scholarly journals Curved orogenic belts, back-arc basins, and obduction as consequences of collision at irregular continental margins

Geology ◽  
2021 ◽  
Author(s):  
Nicholas Schliffke ◽  
Jeroen van Hunen ◽  
Frédéric Gueydan ◽  
Valentina Magni ◽  
Mark B. Allen
Keyword(s):  
Continental Margin ◽  
Three Dimensional ◽  
Oceanic Lithosphere ◽  
Spreading Center ◽  
Continental Margins ◽  
Mechanical Models ◽  
External Forces ◽  
Back Arc ◽  
Orogenic Belts ◽  
Stress Buildup

Continental collisions commonly involve highly curved passive plate margins, leading to diachronous continental subduction during trench rollback. Such systems may feature back-arc extension and ophiolite obduction postdating initial collision. Modern examples include the Alboran and Banda arcs. Ancient systems include the Newfoundland and Norwegian Caledonides. While external forces or preexisting weaknesses are often invoked, we suggest that ophiolite obduction can equally be caused by internal stress buildup during collision. Here, we modeled collision with an irregular subducting continental margin in three-dimensional (3-D) thermo-mechanical models and used the generated stress field evolution to understand resulting geologic processes. Results show how tensional stresses are localized in the overriding plate during the diachronous onset of collision. These stresses thin the overriding plate and may open a back-arc spreading center. Collision along the entire trench follows rapidly, with inversion of this spreading center, ophiolite obduction, and compression in the overriding plate. The models show how subduction of an irregular continental margin can form a highly curved orogenic belt. With this mechanism, obduction of back-arc oceanic lithosphere naturally evolves from a given initial margin geometry during continental collision.

scholarly journals Supplemental Material: Curved orogenic belts, back-arc basins, and obduction as consequences of collision at irregular continental margins

2021 ◽  
Author(s):  
Nicholas Schliffke ◽  
et al.
Keyword(s):  
Short Description ◽  
Continental Margins ◽  
Model Evolution ◽  
Back Arc ◽  
Orogenic Belts

Detailed figures of the model evolution, as well as a short description of the methodology and parameters used.<br>

scholarly journals The tectonic significance of the Cabo Frio Tectonic Domain in the SE Brazilian margin: a Paleoproterozoic through Cretaceous saga of a reworked continental margin

2016 ◽  
Vol 46 (suppl 1) ◽  
pp. 37-66 ◽  
Author(s):  
Renata da Silva Schmitt ◽  
Rudolph Trouw ◽  
William Randall Van Schmus ◽  
Richard Armstrong ◽  
Natasha S. Gomes Stanton
Keyword(s):  
Continental Margin ◽  
Rift Zone ◽  
Oceanic Lithosphere ◽  
Brazilian Coast ◽  
Continental Margins ◽  
Geological Time ◽  
Magmatic Arc ◽  
Tectonic Significance ◽  
Continental Magmatic Arc ◽  
Cabo Frio

ABSTRACT: The Cabo Frio Tectonic Domain is composed of a Paleoproterozoic basement tectonically interleaved with Neoproterozoic supracrustal rocks (Buzios-Palmital successions). It is in contact with the Neoproterozoic-Cambrian Ribeira Orogen along the SE Brazilian coast. The basement was part of at least three continental margins: (a) 1.97 Ga; (b) 0.59 - 0.53 Ga; (c) 0.14 Ga to today. It consists of continental magmatic arc rocks of 1.99 to 1.94 Ga. Zircon cores show a 2.5 - 2.6 Ga inheritance from the ancient margin of the Congo Craton. During the Ediacaran, this domain was thinned and intruded by tholeiitic mafic dykes during the development of an oceanic basin at ca. 0.59 Ma. After the tectonic inversion, these basin deposits reached high P-T metamorphic conditions, by subduction of the oceanic lithosphere, and were later exhumed as nappes over the basement. The Cabo Frio Tectonic Domain collided with the arc domain of the Ribeira Orogen at ca. 0.54 Ga. It is not an exotic block, but the eastern transition between this orogen and the Congo Craton. Almost 400 m.y. later, the South Atlantic rift zone followed roughly this suture, not coincidently. It shows how the Cabo Frio Tectonic Domain was reactivated as a continental margin in successive extensional and convergent events through geological time.

