Structure Of Crystalline Basement Research Articles

Three-dimensional anisotropic inversion and electrostratigraphic imaging of marine magnetotelluric data to understand the control of crustal deformations by pre-existing lithospheric structures in the Mexican Ridges Fold belt, Southwestern Gulf of Mexico

SUMMARY3-D imaging of the lithosphere in the Mexican Ridges fold belt is important for understanding how the crustal deformations in this basin relate to deep tectonic processes and structures inherited from extinct Jurassic seafloor spreading. Here, we use broad-band (0.0001–0.4642 Hz) marine magnetotelluric data from the basin to reconstruct the 3-D anisotropic resistivities of the lithosphere and their spatial gradients. The resistivity gradients maxima enabled independent definition of important geological boundaries (seen on collocated seismic reflection data) and estimation of crustal thickness. We found anomalous layered zones of low resistivity and high electrical anisotropy at 5–8 km depth (coinciding with the regional detachment zone in Eocene shales in 3-D seismic data) and in the upper mantle which we interpret as indicating intense deformation and/or recent magmatic influence. We also found a banded crystalline basement structure across the fossil spreading centre comprising WSW–ENE trending, 6–10 km wide, electrically resistive subvertical sheets with conductive and anisotropic borders, which merge into a basal resistive stock-like body at 15–20 km depth. These are cut or bounded by later NNW trending major faults. These WSW and NNW structural trends correlate with the previously interpreted transform and normal faults that formed during the Late Jurassic opening of the Gulf of Mexico only if rotated clockwise by 25–30°. Surprisingly, the rugged thrust-related seabed is offset at the projected positions of the steep resistive-conductive basement sheets (which also have spatially coincident high magnetic intensity and seismicity) enabling us to infer they represent magmatic intrusions facilitated by pre-existing faults. Their conductive borders spatially coincide with possibly fluid-filled vertical fracture-sets in the overlying sediments seen in seismic data which we interpret as hydrothermal fluid pathways. We infer that a magmatic body recently intruded our study area, its ascent controlled by pre-existing basement structures, and influenced the deformation of the Neogene sequences and the seafloor topography.

The Crustal Structure of the North–South Earthquake Belt in China Revealed from Deep Seismic Soundings and Gravity Data

The North–South earthquake belt (NSEB) is one of the major earthquake regions in China. The studies of crustal structure play a great role in understanding tectonic evolution and in evaluating earthquake hazards in this region. However, some fundamental crustal parameters, especially crustal interface structure, are not clear in this region. In this paper, we reconstructed the crustal interface structure around the NSEB based on both the deep seismic sounding (DSS) data and the gravity data. We firstly reconstructed the crustal structure of crystalline basement (interface G), interface between upper and lower crusts (interface C) and Moho in the study area by compiling the results of 38 DSS profiles published previously. Then, we forwardly calculated the gravity anomalies caused by the interfaces G and C, and then subtracted them from the complete Bouguer gravity anomalies, yielding the regional gravity anomalies mainly due to the Moho interface. We then utilized a lateral-variable density interface inversion technique with constraints of the DSS data to invert the regional anomalies for the Moho depth model in the study area. The reliability of our Moho depth model was evaluated by comparing with other Moho depth models derived from other gravity inversion technique and receiver function analysis. Based on our Moho depth model, we mapped the crustal apparent density distribution in the study area for better understanding the geodynamics around the NSEB.

The role of precursory structures on Tertiary deformation in the Black Forest—Hegau region

