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.

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