Journal articles on the topic 'Deep crustal structures'
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1
Clark, Elizabeth A., and Frederick A. Cook. "Crustal-scale ramp in a Middle Proterozoic orogen, Northwest Territories, Canada." Canadian Journal of Earth Sciences 29, no. 1 (January 1, 1992): 142–57. http://dx.doi.org/10.1139/e92-014.
Abstract:
Deep crustal seismic data from the Fort Goodhope area, Northwest Territories, Canada, image crustal structures associated with Middle Proterozoic compressional deformation. These include 10–20 km wide antiforms and thrust faults that lie above a west-dipping crustal-scale ramp with at least 10 km of vertical relief. The deformation is interpreted as being associated with structures observed in the subsurface to the east and may be partly coeval with deformation originally detected in outcrop in the Rackla Range of the Wernecke Mountains. These new deep crustal profiles, coupled with data to the east that delineate structures to 15 km depth, reveal large-scale similarity between this Middle Proterozoic orogen and many Phanerozoic compressional orogens.
2
Kivior, Irena, David Boyd, David Tucker, Stephen Markham, Francis Vaughan, Fasil Hagos, and Leslie Mellon. "Deep crustal structures interpreted from potential field data along deep seismic sounding transects in Australia." APPEA Journal 55, no. 2 (2015): 450. http://dx.doi.org/10.1071/aj14085.
Abstract:
Energy spectral analysis techniques have been applied to magnetic and gravity data acquired across the Olympic Dam cratonic area in Australia and sedimentary basins along the Equatorial Margin of Brazil. Analysis has been conducted along two Deep Seismic Sounding lines (DSS) acquired by Geoscience Australia. There is a good correlation between interfaces found in this analysis and structures interpreted from the seismic data. Interpretation of gravity data using energy spectral analysis along the DSS survey lines show a number of deep crustal structures are evident, including the Moho which was detected using gravity data, while similar analysis of the magnetic data show indications of the Curie isotherm. In addition, the analysis was extended away from the seismic lines to detect many deep crustal horizons and structures at considerable distances from the DSS lines. The results obtained from energy spectral analysis across this area in Australia encouraged the application of this technique on the Equatorial Margin of Brazil, where the potential field data is of much lower resolution. This suggests that a much wider application of this approach could be highly valuable to investigate the deep structure under other sedimentary basins and to assist heat flow studies.
3
Siler, Drew L., and B. Mack Kennedy. "Regional crustal-scale structures as conduits for deep geothermal upflow." Geothermics 59 (January 2016): 27–37. http://dx.doi.org/10.1016/j.geothermics.2015.10.007.
4
Louie, J. N., and J. E. Vidale. "Array analysis of reflector heterogeneity." GEOPHYSICS 56, no. 4 (April 1991): 565–71. http://dx.doi.org/10.1190/1.1443074.
Abstract:
In deep crustal reflection study, as in conventional exploration seismology, it is important to determine the geometry of the physical contrasts between rocks that cause reflections, to make reliable geologic interpretations. Fundamentally different reflecting structures produce similar signatures in stacked seismic sections. We have developed a method that uses prestack records to differentiate lateral structural variations from lateral reflectivity variations and laterally homogeneous structures. Full‐wave acoustic multioffset synthetics of canonical 2-D reflector configurations, analyzed by statistically enhanced slant‐stack processes, show that lateral heterogeneity such as a wavy reflector can be identified from changes in slowness across a receiver array as a function of time. Application of these methods to deep crustal reflections, recorded in the Mojave Desert of southern California, identifies laterally heterogeneous midcrustal structures and is consistent with a laterally homogeneous Moho.
5
Botev, Emil, and Edelvays Spassov. "Deep velocity structure of crust and upper mantle in the central parts of Balkan Region." Geologica Balcanica 20, no. 2 (April 30, 1990): 71–79. http://dx.doi.org/10.52321/geolbalc.20.2.71.
Abstract:
Some velocity characteristics of the crust and upper mantle in the central part of the Balkan region are studied on the basis of about 1000 local and teleseismic earthquakes, registered on the 32 seismic stations. An approach for estimation of the large anisotropic structures effects is used together with the general consideration about the connection between the time residuals and velocity inhomogeneities. The main features of the inhomogeneities in the crust and upper mantle are drscussed in relation with some gravity, heat flow and seismotectonic data. The distribution of the crustal inhomogeneities in general corresponds to the configuration of the morphotectonic structures in Bulgaria. The subcrustal inhomogeneities are discordant with the surface structures, but their orientation is in coincidence with the Trans-Balkan seismolineament system. This fact indicates that the crustal seismicity in the region is probably controlled by the upper mantle structures. The high-velocity structures in the deep upper mantle beneath the Rhodope massif probably represent a paleosubduction at a depth more than 300 km.
6
Erkhow, V. A. "Deep structure and metallogeny of the earth's crust." Exploration Geophysics 20, no. 2 (1989): 37. http://dx.doi.org/10.1071/eg989037.
Abstract:
Considerable experience with integrated geological and geophysical studies has enabled definition of deep crustal structures and, within limits, composition and processes within the deep crust, and to determine their association with metallogeny in the USSR.By means of seismic experiments, stratification of the Earth's crust and the upper mantle to a depth of about 100 km has been revealed. Numerous heat flow data have been compiled. Magneto-telluric soundings made it possible to determine the position of conductive strata in the crust and upper mantle for a number of areas. Gravity surveys coupled with the results of seismic profiling enabled the finding of a number of empirical laws that are useful for investigation into the deep crust. Magnetic data analysis has enabled evaluation of the magnetic layering of the deep crust. Kimberlite and ore provinces can be considered examples of these concepts.For more detailed studies of deep crustal structure the territory of the USSR is the subject of a system of regional investigation of the deep crust and upper mantle. This system is based principally upon a network of interconnected regional profiles (geotraverses) tied to deep and superdeep boreholes. The system includes predicted geophysical observations to control investigation of the geophysical field data. The geotraverse network is the basis for detailed studies within the bounds of petroleum and ore provinces.The most accurate data obtained allows the formation of a crustal model and reveals empirical relationships with metallogeny.Based on the deep crustal structure data a regional oregenesis prediction map has been made. The endogenous mineralization prediction was based on special features of the upper layering of the crust and on data relating to deep crustal permeability zones.
7
Benn, Keith, Warner Miles, Mohammad R. Ghassemi, and John Gillett. "Crustal structure and kinematic framework of the northwestern Pontiac Subprovince, Quebec: an integrated structural and geophysical study." Canadian Journal of Earth Sciences 31, no. 2 (February 1, 1994): 271–81. http://dx.doi.org/10.1139/e94-026.
Abstract:
Structural mapping, gravity and magnetic modelling, and interpretation of a deep-seismic profile in the northwestern Pontiac Subprovince outline the crustal structure and early structural development of the region. Penetrative D1 fabrics in the Pontiac Group and in the underlying Opasatica Gneiss may record south-vergent thrusting of a high-grade nappe. D2 and D3 structures record southeast-vergent folding and thrusting within the Pontiac Group. Steeply dipping northeast-trending ductile shear zones may represent oblique ramps initiated during D1. Gravity and magnetic model profiles are consistent with north-dipping structures in the shallow crust, and indicate that the Pontiac Group is a wedge underlain by north-dipping slabs of different densities and magnetic susceptibilities. Interpretation of a seismic reflection profile shows mid-crustal duplex structures overlying a deeper thrust between 16 and 24 km. From the surface to the deep crust, the structure of the northwestern Pontiac Subprovince records south- to southeast-directed thrusting and important crustal thickening during a collisional event. In light of field observations, available isotopic ages suggest that D1 deformation began no earlier than 2694 Ma, and that deformation continued until at least 2668 Ma.
8
Louie, John N., and Robert W. Clayton. "The nature of deep crustal structures in the Mojave Desert, California." Geophysical Journal International 89, no. 1 (April 1987): 125–32. http://dx.doi.org/10.1111/j.1365-246x.1987.tb04398.x.
9
Schmidt, J., D. Dyrelius, H. Palm, A. Egorkin, N. Yasulievich, E. Zolotov, and J. J. Doody. "The CABLES project: Imaging deep crustal structures in the Scandinavian Caledonides." GFF 118, sup004 (October 1996): 97. http://dx.doi.org/10.1080/11035899609546415.
10
Stadtlander, Ralf, and Larry Brown. "Turning waves and crustal reflection profiling." GEOPHYSICS 62, no. 1 (January 1997): 335–41. http://dx.doi.org/10.1190/1.1444135.
