Computing LPO for Geodynamic Models in ASPECT

2020 ◽  
Author(s):  
Magali Billen ◽  
Menno Fraters
Keyword(s):  
Water Content ◽  
Flow Pattern ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Flow Patterns ◽  
Mantle Flow ◽  
Lattice Preferred Orientation ◽  
Axis Alignment ◽  
Geodynamic Models ◽  
Initial Results

<p>When modeling subduction processes, the results are usually constrained by looking at the geological surface expressions, geochemistry and geophysical observations such as tomography and seismic anisotropy. Of these observations, seismic anisotropy is the only type of observation that can potentially be directly linked to the spatial flow pattern in the mantle. Seismic anisotropy in the mantle is due to lattice-preferred orientation (LPO) of olivine minerals. In subduction environments, which can have complex and changing flow patterns, it is not expected that the LPO necessarily aligns with the flow pattern. This is partly due to the fact that it takes time to realign the LPO and partly because the olivine fast axis alignment depends on the water content and the magnitude of stress. To overcome this problem, the LPO must be computed for realistic and end member subduction zones in order to be able to relate seismic anisotropy to mantle flow and thereby slab dynamics.</p><p>There are many ways to compute LPO. For this study we have used DREX (Kaminski et al., 2004), because the underlying method is accurate and fast enough for use in geodynamic models. To achieve a good and native integration with ASPECT (Kronbichler et al., 2012; Heister et al., 2017; Bangerth et al,. 2019), we have rewritten DREX in CPP as a plugin for ASPECT. In this presentation we will show how it was implemented and what the limitations and possibilities are. Furthermore, we will show initial results from 3D subduction models to study the link between seismic anisotropy and mantle flow.</p>

scholarly journals Strain-Induced Fabric Transition of Chlorite and Implications for Seismic Anisotropy in Subduction Zones

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 503
Author(s):  
Dohyun Kim ◽  
Haemyeong Jung ◽  
Jungjin Lee
Keyword(s):  
Shear Strain ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Shear Plane ◽  
Shear Direction ◽  
S Wave ◽  
Lattice Preferred Orientation ◽  
Back Arc

Seismic anisotropy of S-wave, trench-parallel or trench-normal polarization direction of fast S-wave, has been observed in the fore-arc and back-arc regions of subduction zones. Lattice preferred orientation (LPO) of elastically anisotropic chlorite has been suggested as one of the major causes of seismic anisotropy in subduction zones. However, there are two different LPOs of chlorite reported based on the previous studies of natural chlorite peridotites, which can produce different expression of seismic anisotropy. The mechanism for causing the two different LPOs of chlorite is not known. Therefore, we conducted deformation experiments of chlorite peridotite under high pressure–temperature conditions (P = 0.5–2.5 GPa, T = 540–720 °C). We found that two different chlorite LPOs were developed depending on the magnitude of shear strain. The type-1 chlorite LPO is characterized by the [001] axes aligned subnormal to the shear plane, and the type-2 chlorite LPO is characterized by a girdle distribution of the [001] axes subnormal to the shear direction. The type-1 chlorite LPO developed under low shear strain (γ ≤ 3.1 ± 0.3), producing trench-parallel seismic anisotropy. The type-2 chlorite LPO developed under high shear strain (γ ≥ 5.1 ± 1.5), producing trench-normal seismic anisotropy. The anisotropy of S-wave velocity (AVs) of chlorite was very strong up to AVs = 48.7% so that anomalous seismic anisotropy in subduction zones can be influenced by the chlorite LPOs.

Change of olivine a-axis alignment induced by water: Origin of seismic anisotropy in subduction zones

2012 ◽  
Vol 317-318 ◽  
pp. 111-119 ◽  
Author(s):  
Tomohiro Ohuchi ◽  
Takaaki Kawazoe ◽  
Yu Nishihara ◽  
Tetsuo Irifune
Keyword(s):  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Water Origin ◽  
Axis Alignment

A physical model for the volume and composition of melt produced by hydrous fluxing above subduction zones

1991 ◽  
Vol 335 (1638) ◽  
pp. 355-364 ◽  
Keyword(s):  
Water Content ◽  
Physical Model ◽  
Subduction Zones ◽  
Source Region ◽  
Water Flux ◽  
Fluid Phase ◽  
Vertical Movement ◽  
Mantle Flow ◽  
Hydrous Minerals ◽  
Water Contents

Thermal models of subduction zones, restrict the melt source region to a domain at sufficiently high temperature with water present (either as a free phase or in hydrous minerals). Water, released into the mantle by slab dehydration, traverses the wedge horizontally by a combination of (i) vertical movement as a fluid phase and (ii) fixed in amphiboles carried by the induced mantle flow; only in mantle hotter than amphibole stability can melts escape upwards. We develop a one-dimensional model for the source region fluxed with water. The induced mantle flow advects heat laterally to balance the latent heat of melting, in a column where the liquidus of the melt is depressed by its water content. Melt flux, fraction, temperature and water content are calculated assuming steady state. Melt compositions are predicted from the melt fraction distribution as a function of depth, constrained by the experimental data of Green. On investigating a range of plausible models, we find that the average degrees of melting predicted vary from ca . 2 to 8% . The predicted primary magmas are mafic high magnesium basalts with water contents ranging from 1.6 to 6 wt% , and temperatures from 1160 to 1290 °C. Models with shallower depths of segregation have higher degrees of melting and lower water contents. The volumes predicted by the physical model are a strong function of the water flux assumed to enter the source region. Previous estimates of are growth would suggest either low water fluxes or that not all the melt reaches the arc crust.

