Suite · granite

Zoroaster Granite

The pale ~1.7-billion-year-old granite that intrudes the Vishnu Schist — the light dikes cutting the dark walls of the Grand Canyon's Inner Gorge.

Also known as: Zoroaster, Zoroaster Plutonic Complex

Proterozoic — long before animals, a world of microbes and bare rock

The world back then

Deep in the Proterozoic, about 1.7 billion years ago, and there's nowhere to stand — you're kilometers down in the crust, where molten granite is forcing its way into older rock as volcanic arcs slam together to build early North America. Blistering heat, crushing pressure, total dark. No air, no light, no surface, no life but single cells in a sea far above.

That frozen magma is the pink lightning laced through the black walls, and you drift past it in the daylight it took a billion years to reach. It cooled deep in the dark and rose miles just so you could glance at it between rapids. On top of the world, in the sun — the best seat in all of time.

Trail Talk

The non-geologist version — for when someone starts nerding out and you want in.

The gist: The pink veins cutting through the black rock at the bottom of the Grand Canyon — molten granite squeezed into the ancient basement.
Drop this: The light-on-dark pattern is the tell: pink granite forced into cracks in the darker Vishnu schist, then frozen solid. Roughly the same age, opposite color.
Or just say: The pink lightning frozen into the oldest walls in the canyon.
Rock band: Pink and white granite shot through the black schist like frozen lightning, light-on-dark, the oldest, brightest streaks in the whole canyon. Cosmic contrast, man — molten rock caught mid-strike a billion-plus years ago. Stare into the Granite Gorge and the whole light show hums.

Recognize it in the field

Typical color: pink to white (light-on-dark against the schist)
Weathers as: Light-colored dikes and plutons cross-cutting the dark schist — the classic light-on-dark pattern of the Granite Gorge walls.
Grain: coarse (granite) to very coarse (pegmatite)

Look for

pale granite and pegmatite dikes and plutons
cross-cuts the vertical schist foliation (discordant)
calc-alkaline, volcanic-arc affinity
no baking of the country rock (relatively shallow emplacement)

How this rock was made

Subduction-related arc molten-rock activity (magmatism) during the collisions that built early North America ~1.7 Ga.

The setting: deep-crustal arc molten-rock activity (magmatism) (Yavapai orogeny)

Intrusive bodies (plutons and dike swarms), not a bedded unit — extent throughout the Granite Gorges.

In the rock record

Zoroaster Granite you are here

Cuts across Vishnu Schist (an intrusive body, not a layer).

See the full regional rock columns →

Where to see it

Regions: Grand Canyon (Inner Gorge)

Upper and Lower Granite Gorges, Colorado River corridor

Float past it: Grand Canyon