Abstract:
In the past, steeply dipping features were often recognized on seismic reflection profiles only from indirect evidence such as vertical offsets of cross‐cutting structures. New imaging algorithms, as for example, turning wave migration have had dramatic success in delineating steep, even‐overturned reflectors in sedimentary environments. Evaluation of the applicability of this technology to deep seismic recordings indicates that steep‐dip and turning wave migration will have limited practicality, generally, in the imaging of basement features because of the weak velocity gradients involved and the corollary requirement for large recording offsets. A potential exception arises when the basement structures to be imaged lie beneath a significant thickness of relatively young (i.e., steep velocity gradient) sedimentary cover.
11
Kim, Heejung. "Need for Seismic Hydrology Research with a Geomicrobiological Focus." Sustainability 13, no. 16 (August 4, 2021): 8704. http://dx.doi.org/10.3390/su13168704.
Abstract:
Earthquakes cause deformation in previously stable groundwater environments, resulting in changes to the hydrogeological characteristics. The changes to hydrological processes following large-scale earthquakes have been investigated through many physicochemical studies, but understanding of the associated geomicrobiological responses remains limited. To complement the understanding of earthquakes gathered using hydrogeochemical approaches, studies on the effects of the Earth’s deep crustal fluids on microbial community structures can be applied. These studies could help establish the degree of resilience and sustainability of the underground ecosystem following an earthquake. Furthermore, investigations on changes in the microbial community structure of the Earth’s deep crustal fluids before and after an earthquake can be used to predict an earthquake. The results derived from studies that merge hydrogeochemical and geomicrobiological changes in the deep crustal fluids due to the effect of stress on rock characteristics within a fault zone can be used to correlate these factors with earthquake occurrences. In addition, an earthquake risk evaluation method may be developed based on the observable characteristics of fault-zone aquifers.
12
Dinh, Van-Toan, Steven Harder, Bor-Shouh Huang, Viet-Bac Trinh, Van-Tuyen Doan, Hop-Phong Lai, Anh-Vu Tran, Hong Quang-Thi Nguyen, and Van-Duong Nguyen. "An overview of northern Vietnam deep crustal structures from integrated geophysical observations." Terrestrial, Atmospheric and Oceanic Sciences 29, no. 4 (2018): 371–86. http://dx.doi.org/10.3319/tao.2018.01.02.01.
13
de Wit, M. "Crustal structures across the central Kaapvaal craton from deep-seismic reflection data." South African Journal of Geology 107, no. 1-2 (June 1, 2004): 185–206. http://dx.doi.org/10.2113/107.1-2.185.
14
WANG, Shuai-Jun, Xian-Kang ZHANG, Cheng-Ke ZHANG, Fu-Yun WANG, Jin-Ren ZHAO, Jian-Shi ZHANG, Bao-Feng LIU, Su-Zhen PAN, and Yu-Jie GAI. "2-D Crustal Structures Along Wuqing-Beijing-Chicheng Deep Seismic Sounding Profile." Chinese Journal of Geophysics 50, no. 6 (November 2007): 1525–34. http://dx.doi.org/10.1002/cjg2.1172.
15
RICHARDS, JEREMY P. "Lineaments Revisited." SEG Discovery, no. 42 (July 1, 2000): 1–20. http://dx.doi.org/10.5382/segnews.2000-42.fea.
Abstract:
ABSTRACT Large-scale crustal lineaments are recognized as corridors (up to 30 km wide) of aligned geological, structural, geomorphological, or geophysical features that are distinct from regional geological trends such as outcrop traces. They are commonly difficult to observe on the ground, the scale of the features and their interrelationships being too large to map except at a regional scale. They are therefore most easily identified from satellite imagery and geophysical (gravity, magnetic) maps. Lineaments are believed to be the surface expressions of ancient, deep-crustal or trans-lithospheric structures, which periodically have been reactivated as planes of weakness during subsequent tectonic events. These planes of weakness, and in particular their intersections, may provide high-permeability channels for ascent of deeply derived magmas and fluids. Optimum conditions for magma penetration are provided when these structures are placed under tension or transtension. In regions of subduction-related magmatism, porphyry copper and related deposits may be generated along these lineaments because the structures serve to focus the ascent of relatively evolved magmas and fluid distillates from deep-crustal magma reservoirs. However, lineament intersections can only focus such activity where a magma supply exists, and when lithospheric stress conditions permit. A comprehensive understanding of regional tectono-magmatic history is therefore required to interpret lineament maps in terms of their prospectivity for mineral exploration.
16
Sénéchal, Guy, Marianne Mareschal, Andrew J. Calvert, Gilles Grandjean, Claude Hubert, and John Ludden. "Integrated geophysical interpretation of crustal structures in the northern Abitibi belt: constraints from seismic amplitude analysis." Canadian Journal of Earth Sciences 33, no. 9 (September 1, 1996): 1343–62. http://dx.doi.org/10.1139/e96-101.
Abstract:
We present a processing sequence that attempts to balance geometrical and amplitude analyses in order to recover the maximum information from deep seismic reflection data. The approach, which is guided by the interpretation of other deep geophysical data sets (magnetotellurics, refraction), is applied to Lithoprobe seismic reflection line 28 across the central and northern Abitibi belt. We show, in particular, how amplitude analyses help to quantify the depth of penetration of seismic energy as well as the crustal reflectivity. Apparent lateral variations of deep structures (e.g., the Moho) can be directly related to the high levels of noise that limit the signal penetration depth. We propose a geological model that satisfies all deep geophysical constraints. In this model, the mid crust south of Casa-Berardi tectonic zone consists of imbricated volcanic–plutonic and sedimentary lithologies, which are probably comparable to the mid-crustal section of the Kapuskasing structural zone, and in this paper are referred to as "the Abitibi plate." The lithologies are characterized by high reflectivity, while north of Casa-Berardi tectonic zone the mid crust is dominantly Opatica plutonic lithologies, of lower reflectivity. In this scenario, supracrustal rocks of the Abitibi belt overlie the Opatica plutonic belt, whereas the Abitibi plate extends beneath the Opatica plutonic belt. The boundary between the Opatica plutonic belt and the Abitibi plate is a northward-dipping décollement extending from mid crust in the south to lower crust in the north. The Casa-Berardi tectonic zone appears to be a crustal boundary affecting upper and middle crust down to 20 km, between northern polycyclic terranes and southern monocyclic ones. The uniformity of the lower crust suggests that its formation was decoupled from that of the intermediate to upper crust.
17
Bouzidi, Youcef, Douglas R. Schmitt, Ronald A. Burwash, and Ernest R. Kanasewich. "Depth migration of deep seismic reflection profiles: crustal thickness variations in Alberta." Canadian Journal of Earth Sciences 39, no. 3 (March 1, 2002): 331–50. http://dx.doi.org/10.1139/e01-080.
Abstract:
Variations in crustal thickness provide important clues as to the formation of the crust, present-day isostatic equilibrium, and crustal stress. The map of the topography of the Mohorovicic discontinuity in Alberta is revised using 1900 km of reanalysed seismic reflection profiles acquired as part of the Lithoprobe Alberta Basement Transect. Time sections were depth migrated using a parallelized algorithm that accounts for steeply dipping structures. The migration process employed a geologically consistent velocity model of the metamorphic crust derived from earlier refraction experiments and constrained by compilations of high-pressure rock velocity measurements. We found that knowledge of the velocities in the sedimentary column strongly influenced the quality of the migration calculations. The Mohorovičić discontinuity is generally distinguished in these profiles, on the basis of sharp changes in reflectivity, at depths of 3548 km. Sharp reflections from this boundary are rare. A number of geologic features are of note in these lines. A localized (~50 km extent) crustal thinning is observed in the Peace River region; this thinning is consistent with an adjacent oxygen isotopic anomaly indicative of crustal extension. In central Alberta, the Mohorovičić discontinuity topography is suggestive of a sharp jump of 10 km indicative of mantle faulting associated with the Snowbird tectonic zone. In southern Alberta, the crust thickens substantially across the Vulcan structure, with the greatest thickness correlating with the Vulcan structure itself indicating a collisional origin as noted by other authors.
18
Green, Ronald, F. C. Ludbey, and Marino. "New equipment for the investigation of deep crustal structures using the resistivity method." Geoexploration 23, no. 2 (June 1985): 207–16. http://dx.doi.org/10.1016/0016-7142(85)90056-0.
19
Li, ChunFeng, Bing Chen, and ZuYi Zhou. "Deep crustal structures of eastern China and adjacent seas revealed by magnetic data." Science in China Series D: Earth Sciences 52, no. 7 (July 2009): 984–93. http://dx.doi.org/10.1007/s11430-009-0096-x.
