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Neotectonics, remote sensing and erosion cut of ore-controlling structures of the Mnogovershinnoe gold-silver deposit (Khabarovsk Krai, Russian Far East)
Abstract and Figures
The Mnogovershinnoe epithermal gold-silver deposit is located on the northern part of the East Sikhote-Alin magmatic belt of Northeast Russia. This deposit is related to the intrusion of a large multiphase Paleogene Bekchiul granitoid pluton. The research area underwent several episodes of intrusion magmatism, volcanism and isostatic uplifting because of its location at the junction point of large tectonic structures of Asia. The integration of in situ observations, geological mapping data, analysis of the Landsat 8 images and digital elevation data provides insights into the Meso-Cenozoic evolution of the Bekchiul magmatic center. Events in the Neogene-Quaternary were sufficiently restored by detecting areas with anomalous differences from the base level surfaces for the second- and third-order streams and numerical modeling. The anomalous values of the base levels difference far exceed the amplitude of sea level regression during the Neo-Pleistocene. The proposed methodological approach considered isostatic uplifting and sustaining activity as guiding factors in the development of the Bekchiul volcano-plutonic center.
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... To test the reliability of our own interpretations we applied to the computed relief grid an automatic lineament extraction process through the pyLEFA software developed by Shevyrev (2018Shevyrev ( , 2019. This image analysis software includes image binarization by Canny (1986) edge detection approach and the linear Hough transform algorithm for detecting linear features. ...
... 6. a) Continental local relief (2.5 km radius) versus oceanic bathymetry and interpretation of main topographic linear breaks through the Patagonian region, coincident with extrapolation of fracture zones. b) Automatic lineament detection (length > 25 km) applied over the relief grid using the pyLEFA software of image analysis developed by Shevyrev (2018Shevyrev ( , 2019. Highlighted in red color are the ENE-WSW lineament orientations (N70-90 • and N250-270 • ). ...
... truncation of degree/order N of the harmonic expansion) (Fig. 10). These ENE trending linear features are also detected through the resulting solutions of an automatic lineament processing with the pyLEFA software (Shevyrev, 2018(Shevyrev, , 2019 plotted over slope direction maps of the Tzz grids. ...
A set of fracture zones left by transform faults segmenting the active Chile Ridge that separates the Nazca and Antarctica Plates has been subducting beneath western Patagonia in the last 18 Myr. The subduction direction of these fractures zones has remained almost unaltered during this time lapse since these intersected the Chilean trench. In this context, the analyzed Patagonian sector is associated with the subduction of a highly buoyant oceanic floor due to its relatively young age that contrasts with the ocean floor bathymetry to the north where oceanic crust gets progressively older up to the Eocene and consequently isostatically subsides. Short-term elastic deformational patterns associated with the earthquake cycle have been linked to this segmentation imposed by subducting fracture zones in previous works. Similarly, this work explores the relationship between long-term topography, seismicity, gravity, and magnetic anomalies as a proxy for upper crustal structure, deformation, exhumation, and consequently surface geology segmented nature associated with this pattern of oceanic fracture zones. Through these analyses, we have identified a series of ENE structural trends or lineaments across the continental crust that could be directly related to the segmented mechanical behavior of the plate interface and enhanced by particular climatic and tectonic history of the Patagonian region. These evidences could contribute to the understanding of how fracture zones can control, to a certain extent, the segmented nature of the upper plate in a subduction setting.
... Velocities of such flow depend on media viscosity and have been measured by in-situ observations (e.g., Turcotte & Schubert, 2014, p. 283) or could be found by numerical modelling (Gerya, 2010). Density difference of 0.05 g/cm 3 has emerged from uplift velocity of 2.85 mm/yr, as indicated by modelling of quartz core buoyant flow in Bekchiul massif (northern Sikhote-Alin), which caused anomalous erosion cut and post-ore dislocations (Shevyrev, 2019). A similar process takes place in case of salt diapirism, when rock salt (withdynamic viscosity range of 5Á10 17 -10 20 PaÁs (Albertz and Ings, 2012)) forms dome-like structures. ...
... Erosion remnants, in contrast to active uplifts, generally vary with small differences in base erosional surfaces. A previous research, completed for the Bekchiul massif, showed evidence of coincidence between intrusive rocks of decreased density and local positive anomalies of base level values for the Meso-Cenozoic uplifts, expressed as BEDS23 (Shevyrev, 2019). ...
... Small size impedes discovery of similar objects, when thorough description of its tectonic position supports prospective efforts for Cu-porphyry deposits of the Albian-Cenomanian ore epoch in the Sikhote-Alin orogen. Our research involves analysis of base level values for outlining areas with abnormal behaviour of erosional base as the extinct narrow decompression zone of the upper mantle(Shevyrev, 2019). This analysis allows us to suggest the position(s) of multiphase intrusions similar to the Lazurnoe suite but still un-eroded.4 ...
The research site includes part of the East Asian region within areas of South‐East Russia and the boundary part of North‐East China. The region has abundant precious metal deposits: gold and platinum group elements. The spatial distribution of these deposits is controlled by details of crustal and mantle geodynamics including the presence of faults of different types and kinematics, active plume, as well as by the position of the region above a stagnant oceanic slab. Spatial analysis of position, geodynamics, and synchronous formation of the largest East Asian gold districts (e.g., Aldan, Baley, and Jiaodong) and platinum‐bearing massifs provide insights to their connection with mantle plumes and permeable zones at stagnant slabmargins. The occurrence of ore deposits and mineralization of precious metals inside the slab area is related to disjunctive structures of lower crust and upper mantle, such that their resources are considerably lower. This article considers numerical modeling of permeable tectonic structures exposed into mantle upwelling along active continental margins inside the slab area. Small‐scale structures of this type potentially hold two‐phase alkaline massifs, which control the positions of intra‐slab ore deposits, like the Lazurnoe Au–Mo–Cu porphyry deposit, situated in the southern part of the Sikhote–Alin belt. The small sizes of similar massifs impede their discovery, emphasizing the importance of the proposed prospective model for precious metal‐bearing porphyry deposits in Western Pacific mobile belts.
... In island arc settings, mineral deposits/occurrences of rare and precious metals related to hydrothermally-altered volcanogenic-sedimentary assemblages can be recognized through appropriate techniques for processing certain spaceborne or airborne images. Prospecting and exploration of island arc mineral resources can thus be supported by mineral prospectivity mapping using remote sensing data based on previous works (e.g., Crósta, 2003;Aydal et al., 2007;Babu et al., 2015;Shevyrev, 2019;Zhang et al., 2019;Shevyrev and Carranza, 2020;Yousefi et al., 2021;Safwat et al., 2022). Although the environment (e.g., vegetation, ground cover) and climate can complicate the recognition of mineralizationrelated alteration haloes, their influence can be reduced through appropriate image processing techniques. ...
Exploration for strategic mineral resources, like precious metals, in remote areas of the Greater Kurile Chain is challenging. Climate and weather conditions, dissected relief, soil and forest cover in this region impede acquisition of geological data. Mineral exploration requires development of fast and cost-effective methods that allow processing of insufficient and fragmented data like spaceborne images. Consideration of specific defoliation technique of directed principal components (DPC) and mineral mapping as well as application of assessment technique of Maximum Entropy (MaxEnt, also Logistic Regression, logit) led us to use Landsat 8 OLI for modeling of mineralization distribution in the Kunashir and Iturup Islands. DPC analysis is an image enhancement technique that processes two band ratio images. One of these images contains information of the component of interest (e.g., hydrothermal alteration), the other image contains information related to the spectrally interfering component (e.g., vegetation). Computed DPCs with loadings of opposite signs on either of input images, highlight unique contributions of each band ratio. Therefore, DPC analysis allows to decrease influence of noise related to vegetation. MaxEnt is a general-purpose technique of spatial prognosis based on incomplete data; its key feature is to assess the degree of target presence or absence by approximating the probability distribution of maximum entropy or nearest to uniform distribution based on a set of constraints taken from the incomplete data. Mapping based on DPC analysis in this work aimed to outline hydrothermal alteration associated with known mineralization. Division of the study area into zones according to their mineral prospectivity was then achieved with configured, trained and validated MaxEnt model using the datasets pertaining to a part of the Kunashir Island, which is better studied and explored. The trained predictive model was then applied to the less explored Iturup Island. As a result, the predictive model rendered a mineral prospectivity map, which correctly outlines the locations of the known mineralization. The application of the specific computation techniques to spectral data processing allows assessment of the contribution of Landsat 8 band ratios into the directed principal components and their implementation for cost effective prospectivity mapping including known and probable locations of unknown Au–Ag-bearing zones.
