Deciphering petrological signatures of reactive melt stagnation and cooling in the oceanic mantle underneath ultraslow-spreading ridges

The global mid-ocean ridge system creates oceanic crust and lithosphere that covers more than two-thirds of the Earth. Basalts are volumetrically the most important rock type sampled at mid-ocean ridges. For this reason, our present understanding of upper mantle dynamics and the chemical evolution of the earth is strongly influenced by the study of mid-ocean ridge basalts (MORB). However, MORB are aggregates of polybarically generated small melt increments that can undergo a variety of physical and chemical processes during their ascent and consequently affect their derivative geochemical composition. Therefore, MORB do not represent “direct” windows to the underlying upper mantle. Abyssal peridotites, upper mantle rocks recovered from the ocean floor, are the residual complement to MORB melting and provide essential information on melt extraction from the upper mantle. In this study, abyssal peridotites are examined to address these overarching questions posed by previous studies of MORB: How are basaltic melts formed in the mantle, how are they extracted from the mantle and what physical and chemical processes control mantle melting? The number of studies on abyssal peridotites is small compared to those on basalts, in part because seafloor exposures of abyssal peridotites are relatively rare. For this reason, abyssal peridotite characteristics need to be considered in the context of subaerially exposed peridotites associated with ophiolites, orogenic peridotite bodies and basalt-hosted xenoliths. However, orogenic peridotite bodies are mainly associated with passive continental margins, most ophiolites are formed in supra-subduction zone settings, and peridotite xenoliths are often contaminated by their host magma. Therefore, studies of abyssal peridotites are essential to understanding the primary characteristics of the oceanic upper mantle free from the influence of continental rifting, subduction and tectonic emplacement processes. Nevertheless, numerous processes such as melt stagnation and cooling-induced, inter-mineral exchange can affect residual abyssal peridotite compositions after the cessation of melting. The aim of this study is to address these post-melting modifications of abyssal peridotites from a petrological-geochemical perspective. The samples in this study were dredged along the axis of the ultraslow-spreading Gakkel Ridge in the Arctic Ocean within the “Sparsely Magmatic Zone”, a 100 km ridge section where only mantle rocks are exposed. During two expeditions (ARK XVII-2 in 2001 and ARK XX-2 in 2004), exceptionally fresh peridotites were recovered. The boulders and cobbles collected cover a range of mantle rock compositions, with most characterized as plagioclase-free spinel peridotites or plagioclase- spinel peridotites. This thesis investigates melt stagnation and cooling processes in the upper mantle and is divided into two parts. The first part focuses on processes in the stability field of spinel peridotites (>10 kb) such as melt refertilization and cooling related trace element exchange, while the second part investigates processes in the stability field of plagioclase peridotites (< 10 kb) such as reactive melt migration and melt stagnation. The dissertation chapters are organized to follow the theoretical ascent of a mantle parcel upwelling beneath the location where the samples were collected.

Stagnation and Change in Islamic History

There appear to be two seemingly contradictory images of economic change in the Islamic World and mixed evidence on whether Islamic societies have been open or conservative against modern ideas, technological advancements, and legal developments. Whereas a conservative attitude has been dominant in some societies and time periods, Muslims were at the forefront of scientific, technological, and legal developments in others. Rather than rely on ad hoc assumptions about the attitudes and characteristics of societies or the inherent qualities of new developments, this paper explains attitudes towards change by studying the political economy of the relationship between the rulers and the legal community. I extend recent theories of endogenous institutional change to develop a framework based on how rulers and legal community reacted to new developments immediately and how their strategic interaction unleashed an endogenous process toward change in the long run. Using this framework, I identify conditions under which new ideas, technologies, and legal developments have resulted in immediate change in Islamic societies. I also examine the process of change in the long run, whether and how immediate outcomes could be sustained over time as strategic interaction continued repeatedly.

On the circulation and the position of the forward stagnation point on airfoils

Lift and velocity circulation around airfoils are two aspects of the same phenomenon when airfoils are not stalled and the Kutta—Joukowski theorem applies. This theorem establishes a linear dependence between lift and circulation, which breaks when stalling occurs. As the angle of attack increases beyond this point, the circulation vanishes. Since the circulation determines to a great extent the position of the forward stagnation point on an airfoil, the measurement of this position is an easy and simple way to determine the circulation, which is of help in understanding the role of the latter in the generation of aerodynamic forces on airfoils.

From stabilisation to stagnation. Viktor Yanukovych's reforms. OSW Point of View Number 32, March 2013

After winning the 2010 presidential election, Viktor Yanukovych and his government developed an ambitious and comprehensive programme of reforms across key areas of social and political life. The return to a presidential system of government created the ideal conditions for the introduction of deep reforms: it allowed Viktor Yanukovych to consolidate more power than any other Ukrainian president before him.The authorities launched an overhaul of the tax and the pension systems, and of the Ukrainian gas sector. Kyiv also completed its negotiations on an Association Agreement with the EU and on a Deep and Comprehensive Free Trade Area. However, the reformist zeal of Ukraine’s political elite progressively diminished as the parliamentary election approached, the economy slowed down, and the polls showed a decline in support for the ruling Party of Regions. Many of the reforms still remain in the planning stages, and in many areas the government has moved backwards. Viktor Yanukovych has proved unable to make systemic changes, and has increasingly used his powers to crush political opposition in Ukraine. The outcome of the latest parliamentary elections prevents the formation of a stable parliamentary majority, which in turn, removes any chance of reform before the 2015 presidential ballot.

Tajikistan: a chronic stagnation. OSW COMMENTARY NUMBER 200/15.03.2016

Since gaining its independence Tajikistan has faced severe political, economic and social problems. The last several months has seen a clear increase in their intensity. This is in part caused by the deteriorating economic situation in Russia and the significant fall of remittances from the Tajik labour migrants in Russia, as well as by President Emomali Rahmon’s rising authoritarianism. Despite this intensification, qualitatively speaking Tajikistan’s problems have been unchanged for years. Besides the state’s structural weakness, the main cause is the ongoing neo-colonial dependence on Russia, which effectively limits Dushanbe’s room for political manoeuvre and keep Tajikistan in Russia’s sphere of control. This dependence on the one hand protects the country from collapsing, but on the other it precludes the development of the state, resulting in Tajikistan’s enduring stagnation. Similar processes also take place in other countries of post-Soviet Central Asia. However, in the case of Tajikistan the dependence and stagnation it causes are the strongest and their mechanisms most easily observed.

Rate of heat-transfer near the stagnation point of a blunt body of revolution, in the presence of a magnetic field.

"Prepared for the Air Force Ballistic Missile Division, Headquarters Air Research and Development Command, under contract AF04(647)-127, call no. 4."

Ionization nonequilibrium effects on the magnetogasdynamic interaction in the stagnation region of an axisymmetric blunt body.

"ASD-TDR-62-1078. Contract no. AF33(616)-8055."

Introduction a l'étude philosophique du droit, précédée d'un discours sur les causes de la stagnation de la science du droit en France /

Mode of access: Internet.

Theoretical analysis of the downstream influence of stagnation point mass transfer.

"Aeronautical Research Laboratory. Contract no. AF 33(616)-7064. Project no. 7064."

Helium injection into the boundary layer at an axisymmetric stagnation point

"Contract no. AF 33(616)-7661, Project no. 7064, Task no. 70169."

An experimental study of the effect of mass injection at the stagnation point of a blunt body,

"Army Ordnance contract no. DA-04-495-Ord-19."

Urban economics : a guide to research on waste, poverty and stagnation in cities /

"Preliminary and confidential; for technical review only; July 1962."