20
Revinskiy, Yuriy Alekseevich, and Tat’yana Viktorovna Sharova. "Crustal waveguides of sedimentary deposits and conditions for their operation." NEWS of the Ural State Mining University 4 (December 15, 2022): 96–102. http://dx.doi.org/10.21440/2307-2091-2022-4-96-102.
Abstract:
The relevance of the article is determined by the need to develop the theory of crustal waveguides as a new look at the processes of formation of various hydrocarbon deposits. The purpose – identification of new structures – crustal waveguides – active fluid-saturated zones, within which certain types of traps for hydrocarbons can be formed. Research methods. The article analyzes literature sources that consider the phenomenon of oil formation as a result of the evolution of fluid-saturated zones of crustal waveguides and data from X-ray diffraction and electron microscopic analyzes of layered silicates. Results. The conditions for the operation of crustal waveguides are considered from the standpoint of the presence of free matter, methods of its delivery and energy sources, and features of the formation of their structure. The data of studies of the mineral composition of the rocks of the North-Tazovskaya depression of Western Siberia and the features of their hydrothermal-metasomatic alterations are presented. Minerals and their parageneses have been established, indicating the presence of hydrothermal processes accompanying crustal waveguides. The article argues that the processes of alteration of host rocks in various zones of crustal waveguides lead to the formation of special hydrocarbon traps of an unconventional type, established for deep Jurassic and pre-Jurassic deposits in the north of Western Siberia. The theory of crustal waveguides makes it possible to find the relationship between the formation of oil and gas fields and the geoenergetic aspects of the problem of the removal of intraterrestrial heat in various forms, the main of which is hydrothermal activity. The conclusions summarize the main provisions of the theory of crustal waveguides of sedimentary deposits, the conditions for their operation. The necessary conditions are: the presence of free matter in deep zones, energy sources of self-oscillations of the sedimentary strata and deep faults containing them as a result of unloading the stress field of a special kind, taking into account the depths of their formation. Conclusions are also drawn about the mineral composition of hydrothermal solutions associated with crustal waveguides, which affect host rocks and lead to the formation of a new type of metasomatic traps for hydrocarbons.
21
Yakymchuk, Mykola, Ignat Korchagin, and Valery Soloviev. "Some Results of Direct FR Technology Applied to Study Methane Seepage Areas in the Arctic Region." Advances in Geological and Geotechnical Engineering Research 5, no. 3 (July 19, 2023): 25–38. http://dx.doi.org/10.30564/agger.v5i3.5792.
Abstract:
The experimental study of the seepage processes' sources formation in structures of the Arctic Region was carried out using modified methods of frequency-resonance (FR) processing and decoding of satellite images and photographs with the vertical scanning of the cross-sections. The newly obtained results show that the intensity and dynamics of the methane seeps and pockmarks fields’ formation depend on active deep degassing processes in the continental margin structures. The use of direct FR-sounding technologies allows for determining the probable origin and depth of geological sources of gas migration at marginal migration centers in Greenland, and Norwegian and Barents Seas. New results confirm the crust-mantle gas fluids’ influence on the nature and degassing processes features in the scan points of polar marginal structures. These data are important arguments in favor of the “volcanic model” of various structural elements formation in this and other regions. The FR technologies data also showed a possibility of seeps use as shallow and deep hydrocarbon field indicators in gas emission areas. These independent data can be used in compiling models of the deep lithosphere structure and possible mechanisms of abiogenetic hydrocarbon formation in Arctic margin structures. The authors suppose that hydrocarbons through deep channels migrate (from 57 km deep) to the upper crustal horizons where their fields can form. During this migration, gas seeps and pockmarks are formed on the sea bottom and part of the gas can migrate into the atmosphere. Data show that basaltic volcanoes in Greenland scan points can be the real channels through which hydrogen migrates to the upper crustal horizons and further into the atmosphere. Active gas migration in Arctic seepage areas can be an important factor in the global climate change processes.
22
Mitchell, A. H. G., and J. C. Carlile. "Mineralization, antiforms and crustal extension in andesitic arcs." Geological Magazine 131, no. 2 (March 1994): 231–42. http://dx.doi.org/10.1017/s001675680001075x.
Abstract:
AbstractThe distribution and stratigraphic position of porphyry copper and epithermal gold deposits in andesitic arcs of the western Pacific and eastern Europe suggest that porphyry copper and epithermal vein deposits of adularia–sericite type develop successively under different stress regimes in an evolving arc, rather than being genetically related as commonly supposed. Absence of coeval high-level stocks in the root zones of many adularia-sericite deposits suggests that circulation of the dominantly meteoric hydrothermal fluids is not driven by shallow intrusions. The location of several world-class deposits on basement geanticlines, and on more localized antiforms of which at least one has been interpreted as a metamorphic core complex, implies that elevation of the arc, emplacement of magmatic sills at depth and adularia–sericite type gold mineralization are genetically related to subduction-induced crustal extension. Ascent of deep hydrothermal fluids, predominantly meteoric but with a metamorphic or magmatic component, may be controlled by regional low-angle structures at depth, analogous to those inferred for some mesothermal gold deposits. Mineralization at shallow (epithermal) depths in high-angle structures largely reflects the high geothermal gradient and mixing of deep fluid with cool meteoric water in or at the base of the permeable volcanic cover. Andesitic magmatism may resume following porphyry copper mineralization, adularia–sericite epithermal gold mineralization, or continued extension to form a ‘back arc’ spreading system, depending on the relative plate motion.
23
He, Lanfang, Qinyun Di, Zhongxing Wang, Jianqing Lai, Guoqiang Xue, and Wenbo Guo. "Crustal Structures of the Qimantagh Metallogenic Belt in the Northern Tibetan Plateau from Magnetotelluric Data and Their Correlation to the Distribution of Mineral Deposits." Minerals 13, no. 2 (February 4, 2023): 225. http://dx.doi.org/10.3390/min13020225.
Abstract:
Crustal structure and fluid or melt originating in the deep crust and mantle are critical in regional magmatic mineral systems. However, the crustal structure and the processes that entrain and focus fluids from a deep-source region to a metallogenic belt remain relatively undisclosed. We present a magnetotelluric (MT) study of the eastern Qimantagh Metallogenic Belt (QMB) in the northern Tibetan Plateau. Data from 33 MT stations in two sections and 7 dispersed stations are acquired using a surface electromagnetic prospecting (SEP) system in frequency band ranges from 320 Hz to 0.00034 Hz. Data are converted by Bostick conversion and two-dimensional (2D) nonlinear conjugate gradient inversion. Our MT results reveal the geoelectrical crustal structure of the QMB, which consists of a southern low-resistivity domain that reflects the Kumukuri rift, a high-resistivity middle domain that represents the southern QMB in the central Kunlun belt, and a northern low-resistivity domain that covers the northern QMB and southwestern Qaidam block. We present a comprehensive tectonic and geophysical model of QMB based on the MT interpretation and geological analysis. We infer the high-resistivity domain as a reflection of a rigid crust and detached lithospheric mantle, this belt separate the QMB into northern and southern QMB. Most of the mineral deposits are found in the northern low-resistivity domain of QMB. Our study and findings provide an understanding of the tectonic evolution of the northern Tibetan Plateau, the crustal structure that controls the temporal and spatial distribution of magmatic rocks, and the geological signature associated with mineral deposits.
24
Lynn, C. Elissa, Frederick A. Cook, and Kevin W. Hall. "Tectonic significance of potential-field anomalies in western Canada: results from the Lithoprobe SNORCLE transect." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1239–55. http://dx.doi.org/10.1139/e05-037.
Abstract:
Potential-field anomalies within the Lithoprobe SNORCLE (Slave Northern Cordillera Lithospheric Evolution) transect area provide geometrical constraints for regional crustal and lithospheric structures, as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles. Areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections, and forward modelling provides tests of different interpretations of deep (crustal and upper mantle) density structures. In a key result from modelling, a Paleoproterozoic subduction zone beneath the Wopmay orogen probably consists of high-density rocks, such as eclogite, within the upper mantle. This result supports the concept of moderate- to low-angle intra-lithospheric sutures. On an even larger scale, applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus provide means to track patterns across structural grain. For example, gravity and magnetic trends that are associated with Precambrian rocks of the Canadian Shield can, in some cases, be followed across much of the Cordillera. This result is consistent with North American Precambrian rocks composing much of the crust in the Cordillera and thus that the addition of "new" lithosphere during Mesozoic early Tertiary accretion has been relatively minor.
