6. Tectonics of continents

2015 ◽  
pp. 89-109
Author(s):  
Peter Molnar
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Oceanic Lithosphere ◽  
Mountain Range ◽  
Continental Lithosphere ◽  
Mountain Ranges ◽  
Horizontal Dimension ◽  
The World ◽  
The Alps ◽  
Thin Crust

‘Tectonics of continents’ shows that the much greater thickness of continental than oceanic crust makes continental and oceanic lithosphere behave differently. First, because crust is less dense and therefore buoyant, compared with the mantle, thick continental crust resists subduction into the asthenosphere. Slices of the upper part of the crust detach from underlying parts and become stacked atop one another to form a mountain range, like the Alps or Himalaya. Second, continental lithosphere is weaker than oceanic lithosphere and when put under stress it deforms. When the horizontal dimension of a region of continental crust is shortened, the crust thickens. Because of isostasy, thick buoyant crust stands higher than thin crust, creating mountain ranges. Various mountain ranges around the world are used to illustrate these principles.

scholarly journals EVIDENCE OF MANTLE INHERITANCE ON THE ULTRA-DISTAL WESTERN IBERIAN MARGIN FROM TRANSFORMED TOTAL MAGNETIC ANOMALY

2018 ◽  
Vol 36 (3) ◽  
pp. 1 ◽  
Author(s):  
Luizemara Soares Alves Szameitat ◽  
Francisco José Fonseca Ferreira ◽  
Gianreto Manatschal ◽  
Monica da Costa Pereira Lavalle Helbron
Keyword(s):  
Steady State ◽  
Magnetic Anomaly ◽  
Oceanic Crust ◽  
Oceanic Lithosphere ◽  
Magnetic Data ◽  
Continental Lithosphere ◽  
Flow Lines ◽  
Passive Margins ◽  
Magnetic Features ◽  
Iberian Margin

ABSTRACT. Inheritance on continental lithosphere is considered as an important aspect on passive margins, since they may control magmatic budget and strain evolution during rifting and lithospheric breakup. On the distal Western Iberian margin, the transition to a steady state oceanic crust was little sampled and less investigated, in comparison to the more proximal parts near to the continental edge. In this work, we use marine magnetic data to analyze some aspects of the transition between the zone of exhumed continental mantle (ZECM) and the unequivocal oceanic crust, using transformed magnetic data. We observe that the end of the ZECM presents some straight magnetic features, especially at the eastern limit of the J anomaly. These magnetic lineaments are consistent with Early Cretaceous flow lines of the Iberian Plate. Straight structures are not expected in a newly formed oceanic lithosphere. Instead, it seems to be controlled by mantle inheritance. These straight magnetic features may indicate basement inheritance controlling magmatic insertions at the beginning of the oceanic crust formation.Keywords: Iberia, Magnetometry, Ocean-Continent Transition, Inherited Structures, Magma-Poor Margin. RESUMO. Estruturas herdadas na litosfera continental são um aspecto importante em margens passivas, pois poderão condicionar a entrada de magma e a evolução da deformação durante o rifteamento e quebra litosférica. Na porção distal da Margem Ibérica Ocidental, a transição da crosta continental até a crosta oceânica bem estabelecida possui menos dados e é menos investigada em comparação com a porção junto do limite de crosta continental. Neste trabalho, usamos dados magnéticos marinhos para analisar alguns aspectos entre a zona de exumação mantélica e a crosta oceânica inequívoca, através de dados magnéticos transformados. Observa-se que o final da zona de exumação mantélica apresenta algumas feições retilíneas, especialmente no limite leste da Anomalia J. Estes lineamentos magnéticos estão em conformidade com linhas de fluxo mesozoicas da Placa Ibérica. Feições retilíneas não são esperadas em uma litosfera oceânica neoformada. Ao contrário, estas aparentam ser um controle dado por estruturas pretéritas do manto. Portanto, estas feições magnéticas retilíneas sugerem uma herança do embasamento continental controlando as intrusões magmáticas no início da formação da crosta oceânica.Palavras-chave: Ibéria, Magnetometria, Transição Continente-Oceano, Estruturas Herdadas, Margem Pobre em Magma. 