... The program includes preliminary image processing, algorithms for detecting contours, highlighting linear elements, accounting for the number of linear elements, combining collinear linear elements into lineaments, finding the fractal dimension of image contours, exporting cartographic raster (.geotiff) and linear elements (.shp) [18]. The algorithm comprises [19]: ...
This work is to study earthquake precursors using lineament analysis of five Mw3 earthquakes that occurred in 2018 on the territory of the Tashkent geodynamic polygon in Uzbekistan. The Landsat 8 satellite images were processed using the automated lineament detection method in the LEFA software. The processing steps included image preprocessing with graphic filters, edge detection using Canny's algorithm, the definition of a vector of linear elements based on the probabilistic Hough transform and combining collinear linear elements into lineaments. The analysis of the cyclicity of precursors before and after earthquakes was based on the study of the distribution of the lineaments trend in the study area using rose diagrams and lineaments density maps. The results showed a change in the dynamics of the lineament structure. The statistical analysis of lineaments revealed that the number and orientation of lineaments changed significantly about 2–4 months before an earthquake, and after 2–3 months, the system gradually returned to its initial state. The rapid increase in lineaments density began almost 20 days before the event, reaching a maximum about 4 days before the earthquake, and its decrease began 16 days after the earthquake. The main trends observed in the lineament map showed dominant trends in NS, EW, and the subdominant directions were in NW–SE, NE–SW, which coincided with main directions of the faults.
... The data provided in the text and Fig. 2 indicate the high informativity of the geophysical methods used to interpret the features of the geological structure of the region and possible impact of the deep-seated fault zones on localization of oil-and-gas and ore deposits in the Earth's crust. Further concretization of the discussed ideas and increased reliability of conclusions will be achieved by a larger use of modern methods of gravimetry, seismic tomography and remote sensing (James et al. 2011;Sigloch 2011;Jian and Chun-Feng 2015;Kuiper and Wakabayashi 2018;Fletcher et al. 2020;Shevyrev 2019). ...
Areas of noble, rare metal and polymetallic mineralization and hydrocarbon fields on the Southern Kuril Islands and Sakhalin, in the Okhotsk Sea are located above deep fault zones in the oceanic lithosphere. Such fracture zones, including the Nosappu (Tuskarora), Iturup and Urup transform faults, are known at the southwestern end of the Kuril–Kamchatka Trench, on the northwestern margin of the Pacific Plate. Seismic tomography has established the northwestern continuation of these faults in the oceanic slab, which has been subducted into the mantle transition zone; the former has also been confirmed by focal mechanism solutions of the hypocenters of deep (up to 700 km) earthquakes. In the oceanic lithosphere the fracture zones in the areas of synfault extension enabled the formation of permeable channels that convey asthenospheric heat and fluids. In the southern Sea of Okhotsk area, these fluids penetrate the mantle wedge, initiating metasomatic processes in the sub-lithospheric mantle and the creation of primary magmatic reservoirs in the lower continental lithosphere. Further migration of these fluids enabled the formation intermediate magma chambers in the crust and of domes and ore bodies. Hydrocarbons are abiogenic and of mantle origin and occur in complex, faulted and folded Cenozoic basins.
The largest Au–Ag deposits in the eastern Asian region occur along the borders of cratons and superterranes. Meanwhile, intra-terranean areas host numerous small deposits, the prospecting and exploration of which are complicated by natural factors. The target areas of the Kema Terrane and the Kema Metallogenic Belt (Sikhote–Alin Superterrane, Southeast Russia) stretch along the coast of the Japan Sea to the north from latitude 45 as a part of the Sikhote–Alin Superterrane. The Kema Terrane is an Early Cretaceous back-arc basin, and it is overlain by a volcanic–sedimentary cover that is intruded by now partially eroded Late Cretaceous and Paleogene acidic plutons. This terrane includes epithermal occurrences of Au–Ag mineralization that are related to volcanic uplifts and associated with metasomatically and hydrothermally altered volcanic rocks. Field mapping in this terrane is extremely complicated by dissected relief and dense forest cover. The novelty of this research includes overcoming difficulties in delineating new prospective areas with machine learning and decreasing vegetation effects for prospecting epithermal Au–Ag deposits. The model uses fragmented and incomplete data in combination with field sampling and laboratory analysis of alteration minerals, which accompany Au–Ag mineralization. “Mineral” images derived from directed principal component (DPC) analysis of ASTER bands were used as evidence to complement information on mineral assemblages derived from field sampling. The DPC analysis helped in partial removal of the influence of sparse and moderately dense vegetation on ASTER multispectral data. A mineral occurrence probability map (MOPM) was generated by implementation of the maximum entropy (MaxEnt) method on the DPC-derived “mineral” images. This map delineates discovered deposits not used in model training and reveals previously unknown areas with high mineral occurrence probability.
The article presents results of the research of disjunctive dislocations of the earth's crust in northern part of the Sakhalin Island by analyzing the fields of lineaments, which identified on basis of satellite surveys using the LEFA software package. The object of research was chosen not by chance: eastern part of territory of the north of Sakhalin Island is quite well studied by geological and geophysical methods in order to identify oil and gas-bearing structures, as well as in connection with the close attention to it after catastrophic Neftegorsk earthquake on May 28, 1995. The result of work of the predecessors made it possible for verify the reliability of results obtained and assess of prospects to using automated decryption technologies to identify seismically active zones. The purpose of work was to create maps of active fault zones on studied territory. In process of the work, the SRTM data and Landsat-8 satellite images for 2015-2020, obtained in eight spectral channels, were analyzed using algorithms for detecting the location of lineaments based on methods of mathematical processing of images using different algorithms. It was revealed that images obtained in the red, infrared zones of the electromagnetic spectrum (4, 5, 6, 7), and the panchromatic channel (8) are most informative for identifying disjunctive disorders. Based on the data obtained, maps of disjunctive disorders of Sakhalin Island on scale of 1: 500,000 compiled. The article has certain novelty due to fact that the LEFA technological techniques were first used for research the geologically complex structures of Northern Sakhalin. The main results of the work will be useful in choosing places for construction of economic and industrial facilities, as well as in the exploration, search and operation of mineral deposits.
Herein we provide an overview of science and technology involved in remote sensing, and outlines some practical constraints in applications to geological problems. We further summarize diagnostic spectral features of important geological material that can be detected using satellite- and air-borne remote sensing. Finally, the papers contained in the special issue are briefly introduced.
Uplift and subsidence alternate throughout the life cycle of a volcano mirroring magma accumulation, migration and/or gas pressurization, and magma cooling or depressurization, respectively. The unusual occurrence of coeval inflation and deflation is difficult to reconcile with the recharging or cooling of a single magma chamber, or hydrological processes. Here, we show a persistent flank uplift and central subsidence at Colli Albani volcano near Rome (Italy), by mapping about twenty years of deformation by InSAR data. The magmatic helium signature increases in correspondence with N-S faults along the western slope of Colli Albani, which are therefore
interpreted as deep-seated structures directly or indirectly connected with an underlying magma reservoir. Deformation modelling shows that these faults are pathways for fresh magma intrusion, whereas a residual magma is cooling below the deflating caldera. Therefore, magma recharge at depth is controlled by major faults along which the vents of the most recent activity (< 200 ka ago) concentrate in the western side of the volcano and not by the caldera structures. We demonstrate that the Colli Albani magmatic system is slowly rejuvenating, posing a volcanic threat for Rome.
