scholarly journals Thermo‐Mechanical State of Ultraslow‐Spreading Ridges with a Transient Magma Supply

2021 ◽  
Author(s):  
Qingkai Fan ◽  
Jean‐Arthur Olive ◽  
Mathilde Cannat
Keyword(s):  
Mechanical State ◽  
Magma Supply ◽  
Spreading Ridges

The Xigaze ophiolite: fossil ultraslow-spreading ocean lithosphere in the Tibetan Plateau

2020 ◽  
pp. jgs2020-208
Author(s):  
Tong Liu ◽  
Chuan-Zhou Liu ◽  
Fu-Yuan Wu ◽  
Henry J.B. Dick ◽  
Wen-Bin Ji ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Spreading Rate ◽  
Southwest Indian Ridge ◽  
The Tibetan Plateau ◽  
Crustal Accretion ◽  
Ocean Ridges ◽  
Magma Supply ◽  
Spreading Ridges ◽  
Ocean Lithosphere ◽  
Lower Crustal

The crust and mantle in both ophiolites (fossil ocean lithosphere) and in modern oceans are enormously diverse. Along-axis morphology and lower crustal accretion at ultraslow-spreading ocean ridges are fundamentally different from those at faster-spreading ridges, and are key to understanding how crustal accretion varies with spreading rate and magma supply. Ultraslow-spreading ridges provide analogs for ophiolites, to identify those that may have formed under similar conditions. Parallel studies of modern ocean lithosphere and ophiolites therefore can uniquely inform the origin and genesis of both. Here we report the results of structural and petrological studies on the Xigaze ophiolite in the Tibetan Plateau, and compare it to the morphology and deep drilling results at the ultraslow-spreading Southwest Indian Ridge. The Xigaze ophiolite has a complete but laterally discontinuous crust, with discrete diabase dikes/sills cutting both mantle and lower crust. The gabbro units are thin (∼350 m) and show upward cyclic chemical variations, supporting for an episodic and intermittent magma supply. These features are comparable to the highly focused magmatism and low magma budget at modern ultraslow-spreading ridges. Thus we suggest that the Xigaze ophiolite represents an on-land analog of ultraslow-spreading ocean lithosphere.

Evidence for Multi-stage Melt Transport in the Lower Ocean Crust: the Atlantis Bank Gabbroic Massif (IODP Hole U1473A, SW Indian Ridge)

2020 ◽  
Author(s):  
Wei-Qi Zhang ◽  
Chuan-Zhou Liu ◽  
Henry J B Dick
Keyword(s):  
Shear Zones ◽  
Geochemical Data ◽  
Spreading Ridge ◽  
Ocean Crust ◽  
Magma Supply ◽  
Spreading Ridges ◽  
Melt Transport ◽  
Atlantis Bank ◽  
Indian Ridge ◽  
Compositional Zonation

Abstract The architecture of lower oceanic crust at slow- and ultraslow-spreading ridge is diverse, yet the mechanisms that produce this diversity are not well understood. Particularly, the 660-km2 gabbroic massif at Atlantis Bank (Southwest Indian Ridge) exhibits significant compositional zonation, representing a high magma supply end member for accretion of the lower ocean crust at slow and ultraslow-spreading ridges. We present the petrographic and geochemical data of olivine gabbros from the 809-metre IODP Hole U1473A at Atlantis Bank gabbroic massif. Structurally, the upper portion of U1473A consists of a ∼600-metre shear zone; below this, the hole is relatively undeformed, with several minor shear zones. Olivine gabbros away from the shear zones have mineral trace element compositions indicative of high-temperature reaction with an oxide-undersaturated melt. By contrast, olivine gabbros within shear zones display petrographic and chemical features indicative of reaction with a relatively low-temperature, oxide-saturated melt. These features indicate an early stage of primitive to moderately evolved melt migration, followed by deformation-driven transport of highly evolved Fe–Ti-rich melts to high levels in this gabbroic massif. The close relationship between shear zones and the reaction with oxide-saturated melts suggests that syn-magmatic shear zones provide a conduit for late-stage, Fe–Ti-rich melt transport through Atlantis Bank lower crust. This process is critical to generate the compositional zonation observed. Thus, the degree of syn-magmatic deformation, which is fundamentally related to magma supply, plays a dominant role in developing the diversity of lower ocean crust observed at slow- and ultraslow-spreading ridges.

