Geochemical and isotopic (Nd, O, and Pb) constraints on granite sources in the Humber and Dunnage zones, Gaspésie, Quebec, and New Brunswick: implications for tectonics and crustal structure

Siluro–Devonian granitoids span a wide compositional range (~50–76% SiO2) and can be subdivided into two groups: (i) monzonitic or incompatible element enriched with affinities to within-plate magmatism (WPG); and (ii) calc-alkalic or incompatible element depleted with supra-subduction zone affinities (VAG). Granitoid εNd(T = 0.4 Ga) values range from −1 to +5.5; most lie between +3 and +5.5. 207Pb/204Pb isotopic compositions range from 15.52 to 15.61; most fall between ~15.55 and 15.59. Most δ18O values lie between +5.5 and +8‰. No well-established trends exist between SiO2 and isotopic composition, and isotopic compositions do not differ between the two trace element defined granitoid groups.Though Pb isotopic data are consistent with a major contribution to the granitoids from Proterozoic-aged Laurentian plate rocks (i.e., Grenville basement), Nd and O isotopic data are not. These isotopic data are consistent with major source components derived from early Paleozoic depleted or supra-subduction zone affected mantle and (or) crustal rocks derived from the early Paleozoic mantle(s). These protoliths would not have seen significant interaction with time-integrated old crustal material or surficial processes. Granitoid Pb isotopic data can be reconciled with an early Paleozoic mantle–crust origin, but it may also be that the Pb isotopes are decoupled from other isotopic systems. In either case, Nd and O isotopic data clearly prohibit the involvement of significant amounts of Grenville crust and suggest that seismic-reflection data do not define crustal blocks, or at least not blocks having a tectonic and geologic history easily related to the surface geology.

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Recent tectonic reorganization of the Nubia-Eurasia convergent boundary heading for the closure of the western Mediterranean

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.182.4.279 ◽

2011 ◽

Vol 182 (4) ◽

pp. 279-303 ◽

Cited By ~ 75

Author(s):

Andrea Billi ◽

Claudio Faccenna ◽

Olivier Bellier ◽

Liliana Minelli ◽

Giancarlo Neri ◽

...

Keyword(s):

Subduction Zone ◽

Mediterranean Area ◽

Western Mediterranean ◽

Small Scale ◽

The West ◽

Seismic Reflection Data ◽

Basin Inversion ◽

The North ◽

Reflection Data ◽

Back Arc

Abstract In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian (W-Africa) northward subduction beneath Eurasia, subduction has almost ceased, as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic reflection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the convergent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two back-arc oceanic basins (Algerian-Liguro-Provençal and Tyrrhenian basins) and it is now mainly active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provençal, Algerian, and Alboran (partly) margins. Onset of compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins following a similar propagation of the cessation of the subduction, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced on the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to really start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. Part of the contractional deformation may have shifted toward the north in the Liguro-Provençal basin possibly because of its weak rheological properties compared with those of the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are strongly heterogeneous along the boundary. These features prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred to follow a Wilson Cycle (at a small scale) with the following main steps : (1) northward Nubian subduction with Mediterranean back-arc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive onset of compression, from west to east, in the former back-arc domain and consequent basin inversion (since ~8–10 Ma); (4) possible future subduction of former back-arc basins.

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Paleo-Proterozoic thick-skinned tectonics: Lithoprobe seismic reflection results from the eastern Trans-Hudson Orogen

Canadian Journal of Earth Sciences ◽

10.1139/e94-042 ◽

1994 ◽

Vol 31 (3) ◽

pp. 458-469 ◽

Cited By ~ 37

Author(s):

D. J. White ◽

S. B. Lucas ◽

Z. Hajnal ◽

A. G. Green ◽

J. F. Lewry ◽

...

Keyword(s):

Seismic Reflection ◽

Apparent Contradiction ◽

Seismic Reflection Data ◽

Crustal Rocks ◽

Reflection Data ◽

Granulite Belt ◽

Northwestern Margin ◽

Flin Flon ◽

Lower Crustal ◽

Superior Craton

New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and Saskatchewan) provide striking images of juvenile paleo-Proterozoic arc rocks (Flin Flon and Kisseynew belts) juxtaposed against the deformed northwestern margin of the Archean Superior craton. Crustal imbrication on a scale imaged in few other orogens is observed within the Flin Flon Belt where a package of shallowly east-dipping reflections extends from the surface to 14 s. These reflections are attributed to middle to lower crustal arc rocks that appear to have been stacked below a major detachment that underlies the upper crustal rocks of the Flin Flon Belt. Surprisingly, the seismic images show the juvenile arc rocks dipping moderately eastward beneath the craton in apparent contradiction to existing tectonic models. Geological and geochronological evidence suggest that the observed crustal imbrication probably reflects late-collisional or postcollisional convergence rather than earlier oceanic subduction polarity. The east-dipping reflection fabric, marking a Hudsonian tectonic overprint, extends across the Superior Boundary Zone up to the Pikwitonei Granulite Belt where upper crustal reflections are west dipping. An east-dipping seismic boundary between these domains, which soles into the mid-crust, may represent a west-verging thrust fault along which the crust of the Archean Superior craton was uplifted.

