scholarly journals Plate-tectonic evolution of the Earth: bottom-up and top-down mantle circulation

2016 ◽  
Vol 53 (11) ◽  
pp. 1103-1120 ◽  
Author(s):  
W.G. Ernst ◽  
Norman H. Sleep ◽  
Tatsuki Tsujimori
Keyword(s):  
Mantle Convection ◽  
Ultrahigh Pressure ◽  
Return Flow ◽  
Plate Tectonic ◽  
Magma Ocean ◽  
Top Down ◽  
Bottom Up ◽  
Near Surface ◽  
The Earth ◽  
Over Time

Intense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below low-pressure solidi of dry peridotite, basalt, and granite, ∼1300, ∼1120, and ∼950 °C, respectively. At less than half their T solidi, rocky materials existed as thin lithospheric slabs in the near-surface Hadean Earth. Stagnant-lid convection may have occurred initially but was at least episodically overwhelmed by subduction because effective, massive heat transfer necessitated vigorous mantle overturn in the early, hot planet. Bottom-up mantle convection, including voluminous plume ascent, efficiently rid the Earth of deep-seated heat. It declined over time as cooling and top-down lithospheric sinking increased. Thickening and both lateral extensional + contractional deformation typified the post-Hadean lithosphere. Stages of geologic evolution included (i) 4.5–4.4 Ga, magma ocean overturn involved ephemeral, surficial rocky platelets; (ii) 4.4–2.7 Ga, formation of oceanic and small continental plates were obliterated by return mantle flow prior to ∼4.0 Ga; continental material gradually accumulated as largely sub-sea, sialic crust-capped lithospheric collages; (iii) 2.7–1.0 Ga, progressive suturing of old shields + younger orogenic belts led to cratonal plates typified by emerging continental freeboard, increasing sedimentary differentiation, and episodic glaciation during transpolar drift; onset of temporally limited stagnant-lid mantle convection occurred beneath enlarging supercontinents; (iv) 1.0 Ga–present, laminar-flowing asthenospheric cells are now capped by giant, stately moving plates. Near-restriction of komatiitic lavas to the Archean, and appearance of multicycle sediments, ophiolite complexes ± alkaline igneous rocks, and high-pressure–ultrahigh-pressure (HP–UHP) metamorphic belts in progressively younger Proterozoic and Phanerozoic orogens reflect increasing negative buoyancy of cool oceanic lithosphere, but decreasing subductability of enlarging, more buoyant continental plates. Attending supercontinental assembly, density instabilities of thickening oceanic plates began to control overturn of suboceanic mantle as cold, top-down convection. Over time, the scales and dynamics of hot asthenospheric upwelling versus lithospheric foundering + mantle return flow (bottom-up plume-driven ascent versus top-down plate subduction) evolved gradually, reflecting planetary cooling. These evolving plate-tectonic processes have accompanied the Earth’s thermal history since ∼4.4 Ga.

scholarly journals Ordering global governance complexes: The evolution of the governance complex for international civil aviation

2021 ◽  
Author(s):  
Mette Eilstrup-Sangiovanni
Keyword(s):  
Global Governance ◽  
International Institutions ◽  
Historical Data ◽  
Civil Aviation ◽  
Top Down ◽  
Bottom Up ◽  
Governance Systems ◽  
Governance Effectiveness ◽  
Political Agents ◽  
Over Time

AbstractMany observers worry that growing numbers of international institutions with overlapping functions undermine governance effectiveness via duplication, inconsistency and conflict. Such pessimistic assessments may undervalue the mechanisms available to states and other political agents to reduce conflictual overlap and enhance inter-institutional synergy. Drawing on historical data I examine how states can mitigate conflict within Global Governance Complexes (GGCs) by dissolving or merging existing institutions or by re-configuring their mandates. I further explore how “order in complexity” can emerge through bottom-up processes of adaptation in lieu of state-led reform. My analysis supports three theoretical claims: (1) states frequently refashion governance complexes “top-down” in order to reduce conflictual overlap; (2) “top-down” restructuring and “bottom-up” adaptation present alternative mechanisms for ordering relations among component institutions of GGCs; (3) these twin mechanisms ensure that GGCs tend to (re)produce elements of order over time–albeit often temporarily. Rather than evolving towards ever-greater fragmentation and disorder, complex governance systems thus tend to fluctuate between greater or lesser integration and (dis)order.