25
Rivers, Toby, and Walfried Schwerdtner. "Post-peak Evolution of the Muskoka Domain, Western Grenville Province: Ductile Detachment Zone in a Crustal-scale Metamorphic Core Complex." Geoscience Canada 42, no. 4 (December 7, 2015): 403. http://dx.doi.org/10.12789/geocanj.2015.42.080.
Abstract:
The Ottawa River Gneiss Complex (ORGC) in the western Grenville Province of Ontario and Quebec is interpreted as the exhumed mid-crustal core of a large metamorphic core complex. This paper concerns the post-peak evolution of the Muskoka domain, the highest structural level in the southern ORGC that is largely composed of amphibolite-facies straight gneiss derived from retrogressed granulite-facies precursors. It is argued that retrogression and high strain occurred during orogenic collapse and that the Muskoka domain acted as the ductile detachment zone between two stronger crustal units, the underlying granulite-facies core known as the Algonquin domain and the overlying lower grade cover comprising the Composite Arc Belt. Formation of the metamorphic core complex followed Ottawan crustal thickening, peak metamorphism and possible channel flow, and took place in a regime of crustal thinning and gravitational collapse in which the cool brittle–ductile upper crust underwent megaboudinage and the underlying hot ductile mid crust flowed into the intervening megaboudin neck regions. Post-peak crustal thinning in the Muskoka domain began under suprasolidus conditions, was facilitated by widespread retrogression, and was heterogeneous, perhaps attaining ~90% locally. It was associated with a range of ductile, high-temperature extensional structures including multi-order boudinage and associated extensional bending folds, and a regional system of extension-dominated transtensional cross-folds. These ductile structures were followed by brittle–ductile fault propagation folding at higher crustal level after the gneiss complex was substantially exhumed and cooled. Collectively the data record ~60 m.y. of post-peak extension on the margin of an exceptionally large metamorphic core complex in which the ductile detachment zone has a true thickness of ~7 km. The large scale of the core complex is consistent with the deep level of erosion, and the long duration of extensional collapse is compatible with double thickness crust at the metamorphic peak, the presence of abundant leucosome in the mid crust and widespread fluid-fluxed retrogression, collectively pointing to the important role of core complexes in crustal cooling after the peak of the Grenvillian Orogeny.RÉSUMÉLe complexe gneissique de la rivière des Outaouais (ORGC) dans la portion ouest de la Province de Grenville au Québec et en Ontario est interprété comme le cœur d’un grand complexe métamorphique à coeur de noyau. Le présent article porte sur l’évolution post-pic du domaine de Muskoka, soit le niveau structural le plus élevé de l’ORGC composé en grande partie d’orthogneiss au faciès amphibolite dérivés de précurseurs au faciès granulite. Nous soutenons que la rétromorphose et les grandes déformations se sont produites durant l’effondrement orogénique et que le domaine de Muskoka en a été une zone de détachement ductile entre deux unités crustales plus résistantes, le cœur au faciès granulite sous-jacent étant le domaine Algonquin, et la chapeau sus-jacent à plus faible grade de métamorphisme comprenant le Ceinture d’Arc Composite. La formation du complexe métamorphique à coeur de noyau est survenue après l’épaississement crustale ottavien, le pic métamorphique et le possible flux en chenal, et s’est produit en régime d’amincissement crustal et d’effondrement gravitationnel au cours duquel la croûte supérieure refroidie a subit un mégaboudinage et où la croûte moyenne chaude et ductile sous-jacente a flué dans les régions entre les mégaboudins. L’amincissement crustale post-pic dans le domaine de Muskoka, qui a débuté en conditions suprasolidus, a été facilité par une rétromorphose généralisée, hétérogène, atteignant à peu près 90 % par endroits. Celle-ci a été associée avec une gamme de structures d’extension ductiles de haute température, incluant du boudinage de plusieurs ordres de grandeur et de plis de flexure d’extension, ainsi qu’un système régional de plis croisés d’origine transtensionnelle. À ces structures ductiles a succédé une phase de plissement de propagation de failles cassantes à ductiles à un plus haut niveau crustal, après que le complexe gneissique ait été exhumé et se soit refroidi. Prises ensemble, les données indiquent une extension post-pic sur la marge d’un complexe métamorphique à coeur de noyau exceptionnellement grand aux environs de 60 m.y. et dans laquelle la zone de détachement montre une épaisseur véritable d’environ 7 km. La grandeur de l’échelle du complexe métamorphique à coeur de noyau concorde avec le fort niveau d’érosion, et la grande durée de l’effondrement d’extension est compatible avec une croûte de double épaisseur au pic de métamorphisme, la présence de leucosomes abondants dans la croûte moyenne et d’une rétromorphose à flux fluidique généralisée, l’ensemble indiquant l’importance du rôle des complexes métamorphiques à coeur de noyau dans le refroidissement de la croûte après le pic de l’orogenèse grenvillienne.
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Michel, H. Karin, K. E. Louden, F. Marillier, and I. Reid. "The seismic velocity structure of northern Appalachian crust around western Newfoundland." Canadian Journal of Earth Sciences 29, no. 3 (March 1, 1992): 462–78. http://dx.doi.org/10.1139/e92-040.
Abstract:
The crustal velocity structure beneath western Newfoundland is constrained by a reanalysis of older, regional refraction profiles together with an analysis of one new profile. Initial interpretation of the older data gave inconsistent and discontinuous structures that are difficult to reconcile with more recent deep reflection profiles. We also show that traveltimes predicted by the earlier models often do not yield acceptable fits to the original observations. Our reinterpretation reveals a simpler pattern, in which the crust is characterized by a persistent, high-velocity, lower crustal (HVLC) layer. This layer has velocities of 7.0–7.9 kmls and thicknesses of 5–23 km. It is thickest beneath the Grenville crustal block, east of the Appalachian structural front, and thins or is possibly absent within the Central block. Analysis of the new, much higher resolution profile off western Newfoundland confirms the existence of the HVLC layer with a velocity of 7.2 kmls and thicknesses of 11–19 km, increasing to the northeast. The upper crust has well-defined velocities of 6.2–6.4 kmls and is overlain by a complex sandwich of sediment layers with principal velocities of 3.9, 4.95, and 5.58 kmls and maximum total thicknesses of 8.5 km in the south to 5.5 km in the north. Total crustal thickness varies from 39 to 43 km from south to north. Comparison of the velocity–depth models with the pattern of deep crustal reflectivity revealed by deep multichannel profiles shows that the HVLC layer is coincident with a zone of flat-lying reflectors that terminate to the west at the base of the crust beneath the Appalachian structural front. The HVLC may continue eastward to cover a broad region of central Newfoundland as suggested by the older data, but its association with the reflectivity is not clear.
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Beaudoin, Georges, D. F. Sangster, and C. I. Godwin. "Isotopic evidence for complex Pb sources in the Ag–Pb–Zn–Au veins of the Kokanee Range, southeastern British Columbia." Canadian Journal of Earth Sciences 29, no. 3 (March 1, 1992): 418–31. http://dx.doi.org/10.1139/e92-037.
Abstract:
In the Kokanee Range, more than 370 Ag–Pb–Zn–Au vein and replacement deposits are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks. The Kokanee Range forms the hanging wall of the Slocan Lake Fault, an Eocene, east-dipping, low-angle normal fault. The Pb isotopic compositions of galenas permit the deposits to be divided into four groups that form linear arrays in tridimensional Pb isotopic space, each group having a distinct geographic distribution that crosses geological boundaries. The Kokanee group Pb is derived from a mixture of local upper crustal country rocks. Ainsworth group Pb and Sandon group Pb plot along a mixing line between a lower crustal Pb reservoir and the upper crustal Pb reservoir. The Ainsworth group Pb isotopic signature is markedly lower crustal, whereas the Sandon group Pb is slightly lower crustal. The Bluebell group Pb plots along a mixing line between a depleted upper mantle Pb reservoir and the lower crustal Pb reservoir.The geographic distribution and the Pb isotopic composition of each group probably reflect deep structures that permitted mixing of lower crustal, upper crustal, and mantle Pb by hydrothermal fluids. Segments of, or fluids derived from, the lower crust and the upper mantle were leached by, or mixed with, evolved meteoric water convecting in the upper crust. Fracture permeability, hydrothermal fluid flow, and mineralization resulted from Eocene crustal extension in southeastern British Columbia.
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Moser, D. E. "The geology and structure of the mid-crustal Wawa gneiss domain: a key to understanding tectonic variation with depth and time in the late Archean Abitibi–Wawa orogen." Canadian Journal of Earth Sciences 31, no. 7 (July 1, 1994): 1064–80. http://dx.doi.org/10.1139/e94-096.
