scholarly journals SUBDUCTION EROSION AT PACIFIC-TYPE CONVERGENT MARGINS

2021 ◽  
Vol 40 (6) ◽  
pp. 3-19
Author(s):  
I.Yu. Safonova ◽  
◽  
А.I. Khanchuk ◽  
Keyword(s):  
Continental Crust ◽  
Driving Forces ◽  
Accretionary Prism ◽  
Convergent Margins ◽  
Island Arcs ◽  
The Pacific ◽  
Tectonic Erosion ◽  
Definition Of ◽  
Orogenic Belts ◽  
Oceanic Slab

The paper presents a review of processes of subduction or tectonic erosion at the Pacific-type convergent margins (PTCM) including definition of “tectonic erosion”, its triggers, driving forces and consequences. We review examples of tectonic erosion at the Circum-Pacific PTCMs and at the fossil PTCMs of the Paleo-Asian Ocean (PAO) currently hosted by the Central-Asian Orogenic Belt (CAOB). Recent geological and stratigraphic studies have shown two types of PTCMs: accreting and eroding. Accreting PTCMs consist of older deposits of accretionary and frontal prisms and grow oceanward, i.e. the trench retreats. Eroding PTCMs are characterized by the destruction of the prism, approaching arc and trench and typically form during shallow-angle and fast subduction of an oceanic slab with oceanic floor topographic highs. The mechanism of tectonic erosion includes destruction of oceanic slab, island arcs, accretionary prism, fore-arc and related prism. Tectonic erosion is a common phenomenon at many Circum-Pacific PTCMs, e.g., in South America, Tonga and Nankai troughs, Alaska. Accretion and subduction of oceanic rises contributes greatly to the processes of formation, transformation and destruction of continental crust at PTCM. The episodes of tectonic erosion can be also reconstructed for an ancient ocean, for example, for the PAO, which evolution and suturing formed the CAOB. Many CAOB foldbelts (Altai, Tienshan, eastern Kazakhstan, Transbaikalia, Mongolia) carry signs of disap-pearance of big volumes of continental crust (arcs). Studying processes responsible not only for the formation of continental crust, but also for the disappearance of big volumes of crustal mate-rial is important for correct evaluation of the nature of intra-continental orogenic belts, e.g., CAOB, and development of reliable tectonic models.

Plate Tectonics

2021 ◽  
pp. 114-136
Author(s):  
Elisabeth Ervin-Blankenheim
Keyword(s):  
Plate Tectonics ◽  
Plastic Material ◽  
Convergent Margins ◽  
Island Arcs ◽  
Mountain Ranges ◽  
Ocean Ridges ◽  
Rock Types ◽  
The Pacific ◽  
The Pacific Ocean ◽  
The Many

Plate tectonics, the grand unifying theory of geology, and its relation to the Earth is explained in this chapter. The planet transforms through time by means of the movement of rigid plates carrying the continents riding on the plastic material in the Earth’s upper mantle. Three major plate boundaries are divergent margins, where new ocean floor is being created along mid-ocean ridges and plates separate from one another; convergent margins, where the material is subducted and consumed as different types of plates collide, creating trenches, island arcs or mountain ranges, and transform boundaries; and where plates slide past one another. Besides the three predominant boundaries, hot spots caused by mantle plumes and diffuse boundaries make up additional dynamic forces in tectonics. Beyond these categories, geologists still are learning about tectonics; some boundaries are unknown or speculative. Plate tectonics explains why many of the Earth’s hazards are found where there are. Earthquakes trace many plate margins, as do volcanoes. The area around the Pacific Ocean is called the “Ring of Fire” because of the many volcanoes related to subducting plates. Tectonics accounts for why certain rocks are located where they are; for example, all rock types are found at convergent margins. The theory also predicts where valuable mineral and economic deposits are located.

Fate of sediments on the descending plate at convergent margins

1981 ◽  
Vol 301 (1461) ◽  
pp. 233-251 ◽  
Keyword(s):  
Continental Crust ◽  
Sedimentary Cover ◽  
Indirect Evidence ◽  
Accretionary Prism ◽  
Oceanic Lithosphere ◽  
Silica Content ◽  
Isotopic Ratios ◽  
Convergent Margins ◽  
Arc Magmas ◽  
Sediment Cover