The history of South Atlantics spreading ridges development and time -- space position of Bouve triple connection

1999 ◽  
Vol 1 (5) ◽  
pp. 423-443 ◽  
Author(s):  
E. P. Dubinin ◽  
N. M. Sushchevskaya ◽  
A. L. Grokhol'skiy
Keyword(s):  
Spreading Ridges ◽  
Time Space ◽  
History Of

The Absolute Constitution

2018 ◽  
Author(s):  
Benjamin A. Schupmann
Keyword(s):  
State Theory ◽  
Public Order ◽  
Constitutional Theory ◽  
Mechanical State ◽  
Equal Chance ◽  
Basic Purpose ◽  
The Absolute

Chapter 4 analyzes Schmitt’s constitutional theory and how it complements his state theory. It begins with Schmitt’s criticism of the predominant positivist conception of the constitution. Schmitt argued that the positivists’ “relativized” conception of the constitution was committed above all to the equal chance of any belief to be enacted into law. This chapter then analyzes Schmitt’s counterargument that, without a prior and “absolute” commitment to some substantive value, a constitution could not fulfill its basic purpose of providing a clearly defined and stable public order. Schmitt’s typology of Relative and Absolute Constitution maps onto his state theoretical distinction between mechanical state and absolute state. This chapter concludes by discussing Schmitt’s later analysis of the concept nomos and how his analysis builds on and develops his earlier work on the concept of the absolute constitution.

scholarly journals A Damage Model to Trabecular Bone and Similar Materials: Residual Resource, Effective Elasticity Modulus, and Effective Stress under Uniaxial Compression

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1051
Author(s):  
Gennady Kolesnikov ◽  
Rudolf Meltser
Keyword(s):  
Mathematical Modeling ◽  
Trabecular Bone ◽  
Bone Tissue ◽  
Uniaxial Compression ◽  
Effective Stress ◽  
Analytical Solutions ◽  
Energy Criterion ◽  
Empirical Models ◽  
Mechanical State ◽  
Similar Materials

Experimental research of bone strength remains costly and limited for ethical and technical reasons. Therefore, to predict the mechanical state of bone tissue, as well as similar materials, it is desirable to use computer technology and mathematical modeling. Yet, bone tissue as a bio-mechanical object with a hierarchical structure is difficult to analyze for strength and rigidity; therefore, empirical models are often used, the disadvantage of which is their limited application scope. The use of new analytical solutions overcomes the limitations of empirical models and significantly improves the way engineering problems are solved. Aim of the paper: the development of analytical solutions for computer models of the mechanical state of bone and similar materials. Object of research: a model of trabecular bone tissue as a quasi-brittle material under uniaxial compression (or tension). The new ideas of the fracture mechanics, as well as the methods of mathematical modeling and the biomechanics of bone tissues were used in the work. Compression and tension are considered as asymmetric mechanical states of the material. Results: a new nonlinear function that simulates both tension and compression is justified, analytical solutions for determining the effective and apparent elastic modulus are developed, the residual resource function and the damage function are justified, and the dependences of the initial and effective stresses on strain are obtained. Using the energy criterion, it is proven that the effective stress continuously increases both before and after the extremum point on the load-displacement plot. It is noted that the destruction of bone material is more likely at the inflection point of the load-displacement curve. The model adequacy is explained by the use of the energy criterion of material degradation. The results are consistent with the experimental data available in the literature.

Sign in / Sign up

Export Citation Format

Share Document