I am a PhD student at the University of Potsdam and at the Helmholtz Centre Potsdam GFZ in section 2.5 Geodynamic modeling. I develop numerical regional scale models of the Earth to better understand the mechanism behind the evolution of the surface and its deformation at convergent margins. In particular, my studies focus on the role of subduction dynamics and its interaction with the overriding plate.
I am also interested in developing new tools to simulate the active tectonics of the Earth. During my studies, I have created a code that calculates the coseismic contribution of earthquakes to the gravity field (the code is available upon request). Additionally, I have been involved in paleomagnetic studies, including measuring the Anisotropy of Magnetic Susceptibility to gain a deeper understanding of the mode of emplacement of plutons, as well as calculating paleomagnetic pole positions and discussing their implications for the closure age of the Mongol-Okhotsk ocean.
I have also participated to many fied school and works some pictures are accessible here
The nature of the North-South change of the magnitude of tectonic shortening in Central Andes at Altiplano-Puna latitudes: a thermomechanical modeling approach
Advisor: Prof. Stephan Sobolev
Keywords: Andes, geodynamics, subduction, shortening, orogen, plateau
The subduction of the oceanic Nazca Plate under the continental South American Plate has been active since at least 180 Ma. However, the cause of the initiation of the shortening of the Andes during less than last 50 My or less, and the reasons behind the spatial and temporal variation in the magnitude of the shortening are still debated (Oncken et al., 2012). In the case of the Central Andes, the South American plate is advancing westwards forcing the trench to retreat and the Nazca plate to roll-back. However, paleo-reconstructions of the margin position demonstrate that the trench velocity slowed down over the last ~50 My and became lower than the South American plate velocity. This difference of velocity is expressed by the shortening of the Andes. One reason for this decrease of velocity at the trench can be the anchoring of the slab in the lower mantle (Faccenna et al., 2017). Although this hypothesis provides an explanation for the initiation of shortening, it cannot explain the observed pulses of shortening (Oncken et al., 2012) as well as latitudinal variations of its magnitude (~300 km at ~18-21°S to ~100 km at 15°S latitude) . In central Andes, weakening mechanisms of the overriding plate (OP) such as lithospheric delamination have intensified the tectonic shortening and contributed to formation of the Altiplano-Puna plateau (Sobolev et al., 2006). Moreover, the difference in deformation style of the foreland basin, thick-skinned (e.g the Puna) and thin-skinned (e.g the Altiplano), respectively, is correlated with variations in the magnitude of shortening. Nevertheless, the influence of the strength variations in the OP on the subduction dynamics in the case of the central Andes has been poorly explored so far. Our hypothesis is that OP strength variations result in variable rates of trench roll-back. To test this hypothesis and in try to reproduce observed spatial and temporal variations of tectonic shortening in central Andes, we have built an E-W-oriented 2D geodynamic model along the Altiplano-Puna plateau which incorporated the flat subduction episode at ~35 Ma and following evolution of the lithospheric deformation. For that purpose, we used the FEM geodynamic code ASPECT. The model is semi-dynamic, which means that the oceanic plate evolves dynamically (i.e. buoyancy-driven), while the OP velocity is prescribed. Example of the model replicating deformation patterns and lithospheric structure at latitude 21 °S at present time is shown in Figure 1. We will discuss our new findings that demonstrate that not all key factors driving orogeny in central Andes have been considered in modelling studies so far.
References Faccenna, C., Oncken, O., Holt, A. F., & Becker, T. W. (2017). Initiation of the Andean orogeny by lower mantle subduction. Earth and Planetary Science Letters, 463, 189-201. Oncken, O., Boutelier, D., Dresen, G., & Schemmann, K. (2012). Strain accumulation controls failure of a plate boundary zone: Linking deformation of the Central Andes and lithosphere mechanics. Geochemistry, Geophysics, Geosystems, 13(12). Sobolev, S. V., Babeyko, A. Y., Koulakov, I., & Oncken, O. (2006). Mechanism of the Andean orogeny: insight from numerical modeling. In The Andes (pp. 513-535). Springer, Berlin, Heidelberg.
Earthquakes impact on GRACE gravimetric signal at global scale
Advisors: Dr. Maxime MOUYEN, Prof. Philippe STEER et Prof. Laurent LONGUEVERGNE
Keywords: GRACE, Scaling laws, Earthquake, Gravity change
GRACE Satellite (Gravity Recovery And Climate Experiment) allows to measure monthly tiny variation of the terrestrial gravity field since april 2002. These variations are due to mass redistribution and can come from hydrology (Glacial melting, fluids circulation in groundwater), sedimentary (transport of sediments) and also seismic. The goal of this study is to model the co-seismic gravimetric signal associated to the global seismicity recorded in the GCMT (Global Centroid Moment Tensor) catalog on the observable time period of GRACE to finally correct it. This will give us access to gravity signal of reduced amplitude. The co-seismic signal is modelled using seismic rupture parameters defined either by model or by scaling law. A global cumulated co-seismic map of gravity variations between 2002 and 2014 is calculated. Models are then compared to GRACE data from the Center for Space Research (CSR, Austin Texas). For high magnitude (Mw≥8), similitude are shown between the model and gravity variations observed from GRACE. However for smaller magnitude (Mw<8) gravimetric effect is hardly verifiable.
Topographic evolution of Deccan traps by Digital Elevation Map modelling approaches.
Advisors: Prof. Claudio FACCENNA and Dr. Andrea SEMBRONI
Keywords: Western gates, flexure, dynamic, residual, isostasy, topography.
