Космоструктурные позиции золоторудных объектов заангарской части Енисейского кряжа

Изучены космоструктуры заангарский части Енисейского кряжа по материалам мультиспектральных космических систем Modis и Landsat ETM+. Выделены четыре системы кольцевых структур первого порядка, интерпретируемые как глубинные очаги гранитизации. Показаны закономерности размещения золотого оруденения в космогеологических структурах. Выделенные разноранговые космогеологические структуры находят отражение в аномальных структурах геохимических полей

Heat transfer processes in the upper crust: influence of structure, fluid flow, and palaeoclimate

Numerical models constrained by geological and geophysical data form the basis of understanding the thermal regime of the Earth's crust. This dissertation focuses on modelling heat transport in the upper crust, studying the relative contributions of different processes to the specific heat flow distribution. Its vertical variation is a well known fact, caused by different processes such as changes in surface temperature, fluid flow, and heterogeneity. In particular, the first one can provide valuable information. Since the subsurface temperatures are directly related to past temperatures, their inversion into ground surface temperature histories are the only method available in palaeoclimatology to construct palaeotemperatures without using indirect proxy methods. Furthermore, a general better understanding of the processes affecting the thermal regime of the upper crust is needed for better downward continuation of thermal data, which is important for considerations about the thermal evolution of the lithosphere. A large geothermal data set from the Kola peninsula is processed and described in detail in order to prepare it for a numerical case study simulating heat transport processes in the Kola super-deep hole area. The data set includes 3400 measurements of thermal conductivity on 1375 samples from 21 boreholes with a depth up to 1.6 km and 36 temperature logs. The modelling involves 3-D forward simulation of both conductive and advective heat and mass transfer, and 1-dimensional inverse modelling for the palaeoclimatic ground temperature changes in the study area. Steady-state and transient 3-D models as well as the inverse modelling allow to estimate and quantify systematically the influence of fluid flow, spatial heterogeneity of thermal properties of rock, and palaeoclimate on the subsurface temperature field. Being aware that the information on permeability is sparse, the modelling results suggest that advection has a major influence on the vertical specific heat flow distribution. This is confirmed by inversion results which show higher temperatures during the last glacial maximum than in other areas, indicating an insulating effect of a persisting ice cover. However, forward modelling demonstrates that transient changes in surface temperature cannot be totally neglected, because their influence may reach more than half of the magnitude of the advective effects, depending on the assumed permeability and the particular climate model. The northern location of the study area required to implement latent heat effects by thawing and freezing of pore water in the numerical forward and inverse codes. So far, most geothermal investigations on past ground temperature histories in northern areas and during cold climatic episodes have not taken into account these effects. Depending on different parameters, such as the freezing period, surface temperature, and porosity, the influence on modelling results can be substantial. Since the modelling results show that latent heat effects can be neglected in the low porosity crystalline environment of the Kola area, the impact of freezing processes is shown for an example in the East European Platform. Whereas the inversions including freezing effects yield a postglacial warming of about 18 K, the neglect of latent heat effects would overestimate this result by some 6 K. This result is generalised by a study about the freezing and thawing processes in subsurface inverse modelling for a wide range of the above-named parameters. This allows to provide a more universal characterisation of the influence of latent heat effects on past temperature reconstructions by inversion. For possible corrections of existing ground surface temperature histories derived from borehole measurements, parametric relationships are developed which describe quantitatively the magnitude of these effects in terms of porosity, basal specific heat flow, present-day and past ground surface temperature history. Since a large number of synthetic model runs were were required, it was necessary to modify the applied Tikhonov inversion method. In this approach, a regularisation parameter has to be determined, representing a trade-off between data fit and model smoothness. This is achieved by the general cross validation method which makes the inversion for past temperatures faster, more automatic, and more objective. It is employed in a synthetic example, as well case studies from the Kola ultra-deep drilling site and another borehole from northeastern Poland. Although the convergence of the inversion iterations are rather different in these three cases, a satisfactory final result was obtained in each of them. Thus, this novel approach in the field of palaeotemperature inversions contributes to the current efforts to optimise the inversion methods for palaeotemperature reconstructions

Temperature measured in permafrost borehole at ICDP site 5011-3 in El'gygytgyn Crater, 2008-2011

