Seeing the Craton

Granite quarry near Milbank, South Dakota, in the southwest part of the Superior Craton.

"Craton" comes from the Greek word κράτος, meaning strength.

Seeing the Craton 

Northeast South Dakota, sculpted by glaciers,

landscapes so young, almost infantile,

ice melted just 12,000 years ago.

Glacial floods scoured a deep oversized

valley for the Minnesota River.

I went there to see the craton.

Craton—aged worn-down but strong

rocks hinting at what they once were:

volcanic, sedimentary, intrusive

2.6, 3.5, maybe even 4 billion years ago.

Older even than plate tectonics—

mad dance of Earth's giant plates

recycling crust and leaving none

older than ca. 2 billion years

except for cratons.

Cratons, why are you still here?!

You reside on every continent

yet we know so little.

Perhaps these elderly cratons

wear exceptionally thick undercoats

donned before tectonic chaos began,

back when mantle was hotter

solidifying into stronger threads.

Will they ever tell us?

"cratons are like great-grandmothers at family gatherings, while younger crust moves excitedly around them, they sit quietly, occasionally remarking on how different things were when they were young." Simon Wellings, Cratons – old and strong

2.6 billion-yr-old Milbank granite: brick red feldspar, gray smoky quartz, black biotite mica.

Milbank granite holds a high gloss polish (note reflections); Dakota Granite offices.

Inside the Milbank Chamber of Commerce building.

Old quarry, now accessible to the public (45.2085101 -96.5168962).

Sources

Frost, CD, et al. 2023. Creating Continents: Archean Cratons Tell the Story. GSA Today 33.

Kirk, K. 2023 (March). Dakota Mahogany: Core of the Continent. Natural Stone Institute.

Paul, Jyotirmoy. 2021. Cratons, why are you still here? Eos, 102, 25 March. 

Wellings, S. 2012 (December). Cratons – old and strong Metageologist