Continental drift not push-me but pull-you, the Rockhall Plateau

 A funny thing happened when I showed my last blog post to my mom: "what is that blob right above where it says 'Atlantic Ocean'?". Widow and mother to geologists, she learned to read maps: she spotted the Rockhall Rise as it shows in the zoomed-in view below; it's also known as Rockhall Plateau (Perplexity), briefly a piece of crust left behind in the spreading of the North Atlantic. The tectonic plate margins, incl. the mid-Atlantic Ridge top right, are highlighted in cyan below. Same as the second-last blogpost showed interesting geomorphology only seen in North polar view, this portion of the far North Atlantic also shows better than in a normal or equatorial map view shown at right.

click to enlarge (can be slow), original

I first heard of the Rockhall Plateau in then-new plate tectonics classes by John Dewey & Kevin Burke (Can. Jour. Earth Sci.) @ Univ. of Calgary in 1980, and then Ed Farrar (Queen's U.) @ Queen's Uni. in 1982, resp. in W & E Canada. They distinguished rafts left behind like this, from fragments left in place like the Seychelles & Reunion in the Indian Ocean. The discussion resulted 40 yrs later in seeing tectonic plates dragged by sinking ocean trenches at the margins, rather than pushed by mid oceanic ridges at the center (Perplexity). See also this blog post about continent & ocean rafts & terranes re: exhuming my thesis 40 yrs later.

click to enlarge (can be slow), original

So what my mom spotted jumps out if you look at it carefully above:

• the Reykjanes Ridge portion of the mid-Atlantic Ridge shows a spread at a slight angle (dashed line) to the median itself (cyan), with matching original continental shelf margins (brown)
• the Rockhall Plateau is however separated from the UK Ireland mass by a trough with matching continental shelf outlines (blue), not unlike the original brown ones
• if the mid-oceanic ridge were the motor, the plateau would have been pressed against not separated from the NW Europe continental mass
• the small offset orphaned ridge next to the Faroe Islands further underscores the pull you rather than the push me aspect
• this is a patent example on geomorphology alone, and a keen eye, of the slab pull driver of plate tectonics, rather than ridge push or mantle drag theories detailed in the Perplexity link above.

Thanks to @John Nelson LinkedIn post here, w far superior cartography on global plate tectonics, inspired in turn by his daughter - this rattled about in my brain and y'all prompted me to post it - aptly enough, our posts bridge International Women's Day!