Role of the Adria plate structural heterogeneities on the dynamics of the Central-Western Mediterranean region

2021 ◽  
Author(s):  
Rosalia Lo Bue ◽  
Manuele Faccenda ◽  
Jianfeng Yang
Keyword(s):  
Steady State ◽  
Continental Margin ◽  
Mediterranean Region ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Western Mediterranean ◽  
Mantle Flow ◽  
Crystal Preferred Orientation ◽  
The Mediterranean ◽  
Structural Heterogeneities

<p>In the geodynamic context of the slow Africa-Europe plates convergence, the Central-Western Mediterranean region has been involved in a complex subduction process, which in the last 30 Myr was characterized by the rapid retreat of the Ionian slab, the opening of back-arc extensional basins (i.e., Liguro-Provençal, Algerian, Alboran, and Tyrrhenian basins) and episodes of slab lateral tearing, segmentation and break-off.  A proper modelling of 3-D mantle flow evolution beneath the Mediterranean could provide important clarifications about the complex mantle dynamics of this region and help us understanding the interaction between surface tectono-magmatic processes and mantle convection patterns. </p><p>The mantle flow and its relations with plate horizontal and vertical motions can be determined by measuring seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals. Seismic anisotropy is widespread in the Mediterranean and it shows an intricate pattern that likely has some relations with the recent (20-30 Myr) behavior of subducting slabs. The extrapolation of the mantle flow from seismic anisotropy is neither simple nor always warranted, especially at subduction zones where complex and non-steady-state 3D flow patterns may establish.  A promising approach, which helps reducing the number of plausible models that can explain a given anisotropy dataset, is to compare seismic measurements with predictions of numerical and experimental flow models (Long et al.,2007). Recently, Faccenda and Capitanio (2013) and Faccenda (2014) have extended this methodology to account for the non-steady state evolution typical of many subduction zones, yielding mantle fabrics that are physically consistent with the deformation history.</p><p>In this study, we apply a similar modelling approach to the complex Central-Western Mediterranean convergent margin. We use the wealth of observations from the Mediterranean region available in the literature to design and calibrate 3D thermo-mechanical subduction modelling. We test different initial configurations defined at 30 Ma according to the paleogeographic and tectonic reconstructions derived from (Lucente and Speranza, 2001; Carminati et al., 2012; van Hinsbergen et al., 2014) in order to optimize the fit between predicted and observed slabs position and obtain a final model configuration resembling the present-day surface and deeper structures.</p><p>In particular, here we want to evaluate the influence on rollback rates, trench shape and the occurrence and timing of slab tears (Mason et al., 2010) of structural heterogeneities within the Adria plate as proposed by (Lucente and Speranza, 2001). In all models, subduction migrates south-eastward driven by the subducting oceanic lithosphere, and slab lateral tearing or break-off occurs when a continental margin enters the trench. More importantly, we show that the presence of a stiffer continental promontory in central Adria together with a thinned continental margin in the Umbria-Marche region plays a fundamental role on (i) the development of a slab window below the Central Apennines, (ii) the retreat of the Northern Apenninic trench till the Adriatic Sea, and (iii) the retreat of the Ionian slab till the present-day position.</p>

Lattice preferred orientation of talc and implications for seismic anisotropy

2020 ◽  
Author(s):  
Jungjin Lee ◽  
Haemyeong Jung ◽  
Reiner Klemd ◽  
Matthew Tarling ◽  
Dmitry Konopelko
Keyword(s):  
High Pressure ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Preferred Orientation ◽  
Azimuthal Anisotropy ◽  
Hydrous Minerals ◽  
Ultra High Pressure ◽  
Lattice Preferred Orientation ◽  
Radial Anisotropy ◽  
First Time

<p>Strong seismic anisotropy is generally observed in subduction zones. Lattice preferred orientation (LPO) of olivine and elastically anisotropic hydrous minerals has been considered to be an important factor causing anomalous seismic anisotropy. For the first time, we report on measured LPOs of polycrystalline talc. The study comprises subduction-related ultra-high-pressure metamorphic schists from the Makbal Complex in Kyrgyzstan-Kazakhstan and amphibolite-facies metasomatic schists from the Valla Field Block in Unst, Scotland. The here studied talc revealed a strong alignment of [001] axes (sub)normal to the foliation and a girdle distribution of [100] axes and (010) poles (sub)parallel to the foliation. The LPOs of polycrystalline talc produced a significant P–wave anisotropy (AVp = 72%) and a high S–wave anisotropy (AVs = 24%). The results imply that the LPO of talc influence both the strong trench-parallel azimuthal anisotropy and positive/negative radial anisotropy of P–waves, and the trench-parallel seismic anisotropy of S–waves in subduction zones.</p>

Lattice preferred orientation of talc and implications for seismic anisotropy in subduction zones

2020 ◽  
Vol 537 ◽  
pp. 116178 ◽  
Author(s):  
Jungjin Lee ◽  
Haemyeong Jung ◽  
Reiner Klemd ◽  
Matthew S. Tarling ◽  
Dmitry Konopelko
Keyword(s):  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Preferred Orientation ◽  
Lattice Preferred Orientation

Lattice preferred orientation, water content, and seismic anisotropy of orthopyroxene

2010 ◽  
Vol 21 (5) ◽  
pp. 555-568 ◽  
Author(s):  
Haemyeong Jung ◽  
Munjae Park ◽  
Sejin Jung ◽  
Jaeseok Lee
Keyword(s):  
Water Content ◽  
Seismic Anisotropy ◽  
Preferred Orientation ◽  
Lattice Preferred Orientation
Sign in / Sign up

Export Citation Format

Share Document