scholarly journals Buoyancy versus shear forces in building orogenic wedges

Solid Earth ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1749-1775
Author(s):  
Lorenzo G. Candioti ◽  
Thibault Duretz ◽  
Evangelos Moulas ◽  
Stefan M. Schmalholz
Keyword(s):  
Phase Equilibria ◽  
Equations Of State ◽  
Great Depth ◽  
Plate Motion ◽  
Crustal Material ◽  
High Grade ◽  
Shear Forces ◽  
Orogenic Wedge ◽  
Tectonic Style ◽  
The Impact

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.

Subduction channel vs. orogenic wedge model: numerical simulations, impact of serpentinites and application to the Alps

2020 ◽  
Author(s):  
Lorenzo G. Candioti ◽  
Stefan M. Schmalholz ◽  
Thibault Duretz
Keyword(s):  
Channel Model ◽  
Thermal Relaxation ◽  
Passive Margin ◽  
Crustal Material ◽  
Subduction Channel ◽  
Passive Margins ◽  
Coupled Equations ◽  
Orogenic Wedge ◽  
Simulation Results ◽  
The Impact

<p>In this study, we use a state-of-the-art 2D numerical algorithm solving the standard thermo-mechanically coupled equations of continuum mechanics for slow flowing viscoelastoplastic material to model the evolution of rifting, thermal relaxation and convergence-to-collision of Alpine-type orogens in three stages. (1) A ca. 360 km wide basin that is floored by exhumed mantle and bounded by two conjugate magma-poor hyper-extended passive margins is generated during a 50 Myrs rifting period. An absolute extension velocity of 1 cm/yr is applied. (2) The passive margin system is thermally equilibrated during a subsequent cooling period of 60 Myrs without significant deformation in the lithosphere (no extension velocity). At this stage, we parameterise a serpentinization front on top of the exhumed mantle by replacing the dry peridotitic mantle by serpentinized mantle in one series of simulations. The thermally equilibrated system is used as a self-consistently generated initial configuration for the subsequent period of convergence lasting for 70 Myrs applying an absolute convergence velocity of 1.5 cm/yr. Values for the duration of deformation periods and for deformation velocities are chosen to allow for comparison between simulation results and petrological data from the Central and Western Alps. Density of all materials is either precomputed for characteristic bulk rock compositions and read in from precomputed thermodynamic look-up tables (Perple_X), or calculated during run time via a linearized equation of state (EOS).</p><p> </p><p>We quantify (1) the impact of a serpentinization front of the exhumed mantle on the subduction dynamics by increasing systematically the strength of the serpentinites, (2) the peak pressure and temperature conditions of subducted crustal material from the passive margins of the overriding and subducting plate by tracking pressure (P)-temperature (T)-time (t)-depth (z) paths of selected particles and (3) the driving forces of the system. Last, (4) the impact of metamorphic phase transitions is investigated by parameterising densification of crustal material. We compare the results of simulations in which density is computed as a simple linearized EOS to results of simulations in which density is a more realistic function of P and T using precomputed thermodynamic look-up tables.</p><p> </p><p>We discuss geometric similarities between the simulation results and 2D geodynamic reconstructions from field data, quantify the P-T-t-z-history of selected particles and compare it to P-T-t data obtained from natural rocks. First results indicate that the strength of the serpentinites controls whether the deformation within the orogenic core is driven by buoyancy forces (subduction channel model) or by far-field tectonic forces (orogenic wedge model). There is a transition from subduction channel to orogenic wedge model from low to intermediate strength of the serpentinites.</p>

scholarly journals Buoyancy versus shear forces in building orogenic wedges

2021 ◽  
Author(s):  
Lorenzo G. Candioti ◽  
Thibault Duretz ◽  
Evangelos Moulas ◽  
Stefan M. Schmalholz
Keyword(s):  
Shear Strength ◽  
Phase Equilibria ◽  
Continental Crust ◽  
Driving Forces ◽  
Interface Strength ◽  
Shear Forces ◽  
Plate Interface ◽  
Orogenic Wedge ◽  
Buoyancy Forces ◽  
Orogenic Belts

