Trondhjemite
“The pale granite of the early Earth”
Trondhjemite is a light-colored, sodium-rich intrusive igneous rock belonging to the tonalite-trondhjemite-granodiorite (TTG) suite. These rocks are among the oldest on Earth and formed the cores of the earliest continents during the Archean eon, over 2.5 billion years ago.
plagioclase (oligoclase), quartz, biotite (minor), hornblende (minor)
Trondheim (Norway), Pilbara (Western Australia), Canadian Shield, Barberton (South Africa), Finland
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TTG rocks like trondhjemite make up much of Earth's oldest continental crust — they tell us that plate tectonics or a similar process was already operating over 3 billion years ago.
Test Your Knowledge
Why are TTG (tonalite-trondhjemite-granodiorite) rocks significant for understanding early Earth?
Photo Attribution
Title: Grimstad e39 inntjore west IMG 3853 geology tonalite-trondhjemite and gneiss.JPG
Author: Bjoertvedt
License: CC BY-SA 3.0
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