Partial melting of subducted oceanic crust and isolation of its residual eclogitic lithology

1991 ◽  
Vol 335 (1638) ◽  
pp. 407-418 ◽  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Oceanic Crust ◽  
Significant Proportion ◽  
Oceanic Lithosphere ◽  
Rutile Phase ◽  
Island Arc ◽  
Plate Boundaries ◽  
Water Release ◽  
Depleted Mantle

Oceanic lithosphere is produced at mid-ocean ridges and reinjected into the mantle at convergent plate boundaries. During subduction, this lithosphere goes through a series of progressive dehydration and melting events. Initial dehydration of the slab occurs during low pressure metamorphism of the oceanic crust and involves significant dewatering and loss of labile elements. At depths of 80-120 km water release by the slab is believed to lead to partial melting of the oceanic crust. These melts, enriched in incompatible elements (excepting Nb, Ta and Ti), fertilize the overlying mantle wedge and produce the enriched peridotitic sources of island arc basalts. Retention of Nb, Ta and Ti by a residual mineral (e.g. in a rutile phase) in a refractory eclogitic lithology within the sinking slab are considered to cause their characteristic depletions in island arc basalts. These refractory eclogitic lithologies, enriched in Nb, Ta and Ti, accumulate at depth in the mantle. The continued isolation of this eclogitic residuum in the deep mantle over Earth ’s history produces a reservoir which contains a significant proportion of the Earth’s Ti, Nb and Ta budget. Both the continental crust and depleted mantle have subchondritic Nb /La and Ti/Zr ratios and thus they cannot be viewed strictly as complementary geochemical reservoirs. This lack of complementarity between the continental crust and depleted mantle can be balanced by a refractory eclogitic reservoir deep in the mantle, which is enriched in Nb, Ta and Ti. A refractory eclogitic reservoir amounting to ca . 2% of the mass of the silicate Earth would also contain significant amounts of Ca and Al and may explain the superchondritic Ca/Al value of the depleted mantle.

scholarly journals Population Trends and Urbanisation in Mountain Ranges of the World

Land ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 255
Author(s):  
Daniele Ehrlich ◽  
Michele Melchiorri ◽  
Claudia Capitani
Keyword(s):  
Rural Areas ◽  
Population Change ◽  
Population Trends ◽  
Time Range ◽  
Mountain Range ◽  
Mountain Areas ◽  
Population Total ◽  
Mountain Ranges ◽  
The World ◽  
Mountain Population

This study assesses the global mountain population, population change over the 1975–2015 time-range, and urbanisation for 2015. The work uses the World Conservation Monitoring Centre (WCMC) definition of mountain areas combined with that of mountain range outlines generated by the Global Mountain Biodiversity Assessment (GMBA). We estimated population change from the Global Human Settlement Layer Population spatial grids, a set of population density layers used to measure human presence and urbanisation on planet Earth. We show that the global mountain population has increased from over 550 million in 1975 to over 1050 million in 2015. The population is concentrated in mountain ranges at low latitudes. The most populated mountain ranges are also the most urbanised and those that grow most. Urbanisation in mountains (66%) is lower than that of lowlands (78%). However, 34% of the population in mountains live in cities, 31% in towns and semi-dense areas, and 35% in rural areas. The urbanisation rate varies considerably across ranges. The assessments of population total, population trends, and urbanisation may be used to address the issue “not to leave mountain people behind” in the sustainable development process and to understand trajectories of change.

scholarly journals Thermo-mechanical numerical model of the transition from continental rifting to oceanic spreading: the case study of the Alpine Tethys

2016 ◽  
Vol 155 (2) ◽  
pp. 250-279 ◽  
Author(s):  
ANNA MARIA MAROTTA ◽  
MANUEL RODA ◽  
KATYA CONTE ◽  
MARIA IOLE SPALLA
Keyword(s):  
Comparative Analysis ◽  
Numerical Model ◽  
Transition Zone ◽  
Oceanic Lithosphere ◽  
Northern Apennines ◽  
Continental Lithosphere ◽  
Continental Rifting ◽  
Lithospheric Extension ◽  
Natural Data ◽  
The Alps