We use tectonic subsidence patterns from wells and stratigraphic sections to describe the mid-Miocene to present tectonic subsidence history of the Rio Grande rift. Tectonic subsidence and therefore rift opening were quite fast until ca. 8 Ma, with net subsidence rates (~25-65 mm/k.y.) comparable to those of the prerupture phase of rifted continental margins. The rapid subsidence was followed by a late Miocene-early Pliocene unconformity that developed mainly along the flanks of most rift basins. The age of its associated lacuna is spatially variable but falls within 8-3 Ma (mostly 7-5 Ma) and thus is synchronous with eastward tilting of the western Great Plains (ca. 6-4 Ma). Tectonic subsidence rates either remained similar or decreased after the Miocene-Pliocene unconformity. North of 35°N, our analysis of geoid-to-elevation ratios suggests that, at present, topography of the Rio Grande rift region is compensated by a component of mantle-driven dynamic uplift. Previous work has indicated that this dynamic uplift is caused by focused vertical flow in the upper mantle resulting from slab descent and fragmentation of the Farallon slab, and Rio Grande rift opening, which affected the Rio Grande rift area beginning in the late Miocene. The spatial distribution and timing of the unconformity, as well as eastward tilting of the western Great Plains, can be explained by this dynamic mantle uplift, with contributions from variations in rift opening tectonics and climate. The focused mantle upwelling is not associated with increased rift opening rates.
This paper summarises developments in understanding sea level change during the Quaternary in Scotland since the publication of the Quaternary of Scotland Geological Conservation Review volume in 1993. We present a review of progress in methodology, particularly in the study of sediments in isolation basins and estuaries as well as in techniques in the field and laboratory, which have together disclosed greater detail in the record of relative sea level (RSL) change than was available in 1993. However, progress in determining the record of RSL change varies in different areas. Studies of sediments and stratigraphy offshore on the continental shelf have increased greatly, but the record of RSL change there remains patchy. Studies onshore have resulted in improvements in the knowledge of rock shorelines, including the processes by which they are formed, but much remains to be understood. Studies of Late Devensian and Holocene RSLs around present coasts have improved knowledge of both the extent and age range of the evidence. The record of RSL change on the W and NW coasts has disclosed a much longer dated RSL record than was available before 1993, possibly with evidence of Meltwater Pulse 1A, while studies in estuaries on the E and SW coasts have disclosed widespread and consistent fluctuations in Holocene RSLs. Evidence for the meltwater pulse associated with the Early Holocene discharge of Lakes Agassiz–Ojibway in N America has been found on both E and W coasts. The effects of the impact of storminess, in particular in cliff-top storm deposits, have been widely identified. Further information on the Holocene Storegga Slide tsunami has enabled a better understanding of the event, but evidence for other tsunami events on Scottish coasts remains uncertain. Methodological developments have led to new reconstructions of RSL change for the last 2000 years, utilising state-of-the-art GIA models and alongside coastal biostratigraphy to determine trends to compare with modern tide gauge and documentary evidence. Developments in GIA modelling have provided valuable information on patterns of land uplift during and following deglaciation. The studies undertaken raise a number of research questions which will require addressing in future work.
A neotectonic structural interpretation was conducted in the Fujian Province, west of the Taiwan Strait, by using computer image processing and 3D visualizations to enhance linear structural traces. The major faults in this area can be grouped into two conjugate shear fracture zones, with one trending to the northeast and the other trending to the northwest. PS-InSAR technology uses stable permanent target scatterer points to determine deformation rates and can effectively reduce the influence of spatiotemporal decorrelations and atmospheric anomalies that affect conventional D-InSAR techniques and prevent the formation of interference fringes. This study focuses on the fault zones located in the Quanzhou area of Fujian Province, where the 1604 M7.5-8.0 historic earthquake occurred. In total, 22 scenes of ERS SAR data from 1996 to 1999 were processed using PS-InSAR methods. The results show that the line of sight direction displacement rate of the main fault in the study area is 3-5 mm/yr, which indicates that the faults in this area are still active and subject to earthquake risk.
The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian land masses. The presently shallow (~ 53 m) strait was exposed during the sea-level lowstand of the last glacial period, which permitted human migration across a land bridge referred to as Beringia. Proxy studies (stabile isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9–11.7 ka). Here we provide new information on the deglacial and post-glacial evolution of the Arctic-Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 ka in the earliest Holocene, which is later when compared to several previous studies. Our key evidence is based on a well dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting around 11 ka is observed. The shift corresponds to Meltwater Pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and submergence of the large Beringia Land Bridge. Although precise rates of sea-level rise cannot be quantified, our new results suggest that the late deglacial sea-level rise was rapid, and occurred after the end of the Younger Dryas stadial.
The patterns of fractures in deformed rocks are rarely uniform or random. Fracture orientations, sizes, and spatial distributions often exhibit some kind of order. In detail, relationships may exist among the different fracture attributes, e.g. small fractures dominated by one orientation, larger fractures by another. These relationships are important because the mechanical (e.g. strength, anisotropy) and transport (e.g. fluids, heat) properties of rock depend on these fracture attributes and patterns. This paper describes FracPaQ, a new open source, cross-platform toolbox to quantify fracture patterns, including distributions in fracture attributes and their spatial variation.
An accurate picture of relative sea-level (RSL) change is a prerequisite for understanding the Quaternary history of Ireland. Consequently, sea-level research has been a prominent feature of Irish Quaternary science since its foundations in the 19th century. Over the intervening years, the methods used to study past RSL have evolved, although many of the fundamental challenges associated with its precise reconstruction remain. Ireland’s RSL history is complex and highly variable in space and over time. The quest to better understand the multiple, interacting processes driving these changes is a work in progress. This chapter provides a synopsis of RSL change around the coast of Ireland, with particular reference to recently published work and areas of current debate. It reviews the information obtained from the study of raised shorelines, focussing on the evidence for ‘pre-glacial’ sea levels. It then examines the general patterns of RSL change since the Last Glacial Maximum as inferred from geological data and geophysical modelling. The chapter concludes by briefly discussing the timing and significance of RSL maxima and minima around the Irish coast along with their implications for Ireland’s physical connection to Britain and Europe.
Understanding the effects of glacial isostatic adjustment (GIA) of the British Isles is essential for the assessment of past and future sea-level trends. GIA has been extensively examined in the literature, employing different research methods and observational data types. Geological evidence from palaeo-shorelines and undisturbed sedimentary deposits has been used to reconstruct long-term relative sea-level change since the Last Glacial Maximum. This information derived from sea-level index points has been employed to inform empirical isobase models of the uplift in Scotland using trend surface and Gaussian trend surface analysis, as well as to calibrate more theory-driven GIA models that rely on Earth mantle rheology and ice sheet history. Furthermore, current short-term rates of GIA-induced crustal motion during the past few decades have been measured using different geodetic techniques, mainly continuous GPS (CGPS) and absolute gravimetry (AG). AG-measurements are generally employed to increase the accuracy of the CGPS estimates. Synthetic aperture radar interferometry (InSAR) looks promising as a relatively new technique to measure crustal uplift in the northern parts of Great Britain, where the GIA-induced vertical land deformation has its highest rate. This literature review provides an in-depth comparison and discussion of the development of these different research approaches.
We sampled six coral microatolls that recorded the relative sea level changes over the last 230 years east of Martinique, on fringing reefs in protected bays. The microatolls are cup-shaped, which is characteristic of corals that have been experiencing submergence. X-ray analysis of coral slices and reconstructions of the highest level of survival (HLS) curves show that they have submerged at rates of a few millimeters per year. Their morphology reveals changes in submergence rate around 1829 ± 11, 1895, and 1950. Tide gauges available in the region indicate a regional sea level rise at a constant mean rate of 1.1 ± 0.8 mm/yr, which contrasts with our coral record, implying additional tectonic subsidence. Comparing our coral morphology with that of synthetic corals generated with Matlab by using the Key West tide gauge record (Florida), we show that their growth was controlled by tectonics and that a sudden relative sea level increase drowned them around 1950. Simple elastic models show that this sudden submergence probably occurred during the 21 May 1946 earthquake, which ruptured the plate interface in front of Martinique, in the mantle wedge, in an area of sustained seismic activity. The 1839 M8+ earthquake probably occurred in the same area. Long-term subsidence of microatolls indicates that this deep portion of the megathrust is probably locked down to 60 km depth during the interseismic period. Our oldest coral recorded a long-lasting period (50 years) of stable relative sea level after the 1839 earthquake, indicating that transient interseismic strain rate variations may occur in the Lesser Antilles.
Tectonically active areas, such as forearc regions, commonly show contrasting relief, differential tectonic uplift, variations in erosion rates, in river incision, and in channel gradient produced by ongoing tectonic deformation. Thus, information on the tectonic activity of a defined area could be derived via landscape analysis. This study uses topography and geomorphic indices to extract signals of ongoing tectonic deformation along the Mexican subduction forearc within the Guerrero sector. For this purpose, we use field data, topographical data, knickpoints, the ratio of volume to area (RVA), the stream-length gradient index (SL), and the normalized channel steepness index (ksn).
