Calcite twinning strains associated with Laramide uplifts, Wyoming Province

ABSTRACT We report the results of 167 calcite twinning strain analyses (131 limestones and 36 calcite veins, n = 7368 twin measurements)t from the Teton–Gros Ventre (west; n = 21), Wind River (n = 43), Beartooth (n = 32), Bighorn (n = 32), and Black Hills (east; n = 11) Laramide uplifts. Country rock limestones record only a layer-parallel shortening (LPS) strain fabric in many orientations across the region. Synorogenic veins record both vein-parallel shortening (VPS) and vein-normal shortening (VNS) fabrics in many orientations. Twinning strain overprints were not observed in the limestone or vein samples in the supracrustal sedimentary veneer (i.e., drape folds), thereby suggesting that the deformation and uplift of Archean crystalline rocks that form Laramide structures were dominated by offset on faults in the Archean crystalline basement and associated shortening in the midcrust. The twinning strains in the pre-Sevier Jurassic Sundance Formation, in the frontal Prospect thrust of the Sevier belt, and in the distal (eastern) foreland preserve an LPS oriented approximately E-W. This LPS fabric is rotated in unique orientations in Laramide uplifts, suggesting that all but the Bighorn Mountains were uplifted by oblique-slip faults. Detailed field and twinning strain studies of drape folds identified second-order complexities, including: layer-parallel slip through the fold axis (Clarks Fork anticline), attenuation of the sedimentary section and fold axis rotation (Rattlesnake Mountain), rotation of the fold axis and LPS fabric (Derby Dome), and vertical rotations of the LPS fabric about a horizontal axis with 35% attenuation of the sedimentary section (eastern Bighorns). Regional cross sections (E-W) across the Laramide province have an excess of sedimentary veneer rocks that balance with displacement on a detachment at 30 km depth and perhaps along the Moho discontinuity at 40 km depth. Crustal volumes in the Wyoming Province balance when deformation in the western hinterland is included.

About characteristic features of naftides in connection with the process of formation of deposits

Studies have been carried out to assess the qualitative features of fluids, aimed at identifying the regularities in the differentiation of the properties of naphthides during the formation of hydrocarbon deposits outside anticlinal structures. Due to the exhaustion of hydrocarbon reserves associated with anticlinal traps, the main attention is paid to the composition of fluids confined specifically to non-anticlinal structures – to traps of a combined structure. Physicochemical properties, trace element (TE) composition, phase states of naphthides in deposits affected by hypergenetic or catagenetic processes have been analyzed using specific examples; in regions with a possible additional inflow of hydrocarbons (Romashkino group of fields in the Republic of Tatarstan); in the crystalline basement of sedimentary basins. The results of the analysis make it possible to predict the characteristic features of fluids in traps of various types at certain levels of the processes of oil formation, secondary transformation and destruction of accumulations, mainly due to the tectonic regime of the sedimentary basin. With prolonged lateral migration, at great depths with good isolation from surface weathering agents, light oils, depleted in TE, more often of nickel specialization, are found in lithologically and stratigraphically screened traps, and gas condensate accumulations are possible. At shallow depths with poor regional or local seals, heavy, highly viscous hypergene-transformed oils, natural bitumens with high concentrations of industrially significant metals V, Ni, Co, Mo Cd, U were found in traps of pinch-out zones and various types of trap screening. tectonically-screened traps) with a multiphase filling of traps and, at the same time, the influence and inflow of deep ones, i.e. more catagenically transformed fluids, it is possible to detect light oils of the nickel type or gas condensates enriched with elements of “magmatic emanations” – As, Hg, Al, B, rare earth elements. Oils filling combined traps in the crystalline basement within platform oil and gas basins, as a rule, do not differ in their compositional peculiarities in comparison with oils in overlying or adjacent parts of the sedimentary section.

Technique for the imaging crystalline basement according to the DSS data

The method of deep seismic sounding (DSS), the observation systems in which are characterized by an irregular arrangement of both sources and receivers along the profile, a significant step between receivers, as well as maximum source-receiver distances exceeding several hundred kilometers, makes it possible to obtain an image of the crystalline basement using seismic migration fields of reflected/refracted waves. The main part of the existing migration methods, the use of which makes it possible to form an image of the deep structure of the study area in the dynamic characteristics of the recorded wave field, is focused on processing seismic data obtained by the method of reflected waves with multiple overlap observation systems (MOV—CDP). And, as a rule, these migration methods are designed for a smooth change in speed with depth. At the same time, at the boundary of the crystalline basement, the speed changes very sharply, which must be taken into account when processing data using migration. The proposed method for constructing an image of the crystalline basement is based on the use of finite-difference migration of the field of reflected/refracted waves, which was developed at the Institute of Geophysics named after S. I. Subbotin National Academy of Sciences of Ukraine. This migration method is designed to isolate supercritically reflected and refracted waves recorded from the basement in the far zone of the source and takes into account the full trajectory of waves passing through a two-layer medium, at the boundary of which there is a significant jump in velocity. Thus, the migration of the field of reflected/refracted waves makes it possible to obtain a correct image of the structure of the refractive layer of the crystalline basement. The article describes in detail the algorithm of the technique for constructing an image of the crystalline basement using finite-difference migration of the field of reflected/refracted waves and its difference from similar methods of migration. The advantages and disadvantages of the proposed method are shown when solving problems of regional seismic research. Explained and illustrated the features of constructing the image of violations on the border of the foundation. The effectiveness of the technique is demonstrated on a model example and real seismic data observed by the DSS method on the territory of Ukraine.