Indian topography is a key for our understanding of geodynamic processes. The kinematic of Indian plate as the formation of the Himalaya mountain chain building are factors that allow to constrain models. Drifting of India is marked by many events as microcontinents break up (e.g. Mascarene and Seychelles blocs) associated to wide basalt flow emplacement. Thus basalt flow are really good markers to discuss about topographic evolution. The Main Deccan Traps province is one of the best preserved LIP in the world. The basalt layers reach a maximum thickness off ~1800 on the western coast and are gently inclined eastward (<4° inland) over a longwavelength (λ> 500 km). The question of the process that could cause this tilting is a lot debated and topographic evolution using paleoplanation surfaces approaches have already been carry out by many authors (Gunnell 1998; Widdowson, 1997; Seth 2007). In our study, we used modeling using GIS to propose an answer. We assume that most of the vertical motion was already achieved prior the monsoon impact (>15Ma). We have isolated the different major components of the topography ZElevation = ZDyn + ZIso + ZFlex+ ZErod (Becker et al., 2014a). Results shows that inland erosion and unloading cannot explains the homogeneous uplift of the coast and tilting. The long wavelenght tilting of the topography is not the consequence of the coastal erosion of the western passive margin, unloading and its flexuration (Te = 10-13 km explains ~140 km inland). An effective elastic thickness of Te = ~50 km-70 km fit with the central Deccan trapps topography. Two majors candidates are proposed : the first, dynamic topography obtained by converting free-air gravity anomalies (Craig et al, 2011) shows slightly low contribution over the trapps. This is verify by substrating all component estimated exept the dynamic topography to the present topography (Becker et al., 2014). The second, isostatic topography is obtained considering buoyant homogeneous crust over an homogeneous mantle lithosphere and mantle asthenosphere. The substraction of the isostatic topography to the present topography produce a low residual topography implying that the major part of the topography is attributed to isostasy. Therefore the the longwavelength tilting is caused by a thinning of the mantle lithosphere under the Western Ghats Escarpement.
Paleomagnetic study of the upper jurassic granitic massif of Qiltianling (South China) and its tectonic implication on the age of closure of the Mongol-Okhotsk Ocean.
Advisors: Prof. Yan CHEN and Hongsheng LIU
Keywords: Qitianling, Mongol-Okhotsk, paléomagnétisme, tectonique, fabrique, magnétique, rémanence.
The age of closure of the Mongol-Okhotsk Ocean has already been discussed for a long time. To better constrain its age of closure, a study of the magnetic fabric and a paleomagnetic study have been carried on the Qitianling pluton during this research project. Observations on the field show that the pluton didn’t undergone any visible deformation. Study on the Anisotropy of Magnetic Susceptibility confirms it. Analysis shows that an oblate shape and a horizontal foliation are dominant, which could indicate that the pluton has not been tilted. Magnetites of pseudo-singledomain have been recognized as the mineral carrier of the magnetic remanence. Progressive demagnetization carried on 131 samples, allow us to isolate 2 directional magnetic components: one is the Low Temperature Component (CBT), close to the current value of the geomagnetic field and one other is the High Temperature Component (CHT). Isolate directions of the high temperature component show that the 3 granitic phases cannot be distinguished and have a weak rate of reverse (~16%). U-Pb datations on zircons give an average age of 155 Ma (Zhu et al., 2009). These datations have measured the age at the temperature of closure of their isotopic system at 850°C. Magnetite gets its magnetic remanence at 580°C. A cooling of 50°C/Ma compatible with the rate of reversal geomagnetic field shows that the age of acquisition of the magnetic remanence by the pluton could be estimated around 150 Ma. The compatibility of the paleomagnetic direction allow us to calculate an average direction (CHT), and transform it in a paleomagnetic pole of the South China Block (SCB) of 150 M a: 84,1°N, 192,9°E and α95=7,3. By comparing this paleomagnetic pole with those from the North China Block (NCB) and from Siberia, results indicate that NCB and SCB was already stuck together and considered as a single block. This single block had a relative displacement of 1300±800 km in paleolatitude with the Siberia block for 150 Ma. This value indicates that the Mongol-Okhotsk Ocean was still opened to the Upper Jurassic with a minimum width of ~500 km. This result contrasts with the previous studies which have estimated a width of ~1500km (Enkin et al., 1992) or ~3000km (Pei et al., 2011).
The require ASM study I practicated is part of a publication LIU, Hongsheng, MARTELET, Guillaume, WANG, Bo, et al. Incremental emplacement of the late Jurassic mid‐crustal, lopolith‐like Qitianling pluton, South China, revealed by AMS and Bouguer gravity data. Journal of Geophysical Research: Solid Earth, 2018.
Finite strain analysis using Meere and Mulchrone method
Advisors:Prof. Patrick A.Meere.
Example: Trabeg Formation Conglomerate (Tb1)
Rf is the ratio between each axis (major axis/minor axis) of the average ellipse of each grain and phi is the angle regarding to the vertical axis. Left rotation is negative and right rotation is positive.
Rs (=average of Rf) results from different samples of the same formation show small strain rate variations using the Muchrone 2001 method.
Average Rs result from different method show wide variations from one method to another.
Here are others websites that I have done : SciANS is a Wordpress blog where I can discuss of publications, hobbies, it also allows me to make a bridge for all the other links below. Knowlapps-Geolapps, its first purpose was to share my passion about science and discoveries. You will also find some pictures and videos about divers trips that I have done during my free time as well as few lectures and report made while I was undergraduate. You can also follow me on social networks -Youtube -instagram Minerallov -Google plus - Google Map contributor Lv8 with more than 1 300 000 views. -LinkedIn -Twitter -Facebook