The results of the applied landscape analysis reveal considerable variations in relief, topography and geomorphic indices values along the Guerrero sector of the Mexican subduction zone. We argue that the reported differences are indicative of tectonic deformation and of variations in relative tectonic uplift along the studied forearc. A significant drop from central and eastern parts of the study area towards the west in values of RVA (from ∼500 to ∼300), SL (from ∼500 to ca. 400), maximum SL (from ∼1500–2500 to ∼1000) and ksn (from ∼150 to ∼100) denotes a decrease in relative tectonic uplift in the same direction. We suggest that applied geomorphic indices values and forearc topography are independent of climate and lithology. Actual mechanisms responsible for the observed variations and inferred changes in relative forearc tectonic uplift call for further studies that explain the physical processes that control the forearc along strike uplift variations and that determine the rates of uplift. The proposed methodology and results obtained through this study could prove useful to scientists who study the geomorphology of forearc regions and active subduction zones.
Enabled by recently gained understanding of deep-seated and surficial Earth processes, a convergence of views between geophysics and sedimentary geology has been quietly taking place over the past several decades. Surface topography resulting from lithospheric memory, retained at various temporal and spatial scales, has become the connective link between these two methodologically diverse geoscience disciplines. Ideas leading to the hypothesis of plate tectonics originated largely with an oceanic focus, where dynamic and mostly horizontal movements of the crust could be envisioned. But when these notions were applied to the landscapes of the supposedly rigid plate interiors, there was less success in explaining the observed anomalies in terrestrial topography. Solid-Earth geophysics has now reached a developmental stage where vertical movements can be measured and modeled at meaningful scales and the deep-seated structures can be imaged with increasing resolution. Concurrently, there have been advances in quantifying mechanical properties of the lithosphere (the solid outer skin of Earth, usually defined to include both the crust and the solid but elastic upper mantle above the asthenosphere). The lithosphere acts as the intermediary that transfers the effects of mantle dynamics to the surface. These developments have allowed us to better understand the previously puzzling topographic features of plate interiors and continental margins. On the sedimentary geology side, new quantitative modeling techniques and holistic approaches to integrating source-to-sink sedimentary systems have led to clearer understanding of basin evolution and sediment budgets that allow the reconstruction of missing sedimentary records and past geological landscapes.
Copyright © 2015, American Association for the Advancement of Science.
Spatial distribution of fluvial sediments in the Hron Upland area situated at the eastern part of the Danube Basin was investigated in purpose to reconstruct Pleistocene river basin development. The distribution of river accumulation terraces was detected on the basis of a database of 1900 wells. Base level of the terraces, interpolated for two sub-areas, was the main tool for distinguishing terrace levels. The interpolation was controlled with spatial autocorrelation analysis using Moran’s I method. Three terrace systems of rivers paleo-Hron, paleo-Žitava and paleo-Danube were identified, different in geometry, layout of the terraces and petrography of the sediment. The paleo-Hron terrace system consists of six wide north-south oriented levels retreating to the east, while terraces of paleo-Žitava are only erosive remnants of four levels retreating to the northwest. Two levels of the paleo-Danube terrace system are situated in the southern part of the researched area, oriented in west-east direction. Accumulation of the terraces started on the Pliocene-Pleistocene boundary, what is indicated by fossil mammals found in the highest terrace levels. Asymmetric uplift of the Hron Upland area reached its maximum in the south, in the Transdanubian Range Mts. realm. In the study area it reached 80 m, with average movement velocity of 0.03 mm.a-1. Uplift formed first separate river basins of the paleo-Hron and paleo-Žitava in Lower Pleistocene, followed by shift of paleo-Danube to the studied area during the Midle to Upper Pleistocene. The riverbed (channel) dynamics was connected with strong erosion together with incision into the Danube Bend Gate. Brittle tectonics influenced the terrace levels negligible, an exception being the paleo-Danube terrace in the south with 10 to 15 m offsets of normal faults.
The Atlas Mountains of Morocco, an example of an intracontinental mountain belt, display only modest tectonic shortening, yet have unusually high topography. We present new evidence from receiver functions and shear-wave splitting for localized, nearly vertical offset deformation of both crust-mantle and lithosphere-asthenosphere interfaces at the flanks of the High Atlas. These offsets coincide with the locations of Jurassic-aged normal fault reactivation that led to tectonic inversion of the region during the Cenozoic. This suggests that a lithospheric-scale discontinuity is involved in orogeny. Another significant step in lithospheric thickness is inferred within the Middle Atlas. Its location corresponds to the source of regional Quaternary alkali volcanism, where the influx of melt induced by the shallow asthenosphere appears to be restricted to the lithospheric-scale fault on the northern side of the range. Inferred stretching axes from shear-wave splitting are aligned with the highest topography, suggest- ing along-strike asthenospheric shearing in mantle flow guided by lithospheric topography. Isostatic modeling based on these improved crustal thickness and offset estimates indicates that lithospheric thinning alone does not explain the anomalous Atlas topography. Instead, an upwelling component induced by a hot mantle anomaly is also required to support the Atlas, suggesting that the timing of uplift is contemporaneous with the recent volcanism in the Middle Atlas. These observations provide a refined understanding of intracontinental orogeny and localized volcanism.
The role of mantle–lithosphere interactions in shaping surface topography
has been long debated1–3. In general3,4, it is supposed that
mantle plumes and vertical mantle flows result in axisymmetric, longwavelength
topography, which strongly differs from the generally
asymmetric short-wavelength topography created by intraplate tectonic
forces. However, identification of mantle-induced topography
is difficult3, especially in the continents5. It can be argued therefore
that complex brittle–ductile rheology and stratification of the continental
lithosphere result inshort-wavelengthmodulationandlocalization
of deformation induced by mantle flow6. This deformation
should also be affected by far-field stresses and, hence, interplay with
the ‘tectonic’ topography (for example, in the ‘active/passive’ rifting
scenario7,8). Testing these ideas requires fully coupled three-dimensional
numerical modelling of mantle–lithosphere interactions, which so
far has not been possible owing to conceptual and technical limitations
of earlier approaches. Here we present new, ultra-high-resolution, threedimensional
numerical experimentsontopographyovermantle plumes,
incorporating a weakly pre-stressed (ultra-slow spreading), rheologically
realistic lithosphere. The results show complex surface evolution, which
is very different fromthe smooth, radially symmetric patterns usually
assumed as the canonical surface signature ofmantle upwellings9. In
particular, the topography exhibits strongly asymmetric, small-scale,
three-dimensional features, which include narrow and wide rifts,
flexural flank uplifts and fault structures. This suggests a dominant
role for continental rheological structure and intra-plate stresses in
controlling dynamic topography, mantle–lithosphere interactions,
and continental break-up processes above mantle plumes.
New evidence combined with a detailed re-evaluation of postglacial fault movements, seismic activity and shoreline sequences suggests that the period of deglaciation and the early Holocene was more seismically active than the mid to Late Holocene. It is proposed that the large-scale lateral displacements formerly proposed can not be justified, rather all postglacial fault movements appear to be limited to metre-scale vertical movements along pre-existing fault lines. In addition, it is argued that the Younger Dryas ice advance may have produced localised crustal redepression but not the more widespread impact formerly proposed. Both tectonic and postglacial rebound stresses, however, may be needed to explain the contemporary seismotectonics of the Scottish Highlands.
The Cenozoic tectonic evolution of the Kurile-Kamchatkan arc system has
been reconstructed based on the spatial-tectonic setting of the
volcanic-rock formations and their petrologic-geochemical
characteristics, using gravity and seismic data. Three volcanic arc
trench systems of different ages that become successively younger toward
the Pacific have been recognized in the region: the West Kamchatka
(Eocene), Mid-Kamchatka-Kurile (Late Oligocene-Quaternary), and Recent
Kurile-Kamchatka systems. The Kamchatka volcanic belts are viewed as the
products of these systems, which originated above the subduction zones.
The geometry of the present-day Kurile-Kamchatka subduction zone and
dynamics of contemporary volcanism can be defined from seismic data. The
contemporary Kurile-Kamchatka arc can be subdivided into individual
segments in accord with its tectonic evolution and geodynamics. The East
Kamchatka segment represents the initial subduction stage (7-10 Ma ago)
of the Pacific Plate. The Petropavlovsk segment (the Malka-Petropavlovsk
zone of transverse faults) is a zone of discordant superposition of the
contemporary Kurile-Kamchatka arc over the older Mid-Kamchatka arc.
