F. A. Letnikov

Silurian granites of northern Kazakhstan: U-Pb age and tectonic position

The isotopic-geochronological studies of zircons from granites of the Borovoe, Makinsk, and Zhukei massifs located in the eastern part of the Precambrian Kokchetav median massif revealed that they were formed during the relatively brief period from 431 to 423 Ma ago, which allowed them to be united into the Early Silurian Borovoe Complex.

Genesis of Manganese Ores and Their Position in Sedimentary Basins of the Eastern Segment of the Paleoasian Ocean: Sm-Nd Isotopic and Geochemical Evidence

The first geochemical and Sm-Nd isotopic characteristics of Neoproterozoic-Cambrian manganese ores from the south folded framing of the Siberian Craton have been obtained. For manganese ores from the Podikat deposit, Tsagan-Zaba and, in part, for Slyudyanka ore manifestations, an explicit positive Eu anomaly and variable Ce behavior are typical no depending on degree of metamorphism. In the rocks of Itantsa ore manifestation and, in part, in those of Slyudyanka, REEs have distribution patterns similar to the normal sedimentary pattern and are characterized by a gentle slope with a negative Eu anomaly and by the absence of a Ce anomaly. With the geochemical peculiarities, including REE distribution in them, on aggregate, reconstruction of vast hydrothermal fields within the south framing of the Siberian Craton and spatial position of the studied manganese basins relative to the craton has become possible.

Energy parameters of deep fluid systems

Endogenous fluid systems play the role of universal energy carriers participating in practically all petrolog� ical processes [1]. Therefore, estimation of their energy parameters is very important. The fluids form a convective heat flux during their upward migration within the geological section and release their heat energy into the environment. The released heat can initiate the processes of metamorphic transformation, granitization, metasomatosis, and rock melting. It is clear that the amount of the transferred heat would depend on many factors, in particular, on the depth of the source, and correspondingly, on the thermody� namic conditions of the fluid system formation, which will reflect first of all in the component composition of the gas mixture. The other, not less important factors are the velocity of ascent (approximation to the adia� bat) and the amount of fluid with respect to the volume of the rocks. Earlier, we studied the energy parameters of individual gases up to the depths of 200 km [2, 3]. It was shown that the maximum energy input to the total heat transport is related to hydrogen and deoxidized gases. The objective of this work is to get a quantitative estimate of the ability of deep fluids to transport heat energy during their ascent from the depths of 1000 km, which corresponds to the conditions of the lower man� tle with account for the variation in the component composition. The solution of this problem is in the calculation of enthalpy for the main fluid components (

Contribution of biogenic and volcanogenic factors to formation of ferromanganese nodules of Olkhon Island (Lake Baikal)

The first data on the structure, textural features, and geochemical and mineral composition of Fe–Mn nodules of the Sasin Formation, Olkhon Island (Baikal), have been determined. A significant role in the formation of the nodules was played by hydrothermal processes with varying contributions of hydrogenic factors. The presence of reduced inclusions in the nodules and their textural features indicate the presence of various components of organic matter in the nodules, creating the conditions for local concentration of ore components. Activation of hydrothermal processes is typical for the Baikal Rift Zone in the Late Miocene–Early Pliocene, which is reflected in the composition of Fe–Mn nodules from the Sasin Formation.

Riftogenesis Attractor Structures in the Lithosphere of the Baikal Rift System: Nature and Formation Mechanism

The results of fluid regime and seismic source studysuggest that the formation and arrangement of the riftogenesis attractor structures (RAS) in the lithosphereof the Baikal Rift System (BRS) are caused by thedynamics and energy release of the fluid systems. Themechanism of RAS formation and functioning arebased on the processes of selforganization in fluidizedmelts and rocks at different decompression regimes.The absolute majority of fluid systems of the lithosphere are open dissipative ones with selforganizationprocesses typical for them; the degree of manifestationof these selforganization processes depends on theenergy state of the system and the position relative tothe equilibrium state [1]. The lithosphere was selforganized on a global level in the Early Archaean,when the energy potential of dissipation was maximaland degassing was of an areal character. As the energypotential of fluid transfer decreased, the style of allendogenous processes changed from areal to belt andlinear at the boundary between the Archaean and Proterozoic. Later on, processes of lithosphere fluidization were located along linear zones of energy dissipation (deep faults). The deeper mantle levels werereached by a fault, the higher the solvent ability andenergy capacity of a fluid were, the stronger the selforganization of matter in the fault was. As a result,hightemperature massdemanding deep fluid systemsformed and then melting sources, zones of regionalmetasomatosis, and autonomous orebearing fluidsystems were organized on their basis in the upperlithosphere.The role played by deep fluids in the formation ofregional tectonic structures is exceptionally great, soany tectonic zone of higher fluid conductivitybecomes a selforganizing system in the future. Notethat the role played by tectonic factor is obviouslydeterminative at the first stage, but fluid systemsbecome so at the following stages. It is fluid systemsthat are forces breaking and restructuring the lithosphere after the influence of the tectonic factor finished. For the structures of this kind, three evolutionstages are distinguished: (1) disturbance of stationarity, (2) growth of the system’s energy potential withenergy absorption and the system’s selforganization,and (3) reduction of the energy potential and fade outof the system as an active fluidconductor. Analysis ofthe global geochronological data on the “lifetime” offluidized zones in the lithosphere indicates that theselonglived systems evolve under an oscillating regime.In the hierarchy of natural systems, intracontinental rift systems, consisting of deep fault zones andzones functioning in a relatively narrow thermodynamical regime, are classified as mesosystems [2]. It isknown that processes of different kinds run in openstationary systems, but the average parameters of theseprocesses do not change in any chosen time interval,while they vary in different parts of the system [3].These systems that change in space and time are identified as dynamic ones [4], and it follows from the theory that dissipative dynamic systems in geological–geophysical media must have spatiotemporal attractors, which are classified as riftogenesis attractors interms of the lithosphere of the rift zone; riftogenesisattractors are the zones in the medium and time periods, where and when earthquakes with normal faultingmechanisms dominate. Based on the data on earthquake source parameters in the BRS lithosphere, threeRASs are distinguished (Fig. 1) [5], and the timeattractors reflect the “assembling” structure in termsof an evolutionary scenario with bifurcation of tripleequilibrium [6]. In accordance with the actualismprinciple, RASs are considered as attributes of theBRS Cenozoic dynamics [7], and the three stages ofvolcanic activation are explained by consecutive origination and development of the three RASs: firstly inthe South Baikal Basin (Late Cretaceous–Paleocene),then in the Khubsugul Basin (Eocene–Oligocene),and finally in the Muya Basin (postOligocene). Two“rifting” stages [8], growing rates of rift processes, andpropagation of riftogenesis in the southwest andnortheast directions from the South Baikal Basin arerelated to the appearance and twoway evolution of the

