Depth Of Crystalline Basement Research Articles

Ambient noise tomography of an iron-oxide copper–gold (IOCG) deposit under thick cover

As most outcropping and shallow mineral deposits have been found, new technology is imperative to finding the hidden critical mineral deposits required for the renewable energy transition. One such seismic technique, called ambient noise tomography (ANT), has shown promise in recent years as a low cost and low environmental impact passive method of three-dimensional (3D) imaging of shear-wave velocity structure of the Earth. Over the last twenty years the method has been well-established in academia to image crustal and regional scale geological features but has seldom been used at the mineral exploration deposit-scale. In this paper we show the application of seismic ANT at an IOCG deposit in South Australia under more than 750 m of sedimentary cover. A 100-site survey in a 10 by 10 grid with site spacing of 1 km, using 3-component nodal seismometers with a natural-frequency of 5 Hz, was conducted over a two-week period. Data were inverted to generate a 3D velocity model to a depth of 2 km. When compared to drillholes in the survey area, the tomographic model delineates cover sequence lithologies and the depth of crystalline basement. A velocity anomaly in the basement has characteristics of a potential IOCG deposit and is aligned with a gravity anomaly due to brecciated haematite. The results of the paper indicate that ANT is a useful tool for deep cover mineral exploration that can potentially expedite the discovery of new deposits.

Detecting sub-basalt Mesozoic sediments and active tectonics in the Narmada-Tapti Rift Zone, central India

To obtain structural information below basalt cover using conventional seismic reflection has always been a challenge due to the high impedance of the basaltic layer. This study enumerates P-wave refraction tomography to image the shallow structure along three long offset profiles in the Deccan Volcanic Province, one of the world's largest flood basalt volcanic regions. The travel time inversion is performed to obtain a starting model for the wavefield inversion, and synthetic tests are used to estimate the resolution. Our results show an abrupt increase of crystalline basement depth from 1.5 to 3 km across the Narmada South Fault. The shallow basement depth coincides with a 70-km-wide sub-basalt (>1.5 km deep) seismic shadow zone between the Narmada and Tapti rivers, associated with the sub-basalt graben caused by a crustal extension that contains sediments or a combination of basalt and sediments. The basaltic layer appears to be highly heterogeneous in velocity and thickness, and the degree of heterogeneity increases laterally and vertically with depth within the layer. It is quite likely that these sub-basalt sediments could be the potential zone for hydrocarbon, similar to the exposed Vindhyan in the north and Gondwana sediments in the south of our study area. Another intriguing feature is the Barwani Sukta Fault, which controls the tectonics of the region by dividing the basement configuration. We also compare our tomographic model with those determined from previously obtained seismic, gravity, and surface mapping. The tomographic image clearly shows that numerous faults are reaching up to the basement and extending laterally. We suggest that these neo-tectonic faults may be capable of generating large-magnitude earthquakes, including the 21 May 1997 (mb 6.0) Jabalpur earthquake.

High-Resolution Crustal S-wave Velocity Model and Moho Geometry Beneath the Southeastern Alps: New Insights From the SWATH-D Experiment

