orogenic wedge
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Minerals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 988
Author(s):  
Marián Putiš ◽  
Ondrej Nemec ◽  
Martin Danišík ◽  
Fred Jourdan ◽  
Ján Soták ◽  
...  

The composite Albian–Eocene orogenic wedge of the northern part of the Inner Western Carpathians (IWC) comprises the European Variscan basement with the Upper Carboniferous–Triassic cover and the Jurassic to Upper Cretaceous sedimentary successions of a large oceanic–continental Atlantic (Alpine) Tethys basin system. This paper presents an updated evolutionary model for principal structural units of the orogenic wedge (i.e., Fatricum, Tatricum and Infratatricum) based on new and published white mica 40Ar/39Ar geochronology and P–T estimates by Perple_X modeling and geothermobarometry. The north-directed Cretaceous collision led to closure of the Jurassic–Early Cretaceous basins, and incorporation of their sedimentary infill and a thinned basement into the Albian–Cenomanian/Turonian accretionary wedge. During this compressional D1 stage, the subautochthonous Fatric structural units, including the present-day higher Infratatric nappes, achieved the metamorphic conditions of ca. 250–400 °C and 400–700 MPa. The collapse of the Albian–Cenomanian/Turonian wedge and contemporary southward Penninic oceanic subduction enhanced the extensional exhumation of the low-grade metamorphosed structural complexes (D2 stage) and the opening of a fore-arc basin. This basin hemipelagic Coniacian–Campanian Couches-Rouges type marls (C.R.) spread from the northern Tatric edge, throughout the Infratatric Belice Basin, up to the peri-Pieniny Klippen Belt Kysuca Basin, thus tracing the south-Penninic subduction. The ceasing subduction switched to the compressional regime recorded in the trench-like Belice “flysch” trough formation and the lower anchi-metamorphism of the C.R. at ca. 75–65 Ma (D3 stage). The Belice trough closure was followed by the thrusting of the exhumed low-grade metamorphosed higher Infratatric complexes and the anchi-metamorphosed C.R. over the frontal unmetamorphosed to lowest anchi-metamorphosed Upper Campanian–Maastrichtian “flysch” sediments at ca. 65–50 Ma (D4 stage). Phengite from the Infratatric marble sample SRB-1 and meta-marl sample HC-12 produced apparent 40Ar/39Ar step ages clustered around 90 Ma. A mixture interpretation of this age is consistent with the presence of an older metamorphic Ph1 related to the burial (D1) within the Albian–Cenomanian/Turonian accretionary wedge. On the contrary, a younger Ph2 is closely related to the late- to post-Campanian (D3) thrust fault formation over the C.R. Celadonite-enriched muscovite from the subautochthonous Fatric Zobor Nappe meta-quartzite sample ZI-3 yielded a mini-plateau age of 62.21 ± 0.31 Ma which coincides with the closing of the Infratatric foreland Belice “flysch” trough, the accretion of the Infratatricum to the Tatricum, and the formation of the rear subautochthonous Fatricum bivergent structure in the Eocene orogenic wedge.


2021 ◽  
Author(s):  
Erica D. Erlanger ◽  
Maria Giuditta Fellin ◽  
Sean D. Willett

Abstract. Analysis of new detrital apatite fission-track (AFT) ages from modern river sands, published bedrock and detrital AFT ages, and bedrock apatite (U-Th)/He (AHe) ages from the Northern Apennines provide new insights into the spatial and temporal pattern of erosion rates through time across the orogen. The pattern of time-averaged erosion rates derived from AHe ages from the Ligurian side of the orogen illustrates slower erosion rates relative to AFT rates from the Ligurian side and relative to AHe rates from the Adriatic side. These results are corroborated by an analysis of paired AFT and AHe thermochronometer samples, which illustrate that erosion rates have generally increased through time on the Adriatic side, but decreased through time on the Ligurian side. Using an updated kinematic model of an asymmetric orogenic wedge, with imposed erosion rates on the Ligurian side that are a factor of two slower relative to the Adriatic side, we demonstrate that cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data. These results suggest that horizontal motion is an important component of the overall rock motion in the wedge, and that the asymmetry of the orogen has existed for at least several million years.


Solid Earth ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1749-1775
Author(s):  
Lorenzo G. Candioti ◽  
Thibault Duretz ◽  
Evangelos Moulas ◽  
Stefan M. Schmalholz

Abstract. The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins. Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision. We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material. Densities are determined by linearized equations of state or by petrological-phase equilibria calculations. The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, FB/FD=ArF, which controls the mode of orogenic wedge formation: ArF≈0.5 causes thrust-sheet-dominated wedges, ArF≈0.75 causes minor wedge formation due to relamination of subducted crust below the upper plate, and ArF≈1 causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (>80 km). Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres. We suggest that during the formation of the Pyrenees ArF⪅0.5 due to the absence of high-grade metamorphic rocks, whereas for the Alps ArF≈1 during exhumation of high-grade rocks and ArF⪅0.5 during the post-collisional stage. In the models, FD increases during wedge growth and subduction and eventually reaches magnitudes (≈18 TN m−1) which are required to initiate subduction. Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 Ma and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate.