Within the South Kamchatka segment subduction remained practically
unchanged since the Late Oligocene, i.e., since the origin of the
Mid-Kamchatka-Kurile arc system, as well as within the three Kurile
segments. Geodynamics controlled magma generation and is imprinted in
the petrochemical properties of the volcanic rocks. Typical arc magmas
are generated at the steady-state geodynamic regime of subduction. Lavas
of an intraplate geochemical type are generated at initial and final
stages of subduction, and also at the Kamchatka-Aleutian junction.
The Hexi Corridor is the northmost foreland basin of the Tibetan Plateau and its formation is controlled by the northern marginal fault of Tibet, Altyn Tagh Fault (ATF)-North Qilian Shan marginal Fault (NQF), and the southern Kuantan Shan-Longshou Shan Fault (KLF). So its study is important to understanding the mechanism of Tibet formation and its influence on global climate change. The oldest Cenozoic sediments in the Corridor is the Huoshaogou Formation which consists of terrigenous fine conglomerate, sandstone, sandy mudstone and mudstone, depositing in al-luvial to lacustrine and fan delta sedimentary environments. Detailed paleomagnetic measurements of this sequence at Yumen clearly reveal eleven pairs of normal and reversed polarities. Fossil mammals found around the section support that most of the observed polarities can be well correlated with chrons between 13n and 18r of the standard geomag-netic polarity time scale, yielding ages of 40.2–33.35 Ma. The mean declinations of this sequence and its immediately above stratigraphy indicate an 18.3° rapid clockwise rotation of the Hexi Corridor. Since this sequence has been strongly folded and is capped by an angular unconformity, we think that the presence of the thick alluvial fan conglomeration at the bottom of the foreland basin may indicate the initial de-formation and uplift of the northern Qilian Shan. This proc-ess could occur at latest at 40.2 Ma, driven by the faults NQF and KLF that thrust onto the Hexi corridor respectively from its southern and northern margins. These faults are in an early response to the collision of India with Asia, while the unconformable termination and rotation of the Huoshaogou Formation at ∼33.35 Ma indicate other early episode of rapid tectonic deformation and uplift of the northern Tibet.
Density contrasts in the lower mantle, recently imaged using seismic tomography, drive convective flow which results in kilometers of dynamically maintained topography at the core-mantle boundary and at the earth's surface. The total gravity field due to interior density constrasts and boundary topography predicts the largest wavelength components of the geoid remarkably well. Neglecting dynamic surface deformation leads to geoid anomalies of opposite sign than are observed.
We present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate. The experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations. The quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision. We focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography. We show that the transient phase is strongly dependent on the initial internally drained area, which is found to decrease exponentially with time. The topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero. Steady state surfaces are characterized by a well-defined slope–area power law with a constant exponent of -0.12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero. These results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment. Uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model. Reappraising published results on the linear dependency between mean elevation, or relief, and denudation rate, we suggest that an erosion threshold is worth considering for large-scale systems.
The Korea (Tsushima) Strait is an important seaway through which the warm Tsushima Current flows into the East Sea (Japan
Sea). A paleogeographic map constrained by a regional sea-level curve developed on the basis of a number of recent 14C radiocarbon dates suggests that the Korea Strait was not closed during the last glacial period. Rather, it was open as a
channel-like seaway linking the western North Pacific and the East Sea. Some fraction of the paleo-Tsushima Current inflow
presumably continued at that time through the Korea Strait. The activity of the paleo-Tsushima Current is evidenced by the
distribution pattern of river-derived lowstand deposits, consisting of a beach/shoreface complex and lowstand deltaic wedges.
The pattern of fluvial incision across the Himalayas of central Nepal is estimated from the distribution of Holocene and Pleistocene terraces and from the geometry of modern channels along major rivers draining across the range. The terraces provide good constraints on incision rates across the Himalayan frontal folds (Sub-Himalaya or Siwaliks Hills) where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces. Farther north and upstream, in the Lesser Himalaya, prominent fill terraces were deposited, probably during the late Pleistocene, and were subsequently incised. The amount of bedrock incision beneath the fill deposits is generally small, suggesting a slow rate of fluvial incision in the Lesser Himalaya. The terrace record is lost in the high range where the rivers are cutting steep gorges. To complement the terrace study, fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate. This approach allows quantification of the effect of variations in channel slope, width, and discharge on the incision rate of a river; the determination of incision rates requires an additional lithological calibration. The two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared. In the Sub-Himalaya, river incision is rapid, with values up to 10-15 mm/yr. It does not exceed a few millimeters per year in the Lesser Himalaya, and rises abruptly at the front of the high range to reach values of ~4-8 mm/yr within a 50-km-wide zone that coincides with the position of the highest Himalayan peaks. Sediment yield derived from the measurement of suspended load in Himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range. The observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat-ramp-flat geometry of the Main Himalayan Thrust fault. The morphology of the range reflects a dynamic equilibrium between present-day tectonics and surface processes. The sharp relief together with the high uplift rates in the Higher Himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the Tibetan Plateau driven by late Cenozoic climate change, or late Miocene reactivation of the Main Central Thrust.
Seismic tomography based on P-wave travel times and improved earthquake
locations provides further evidence for mantle-wide convective flow. The
use of body waves makes it possible to resolve long, narrow structures
in the lower mantle some of which can be followed to sites of
present-day plate convergence at the Earth's surface. The transition
from subduction-related linear structures in the mid-mantle to
long-wavelength heterogeneity near the core-mantle boundary remains
enigmatic, but at least some slab segments seem to sink to the bottom of
the mantle.
The last glacial cycle was characterized by substantial millennial-scale climate fluctuations, but the extent of any associated changes in global sea level (or, equivalently, ice volume) remains elusive. Highstands of sea level can be reconstructed from dated fossil coral reef terraces, and these data are complemented by a compilation of global sea-level estimates based on deep-sea oxygen isotope ratios at millennial-scale resolution or higher. Records based on oxygen isotopes, however, contain uncertainties in the range of +/-30 m, or +/-1 degrees C in deep sea temperature. Here we analyse oxygen isotope records from Red Sea sediment cores to reconstruct the history of water residence times in the Red Sea. We then use a hydraulic model of the water exchange between the Red Sea and the world ocean to derive the sill depth-and hence global sea level-over the past 470,000 years (470 kyr). Our reconstruction is accurate to within +/-12 m, and gives a centennial-scale resolution from 70 to 25 kyr before present. We find that sea-level changes of up to 35 m, at rates of up to 2 cm yr(-1), occurred, coincident with abrupt changes in climate.
A complete suite of closed analytical expressions is presented for the surface displacements, strains, and tilts due to inclined shear and tensile faults in a half-space for both point and finite rectangular sources. These expressions are particularly compact and free from field singular points which are inherent in the previously stated expressions of certain cases. The expressions derived here represent powerful tools not only for the analysis of static field changes associated with earthquake occurrence but also for the modeling of deformation fields arising from fluid-driven crack sources.
Cambridge Core - Structural Geology, Tectonics and Geodynamics - Introduction to Numerical Geodynamic Modelling - by Taras Gerya
Tectonic movements among the African, Arabian, Aegean, and Anatolian Plates have deformed the eastern Mediterranean Basin. Since the late Pliocene, these movements caused transtensional opening of the NE-trending Antakya Graben. Tectonic uplift coupled with Quaternary sealevel fluctuations has produced several stacked marine terraces along the Mediterranean coasts on the Antakya Graben. Here, molluscs from terrace deposits that sit on both Graben flanks at elevations between ~ 3 and ~ 175 m were dated using standard electron spin resonance (ESR) dating. For molluscs in situ in the terraces, the ESR ages ranged from ~ 8.3 to ~ 214 ka, but most of the dated terraces contained molluscs reworked from several earlier deposits due to later tectonic movements, sealevel fluctuations, and associated sedimentary processes. By dating in situ fossils, such as Lithophaga, within or just above the basal contacts for the marine terraces, uplift rates were calculated on both sides of the Antakya Graben. North of the Asi River, the regional uplift rate ranges from ~ 0.43 ± 0.11 mm/yr at Samandağ to as high as 2.08 ± 0.70 mm/yr at Mağaracık Dump. South of the Asi River, uplift rates range from 0.81 ± 0.14 mm/yr at the Cliffside terrace to 2.33 ± 0.60 mm/yr at Meydan Dump I. Rather than regional movements, however, local active normal or transtensional faults, such as the Gözene, Altın, and Sinanlı Faults mainly uplifted these deposits.