The evolution of the continents and of continental crust is strongly dependent on the trajectory of the sedimentary cover on the descending oceanic lithosphere at arc systems. Although direct calculations of accretion are not reliable, indirect evidence strongly suggests that most of the sediment cover is either accreted or underplated (subcreted) to the upper plate. This evidence includes the increased thickening of accretionary prism beneath parts of the inner trench slope that cannot be explained by deformation within the prism and by protolith composition both in subophiolitic metamorphics and in blueschist terrains. That a small fraction of this sediment cover is transported to depths of at least 100 km is demonstrated in several ways. Flux calculations of mass and selected elements through arc systems require addition of a few tens of metres of sediment to the arc magmas. Global correlations of variations between arc magma characteristics and regional geological parameters show: (1) a strong correlation between silica content of average arc magmas and thickness or maturity of crust in the upper plate, attributed to upper plate contamination; (2) regional variations in 87 Sr/ 86 Sr and Pb isotopic ratios of arc basalts that correlate spatially with isotopic ratios in the non-calcareous components of pelagic sediments. This correlation is argued to reflect the variation of terrigenous material in the basal pelagics that are involved in magma production. Subduction of continental crust to depths of 100 km, either as part of the descending plate or by tectonic erosion of the upper plate is not supported by these correlations. Recycling rates of continental crust by accretion and subcretion and of mantle by subduction of oceanic lithosphere in contemporary arcs are very large compared with the growth rate of continental crust, which appears similar to the magma production rates in arc systems. This present production rate of continental crust is very much smaller than that during early Earth history, and is compatible with Phanerozoic ocean freeboard changes. In addition, average SiO 2 and K 2 O contents of contemporary arc magmas are much lower than those estimated for mean continental crust, leading to the conclusion that the magmas being produced at active arcs cannot be used as a model for the development of most of the Earth’s continental areas.

scholarly journals Terrains of the main geodynamical types in the structures of Ural-Timan areal and the Eurasia North-Eastern segment

LITOSFERA ◽  
2018 ◽  
pp. 779-796
Author(s):  
Viktor A. Koroteev ◽  
Viktor M. Necheukhin ◽  
Artur A. Krasnobaev ◽  
Elena N. Volchek
Keyword(s):  
Continental Crust ◽  
Structural Elements ◽  
Russian Plate ◽  
The Pacific ◽  
North Eastern ◽  
Collision Processes ◽  
Points Of View ◽  
Orogenic Belts ◽  
Selection Of ◽  
Radiometric Data

Subject of study. Different points of view on the concept of structures of the terrain type and their role in the addition of orogenic belts are considered. Materials and methods. We used our own research and analysis of the latest publications about the Ural-Timan region and the Pacific belt, on the territory of the Northeast segment of Eurasia, as well as currently known isotope radiometric data. It was used also the result of geophysical seismotectonic and paleomagnetic explorations. Results. It has been established that in the composition of the Ural-Timan structural area, along with the Proterozoic and Paleozoic associations of the orogenic belts and the Riphean sedimentary series of protrusions of the Russian Plate, structural formations that correspond to the terrain of the continental crust take part. They are the most characteristic for the Ural orogenic belt, which belongs to the group of epiokean-type belts, associated with the transformation of ocean basins with the active participation of accretion and collision processes. The parametric features of these terrains include the ancient age characteristics of terrain rocks, their position in the belt structure, as well as the presence of relics of subhorizontal layered structural elements. The discordant blocks of migmatites, gneisses and other metamorphic rocks of Precambrian age, which make up the terrains, was the basis for the introduction of the term “terranes of the ancient continental crust”. By connection with the source, exotic and endemic, and simple and complex terrains are distinguished by structure. The geodynamics of including terrains of the ancient continental crust into the structure of orogenic belts is associated with horizontal movements of fragments of the ancient lithosphere in oceanic paleobasins to the periphery of the Russian Plate and their localization in belt structures. The formation of these terrains in the structures of the orogenic belts is completed by the formation of the intra-terrain massifs of granitoids and belts of volcanic-intrusive series. Supporters of a different methodology, dominant among researchers of the Pacific Belt of the Northeast Segment of Eurasia, refer to terrains all the structural elements that perform orogenic belts, because they believe that they have undergone horizontal movements and are in allochtonous occurrence. Conclusions. It has been established that in different geological provinces the term terrain has its own characteristics. This was the basis for the selection of two geodynamic types of terrains.

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.

Simultaneous heat and mass transfer during evaporation from a film of liquid into the turbulent gas

1982 ◽  
Vol 47 (3) ◽  
pp. 766-775 ◽  
Author(s):  
Václav Kolář ◽  
Jan Červenka
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Liquid Film ◽  
Heat And Mass Transfer ◽  
Driving Forces ◽  
Proper Definition ◽  
Definition Of ◽  
Simultaneous Heat ◽  
Theory And Experiment

The paper presents results obtained by processing a series of published experimental data on heat and mass transfer during evaporation of pure liquids from the free board of a liquid film into the turbulent gas phone. The data has been processed on the basis of the earlier theory of mechanism of heat and mass transfer. In spite of the fact that this process exhibits a strong Stefan's flow, the results indicate that with a proper definition of the driving forces the agreement between theory and experiment is very good.