scholarly journals Polar Wandering and Mantle Convection

1972 ◽  
Vol 48 ◽  
pp. 212-214 ◽  
Author(s):  
H. Takeuchi ◽  
N. Sugi
Keyword(s):  
Mass Transfer ◽  
Mantle Convection ◽  
Orogenic Belt ◽  
Return Flow ◽  
Oceanic Ridge ◽  
Absolute Value ◽  
The Earth ◽  
Belt System ◽  
Ridge System

According to the mantle convection theory, mantle materials come up to the surface of the Earth at the mid-oceanic ridge system, go off in two horizontal directions, and finally at the trench and orogenic belt system they return to the interior of the Earth. We assume no return flow in the deeper part of the mantle and calculate the change of products of inertia of the Earth due to the above mass transfer. The polar wandering thus calculated is towards the direction of about 90° east and its absolute value is about 0.9 × 10−2 s/yr.

Imprinting Beyond the Founding Phase: How Sedimented Imprints Develop over Time

2020 ◽  
Vol 31 (6) ◽  
pp. 1579-1600
Author(s):  
Lien De Cuyper ◽  
Bart Clarysse ◽  
Nelson Phillips
Keyword(s):  
Process Model ◽  
External Environment ◽  
Top Down ◽  
Bottom Up ◽  
Social Venture ◽  
Changes Over Time ◽  
Over Time ◽  
Do So

In this study, we build on the foundational observations of Selznick and Stinchcombe that organizations bear the lasting imprint of their founding context and explore how characteristics shaped during founding are coherently carried forward through time. To do so, we draw on an ethnography of a social venture where the entrepreneurs left soon after founding. In examining how an initial organizational imprint evolves beyond a venture’s founding phase, we focus on the actions and interactions of organizational members, the founders’ imprint, the venture’s new leadership, and the external environment. The process model we develop shows how the organizational imprint evolves as a consequence of the interplay between top-down and bottom-up forces. We first find that the initial imprint is transmitted through a bottom-up mechanism of imprint reinforcement, and second, that the venture is reimprinted after the founding period through two processes which we call imprint reforming and imprint coupling. The result of this is the formation of a sedimented imprint. Our findings further illuminate that, although the initial imprint sticks, its function and manifestation changes over time.

scholarly journals SEJARAH PEMBANGUNAN HUKUM PERBANKAN SYARIAH DI INDONESIA

2020 ◽  
Vol 6 (2) ◽  
pp. 250-273
Author(s):  
Khotibul Umam
Keyword(s):  
Banking System ◽  
Policy Changes ◽  
Top Down ◽  
Bottom Up ◽  
Banking Services ◽  
Indonesian Government ◽  
Gradual Process ◽  
Historic Development ◽  
Conventional Banks ◽  
Over Time

In this article the author traces the historic development of Islamic or sharia banking in Indonesia and this will be done by analysing the evolution of a series of successive laws promulgated over time.  From these laws (Law Nos. 7/1992; 10/1998 and 21/2008) we can discern, how over the years, the Indonesian government gradually accept and recognized sharia banking principles, resulting in the establishment of Sharia Banks alongside conventional Banks.  These successive laws also shows the gradual process of policy changes which involves a top-down, bottom up and again a top down approach. Through this process, Sharia Banks develops in Indonesia and has been able to meet society’s need not only for a modern banking system, but also more importantly, providing banking services in line with the sharia. 

