ELITE NETZWERK BAYERN

English  Sprachen Icon  |  Gebärdensprache  |  Leichte Sprache  |  Kontakt


Forschungsarbeit

Arabian-Eurasian plate convergence: Do mountains slow down
plate motion?

By Jacqueline Austermann (22.02.2012)

In contrast to the Earth’s surface its interior is very hot. In order to compensate this imbalance, heat is transported through the Earth’s mantle and reaches the surface in form of hot rocks and lavas that are pushed up onto the surface at volcanic eruptions or along mid-ocean ridges. On the other hand slabs of colder material sink back into the Earth’s interior. This heat transport which is accommodated by mass transport is called convection. Due to its distinct properties the Earth forms a rigid outer shell – the Earth’s crust – which is broken into a series of plates (there are about 15 major plates). Driven by a moving interior these plates travel on the surface of the Earth with different velocities which leads to forces that build up at plate boundaries. Once those forces exceed a certain threshold, plates slide over the previously locked portion of the boundary and release stored energy. This process causes earthquakes which pose a severe threat to human civilization living in these regions. Unfortunately this is demonstrated on a regular basis for example by the high magnitude earthquake close to Japan in 2011. Understanding the force budget along plate boundaries is therefore an integral part of research in Earth Sciences.

In my master’s thesis I looked at the plate boundary between Arabia and Eurasia. The Arabian plate is relatively small and mainly consists of the Arabian Peninsula (see figure). The Eurasian plate on the other hand covers all of Europe, the adjacent Atlantic Ocean and most of Asia. It is one of the world’s biggest plates. The boundary between the Arabian and European plate is a convergent plate boundary where the Arabian plate moves towards Eurasia at a relative speed of around 2-3 cm per year. Wherever two continental plates converge (= move towards each other) the excess mass doesn’t penetrate into the mantle but piles up at the plate boundary in a process of faulting and folding. These continental collisions lead to the biggest orogens that exist on Earth, like the Himalayans or the Alps. The Arabian-Eurasian plate boundary region contains the Zagros Mountains and numerous other Mountain chains and plateaus. The elevated region is mainly concentrated in the country of Iran. The uplifted mountain belt which is located on top of the plate boundary increases the friction in the convergence zone (like a brake in a car) and leads to resistive forces along the boundary that can potentially cause the convergence to slow down. It is however unclear how those forces compare in magnitude to other plate driving forces like the viscous drag from the mantle or the pull of subducting slabs. I therefore wanted to quantitatively investigate the correlation between continental collision and plate convergence.

I reconstructed the velocity of Arabia relative to Eurasia for the last 12 Million years. Relative motion between two plates can be reconstructed with good accuracy if they share a mid oceanic ridge. Since this is not the case for Arabia and Eurasia I used a plate circuit via Africa and North America to make this reconstruction. It is visible that the convergence did in fact decrease from 12 Million years ago until today by about a cm per year (which is approximately 30%).

Figure 1: Topographic map of the Middle East region with black outlines of plate boundaries.[Bildunterschrift / Subline]: Figure 1: Topographic map of the Middle East region with black outlines of plate boundaries. The Zagros Mountains and the Iranian Plateau are visible through their elevated topography. The arrow shows today’s plate velocity of the Arabian plate relative to Eurasia. Topography from ETOPO (Amante and Eakins 2009), plate boundaries from Bird (2003) and plate velocity from Vernant et al. (2004).

The research hypothesis I tested was whether the coeval orogeny (= process of mountain formation, especially by folding and faulting of the earth's crust) of the Zagros Mountains was the cause for the slowdown of Arabian-Eurasian plate convergence.

In order to test this correlation between convergence rate and uplift I used a global plate tectonic model which solves the conservation of mass and momentum in finite elements on a sphere. It utilizes values for global plate geometries, topography, surface heat flow, crustal thickness, underlying mantle flow and more to calculate an instantaneous kinematic snapshot of the Earth, i.e. the velocity of each plate. For today these input parameters are well constrained and as output we obtain present-day plate motions. In a subsequent step I did a global tectonic model for a scenario corresponding to 12 Million years ago. I adjusted the topography in the Middle Eastern region according to geologic constraints and recomputed plate velocities. The result showed in fact a higher convergence rate at that time which is in agreement with the direction and magnitude of the reconstructed value.

I furthermore tested the effect of any other possible coeval tectonic mechanism that might have interfered with this process but concluded that indeed the orogeny or increase in topography on this plate boundary was the driving factor for the slowdown of convergence. This implies that the frictional forces due to mountain belts play a major role in the force budget of tectonic plates.

References:

C. Amante and B. W. Eakins, 2009. ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-24, 19 pp.

P. Bird, 2003. An updated digital model of plate boundaries, Geochemistry Geophysics Geosystems, 4(3), 1027.

P. Vernant, F. Nilforoushan, D. Hatzfeld, M. Abbassi, C. Vigny, F. Masson, H. Nankali, J. Martinod, A. Ashtiani, R. Bayer, F. Tavakoli, and J. Chéry, 2004. Contemporary Crustal Deformation and Plate Kinematics in Middle East Constrained by GPS measurements in Iran and Northern Oman, Geophys. J. Int., 157, 381-398.


Stations
  • Since 2011
  • PhD student at the Harvard University in Geophysics
  • 2009 - 2011
  • Master of Science at the Ludwig Maximilians Universität München in Geophysics
  • 2006 - 2009
  • Bachelor of Science at the Technische Universität Darmstadt in Physics (two semsters at the Universidade de Sao Paulo, Brasilien)

Internships
  • 08 - 10/2009
  • Internship at Deloitte & Touche GmbH - Department Deloitte Cert Umweltgutachter GmbH in Düsseldorf
  • 08/2007
  • Max Planck Institute für Polymerforschung in Mainz

Publications
  • - J. Austermann, G. Iaffaldano, H.-P. Bunge, 2011. The competing roles of Zagros orogeny and Tethys slab-break-off in slowing down Arabia/Eurasia convergence since ~12 Ma. In review.
  • - J. Austermann, Z. Ben-Avraham, P. Bird, O. Heidbach, G. Schubert, J. M. Stock, 2011. Quantifying the forces needed for the rapid change of Pacific plate motion at 6 Ma. Earth and Planetary Science Letters, 307, 3-4, pp. 289-297.
  • - M. Schmelzeisen, J. Austermann, M. Kreiter, 2008. Plasmon mediated confocal dark-field microscopy. Optics Express, Vol. 16, Issue 22, pp. 17826-17841.