Granite genesis and the mechanics of convergent orogenic belts with application to the southern Adelaide Fold Belt

1992 ◽  
Vol 83 (1-2) ◽  
pp. 83-93 ◽  
Author(s):  
Mike Sandiford ◽  
John Foden ◽  
Shaohua Zhou ◽  
Simon Turner
Keyword(s):  
Numerical Models ◽  
Thin Sheet ◽  
Causative Factor ◽  
Crustal Thickening ◽  
Low Grade ◽  
Strong Temperature Dependence ◽  
Fold Belt ◽  
Lithospheric Deformation ◽  
Granite Formation ◽  
Mechanical Models

ABSTRACTTwo models for the heating responsible for granite generation during convergent deformation may be distinguished on the basis of the length- and time-scales associated with the thermal perturbation, namely: (1) long-lived, lithospheric-scale heating as a conductive response to the deformation, and (2) transient, localised heating as a response to advective heat sources such as mantle-derived melts. The strong temperature dependence of lithospheric rheology implies that the heat advected within rising granites may affect the distribution and rates of deformation within the developing orogen in a way that reflects the thermal regime attendant on granite formation; this contention is supported by numerical models of lithospheric deformation based on the thin-sheet approximation. The model results are compared with geological and isotopic constraints on granite genesis in the southern Adelaide Fold Belt where intrusion spans a 25 Ma convergent deformation cycle, from about 516 to 490 Ma, resulting in crustal thickening to 50–55 km. High-T metamorphism in this belt is spatially restricted to an axis of magmatic activity where the intensity and complexity of deformation is significantly greater, and may have started earlier, than in adjacent low-grade areas. The implication is that granite generation and emplacement is a causative factor in localising deformation, and on the basis of the results of the mechanical models suggests that granite formation occurred in response to localised, transient crustal heating by mantle melts. This is consistent with the Nd- and Sr-isotopic composition of the granites which seems to reflect mixed sources with components derived both from the depleted contemporary mantle and the older crust.

scholarly journals Thermal Finite Element Modelling of the Laser Beam Welding of Tailor Welded Blanks through an Equivalent Volumetric Heat Source

2021 ◽  
Author(s):  
Vito Busto ◽  
Donato Coviello ◽  
Andrea Lombardi ◽  
Mariarosaria De Vito ◽  
Donato Sorgente
Keyword(s):  
Finite Element ◽  
Heat Source ◽  
Numerical Models ◽  
Laser Beam Welding ◽  
Welding Process ◽  
Butt Joint ◽  
Volumetric Heat Source ◽  
Tailor Welded Blanks ◽  
Mechanical Models ◽  
Physical Phenomena

Abstract In last decades, several numerical models of the keyhole laser welding process were developed in order to simulate the joining process. Most of them are sophisticated multiphase numerical models tempting to include all the several different physical phenomena involved. However, less computationally expensive thermo-mechanical models that are capable of satisfactorily simulating the process were developed as well. Among them, a moving volumetric equivalent heat source, whose dimensions are calibrated on experimental melt pool geometries, can estimate some aspects of the process using a Finite Element Method (FEM) modelling with no need to consider fluid flows. In this work, a double-conical volumetric heat source is used to arrange a combination of two half hourglass-like shapes with different dimensions each other. This particular arrangement aims to properly assess the laser joining of a Tailor Welded Blank (TWB) even in case of butt joint between sheets of different thicknesses. Experiments of TWBs made of 22MnB5 steel sheets were conducted in both equal and different thicknesses configurations in order to validate the proposed model. The results show that the model can estimate in a satisfactory way the shape and dimensions of the fused zone in case of TWB made of sheets with different thickness.

scholarly journals Crustal thickening under the palaeo-meso-Proterozoic Delhi Fold Belt in northwestern India: evidence from deep reflection profiling