The long-term evolution of the Earth mantle with a basal magma ocean

2021 ◽  
Author(s):  
Stephane Labrosse ◽  
Adrien Morison ◽  
Daniela Bolrão ◽  
Antoine Rozel ◽  
Maxim Ballmer ◽  
...  
Keyword(s):  
Phase Equilibrium ◽  
Mantle Convection ◽  
Large Scale ◽  
Seismic Velocity ◽  
Fractional Crystallisation ◽  
Magma Ocean ◽  
Compositional Evolution ◽  
The Core ◽  
The Earth ◽  
Flow Through

<p>The early evolution of the Earth was likely affected by a large scale magma ocean, in particular in the aftermath of the giant impact that formed the Moon. The exact structure and dynamics of the Earth following that event is unknown but several possible scenarios feature the existence of a basal magma ocean (BMO), whose last remaining drops may explain the current seismically detected ultra low velocity zones. The presence of a BMO covering the core carries many implications for the dynamics and evolution of the overlying solid mantle. The phase equilibrium between the magma and the solid mantle allows matter to flow through the boundary by melting and freezing. In practice, convective stresses in the solid create a topography of the interface which displaces the equilibrium. Heat and solute transfer in the liquid acts to erase this topography and, if this process is faster than that the producing topography, the boundary appears effectively permeable to flow. This leads to convective motions much faster than in usual mantle convection. We developed a mantle convection model coupled to a model for the thermal and compositional evolution of the BMO and the core that takes into account the phase equilibrium at the bottom of the solid mantle. It also includes the fractional crystallisation at the interface and net freezing of the magma ocean. Early in the history, convection in the mantle is very fast and dominated by down-welling currents. As fractional crystallisation proceeds, the magma ocean gets enriched in FeO which makes the cumulate to also get richer. Eventually, it becomes too dense to get entrained by mantle convection and starts to pile up at the bottom of the mantle, which inhibits direct mass flow through the phase change boundary. This allows a thermal boundary layer and hot plumes to develop.</p><p>This model therefore allows to explain the present existence of both residual partial melt and large scale compositional variations in the lower mantle, as evidenced by seismic velocity anomalies. It also predicts a regime change between early mantle convection dominated by down-welling flow to the onset of hot plumes in the more recent past.</p>

Interior dynamics of tidally-locked super-Earths: the case of LHS 3844b

2020 ◽  
Author(s):  
Tobias G. Meier ◽  
Dan J. Bower ◽  
Tim Lichtenberg ◽  
Paul J. Tackley
Keyword(s):  
Yield Stress ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
High Yield ◽  
Large Temperature ◽  
Return Flow ◽  
Plastic Yielding ◽  
Near Surface ◽  
First Case ◽  
Stress Criteria

<p>The vigour and style of mantle convection in tidally-locked super-Earths may be substantially different from Earth's regime. Earth's surface temperature is spatially uniform at 300 K, which is sufficiently cold to drive strong downwellings into the interior (i.e. subduction). In contrast, a tidally-locked super-Earth can have a large temperature contrast between the dayside and nightside, which we infer could lead to a dichotomy of the interior dynamics. We therefore use constraints from astrophysical observations to infer the possible pattern of flow in the interior of a tidally-locked super-Earth, using super-Earth LHS 3844b as a case study. We run mantle convection models using the code StagYY with two-dimensional spherical annulus geometry and parameters from the literature that are appropriate for LHS 3844b. The majority of the mantle is either perovskite or post-perovskite with the phase transition occurring around 1700 km depth (the total mantle depth is 3757 km). An upper and lower bound for the viscosity of post-perovskite is provided by previous theoretical calculations. We include plastic yielding to model the brittle nature of the lithosphere; plastic yielding occurs when the local stress state exceeds a prescribed yielding criteria and is commonly applied in studies of Earth to produce surface behaviour similar to plate tectonics.</p><p>For a low yield stress criteria (promoting a weak lithosphere), we find that plumes are generally evenly distributed between the dayside and nightside, albeit strong downwellings form on the nightside. Plumes on the nightside have less lateral mobility than on the dayside because they are confined by downwellings either side. In contrast, for a high yield stress criteria, the interior dynamics are mostly driven by a prominent downwelling on the dayside which flushes hot material from the lower thermal boundary layer around the CMB towards the nightside where plumes preferentially arise. This, in turn, leads to a return flow of colder material from the near surface of the nightside towards the dayside. This seemingly counterintuitive pattern of flow is a consequence of weak lithosphere (due to temperature) on the dayside that is able to deform and thereby subduct, whereas lithosphere on the nightside is too stiff to subduct.</p><p>Our models therefore show that the vigour of convection and the distribution of upwellings and downwellings of tidally locked super-Earths are sensitive to the strength of the lithosphere: plumes can either be equally distributed around the planet or preferentially occur on the nightside. In the first case, the cold downwellings are also equally distributed but more prominent on the nightside, whereas in the second case they are preferentially on the dayside. Somewhat unexpected, we do not observe a preference for hot plumes to congregate on the dayside. Our results have implications for space missions such as TESS, CHEOPS, JWST, PLATO and ARIEL that will discover and characterise super-Earths, thereby potentially probing for signals of volatile outgassing and volcanism.</p>

