Numerical modelling of magma dynamics coupled to tectonic deformation of lithosphere and crust

Many unresolved questions in geodynamics revolve around the physical behaviour of the two-phase system of a silicate melt percolating through and interacting with a tectonically deforming host rock. Well-accepted equations exist to describe the physics of such systems and several previous studies have successfully implemented various forms of these equations in numerical models. To date, most such models of magma dynamics have focused on mantle flow problems and therefore employed viscous creep rheologies suitable to describe the deformation properties of mantle rock under high temperatures and pressures. However, the use of such rheologies is not appropriate to model melt extraction above the lithosphere-asthenosphere boundary, where the mode of deformation of the host rock transitions from ductile viscous to brittle elasto-plastic. Here, we introduce a novel approach to numerically model magma dynamics, focusing on the conceptual study of melt extraction from an asthenospheric source of partial melt through the overlying lithosphere and crust. To this end, we introduce an adapted set of two-phase flow equations, coupled to a visco-elasto-plastic rheology for both shear and compaction deformation of the host rock in interaction with the melt phase. We describe in detail how to implement this physical model into a finite-element code, and then proceed to evaluate the functionality and potential of this methodology using a series of conceptual model setups, which demonstrate the modes of melt extraction occurring around the rheological transition from ductile to brittle host rocks. The models suggest that three principal regimes of melt extraction emerge: viscous diapirism, viscoplastic decompaction channels and elasto-plastic dyking. Thus, our model of magma dynamics interacting with active tectonics of the lithosphere and crust provides a novel framework to further investigate magmato-tectonic processes such as the formation and geometry of magma chambers and conduits, as well as the emplacement of plutonic rock complexe

Comparing thin-sheet models with 3-D multilayer models for continental collision

Various models have been proposed to explain tectonic deformations during continent collision. A frequently applied model is the thin viscous sheet model which is however not fully 3-D and assumes a priori diffuse thickening as the dominant deformation style. We compare a fully 3-D multilayer numerical model with a corresponding thin viscous sheet numerical model for the scenario of continent indentation. In our comparison we focus on the three basic viscous deformation styles thickening, buckling (folding) and lateral crustal flow. Both numerical models are based on the finite element method (FEM) and employ either a linear or power-law viscous rheology. The 3-D model consists of four layers representing a simplified continental lithosphere: strong upper crust, weak lower crust, strong upper mantle and weak lower mantle. The effective viscosity depth-profile in the 3-D model is used to calculate the depth-averaged effective viscosity used in the thin-sheet model allowing a direct comparison of both models. We quantify the differences in the strain rate and velocity fields, and investigate the evolution of crustal thickening, buckling and crustal flow resulting from the two models for two different phases of deformation: (1) indentation with a constant velocity and (2) gravitational collapse after a decrease of the indenting velocity by a factor of 5. The results indicate that thin-sheet models approximate well the overall large-scale lithospheric deformation, especially during indentation and for a linear viscous rheology. However, in the 3-D model, additional processes such as multilayer buckling and lower crustal flow emerge, which are ignored in the thin-sheet model but dominate the deformation style in the 3-D model within a range of a few hundreds of kilometres around the collision zone and indenter corner. Differences between the 3-D and thin-sheet model are considerably larger for a power-law viscous than for a linear viscous rheology. Buckling and lower crustal flow are significant in the 3-D model with power-law viscous rheology. For example, fibre strain rates due to buckling can be several hundred per cent different to the depth-averaged strain rate and the lateral mass flow of lower crustal material can be up to six times more than the flow of upper crustal material. Our results also show that the horizontal velocity fields of the upper crust and upper mantle remain nearly identical in the 3-D model during indentation despite their mechanical decoupling due to an intermediate weak lower crust. This result questions the validity of using similarities between velocities from the surface global positioning system (GPS) and mantle shear wave splitting data as evidence for a mechanically coupled lithosphere. 3-D multilayer models provide a more complete picture of continental collision than thin-sheet models as they enable studying the timing, locality and relative importance of different processes simultaneously which is especially important for the hundreds of kilometre scale around the collision zone and indenter corners. 3-D models are, however, still computationally challenging and we, therefore, also present results of a computational performance test of several solution algorithm