This study focuses on the temperature field observed in boreholes drilled as part of interdisciplinary scientific campaign targeting the El'gygytgyn Crater Lake in NE Russia. Temperature data are available from two sites: the lake borehole 5011-1 located near the center of the lake reaching 400 m depth, and the land borehole 5011-3 at the rim of the lake, with a depth of 140 m. Constraints on permafrost depth and past climate changes are derived from numerical simulation of the thermal regime associated with the lake-related talik structure. The thermal properties of the subsurface needed for these simulations are based on laboratory measurements of representative cores from the quaternary sediments and the underlying impact-affected rock, complemented by further information from geophysical logs and data from published literature. The temperature observations in the lake borehole 5011-1 are dominated by thermal perturbations related to the drilling process, and thus only give reliable values for the lowermost value in the borehole. Undisturbed temperature data recorded over more than two years are available in the 140 m deep land-based borehole 5011-3. The analysis of these observations allows determination of not only the recent mean annual ground surface temperature, but also the ground surface temperature history, though with large uncertainties. Although the depth of this borehole is by far too insufficient for a complete reconstruction of past temperatures back to the Last Glacial Maximum, it still affects the thermal regime, and thus permafrost depth. This effect is constrained by numerical modeling: assuming that the lake borehole observations are hardly influenced by the past changes in surface air temperature, an estimate of steady-state conditions is possible, leading to a meaningful value of 14 ± 5 K for the post-glacial warming. The strong curvature of the temperature data in shallower depths around 60 m can be explained by a comparatively large amplitude of the Little Ice Age (up to 4 K), with low temperatures prevailing far into the 20th century. Other mechanisms, like varying porosity, may also have an influence on the temperature profile, however, our modeling studies imply a major contribution from recent climate changes

The influence of short and long term climate changes on the temperature field at the Lake El’gygytgyn site: results from borehole data and modelling

El’gygytgyn Crater Lake in NE Russia was formed by an asteroid impact 3.6 Myr ago. Since 2008 and 2009, an interdisciplinary drilling campaign has been carried out that is part of the International Continental Drilling Program (ICDP). After successful core recovery, the aim is to interpret the longest time-continuous record of climate change in the terrestrial Arctic and to set it in context with data from other marine and terrestrial sites for a better understanding of Earth’s varying climate. There are two wells from which temperature data are available. One lies beneath the lake, whereas the other one is drilled in the permafrost at the shoreline. In the latter one, a continuous temperature record over two years gives valuable information on the annual variation of ground surface temperatures, as well as indications of the deeper variation of temperatures down to a bottom depth of 140 m below surface. Numerical studies regarding the show that long term past temperature changes have a significant impact on the temperature distribution at depth and thus permafrost thickness. Particularly, the amplitude of the last glacial maximum appears to be strongly evident even in the shallow borehole data. Here, we follow up this work and focus on the thermal processes in the upper surface, studying the possi- ble influence of changing lake levels and thus the spatial and temporal variation of the talik’s dimension. Additionally, we perform sensitivity studies with regard to short and long term varying climate histories in order to quantify their influence on the subsurface temperature field. Statistical approaches help to determine uncertainty ranges within these simulations

Past climate changes and permafrost depth at the Lake El’gygytgyn site: implications from data and thermal modeling

This study focuses on the temperature field observed in boreholes drilled as part of interdisciplinary scientific campaign targeting the El’gygytgyn Crater Lake in NE Russia. Temperature data are available from two sites: the lake borehole 5011-1 located near the center of the lake reaching 400m depth, and the land borehole 5011-3 at the rim of the lake, with a depth of 140 m. Constraints on permafrost depth and past climate changes are derived from numerical simulation of the thermal regime associated with the lake-related talik structure. The thermal properties of the subsurface needed for these simulations are based on laboratory measurements of representative cores from the quaternary sediments and the underlying impact-affected rock, complemented by further information from geophysical logs and data from published literature. The temperature observations in the lake borehole 5011-1 are dominated by thermal perturbations related to the drilling process, and thus only give reliable values for the lowermost value in the borehole. Undisturbed temperature data recorded over more than two years are available in the 140m deep land-based borehole 5011-3. The analysis of these observations allows determination of not only the recent mean annual ground surface temperature, but also the ground surface temperature history, though with large uncertainties. Although the depth of this borehole is by far too insufficient for a complete reconstruction of past temperatures back to the Last Glacial Maximum, it still affects the thermal regime, and thus permafrost depth. This effect is constrained by numerical modeling: assuming that the lake borehole observations are hardly influenced by the past changes in surface air temperature, an estimate of steady-state conditions is possible, leading to a meaningful value of 14±5K for the post-glacial warming. The strong curvature of the temperature data in shallower depths around 60m can be explained by a comparatively large amplitude of the Little Ice Age (up to 4 K), with low temperatures prevailing far into the 20th century. Other mechanisms, like varying porosity, may also have an influence on the temperature profile, however, our modeling studies imply a major contribution from recent climate changes