N. M. Sushchevskaya

The Amount of Recycled Crust in Sources of Mantle-Derived Melts

One proposed strategy for controlling the transmission of insect-borne pathogens uses a drive mechanism to ensure the rapid spread of transgenes conferring disease refractoriness throughout wild populations. Here, we report the creation of maternal-effect selfish genetic elements in Drosophila that drive population replacement and are resistant to recombination-mediated dissociation of drive and disease refractoriness functions. These selfish elements use microRNA-mediated silencing of a maternally expressed gene essential for embryogenesis, which is coupled with early zygotic expression of a rescuing transgene.The phosphoinositide phosphatase PTEN is mutated in many human cancers. Although the role of PTEN has been studied extensively, the relative contributions of its numerous potential downstream effectors to deregulated growth and tumorigenesis remain uncertain. We provide genetic evidence in Drosophila melanogaster for the paramount importance of the protein kinase Akt [also called protein kinase B (PKB)] in mediating the effects of increased phosphatidylinositol 3,4,5-trisphosphate (PIP3) concentrations that are caused by the loss of PTEN function. A mutation in the pleckstrin homology (PH) domain of Akt that reduces its affinity for PIP3 sufficed to rescue the lethality of flies devoid of PTEN activity. Thus, Akt appears to be the only critical target activated by increased PIP3 concentrations in Drosophila.Using genomic and mass spectrometry-based proteomic methods, we evaluated gene expression, identified key activities, and examined partitioning of metabolic functions in a natural acid mine drainage (AMD) microbial biofilm community. We detected 2033 proteins from the five most abundant species in the biofilm, including 48% of the predicted proteins from the dominant biofilm organism, Leptospirillum group II. Proteins involved in protein refolding and response to oxidative stress appeared to be highly expressed, which suggests that damage to biomolecules is a key challenge for survival. We validated and estimated the relative abundance and cellular localization of 357 unique and 215 conserved novel proteins and determined that one abundant novel protein is a cytochrome central to iron oxidation and AMD formation.

Remnants of Gondwanan continental lithosphere in oceanic upper mantle: Evidence from the South Atlantic Ridge

Dredged glass from the southern Mid-Atlantic Ridge near the Bouvet Triple Junction has unique major element, trace element, and isotopic composition, distinct from typical mid-ocean ridge basalts, It is a high-Mg (Mg# 67.8), high-Ni (NiO 290 ppm) andesite depleted in highly incompatible and heavy rare-earth elements with an isotopic signature of ancient continental lithosphere (i.e., low (206)Pb/(204)Pb and Nd-143/Nd-144 and high Sr-87/Sr-86 and delta O-18). The origin of this glass is attributed to melting of a Precambrian garnet-bearing, mafic lithology, possibly related to lower crustal blocks stranded in the upper mantle during breakup of Gondwana and opening of the Atlantic. This composition can be used to explain anomalous geochemical features of oceanic rocks in the Southern Hemisphere.

Evolution of the Karoo-Maud mantle plume in antarctica and its influence on the magmatism of the early stages of Indian ocean opening

New results on the petrochemistry and geochemistry of dolerites from the Schirmacher Oasis shed light on the development of the Karoo-Maud plume in Antarctica. The basalts and dolerites are petrologically identical to the rocks of western Dronning Maud Land (DML), which were previously studied and interpreted as a manifestation of the Karoo-Maud plume in Antarctica. The spatial distribution of the dikes suggests eastward spreading of the plume material, up to the Schirmacher Oasis for at least 10 Ma. The geochemical characteristics of magmas from the Schirmacher Oasis reflect the influence of crustal contamination, which accompanied both the ascent and spreading of the plume. The magmas of the initial stage of plume activity (western DML) appeared to be the most contaminated in crustal components.It was found that the geochemical characteristics of Mesozoic magmas from the Schirmacher Oasis are identical to those of enriched tholeiites from the Afanasy Nikitin Rise and the central Kerguelen Plateau (Hole 749), which indicates that their enrichment was related to the ancient material of the Gondwana continent. This was caused by the opening of the Indian Ocean under the influence of the Karoo-Maud plume. This process was peculiar in that it occurred in the presence of nonspreading blocks of varying thickness, for instance, Elan Bank in the central Kerguelen Plateau, and was accompanied by the formation of intraplate volcanic rises, which are documented in the seafloor relief of basins around Antarctica. The geochemical characteristics of igneous rocks from the resulting rises (Afanasy Nikitin, Kerguelen, Naturaliste, and Ninetyeast Ridge) indicate the influence of processes related to crustal assimilation. The magmatism that occurred 40 Ma after the main phase of the Karoo-Maud volcanism at the margins of the adjacent continents of Australia (Bunbury basalts) and India (Rajmahal trapps) could be generated by the Karoo-Maud plume flowing along the developing spreading zone. The plume moved subsequently and was localized at the Kerguelen Plateau, where it occurs at present as an active hotspot.