Abstract:
The amphibolite-facies central Wawa gneiss domain (CWGD) preserves structures that developed at the mid-crustal level of the ca. 2.7 Ga Abitibi–Wawa orogen in the southern Superior Province. The relative ages of these domainal structures are documented and brackets on their absolute ages established using existing U–Pb age data. Correlation of tectonic events within the CWGD, and comparison of these events with the evolution of other structural levels of the orogen, has led to subdivision of orogenesis into five stages. During stage 1 (2700–2680 Ma), 2.9 and 2.7 Ga rocks were tightly folded and (or) thrusted at all crustal levels in at least one thick-skinned compression event. During stage 2 (2680–2670 Ma), folding and thrusting of Timiskaming-age sediments at high levels of the orogen was thin-skinned and had no effect on CWGD gneisses. During stage 3 (2670–2660 Ma), while the upper crust was relatively stable, a 1 km thick package of volcanics and sediments, the Borden Lake belt, was underthrust northwards to depths of 30 km and in-folded with orthogneiss of the CWGD. During stage 4 (2660–2637 Ma), coeval east–west extension and granulite metamorphism of the middle crust produced gently dipping shear zones that overprinted earlier fold structures in the CWGD and lower structural levels of the orogen. This took place with minimal effect on the upper crust. Stage 5 (2630–2580 Ma) marks a period of east–west shortening and (or) fault reactivation in the Kapuskasing uplift and upper-crustal greenstone belts that allowed penetration of deep-crustal metamorphic fluids into the latter. In general, analysis of the structural evolution of the CWGD indicates that deformation and metamorphism in the middle crust of the Abitibi–Wawa orogen outlasted that at upper-crustal levels, resulting in the generally shallower dips of planar fabrics in the deeper structural levels of the Kapuskasing uplift crustal cross section.
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Jamaludin, Siti Nur Fathiyah, Manuel Pubellier, and Benjamin Sautter. "Shallow vs. Deep Subsurface Structures of Central Luconia Province, Offshore Malaysia Reveal by Aeromagnetic, Airborne Gravity and Seismic Data." Applied Sciences 11, no. 11 (May 31, 2021): 5095. http://dx.doi.org/10.3390/app11115095.
Abstract:
Across the Luconia continental shelf, the nature and structures of the crust are lacking geological understanding and precise characterization. Newly acquired, aeromagnetic, and airborne gravity data were used to assess deep and shallow sub-surface signals within the Central Luconia Province, off the coast of Sarawak, offshore Malaysia. Regional aeromagnetic anomalies appear to primarily reflect deep crustal features while depth (Z) tensors of airborne gravity anomalies evidence shallow subsurface structures. Strike directions of the interpreted structural trend on aeromagnetic and airborne gravity anomalies maps are measured and plotted into rose diagrams to distinguish the structural orientations for all datasets. Signature patterns extracted from the depth profiles were correlated with parallel seismic lines and nearest exploration wells and coincide well with the top of carbonate for Cycle IV/V and structures seen within the Cycle I and II sediments. The orientation of faults/lineaments at shallower depth is dominated by a NW-SE orientation, similar with the faults extracted from two recently published structural maps. Deeper subsurface sections yielded E-W to NWW-SEE dominant directions which were never presented in the published literature. The E-W oriented anomalies are postulated to represent the remnants of the accretion between the Luconia crustal block and southern boundary of the Palawan block. The NW-SE trend follows the same direction as prominent faults in the region. The insight into shallow and deep subsurface structures in Central Luconia Province imaged through airborne gravity and aeromagnetic data should provide guidelines and complementary information for regional structural studies for this area, particularly in combination with detailed seismic interpretation. Further evaluation on the response of Air-FTG® gravity and aeromagnetic could lead to the zonation of potential basement highs and hydrocarbon prospects in this area.
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Kivior, Irena, David Boyd, David Tucker, Stephen Markham, Francis Vaughan, Fasil Hagos, and Leslie Mellon. "Deep Crustal Structures Interpreted from Potential Field Data along the Deep Seismic Sounding Transect across Olympic Dam, South Australia." ASEG Extended Abstracts 2013, no. 1 (December 2013): 1–4. http://dx.doi.org/10.1071/aseg2013ab156.
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Andrés, Juvenal, Puy Ayarza, Martin Schimmel, Imma Palomeras, Mario Ruiz, and Ramon Carbonell. "What can seismic noise tell us about the Alpine reactivation of the Iberian Massif? An example in the Iberian Central System." Solid Earth 11, no. 6 (December 18, 2020): 2499–513. http://dx.doi.org/10.5194/se-11-2499-2020.
Abstract:
Abstract. The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: the Duero Basin to the north, located at 750–800 m, and the Tajo Basin to the south, lying at 450–500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data are able to constrain the geometry of this crustal root, which appears to be defined by a northward lower-crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. In addition, the lower crust might have thinned, allowing coupled deformation at both crustal levels. This implies that the reactivated upper-crustal fractures can reach lower-crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constraints on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. The results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF (Central Iberian Massif DEFormation Mechanisms) profile. Although the resolution of the dataset features limited resolution (0.5–4 Hz, stations placed at ∼ 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny.
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Shao, J., G. He, and L. Zhang. "Deep crustal structures of the Yanshan intracontinental orogeny: a comparison with pericontinental and intercontinental orogenies." Geological Society, London, Special Publications 280, no. 1 (2007): 189–200. http://dx.doi.org/10.1144/sp280.9.
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LI, Song-Lin, Xian-Kang ZHANG, Cheng-Ke ZHANG, Jin-Ren ZHAO, and Shuang-Xi CHENG. "A Preliminary Study on Crustal Velocity Structures of Maqin-Lanzhou-Jingbian Deep Seismic Sounding Profile." Chinese Journal of Geophysics 45, no. 2 (March 2002): 209–16. http://dx.doi.org/10.1002/cjg2.233.
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Jozwiak, Waldemar. "Large-Scale Crustal Conductivity Pattern in Central Europe and Its Correlation to Deep Tectonic Structures." Pure and Applied Geophysics 169, no. 10 (November 27, 2011): 1737–47. http://dx.doi.org/10.1007/s00024-011-0435-7.
35
Abramovitz, T., and H. Thybo. "Pre-Zechstein structures around the MONA LISA deep seismic lines in the southern Horn Graben area." Bulletin of the Geological Society of Denmark 45 (January 30, 1999): 99–116. http://dx.doi.org/10.37570/bgsd-1998-45-10.
Abstract:
Seismic reflection data from the Horn Graben area in the southeastern part of the North Sea, off-shore Denmark, have been interpreted to illustrate the upper crustal structures around the MONA LISA deep seismic lines. The study area comprises the southern Horn Graben area and the eastern part of East North Sea High, where the Caledonian collision suture between Baltica and Eastern Avalonia bends such that the strike direction changes from ESE in the south to NNW in the north. Integrated interpretation of normal-incidence reflection data and wide-angle refraction data reveals substantial occurrences of lower and upper Palaeozoic strata in the area, thickest below the Horn Graben. This may indicate that Horn Graben developed as a graben structure during late Palaeozoic in the former Caledonian foredeep. On the northern and eastern parts of the MONA LISA deep seismic reflection lines 1 and 3, the main E- dipping boundary fault of the southern Horn Graben segment appears to be listric at depth with a sub-horizon-tal detachment at the top of the reflective lower crust. We have mapped the lateral extent of the lower Permian, volcanic Rotliegend reflector in the study area on the basis of seismic lines from the RTD-81 survey. Dipping reflections observed in the sedimentary strata below the Rotliegend reflector are interpreted as Cal-edonian structures generated by folding and deformation in Lower Palaeozoic Baltica shelf sediments in the Caledonian foreland basin. A sequence of S- and W-dipping reflections above 4 s twt are interpreted as preserved Caledonian thrusts in the upper crustal frontal part of the SW-dipping Caledonian Deformation Front.
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Clowes, R. M., F. A. Cook, A. G. Green, C. E. Keen, J. N. Ludden, J. A. Percival, G. M. Quinlan, and G. F. West. "Lithoprobe: new perspectives on crustal evolution." Canadian Journal of Earth Sciences 29, no. 9 (September 1, 1992): 1813–64. http://dx.doi.org/10.1139/e92-145.