Structural inheritance of preexisting crustal discontinuities is widely accepted to have played a crucial role during the Cenozoic tectonic evolution of the northern Alpine foreland. It is recognised as a process that can strongly influence local fault kinematics and strain patterns. The case study presented herein is dedicated to the tectonic analysis of the Freiburg–Bonndorf–Bodensee Fault Zone (FBBFZ) located at the external margin of the northern Alpine Molasse Basin and extending into the crystalline Black Forest Massif. The structure and kinematics of this crustal-scale fault zone are investigated by means of a regional analysis of locally mapped faults, kinematic analysis of outcrop-scale fractures and slip vector modelling. The exceptional possibility of analysing the fault zone exposed from basement to cover allowed for an evaluation of interaction between precursory structures and subsequent deformation features. The results of this study show that the crystalline basement structures exposed along the FBBFZ had a strong imprint on the map-scale fault pattern observable in the Mesozoic and Tertiary sequences. Kinematic analysis of outcrop-scale fracture systems in the latter units yields evidence for local multi-directional extension and strike-slip faulting during Miocene to recent times. While these observations may evoke the interpretation of a multistage palaeostress history along the FBBFZ, slip vector modelling of a very well exposed FBBFZ segment suggests that the various strain records can alternatively be explained by one single regional stress tensor and be related to superordinate deep-seated strike-slip deformation.

Conjugate zone between the northern termination of the Baikal-Patom Foldbelt and the Siberian Craton: Structure of the crystalline basement

New data on the deep structure of the crystalline basement in the conjugate zone between the northern termination of the Baikal-Patom Foldbelt and the Siberian Craton are discussed. Digital processing of the data of a high-precision airborne geophysical (magnetic, gravity, radiometric) surveys on a scale of 1: 50000 allows us to construct 3D models of the petrophysical properties of the rocks and to ascertain the main features of the deep structure of the pre-Riphean crystalline basement overlapped by a thick sedimentary cover. The Archean and Paleoproterozoic metamorphic and plutonic petrophysical complexes are identified, and their vertical and horizontal relationships are outlined. Horizontal tectonic movements and overthrusting for many tens of kilometers are interpreted in the internal structure of the crystalline basement. The tectonic overriding of the marginal part of the Siberian Craton by nappes of the Baikal-Patom Foldbelt is proved. In particular, the completely detached, allochthonous position of the Kotuikan Zone along which the Magan and Daldyn terranes cojugate with the Aldan Province in the south of the craton is established. This compels us to consider a re-evaluation of the currently accepted concept concerning the structure and formation history of the basement of the ancient Siberian Craton.

Ray hit analysis method and its application to complex upper crustal structure survey

Based on the results obtained from Pg wavefront imaging in active source deep seismic sounding, we propose a new ray hit analysis method for high-resolution seismic refraction profile data processing. This method can be used to further determine possible refraction interface, especially spatial location of basement and its pattern characteristics in complex upper crustal structure region, making data processing for high-resolution refraction profiles more fine. We use this method to study the crystalline basement structure of east part of A’nyemaqen suite zone at northeast side of Qinghai-Xizang Plateau and the basement patterns as well as its spreading features at the east part of Anemaqen suite zone and its adjacent region were determined.

Detection of subtle basement faults with gravity and magnetic data in the Alberta Basin, Canada: A data-use tutorial

Editor's note: This paper is based on a presentation at the 2003 Canadian Society of Petroleum Geologists/Canadian Society of Exploration Geophysicists Joint Convention in Calgary. Exploration for a wide range of mineral deposits is critically dependent on knowledge of the location and age of fractures and faults. Oil and gas fields in many sedimentary basins are distributed along fault-controlled linear trends, and fault identification is often used effectively for target-area selection in hydrocarbon exploration. Similarly, mineral deposits in various geologic settings are commonly associated with fluid-conducting faults. In the platformal, Phanerozoic Alberta sedimentary basin in western Canada (Figure 1), two fundamentally different types of crystalline-basement structure, formed in different tectonic conditions, are recognized (Lyatsky et al., 1999): Figure 1. Location of the northern Alberta study area in relation to main regional geologic features. 1. Archean and Early Proterozoic (Hudsonian and older) ductile orogenic structures, and 2. Middle Proterozoic to Recent cratonic ones. The influence of ancient ductile structures on the Alberta Basin seems largely confined to the control on Early Paleozoic depositional and drape patterns by the Precambrian erosional basement relief, which may to some extent be related to the basement lithology distribution controlled by ductile ancient structures. These structures were mostly healed and innactive during the Phanerozoic development and evolution of the Alberta Basin, and thus of limited significance to fluid migration. Their geophysical expression typically consists of large magnetic and gravity anomalies, which often obscure the potential-field signatures of the desirable brittle faults. The steep, brittle basement faults in the western Canadian platforms and Cordilleran foreland, although much more subtle than their spectacular counterparts in western United States, exerted considerable syn- and postdepositional influence on the Phanerozoic sedimentary cover. Occasionally, brittle faults and fractures follow the older orogenic basement structures, but commonly cut across them. Even when subresolution seismically, many …