Abstract. Orogenic belts formed by collision are impressive manifestations of plate tectonics. Observations from orogenic belts, like the Western Alps, indicate an important involvement of the mantle lithosphere, significant burial and exhumation of continental and oceanic crustal rocks and the importance of the plate interface strength that can be modified, for example, by the presence of serpentinites. A popular model for the formation of such belts is the so-called orogenic wedge model. However, most wedge models consider crustal deformation only and do, hence, not consider subduction, the impact of related buoyancy forces arising from density differences between subducted crust and surrounding mantle and the effects of different plate interface strength. Here, we quantify the relative importance of buoyancy and shear forces in building collisional orogenic wedges. We leverage two-dimensional (2D) petrological-thermo-mechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. We compare simulations employing density fields calculated with linearized equations of state with simulations employing density fields calculated by phase equilibria models including metamorphic reactions. Further, we consider serpentinisation of the mantle material, exhumed in the hyperextended basin. Our models show that differences in density structure and in shear strength of serpentinites or upper crust have a strong impact on the evolution of orogenic wedges. Higher serpentinite strength causes a dominance of shear over buoyancy forces, resulting in either thrust-sheet dominated orogenic wedges, involving some diapiric exhumation at their base, or relamination of crustal material below the overriding plate. Lower serpentinite strength (equal importance of shear and buoyancy forces) generates orogenic wedges that are dominated by diapiric or channel-flow exhumation. Deep subduction (> 80 km) and subsequent surface exhumation of continental crust along the subduction interface occurs in these models. Employing phase equilibria density models decreases the average buoyancy contrasts, allows for deeper subduction of continental crust and reduces the average topography of the wedge by several kilometers. A decrease of upper crustal shear strength causes smaller maximal crustal burial depths. Progressive subduction of continental crust increases upward-directed buoyancy forces of the growing wedge and in turn increases horizontal driving forces. These driving forces eventually reach magnitudes (≈ 18 TN m−1) which were required to initiate subduction during convergence. We suggest that the evolving relation between shear and buoyancy forces and the increase of horizontal driving force related to the growing Alpine orogenic wedge has significantly slowed down (or choked) subduction of the European plate below the Adriatic one between 35 and 25 Ma. This buoyancy-related choking could have caused the reorganization of plate motion and the initiation of subduction of the Adriatic plate. We discuss potential applications and implications of our model results to the Pyrenean and Alpine orogenies.

THE LANDSCAPE INVESTIGATIONS AS NECESSARY PART OF BIOLOGICAL STUDY IN THE COASTAL ZONE TO THE QUESTION OF THE IMPACT OF CLIMATE CHANGE ON THE ECOLOGICAL STATE OF ARTIFICAL

2017 ◽  
Author(s):  
Artem Lapenkov ◽  
Artem Lapenkov ◽  
Yury Zuyev ◽  
Yury Zuyev ◽  
Nadezhda Zuyeva ◽  
...  
Keyword(s):  
Coastal Zone ◽  
Benthic Communities ◽  
Great Depth ◽  
Research Strategy ◽  
Biological Study ◽  
Lake Ladoga ◽  
Coastal Zones ◽  
Investigation Methods ◽  
Ground Conditions ◽  
The Impact