Abstract:
Lithoprobe is Canada's national, collaborative, multidisciplinary earth science research program directed toward an enhanced understanding of how the North American continent evolved. Research in its eight transects or study areas, which span the country from Vancouver Island to Newfoundland and geological time from 4 Ga to the present, is spearheaded by seismic reflection surveys. These, combined with many other studies, are providing new insight into the varied tectonic processes that have been active in forming the continent. Results from the Southern Cordillera transect show that Mesozoic crustal growth occurred in the central and eastern Cordillera by the accretion and amalgamation of exotic terranes, the collision of which resulted in the generation of crustal-scale antiforms and duplexes. After the principal periods of compression, this area was affected by a major episode of extension that led to the unroofing of the metamorphic core complexes. Farther to the west, past and present subduction processes have eroded the lower lithosphere of accreted terranes and left underplated sediments and oceanic lithosphere. The Lithoprobe East transect, covering the Paleozoic Newfoundland Appalachians and Mesozoic rifted Atlantic margin, reveals three lower crustal blocks, each with distinctive reflection signatures on marine seismic data. Structures of the geologically established tectono-stratigraphic domains, imaged clearly by new onshore reflection data, sole at upper crustal to mid-crustal levels, suggesting that much of the surface stratigraphy is allochthonous to the lower crustal blocks. At the ocean–continent transition, interpretations suggest underplating of thinned continental crust by basaltic melt during the rifting process.In Lake Superior, data from the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) transect reveal the complex structures of the late Middle Proterozoic Keweenawan rift, which is up to 35 km deep, that almost split North America. The GLIMPCE data in Lake Huron show a spectacular series of east-dipping crustal-scale reflections that coincide with the Grenville front tectonic zone. These and other data have led to a two-stage model involving collision of an exotic terrane with the southern Superior cratonic margin in the late Early Proterozoic followed by stacking–crustal penetrating imbrication and ramping associated with the Middle Proterozoic Grenvillian orogeny. The Archean Kapuskasing structural zone, a prominent northeast-trending feature that cuts obliquely across the dominant east-west structures of the Superior Province, is interpreted as a thin thrust sheet, soled by a variably reflective décollement, above which about 70 km of crustal shortening has occurred to bring mid-crustal to lower crustal rocks to the surface, and below which the Moho deepens. The shortening may have been accomplished by brittle faulting and erosion at levels above 20 km and ductile folding or faulting in the lower crust. Preliminary studies in the Archean Abitibi greenstone belt indicate that two major fault zones, the Larder Lake–Cadillac and Porcupine–Destor, which host significant mineralization, were generated by crustal-scale thrust and (or) strike-slip tectonics. Archean crustal sections are as structurally diverse and complex as their Proterozoic and Phanerozoic counterparts. The reflection Moho has highly variable characteristics as imaged within transects and among different transects. Crustal and Moho reflectivity observed in the various transects is caused by a wide range of features, including fault–shear zones, lithologic contacts, compositional layering, fluids in zones of high porosity, and anisotropy.
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Zuza, Andrew V., Charles H. Thorman, Christopher D. Henry, Drew A. Levy, Seth Dee, Sean P. Long, Charles A. Sandberg, and Emmanuel Soignard. "Pulsed Mesozoic Deformation in the Cordilleran Hinterland and Evolution of the Nevadaplano: Insights from the Pequop Mountains, NE Nevada." Lithosphere 2020, no. 1 (August 25, 2020): 1–24. http://dx.doi.org/10.2113/2020/8850336.
Abstract:
Abstract Mesozoic crustal shortening in the North American Cordillera’s hinterland was related to the construction of the Nevadaplano orogenic plateau. Petrologic and geochemical proxies in Cordilleran core complexes suggest substantial Late Cretaceous crustal thickening during plateau construction. In eastern Nevada, geobarometry from the Snake Range and Ruby Mountains-East Humboldt Range-Wood Hills-Pequop Mountains (REWP) core complexes suggests that the ~10–12 km thick Neoproterozoic-Triassic passive-margin sequence was buried to great depths (>30 km) during Mesozoic shortening and was later exhumed to the surface via high-magnitude Cenozoic extension. Deep regional burial is commonly reconciled with structural models involving cryptic thrust sheets, such as the hypothesized Windermere thrust in the REWP. We test the viability of deep thrust burial by examining the least-deformed part of the REWP in the Pequop Mountains. Observations include a compilation of new and published peak temperature estimates (n=60) spanning the Neoproterozoic-Triassic strata, documentation of critical field relationships that constrain deformation style and timing, and new 40Ar/39Ar ages. This evidence refutes models of deep regional thrust burial, including (1) recognition that most contractional structures in the Pequop Mountains formed in the Jurassic, not Cretaceous, and (2) peak temperature constraints and field relationships are inconsistent with deep burial. Jurassic deformation recorded here correlates with coeval structures spanning western Nevada to central Utah, which highlights that Middle-Late Jurassic shortening was significant in the Cordilleran hinterland. These observations challenge commonly held views for the Mesozoic-early Cenozoic evolution of the REWP and Cordilleran hinterland, including the timing of contractional strain, temporal evolution of plateau growth, and initial conditions for high-magnitude Cenozoic extension. The long-standing differences between peak-pressure estimates and field relationships in Nevadan core complexes may reflect tectonic overpressure.
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Hall, Jeremy, Richard J. Wardle, Charles F. Gower, Andrew Kerr, Kevin Coflin, Charlotte E. Keen, and Peter Carroll. "Proterozoic orogens of the northeastern Canadian Shield: new information from the Lithoprobe ECSOOT crustal reflection seismic survey." Canadian Journal of Earth Sciences 32, no. 8 (August 1, 1995): 1119–31. http://dx.doi.org/10.1139/e95-093.
Abstract:
As part of the Eastern Canadian Shield Onshore–Offshore Transect (ECSOOT), Lithoprobe acquired 1250 km of deep seismic reflection data along the coast of Labrador and across Ungava Bay, to image evidence of Proterozoic crustal accretion to the Archean nuclei of the Nain and Superior provinces of the Canadian Shield. The relatively pristine Archean crust of the Nain Province has low reflectivity and generally lacks systematic reflector orientations. Reworking of Archean crust on the margins of the Makkovik Province has little effect on this weak signature. In contrast, the Archean crust in the Eastern Churchill (Rae) Province appears to have been overprinted by a strongly developed, whole-crustal, easterly dipping reflection fabric, interpreted to result from Proterozoic collision of the Nain and Superior provinces in the paired New Quebec and Torngat orogens. Juvenile Proterozoic crust in the Makkovik and Grenville provinces also shows strong whole-crustal dipping reflection fabrics, interpretable as outwardly verging structures associated with collisional mobile belts. Crustal thickness varies from 35 to 45 km in Proterozoic provinces, except where thinner in areas probably affected by Mesozoic extension associated with rifting of the Labrador Sea. Dipping reflectors in the mantle are commonly associated with strong lower-crustal dipping reflections in a manner similar to that observed in some modern orogens. The ECSOOT data show that Proterozoic crust in this area has structural forms comparable with those of modern orogens and, inferentially, its tectonic development was controlled by very similar collisional processes.
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Culshaw, N. G., J. W. F. Ketchum, N. Wodicka, and P. Wallace. "Deep crustal ductile extension following thrusting in the southwestern Grenville Province, Ontario." Canadian Journal of Earth Sciences 31, no. 1 (January 1, 1994): 160–75. http://dx.doi.org/10.1139/e94-013.
Abstract:
Two lithotectonic assemblages in southern Britt domain have different histories of plutonism, metamorphism, structural development, and mafic dyke emplacement. These differences are accounted for by postulating that a cryptic Grenvillian thrust separates the assemblages. Amphibolite-facies extensional shear along the Central Britt shear zone (CBSZ) overprinted the thrust, obscuring kinematic evidence for its existence. The structurally lower Bayfield–Nadeau Island assemblage contains orthogneiss suites of disparate age, lesser amounts of supracrustal rocks deposited before intrusion of the youngest orthogneiss, pre-Grenvillian and Grenvillian metamorphic assemblages, and at least three mafic dyke suites. The overlying Ojibway – Sand Bay assemblage contains only younger orthogneiss with Grenvillian metamorphic assemblages, volumetrically important supracrustal rocks that are younger than the youngest orthogneiss, and lacks cross-cutting mafic dykes.Comparable tectono-stratigraphic changes are present across the thrust boundary separating the Ojibway – Sand Bay assemblage and the basal Parry Sound assemblage. Extensional shearing did not strongly overprint this boundary and it therefore serves as a relatively unmodified analogue of the overprinted boundary.Extension on the CBSZ overlapped formation of transverse ductile folds (hinges parallel to the extension–transport direction). These folds and the CBSZ dominate the crustal architecture at this level and are interpreted to be late orogenic structures formed during a gravity-assisted shape adjustment of the orogenic wedge. Thermal softening of the lower crust caused by thrust thickening may have allowed this to occur.
