HOW GEOLOGISTS AND GEOCHEMISTS CAN HELP SOLVE THE 50-YEAR PROBLEM OF THE PLATE DRIVING MECHANISM

In the decade 1965-1975, plate tectonics overthrew the previous paradigm of continental fixism and revolutionized our understanding of shallow-Earth geology and geochemistry in great detail. For the subsequent half-century, although seismic tomography has gradually clarified the large-scale features of the deep Earth, geodynamicists have struggled to understand the plate driving mechanism, reaching little agreement, so that their papers traditionally contain a statement that the driving mechanism remains obscure.

Yet the geology and geochemistry of sedimentary, igneous, and metamorphic rocks at the surface reflect motions in the deep Earth, with two advantages to complement the traditional data of geodynamics: (1) this information is highly detailed, down to the km or even mm scale, and (2) it records Earth history back through the Proterozoic and even into Archean. However, geological information is rarely used in studies of the driving mechanism, perhaps because it is unfamiliar to most geodynamicists.

In a paper almost 40 years ago (1982, JGR, v. 87, p. 6697), I used geological evidence to argue that continents move because they have deep roots coupled to sub-asthenosphere motions (“continental undertow”) and that asthenosphere is forced to flow through gaps in the continental roots, dragging surface geology eastward beneath the Caribbean and Drake Passage. Over four decades, more and more geological and geochemical evidence has been found by numerous researchers to support the continental undertow hypothesis. For example, undertow explains the otherwise mysterious, long-continuing continental collisions deforming the Tethyan belt from the Alps to the Himalayas (Alvarez, 2010, EPSL, v. 296, p. 434; Becker & Facenna, 2011, EPSL, v. 310, p. 453), and has been confirmed by detailed geological studies in the Caribbean (Pindell & Kennan, 2009, Geol. Soc. London Sp. Pub. 328, p. 1; Altamira & Burke, 2015, AAPG Mem. 108, p. 39) and gravity studies of the Drake Passage (Martos et al., 2014, GRL, v. 41, p. 43; 2019, JGR, v. 124, p. 10,735). However, the geologically based undertow concept has not yet influenced the geodynamics community. Nor has it come together to create a community of geologically oriented contributors to the problem of the driving mechanism of plate tectonics. It is time!