We compiled a dataset of continuous recordings from the temporary and permanent seismic networks to compute the high-resolution 3D S-wave velocity model of the Southeastern Alps, the western part of the external Dinarides, and the Friuli and Venetian plains through ambient noise tomography. Part of the dataset is recorded by the SWATH-D temporary network and permanent networks in Italy, Austria, Slovenia and Croatia between October 2017 and July 2018. We computed 4050 vertical component cross-correlations to obtain the empirical Rayleigh wave Green’s functions. The dataset is complemented by adopting 1804 high-quality correlograms from other studies. The fast-marching method for 2D surface wave tomography is applied to the phase velocity dispersion curves in the 2–30 s period band. The resulting local dispersion curves are inverted for 1D S-wave velocity profiles using the non-perturbational and perturbational inversion methods. We assembled the 1D S-wave velocity profiles into a pseudo-3D S-wave velocity model from the surface down to 60 km depth. A range of iso-velocities, representing the crystalline basement depth and the crustal thickness, are determined. We found the average depth over the 2.8–3.0 and 4.1–4.3 km/s iso-velocity ranges to be reasonable representations of the crystalline basement and Moho depths, respectively. The basement depth map shows that the shallower crystalline basement beneath the Schio-Vicenza fault highlights the boundary between the deeper Venetian and Friuli plains to the east and the Po-plain to the west. The estimated Moho depth map displays a thickened crust along the boundary between the Friuli plain and the external Dinarides. It also reveals a N-S narrow corridor of crustal thinning to the east of the junction of Giudicarie and Periadriatic lines, which was not reported by other seismic imaging studies. This corridor of shallower Moho is located beneath the surface outcrop of the Permian magmatic rocks and seems to be connected to the continuation of the Permian magmatism to the deep-seated crust. We compared the shallow crustal velocities and the hypocentral location of the earthquakes in the Southern foothills of the Alps. It revealed that the seismicity mainly occurs in the S-wave velocity range between ∼3.1 and ∼3.6 km/s.

Geological structure of South Caspian depression and onshore of Azerbaijan based on temperature data and gravimetric modelling

The paper aims to justify the thickness of sedimentary cover along the aquatory of South Caspian basin and Azerbaijan onshore (including South and Middle Kur basin and Yevlakh-Aghjabedy downfall), the cover thickness of crystalline basement, specifying its structural position and key tectonic borders, as well as the confirmation of some issues on geodynamic evolution. Such comparison was carried out via published seismic temperature, gravimetric and magnitometric data. Definite dependences of geothermal gradients, the thickness of sedimentary cover and crystalline basement depth have been specified.

АНАЛІЗ ГІДРОГЕОЛОГІЧНИХ І ГЕОТЕРМІЧНИХ ХАРАКТЕРИСТИК ГЕОТЕРМАЛЬНИХ ОБ’ЄКТІВ УКРАЇНИ

На основі матеріалів «Державного інформаційного геологічного фонду України» створено базу даних геотермальних об’єктів, в яку увійшло 655 об’єкта, які охоплюють 12 адміністративних областей України і близько 54 % існуючих родовищ вуглеводнів. Основними геотермічними і гідрогеологічними характеристиками об’єктів бази даних є: глибина залягання, літологія і склад порід, геологічний вік порід, товщина продуктивного горизонту, пластова температура і пластовий тиск, дебіт свердловини, зниження рівня води у водоносному горизонті під час випробування, мінералізація, газовий склад і вміст природного газу у підземних водах.
 Аналіз гідрогеологічних і геотермічних характеристик геотермальних об’єктів виконано на основі структурно-гідрогеологічного принципу, тобто усі об’єкти розглядались стосовно крупних гідрогеологічних структур з єдиними регіональними межами і умовами формування родовищ підземних вод. Було проаналізовано чотири гідрогеологічні структури: Закарпатський внутрішній прогин, Прикарпатський передгірний прогини, Дніпровсько-Донецький артезіанський басейн та Причорноморський артезіанський басейн. Для кожної структури побудовано діаграми розподілу пластових температур, глибин залягання і мінералізації підземних вод в геотермальних об'єктах бази даних.
 Аналіз показав, що умови формування геотермальних родовищ в першу чергу залежать від теплового фону земних надр, але на процеси формування родовищ дуже істотний вплив має глибина залягання кристалічного фундаменту, розташування областей живлення і розвантаження термоводоносних горизонтів, глибина сучасного водообміну, літологічний склад водовмісних порід.
 Створена база даних геотермальних об’єктів України може бути використана під час вибору першочергових проектів освоєння геотермальних ресурсів, а також для стратегічного планування геотермальної галузі в цілому. Бібл. 10, рис. 14.