AbstractWe develop a two-dimensional thermo-mechanical numerical model in which the formation of oceanic crust and serpentinite due to the hydration of the uprising mantle peridotite has been implemented, with the aim of discussing the behaviour of the lithosphere of the Alps and Northern Apennines during the transition from continental rifting to ocean spreading of the Alpine Tethys. The predictions of the model are compared with natural data related to the Permian–Triassic high-temperature – low-pressure (HT-LP) metamorphism affecting the continental lithosphere and data from the JurassicP–Tevolution of the oceanic lithosphere from the Alps and the Northern Apennines. Our analysis indicates that a thinned continental crust, an ocean–continent transition zone and an oceanic lithosphere characterize the final structure of the system in a poor magma rift pre-Alpine configuration. We also find that mantle serpentinization starts before crustal break-up and that denudation occurs before ocean spreading. The mantle denudation starts several million years before the gabbros/basalt formation, generating an ocean–continent transition zone from the passive continental margin to the oceanic lithosphere of size 160–280 km. The comparative analysis shows that the extension of a hot and weak lithosphere, which promotes the development of hyperextended Alpine margins, better agrees with the natural data. Finally, our comparative analysis supports the hypothesis that the lithospheric extension preceding the opening of the Alpine Tethys did not start in a stable continental lithosphere, but developed by recycling part of the old Variscan collisional suture.

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 Glaciochemistry and pigment producing ability of bacteria from roof of the world, the glaciers of Karakoram, Pakistan

2021 ◽  
Author(s):  
Noor Hassan ◽  
Muhammad Rafiq ◽  
Abdul Haleem ◽  
Aamir Ali Shah ◽  
Fariha Hasan
Keyword(s):  
Bacterial Species ◽  
Rpob Gene ◽  
Mountain Range ◽  
Bacterial Strains ◽  
Mountain Ranges ◽  
The World ◽  
Alternative Sources ◽  
Geochemical Analyses ◽  
Pigmented Bacteria

Abstract The Karakoram Mountain Range (KMR) is one of the largest mountain ranges in the world, with ~ 37% of its area glaciated. Here, we present the geochemistry of ice, sediment and meltwaters sampled from Ghulmet, Ghulkin and Hopar glaciers of the Karakoram Range, Pakistan, in addition to the first information on the diversity of pigmented bacteria evaluated using culture-dependent techniques. Geochemical analyses revealed Ca2+ and SO42− to be the most abundant cation and anion species across all glacial samples, respectively. Total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were found in the sediments of all glaciers studied in current research. Bacterial species were capable of producing a variety of different pigments, including alloxanthin, astaxanthin, bacterioruberin, β-carotene, 19'-hexanoyloxyfucoxanthin, peridinin, violacein and zeaxanthin. Culturable bacterial diversity was studied using two molecular biomarkers, 16S rRNA and rpoB gene, with a total of 82 bacterial strains representing 25 genera identified across all glacial samples. This study provides the first characterization of glacier-associated, pigment-producing bacterial communities from the KMR. Findings are important for considerations of alternative sources of conventional pigment production in industrial fields.

The continental and oceanic crust and lithosphere in the Archaean: isostatic, thermal, and tectonic models

1984 ◽  
Vol 21 (12) ◽  
pp. 1426-1441 ◽  
Author(s):  
E. G. Nisbet
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Southern Africa ◽  
Oceanic Lithosphere ◽  
Calc Alkaline ◽  
Late Archaean ◽  
Ocean Ridges ◽  
Low Viscosity ◽  
Thermal Data ◽  
Greenstone Belts

Simple isostatic models of the development of selected Archaean basins and greenstone belts can be used to constrain models of the Archaean lithosphere. Geophysical, geochemical, and thermal data imply that in southern Africa the late Archaean crust was probably comparable in thickness to the modern continental crust, and the whole lithosphere was perhaps over 80–100 km thick. Two Archaean belts studied may have developed by stretching of the order of 1.3–1.6:1. Isostatic and thermal data and petrological assumptions allow the construction of simple models of the Archaean oceanic lithosphere. Oceans were probably deep: mid-ocean ridges were probably subaqueous and fed by komatiitic liquids. Calc-alkaline volcanism in the Archaean may have been produced as a consequence of the subduction of hydrated komatiitic oceanic crust into a hot, low-viscosity asthensophere.

scholarly journals Episodic construction of the early Andean Cordillera unravelled by zircon petrochronology