Energy Parameters of Ore-Forming Deep Fluid Systems

The energy parameters of ore-forming deep fluid systems (enthalpy and Gibbs free energy) for compounds of S, Cl, and B have been estimated by thermodynamic methods at a lithosphere depth of 1000–20 km. At a depth of 1000 km, ore-forming fluids are dominated by BF3. With a decrease in a depth to 100–20 km, the range of fluid ore-forming systems becomes wider due to the B, F, Cl, and S compounds providing a real basis for development of the voluminous ore-forming fluid systems at the top of the lithosphere.

Transport and Crystallization of Noble Platinum in Supercritical C–O–H Fluid

Experimental data is provided for the transport of platinum in a supercritical C–O–H fluid system. The transfer of platinum in space with its condensation on the surface of native carbon (diamond and amorphous carbon) in the form of micro- and nanocrystals, shapeless particles, and filamentous formations is established for the first time. The dominant participation of platinum in the formation of carbon micro- and nanotubes is demonstrated. The results are important in modeling the formation of noble metal deposits with deep fluid carbon systems.

Main stages of tectonomagmatic activity of the Tuva–Mongolian microcontinent in the Precambrian: data on the U–Pb age of zircons

The U–Pb age of zircons from Ediacaran sandstones of the cover of the Tuva–Mongolian microcontinent and the rocks of its Early Precambrian basement (Gargan block) was analyzed by the LA–ICP–MS method. The major stages of tectonomagmatic activity of this block include the Neoarchean, Paleoproterozoic (no younger than 2 Ga), and Neoproterozoic. Comparison of the age of zircons from Ediacaran terrigenous rocks of the Tuva–Mongolian microcontinent and sandstones of the reference sections of the Ediacaran shelf of the Siberian platform undeniably indicates their independent accumulation.

Sedimentary complexes of the cover of the Dzabkhan continental block: Different sedimentary basins and source areas

The geochemical and Sm–Nd isotope characteristics of Late Precambrian and Early Cambrian sandstones previously related to the sedimentary cover of the Dzabkhan continental block are reported. It is established that the Riphean and Vendian sedimentary rocks of the Ul’zitgol’skaya and Tsaganolomskaya Formations were accumulated within the Dzabkhan continental block as a result of recycling of the terrigenous deposits formed at the expense of destruction of basement rocks and younger granite. The formation of terrigenous rocks of the Bayangol’skaya Formation after a gap in sedimentation occurred in the sedimentary basin, where only the Late Riphean formations of the juvenile crust, probably of the Dzabkhan–Mandal block were the sources, without the contribution of the ancient crustal material. The Tsaganolomskaya and Bayangol’skaya Formations were formed in different sedimentary basins and cannot be related to the same complex.

Nd isotope systematics of the Vendian–Early Cambrian sedimentary ores in the northern segment of the Paleoasian Ocean

Isotope–geochemical studies of Mn, P, and Ba ores were performed in order to establish the influence of submarine hydrotherms on the formation of Early Cambrian sedimentary rocks of the southern environs of the Siberian Platform. Based on study of the geochemical and isotope (εNd) characteristics of the shallow-water Mn and Ba ores and phosphorites of southern environs of the Siberian Platform with similar ages, two types of sedimentary basins of the different geodynamic origins were distinguished: intraplate oceanic and those of the active continental margin, for which the sources of ore materials differ by the proportions of the mantle and contaminated crustal matter.