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

Abstract

Abstract. The geotherm in subduction zones 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 may strongly vary due to changes in the angle between the trench and the plate convergence vector, i.e., the subduction obliquity, due to trench curvature. We currently observe such curvature in, e.g., the Marianas, Chile and Aleutian trenches. Recently, strong along-strike variations in subduction obliquity were proposed to have caused a major temperature contrast between Cretaceous geological records of western and central Turkey. We test here whether first-order temperature variation in a subduction zone may be caused by variation in the trench geometry using simple thermo-kinematic finite-element 3-D numerical models. We prescribe the trench geometry by means of a simple mathematical function and compute the mantle flow in the mantle wedge by solving the equation of mass and momentum conservation. We then solve the energy conservation equation until steady state is reached. We analyze the results (i) in terms of mantle wedge flow with emphasis on the trench-parallel component and (ii) in terms of temperature along the plate interface by means of maps and the depth–temperature path at the interface. In our experiments, the effect of the trench curvature on the geotherm is substantial. A small obliquity yields a small but not negligible trench-parallel mantle flow, leading to differences of 30 °C along-strike of the model. Advected heat causes such temperature variations (linked to the magnitude of the trench-parallel component of velocity). With increasing obliquity, the trench-parallel component of the velocity consequently increases and the temperature variation reaches 200 °C along-strike. Finally, we discuss the implication of our simulations for the ubiquitous oblique systems that are observed on Earth and the limitations of our modeling approach. Lateral variations in plate sinking rate associated with curvature will further enhance this temperature contrast. We conclude that the synchronous metamorphic temperature contrast between central and western Turkey may well have resulted from reconstructed major variations in subduction obliquity.

Mafic High‐Pressure Rocks Are Preferentially Exhumed From Warm Subduction Settings

“…Three-dimensional flow effects (e.g., Bengtson & van Keken, 2012;Morishige & van Keken, 2014;Plunder et al, 2018;Wada et al, 2015) may also increase the temperature at the top of the slab, although this should not affect the forearc OC structure significantly once the cold forearc mantle has been established. Three-dimensional flow effects (e.g., Bengtson & van Keken, 2012;Morishige & van Keken, 2014;Plunder et al, 2018;Wada et al, 2015) may also increase the temperature at the top of the slab, although this should not affect the forearc OC structure significantly once the cold forearc mantle has been established.…”

“…There are many occasions where these warmer conditions are a natural part of subduction zone evolution and do not require arbitrary heat sources: subduction of young oceanic lithosphere (including the subduction of small back-arc basins), the initiation of subduction, the initial evolution of the forearc mantle for young subduction systems, and the termination of subduction by slab breakoff or subduction of an mid-oceanic ridge. Three-dimensional flow effects (e.g., Bengtson & van Keken, 2012;Morishige & van Keken, 2014;Plunder et al, 2018;Wada et al, 2015) may also increase the temperature at the top of the slab, although this should not affect the forearc OC structure significantly once the cold forearc mantle has been established. Figure 5b shows that models of subducting young oceanic lithosphere predicts average OC conditions similar to the average rock record.…”

Collision Chronology Along the İzmir‐Ankara‐Erzincan Suture Zone: Insights From the Sarıcakaya Basin, Western Anatolia

“…Also, thick‐skinned deformation in the west preceded Middle‐Late Eocene thick‐skinned deformation in central Anatolia (e.g., Kaymakci et al, ; Nairn et al, ). This along‐strike change in deformation remains unexplained in collision models but could be a result of changes in lithology, basement thickness, preexisting structures, or effects of oblique subduction on orogen dynamics (Plunder et al, ).…”

“…Today, the Tavşanlı Zone comprises, from highest to lowest structural levels, Eocene and Neogene siliciclastic and volcanic rocks of the peripheral Eskişehir foreland basin, obducted Cretaceous ophiolites of the İAESZ, metamorphosed Paleozoic basement, and Late Cretaceous and Eocene‐early Oligocene granitoids intruded into the ophiolites and basement (Harris et al, ; Okay et al, ; Okay & Whitney, ; Şengüler & Izladi, ; Sherlock et al, ). The HT/LP Kırşehir Block in central Anatolia (also known as the Kırşehir Massif or Central Anatolian Crystalline Complex) is arguably either a distinct terrane (e.g., Görür et al, ) or the lateral continuation of the Tavşanlı Zone (van Hinsbergen et al, ; Plunder et al, ; Yaliniz et al, ).…”

“…Contemporaneous Paleocene collision of Tavşanlı‐KB with the Pontides was followed by a Miocene collision of the eastern ATB with the Pontides (Gürer et al, ; Gürer & van Hinsbergen, ; van Hinsbergen et al, ). Key to this model is the interpretation that contrasting metamorphic grades between the KB and Tavşanlı Zone resulted from NE verging oblique subduction of the KB into an east dipping subduction zone (Lefebvre et al, ; Plunder et al, ). The synchronous model does not advocate for or against an Intra‐Tauride suture but allows for an oceanic basin separating the Tavşanlı‐KB from the rest of the ATB.…”