴Pb) data can fit NHLR. These isotopic features cannot be explained by mixing between a strong depleted upper mantle and subducted material, which implies that there existed plume magma components from the primitive lower mantle. Whereas Nd and Pb isotopic compositions for LT2, HT2 and MORB-IAB related to the Tethyan opening and subduction indicate that the magmas were derived from random mixing between strong depleted upper mantle, primitive mantle and recycled continental crust components. Sr isotopic compositions for all rocks demonstrate mainly sea-water influence from subducted oceanic crusts. Therefore, the geochemical data from the Permian EFB and MORB-IAB recorded the whole process from the Tethyan plate subduction through asthenosphere upwelling to development of the Emeishan mantle plume.

This paper is aimed at characterizing the Permian-Triassic mafic-ultramafic magmatism of the southeastern segment of Eurasia. Given a sinistral strike-slip fault in the Song Hong zone (ASRR) that occurred at about 40-25 Ma, the ultramafic-mafic complexes of the Song Da zone and intrusive bodies of the Cao Bang complex are considered the southwestern flank and southeastern continuation of the Emeishan traps, respectively. It has been shown that petrochemical and geochemical characteristics of the products of the Permian-Triassic ultramafic-mafic magmatism are controlled by effects of the interaction of a mantle-derived plume with blocks characterized by different structure of the lithosphere. It is supposed for the Song Da rift zone that heavily depleted mantle is in places beneath the continental lithosphere. Geochemical features of the picrites from northeastern Vietnam (Cao Bang complex) indicate that the subduction-related lithosphere mantle is present there. High contents of PGE in picritoids and basaltoids of the Permian-Triassic step in southeastern Asia are bearing on the plume originated in the lower mantle.

Comprehensive studies with the use of geological, petrologo-geochemical, and thermobarogeochemical methods have revealed specific features of the formation of Paleoasian ocean structures. Because of intense secondary alteration of rocks, it is especially important to analyze melt inclusions, which have retained the direct signature of ancient magmatic systems. Data on inclusions testify to the formation of boninites by crystallization of high-temperature (1330-1150

The Early Paleoproterozoic (2.5-2.3 Ga) Baltic large igneous province (BLIP) of siliceous high-magnesium series (SHMS) is localized in the eastern Baltic Shield. Within the Kola and Karelian cratons, the BLIP is made up of volcanics (from low-Ti picrites and basalts through andesites to dacites and rhyolites) in rift structures, gabbronorite dike swarms, and large layered mafic-ultramafic intrusions. Small synkinematic mafic-ultramafic intrusions are abundant in the Belomorian mobile belt. All this suggests the existence of mantle superplume beneath the region at that time. The major difference of the BLIP from Phanerozoic large igneous provinces is the composition of magmatic melts: In the BLIP, they were close in geochemistry to subduction-related magmas but were generated in within-plate environment. This suggests that the SHMS magmas were generated as a result of the melting of highly depleted mantle source and the subsequent large-scale assimilation of the lower-crust matter by primary mantle-derived high-temperature magmas during their ascent to the surface. Magmatic systems of the BLIP include four activity levels: (1) head of local plumes, where primary mantle-derived melts were generated; (2) lower crust, where mantle-derived magmas were contaminated by crustal matter and transformed into SHMS magmas; (3) upper crust, where transitional magma chambers (preserved as large layered intrusions) were localized; and (4) volcanic plateaus at the surface and subvolcanic sills beneath them.

Several Late Mesoproterozoic (0.9-1.1 Ga) tholeiitic dyke swarms crop out along the eastern border of the Sao Francisco Craton (SFC, Brazil), inside the Neoproterozoic Aracuai mobile belt (Diamantina and Conceicao do Mato Dentro) and in Archean-Paleoproterozoic terrains (Belo Horizonte, Olivenca-Itabuna and Salvador). These last dykes were virtually unaffected by the Brasilian metamorphic events and show well-preserved magmatic textures and phases.
All the dykes are characterized by high (>2 wt%) and low (<2 wt%) TiO₂ contents and show similar major element compositions, while important differences concern incompatible element contents and ratios. The southern SFC dykes (Diamantina, Conceicao do Mato Dentro and Belo Horizonte) show Nb/Y and Zr/Y ratios up to ~6 times higher than the northern ones (Olivenca-Itabuna and Salvador) implying variable residual source garnet and then heterogeneous mantle sources, due to the tholeiitic nature of these dykes. Furthermore, geochemical features as La/Nb in the ~0.7-1.9 range and Sr-Nd isotopic compositions recall both OIB (

