Extensional shear zones as imaged by reflection seismic lines: the Larderello geothermal field (central Italy)

Abstract. In NE Poland, the Eastern European Craton (EEC) crust of the Fennoscandian affinity is concealed under a Phanerozoic platform cover and penetrated by the sparse deep research wells. Most of the inferences regarding its structure rely on geophysical data. Until recently, this area was covered only by the refraction/wide-angle reflection (WARR) profiles, which show a relatively simple crustal structure with a typical cratonic 3-layer crust. ION Geophysical PolandSPAN™ regional seismic program, acquired over the marginal part of the EEC in Poland, offered a unique opportunity to derive a detailed image of the deeper crust. Here, we apply extended correlation processing to a subset (~950 km) of the PolandSPAN™ dataset located in NE Poland, which enabled us to extend the nominal record length of the acquired data from 12 to 22 s (~60 km depth). Our new processing revealed reflectivity patterns, that we primarily associate with the Paleoproterozoic crust formation during the Svekofennian (Svekobaltic) orogeny and which are similar to what was observed along the BABEL and FIRE profiles in the Baltic Sea and Finland, respectively. We propose a mid- to lower-crustal lateral flow model to explain the occurrence of two sets of structures that can be collectively interpreted as kilometre-scale S-C' shear zones. The structures define a penetrative deformation fabric invoking ductile extension of hot orogenic crust. Localized reactivation of these structures provided conduits for subsequent emplacement of gabbroic magma that produced a Mesoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) suite in NE Poland. Delamination of overthickened orogenic lithosphere may have accounted for magmatic underplating and fractionation into the AMCG plutons. We also found sub-Moho dipping mantle reflectivity, which we tentatively explain as a signature of the crustal accretion during the Svekofennian orogeny. Later tectonic phases (e.g. Ediacaran rifting, Caledonian orogeny) did not leave a clear signature in the deeper crust, however, some of the subhorizontal reflectors below the basement, observed in the vicinity of the AMCG Mazury complex, can be alternatively linked with lower Carboniferous magmatism.

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A new interpretation of geological structure of Tempoku Coal Field by crooked-line survey

Exploration Geophysics ◽

10.1071/eg992241 ◽

1992 ◽

Vol 23 (2) ◽

pp. 241

Author(s):

O. Nakano ◽

M. Endo ◽

E. Ishii ◽

H. Watanabe

Keyword(s):

Large Scale ◽

Geological Structure ◽

Seismic Survey ◽

Coal Field ◽

Coal Seams ◽

Reflection Seismic ◽

Line Method ◽

Northern Island ◽

New Interpretation ◽

Seismic Lines

Tempoku Coal Field is located in the northern area of Japan's northern island, Hokkaido. Here the exploration target, the Soya Coal-Bearing Formation, is of Tertiary age overlying Cretaceous basement. The regional structure of the area is characterised by a series of synclines and anticlines trending north-northwest, with several reverse faults. A suite of surveys was carried out in 1991, in the Asajino area in the central part of the coal field. The study included drilling, vertical seismic profiling, and trenching, as well as a reflection seismic survey with the crooked-line method, which is the subject of this paper. The crooked-line method was adopted because of the mountainous terrain of the area. The seismic lines were laid out along existing tracks and valleys. The main geological structure of the area had long been considered to be a monotonous series of folds. However, the 1991 survey revealed a large-scale thrust-related structure in the main coal seams, which presented clear reflectors. Together with the data from other surveys, a reinterpretation of the structure of the Asajino area is proposed.