Shaping and Being Shaped: How Organizational Structure and Managerial Discretion Co-evolve in New Managerial Roles

2018 ◽  
Vol 64 (3) ◽  
pp. 619-658 ◽  
Author(s):  
Sukhbir Sandhu ◽  
Carol T. Kulik
Keyword(s):  
Organizational Structure ◽  
Managerial Discretion ◽  
Top Down ◽  
Bottom Up ◽  
Organizational Configurations ◽  
Managerial Roles ◽  
The Rich ◽  
Sustainability Initiatives ◽  
Sustainability Program ◽  
Over Time

As new roles emerge in organizations, it becomes critical to understand how organizational structure can impede or enable the managerial discretion available to role incumbents. We leverage the rich context provided by the emergent role of sustainability managers to examine the interplay between the top-down forces of structure and the bottom-up influences of managerial discretion in shaping new organizational roles over time. We analyzed qualitative data collected from in-depth interviews with sustainability managers in 21 case study organizations in India and Australia, supplemented with archival and observational data. We identified three organizational configurations, with varying levels of top-down structural and bottom-up managerial discretion dynamics at play. Each configuration had different implications for the manager’s role. Our analysis suggests that the third configuration—with semi-structured formalization and a decentralized sustainability program—provided the most conducive conditions for managers to use their discretion to champion innovative sustainability initiatives. New managerial roles in the other configurations, however, do not have to be static. With the maturation of organizational programs and active championing by managers, the structuring of organizational functions and managerial roles can co-evolve. Our findings describe a process of “shaping and being shaped,” as structure and managerial discretion co-evolve over time.

Power, culture and method in comparative law

2009 ◽  
Vol 5 (1) ◽  
pp. 69-85 ◽  
Author(s):  
Reza Banakar
Keyword(s):  
Review Essay ◽  
Comparative Studies ◽  
Comparative Law ◽  
Methodological Framework ◽  
Cultural Perspective ◽  
Legal Research ◽  
Top Down ◽  
Bottom Up ◽  
Cultural Terms ◽  
Over Time

This review essay draws on a recently edited handbook by Esin Örücü and David Nelken to reflect on the methodological concerns and challenges of comparative law and sociolegal research. It argues that the contextualisation of laws should be regarded as the indispensable methodological characteristic of all comparative studies of law that aspire to transcend the understanding of law as a body of rules and doctrine. It further argues that although the cultural perspective facilitates contextualisation of the law, a cultural understanding is neither a precondition for undertaking comparative legal research nor necessarily the correct approach under all circumstances; for certain aspects of law and legal behaviour need not be conceptualised in cultural terms. The essay concludes by proposing that the combination of top-down and bottom-up approaches could provide a meta-methodological framework within which specific comparative techniques can be employed. Such a framework will enable comparatists and sociolegal researchers to account for how law interacts with, and simultaneously manifests itself at, the macro-, micro- and the intermediary meso-levels of society over time.

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