Geology ◽  
2021 ◽  
Author(s):  
Sean P. Long ◽  
Delores M. Robinson

Documenting the structural evolution of the Himalayan orogen is fundamental for understanding the dynamics of collisional orogenesis. We argue that the importance of deformation in the frontal, Lesser Himalayan–Subhimalayan (LH-SH) portion of the Himalayan thrust belt for driving crustal thickening over the past ~15–13 m.y. has long been overlooked. To quantify its contribution to thickening, we measured parameters from 22 published cross sections that span the length of the orogen. The mean structural uplift accomplished by the LH-SH thrust belt increases from 10–15 km in the eastern half of the orogen to 15–23 km in the western half. An antiformal culmination constructed by LH duplexing is observed across the orogen and increases in structural height (to as much as 15–20 km) and north-south width moving westward. Construction of the culmination was the primary mechanism for building and maintaining wedge taper. The westward scaling of culmination size is accompanied by doubling and tripling of LH-SH shortening and accretion magnitude, respectively; when combined with a consistent orogen-wide modern taper angle (11° ± 2°), this indicates that duplexing facilitated the growth of an overall larger orogenic wedge moving westward. Following the initial southward propagation of deformation into LH rocks at ca. 15–13 Ma, the Himalayan orogenic wedge has been characterized by stacking of multiple thin, smalldisplacement thrust sheets to develop a high-taper orogenic wedge. Thus, LH-SH deformation has had a profound effect on driving thickening, exhumation, and the attainment of high elevations since the middle Miocene.


2021 ◽  
Vol 47 (2) ◽  
Author(s):  
Andrzej Michał Dalętka

Despite the increasing technological level of the reflection seismic method, the imaging of fold and thrust belts remains a demanding task, and usually leaves some questions regarding the dips, the shape of the subthrust structures or the most correct approach to velocity model building. There is no straightforward method that can provide structural representation of the near-surface geological boundaries and their velocities. The in-terpretation of refracted waves frequently remains the only available technique that may be used for this purpose, although one must be aware of its limitations which appear in the complex geological settings. In the presented study, the analysis of velocity values obtained in the shallow part of Carpathian orogenic wedge by means of various geophysical methods was carried out. It revealed the lack of consistency between the results of 3D refraction tomography and both the sonic log and uphole velocities. For that reason, instead of the indus-try-standard utilization of tomography, a novel, geologically-consistent method of velocity model building is pro-posed. In the near-surface part, the uphole velocities are assigned to the formations, documented by the surface geologic map. Interpreted time-domain horizons, supplemented by main thrusts, are used to make the velocity field fully-compatible with the litho-stratigraphic units of the Carpathians. The author demonstrates a retrospective overview of seismic data imaging in the area of the Polish Carpathian orogenic wedge and discusses the most recent global innovations in seismic methodology which are the key to successful hydrocarbon exploration in fold and thrust regions.


Geology ◽  
2021 ◽  
Author(s):  
M. Soret ◽  
K.P. Larson ◽  
J. Cottle ◽  
A. Ali

The mechanisms and processes active during the transition from continental subduction to continental collision at the plate interface are largely unknown. Rock records of this transition are scarce, either not exposed or obliterated during subsequent events. We examine the tectono-metamorphic history of Barrovian metamorphic rocks from the western Himalayan orogenic wedge. We demonstrate that these rocks were buried to amphibolite-facies conditions from ≤47 Ma to 39 ± 1 Ma, synchronously with the formation (46 Ma) and partial exhumation (45–40 Ma) of the ultrahigh-pressure eclogites. This association indicates that convergence during continental subduction was accommodated via development of a deep orogenic wedge built through successive underplating of continental material, including the partially exhumed eclogites, likely in response to an increase in interplate coupling. This process resulted in the heating of the subduction interface (from ~7 to ~20 °C/km) through advective and/or conductive heat transfer. Rapid cooling of the wedge from 38 Ma, coeval with the formation of a foreland basin, are interpreted to result from indentation of a promontory of thick Indian crust.


2021 ◽  
Vol 9 ◽  
Author(s):  
Anne Obermann ◽  
Elmer Ruigrok ◽  
Irene Bianchi ◽  
György Hetényi

We use a novel technique named global-phase seismic interferometry (GloPSI) to image the lithospheric structure, and in particular the Moho, below two parallel north-south transects belonging to the GANSSER network (2013–2014). The profiles cross the Himalayan orogenic wedge in Bhutan, a tectonically important area within the largest continent-continent collision zone on Earth that is still undergoing crustal thickening and represents a challenging imaging target for the GloPSI approach. GloPSI makes use of direct waves from distant earthquakes and receiver-side reverberations with near vertical incidence. Reflections are isolated from earthquake recordings by solving a correlation integral and are turned into a reflectivity image of the lithosphere below the arrays. Our results compare favorably with first-order features observed from a previous receiver function (RF) study. We show that a combined interpretation of GloPSI and RF results allows for a more in-depth understanding of the lithospheric structure across the orogenic wedge in Bhutan.


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