Coastal zones have great diversity of resources. The shallow water zones contain the most of plant and benthic communities. A description of relief and type of ground is needed for the rigorous monitoring of biota and environmental condition of coastal zone. Generally, on the basis of these data the investigation methods of the coastal zone are selected. The shallows research strategy has been developed by us for northern part of the Lake Ladoga. If the coastal areas are characterized by great depth and flat topography, then sonar’s can be used to describe them and samples of ground can be taken by bottom grabs. In the Lake Ladoga these methods don’t operate correctly by reason of the compound bottom relief and the fact that a sizeable part of the bottom is occupied by hard ground. Therefore, our investigations base on the diving transect method of Golikov and Skarlato (1965). A diver moves along transects. He registers the depth, length to coastline, water temperature, relief and ground, edificators and records video. In the laboratory all these data are decoded and used for mapping of bays. Studies of plant communities have been performed and strategy for research of benthic communities in complex relief and hard ground conditions has been developed based on the descriptions of shallow waters. Description of the Malay Nikonovskia Bay bottom has given an opportunity to estimate changes in the bottom of the bay under the influence of the trout farm.

scholarly journals Droplet impact onto a spring-supported plate: analysis and simulations

2021 ◽  
Vol 128 (1) ◽  
Author(s):  
Michael J. Negus ◽  
Matthew R. Moore ◽  
James M. Oliver ◽  
Radu Cimpeanu
Keyword(s):  
High Speed ◽  
Flexible Substrate ◽  
Practical Importance ◽  
Hybrid Approach ◽  
Hydrodynamic Pressure ◽  
Analytical Framework ◽  
Canonical System ◽  
Linear Process ◽  
Plate Motion ◽  
The Impact

AbstractThe high-speed impact of a droplet onto a flexible substrate is a highly non-linear process of practical importance, which poses formidable modelling challenges in the context of fluid–structure interaction. We present two approaches aimed at investigating the canonical system of a droplet impacting onto a rigid plate supported by a spring and a dashpot: matched asymptotic expansions and direct numerical simulation (DNS). In the former, we derive a generalisation of inviscid Wagner theory to approximate the flow behaviour during the early stages of the impact. In the latter, we perform detailed DNS designed to validate the analytical framework, as well as provide insight into later times beyond the reach of the proposed analytical model. Drawing from both methods, we observe the strong influence that the mass of the plate, resistance of the dashpot, and stiffness of the spring have on the motion of the solid, which undergo forced damped oscillations. Furthermore, we examine how the plate motion affects the dynamics of the droplet, predominantly through altering its internal hydrodynamic pressure distribution. We build on the interplay between these techniques, demonstrating that a hybrid approach leads to improved model and computational development, as well as result interpretation, across multiple length and time scales.

scholarly journals Impact of Pathological Stratification on the Clinical Outcomes of Advanced Well-Differentiated/Dedifferentiated Liposarcoma Treated with Trabectedin

Cancers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1453
Author(s):  
Chiara Fabbroni ◽  
Giovanni Fucà ◽  
Francesca Ligorio ◽  
Elena Fumagalli ◽  
Marta Barisella ◽  
...  
Keyword(s):  
Clinical Outcomes ◽  
Proportional Hazards ◽  
Case Series ◽  
Progression Free Survival ◽  
Cox Proportional Hazards ◽  
Low Grade ◽  
High Grade ◽  
Retrospective Case ◽  
Well Differentiated ◽  
The Impact

Background. We previously showed that grading can prognosticate the outcome of retroperitoneal liposarcoma (LPS). In the present study, we aimed to explore the impact of pathological stratification using grading on the clinical outcomes of patients with advanced well-differentiated LPS (WDLPS) and dedifferentiated LPS (DDLPS) treated with trabectedin. Patients: We included patients with advanced WDLPS and DDLPS treated with trabectedin at the Fondazione IRCCS Istituto Nazionale dei Tumori between April 2003 and November 2019. Tumors were categorized in WDLPS, low-grade DDLPS, and high-grade DDLPS according to the 2020 WHO classification. Patients were divided in two cohorts: Low-grade (WDLPS/low-grade DDLPS) and high-grade (high-grade DDLPS). Results: A total of 49 patients were included: 17 (35%) in the low-grade cohort and 32 (65%) in the high-grade cohort. Response rate was 47% in the low-grade cohort versus 9.4% in the high-grade cohort (logistic regression p = 0.006). Median progression-free survival (PFS) was 13.7 months in the low-grade cohort and 3.2 months in the high-grade cohort. Grading was confirmed as an independent predictor of PFS in the Cox proportional-hazards regression multivariable model (adjusted hazard ratio low-grade vs. high-grade: 0.45, 95% confidence interval: 0.22–0.94; adjusted p = 0.035). Conclusions: In this retrospective case series, sensitivity to trabectedin was higher in WDLPS/low-grade DDLPS than in high-grade DDLPS. If confirmed in larger series, grading could represent an effective tool to personalize the treatment with trabectedin in patients with advanced LPS.

