Saturday, August 11, 2012


While on vacation last week to Montreal, I learned that Mont Royal sits on a volcanic complex or more precise is a remnant of one.   In particular, 125 mya southern Quebec, Canada was above a volcanic hotspot (region where magma is close to the surface a.k.a. plume).  Mont Royal (or Mount Royal) as well as the rest of the Monteregian Hills are the remains since they are more resistant to erosion.  The hotspot known as the New England Hotspot, is similar to the more famous hotspots currently over Hawaii and Yellowstone.

Apparently, the hotspot had its beginnings 200 mya in an area northwest of Hudson Bay, as the plate moved the plume was recorded in 150 million year old rocks in Ontario.  Continued movement of the North American Plate produced Mont Royal 125 mya.  It was recorded again in rocks from the White Mountains of New Hampshire and from 100 to 80 mya the hotspot created the New England Seamount chain of the coast of North America.  The hot spot became active again 75 mya as it produced the Corner Rise Seamounts.  The Mid-Atlantic ridge has overridden the hotspot and formed the Great Meteor Seamount chain 20 to 10 mya.

Figure 1 (from NOAA)

Figure 1 shows the plate movement over hotspot from formation of Mont Royal ~125 mya to the Great Meteor Seamont chain ~10 mya.

For the rock hounds (weird people who worry about such things and collect them), the Mont Royal country rock is a grey limestone (CaCO3) which was intruded  by magma.  Where the magma was in contact with the limestone marble was produced.  Inside the chamber the magma crystallized to form a dark gabbro of which I have a sample [ROCK HOUND].  The gabbro consists of the following minerals; pyroxene ([Fe,Mg]Si2O6), olivine ([Fe,Mg]SiO4), and plagioclase (CaAl2Si2O8).

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