Kumagai and Itô, since August 7, 1957, have been carrying out the measurements of creep, by bending, of two large beams of granite of a size of 215 × 12.3 × 6.8 cm. The results obtained in 7, 10 and 13 years were published in this journal: Vol. 14 (p. 507), Vol. 17 (p. 925) and Vol. 20 (p. 185), respectively. Those obtained hitherto in nearly 20 years are given in this paper, which shows that the creep rate today is almost the same as that 10 years ago. And we have come to the conclusion that granite can do a plastic flow with a vanishingly small yield stress, i.e. a viscous flow. The viscosity of granite under the normal temperature and pressure is 3~6×10²⁰ poises as found from the general trend of the creep. Itô and Sasajima, since August, 1974, have been carrying out the similar measurements on three granite and three gabbro beams of smaller sizes, 21×2.5×2.0 cm and 16×2.0×1.5 cm, respectively. In these experiments, an optical flat was set on the upper polished surface of the beam bent convex upward to produce interference fringes of Na-D monochromatic light. By analysing the fringes, the profile of the upper surface was determined to an accuracy of one-tenth of one wavelength. The routine determination of the profile gave a change in the amount of bending with time. Although only 2.5 years have passed, it has been found that the secondary creep of the granite specimens in the general trend is comparable with that found in the previous experiment. As for the gabbro specimens, such a creep has not yet been observed clearly. During the above two experiments, it has been observed that the creep does not show a steady and monotone progress, but does a repeated “return-back” with an irregular interval of more or less than one year. This strange phenomenon was first noticed after correcting the results of the former experiment for the annual variation of humidity. The latter experiment, being carried out in a constant humidity of neary 100%, shows a similar phenomenon. © 1978, The Society of Materials Science, Japan. All rights reserved.
The Mnogovershinnoe ore deposit is part of the Bekchiul volcano-plutonic complex, located on the northern flank of the East-Sikhote-Alinsky belt in SE Russia. The complex was developed in two stages during the Senonian (Upper Cretaceous) and Paleocene-Eocene. The early stage is represented by a poorly differentiated andesite-granodiorite association and the late stage is marked by subalkaline monzodiorite-granite intrusions. The vein-metasomatic zones with Au-Ag mineralization are associated with magmatic units of the early stage and are crosscut by large dikes of the late stage. The deposit shows features of epithermal mineralization and a higher temperature overprint. The total ca. 1000 m zone of productive mineralization shows vertical zoning characterized by gold-sulfosalt-sulfide, gold-sulfide, then gold-telluride-sulfide, and telluride-sulfide, from bottom to top. The hydrothermal system of the deposit shows evidence for mixing between fluids derived from the volcano-plutonic units and meteoric water. The mineralization is inferred to have formed from the mixing between these fluids and by the fluctuations of fluid pressure in the system.
Identifying the onset of volcano unrest and providing an unequivocal identification of volcano reawakening remain challenging problems in volcanology. At Piton de la Fournaise, renewal of eruptive activity in 2014–2015, after 41 months of quiescence and deflation, was associated with long-term continuous edifice inflation measured by GNSS. Inflation started on June 9, 2014, and its rate progressively increased through 2015. Inflation onset was rapidly followed by an eruption on June 20–21, 2014, showing that volcano reactivation can be extremely fast, even after long non-eruptive phases. This short-lived eruption involved a shallow source (1.3–1.9 km depth below the summit). The inflation that followed, and eruptions in 2015, involved a larger depth range of fluid accumulation, constrained by inverse modeling at ca. 3.9 to 1.2–1.7 km depth. This time evolution reveals that volcano reawakening was associated with continuous pressurization of the shallowest parts of its plumbing system, triggered by progressive upwards transfer of magma from greater depth. A deep magma pulse occurred in mid-April 2015 and was associated with deep seismicity (3 to 9.5 km depth) and CO2 enrichment in fluids emitted by summit fumaroles. From this date, ground deformation accelerated and the output rates of eruptions increased, culminating in the long-lasting, large-volume, August–October eruption (~ 36 Mm3). This evolution suggests that deep magma/fluid transfer through an open conduit system first provoked the expulsion of the top of the plumbing system in June 2014, and then induced the progressive vertical transfer of the entire plumbing system down to 9 km (four eruptions in 2015). The new sustained feeding of the volcano was also at the origin of the hydrothermal system perturbation and the acceleration of the eastern flank motion, which favor lateral dike propagation and the occurrence of frequent and increasingly large eruptions. Our results highlight the fast and progressive way in which basaltic magmatic systems can wake up.
We sampled six coral microatolls that recorded the relative sea level changes over the last 230 years east of Martinique, on fringing reefs in protected bays. The microatolls are cup-shaped, which is characteristic of corals that have been experiencing submergence. X-ray analysis of coral slices and reconstructions of the highest level of survival (HLS) curves show that they have submerged at rates of a few millimeters per year. Their morphology reveals changes in submergence rate around 1829 ± 11, 1895, and 1950. Tide gauges available in the region indicate a regional sea level rise at a constant mean rate of 1.1 ± 0.8 mm/yr, which contrasts with our coral record, implying additional tectonic subsidence. Comparing our coral morphology with that of synthetic corals generated with Matlab by using the Key West tide gauge record (Florida), we show that their growth was controlled by tectonics and that a sudden relative sea level increase drowned them around 1950. Simple elastic models show that this sudden submergence probably occurred during the 21 May 1946 earthquake, which ruptured the plate interface in front of Martinique, in the mantle wedge, in an area of sustained seismic activity. The 1839 M8+ earthquake probably occurred in the same area. Long-term subsidence of microatolls indicates that this deep portion of the megathrust is probably locked down to 60 km depth during the interseismic period. Our oldest coral recorded a long-lasting period (50 years) of stable relative sea level after the 1839 earthquake, indicating that transient interseismic strain rate variations may occur in the Lesser Antilles.
Late Jurassic - Cretaceous magmatism is treated from positions of evolutional development of rift-grabens (RG). Variously oriented segments of the East Sikhote-Alin volcano-plutonic belt are distinguished as independent magmatic structures, and are shown to be genetically related to the Amur and Primorie RG. In the Primorie RG successively formed volcanogenic-sedimentary complexes are recognized: 1) riftogenic (Middle-Late Jurassic) - basaltic-cherty; 2) graben (Berriassian-Valanginian) - basaltic-terrigenous; and 3) island-arc (volcanic-island) (Aptian-Albian) - basaltoid, with volcanogenic molasse deposits. It has been concluded that the through (Jurassic to Aptian-Albian) character of basaltic magmatism with diminishing volumes of chert accumulation and a growing (up to avalanching) turbidite supply reflects the RG development from a rift with a sub-oceanic crust to its total compensation by Cretaceous volcanogenic-terrigenous sediments attended by synsedimentary increase by addition (i.e. by accretion) of accretionary prisms and formation of an olistostrome. The evolution of Early Cretaceous volcanism in the graben and volcanic-island stages of the Primorie rift-graben (PRG) (Neocomian-Albian) reveals fairly distinctively an objectively regulated Ti and Na decline up to complete absence of sodic rocks in the Middle - Late Albian volcanics, and conversely, an increase in alumina content up to formation of high-alumina and extremely aluminiferous rocks in the final stage of rift closing. It is shown that basite (riftogenic) Late Jurassic - Neocomian volcanism in the RG was synchronous with the formation of basite-ultrabasite intrusive complexes in the contiguous horst-accretionary compression structures. A coincidence is recognized between lateral Cretaceous intrusive magmatism (with the formation of corresponding series) and direction of the increase by addition (accretion) of accretionary prisms from the horst-accretionary systems to the RG axial zones. It is demonstrated that in the course of the Amur RG closing, the western boundary of the zone of formation of oceanic-type basaltic-cherty associations migrated east, and in the same direction marine conditions of volcanism were gradually changed by a continental environment, which is referred to a gradual closing of the RG and migration of an intracontinental sea oceanward. Close tectono-magmatic interrelationships between the development of RG and the associated horst-accretionary systems do not permit these structures (or their separate fragments) to be rated as terranes formed independently of one another.