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The application of ambient noise and reflection seismic exploration in an urban active fault survey

Interpretation ◽

10.1190/int-2020-0085.1 ◽

2020 ◽

Vol 8 (4) ◽

pp. SU1-SU10

Author(s):

Xiaoqiong Lei ◽

Jun Zhang ◽

Wenyuan Jin ◽

Chen Han ◽

Xiwei Xu

Keyword(s):

High Resolution ◽

Ambient Noise ◽

Active Fault ◽

Active Faults ◽

Seismic Exploration ◽

Deep Penetration ◽

Seismic Surveys ◽

Reflection Seismic ◽

Active Source ◽

Seismic Lines

As the detection of urban active faults becomes increasingly important, high-resolution detection of urban blind active faults is very important for urban planning, land use, and disaster risk reduction. However, it is difficult to determine the corresponding surface positions in the city environment for noise and building restrictions. The active source reflection seismic technique is considered the best technique to image faults with a high resolution and deep penetration. However, urban geophysical exploration must often consider the complex urban environment, which includes moving vehicles, dense power grids, and irregular buildings. These features make active source reflection seismic exploration difficult for wide application due to its drawbacks of high cost and the necessary use of explosives. In contrast, ambient noise seismic surveys have the advantages of continuous ambient noise sources, low cost, and fast deployment. These advantages are good for urban exploration. Although ambient noise seismic surveys have a lower resolution than active seismic surveys, their ultrahigh-density layout can improve the resolution. We have conducted two active source seismic lines and two ambient noise seismic lines near the Huangzhuang-Gaoliying fault (HGF) in a northern suburb of Beijing. The autocorrelation and crosscorrelation results are consistent with the active source reflection seismic results. They revealed the location of the HGF, which is composed of a set of steep dip faults. The study of the combination of the two techniques demonstrates that ambient noise seismic surveys are effective for urban active fault detection, especially for larger scale area surveys, and active source reflection seismic surveys can be used for detailed surveys. The combination of the two techniques has a higher efficiency and lower costs and can be widely used in blind urban active fault surveys.

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Lift-off moraines: markers of last ice-flow directions on the Scotian Shelf

Canadian Journal of Earth Sciences ◽

10.1139/e00-066 ◽

2000 ◽

Vol 37 (12) ◽

pp. 1723-1734 ◽

Cited By ~ 9

Author(s):

Michael R Gipp

Keyword(s):

High Resolution ◽

Continental Margin ◽

Flow Direction ◽

Seismic Profiles ◽

Scotian Shelf ◽

Ice Flow ◽

Reflection Seismic ◽

Flow Directions ◽

Lift Off ◽

Seismic Lines

Lift-off moraines are acoustically incoherent, subparallel ridges observed on sidescan sonograms and high-resolution reflection seismic profiles on the southeastern continental margin of Canada. They are up to 3 m high, 2080 m wide, and are commonly overlain by stratified proglacial sediments. Although little is known about them, detailed study of high-resolution seismic profiles from the Emerald Basin and the LaHave Basin, on the Scotian Shelf, show that their height:width ratio varies with the sounderseabed separation, suggesting that the ridges may be narrower than they appear. Their morphology is similar to DeGeer moraines or cross-valley moraines, which form perpendicular to ice-flow direction. As their orientations can be estimated at the intersection of seismic lines, they can be used to estimate ice-flow directions. Since proglacial sediments are draped directly over top of them, they are assumed to record the direction of last ice flow. This directional data suggests that ice retreated not only northward (to Nova Scotia), but also toward local topographic highs on the continental shelf, which acted as anchoring points for ice rises around both the Emerald and LaHave Basins. This pattern of ice-flow directions suggests that ice flowed from the high ground of banks, converging into basin deeps, suggesting that small moraines within the basins are probably of interlobate origin.

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Study of the Bouillante Bay (West Basse-Terre Island shelf): contribution of geophysical surveys to the understanding of the structural context of Guadeloupe (French West Indies - Lesser Antilles)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.181.1.51 ◽

2010 ◽

Vol 181 (1) ◽

pp. 51-65 ◽

Cited By ~ 13

Author(s):

Isabelle Thinon ◽

Pol Guennoc ◽

Adnand Bitri ◽

Catherine Truffert

Keyword(s):