Geochemical features of the quaternary lamproitic lavas of Gaussberg Volcano, East Antarctica: Result of the impact of the Kerguelen plume

Petrological-geochemical data were obtained on the lamproites of the Gaussberg Volcano located at the eastern Antarctic coast and compared with data on the magmatic rocks developed in the East Antarctica and Indian Ocean in relation with the Kerguelen plume. It was shown that the lamproites were derived from the ancient Gondwana lithosphere repeatedly modified at the early stages of its evolution, including significant enrichment in volatiles, lithophile elements, and radiogenic Sr and Pb isotopes.The Gaussberg Volcano located on the eastern Antarctic continental margin falls in the distribution field of the Kerguelen plume, which formed 130 Ma within the incipient Indian Ocean and is continuing to operate at present, forming volcanic rocks of Heard Island in the last ka. Manifestations of alkaline magmatism at the Antarctic margin around 56 ka (Mt. Gaussberg) indicate a sublithospheric spreading of mantle plume in the southwestern direction.

Geochemistry of Neogene magmatism at Spitsbergen Island

Petrological and geochemical data obtained on Neogene magmatism restricted to a deep fault in Andree Land at Spitsbergen Island, which was related to the overall restyling of the Arctic territory at 25–20 Ma, indicate that the derivation of the Neogene magmas was significantly affected by the continental pyroxenite mantle. The Neogene basalts are noted for a radiogenic isotopic composition of Pb (207Pb/204Pb= 15.5–15.55, 206Pb/204Pb = 18.4–18.6, 208Pb/204 Pb = 38.4–38.6) and Sr(87Sr/86Sr = 0.7038–0.7048) at low 143Nd/144Nd = 0.5129. Melts of this type are the extremely enriched end member of the isotopic mixing of a depleted and enriched sources and determine a geochemical trend that passes through the compositions of alkaline magmas from Quaternary volcanoes at Spitsbergen and weakly enriched tholeiites of the Knipovich Ridge, which started to develop simultaneously with the onset of Neogene magmatism in the western part of Spitsbergen. The composition of the liquidus olivine (which is rich in NiO) indicates that melting occurred in the olivine-free mantle. Our data thus testify that a significant role in the genesis of the Neogene magmas was played by continental pyroxenite mantle.

The structure of the Knipovich-Mohns junction (North Atlantic)

In 2007, the Geological Institute of the Russian Academy of Sciences (GIN RAS) carried out investigations in the North Atlantic, in the southern part of the Knipovich Ridge extending for 600 km from the Mohns spreading ridge to the Molloy fault zone (chief of the cruise A.V. Zaionchek). The investigations were conducted according to the Program of the RAS Presidium entitled “Basic Problems of Oceanology: World Ocean Physics, Geology, Biology, Ecology” (Project “Regularities of the Structure and Formation of the Oceanic Crust in Characteristic Regions of the Atlantic Ocean: Tectonics, Magmatism, Composition and Genesis of Fe‐Mn Deposits,” supervisor Academician Yu.M. Pushcharovskii). The problem facing the expedition was to study the geological structure of the Knipovich‐Mohns junction. With the help of the R/V Akademik Nikolaj Strakhov (Cruise 25), there were conducted complex areal, medium-scale, regional geological study of the selected object, which involved echo-sounding with SeaBat 7150 multibeam sounder, continuous seismic profiling (CSP), high-frequency sounding with the Edgetech 3300 profiler, and bottom dredging (Fig. 1). Within the region of 74 ° N, south of the Greenland Fault Zone (FZ) extending southeastward, the Mohns spreading ridge passes into the north‐south-trending Knipovich Ridge. The peculiarity of both ridges is that these are unified extensive spreading structures not broken into segments by transform faults. The ridges differ in the time and conditions of formation. From the beginning of formation, regular and steady growth of the oceanic crust in the rift zone was characteristic of the Mohns Ridge, which is marked by the symmetrical and natural position of linear magnetic anomalies relative to the rift valley axis [1, 2]. The Knipovich Ridge began forming under unsteady geodynamic conditions, which was reflected in the disordered position and fragmentation of magnetic anomalies. The region of the Mohns and Knipovich junction attracts the attention of researchers in that this is a unique area where one spreading ridge passes into another with rift valley structures gradually bending by 40 ° without apparent transform faults serving as accommodation zones for stresses generated in the course of plate motions. Hence, the geodynamics of structures in this key region has been the subject of investigations.

Conditions of Quaternary magmatism at Spitsbergen Island

Petrological and geochemical data obtained on the Quaternary lavas of volcanoes at Spitsbergen Island indicate that the rocks were produced via the deep-seated crystallization of parental alkaline magmas at 8–10 kbar. The character of clinopyroxene enrichment in incompatible elements indicates that the mineral crystallized from more enriched melts than those inferred from the composition of the host lavas. These melts were close to the parental melts previously found as veinlets in mantle hyperbasite xenoliths in the lavas. According to the character of their enrichment in Pb and Sr radiogenic isotopes and depletion in Nd, the basalts from Spitsbergen Island define a single trend with the weakly enriched tholeiites of the Knipovich Ridge, a fact suggesting the closeness of the enriched sources beneath the continental margin of Spitsbergen and beneath the spreading zone. Magmatic activity at Spitsbergen was related to the evolution of the Norwegian-Greenland basin, which evolved in pulses according to the shift of the spreading axes. The most significant of the latter events took place in the Neogene, when the Knipovich Ridge obtained its modern position near the western boundary of Spitsbergen. Early in the course of the evolution, the emplacement of alkaline melts generated at Spitsbergen into the oceanic mantle could form the enriched mantle, which was later involved in the melting process beneath the spreading zone.