The analysis of geomorphic and biostratigraphic data on four key Late Glacial complexes located in the mountains of Chersky Range and Kolyma Upland has demonstrated that the Last Glaciation had reached its maximum in the second part of Karginsky Termochrone (MIS 3) and it had formed in the conditions of moderate humid and cool (subarctic) climate. The Glaciation had considerably reduced to the end of Karginsky Termochrone (MIS 3). During Sartan Cryochrone (MIS 2) the degradation of the Glaciation had continued and the Periglacial Area was widespread and accompanied with eolian and permafrost processes. On the boundary of Pleistocene and Holocene the small cirque-type glaciation had occurred due to the marine transgression. The Last Holocene glacial activity is related to Neoglacial Epoch and it appeared with the rock glaciers formation development.
A complete set of closed analytical expressions is presented in a unified manner for the internal displacements and strains due to shear and tensile faults in a half-space for both point and finite rectangular sources. Several practical suggestions to avoid mathematical singularities and computational instabilities are presented. -from Author
This paper describes two sets of results of long-term creep tests by bending of rock beams, one for large granite beams (215×12.5×6.8cm) loaded since 1957 and the other for small beams of granite (21×2.5×2.0cm) and gabbro (16×2.0×1.5cm) loaded since 1974. The results during last 27 years for the large beams and 10 years for the small beams are summarized as follows.(1) The creep curve of each specimen showed an undulatory pattern accompanying “turn-backs” in deflection. The most remarkable turn-back gave a reduction of over 10% on the total deflection in the duration of about 650 days.(2) The initial and the delayed deflections due to elasticity changed depending upon specimens. With the small specimens, the delayed deflection lasted for 200 to 300 days, reaching 10 to 45% of the initial deflection.(3) Owing to reconstruction of the laboratory buildings, the large specimens were obliged to move twice after 10 years and 24 years since the start of the experiments. The creep curve for the unloaded beam (the maximum bending stress of 12.8kg/cm2) showed a discontinuous increase in deflection after the first move and a discontinuous decrease after the second move, surprisingly with no change in the creep rate in the general trend. On the other hand, the creep curve for the center-loaded beam (the maximum bending stress of 24.8kg/cm2) was not affected by these two moves.(4) Taking the general trend as the secondary creep, the viscosity of the tested specimens was calculated by neglecting the yield stress. It was 3×1020 to 6×1020 poise for granite and 0.9×1021 to 6×1021 poise for gabbro.
Southeastern Russia occupies an area south of the Siberian Platform and east of Lake Baikal, up to the coasts of the Sea of Okhotsk and the Sea of Japan. Most of PGE placers are localized south of the Siberian Platform, mainly within the Baikal-Aldan-Stanovoi megablock. Noble-metal placers formed by PGE minerals in varying amounts are associated with the regional mafic-ultramafic complexes of different ages, namely, layered, zoned (ring) massifs and ophiolite fields. PGE mineralization is also found in layered carbonaceous strata of different ages and in several brown-coal deposits localized in the Cenozoic zones of dispersed rifting and intraplate magmatism. One of the magmatism centers is the Ussuri plume structure. The widespread regional manifestations of plume magmatism of different ages permit the development of a new approach to study the additional factors that affected the formation and localization of PGE mineralization. Based on geological, geophysical, geochemical, and mineralogical data, we have established that the conditions favorable for the formation of platinum-bearing deposits were mainly due to ore-generating plume magmatism. This magmatism gave rise to layered (in the Neoarchean and Proterozoic) and zoned (in the Phanerozoic) mafic-ultramafic massifs, which were later subjected to ore-producing magmatogene-fluid-metasomatic processes. The most favorable conditions for PGE concentration appeared in zones where late granite deposits were superposed on early layered, zoned massifs, ophiolite complexes, and layered carbonaceous strata.
We present seismic images of the mantle beneath East Russia and adjacent regions and discuss geodynamic implications. Our mantle tomography shows that the subducting Pacific slab becomes stagnant in the mantle transition zone under Western Alaska, Bering Sea, Sea of Okhotsk, Japan Sea, and Northeast Asia. Many intraplate volcanoes exist in these areas, which are located above the low-velocity zones in the upper mantle above the stagnant slab, suggesting that the intraplate volcanoes are related to the dynamic processes in the big mantle wedge above the stagnant slab and the deep slab dehydration. Teleseismic tomography revealed a low-velocity zone extending down to 660 km depth beneath the Baikal rift zone, which may represent a mantle plume. The bottom depths of the Wadati–Benioff deep seismic zone and the Pacific slab itself become shallower toward the north under Kamchatka Peninsula, and the slab disappears under the northernmost Kamchatka. The slab loss is considered to be caused by the friction between the slab and the surrounding asthenosphere as the Pacific plate rotated clockwise at about 30 Ma ago, and then the slab loss was enlarged by the slab-edge pinch-off by the hot asthenospheric flow and the presence of Meiji seamounts.
Neogene-Quaternary basalts occur as dispersed volcanic clusters in the vicinity of the Tethyan tectonic belt, possibly representing ‘far-field’ effects of the Early Tertiary collisions of Gondwana fragments with the southern margin of Eurasia. In Indochina, such a ‘Diffuse Igneous Province’ post-dates the 45–42 Ma ‘hard’ India-Asia collision and southeastward, collision induced (c. 30–17 Ma.), extrusion of Indochina. Extrusion was accommodated by left-lateral strike-slip shearing on the Ailao Shan-Red River Fault, coeval with seafloor spreading in the East Viet Nam (South China) Sea. The Indochina basalts mostly comprise shield-building tholeiites capped by small-volume undersaturated types, the latter often bearing mantle xenoliths and ‘exotic’ xenocrysts such as sapphire, zircon. They appeared at c. 17 Ma, more-or-less coinciding with the cessation of both continental extrusion and seafloor spreading. At this point extensional stress appears to have shifted westwards to continental Indochina, with magmatic activity appearing, characteristically, at ‘pull-apart’ basins. However, the relationship of mantle melting beneath this region to its geodynamic setting is controversial, being variously attributed to mantle plumes, extreme lithospheric stretching, and lateral asthenospheric displacement. There is little or no definitive evidence for regional mantle upwelling while lithosphere stretching alone appears to be insufficient to allow for melting, Here, we present geochemical and Sr, Nd, and Pb isotopic (and paleomagnetic data), for cored sections from the Pleiku and Buon Mê Thuột plateaus in south-central Viet Nam, representative in most respects of the Indochina province as a whole. In the Pleiku shield olivine tholeiite flows are intercalated with quartz tholeiites while, in contrast, alkali basalts predominate over olivine tholeiite in the Buon Mê Thuột (BMT) shield. The first of these features (in Pleiku) probably reflects crustal wall-rock reaction while the second (at BMT), suggests an atypical magma supply system, possibly reflecting a contemporaneous change in the regional stress field. In common with most Indochina shields, tholeiites at Pleiku and BMT show slightly higher Mg – for equivalent MgO contents than those of later-stage undersaturated magmas, suggesting the former may have interacted with lithospheric mantle, depleted by prior melting. On the other hand, because the xenolith- and xenocryst-bearing post-shield magmas show near-primitive, uncontaminated character, and probably tap the more fertile asthenosphere, realistic potential temperatures (Tp) may be interpolated, estimates ranging between c. 1440° and 1660 °C, as compared to expected ‘normal’ values (1280–1300 °C). The new data are used to re-examine earlier postulates that thermally anomalous asthenosphere was displaced laterally prior to and during the Early Tertiary India–Asia collision, serving as a potential driver of lithosphere extrusion while allowing for localized, transtensional mantle melting. New paleomagnetic data confirm indications of existing data that there has been little or no tectonic rotation, as predicted by the extrusion model. However, variable asthenospheric flow paths are suggested by the distribution of Pleiku, BMT, and other volcanic centers, matched by geodetic data, suggesting minimal traction between Indochina lithosphere and the underlying ductile mantle.