Assessments of generalized mass-extinction causality scenarios should be made on a statistical - as opposed to an anecdotal or speculative - basis that takes explicit account of the principle that multiple occurrences of valid causal mechanisms should produce demonstrably similar effects. Previous Monte Carlo analyses of single-cause scenarios have suggested that only the time series of subareal LIP volcanic events exhibit sufficient similarity with the time series of local extinction-intensity peaks to support a causal link. Here, this Monte Carlo approach is extended to support consideration of multiple-cause extinction scenarios and applied to the consideration of links between the multiple effects of sea-level regression, bolide impact, and LIP volcanism and the extinction-intensity time series. Results indicate that all multiple-cause scenarios-including those that do not take account of LIP volcanism-exhibit sufficient numbers of positive matches with the extinction-intensity time series to be regarded as potentially valid causes for the overall pattern. Although these results do not alter the previous single-cause results, or the preference for LIP volcanism as the single most likely cause of the extinction-intensity peak distribution, they do underscore the important roles these mechanisms likely played in the formation of these biotic events (e.g., by accentuating or mitigating their magnitudes).

Support is given to the division of the Lower Kimmeridgian into the Pictonia involuta and Rasenia evoluta Zones adopted for West Siberia. It is shown that the Upper Kimmeridgian is recognizable in boreholes, still without zonation. Specific taxonomic differentiation of the Kimmeridgian families and genera of ammonites in the Northern Hemisphere permits recognition of two zoogeographic realms, circumpolar Arctic and Boreal-Atlantic, which taken together form the Panboreal Superrealm. A wide ecotone existed between them, treated as the Greenlandian-Uralian Province. In the Early Kimmeridgian, this province was part of the Arctic Realm, whereas in the Late Kimmeridgian it belonged to the Boreal-Atlantic Realm. The province is subdivided into subprovinces: nominal North Siberian and two West Siberian, western and eastern.

Study was given to the isotopic compositions of carbonate and organic carbons in the deposits of the Baikal Group in western Cisbaikalia. The section of this rock group is considered as a stratotype for the Baikalian, the upper subunit (younger than 850 Ma) of the Upper Riphean series. Results of petrographic, geochemical, and isotope studies show that relatively pure limestones and dolomites, in contrast to mixed carbonate-siliciclastic rocks, might have preserved a near-primary carbon isotope composition despite their strong recrystallization. The studied deposits have high δ¹³C

This paper is concerned with lamproites of the Tomtor massif, which we discovered in borehole cores. The lamproites are of two varieties, olivine and leucitic. Their mineral composition, petrochemistry, and geochemistry are discussed. A technique for restoration of carbonatized lamproites through chemical dissolution of superposed carbonates is proposed. The chemical composition of the insoluble residue gives insight into the composition of intact lamproite varieties. The REE patterns of the Tomtor lamproites are identical to those of Australian olivine lamproites. Taking into account the proximity of the Ebelyakh diamond placer to the Tomtor massif and the discovery of lamproitic magmatism in the latter, we suggest that the Tomtor lamproitic tuffs were the source of the Ebelyakh diamonds.

On September 25, 2002, a brilliant meteor was observed over the Mama-Chuya and Bodaibo Districts of the Irkutsk Region. Its flight was accompanied by significant light, sound, and electrophone phenomena as well as by an air shock wave. A U.S. satellite has recorded the coordinates of two observation points, and many eye-witnesses have testified to this natural phenomenon. On the basis of this information, the path of the meteorite fall has been reconstructed. In 2002-03, three expeditions explored the area where the meteorite had supposedly fallen. The main results of their complex research are reported in this paper.
In addition to the expeditions of the Irkutsk Scientific Center, experts from the Meteorite Agency of the RAS as well as teams of research workers and students from Ekaterinburg and Krasnoyarsk were engaged in the search for the meteorite matter. Neither of these groups succeeded in finding craters, or traces of fall, or fragments of this meteorite.
Examining the snow samples taken along the path of the meteorite flight, we have found mineral particles and spherules, whose origin might be linked to the cosmogenic matter precipitated from the smoke-dust ablation track of the meteorite, and analyzed them using an electron microprobe. Of the greatest interest for study are polymineral spherules and a particle of Ni-bearing pyrites and nickel-iron, whose Fe and Ni proportions correspond to those of kamacite and taenite, typical minerals of meteorites. Analysis of these mineral formations shows that they are not typical of the bedrock and weathering crust of the study area but are, in particular, similar to the spherules (micrometeorites) from the Antarctic ice discovered in the purposeful search for meteorite matter. An important argument for the meteorite origin of the found particles is the fact that the localities where they were found during the expeditions coincide with the areas of damaged and fallen forest along the projected path of the meteor.