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Fore-arc basin deformation in the Andaman-Nicobar segment of the Sumatra-Andaman subduction zone: Insight from high-resolution seismic reflection data

Tectonics ◽

10.1002/2015tc003901 ◽

2015 ◽

Vol 34 (8) ◽

pp. 1736-1750 ◽

Cited By ~ 14

Author(s):

Raphaële E. Moeremans ◽

Satish C. Singh

Keyword(s):

High Resolution ◽

Subduction Zone ◽

Seismic Reflection ◽

Seismic Reflection Data ◽

Reflection Data

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Gas Hydrates in the southern Jalisco subduction zone as evidenced by bottom simulating reflectors in Multichannel Seismic Reflection Data of the 2002 BART/FAMEX campaign

Geofísica Internacional ◽

10.22201/igeof.00167169p.2012.51.4.1234 ◽

2012 ◽

Vol 51 (4) ◽

Author(s):

William L. Bandy ◽

Carlos A. Montera-Gutiérrez

Keyword(s):

Subduction Zone ◽

Gas Hydrates ◽

Seismic Reflection ◽

Seismic Reflection Data ◽

Reflection Data ◽

Bottom Simulating Reflectors ◽

Multichannel Seismic Reflection ◽

Multichannel Seismic Reflection Data

Evidencia de la presencia de hidratos de gas en forma de reflector que simula el fondo marino (BRS) es observado en un perfil sísmico multicanal, México. Los reflectores son encontrados a 0.4 segundos (en el tiempo de viaje doble) bajo el reflector del fondo marino y se extiende a lo largo de 7 km del perfil. Este resultado aunado a otros resultados previos en la parte norte de la zona de subducción de Jalisco sugiere que los hidratos de gas pudieran existir en la región del talud continental de toda la zona de subducción de Jalisco, sin embargo se necesitan mas datos de reflexión sísmica para verificar esta aseveración.

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Three-dimensional shape and structure of the Susitna basin, south-central Alaska, from geophysical data

Geosphere ◽

10.1130/ges02165.1 ◽

2020 ◽

Vol 16 (4) ◽

pp. 969-990

Author(s):

Anjana K. Shah ◽

Jeffrey D. Phillips ◽

Kristen A. Lewis ◽

Richard G. Stanley ◽

Peter J. Haeussler ◽

...

Keyword(s):

Subduction Zone ◽

Seismic Reflection ◽

Three Dimensional ◽

Fold Axis ◽

Seismic Reflection Data ◽

Reflection Data ◽

South Central ◽

Dimensional Shape ◽

Well Data ◽

Three Dimensional Shape

Abstract We use gravity, magnetic, seismic reflection, well, and outcrop data to determine the three-dimensional shape and structural features of south-central Alaska’s Susitna basin. This basin is located within the Aleutian-Alaskan convergent margin region and is expected to show effects of regional subduction zone processes. Aeromagnetic data, when filtered to highlight anomalies associated with sources within the upper few kilometers, show numerous linear northeast-trending highs and some linear north-trending highs. Comparisons to seismic reflection and well data show that these highs correspond to areas where late Paleocene to early Eocene volcanic layers have been locally uplifted due to folding and/or faulting. The combined magnetic and seismic reflection data suggest that the linear highs represent northeast-trending folds and north-striking faults. Several lines of evidence suggest that the northeast-trending folds formed during the middle Eocene to early Miocene and may have continued to be active in the Pliocene. The north-striking faults, which in some areas appear to cut the northeast-trending folds, show evidence of Neogene and probable modern movement. Gravity data facilitate estimates of the shape and depth of the basin. This was accomplished by separating the observed gravity anomaly into two components—one representing low-density sedimentary fill within the basin and one representing density heterogeneities within the underlying crystalline basement. We then used the basin anomaly, seismic reflection data, and well data to estimate the depth of the basin. Together, the magnetic, gravity, and reflection seismic analyses reveal an asymmetric basin comprising sedimentary rock over 4 km thick with steep, fault-bounded sides to the southwest, west, and north and a mostly gentle rise toward the east. Relations to the broader tectonic regime are suggested by fold axis orientations within the Susitna basin and neighboring Cook Inlet basin, which are roughly parallel to the easternmost part of the Alaska-Aleutian trench and associated Wadati-Benioff zone as it trends from northeast to north-northeast to northeast. An alignment between forearc basin folds and the subduction zone trench has been observed at other convergent margins, attributed to strain partitioning generated by regional rheologic variations that are associated with the subducting plate and arc magmatism. The asymmetric shape of the basin, especially its gentle rise to the east, may reflect uplift associated with flat-slab subduction of the Yakutat microplate, consistent with previous work that suggested Yakutat influence on the nearby Talkeetna Mountains and western Alaska Range. Yakutat subduction may also have contributed to Neogene and later reverse slip along north-striking faults within the Susitna basin.

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The reflection Moho beneath the southern Canadian Cordillera

Canadian Journal of Earth Sciences ◽

10.1139/e95-124 ◽

1995 ◽

Vol 32 (10) ◽

pp. 1520-1530 ◽

Cited By ~ 30

Author(s):

Frederick A. Cook

Keyword(s):

Tectonic Activity ◽

Partial Explanation ◽

Seismic Reflection Data ◽

North American Cordillera ◽

Crustal Rocks ◽

The North ◽

Reflection Data ◽

Structural Relief ◽

Structural Levels ◽

Structural Boundary

The transition from the crust to the mantle beneath the Canadian portion of the North American Cordillera varies in depth, geometry, and tectonic age across the orogen. These variations are rarely spatially related to the positions of morphologic or tectonic belts based on surface geology, nor to nearly 25 km of structural relief identified in outcrop and on seismic reflection data. The Moho in this region is thus interpreted to be a long-lived feature, perhaps as old as Proterozoic in the eastern part of the Cordillera, that probably has been active as a structural boundary during periods of crustal contraction and subsequent crustal stretching. Recognition of the Moho and lower crust as a zone of localized tectonic activity provides a partial explanation for the problem of where regional detachments that underlie the foreland thrust and fold belt go as they project westward to deep structural levels beneath the interior of the orogen: they likely project to the base of the crust, where they flatten and cause imbrication of crustal rocks.

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