Gravity Anomalies And Crustal Structure Of The Eastern Part Of The Verkhoyansk Fold-And-Thrust Belt, NE Russia: Evidence From The Junction Area Of The Adycha-Elga And Allakh-Yun Tectonic Zones

The results of geophysical studies of the junction area of the Adycha-Elga and Allakh-Yun tectonic zones of the Verkhoyansk fold-and-thrust belt located on the submerged eastern margin of the Siberian craton are presented. Three structural-mineral complexes are recognized: Archean-Paleoproterozoic, Mesoproterozoic-Middle Carboniferous, and Upper Carboniferous-Early Mesozoic. The Early Jurassic plume-related basaltic volcanism and suprasubduction Late Jurassic-Early Cretaceous granitoids, regional Brungadin and Suntar faults are identified. The goal of the research is to identify deep heterogeneities and clarify the structure of the Earth’s crust in the junction area of the Adycha-Elga and Allakh-Yun tectonic zones of the Verkhoyansk fold-and-thrust belt. The analysis of gravitational anomalies is carried out, their transformations are performed – distinguishing the medium and low-frequency components, the vertical derivative Vzz, and calculating the equivalent distribution of sources of density masses at depth. It is determined that the hidden granitoids of the Adycha-Elga tectonic zone are located mainly in linear zones of decompaction at a depth of about 3.5 km. In the Allakh-Yun zone, a large gravitational minimum has been identified, where it is assumed that there is a magma granitoid chamber occurring at a depth of about 9 km. The model of the deep structure of the territory is based on the analysis of materials on the reference seismic profile 3-DV with the use of gravimetric data and the regional structure of the territory. According to the results of the wave pattern interpretation, the thickness of the lithosphere varies from 41 to 44 km. The thickness of the Upper Carboniferous-Triassic terrigenous rocks is 8-12 km, Mesoproterozoic - Middle Carboniferous carbonate-terrigenous complex is up to 12 km. The Archean-Paleoproterozoic crystalline basement occurs at a depth of 19-21 km. The Conrad discontinuity is assumed at a depth of about 30 km. Intense deformations of the crystalline basement are recognized, and trans-crust faults are identified.

Interdisciplinary Fracture Network Characterization in the Crystalline Basement: A case study from the Southern Odenwald, SW Germany

The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal energy in the Upper Rhine Graben and other regions worldwide. The hydraulic properties of the basement, which are one of the key factors for the productivity of geothermal power plants, are primarily controlled by hydraulically active faults and fractures. While the most accurate in situ information about the general fracture network is obtained from image logs of deep boreholes, such data are generally sparse, costly and thus often not openly accessible. To circumvent this problem, an outcrop analogue study with interdisciplinary geoscientific methods was conducted in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the URG. Using LiDAR scanning, the key characteristics of the fracture network were extracted in a total of five outcrops, additionally complemented by lineament analysis of two different digital elevation models. Based on this, discrete fracture network (DFN) models were developed to calculate equivalent permeability tensors under assumed reservoir conditions. The influence of different parameters, such as fracture orientation, density, aperture and mineralization was investigated. In addition, extensive gravity and radon measurements were carried out in the study area, allowing for more precise localization of fault zones with naturally increased porosity and permeability. Gravity anomalies served as input data for a stochastic density inversion, through which areas of increased open porosity were identified. A laterally heterogeneous fracture network characterizes the Tromm Granite, with the highest natural permeabilities expected at the pluton margin, due to the influence of large shear and fault zones.

К вопросу о рудных формациях благородных и цветных металлов Омолонского террейна (Cеверо-Восток Азии)

The author characterizes gold, silver, copper, lead, and zinc deposits developed within the Omolon craton terrane. Outlined are ore formations (genetic types) including the deposits. The principal features of the terrane metallogeny terrane are shown as determined by the stable structure of the crystalline basement, consolidated in Early Precambrian, which resulted in contraction of the range of mineralization genetic types and in formation of deep ore- and magma-controlling faults and large deposits.