These astounding photos by celebrated fashion photographer Chris Nicholls will have you in awe of the Canadian Shield

The dynamic rocks of the Parry Sound Shear Zone (pictured here) show the formation of the Grenville Province—the southeastern margin of the Canadian Shield, from Labrador to Lake Huron. As continents collided 1 to 1.3 billion years ago to form the supercontinent Rodinia, pale, quartz- and feldspar-rich gneiss and dark, iron-laden amphibolite were stretched, compressed, and layered like shingles. The exposed Grenville was the foundation of a mountain range that may have soared as high as the Himalayas and extended from Mexico to Labrador and into Europe, says Nick Eyles, a professor emeritus of geology at the University of Toronto and the author of Road Rocks Ontario. By about 750 million years ago, the Grenville Mountains had been worn down and then buried beneath younger Paleozoic rocks. “The rock cuts along Hwy. 400 are windows into the deep crustal roots of one of the world’s most famous collision zones,” says Eyles. “They record a major event in the earth’s geological history, preserved in our backyard.” This history is defined by the formation and breakup of successive supercontinents, explains Eyles. Over eons, landmasses drift under the influence of convection currents in the earth’s mantle, colliding to form supercontinents and then breaking into continents separated by oceans. “This continuous cycle has operated for at least three billion years,” says Eyles.

Hwy. 400 traverses the collision zone of ancestral North America and ancestral landmasses of South America—according to some models, at least—as Rodinia was slowly assembled and the ocean between these landmasses closed.

This photograph speaks to the life cycle of the Grenville Mountains. For the rocks on the left to deform plastically, folding like hot candy, the pressure and heat must have been extreme. At right, bands of pink rock “tell us about the cooling phase, when the mountains were in old age,” says Eyles. “Rocks as much as 30 to 40 kilometres underground were slowly uplifted and cooled as the mountains wore down.” The pink dykes, or intrusions, are pegmatite, which forms in cracks as magma cools slowly into large glassy crystals. “These mark the final demise of the once-mighty mountains, as they were levelled to create the undulating Canadian Shield,” says Eyles. “Much later, Ice Age glaciers scoured out the lake basins.” And even later, construction crews left vertical drill holes, remnants of blasting.

The banded rock here is migmatite, a type of gneiss that forms “just shy of the melting point,” says Eyles. “It’s an example of extreme metamorphism.” The layers, neither well-defined nor sharply bounded, show evidence of intermixing. “These rocks were so hot, they were almost melting,” says Eyles. Geologists can also relate the particular mix of minerals—each forming under specific temperatures and pressures—in metamorphic rocks to the depth at which they formed within the earth.

The two dark, oblong “pods” seen here are amphibolite, a metamorphic rock formed deep in the earth from basalt or similar volcanic rocks. The shape shows “that the amphibolite was so ductile from intense heat and pressure that it was pinched out,” says Eyles. Geologists use a French term for blood sausage—boudin—to describe these pods. The force of plates pushing together caused the amphibolite to stretch and break. And stacked boudins, one atop the other, is “a clear sign of intense deformation.”

The slant of the rocks above—dipping towards south-southeast—records the northwest thrust of South America onto the North America plate, explains Eyles. “We call that imbrication,” he says. “You’re looking at plates made of pre-existing older rocks being thrust over other ones. That completely transforms the original rocks. We don’t even know what the protolith, or parent rock, was because it’s been completely buggered up”—shaped, squished, and baked by innumerable forces over eons of time. “I spent a lot of time walking along the outcrops when they were building the 400,” says Eyles. Rock cuts, expecially newly blasted ones, have a charismatic appeal to geologists. “They’re clean, recent exposures,” but they are rapidly attacked chemically by rainwater and snowmelt, resulting in the oxidation and rusting of once-fresh rock surfaces. “It happens very quickly,” says Eyles. “Time marches on. It’s another expression of how the earth’s surface is always changing.”