40
Carr, Sharon D. "Three crustal zones in the Thor–Odin – Pinnacles area, southern Omineca Belt, British Columbia." Canadian Journal of Earth Sciences 28, no. 12 (December 1, 1991): 2003–23. http://dx.doi.org/10.1139/e91-182.
Abstract:
The present crustal architecture of the southern Omineca Belt in the Canadian Cordillera is a product of Eocene extension and crustal thinning superimposed on a crust that was thickened and deformed during Paleozoic and Jurassic to Late Paleocene compression. Amphibolite-facies rocks exposed as gneiss complexes within the Shuswap Metamorphic Complex, in the southern Omineca Belt, were buried during compression and were exhumed in the lower plates of low- to moderate-angle plastic–brittle Eocene extensional faults.In the Thor–Odin – Pinnacles area three crustal zones, which have experienced different deformation and thermal histories, and intervening shear zones can be correlated with Lithoprobe seismic reflection data. The Basement Zone, which comprises crystalline basement and overlying supracrustal gneisses, is bounded above by the Monashee décollement, a deep-seated northeasterly directed Mesozoic–Paleocene thrust fault. In the hanging wall of the décollement, polydeformed gneisses and schists of the Middle Crustal Zone are characterized by Late Cretaceous–early Tertiary ductile strain, plutonism, and thermal quenching. They are bounded at the top by crustal-scale Eocene normal faults that juxtapose Upper Crustal Zone rocks characterized by Jurassic and older structures and a Jura-Cretaceous cooling history.Middle Crustal Zone rocks of the Thor–Odin – Pinnacles area are correlative with part of the Late Proterozoic Horsethief Creek Group and Cambrian to Jurassic strata and host extensive plutons, stocks, and sheets of the syntectonic and posttectonic Late Paleocene – Early Eocene Ladybird granite suite. Field mapping and geochronology indicate that (i) a substantial part of the penetrative compressional polydeformation history and the thermal peak of metamorphism within the Middle Crustal Zone occurred in the Late Cretaceous–Paleocene; (ii) thrusting on the Monashee décollement had ended by 58 Ma; (iii) the onset of extensional deformation either overlapped or closely followed the compressional regime; (iv) Middle Crustal Zone metamorphic and igneous rocks were hot in the Paleocene and cooled rapidly in the early Tertiary because of extensional denudation.
41
Sandrin, A., and H. Thybo. "Deep seismic investigation of crustal extensional structures in the Danish Basin along the ESTRID-2 profile." Geophysical Journal International 173, no. 2 (May 2008): 623–41. http://dx.doi.org/10.1111/j.1365-246x.2008.03759.x.
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Edwards, Sally, and Behnam Talebi. "New deep crustal seismic data acquisition program for NWQ's frontier petroleum basins." APPEA Journal 59, no. 2 (2019): 869. http://dx.doi.org/10.1071/aj18084.
Abstract:
The Georgina and South Nicholson basins and the Isa Superbasin of North West Queensland (NWQ), represent frontier basins earmarked for examination of resource potential under the Strategic Resources Exploration Program. Little exploration has occurred for petroleum resources in these basins although a proven petroleum system exists in both the Isa Superbasin and the Georgina Basin with demonstrated flow at sub-commercial rates. To increase knowledge of the petroleum system, define the extent of the South Nicholson Basin and examine basin architecture, Geoscience Australia acquired deep (to 20-s listening time) seismic data across the South Nicholson Basin and northern Isa Superbasin area in 2017. However, this survey focused on broader structural architecture definition across the Proterozoic Isa Superbasin and South Nicholson and McArthur basins. Little is understood of the petroleum system in the southern Isa Superbasin, or even if this structure is part of the Isa Superbasin, where Proterozoic gas is inferred from mineral boreholes and oil stained Cambrian-aged carbonates exist. To increase understanding of this southern region, the Queensland Government acquired a new NWQ SEEBASE® (depth to basement) model in 2018, and will be undertaking a 2D deep seismic survey within the Camooweal region to better understand the structural architecture, sediment thicknesses and seismic characteristic of packages of this southern area. The seismic survey is centred on the Georgina Basin and will tie into the South Nicholson survey – extending knowledge further south across major structures featured in the SEEBASE® model.
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Murphy, J. Brendan, William J. Collins, and Donnelly B. Archibald. "Logan Medallist 7. Appinite Complexes, Granitoid Batholiths and Crustal Growth: A Conceptual Model." Geoscience Canada 49, no. 3-4 (December 17, 2022): 237–49. http://dx.doi.org/10.12789/geocanj.2022.49.191.
Abstract:
Appinite bodies are a suite of plutonic rocks, ranging from ultramafic to felsic in composition, that are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies and by spectacularly diverse textures, including planar and linear magmatic fabrics, mafic pegmatites and widespread evidence of mingling between coeval mafic and felsic compositions. These features suggest crystallization from anomalously water-rich magma which, according to limited isotopic studies, has both mantle and meteoric components. Appinite bodies typically occur as small (~2 km diameter) complexes emplaced along the periphery of granitoid plutons and commonly adjacent to major deep crustal faults, which they preferentially exploit during their ascent. Several studies emphasize the relationship between intrusion of appinite, granitoid plutonism and termination of subduction. However, recent geochronological data suggest a more long-lived genetic relationship between appinite and granitoid magma generation and subduction.Appinite may represent aliquots of hydrous basaltic magma derived from variably fractionated mafic underplates that were originally emplaced during protracted subduction adjacent to the Moho, triggering generation of voluminous granitoid magma by partial melting in the overlying MASH zone. Hydrous mafic magma from this underplate may have ascended, accumulated, and differentiated at mid-to-upper crustal levels (ca. 3–6 kbar, 15 km depth) and crystallized under water-saturated conditions. The granitoid magma was emplaced in pulses when transient stresses activated favourably oriented structures which became conduits for magma transport. The ascent of late mafic magma, however, is impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magma that forms appinite complexes evaded those rheological barriers because it preferentially exploited the deep crustal faults that bounded the plutonic system. In this scenario, appinite complexes may be a direct connection to the mafic underplate and so its most mafic components may provide insights into processes that generate granitoid batholiths and, more generally, into crustal growth in arc systems.
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Dessa, Jean-Xavier, Marie-Odile Beslier, Laure Schenini, Nicolas Chamot-Rooke, Nicolà Corradi, Matthias Delescluse, Jacques Déverchère, et al. "Seismic Exploration of the Deep Structure and Seismogenic Faults in the Ligurian Sea by Joint Multi Channel and Ocean Bottom Seismic Acquisitions: Preliminary Results of the SEFASILS Cruise." Geosciences 10, no. 3 (March 18, 2020): 108. http://dx.doi.org/10.3390/geosciences10030108.
Abstract:
The north Ligurian margin is a complex geological area in many ways. It has witnessed several phases of highly contrasting deformation styles, at both crustal scale and that of shallower cover tectonics, simultaneously or in quick succession, and with significant spatial variability. This complex interplay is mirrored in the resulting intricate structures that make it hard to identify active faults responsible for both, the significant seismicity observed, and the tectonic inversion undergone by the margin, identified at longer time scales on morphostructural grounds. We present here the first preliminary results of the leg 1 of SEFASILS cruise, conducted in 2018 offshore Monaco, in an effort to answer these questions by means of modern deep seismic acquisitions, using multichannel reflection and wide-angle sea-bottom records. Some first interpretations are provided and point towards an active basement deformation that focuses at the limits between main crustal domains.
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Saibi, Hakim, Diab Bakri Hag, Mohammed Saeed Mohammed Alamri, and Hamdan Abdo Ali. "Subsurface structure investigation of the United Arab Emirates using gravity data." Open Geosciences 13, no. 1 (January 1, 2021): 262–71. http://dx.doi.org/10.1515/geo-2020-0233.
Abstract:
Abstract The crustal structure beneath the United Arab Emirates (UAE) is still relatively unknown. Here, we use regional gravity data to constrain the subsurface density distribution and structure of the crust of the UAE by applying diverse gravity derivatives methods such as horizontal derivative (HDR), analytic signal (AS), and tilt angle (TA) to analyze the subsurface structure and perform three-dimensional (3D) gravity inversion for imaging crustal structure from the surface down to 35 km depth. The results are compared with known geological regional structures and the location of the petroleum fields. The Bouguer anomalies range from −100.8 to 113.5 mGal. The 3D gravity inversion results and the maximum Bouguer values coincide with the ophiolitic Hajar mountains in the east and the successive anticlines (uplifted basement rocks) and synclines in different parts of UAE, which could be promising sites for future mining and petroleum exploration. Also, the 3D density model results and the minimum Bouguer anomalies are located over the Aruma Basin, eastern UAE Platform, and Low Central UAE Platform, which can be the places for deep groundwater aquifers. These new results from HDR, AS, and TA successfully identify known geological structures, especially in the eastern part of UAE.
