If what you say were true, then how do explain the composition of the land under the continental USA.
deep-time does add up.
Do you know that plate tectonic moves roughly at the speed at which your fingernails grow? Yet we know that plates have literally moved across the globe's surface, that's what I mean when I say deep-time adds up. Miniscule changes add up to huge changes. after all 4,600,000,000 years makes for an awful lot of days. I'd love to add up the days, but we know that days were very short during the early part of Earth's formation and slowly increased with time, it would take a very smart person with a lot of time on their hands to do the calculations.
RESEARCH FOCUS: Understanding continental subduction: A work in progress
Mihai N Ducea, MARCH 01, 2016
Geology (2016) 44 (3): 239–240,
A study by Froitzheim et al. (2016, p. 223 in this issue of Geology) adds new constraints to our rapidly evolving ideas and models regarding the process of continental subduction.
Classic plate tectonics concepts suggested that continents do not subduct.
Instead, when two continents collide at a convergent boundary following the consumption of an ocean by subduction, they accommodate the shortening within the lithosphere, which is thickened up to twice the normal values. The subducted oceanic slab that brought the continents together stalls and eventually breaks off and sinks into the mantle due to its negative buoyancy.
In contrast to that view, modern petrologic, tectonic, and geophysical observations have completely changed this picture still prevalent in many textbooks: continental lithosphere does, in fact, subduct to great depths at major long-lived collisional boundaries, and the two colliding plates can be separated by a section of convective upper mantle (mantle wedge) similar to the case of oceanic subduction.
There are three important types of observations supporting those assertions.
First, the discovery over three decades ago (Chopin, 1984) of ultrahigh-pressure (UHP) metamorphic rocks—crustal rocks in which the stable silica polymorph at peak pressure temperature conditions was coesite—documented that continental crustal rocks have been buried to >90–100 km in some orogens. After their initial discovery in the Alps, …
Second, refined plate-tectonic reconstructions and plate kinematics models for the Indo-Asian collision (van Hinsbergen et al., 2012) since its beginning, as early as the Paleocene, make very specific predictions regarding the total amount of shortening along this margin, which is significantly more than what can be accounted for by crustal shortening in the Himalayas (DeCelles et al., 2011). More than 1000 km of Indian lithosphere are missing and must have been subducted under the Asian continent. …
Third, seismic images of the ongoing Pamir–Hindu Kush collision system show that Indian lithosphere is being subducted to as much as 500 km beneath the surface (Sippl et al., 2013).
Between these lines of evidence, a compelling case can be built for the fact that continental lithosphere (crust and mantle) are subductable to great depths and significant distances away from the collision’s principal suture. One can further assume that only a small fraction of subducted continental crust makes it back to the surface of Earth, making UHP rocks extraordinarily important. …
There’s plenty more articles to be found with a little judicious googling.
As for water, wow, that’s a whole new ball of wool to unravel, considering the discoveries of the past decades, but Maddy is demanding another walk, so perhaps later, because it truly is fascinating. You know that water helps lower the melting point of rocks? Do you know that some rocks actually hold water?