Magnetotelluric Studies of Active Continent–Continent Collisions

Abstract

Continent-continent collisions are an important tectonic process and have played a fundamental role in the evolution of the modern continents. A combination of geological and geophysical data has provided new constraints on the structure and temporal evolution of these orogens. Magnetotelluric (MT) studies have been an important part of these studies since they can constrain the fluid content and thermal structure which are key parameters for defining the rheology of the crust and upper mantle. MT studies of the Himalaya have defined the geometry of active faults associated with continued plateau growth. Orogen scale MT studies have shown that both the India-Asia collision (Tibetan Plateau and Himalaya) and the Arabia-Eurasia collision (Eastern Anatolia) have developed a low resistivity mid-crustal layer with upper surface at 10-20 km that is likely due to a combination of partial melt and associated aqueous fluids. The properties of this layer are consistent with a strength contrast that permits crustal flow over geological timescales. The upper mantle from the Moho to at least 100 km beneath both Northern Tibet and the Anatolian Plateau is characterized by low resistivity values (10-30 Xm) indicating the presence of shallow asthenosphere. Future integrated seismic and MT studies of collision zones are needed fully to explore the 3D structures associated with deformation and further constrain geodynamic models.

Electrical resistivity structure at the North-Central Turkey inferred from three-dimensional magnetotellurics

“…In active tectonic settings, existence of large conductive zones in the mid-crustal depths, similar to C 3 , is usually associated with aqueous saline fluids or partial melts (Unsworth 2010). Similar kind of large zones of fluidfilled structures were detected by numerous MT studies (e.g., Tank et al 2005;Wannamaker et al 2009;Becken et al 2011).…”

“…Aqueous saline fluids and partial melts within the rock matrix of geological formations could enhance the bulk conductivity of rocks by several orders of magnitude via ionic conduction. Magnetotelluric (MT) method is able to investigate the geo-electric structure up to several hundreds of kilometers depth and has proven to be capable in designing hypotheses for fluid-induced tectonic mechanisms (e.g., Ritter et al 2005;Jiracek et al 2007;Wannamaker et al 2009;Unsworth 2010). Resistivity variations in the vicinity of the NAF and subsidiary systems were previously linked with seismic behavior by applying the MT method.…”

Continental dynamics of Eastern China: Insights from tectonic history and receiver function analysis

“…If the lower crust has been subjected to high pressures during compressional deformation, eclogitic rocks of high density form in the thickening lower crust thereby creating density instability (Gao et al, 2004;Elkins-Tanton, 2005;Zhang et al, 2012b). Because of this density contrast, the eclogitic lower continental crust together with the underlying lithospheric mantle can be recycled (or delaminated) into the mantle (Kay and Kay, 1993;Vlaar et al, 1994;van Thienen et al, 2004). The density increase leads to gravitational instability of an overthickened lithospheric keel (Lustrino, 2005).…”

On the Coupling of Geodynamic and Resistivity Models: A Progress Report and the Way Forward

“…Excess fluid pressure and/or connectivity can also be produced by dehydration reactions (Wannamaker et al 2002(Wannamaker et al , 2009Becken et al 2008). Fluids enhance the generation of melting with increasing temperature; partial melts form in the crust in active tectonic areas such as subduction zones (e.g., Brasse and Eydam 2008;Heise et al 2010), volcanic belts (e.g., Hill et al 2009) or continental collision zones (Unsworth 2010) and can lead to considerable enhancement in electrical conductivity.…”

“…The India-Asia continent-continent collision zone has been extensively studied by magnetotelluric surveys, many of them as part of the International Deep Profiling of Tibet and Himalaya (INDEPTH) project (Chen et al 1996;Unsworth et al 2004Unsworth et al , 2005Spratt et al 2005;Ye et al 2007;Arora et al 2007). For a review of all MT work that has been carried out in the Himalaya and Tibetan Plateau until 2010, see Unsworth (2010). The most recent studies of the eastern Himalayan have been carried out by Zhao et al (2012) and Wang et al (2013).…”