Mg-K-Fe fluid producing mineral reactions, metasomatism and microfabric development during formation of nodular sillimanite-gneiss in the middle crust

2021 ◽  
Author(s):  
Ane K. Engvik ◽  
Claudia A. Trepmann ◽  
Håkon Austrheim
Keyword(s):  
Stress Condition ◽  
White Mica ◽  
Ore Deposits ◽  
Preferred Orientation ◽  
Reaction Products ◽  
Subsequent Reaction ◽  
Crystallographic Preferred Orientation ◽  
Mineral Reaction ◽  
Metasomatic Fluid ◽  
Mineral Replacement

<p>The Proterozoic gneisses of the Bamble lithotectonic domain (south Norway) underwent intense scapolitisation caused by K- and Mg-rich fluids and extensive albitisation with formation of numerous ore deposits.</p><p>By detailed studies of mineral reaction fabrics we document release of the chemical active Mg, K and Fe-components forming the metasomatic fluid: Breakdown of biotite to muscovite releases K, Mg, Fe, Si and H<sub>2</sub>O. As reaction products tiny Fe-oxide needles are present in the transforming rock. H<sub>2</sub>O is reacting with K-feldspar to produce additional amounts of white mica and quartz. During a subsequent reaction muscovite is replaced to sillimanite again releasing quartz and a K-rich fluid. The reactions form the peculiar sillimanite-nodular quartzite, but also well-foliated sillimanite-mica gneiss.</p><p>Optical and EBSD microfabric studies reveal a shape preferred orientation for quartz, but despite of a pronounced foliation, quartz does not show a crystallographic preferred orientation. A crystallographic preferred orientation is present for mica and sillimanite. Coarse micas show sutured boundaries to quartz, implying low nucleation rates, no crystallographic or surface-energy control during growth and no obvious crystallographic relationship to quartz.</p><p>Our study illustrates the transformation of a quartzofeldspatic lithology into sillimanite-bearing quartzite. The mineral replacement and deformation show ongoing metamorphic reactions during deformation. The microfabric data indicates reaction at non-isostatic stress condition. The deduced mineral replacement reactions document a source of K-, Mg- and Fe-rich metasomatic fluids necessary to cause the pervasive scapolitisation and Fe-deposition in the area. The mineral reactions and deformation produce rocks with a new mineralogy and structure; an increased understanding of these processes is important for the modelling of crustal building and geological history.</p>

Deformation-induced crystallographic-preferred orientation of hcp-iron: An experimental study using a deformation-DIA apparatus

2018 ◽  
Vol 490 ◽  
pp. 151-160 ◽  
Author(s):  
Yu Nishihara ◽  
Tomohiro Ohuchi ◽  
Takaaki Kawazoe ◽  
Yusuke Seto ◽  
Genta Maruyama ◽  
...  
Keyword(s):  
Experimental Study ◽  
Preferred Orientation ◽  
Crystallographic Preferred Orientation

The development of shape- and crystallographic-preferred orientation in CaPtO3 post-perovskite deformed in pure shear

2011 ◽  
Vol 96 (10) ◽  
pp. 1630-1635 ◽  
Author(s):  
R. McCormack ◽  
D. P. Dobson ◽  
N. P. Walte ◽  
N. Miyajima ◽  
T. Taniguchi ◽  
...  
Keyword(s):  
Pure Shear ◽  
Preferred Orientation ◽  
Crystallographic Preferred Orientation

Crystallographic preferred orientation in wüstite (FeO) through the cubic-to-rhombohedral phase transition

2012 ◽  
Vol 39 (8) ◽  
pp. 613-626 ◽  
Author(s):  
P. Kaercher ◽  
S. Speziale ◽  
L. Miyagi ◽  
W. Kanitpanyacharoen ◽  
H.-R. Wenk
Keyword(s):  
Phase Transition ◽  
Rhombohedral Phase ◽  
Preferred Orientation ◽  
Crystallographic Preferred Orientation

Quantifying Intrinsic and Extrinsic Contributions to Elastic Anisotropy Observed in Seismic Tomography Models

2021 ◽  
Author(s):  
John Keith Magali ◽  
Thomas Bodin ◽  
Navid Hedjazian ◽  
Yanick Ricard ◽  
Yann Capdeville
Keyword(s):  
Seismic Tomography ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Texture Evolution ◽  
Scaling Law ◽  
Preferred Orientation ◽  
Elastic Model ◽  
Effective Anisotropy ◽  
Crystallographic Preferred Orientation ◽  
Radial Anisotropy