Study on structure of the Earth’s crust in Thua Thien-Hue province and adjacent areas by using gravity and magnetic data in combination

This paper presents the structural characteristics of the Earth’s crust in Thua Thien-Hue province and adjacent area based on interpretation of gravity and magnetic data in combination. Research results have shown that: The depth of crystalline basement varies complicatedly, in the range of 0–11 km. The depth of Conrad surface increases from Northeast (12 km) to Southwest (18 km) and the depth of Moho surface is 23–34 km; The density of sedimentary layer changes from 2.61 g/cm3 to 2.65 g/cm3. Meanwhile, the density of granitic layer is in the range of 2.68–2.73 g/cm3. The basaltic layer has the density value of 2.88–2.93 g/cm3 and the average density of lower layer of the Earth’s crust is about 3.30 g/cm3; The depth of second-order faults, Red River and A Luoi - Rao Quan, is through the Earth’s crust. Meanwhile, the depth of influence of third-order faults, Chay river, Dong Ha - Phu Vang, Vinh Linh, Hue - Son Tra and Tam Ky - Phuoc Son, is within the thickness of the Earth’s crust.

Towards а design of new generation digital seismic seabed seismographs – current state and future outlook

The paper presents the comparative characteristics of self-pop-up digital seabed seismometers that have been developed since the early 2000s. The requirements for the main technical characteristics that should be considered for developing the new-generation of self-pop-up seabed seismometers have been proposed. The microcontroller and reference frequency generator are the key parts for a seabed seismometer design. The paper provides the development results of these key components, which are essential for the seismometer performance (power consumption and functionality).
 A draft proposal for seabed seismic exploration project in the Russian sector of the Black Sea solving the current actual geological problems is presented. Implementation of the project will contribute to determination of the crystalline basement depth within the Shatsky ridge and the Tuapse depression; detection of P and S wave velocities in the lower part of sedimentary cover and in the basement, and to the refinement of the Earth’s crust thickness. The extension of regional seabed seismic lines from the Turkish to the Russian sector of the Black Sea will give the scientists a clearer picture of the Earth’s crust structure over the whole east Black Sea basin. The results of seabed studies will verify and improve the results of the Black Sea 2011 towed-streamer survey (with 10 km streamer) on the sedimentary cover structure and the Earth’s crust.

Intraplate volcanism in the Danube Basin of NW Hungary: 3D geophysical modelling of the Late Miocene Pásztori volcano

Three-dimensional geophysical modelling of the early Late Miocene Pasztori volcano (ca. 11–10 Ma) and adjacent area in the Little Hungarian Plain Volcanic Field of the Danube Basin was carried out to get an insight into the most prominent intra-crustal structures here. We have used gridded gravity and magnetic data, interpreted seismic reflection sections and borehole data combined with re-evaluated geological constraints. Based on petrological analysis of core samples from available six exploration boreholes, the volcanic rocks consist of a series of alkaline trachytic and trachyandesitic volcanoclastic and effusive rocks. The measured magnetic susceptibilities of these samples are generally very low suggesting a deeper magnetic source. The age of the modelled Pasztori volcano, buried beneath a 2 km-thick Late Miocene-to-Quaternary sedimentary sequence, is 10.4 +/− 0.3 Ma belonging to the dominantly normal C5 chron. Our model includes crustal domains with different effective induced magnetizations and densities: uppermost 0.3–1.8 km thick layer of volcanoclastics underlain by a trachytic-trachyandesitic coherent and volcanoclastic rock units of a maximum 2 km thickness, with a top situated at minimal depth of 2.3 km, and a deeper magmatic pluton in a depth range of 5–15 km. The 3D model of the Danube Basin is consistent with observed high ΔZ magnetic anomalies above the volcano, while the observed Bouguer gravity anomalies correlate better with the crystalline basement depth. Our analysis contributes to deeper understanding of the crustal architecture and the evolution of the basin accompanied by alkaline intraplate volcanism.