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Manatschal, Gianreto, David Ulfbeck, and Jeroen van Gool. "Change from thrusting to syncollisional extension at a mid-crustal level: an example from the Palaeoproterozoic Nagssugtoqidian Orogen (West Greenland)." Canadian Journal of Earth Sciences 35, no. 7 (July 1, 1998): 802–19. http://dx.doi.org/10.1139/e98-030.
Abstract:
The Palaeoproterozoic Nagssugtoqidian Orogen in West Greenland represents a mid- to deep-crustal section through a collisional orogen with a complex intrusive, tectonic, and metamorphic history. In the northeastern central part of the orogen, in the Ussuit area, Palaeoproterozoic intrusive and supracrustal rocks are sandwiched between slices of Archaean rocks forming a stack of lithotectonic units. Juxtaposition of these units occurred during west- to northwest-vergent thrusting along ductile shear zones (= D1) associated with a foliation formed at upper amphibolite facies conditions. D1 structures were folded (= FA) and then reactivated and locally omitted by localized east- to east-northeast-vergent extensional ductile shear zones (= D2) at near-peak metamorphic conditions. Shallowly east-plunging, transport-parallel upright folds (= FB) affect but are also truncated by D2 extensional shear zones, suggesting an interplay between FB folding and D2 shearing, compatible with a scenario of overall shortening perpendicular to fold axial surface during simultaneous extension parallel to fold axes. Consequently, the structures preserved in the Ussuit area document a deformation history which results from a change from thrusting to syncollisional extension occurring in mid- to lower crustal levels at peak metamorphic conditions.
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Proshkina, Z. N., M. G. Valitov, Yu A. Telegin, N. S. Lee, T. N. Kolpashchikova, and N. M. Tsovbun. "DEEP CRUSTAL STRUCTURE IN THE SOUTHERN PART OF THE TATAR TROUGH AND THE DISTRIBUTION OF GAS GEOCHEMICAL ANOMALIES." Tikhookeanskaya Geologiya 42, no. 2 (2023): 36–49. http://dx.doi.org/10.30911/0207-4028-2023-42-2-36-49.
Abstract:
Deep structural features of the structures in the southern part of the Tatar trough were determined based on structural, density and petromagnetic modeling. It was revealed that the morphostructure has a riftogenic nature. The distribution of anomalous methane concentrations in water and the upper part of the sedimentary cover above these objects was studied. It is shown that the sialic crust in the area adjacent to the rift structures has undergone characteristic changes. Possible ways of delivering thermogenic methane to the upper part of the sedimentary cover and the water column were determined.
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Utkin, V. P. "Strike-slip related tectogenesis and structure-forming flow of crustal masses of the Asia-Pacific transition zone." LITHOSPHERE (Russia) 19, no. 5 (November 23, 2019): 780–99. http://dx.doi.org/10.24930/1681-9004-2019-19-5-780-799.
Abstract:
Research subject. This study was aimed at examining the strike-slip related tectogenesis of the Asia-Pacific transition zone (APTZ).Materials and methods. The research was based on the materials collected by the author during long-term fieldwork across the territories of Primorye, Khabarovsk Krai and, partly,Vietnam. Extensive materials on the topic of the APTZ tectogenesis published by researchers fromRussia,China andJapan were analysed. Investigations involved the study of structural and kinematic assemblages representing the forms, directions and time of crustal mass flows under the strike-slip related tectogenesis of the East Asian global strike-slip fault zone (EAGSSFZ).Results. The EAGSSFZ consists of three transit strike-slip fault systems (zones) playing the role of the APTZ basic deep fault structures. Its master system (MS) is NNE (25–30°) trending longitudinally to theAsia edge. The MS is bordered by diagonal NE 50–70° trending near-continental and meridional near-oceanic EAGSSFZ systems. The MS controls the East Asian volcano-plutonic belt (EAVPB), demarcating the APTZ into internal (near-continental) and external (near-oceanic) zones. Two stages of the strike-slip related tectogenesis were established: orogenic-constructive (Jurassic–to–Late-Cretaceous) and riftogenic-destructive (Late Cretaceous–to–Cenozoic). The riftogenic destruction broke the previously formed orogenic foldedthrust structures, thus causing the EAVPB magmatic succession from intracrustal intrusions (Early Cretaceous) to volcanics (Late-Cretaceous-to-Cenozoic). An increase in the crustal destruction during the end of Cretaceous to Cenozoic resulted in the formation of epicontinental sedimentary basins and deep-sea riftogenic depressions of marginal seas. The structure-forming flow of the APTZ crustal masses occurred in the SSW 180–250° direction being opposite and obliquely opposite towards the NNW subduction direction of oceanic plates.Conclusion. The kinematic disconformity as well as the coincidence of the continental crust flow (plate flows) with the direction of inertial-and-equator-oriented forces allowed the author to determine the structuring of the transition zone as a process independent of the geodynamics of oceanic plates and subordinate to the rotational geodynamics of the non-uniformly rotating Earth.
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Chacksfield, B. C., W. De Vos, L. D'Hooge, M. Dusar, M. K. Lee, C. Poitevin, C. P. Royles, and J. Verniers. "A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques." Geological Magazine 130, no. 5 (September 1993): 583–91. http://dx.doi.org/10.1017/s0016756800020884.
Abstract:
AbstractDigital processing and image-based display techniques have been used to generate contour and shaded-relief maps of Belgian aeromagnetic data at a scale of 1:300000 for the whole of Belgium. These highlight the important anomalies and structural trends, particularly over the Brabant Massif. North and vertically illuminated shaded-relief plots, enhanced structural belts trending west–east to northwest–southeast in the Brabant Massif and west–east to southwest–northeast in the core of the Ardennes. The principal magnetic lineaments have been identified from the shaded-relief plots and tentatively correlated to basement structures. Most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures. Magnetic highs within the Brabant Massif are attributed to folded sediments of the Tubize Group. The magnetic basement in the east of Belgium is sinistrally displaced to the north by an inferred deep NNW–SSE crustal fracture. The Bouguer anomaly map of Belgium identifies the Ardennes as a negative area, and the Brabant Massif as a positive area, with the exception of a WNW–trending gravity low in its western part. The southern margin of the Brabant Massif is defined by a steep gravity gradient coincident with the Faille Bordiere (Border Fault). Trial modelling of the gravity and magnetic data, carried out along profiles across the Brabant and Stavelot massifs, has identified probable acid igneous intrusions in the western part of the Brabant Massif, and a deep magnetic lower density body underlying the whole Ardennes region, which is thought to be a distinctive Precambrian crustal block.
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Pryer, Lynn, Jane Blevin, Gabriel Nelson, Guillaume Sanchez, Jen-Deng Lee, Donna Cathro, Rod Graham, and Brian Horn. "Structural architecture and basin evaluation of the North West Shelf." APPEA Journal 54, no. 2 (2014): 474. http://dx.doi.org/10.1071/aj13047.
Abstract:
The WestraliaSPAN 2D regional program extends across all basins of Australia’s North West Shelf (Carnarvon/Roebuck/Browse/Bonaparte basins) and Arafura regions. The survey is designed with long offset and record length (18 sec) acquisition parameters to image the important deep crustal and sub crustal architecture and depositional systems across this complex margin. The regional program provides unique, state-of-the-art depth imaging of deep-basement rift structures of the Westralian Superbasin, as well as the lower crust and Moho. The survey has multiple transects which cross the transition from continental to oceanic crust, that provide insight into the distribution of volcanics and a possible hyper-extended rift margin. An integrated geological and geophysical interpretation encompasses available well, seismic and potential field data. Gravity models were developed to aid in depth conversion and the structural interpretation of the deep crust and Moho. A comprehensive model of basin formation provides the context for regional correlation of tectonostratigraphic packages throughout these linked basin systems, highlighting pre-Jurassic rift basins and their structural controls. While the North West Shelf, Browse and Bonaparte basins are proven and established hydrocarbon provinces, a future step-change in exploration concepts involves an integrated, margin-scale understanding of these basin systems and their potential resources. Collectively, the new dataset and interpretation will aid explorers in understanding the nature and distribution of key petroleum systems elements (reservoir/source/seal) and processes (heatflow, timing of source maturity, expulsion, migration and entrapment).