scholarly journals Up the down escalator: the exhumation of (ultra)-high pressure terranes during on-going subduction

2012 ◽  
Vol 4 (1) ◽  
pp. 745-781 ◽  
Author(s):  
C. J. Warren
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Continental Crust ◽  
Subduction Zones ◽  
Crustal Material ◽  
Time And Space ◽  
Ultra High Pressure ◽  
Tectonic Environment ◽  
Tectonic Style ◽  
Weak Material

Abstract. The exhumation of high and ultra-high pressure rocks is ubiquitous in Phanerozoic orogens created during continental collisions, and is common in many ocean-ocean and ocean-continent subduction zone environments. Three different tectonic environments have previously been reported, which exhume deeply buried material by different mechanisms and at different rates. However it is becoming increasingly clear that no single mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. In order for buoyant continental crust to subduct, it must remain attached to a stronger and denser substrate, but in order to exhume, it must detach (and therefore at least locally weaken) and be initially buoyant. Denser oceanic crust subducts more readily than more buoyant continental crust but exhumation must be assisted by entrainment within more buoyant and weak material such as serpentinite or driven by the exhumation of structurally lower continental crustal material. Weakening mechanisms responsible for the detachment of crust at depth include strain, hydration, melting, grain size reduction and the development of foliation. These may act locally or may act on the bulk of the subducted material. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Subduction zones change in style both in time and space, and exhumation mechanisms change to reflect the tectonic style and overall force regime within the subduction zone. Exhumation events may be transient and occur only once in a particular subduction zone or orogen, or may be more continuous or occur multiple times.

Aggressive Salivary Malignancies at Early Stage: Outcomes and Implications for Treatment

2017 ◽  
Vol 126 (7) ◽  
pp. 525-529 ◽  
Author(s):  
Robert W. Eppsteiner ◽  
Jonathan W. Fowlkes ◽  
Carryn M. Anderson ◽  
Robert A. Robinson ◽  
Nitin A. Pagedar
Keyword(s):  
Radiation Therapy ◽  
Early Stage ◽  
Relative Survival ◽  
Carcinoma Ex Pleomorphic Adenoma ◽  
Adjuvant Radiation ◽  
Major Salivary Gland ◽  
High Grade ◽  
Duct Carcinoma ◽  
The Impact ◽  
Case Basis

Background: Few studies have examined whether the use of adjuvant treatment impacts survival for early stage high-grade salivary tumors. Methods: A retrospective review of the SEER database between 1973 and 2012 was performed. Patients with high-grade major salivary gland tumors including salivary duct carcinoma, carcinoma ex-pleomorphic adenoma, high-grade mucoepidermoid carcinoma, or adenocarcinoma, NOS were identified. Only stage I-II tumors were included. The impact of radiation status on observed and relative survival was examined. Results: Five hundred seventy-four patients with high-grade, early stage salivary tumors met inclusion criteria. Sixty-seven percent of patients received radiation therapy. There was no difference in observed or relative survival based on having received radiation. Conclusions: Adjuvant radiation is indicated for advanced stage tumors or early stage tumors with adverse features. For early stage tumors without adverse features, there was no survival benefit from radiation therapy. Adjuvant radiation should be decided on a case-by-case basis for these patients.

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