1997 ◽  
Vol 129 (3) ◽  
pp. 657-668 ◽  
Author(s):  
H. C. Tewari ◽  
M. M. Dixit ◽  
N. Madhava Rao ◽  
N. Venkateswaralu ◽  
V. Vijaya Rao
Keyword(s):  
Crustal Thickening ◽  
Fold Belt ◽  
Northwestern India

scholarly journals The crystalline units of the High Himalayas in the Lahul–Zanskar region (northwest India): metamorphic–tectonic history and geochronology of the collided and imbricated Indian plate

1990 ◽  
Vol 127 (2) ◽  
pp. 101-116 ◽  
Author(s):  
U. Pognante ◽  
D. Castelli ◽  
P. Benna ◽  
G. Genovese ◽  
F. Oberli ◽  
...  
Keyword(s):  
Shear Zones ◽  
Sensu Stricto ◽  
Crustal Thickening ◽  
Indian Plate ◽  
Low Grade ◽  
Lesser Himalaya ◽  
Medium Temperature ◽  
Polyphase Metamorphism ◽  
Early Palaeozoic ◽  
Northwest India

AbstractIn the High Himalayan belt of northwest India, crustal thickening linked to Palaeogene collision between India and Eurasia has led to the formation of two main crystalline tectonic units separated by the syn-metamorphic Miyar Thrust: the High Himalayan Crystallines sensu stricto (HHC) at the bottom, and the Kade Unit at the top. These units are structurally interposed between the underlying Lesser Himalaya and the very low-grade sediments of the Tibetan nappes. They consist of paragneisses, orthogneisses, minor metabasics and, chiefly in the HHC, leucogranites. The HHC registers: a polyphase metamorphism with two main stages designated as M1 and M2; a metamorphic zonation with high-temperature recrystallization and migmatization at middle structural levels and medium-temperature assemblages at upper and lower levels. In contrast, the Kade Unit underwent a low-temperature metamorphism. Rb–Sr and U–Th–Pb isotope data point to derivation of the orthogneisses from early Palaeozoic granitoids, while the leucogranites formed by anatexis of the HHC rocks and were probably emplaced during Miocene time.Most of the complicated metamorphic setting is related to polyphase tectonic stacking of the HHC with the ‘cooler’ Kade Unit and Lesser Himalaya during the Himalayan history. However, a few inconsistencies exist for a purely Himalayan age of some Ml assemblages of the HHC. As regards the crustal-derived leucogranites, the formation of a first generation mixed with quartzo-feldspathic leucosomes was possibly linked to melt-lubricated shear zones which favoured rapid crustal displacements; at upper levels they intruded during stage M2 and the latest movements along the syn-metamorphic Miyar Thrust, but before juxtaposition of the Tibetan nappes along the late- metamorphic Zanskar Fault.

scholarly journals Analogue earthquakes and seismic cycles: Experimental modelling across timescales

2016 ◽  
Author(s):  
Matthias Rosenau ◽  
Fabio Corbi ◽  
Stephane Dominguez
Keyword(s):  
Numerical Models ◽  
Experimental Modelling ◽  
Rupture Dynamics ◽  
Scale Models ◽  
Analogue Models ◽  
Elastic Rebound ◽  
Earthquake Modelling ◽  
Earthquake Model ◽  
Mechanical Models ◽  
Long Timescales

Abstract. Since the formulation of Reid’s elastic rebound theory 100 years ago laboratory mechanical models combining frictional and elastic elements have joined the forefront of the research on the dynamics of earthquakes. In the last decade, with the advent of high resolution monitoring techniques and new rock analogue materials, laboratory earthquake experiments kept developing from simple spring-slider models to more sophisticated scaled analogue models. This evolution was accomplished by advances in seismology and geodesy which, along with a culmination of large earthquakes, have significantly increased the quality and quantity of relevant observations in nature. We here review the cornerstones of analogue earthquake model developments with a focus on scale models which are directly comparable to observational data on short to long timescales. We revisit the basics of analogue modelling, namely scaling, materials and monitoring, as applied in earthquake modelling. An overview of applications highlights the contributions of analogue earthquake models in bridging timescales of observations including earthquake statistics, rupture dynamics, ground motion and seismic cycle deformation up to seismotectonic evolution. We finally discuss limits, challenges and links to numerical models.