Spectral Analysis and Euler Deconvolution Technique of Gravity Data to Decipher the Basement Depth in the Dehradun-Badrinath Area

Abstract The stratigraphic and tectonic setting in the northwest part of Himalayan belt is complex and thrusted due to the collision of Indian plate and the Eurasian plate. During the past, the Himalaya is divided into four parts; these are Outer Himalaya, Lesser Himalaya, Greater or Higher Himalaya and Tethys Himalaya. The appearance of basement rocks played a significant role in the Himalayan periphery for stratigraphic, structural and tectonic movement. The deformation pattern of the crustal rocks causing the rise of basement rocks which constitutes an integral part of crustal configuration during the evolutionary stages of the Himalaya. In this study, an attempt has been made to estimate the basement depth configuration using spectral analysis and Euler deconvolution technique of gravity data in the northwest Himalaya region. The elevation increases continuously from 500 m to 5100 m in SW to NE direction, however, Bouguer gravity anomaly decreases continuously from -130 mGal to -390 mGal in SW to NE direction due to the isostaic adjustment. Gravity anomaly is very low near Harsil, Badrinath and Joshimath area and observed higher elevation due to the deep rooted basement. However, there are extrusion of crystalline basement in and around the Badrinath area due to the resettlement of geologic process which are overlaid to the top surface of the sedimentary layers. Euler deconvolution technique has been applied to detect the direct basement depth and results show a good correlation with the average depth of the spectral analysis and other works carried by different authors. Three gravity profiles are selected in appropriate places orienting SW-NE direction with a profile length of 160 km, 150 km and 140 km respectively in the study area for calculating the average depth of the basement rock. The average basement depth calculated is around 11.27 km using the spectral analysis technique and results are well correlated with the results of various workers. Euler deconvolution studies along the three selected profiles have been interpreted. It has been observed that there are more number of cluster points falling between depth ranges of 10 to 15 km, dipping in SW to NE direction. Euler’s study shows deep rooted connection near Main Frontal Thrust (MFT), Main Boundary Thrust (MBT), Main Central Thrust (MCT), Bearing Thrust (BT) and Vaikrita Thrust (VT) locations as per profile study. Based on these studies three geological models have been prepared along the profiles showing different tectonic resettlement and depth of crystalline basement. Crystalline rocks exposed at the surface may be due to uplift along the shear in the MCT zone by kinetic flow basically, Munsiayari Thrust (MT) and VT in the of NW-Himalaya region.

A Crustal Model for the Eastern Alps Region and a New Moho Map in Southeastern Europe

In the last two decades, south-central Europe and the Eastern Alps have been widely explored by many seismic refraction experiments (e.g., CELEBRATION 2000, ALP 2002, SUDETES 2003). Although quite detailed images are available along linear profiles, a comprehensive, three-dimensional crustal model of the region is still missing. This limitation makes this region a weak spot in continental-wide comprehensive representations of crustal structure. To improve on this situation, we select and collect 37 published active-source seismic lines in this region. After geo-referencing each line, we sample them along vertical profiles—every 50 km or less along the line—and derive P-wave velocities in a stack of homogeneous layers (separated by discontinuities: depth of crystalline basement, top of lower crust, and Moho). We finally merge the information using geostatistical methods, and infer S-wave velocity and density using empirical scaling relations. We present here the resulting crustal model for a region encompassing the Eastern Alps, Dinarides, Pannonian basin, Western Carpathians and Bohemian Massif, covering the region within \(45^{\circ}\text{--}51^{\circ}\hbox{N}\) and \(11^{\circ} \text{--} 22^{\circ}\hbox{E}\) with a resolution of \(0.2^{\circ} \times 0.2^{\circ}.\) We are also able to extend and update the map of Moho depth in a wider region within \(35^{\circ}\text{--}51^{\circ}\hbox{N}\) and \(12^{\circ}\text{--}45^{\circ}\hbox{E},\) gathering Moho values from the collected seismic lines, other published dataset and using the European plate reference EPcrust as a background. All the digitized profiles and the resulting model are available online.