MONARCHS, TRAVELLERS AND EMPIRE IN THE PACIFIC'S AGE OF REVOLUTIONS

2020 ◽  
Vol 30 ◽  
pp. 77-96
Author(s):  
Sujit Sivasundaram
Keyword(s):  
Pacific Islanders ◽  
Modern World ◽  
Global History ◽  
The Past ◽  
The Pacific ◽  
Cultural Terms ◽  
The Pacific Ocean ◽  
Definition Of ◽  
The Uk ◽  
A Site

AbstractThe Pacific has often been invisible in global histories written in the UK. Yet it has consistently been a site for contemplating the past and the future, even among Britons cast on its shores. In this lecture, I reconsider a critical moment of globalisation and empire, the ‘age of revolutions’ at the end of the eighteenth century and the start of the nineteenth century, by journeying with European voyagers to the Pacific Ocean. The lecture will point to what this age meant for Pacific islanders, in social, political and cultural terms. It works with a definition of the Pacific's age of revolutions as a surge of indigeneity met by a counter-revolutionary imperialism. What was involved in undertaking a European voyage changed in this era, even as one important expedition was interrupted by news from revolutionary Europe. Yet more fundamentally vocabularies and practices of monarchy were consolidated by islanders across the Pacific. This was followed by the outworkings of counter-revolutionary imperialism through agreements of alliance and alleged cessation. Such an argument allows me, for instance, to place the 1806 wreck of the Port-au-Prince within the Pacific's age of revolutions. This was an English ship used to raid French and Spanish targets in the Pacific, but which was stripped of its guns, iron, gunpowder and carronades by Tongans. To chart the trajectory from revolution and islander agency on to violence and empire is to appreciate the unsettled paths that gave rise to our modern world. This view foregrounds people who inhabited and travelled through the earth's oceanic frontiers. It is a global history from a specific place in the oceanic south, on the opposite side of the planet to Europe.

Two new Phallodriline genera of marine Oligochaeta (Annelida: Tubificidae) from the Pacific Northeast

1982 ◽  
Vol 60 (10) ◽  
pp. 2487-2500 ◽  
Author(s):  
H. R. Baker
Keyword(s):  
The Pacific ◽  
Marine Oligochaeta ◽  
Definition Of

Nootkadrilus gen. nov. is characterized by an ental atrial modification, modified penial setae, and stalked posterior prostate glands. Nootkadrilus compressus sp. nov., N. verutus sp. nov., N. grandisetosus sp. nov., N. hamatus sp. nov., N. gracilisetosus sp. nov., and N. frigidus (Brinkhurst, 1971) comb. nov. are separated by shape and numbers of penial setae as well as by details of the atrial and spermathecal systems. Discordiprostatus gen. nov. is established for D. longisetosus (Brinkhurst and Baker, 1979) comb. nov. which is characterized by an anterior diffuse prostate, modified penial setae, and stalked posterior prostate glands. Both Nootkadrilus gen. nov. and Discordiprostatus gen. nov. are included in the subfamily Phallodrilinae. The definition of the Phallodrilinae is modified to include species with both diffuse and stalked prostate glands.

Mahjong

2021 ◽  
Author(s):  
Annelise Heinz
Keyword(s):  
United States ◽  
American Culture ◽  
The United States ◽  
Jewish American ◽  
The Pacific ◽  
Women's Culture ◽  
History Of ◽  
American Heritage ◽  
Cultural Origins ◽  
Definition Of

Mahjong: A Chinese Game and the Making of Modern American Culture illustrates how the spaces between tiles and the moments between games have fostered distinct social cultures in the United States. When this mass-produced game crossed the Pacific it created waves of popularity over the twentieth century. Mahjong narrates the history of this game to show how it has created a variety of meanings, among them American modernity, Chinese American heritage, and Jewish American women’s culture. As it traveled from China to the United States and caught on with Hollywood starlets, high society, middle-class housewives, and immigrants alike, mahjong became a quintessentially American pastime. This book also reveals the ways in which women leveraged a game for a variety of economic and cultural purposes, including entrepreneurship, self-expression, philanthropy, and ethnic community building. One result was the forging of friendships within mahjong groups that lasted decades. This study unfolds in two parts. The first half is focused on mahjong’s history as related to consumerism, with a close examination of its economic and cultural origins. The second half explores how mahjong interwove with the experiences of racial inclusion and exclusion in the evolving definition of what it means to be American. Mahjong players, promoters, entrepreneurs, and critics tell a broad story of American modernity. The apparent contradictions of the game—as both American and foreign, modern and supposedly ancient, domestic and disruptive of domesticity—reveal the tensions that lie at the heart of modern American culture.

scholarly journals Good offices: grasping the place of law in conflict

Legal Studies ◽  
2014 ◽  
Vol 34 (3) ◽  
pp. 469-496 ◽  
Author(s):  
Aoife O'Donoghue
Keyword(s):  
International Law ◽  
Past Century ◽  
Legal Analysis ◽  
International Organisations ◽  
The Past ◽  
The Pacific ◽  
The Subject ◽  
Definition Of ◽  
Settlement Of Disputes ◽  
Violent Conflicts

In the pantheon of approaches open to participants in the pacific settlement of disputes, good offices holds a noteworthy place. The evolution of good offices over the past century is concurrent with a trend of considerable transformation within international law, including – amongst other changes – a move away from a state-led legal order, including in good offices following the emergence of the heads of international organisations as its prime users, and a process of legalisation and specialisation within the subject that has entirely altered its character. These changes have led to a redefinition of good offices that stresses the actor carrying out the role above the form that it takes. To accompany these changes in practice, there is a need for a transformation in the legal analysis and definition of good offices. One potential option in achieving this end is Bell'slex pacificatoria. If good offices is to continue to play a significant role in the settlement of violent conflicts, a fully developed legal analysis is necessary to grasp both its historical development and its potential future role.

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