Source rocks of I- and S-type granites in the Lachlan Fold Belt, southeastern Australia

1984 ◽  
Vol 310 (1514) ◽  
pp. 693-707 ◽  
Keyword(s):  
Volcanic Rocks ◽  
Source Rocks ◽  
Low Grade ◽  
Fold Belt ◽  
Southeastern Australia ◽  
Deep Crust ◽  
Lachlan Fold Belt ◽  
Isotopic Evolution ◽  
Crustal Origin ◽  
Source Materials

Granites and related volcanic rocks derived from both igneous and sedimentary source materials (I- and S-types) are widely distributed in the Palaeozoic Lachlan Fold Belt of southeastern Australia. Many of the granites contain material residual from partial melting of the source rocks, or restite, which enables attempts to be made to calculate source rock compositions. A few of the S-type granites are closely related to regional metamorphic rocks and are of relatively local derivation. Most, however, are intrusive into low-grade rocks and came from deeper levels in the crust; and volcanic equivalents are extensively developed. These dominant S-type rocks have chemical and isotopic properties unlike any known locally exposed sediments. For most of the S-types, and perhaps all of them, no mantle-derived component was present in the source. Chemical and isotopic data on the I-type granites suggest a variety of deep crust sources consisting of mantle-derived material showing differing amounts of isotopic evolution, according to the time since extraction from the mantle. These data do not favour a significant sedimentary component in the sources of even the most isotopically evolved I-type rocks. An origin of the I-type source rocks by crustal underplating is favoured, so that these sources were generally infra-crustal, whereas the S-type sources were of supra-crustal origin.

scholarly journals Isotopic evidence for a Precambrian metamorphic event within the Charcot Land window, East Greenland Caledonian fold belt

1981 ◽  
Vol 29 ◽  
pp. 151-160
Author(s):  
B. T. Hansen ◽  
R. H. Steiger ◽  
A. K. Higgins
Keyword(s):  
Regional Metamorphism ◽  
Metamorphic Event ◽  
Low Grade ◽  
Fold Belt ◽  
Thrust Sheet ◽  
East Greenland ◽  
Grade Metamorphism ◽  
Isotopic Evidence ◽  
Tectonic Window

Rb-Sr, U-Pb and K-Ar analyses on rocks and minerals from a tectonic window below a Caledonian thrust sheet in the westernmost part of the Scoresby Sund region (70°-72°N) give evidence for a Precambrian age of formation. The Charco't Land supracrustal sequence rests on a basement that is probably of Archaean development and older than at least 2100 m.y. The major regional metamorphism of the supracrustal rocks is probably not much older than the intrusion of two post-kinematic bodies, i.e. about 1840 m.y. Low-grade metamorphism in a tillite and low-grade retrogressive overprinting of the supra­crustal rocks are related to Caledonian orogenesis.

scholarly journals Preliminary Rb-Sr age determinations from the North Greenland fold belt, Johannes V Jensen Land, with comments on the metamorphic grade

1981 ◽  
Vol 106 ◽  
pp. 77-84
Author(s):  
N Springer
Keyword(s):  
Sedimentary Rocks ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Fold Belt ◽  
Isotopic Dating ◽  
Field Mapping ◽  
Sedimentary Structures ◽  
The North ◽  
North Greenland ◽  
Age Determinations

This report presents the first Rb-Sr age determinations obtained on low-grade metasediments within the eastern part of the North Greenland fold belt. Samples were collected during the 1979 field mapping in eastem Johannes V. Jensen Land, the results ofwhich have been published elsewhere (Soper et al., 1980). Material selected for this study was taken from moderately folded rocks of the Polkorridoren Group and from the northem part of the fold belt where deformation is intense and sedimentary structures are rarely preserved (fig. 23). The principles and methods of isotopic dating of sedimentary rocks applied in this study have been treated in a recent paper by Clauer (1979).

scholarly journals TECTÔNICA DA FAIXA DE DOBRAMENTOS BRASÍLIA – SETORES SETENTRIONAL E MERIDIONAL.