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
José Joaquín Jara ◽  
Fernando Barra ◽  
Martin Reich ◽  
Mathieu Leisen ◽  
Rurik Romero ◽  
...  
Keyword(s):  
Continental Lithosphere ◽  
Complex Interplay ◽  
Continental Arcs ◽  
The Andes ◽  
Andean Cordillera ◽  
Continental Arc ◽  
The World ◽  
Oceanic Plates ◽  
Orogenic Belts ◽  
Continental Growth

AbstractThe subduction of oceanic plates beneath continental lithosphere is responsible for continental growth and recycling of oceanic crust, promoting the formation of Cordilleran arcs. However, the processes that control the evolution of these Cordilleran orogenic belts, particularly during their early stages of formation, have not been fully investigated. Here we use a multi-proxy geochemical approach, based on zircon petrochronology and whole-rock analyses, to assess the early evolution of the Andes, one of the most remarkable continental arcs in the world. Our results show that magmatism in the early Andean Cordillera occurred over a period of ~120 million years with six distinct plutonic episodes between 215 and 94 Ma. Each episode is the result of a complex interplay between mantle, crust, slab and sediment contributions that can be traced using zircon chemistry. Overall, the magmatism evolved in response to changes in the tectonic configuration, from transtensional/extensional conditions (215–145 Ma) to a transtensional regime (138–94 Ma). We conclude that an external (tectonic) forcing model with mantle-derived inputs is responsible for the episodic plutonism in this extensional continental arc. This study highlights the use of zircon petrochronology in assessing the multimillion-year crustal scale evolution of Cordilleran arcs.

Microseismicity in the Eastern Alps: Preliminary Results From the Swath-D Network

2021 ◽  
Author(s):  
Rens Hofman ◽  
Joern Kummerow ◽  
Simone Cesca ◽  
Joachim Wassermann ◽  
Thomas Plenefisch ◽  
...  
Keyword(s):  
Large Data ◽  
Eastern Alps ◽  
Detection Methods ◽  
Mountain Range ◽  
Network Methods ◽  
Data Volume ◽  
Geophysical Processes ◽  
The Alps ◽  
Mountain Belts ◽  
Surrounding Areas

<p>The AlpArray seismological experiment is an international and interdisciplinary project to advance our understanding of geophysical processes in the greater Alpine region. The heart of the project consists of a large seismological array that covers the mountain range and its surrounding areas. To understand how the Alps and their neighbouring mountain belts evolved through time, we can only study its current structure and processes. The Eastern Alps are of prime interest since they currently demonstrate the highest crustal deformation rates. A key question is how these surface processes are linked to deeper structures. The Swath-D network is an array of temporary seismological stations complementary to the AlpArray network located in the Eastern Alps. This creates a unique opportunity to investigate high resolution seismicity on a local scale.</p><p>In this study, a combination of waveform-based detection methods was used to find small earthquakes in the large data volume of the Swath-D network. Methods were developed to locate the seismic events using semi-automatic picks, and estimate event magnitudes. We present an overview of the methods and workflow, as well as a preliminary overview of the seismicity in the Eastern Alps.</p>

Between the Czech Krkonoše and the German Riesengebirge: Nationalism and Tourism in the Giant Mountains, 1880s–1930s

2021 ◽  
pp. 1-23
Author(s):  
Stanislav Holubec
Keyword(s):  
Nazi Germany ◽  
Mountain Range ◽  
Ethnic Conflicts ◽  
Central European ◽  
European Mountain ◽  
The Alps

Abstract The article deals with Czech and German nationalist discourses and practices in the late 19th and early 20th centuries as they relate to tourism in the Krkonoše/Riesengebirge, the highest Central European mountain range between the Alps and Scandinavia. It will discuss the discourses developed in relation to mountain tourism and nationalism (metaphors of battlefields, wedges, walls, gates, and bastions), different symbolical cores of mountains, and practices of tourist and nationalist organizations (tourist trails and markings, excursions, the ownership of mountains huts, languages used, memorials, and the construction of roads). It will examine how these discourses and practices changed from the first Czech-German ethnic conflicts in the 1800s until the end of interwar Czechoslovakia. Finally, it will discuss the Czech culture of defeat in the shadow of the Munich Agreement, which meant the occupation of the Giant Mountains by Nazi Germany.

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