Numerical modelling of triple-junction tectonics at Karlıova, Eastern Turkey, with implications for regional magma transport

Abstract

Few places on Earth are as tectonically active as the Karlıova region of eastern Turkey. In this region, complex interactions between the Arabian, Eurasian and Anatolian plates occur at the Karlıova Triple Junction (KTJ). The relationship between tectonics and magma propagation in triple-junction tectonic settings is poorly understood. Here we present new field and numerical results on the mechanism of magma propagation at the KTJ. We explore the effects of crustal heterogeneity and anisotropy, in particular the geometry and mechanical properties of many faults and layers, on magma propagation paths under a variety of tectonic loads. We propose that two major volcanic centres in the area, the Turnadağ volcano and the Varto caldera, are both fed by comparatively shallow magma chambers at depths of about 8 km, which, in turn, are fed by a single, much larger and deeper reservoir at about 15-18 km depth. By contrast, the nearby Özenç volcanic area is fed directly by the deeper reservoir. We present a series of two-dimensional and three-dimensional numerical models showing that the present tectonic stresses encourage magma-chamber rupture and dyke injection. The results show that inversion tectonics encourages the formation of magma paths as potential feeder dykes. Our three-dimensional models allow us to explore the local stresses induced by complex loading conditions at the Karlıova triple junction, using an approach that can in future be applied to other similar tectonic regions. The numerical results indicate a great complexity in the potential magma (dyke) paths, resulting from local stresses generated by interaction between mechanical layers, major faults, and magma chambers. In particular, the results suggest three main controls on magma path formation and, eventual eruptions, at KTJ: (1) the geometry and attitude of the associated faults; (2) the heterogeneity and anisotropic of the crust; and (3) mechanical (stress) interactions between deep and shallow magma chambers.

Three‐Dimensional Failure Patterns Around an Inflating Magmatic Chamber

“…Heat transport, magma injection rate, chemical differentiation, tectonic forcing, edifice loading and mechanical heterogeneities all contribute to a first order in bedrock micro‐fracturation and macroscopic deformation. Below, we review the influence of other mechanical parameters, which basically add a stress component to the overall volcanic system, and which therefore mainly shifts the magnitude and location of the stress threshold enabling bedrock failure: Variations in the elastic and plastic properties throughout the bedrock such as the presence of weak layers or weak fault zones, are known to enable the relaxation and rotation of the stress field, which affects the geometries of diking and faulting (Gudmundsson, ; Karaoğlu et al, ; Masterlark, ; Rivalta et al, ). Similarly, a local increase in bedrock permeability such as by meteoritic fluids diminishes the bedrock strength, rotates the stress field and favor its failure (Plateaux et al, ). Regional tectonic stresses also modulate the pressure threshold for bedrock failure around a magma chamber.…”

“…1. Variations in the elastic and plastic properties throughout the bedrock such as the presence of weak layers or weak fault zones, are known to enable the relaxation and rotation of the stress field, which affects the geometries of diking and faulting (Gudmundsson, 1988(Gudmundsson, , 2006Karao glu et al, 2016;Masterlark, 2007;Rivalta et al, 2015). Similarly, a local increase in bedrock permeability such as by meteoritic fluids diminishes the bedrock strength, rotates the stress field and favor its failure (Plateaux et al, 2012).…”

“…This overpressure is assumed to increase faster than thermal heat transfer and viscous relaxation, and the reader is refered to other studies that explore such thermal aspects (Burov et al, ; Gelman et al, ; Gregg et al, ; Jellinek & de Paolo, ; Karlstrom et al, ). The influence of a volcanic edifice, bedrock mechanical heterogeneities and tectonics stresses (Currenti & Williams, ; Karaoğlu et al, ; Menand, ; Pinel & Jaupart, ) are also neglected here but will be briefly discussed later on.…”

“…Elastic dilation at oblate chambers tip open concurrent magma pathways whereas contraction around prolate chambers favors apex failure. (Currenti & Williams, 2014;Karao glu et al, 2016;Menand, 2011;Pinel & Jaupart, 2005) are also neglected here but will be briefly discussed later on.…”

A Directional Crack Damage Memory Effect in Sandstone Under True Triaxial Loading

“…Rocks in the crust may undergo, or have undergone, repeated cycles of stress over time (Heap, Vinciguerra, and Meredith, 2009). In environments with complex stress regimes where stresses may evolve both spatially and temporally, such as volcanoes or active fault zones, some of these rocks may experience not only cyclic stressing but also rotating and/or reorienting stress conditions (Faulkner et al, 2006;Karaoglu et al, 2016;Gudmundsson & Philipp, 2006). In such situations the resulting crack distributions form sequentially and may therefore be highly anisotropic.…”