Ninetyeast Ridge: Magmatism and Geodynamics

The study of magmatism and tectonic structure of the East Indian or Ninetyeast Ridge (NER) reveals the geochemical similarity of mantle sources for the NER and Kerguelen Plateau melts. Magmas related to the Kerguelen plume were derived from an enriched mantle source, whereas the NER tholeiitic basalts originated from a source contaminated by a depleted material. While, depleted basalt varieties were not found within the NER basalts. It was shown that magmatic rocks forming the NER were generated by high degrees (30%) of partial melting within the ancient Wharton spreading ridge due to the activity of the Kerguelen plume, which was located at this time in the vicinity of the ridge. The most significant impact of the plume on the NER structures was recorded at 70–50 Ma ago.

Geochemical evolution of Indian Ocean basaltic magmatism

AbstractA comparison of new and published geochemical characteristics of magmatism in the western and eastern Indian Ocean at the initial and recent stages of its evolution revealed several important differences between the mantle sources of basaltic melts from this ocean. 1.The sources of basalts, from ancient rises and from flanks of the modern Central Indian Ridge within the western Indian Ocean contain an enriched component similar in composition to the source of the Réunion basalts (with radiogenic Pb and Sr and unradiogenic Nd), except for basalts from the Comores Islands, which exhibit a contribution from an enriched HIMU-like component.2.The modern rift lavas of spreading ridges display generally similar geochemical compositions. Several local isotopic anomalies are characterized by the presence of an EM2-like component. However, two anomalous areas with distinctly different enriched mantle sources were recognized in the westernmost part of the Southwestern Indian Ridge (SWIR). The enriched mantle source of the western SWIR tholeiites in the vicinity of the Bouvet Triple Junction has the isotopic ratios indicating a mixture of HIMU + EM2 in the source. The rift anomaly distinguished at 40° E displays the EM1 signature in the mantle source, which is characterized by relatively low 206Pb/204Pb (up to 17.0) and high 207Pb/204Pb, 208Pb/204Pb and 87Sr/86Sr. This source may be due to mixing with material from the continental lithosphere of the ancient continent Gondwana. The material from this source can be distinguished in magmas related to the Mesozoic plume activity in Antarctica, as well as in basalts from the eastern Indian Ocean rises, which were formed by the Kerguelen plume at 100–90 Ma.3.The geochemical heterogeneities identified in the ancient and present-day magmatic products from the western and eastern Indian Ocean are thought to reflect the geodynamic evolution of the region. In the eastern part of the ocean, the interaction of the evolving Kerguelen plume with the rift zones produced magmas with specific geochemical characteristics during the early opening of the ocean; such a dispersion of magma composition was not recognized in the western part of the ocean.

Geochemical and Petrological Characteristics of Mesozoic Dykes from Schirmacher Oasis (East Antarctica)

Olivine-bearing dolerite and gabbro-dolerite dykes intruded host Precambrian metamorphic rocks of oasis Schirmacher most likely represented Jurassic trap activities in this region of Antarctica. Olivine shows a wide composition range between Fo91.5 to Fo55, which proves strong influence of accumulation processes during melt differentiation. Most common olivine compositions correspond to Fo88 – Fo89, which are close to some olivine compositions reported for less-evolved Jurassic basalts in Vestfjella, western Dronning Maud Land. Relative deviations from the QWM buffer are about 1–1.2. Clinopyroxene crystallization followed precipitation of olivine and plagioclase. Clinopyroxene has wide mg# variation range between 81 and 69 and low Cr/Al (0.01–0.14) and Na/Al (0.1–0.15) ratios. Using clinopyroxene composition Schirmacher Oasis dyke samples yield pressure estimations at 2 kbar (by mean temperature – 1,100°C), which points out to a shallow crystallization environment. Similar crystallization pressure was also calculated for western Dronning Maud Land magmas. The isotope compositions of Schirmacher Oasis dolerites demonstrate clearly radiogenic signatures: 87Sr/86Sr: 0.7045–0.7047, 208Pb/204Pb: 37.98–38.2; 207Pb/204Pb: 15.45–15.52; and reflect the crust contamination process, which took place during plume upwelling and emplacement into crust level. The studied plume-related magmatism within the Schirmacher oasis proves the distribution of Karoo-Maud plume in Antarctica, which is determined by the splitting of Gondwana continent and formation of the Indian Ocean, to the east – from Queen Maud Land towards Schirmacher oasis during the period of 10 m.y.