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Pedreira, D., J. A. Pulgar, J. Díaz, J. L. Alonso, J. Gallastegui, and A. Teixell Comment on “Reconstruction of the Exhumed Mantle Across the North Iberian Margin by Crustal-Scale 3-D Gravity Inversion and Geological Cross Section” by Pedrera et al, Tectonics, 0(0), doi: doi:10.1029/2018TC005129.

Abstract

Pedrera et al. (2017) presented a new tectonic model for the Basque‐Cantabrian Basin in the Pyrenean‐Cantabrian belt, based on a geological cross section and the results of a 3‐D gravity modeling that presumably “demands the presence of a high‐density mantle body placed within the crust in order to justify the observed anomalies.” Other authors have discussed before the possibility that the strong gravimetric (and magnetic) anomalies observed over the area could be explained, totally or partially, by bodies of mantle rocks located at shallow depths beneath the sediments of the Basque‐Cantabrian Basin (e.g., Pedreira et al., 2007; Roca et al., 2011; Tugend et al., 2014). However, the contribution by Pedrera et al. (2017) is novel in that it suggested that the present‐day crustal‐scale structure retains largely the morphology of the hyperextended Mesozoic basin and is only slightly modified by the Cenozoic Pyrenean orogeny. In their model, the continental crust is totally removed at present beneath the Cretaceous sediments of the northern part of the Basque‐Cantabrian Basin, so that these sediments are resting on top of the mantle, with the asthenosphere at only ~15‐km depth. The modeled upper surface of the mantle extends laterally to the central Pyrenees, always reaching “shallow crustal levels also locally attaining the topographic surface.” That is to say that in those places of the Pyrenees, there is supposedly only mantle from the topographic surface to the Earth's core, at ~2,900‐km depth.

New and provocative ideas, especially when implying paradigmatic changes, should be particularly convincing in their presentation. These presentations should ideally provide detailed justifications for the decision adopted in the course of the research and take into consideration all the available results from previous studies, or a reinterpretation of them, adding full discussions regarding their implications. The contribution by Pedrera et al. (2017) failed in this attempt. It used inadequate procedures and unrealistic parameter values in the course of the modeling, leading to a final structural model with clear geological inconsistences and contradictions with several geophysical observations. In the following, we briefly describe some of these problems, hoping that Pedrera et al. can clarify them and provide additional arguments in support of their work.

Reference article

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