Theoretical Stress Analysis of Intersecting Cylindrical Shells Subjected to External Forces on Nozzle

2005 ◽  
Vol 128 (1) ◽  
pp. 71-83 ◽  
Author(s):  
Ming-De Xue ◽  
Qing-Hai Du ◽  
Dong-Feng Li ◽  
Keh-Chih Hwang
Keyword(s):  
Cylindrical Shell ◽  
Stress Analysis ◽  
Branch Pipe ◽  
Three Dimensional ◽  
Present Solution ◽  
Mechanical Models ◽  
Applicable Range ◽  
External Forces ◽  
3D Finite Element Method ◽  
Theoretical Stress

The stress analysis based on thin shell theory is presented for a cylindrical shell with a normally intersecting nozzle subjected to three kinds of branch pipe forces, which are tension and two shear forces. The basic mechanical models for the three load cases are presented in order to obtain the solutions independent of the length of the main shell and branch pipe. The applicable range of the present solution is expanded up to d∕D⩽0.8 and λ=d∕DT⩽12 by means of the accurate cylindrical shell equations and continuity conditions and the improved numerical method. The theoretical results are verified by test and three-dimensional (3D) finite element method (FEM) results. The maximum stress for tension force case are in good agreement with WRC Bulletin No. 297 when λ is small. The comparison between the present results and WRC Bulletin No. 107 shows that the latter needs improvement.

scholarly journals CARACTERIZAÇÃO GEOTECTÔNICA DO SETOR SETENTRIONAL DO CINTURÃO RIBEIRA: EVIDÊNCIA DE ACRESÇÃO NEOPROTEROZÓICA NO LESTE DE MINAS GERAIS, BRASIL.

1995 ◽  
Author(s):  
Antônio Gilberto Costa ◽  
Carlos Alberto Rosiére ◽  
Luciano Melo Moreira ◽  
Daniele Piuzana
Keyword(s):  
Continental Margin ◽  
Oceanic Lithosphere ◽  
Minas Gerais ◽  
Island Arc ◽  
Geochemical Data ◽  
Magmatic Arc ◽  
High K ◽  
Alternative Hypotheses ◽  
Back Arc ◽  
Early Neoproterozoic

The early neoproterozoic evolution of eastern Minas Gerais is characterized by a history of a continental margin activity, including the accretion of suspect terranes. The Manhuaçu Terrane is one of those and is represented by a granitic continental plutonic arc and terrigeneous metasediments that reflect a continental margin. A metasedimentary gneiss belt at this margin with shallow to deep marine clastic lithologies as well as metavulcanic and metaplutonic mafic rocks was interpreted as an extensive tectonic segment with suspect development in a back-arc setting. Fragments of a volcanic arc are identified and interpreted as an evidence for a probable island-arc domain. In the studied region the Juiz de Fora and Paraiba do Sul Complexes are domains of these terranes. The distribution of magmatism in the studied region shows from west to east three different suites : 1) tholeiitic, 2) a medium to high-K cal-alkalic and 3) a high-K calc-alcalic/shoshonitic(?) magmatism which attests the evolution of early magmatism arcs (volcanic and plutonic) initially relates to ocean-plate subduction, followed by a continent-continent collision. Petrological, structural and geochemical data of mesoproterozoic/neoproterozoic metamorphic and magmatic suites of rocks are in agreement with the development of an accretionary orogeny. After a vulcanic-(island-arc) and a back-arc basin formation (by rifting of a continental margin with no spreading) in connection with eastward subduction, the island arc was accreted to a continental margin. Further subduction beneath it and a mechanism of flattening of the slab during the subduction process was responsible for the development of as granitic continental plutonic-arc (Andean-type batholith) eastwardly in a compressional setting. Continental plates became sutured and all intervening oceanic lithosphere was subducted beneath one of the converging masses. This resulted in the accretion of the Manhuaçu Microplate to the São Francisco Craton Domain. Plates continued to converge and the inversion of subduction polarity occurs resulting in a new subduction system (westward subduction) to the back of the Manhuaçu Microplate, in a easternward of the Espírito Santo state, with the establishment of a new magmatic arc of late neoproterozoic to eopaleozoic age. In this paper, only the probable early neoproterozoic volcanic (tholeiitic magmatism transitional between N-type MORB and island are basalts) and the plutonic (early continental calc-alkalic magmatism) arcs characterized by rocks with a very particular geochemistry and the back-arc basin setting will be discussed. Two alternative hypotheses to explain the evolution of these terranes may be postulated: 1) an island arc orogeny related to a westward subduction followed by a cordillerean type orogeny. With the advance of the island-arc and continent with offshore sediments, in  different plates, a collision between these domains occurred. The old subduction zone was replaced by another one, eastward directed and the development of a continental magmatic arc occurred. Continental plates became sutured and all intervening oceanic lithosphere was subducted beneath one of the converging masses. Against this model are the presence of metavulcanic basic and intermediate rocks intercalated with marine and continental margin; 2) an extensional ensialic setting (aborted marginal basin) in the continental margin formed during the opening of a rapidly subsiding basin, with moderately rapid mantle upwelling, pronounced thinning of the continental crust and slight crustal contaminanton, without formation of oceanic crust or an island-arc may explain the association of basic metavulcanic rocks with marine and continental metasediments. Here, the low potassium contents of a few studied metavulcanic basic rocks and theire oceanic tholeiitic affinity are not well in agreement with this setting where continental basalts (flood basalts), or rocks ( basalts or basaltics andesites) belong to the high-K calc-alkaline series are expected to occur. Nevertheless, our evidences are not unequivocal enough for theire disapprovals.

