The effect of obliquity on temperature in subduction zones: insights from 3D numerical modeling

Abstract

Abstract. In subduction zones the geotherm is thought to vary as a function of the subduction rate and the age of the subducting lithosphere. Along a single subduction zone the rate of subduction can strongly vary due to changes in the angle between the trench and the plate convergence vector, namely the subduction obliquity. We currently observe such a configuration all around the Pacific (e.g. Marianna, Chile, Aleutians). Subduction obliquity is also supposed in the geological record of Western and Central Turkey. In order to investigate this effect, we designed and computed simple thermo-kinematic finite element 3D 5 numerical models. We prescribe the trench geometry by means of a simple mathematical function and compute the mantle flow in the mantle wedge only by solving the equation of mass and momentum conservation. We then solve the energy conservation equation until steady-state is reached. We analyse the results (i) in terms of mantle wedge flow with emphasis on the trenchparallel component and (ii) in terms of temperature along the plate interface by means of maps and depths-temperature path at the interface. We show that the effect of the trench curvature on the geotherm is substantial. A small obliquity yields a small but 10 not negligible trench parallel mantle flow leading to differences of 50• C along strike of the model. With increasing obliquity, the trench parallel component of the velocity consequently increases and the temperature variation can be as important as 200• C along strike. This can even be larger with varying plate velocity. Finally, we discuss the implication of our simulations for the ubiquitous oblique systems that are observed on Earth, the limitation of our modeling approach and the significance for the geological record with an emphasis on the case study of Western and Central Turkey.

Diachronous demise of the Neotethys Ocean as a driver for non-cylindrical orogenesis in Anatolia

“…U/ Pb zircon crystallization and 40 Ar/ 39 Ar cooling ages from these units suggest that they experienced their climax pressure metamorphismcorresponding or post-dating their accretion from the downgoing African Plate to the overriding, oceanic Anadolu Plate at 90-80 Ma (van Hinsbergen et al, 2016, and references therein). Since both units entered the subduction zone below the Anadolu Plate simultaneously, they must have been lateral equivalents, whereby their contrasting metamorphic grade may have been a result of the stark contrast in the obliquity of the subduction zone in which they were buried (Plunder et al, 2018;van Hinsbergen et al, 2016). There is no known equivalent of the Tavşanlı zone and Kırşehir Block, with contemporaneous ages of metamorphism, known in Eastern Anatolia (Figs.…”

The Geodynamic World Builder: a solution for complex initial conditions in numerical modelling

“…This application creates so-called vtu files which can be visualized by programs like Paraview (paraview.org). Furthermore, we show examples of GWB use with the SEPRAN (van den Berg et al, 2015), ELEFANT (Plunder et al, 2018) and ASPECT codes. The annotated input files to create these models are presented in appendixes A to F and are part of the GWB repository.…”

“…The input file for this example can be found in Appendix B. Figure 4 shows a 3D example defining a subduction geometry similar to the one in Plunder et al (2018). In this example the trench consists of three connected straight lines.…”

“…ELEFANT is a 2D/3D Finite Element code for geodynamic problems (Maffione et al, 2015;Lavecchia et al, 2017;Plunder et al, 2018) written in Fortran. It principally relies on bi/tri-linear velocity-constant pressure elements and uses the Marker-in-Cell technique to track materials.…”

On the choice of finite element for applications in geodynamics

“…Another example of the use of this method is the work of Leng and Zhong (2011), also using AMR, to study thermochemical mantle convection. Both the ELEFANT code with an application to the 3D thermal state of curved subduction zones (Plunder et al, 2018), and the GALE code (Moresi et al, 2012) with application to the 3D shapes of metamorphic core complexes (Le Pourhiet et al, 2012) or oceanic plateau subduction (Arrial and Billen, 2013), use the stabilised Q 1 × Q 1 method. Finally the ADELI code was coupled to a stabilised Q 1 × Q 1 flow solver in the context of lithosphere-asthenosphere interaction studies (Cerpa et al, 2014(Cerpa et al, , 2015(Cerpa et al, , 2018.…”