West Indies ◽

Sedimentary Cover ◽

High Energy ◽

Geothermal Field ◽

Fault System ◽

Lesser Antilles ◽

French West Indies ◽

Reflection Seismic ◽

Structural Context ◽

Geophysical Surveys

Abstract The need to understand the structural context of the Bouillante geothermal field (West Basse-Terre, Guadeloupe, French West Indies) has led to onshore and offshore studies in the “high-energy geothermal fields” project, carried out by ADEME and BRGM. To ascertain the structural context of the island and the offshore continuation of the structures identified onshore, bathymetric, high-resolution reflection seismic and magnetic surveys were conducted on the shelf. The analyses of these detailed data show that the width of the present-day northwestern Basse-Terre shelf has been built by the accumulation of the Pleistocene detrital sediments over a volcanic substratum representing the prolongation on the shelf of an onshore volcanic edifice that bounds the Bouillante Bay on the south. The sedimentary cover has recorded two important regressive phases. Deciphering the structural frame has confirmed that the Bouillante sector is a key geodynamic area where the major tectonic and volcanic structures of the inner arc of the Lesser Antilles join. In this area, the N160° Basse-Terre volcanic axis, the N140° Montserrat-Bouillante volcanic and fault system, the EW Bouillante-Capesterre fault system, linked to the E-W-trending Marie-Galante graben, join up and their relationships have been specified. The N140°E Montserrat-Bouillante fault system ends on a N160° escarpment and basement high which would represent the relay of a major NNW-SSE- strike-slip fault system along the inner arc of the Lesser Antilles, linking the Montserrat-Bouillante fault to that of Les Saintes.

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Fluid geochemistry and geothermometry in the unexploited geothermal field of the Vicano–Cimino Volcanic District (Central Italy)

Chemical Geology ◽

10.1016/j.chemgeo.2014.02.005 ◽

2014 ◽

Vol 371 ◽

pp. 96-114 ◽

Cited By ~ 21

Author(s):

D. Cinti ◽

F. Tassi ◽

M. Procesi ◽

M. Bonini ◽

F. Capecchiacci ◽

...

Keyword(s):

Central Italy ◽

Geothermal Field ◽

Fluid Geochemistry

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Geophysical evidence of pre-sag rifting and post-rifting fault reactivation in the Parnaíba basin, Brazil

10.5194/se-2016-21 ◽

2016 ◽

Cited By ~ 1

Author(s):

D. L. de Castro ◽

F. H. R. Bezerra ◽

R. A. Fuck ◽

Roberta M. Vidotti

Keyword(s):

Early Stage ◽

Pure Shear ◽

Shear Zones ◽

Fault Reactivation ◽

Borehole Data ◽

Reflection Seismic ◽

Continental Scale ◽

Rift Zones ◽

Sag Basin ◽

Parnaíba Basin

Abstract. This study investigated the rifting mechanism that preceding the prolonged subsidence of the Paleozoic Parnaíba basin in Brazil and shed light in the tectonic evolution of this large cratonic basin in the South American platform. From the analysis of aeromagnetic, aerogravity, reflection seismic and borehole data, we concluded the following: (1) Large pseudo-gravity and gravity lows mimic graben structures but are associated with linear supracrustal strips in the basement. (2) Seismic data indicate that rift zones 120–200 km wide and up to 300 km long occur in other parts of the basins. These rift zones mark the early stage of the 3.5-km-thick sag basin. (3) The rifting phase occurred in the Early Paleozoic and had a subsidence rate of 47 m/Myr. (4) This ri fting phase was followed by a long period of sag basin subsidence at a rate of 9.5 m/Myr between the Silurian and the Late Cretaceous, during which rift faults propagated and influenced deposition. These data interpretations support the following successio n of events: (1) After the Brasiliano orogeny (740–580 Ma), brittle reactivation of ductile basement shear zones led to normal and dextral oblique-slip faulting concentrated along the Transbrasiliano Lineament, a continental-scale shear zone that marks the boundary between basement crustal blocks. (2) The post-orogenic tectonic brittle reactivation of the ductile basement shear zones led to normal faulting associated with dextral oblique-slip crustal extension. In the west, the orthogonal fault-inducing rifting resulted in pure-shear extension, producing rift zones that crosscut metamorphic foliations and shear zones within the Parnaíba block. (3) The rift faults experienced multiple reactivation phases. (4) Similar processes may have occurred in coeval basins in the Laurentia and Central African blocks of Gondwana.

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