scholarly journals Supplemental Material: Curved orogenic belts, back-arc basins, and obduction as consequences of collision at irregular continental margins

2021 ◽  
Author(s):  
Nicholas Schliffke ◽  
et al.
Keyword(s):  
Short Description ◽  
Continental Margins ◽  
Model Evolution ◽  
Back Arc ◽  
Orogenic Belts

Detailed figures of the model evolution, as well as a short description of the methodology and parameters used.<br>

Characteristics of Continental Margins

2000 ◽  
Author(s):  
Philip A. Symonds ◽  
Gregory F. Moore
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Continental Margin ◽  
Outer Part ◽  
Deep Ocean ◽  
Oceanic Lithosphere ◽  
Outer Edge ◽  
Continental Margins ◽  
Definition Of ◽  
The Individual

Two major types of morphological features dominate the surface of the Earth—the continents and the oceans, the latter being by far the most significant in that they cover about 71% of the surface. These features are separated by the coastline, which is a transitory boundary. A much more fundamental subdivision of the Earth's surface is in terms of geological provinces composed of either continental or oceanic lithosphere (crust and uppermost mantle), each with their own characteristic lithological, geochemical, and physical properties. The continental margin is the zone separating the thin oceanic crust of the deep ocean basins from the thick continental crust. Continental margins underlie about 28% of the oceans, with the transition from continental to oceanic crust commonly occurring beneath the outer part of continental margins. Thus, a substantial proportion of continental crust (about 20%) lies beneath the oceans. The boundary between these crustal provinces marks the real physical outer edge of the prolongation of the continent beneath the ocean. It is this boundary that is commonly viewed as the absolute natural limit of a claim that a coastal state can make for sovereign rights to explore and exploit the natural resources of the deep seabed and subsoil. The geomorphological and geological characteristics of a continental margin are a function of its tectonic, magmatic, and sedimentary history. Continental margins can differ greatly in their dimensions and style depending on their age and their tectono-magmatic and depositional setting. Important province boundaries, such as the continent-ocean boundary (COB), are always difficult to define with any accuracy on a map because of their complexity and transitional nature. Given this, and the development of legal thought over the last 50 years on defining the various marine jurisdictional zones, it is little wonder that the definition of the outer limit of the seabed and subsoil resource regime on continental margins, the "legal" continental shelf, is a complex blend of legal, geomorphological, geological, and geodetic concepts that can be confusing even to experts in the individual fields.

scholarly journals A critical look at the prediction of the temperature field around a laser-induced melt pool on metallic substrates

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yi Shu ◽  
Daniel Galles ◽  
Ottman A. Tertuliano ◽  
Brandon A. McWilliams ◽  
Nancy Yang ◽  
...  
Keyword(s):  
Laser Beam ◽  
Constant Velocity ◽  
Three Dimensional ◽  
Laser Beams ◽  
Poor Control ◽  
Metallic Substrates ◽  
Melt Pool ◽  
Mechanical Models ◽  
Transport Effects ◽  
Thermal Histories

AbstractThe study of microstructure evolution in additive manufacturing of metals would be aided by knowing the thermal history. Since temperature measurements beneath the surface are difficult, estimates are obtained from computational thermo-mechanical models calibrated against traces left in the sample revealed after etching, such as the trace of the melt pool boundary. Here we examine the question of how reliable thermal histories computed from a model that reproduces the melt pool trace are. To this end, we perform experiments in which one of two different laser beams moves with constant velocity and power over a substrate of 17-4PH SS or Ti-6Al-4V, with low enough power to avoid generating a keyhole. We find that thermal histories appear to be reliably computed provided that (a) the power density distribution of the laser beam over the substrate is well characterized, and (b) convective heat transport effects are accounted for. Poor control of the laser beam leads to potentially multiple three-dimensional melt pool shapes compatible with the melt pool trace, and therefore to multiple potential thermal histories. Ignoring convective effects leads to results that are inconsistent with experiments, even for the mild melt pools here.