Characterization of crystalline basement structures based on three‐dimensional visualization of geologic, geophysical, geohydrological and geochemical data

Characterization of crystalline basement structures based on three‐dimensional visualization of geologic, geophysical, geohydrological and geochemical data

Depositional history of Lower Cretaceous strata in northeastern New Mexico: Implications for regional tectonics and depositional sequences

Lower Cretaceous strata in northeastern New Mexico reflect deposition during marine transgression and regression associated with the Kiowa-Skull Creek cycle. Development of regionally significant unconformities can be directly related to shoreline shifts during this cycle. Topography related to Early Cretaceous tectonic activity on crystalline basement structures, including the Dalhart Basin, Tucumcari Basin, and the intervening Bravo Dome, also had a direct effect on Early Cretaceous deposition and is reflected by thickness trends in marine strata. The Kiowa-Skull Creek transgression was preceded by infilling of paleovalleys represented by the Long Canyon and Campana sandstone beds of the Glencairn Formation and Tucumcari Shale, respectively. The Long Canyon and Campana sandstone beds are equivalent to the Plainview Formation of central Colorado, and together they represent an extensive drainage network, developed over a correlative unconformity, that is preserved throughout most of the southern Western Interior. Glencairn and Tucumcari marine shales represent clastic deposition during Kiowa-Skull Creek transgression and early regression. Base-level drop associated with Kiowa-Skull Creek regression resulted in dramatic shoreline regression and deposition of fluvial channel sandstone in the Dalhart Basin, which maintained a low offshore gradient. This produced an erosional unconformity at the base of Mesa Rica channel sandstone that correlates with the well-documented erosional surface at the base of the Muddy Sandstone in central Colorado. The Tucumcari Basin, which maintained a steeper offshore gradient, accumulated marine-deltaic Mesa Rica Sandstone at this time. Marine strata in both the Tucumcari and Dalhart Basins thin toward the Bravo Dome. Mesa Rica and upper Tucumcari strata represent the only extensive marginal-marine lowstand deposits found on the High Plains to date, associated with the southern arm of the Kiowa-Skull Creek sea. Major Mesa Rica deposition was followed by transgression that infilled only those Mesa Rica fluvial channels that were active at that time and, also, that deposited marine-influenced strata of the basal Pajarito Formation. This event most likely represents onset of the Greenhorn cycle in northeastern New Mexico. Other crystalline basement structures in the northern part of the United States Western Interior Basin were active during Early Cretaceous time. Tectonism in these areas may be related to structures in northeastern New Mexico and thus may be expressions of broad-scale crustal strain in the Early Cretaceous Western Interior that is undocumented by present tectonic models.

Geophysical Investigation of Crystalline Basement Between Dead Sea Rift and Mediterranean Sea

Long seismic refraction lines across central and northern Israel, combined with magnetic and gravity investigations, help to define the total thickness of sedimentary rocks and crystalline basement structure. Significant lateral variations in thickness of the infra-Upper Jurassic sediments seem to be related to tectonic movement and may influence possible deposition of early Mesozoic and Paleozoic reservoir rocks.

Surface structure of crystalline basement in northwestern part of Russian platform, in light of new geophysical data

Basement data have been obtained for an area of about 250,000 km2, with an average spacing of one seismic point to 200 km2. Descriptions are given and a map is shown for the Precambrian crystalline basement surfaces of the Baltic trough, the Latvian saddle, the southwestern part of the Moscow synclise (including the Valday graben, Orsha-Vitebsk trough, southwestern side of the Central Russian trough, Nelidovo-Torzhok high, Tokmovsk arch, etc.), and the Saratov-Ryazan trough. It is concluded that the basement structure in the northwestern Russian platform is of “block nature.”.—R.V. Dietrich