Controls of the lithospheric thermal field of an ocean-continent subduction zone: the southern Central Andes

Abstract

In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essential to determine the controls of the deformation within the upper plate and the dip angle of the subducting lithosphere. In this study, we evaluate the degree of influence of both the configuration of the upper plate and variations of the subduction angle on the lithospheric thermal field of the southern Central Andes (29°–39°S). Here, the subduction angle increases from subhorizontal (5°) north of 33°S, to steep (~30°) in the south. We derived the 3D temperature and heat flow distribution of the lithosphere in the southern Central Andes considering conversion of S wave tomography to temperatures together with steady-state conductive modeling. We found that the orogen is overall warmer than the forearc and the foreland, and that the lithosphere of the northern part of the foreland appears colder than its southern counterpart. Sedimentary blanketing and the thickness of the radiogenic crust exert the main control on the shallow thermal field (< 50 km depth). Specific conditions are present where the oceanic slab is relatively shallow (< 85 km depth) and the radiogenic crust is thin, This configuration results in relatively colder temperatures compared to regions where the radiogenic crust is thick and the slab is steep. At depths >50 km, the temperatures of the overriding plate are mainly controlled by the mantle heat input and the subduction angle. The thermal field of the upper plate likely preserves the flat subduction angle and influences the spatial distribution of shortening.

Long‐Term Lithospheric Strength and Upper‐Plate Seismicity in the Southern Central Andes, 29°–39°S

“…Compressional deformation occurs in the transition zone between the flat and steep sectors of the slab, promoted by increased slab pull (steepening segment; red‐shaded area). The isotherms (Rodriguez Piceda, Scheck Wenderoth, Bott et al., 2021) are marked by dashed blue lines. Light‐gray lines show the interfaces of the model layers (Rodriguez Piceda, Scheck Wenderoth, Gomez Dacal et al., 2021).…”

“…In an attempt to better quantify the efficiency of viscous creep, we also discuss the results in terms of the effective viscosity (η eff ). This parameter is expressed by a power‐law dependence of temperature and strain rate as (Burov, 2011): $$${{\eta}}_{\mathrm{e}\mathrm{f}\mathrm{f}}=\frac{{2}^{\frac{1-\mathrm{n}}{\mathrm{n}}}}{{3}^{\frac{1+\mathrm{n}}{2\mathrm{n}}}}{\mathrm{A}}^{-\frac{1}{\mathrm{n}}}{\dot{\varepsilon }}^{\frac{1}{\mathrm{n}}-1}\mathrm{exp}\left(\frac{\mathrm{H}}{\mathrm{n}\mathrm{R}\mathrm{T}}\right)$$$ the material and temperature distributions used as input were derived from 3D lithospheric‐scale models of the SCA (Rodriguez Piceda, Scheck Wenderoth, Gomez Dacal et al., 2021; Rodriguez Piceda, Scheck Wenderoth, Bott et al., 2021) and described in more detail in Section 2.1.1. The specific mechanical properties assigned to the lithospheric units of the model are subsequently outlined in Section 2.1.2.…”

“…The temperature configuration used as input for the rheological calculations was derived from a thermal model of the SCA (Rodriguez Piceda, Scheck Wenderoth, Bott et al., 2021) covering the same region as the structural model. Crustal and mantle temperatures down to 50 km bmsl were computed assuming steady‐state conductive conditions and using as input the structural model of Rodriguez Piceda, Scheck Wenderoth, Gomez Dacal et al.…”

“… Depth of the (a) 450°C and (b) 650°C isotherms across the modeled area according to the lithospheric‐scale model of Rodriguez Piceda, Scheck Wenderoth, Gomez Dacal et al., 2021; Rodriguez Piceda, Scheck Wenderoth, Bott et al., 2021). Boundaries of the main morphotectonic provinces are also marked with black lines; for abbreviations see Figure 5.1.…”

“…(2021); Rodriguez Piceda, Scheck Wenderoth, Judith et al. (2021) via GFZ Data Services (https://doi.org/10.5880/GFZ.4.5.2021.002). The seismic catalog used in the study is from the International Seismological Center Bulletin (http://www.isc.ac.uk/iscbulletin/).…”