<p>Large-scale seismic anisotropy inferred from seismic observations has been loosely interpreted either in terms of intrinsic anisotropy due to Crystallographic Preferred Orientation (CPO) development of mantle minerals or extrinsic anisotropy due to rock-scale Shape Preferred Orientation (SPO). The coexistence of both contributions misconstrues the origins of seismic anisotropy observed in seismic tomography models. It is thus essential to discriminate CPO from SPO in the effective anisotropy of an upscaled/homogenized medium, that is, the best possible elastic model recovered using finite-frequency seismic data assuming perfect data coverage. In this work, we investigate the effects of upscaling an intrinsically-anisotropic and highly-heterogeneous Earth's mantle. The problem is applied to a 2-D marble cake model of the mantle with a binary composition in the presence of CPO obtained from a micro-mechanical model. We compute the long-wavelength effective equivalent of this mantle model using the 3D non-periodic elastic homogenization technique. Our numerical findings predict that overall, upscaling purely intrinsically anisotropic medium amounts to the convection-scale averaging of CPO. As a result, it always underestimates the anisotropy, and may only be overestimated due to the additive extrinsic anisotropy from SPO. Finally, we show analytically (in 1D) and numerically (in 2D) that the full effective radial anisotropy ξ<sup>*</sup> is approximately just the product of the effective intrinsic radial anisotropy ξ<sup>*</sup><sub>CPO</sub> and the extrinsic radial anisotropy ξ<sub>SPO</sub>:</p><p>ξ<sup>* </sup>= ξ<sup>*</sup><sub>CPO </sub>× ξ<sub>SPO</sub></p><p>Based on the above relation, it is imperative to homogenize a texture evolution model first before drawing interpretations from existing anisotropic tomography models. Such a scaling law can therefore be used as a constraint to better estimate the separate contributions of CPO and SPO from the effective anisotropy observed in tomographic models.</p>

scholarly journals Recrystallization processes, microstructure and crystallographic preferred orientation evolution in polycrystalline ice during high-temperature simple shear

2019 ◽  
Vol 13 (5) ◽  
pp. 1495-1511 ◽  
Author(s):  
Baptiste Journaux ◽  
Thomas Chauve ◽  
Maurine Montagnat ◽  
Andrea Tommasi ◽  
Fabrice Barou ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Simple Shear ◽  
Shear Plane ◽  
Preferred Orientation ◽  
Dislocation Slip ◽  
Crystallographic Preferred Orientation ◽  
Polycrystalline Ice

Abstract. Torsion experiments were performed in polycrystalline ice at high temperature (0.97 Tm) to reproduce the simple shear kinematics that are believed to dominate in ice streams and at the base of fast-flowing glaciers. As clearly documented more than 30 years ago, under simple shear ice develops a two-maxima c axis crystallographic preferred orientation (CPO), which evolves rapidly into a single cluster CPO with a c axis perpendicular to the shear plane. Dynamic recrystallization mechanisms that occur in both laboratory conditions and naturally deformed ice are likely candidates to explain the observed CPO evolution. In this study, we use electron backscatter diffraction (EBSD) and automatic ice texture analyzer (AITA) to characterize the mechanisms accommodating deformation, the stress and strain heterogeneities that form under torsion of an initially isotropic polycrystalline ice sample at high temperature, and the role of dynamic recrystallization in accommodating these heterogeneities. These analyses highlight an interlocking microstructure, which results from heterogeneity-driven serrated grain boundary migration, and sub-grain boundaries composed of dislocations with a [c]-component Burgers vector, indicating that strong local stress heterogeneity develops, in particular, close to grain boundaries, even at high temperature and high finite shear strain. Based on these observations, we propose that nucleation by bulging, assisted by sub-grain boundary formation and followed by grain growth, is a very likely candidate to explain the progressive disappearance of the c axis CPO cluster at low angle to the shear plane and the stability of the one normal to it. We therefore strongly support the development of new polycrystal plasticity models limiting dislocation slip on non-basal slip systems and allowing for efficient accommodation of strain incompatibilities by an association of bulging and formation of sub-grain boundaries with a significant [c] component.

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