scholarly journals Modelling Polycrystalline Materials: An Overview of Three-Dimensional Grain-Scale Mechanical Models

2013 ◽  
Vol 05 (01) ◽  
pp. 1350002 ◽  
Author(s):  
I. Benedetti ◽  
F. Barbe
Keyword(s):  
Three Dimensional ◽  
Constitutive Modelling ◽  
Polycrystalline Materials ◽  
High Fidelity ◽  
Computational Capability ◽  
Mechanical Models ◽  
Three Dimensional Models ◽  
The Individual ◽  
Individual Grains ◽  
Micro Structures

A survey of recent contributions on three-dimensional grain-scale mechanical modelling of polycrystalline materials is given in this work. The analysis of material micro-structures requires the generation of reliable micro-morphologies and affordable computational meshes as well as the description of the mechanical behavior of the elementary constituents and their interactions. The polycrystalline microstructure is characterized by the topology, morphology and crystallographic orientations of the individual grains and by the grain interfaces and microstructural defects, within the bulk grains and at the inter-granular interfaces. Their analysis has been until recently restricted to two-dimensional cases, due to high computational requirements. In the last decade, however, the wider affordability of increased computational capability has promoted the development of fully three-dimensional models. In this work, different aspects involved in the grain-scale analysis of polycrystalline materials are considered. Different techniques for generating artificial micro-structures, ranging from highly idealized to experimentally based high-fidelity representations, are briefly reviewed. Structured and unstructured meshes are discussed. The main strategies for constitutive modelling of individual bulk grains and inter-granular interfaces are introduced. Some attention has also been devoted to three-dimensional multiscale approaches and some established and emerging applications have been discussed.

Opening and closure of Iranian back-arc basins: A seismic tomography view

2021 ◽  
Author(s):  
Nalan Lom ◽  
Abdul Qayyum ◽  
Derya Gürer ◽  
Douwe G. van der Meer ◽  
Wim Spakman ◽  
...  
Keyword(s):  
Seismic Tomography ◽  
Subduction Zones ◽  
Three Dimensional ◽  
Plate Motion ◽  
Limited Information ◽  
Three Dimensional Model ◽  
Slab Geometry ◽  
Novel Approach ◽  
Sanandaj Sirjan Zone ◽  
Back Arc

&lt;p&gt;Iran is a mosaic of continental blocks that are surrounded by Tethyan oceanic relics. Remnants of these oceanic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The ophiolite belts surrounding the CIM are mainly assumed to represent narrow back-arc basins that opened in Cretaceous and closed before the Eocene. Although these ophiolites are exposed as small pieces on continental crust today, they represent oceans wide enough to form supra-subduction ophiolites and arc-related magmatic rocks which suggest that their palaeogeographic width was at least some hundreds of kilometers. Current models for the palaeogeographic dimension, opening and closure of these basins are highly schematic. They usually seem plausible in two-dimensional reconstructions, however a single three-dimensional model explaining whole Iran and its surrounding regions has not been fully accomplished.&amp;#160; This is mostly because while the geological record provides constraints on the origin and ages of the subducted ocean floor, it provides limited information about onset and cessation of the subduction and almost no constraints on the dimension of these oceans and the subduction zones that consumed them.&lt;/p&gt;&lt;p&gt;In this study, we follow a novel approach in estimating the dimension and evolution of these back-arc basin by using seismic tomography. Seismic tomography has revealed that we can image and trace subducted lithosphere relics. Imaged mantle structure is now being used to link sinking slabs with sutures and to define shape of a slab. Systematic comparison of regions where the timing of subduction is reasonably well constrained by geological data showed that slabs sink gradually through the mantle at rates more or less the same. This perspective enabled us to study slab shape as a function of absolute trench motion. While mantle stationary trenches tend to create steep slabs or slab walls, the flat-lying segments are formed where the overlying trenches are mobile relative to the mantle, normal facing during roll-back, overturned during slab advance. &amp;#160;Under the assumption of vertical sinking after break-off, it is also possible to locate the palaeo-trenches. &amp;#160;When combined with absolute plate motion reconstructions, tomographically determined volume and size of the subducted lithosphere can also be used to estimate the size/width of the prehistoric oceans. To this end, we build on and further develop concepts that relate absolute trench motion during subduction to modern slab geometry to evaluate the possible range of dimensions associated with opening and closure of the Iranian back-arc basins.&lt;/p&gt;

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