Shallow Crustal Structures and Buried Active Faults Revealed by Seismic Reflection Profiles in the Northwest of Beijing Plain

AbstractGeological and geophysical studies suggest that there are many buried active faults and buried Quaternary basins below the Beijing plain. In order to investigate shallow crustal structures, geometry of buried faults, fault activity and the relationship between shallow and deep structures in this area, a mid‐deep seismic reflection profile with 60‐fold and several shallow seismic reflection profiles across buried faults were completed in the northwestern region of Beijing plain in 2006. The results show that the depth of crystalline basement is about 3~6 km along the profile. The seismic reflection section shows a set of strong reflected phases with good lateral continuity above the crystalline basement, which should be the sedimentary rock systems of Cenozoic, Mesozoic, and Paleozoic era. Beneath the crystalline basement, there is a series of weak reflected events with poor continuity possibly representing the crystallized rock system with comparatively strong metamorphism or other non‐layered rock systems. The faults revealed by mid‐deep and shallow seismic reflection profiles present consistent upper‐lower relationship and have been significantly active since Quaternary, which play an important role in controlling the rift valley‐horst like basin and range tectonics as well as the thicknesses of Cenozoic strata in this region. The study results can further improve the understanding of the neotectonic activity in the Beijing area, and the used exploration method and technology can serve as a reference for the survey of deep‐shallow structures in other areas.

Tomographic investigation of the upper crustal structure and seismotectonic environments in Yunnan Province

Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the exposed basins, uplifts and faults. The low velocity anomaly corresponding to the volcano also has been revealed. There exits a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrocks are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust maybe shallow. On the other hand, known as the plates’ seam, the Honghe fault has a distinct evidence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a close relationship with the earthquake’s occurrence nowadays. Despite of the ceasing of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. As the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and the upper mantle cannot be released; therefore it accumulates at some appropriate tectonic locations. Moreover, the saturation of the water from the basin, the action of other fluids, and the effects of the outer stress maybe another direct reason account for the strong earthquakes’ occurrence in Yunnan region.

Three‐Dimensional Finite‐Difference Tomography of Upper Crustal Velocity Structure in North China

AbstractWe parameterized the velocity model of North China using square nets. Grid spacing is 1.0km and there are 649×890×16 grid points in the whole velocity model. We obtained three‐dimensional (3‐D) upper crustal velocity structure of North China using 3‐D finite‐difference inversion method and Pg wave data from 30 deep seismic sounding (DSS) profiles in the studied area. The inversion results revealed that the low velocity rhombshaped North China basin is surrounded by high velocity uplifts, and North China basin is comprised of two large fault zones with an uplift in between. The two large fault zones are divided into several small basins. There are many shovel‐like normal faults in the studied area and the depth of crystalline basement varies significantly at different geological structures. All these results suggest that North China has very complicated geological structure and it has the deep structural background for strong earthquakes.

High-Resolution Aeromagnetic Study of the New Madrid Seismic Zone: A Preliminary Report

Abstract A high-resolution aeromagnetic survey, flown over the northern part of the New Madrid seismic zone in the Mississippi embayment, reveals linear features that generally parallel active seismic zones. This parallelism suggests that the linear magnetic features are related to faults. Modeling of these anomalies indicates that the associated magnetic sources are shallow, steeply dipping (>80°) prism-like bodies. Their tops at depths of about 1 km are considerably shallower than the depth of crystalline basement (roughly 3 km). The bodies are typically 2 km wide. A plausible explanation for these bodies is that the magnetization within the sequence of generally nonmagnetic sedimentary rocks has been enhanced within and adjacent to fault zones. Such a magnetic enhancement could arise in several ways, including the emplacement of igneous intrusions, the authigenic growth of pyrrhotite, or the conversion of pyrite to magnetite. Whatever the cause of the magnetization contrast, the apparent relation between linear magnetic features and faults may lead to permissible stress models that accommodate the fault pattern inferred from the magnetic field.