The Jinchang gold deposit is located in the easternmost portion of the Central Asian Orogenic Belt (CAOB), and represents one of the major gold districts in eastern Jilin-Heilongjiang provinces of China. The gold ore bodies are hosted mainly in altered Mesozoic granitoids, breccia pipes and ring and radial faults. Gold mineralization consists of alteration (stockwork in hydrothermally altered granites), breccia, and quartz-sulfide vein-types. Alteration assemblages around the alteration-style ore body show a vertical sequence of potassic, phyllic, and propylitic zones. In this study, we present U-Pb and Lu-Hf isotope data on zircons derived from mineralized granophyric granite, biotite monzogranite, granodiorite, and granite porphyry, and sericite Rb-Sr ages from the Jinchang gold deposit. The results show Pb-206/U-238 ages of 201 +/- 3 Ma (MSWD = 1.1), 203 +/- 4 Ma (MSWD = 1.4), 201 +/- 5 Ma (MSWD = 2.1), and 110 +/- 3 Ma (MSWD = 1.6), respectively. Sericite from the gold-mineralized phyllic-altered granodiorite and granite porphyry returns Rb-Sr isochron ages of 110 +/- 4 Ma (MSWD = 1.04) and 107 +/- 5 Ma (MSWD = 0.91), respectively. Our new data indicate that the gold mineralization at Jinchang took place at ca. 110 Ma and was temporally related to intrusion of the granite porphyry. Zircon epsilon Hf (200 Ma) values of the ca. 200 Ma granites vary from -4.8 to + 8.1, with T-DM
The altitudes of dated raised shorelines in parts of Fennoscandia result from the algebraic sum of isostatic emergence and eustatic submergence. As the isostatic emergence differs systematically from place to place, the eustatic rise can be calculated within narrow limits. Data from New Zealand, some of them new, together with the calculated sea levels with which they are in general agreement, support Fairbridge's recent deduction of a Postglacial sea level higher than the present. In detail, however, Fairbridge's curve of sea-level rise seems to require revision, notably in the elimination of a −15 metre level 9,000 years ago and-possibly also of a +3 to +4 metre level, 5,000 years ago.Acceptance of the calculated sea levels permits computation of the real uplift for localities on the Baltic and Canadian shields. When uplift is plotted against time, the curves obtained for all localities belong to one family, indicating that similar forces were at work at precisely the same times within both shields. This similarity, together with the high rate of uplift, particularly in early Postglacial time, makes it almost certain that isostatic rebound, following melting of the ice, has been real and not illusory.
Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sedimenthosted Au deposits in increasingly peripheral locations; and superjacent high- and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ∼100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer. The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas carbonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal- or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediatesulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the lithocaps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during porphyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeability. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems. Porphyry Cu systems are initiated by injection of oxidized magma saturated with S- and metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to <250°C, caused by solidification of the underlying parental plutons and downward propagation of the lithostatichydrostatic transition. Once the plutonic magmas stagnate, the high-temperature, generally two-phase hypersaline liquid and vapor responsible for the potassic alteration and contained mineralization at depth and early overlying advanced argillic alteration, respectively, gives way, at <350°C, to a single-phase, low- to moderatesalinity liquid that causes the sericite-chlorite and sericitic alteration and associated mineralization. This same liquid also causes mineralization of the peripheral parts of systems, including the overlying lithocaps. The progressive thermal decline of the systems combined with synmineral paleosurface degradation results in the characteristic overprinting (telescoping) and partial to total reconstitution of older by younger alteration-mineralization types. Meteoric water is not required for formation of this alteration-mineralization sequence although its late ingress is commonplace. Many features of porphyry Cu systems at all scales need to be taken into account during planning and execution of base and precious metal exploration programs in magmatic arc settings. At the regional and district scales, the occurrence of many deposits in belts, within which clusters and alignments are prominent, is a powerful exploration concept once one or more systems are known. At the deposit scale, particularly in the porphyry Cu environment, early-formed features commonly, but by no means always, give rise to the best orebodies. Late-stage alteration overprints may cause partial depletion or complete removal of Cu and Au, but metal concentration may also result. Recognition of single ore deposit types, whether economic or not, in porphyry Cu systems may be directly employed in combination with alteration and metal zoning concepts to search for other related deposit types, although not all those permitted by the model are likely to be present in most systems. Erosion level is a cogent control on the deposit types that may be preserved and, by the same token, on those that may be anticipated at depth. The most distal deposit types at all levels of the systems tend to be visually the most subtle, which may result in their being missed due to overshadowing by more prominent alteration-mineralization.
Quantitative geomorphic methods developed within the past few years provide means of measuring size and form properties of drainage basins. Two general classes of descriptive numbers are (1) linear scale measurements, whereby geometrically analogous units of topography can be compared as to size; and (2) dimensionless numbers, usually angles or ratios of length measures, whereby the shapes of analogous units can be compared irrespective of scale.
Linear scale measurements include length of stream channels of given order, drainage density, constant of channel maintenance, basin perimeter, and relief. Surface and crosssectional areas of basins are length products. If two drainage basins are geometrically similar, all corresponding length dimensions will be in a fixed ratio.
Dimensionless properties include stream order numbers, stream length and bifurcation ratios, junction angles, maximum valley-side slopes, mean slopes of watershed surfaces, channel gradients, relief ratios, and hypsometric curve properties and integrals. If geometrical similarity exists in two drainage basins, all corresponding dimensionless numbers will be identical, even though a vast size difference may exist. Dimensionless properties can be correlated with hydrologic and sediment-yield data stated as mass or volume rates of flow per unit area, independent of total area of watershed.
Export Date: 6 March 2013, Source: Scopus, CODEN: ASRSD, doi: 10.1016/j.asr.2012.10.004, Language of Original Document: English, Correspondence Address: Hashim, M.; Institute of Geospatial Science and Technology (INSTeG), Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor Bahru, Malaysia; email: mazlanhashim@utm.my, References: Abete, T., Mazzarini, F., Innocenti, F., Manetti, P., The Yerer-Tullu Wellel extensional structure (central Ethiopia): Evidences from remote sensing, petrologic and geochronologic data (1995) Geosci. Remote Sens. Symp., 1, pp. 374-376;
The hydrothermal ore-forming paleosystem of the Mnogovershinnoe deposit is reconstructed by defining lithothectonic elements
constituting ore-bearing zones with account for their formation mechanisms and positions in the conditional geochronological
scale of the hydrothermal activity and isotopic data. The use of lithotectonic elements for deciphering ore genesis events
made it possible to take into account both synchronously and successively formed parts of ore bodies, which substantially
improved the quality of the reference data for developing a dynamic model of the deposit. The approach proposed for reconstructing
the hydrothermal paleosystem of the Mnogovershinnoe deposit may be used for developing models of other ore objects.
The Western Pacific Triangular Zone (WPTZ) is the frontier of a future supercontinent to be formed at 250 Ma after present. The WPTZ is characterized by double-sided subduction zones to the east and south, and is a region dominated by extensive refrigeration and water supply into the mantle wedge since at least 200 Ma. Long stagnant slabs extending over 1200 km are present in the mid-Mantle Boundary Layer (MBL, 410–660 km) under the WPTZ, whereas on the Core–Mantle Boundary (CMB, 2700–2900 km depth), there is a thick high-V anomaly, presumably representing a slab graveyard. To explain the D″ layer cold anomaly, catastrophic collapse of once stagnant slabs in MBL is necessary, which could have occurred at 30–20 Ma, acting as a trigger to open a series of back-arc basins, hot regions, small ocean basins, and presumably formation of a series of microplates in both ocean and continent. These events were the result of replacement of upper mantle by hotter and more fertile materials from the lower mantle.
TopoToolbox contains a set of Matlab functions that provide utilities for relief analysis in a non-Geographical Information System (GIS) environment. The tools have been developed to support the work flow in combined spatial and non-spatial numerical analysis. They offer flexible and user-friendly software for hydrological and geomorphological research that involves digital elevation model analysis and focuses on material fluxes and spatial variability of water, sediment, chemicals and nutrients. The objective of this paper is to give an introduction to the linear algebraic concept behind the software that employs sparse matrix computations for digital elevation model analysis. Moreover, we outline the functionality of the toolbox. The source codes are freely available in Matlab language on the authors' webpage (physiogeo.unibas.ch/topotoolbox).
Bekchiul gold-bearing volcano-plutonic construction: magmatic associations, features of development, the scheme of formation (Lower Amur region)
- Fatyanov
Fatyanov, I.I., Khomich, V.G., 1997. Bekchiul gold-bearing volcano-plutonic construction:
magmatic associations, features of development, the scheme of formation (Lower
Amur region). Tikhookeanskaya Geol. 16, 32-44 (in Russian).