2012 ◽  
Author(s):  
Alexandre Uhlein ◽  
Marco Antônio Fonseca ◽  
Hildor José Seer ◽  
Marcel Auguste Dardenne
Keyword(s):  
Ductile Deformation ◽  
Low Grade ◽  
Thrust Belt ◽  
Fold Belt ◽  
Central Brazil ◽  
Structural Style ◽  
Deformational History ◽  
Fold And Thrust Belt ◽  
Lithostratigraphic Units ◽  
External Domain

A Faixa neoproterozóica de dobramentos e empurrões Brasília é uma das unidades tectônicas do Brasil Central. Uma análiseestrutural e tectônica da Faixa Brasília é aqui apresentada, com dois domínios estruturais: (1) interno, com unidades alóctones, foliação Spsubhorizontal ou suavemente dobrada e médio a alto grau de metamorfismo. (2) domínio externo, com estrutura de dobras e empurrões,predomínio de foliação Sp e médio a baixo grau de metamorfismo. A leste da Faixa Brasília ocorre o domínio cratônico (Craton do São Francisco), com unidades autóctones, suavemente dobradas. A vergência das dobras e empurrões é, geralmente, para o Cráton do SãoFrancisco. O encurtamento na cobertura é balanceado por zonas de cisalhamento, amplas dobras, falhas de empurrão e inversas e falhastranscorrentes. O estilo da deformação varia com o nível crustal. Assim, no domínio externo da faixa, predomina um estilo thin-skinned,enquanto que no domínio interno, aparecem zonas de deformação dúcteis mais intensas e largas, com metamorfismo mais alto (estilothick-skinned). O segmento sul da Faixa Brasília está mais deformado e provavelmente representa o resultado de uma colisão diacrônica,mais antiga, em relação ao setor setentrional. A mega inflexão dos Pirineus e a zona de superposição pode ser o resultado da interferênciaentre duas faixas neoproterozóicas distintas, com transporte tectônico local de Norte para o Sul.Palavras chave: Faixa móvel neoproterozóica Brasília; estilo nstrutural; evolução geodinâmica. ABSTRACTTECTONICS OF THE BRASÍLIA FOLD BELT: THE NORTHERN AND SOUTHERN PARTS - The Neoproterozoic (ca. 650-580) Ma Brasíliafold-and-thrust-belt is a major tectonic unit in Central Brazil and can be divided into two structural domains (internal and external). In theinternal domain, most surface rocks consist of allochthonous units in a higher metamorphic grade displaying low dipping cleavage,asymmetrical folds and thrusts with significant stratigraphic repetition. The external domain is a typical foreland fold-and-thrust belt wheremedium to low grade metamorphic rocks prevail and present steeply dipping cleavage Sp. Towards the cratonic area (cratonic domain),most lithostratigraphic units are authoctonous with vertical open folds and slaty cleavage. The general vergence of folds and thrust faults inboth domains is towards the east (São Francisco Craton). Shortening of cover across the fold belt is almost always balanced by coverbasementdetachments, fold-and-thrust structures and also by NE or NW trending wrench faults. The style of deformation variesconsiderably across strike due to crustal level. Typical thin-skinned fault-fold morphology in external domain gives rise downwards to morepervasive wide zones of ductile deformation at high metamorphic grades (thick-skinned structures) in the internal domain. The Southernpart of the Brasilia belt has a more complex deformational history than the northern one. This is probably due to structural overprintcaused by a diachronic collision. The Pirineus Inflection, where local vergence is towards the South, may represent the interference zonebetween the the two parts.Keywords: Neoproterozoic Brasília fold-and-thrust belt; structural style; Geodinamic evolution.

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