The Midwest Feeds Consortium: Final Report

The strategic intent of the Midwest Feeds Consortium (MFC) was to decrease the dependence of the U.S. agriculture and aquaculture feed industries on imported marine protein meals and to increase the utilization and export of plant and animal coproduct protein meals to the international aquaculture industry. Replacement of marine meals in feeds traditionally dependent on these protein sources with grains, oilseed, and animal coproduct protein meals common to the U.S. Midwest would be accomplished through innovative, value-added ingredient processing technology. Through systematic, integrated, industry-directed research to develop ingredient composition, quality, digestibility, and economic values, the U.S. and international feed industry would then be able to rapidly incorporate the findings into their ingredient and equipment-purchasing decisions. The work described herein drew heavily upon recommendations developed by the MFC workshop, which was the first United States Department of Agriculture (USDA)-funded undertaking by the Consortium. The priority activities were industry linkages, ingredient processing, ingredient testing, and technology transfer. After the initial workshop, the Consortium underwent several changes in management structure, participants, and directions, which slowed progress considerably. In May 1997, a focus meeting was held in Des Moines, Iowa, between principal Consortium participants to modify priorities and reestablish timelines. The project reemerged with objectives designed to meet the priority issues of the project

On dynamics of fermion generations

The hierarchy of fermion masses and EW symmetry breaking without elementary Higgs is studied on the basis of strong gauge field distributions governing the EW dynamics. The mechanism of symmetry breaking due to quark bilinears condensation is generalized to the case, when higher field correlators are present in the EW vacuum. Resulting wave functional yields several minima of quark bilinears, giving masses of three (or more) generations. Mixing is suggested to be due to kink solutions of the same wave functional. For a special form of this mixing ("coherent mixing") a realistic hierarhy of masses and of CKM coefficients is obtained and arguments in favor of the fourth generation are given. Possible important role of topological charges for CP violating phases and small masses of the first generation is stressed.Comment: 31 pages, typos corrected, references adde

Phenomenology of a Quark Mass Matrix from Six Dimensions and its implication for the Strong CP problem

A model of quark mass matrices from six dimensions, which is nearly democatic in nature and which is previously constructed by two of us (PQH and MS), is studied in detail in this manuscript. We found that not only it fits all the six quark masses as well as the CKM matrix but also that there exists a region in the allowed parameter space of the model where the constraint on the parameter \bar{\theta} of the Strong CP problem is satisfied. This region itself puts a constraint on the CKM parameters \bar{\rho} and \bar{\eta}. As such, through our analysis, there appears to be a deep connection between Strong and Weak CP in this modelComment: RevTeX, 21 pages and 14 figure

The breaking of the flavour permutational symmetry: Mass textures and the CKM matrix

Different ansaetze for the breaking of the flavour permutational symmetry according to S(3)L X S(3)R in S(2)L X S(2) give different Hermitian mass matrices of the same modified Fritzsch type, which differ in the symmetry breaking pattern. In this work we obtain a clear and precise indication on the preferred symmetry breaking scheme from a fit of the predicted theoretical Vckm to the experimentally determined absolute values of the elements of the CKM matrix. The preferred scheme leads to simple mass textures and allows us to compute the CKM mixing matrix, the Jarlskog invariant J, and the three inner angles of the unitarity triangle in terms of four quark mass ratios and only one free parameter: the CP violating phase Phi. Excellent agreement with the experimentally determined absolute values of the entries in the CKM matrix is obtained for Phi = 90 deg. The corresponding computed values of the Jarlskog invariant and the inner angles are J = 3.00 X 10^-5, alpha= 84 deg, beta= 24 deg and gamma =72 deg in very good agreement with current data on CP violation in the neutral kaon-antikaon system and oscillations in the B-Bbar system.Comment: 21 pages, 1 fig. Content enlarged, references added and typos corrected. To be published in Phys Rev

On Neutrinos and Fermionic Mass Patterns

Recent data on neutrino mass differences are consistent with a hierarchical neutrino mass structure strikingly similar to what is observed for the other fermionic masses.Comment: 8pages, 2figure

Test of the Dimopouos-Hall-Raby Ansatz for Fermion Mass Matrices

By evolution of fermion mass matrices of the Fritzsch and the Georgi-Jarlskog forms from the supersymmetric grand unified scale, DHR obtained predictions for the quark masses and mixings. Using Monte Carlo methods we test these predictions against the latest determinations of the mixings, the CP-violating parameter epsilon_K and the B_d^0--Bbar_d^0 mixing parameter r_d. The acceptable solutions closely specify the quark masses and mixings, but lie at the edges of allowed regions at 90% confidence level.Comment: 11 pages, 1 figure (not included