A discussion of “hidden subduction” in orogenic belts

Abstract

The McKenzie et al. (2019) model concerning the cause of the deep earthquakes in the Hindu Kush region in Asia greatly resembles the hidden subduction model proposed earlier. However, in the case of the Hindu Kush, the age of the disappearance of the Tethyan waters was early Jurassic and the sutures were overlain by early Cretaceous sedimentary cover. The question then becomes how long a “subcutaneous” oceanic lithosphere can survive within a continent. It seems that the “oceanic” basement of the North Caspian Depression has been there since the late Palaeozoic, which is encouraging for the McKenzie et al. model. Whether an already subducted slab can also survive for more than 100 million years attached to its continental continuation remains an unanswered question. In the examples with which we are familiar (eastern Turkey, Apennines, Magrebides, Betic and Rif cordilleras), subducted lithosphere became detached at most 25 million years after collision.

Diverse Styles of Lithospheric Dripping: Synthesizing Gravitational Instability Models, Continental Tectonics, and Geologic Observations

“…The ongoing debates over the Isabella Anomaly (e.g., Cox et al., 2016; Pikser et al., 2012; Y. Wang et al., 2013; Yu et al., 2020), Wallowa Anomaly (Darold & Humphreys, 2013), and Nevada Cylinder (Pavlis et al., 2012; van der Meer et al., 2018; Zandt & Humphreys, 2008) suggest that even as tomographic models improve, distinguishing drips from other scenarios such as slab fragments (e.g., Porritt, 2013; Y. Wang et al., 2013) will remain contentious. Tomographic anomalies below active seismic zones in the mantle beneath the SE Carpathians and the Hindu Kush have also been interpreted as both lithospheric drips (Molnar & Bendick, 2019) and remnant oceanic slabs (Şengül Uluocak et al., 2019), igniting a debate on the long‐term strength of continental lithosphere, the fate of fossil slabs during continental suturing, and the origin of intracontinental mantle seismic zones (McKenzie et al., 2019; Şengör & Dewey, 2020).…”

“…Mantle seismicity beneath the SE Carpathians (#16) and Hindu Kush (#19) cluster in a narrow zone situated above a large P‐wave anomaly, and their focal mechanisms indicate rapid vertical stretching consistent with drip necking (Lorinczi & Houseman, 2009; Molnar & Bendick, 2019). The interpretation of these zones as either dripping lithosphere, delaminating lithosphere, or remnant oceanic slabs is a topic of ongoing research (Göğüş et al., 2016; McKenzie et al., 2019; Şengör & Dewey, 2020).…”

“…Wang et al, 2013) will remain contentious. Tomographic anomalies below active seismic zones in the mantle beneath the SE Carpathians and the Hindu Kush have also been interpreted as both lithospheric drips (Molnar & Bendick, 2019) and remnant oceanic slabs (Şengül Uluocak et al, 2019), igniting a debate on the long-term strength of continental lithosphere, the fate of fossil slabs during continental suturing, and the origin of intracontinental mantle seismic zones (McKenzie et al, 2019;Şengör & Dewey, 2020).…”