Woods Hole Oceanographic Institution

Bedrock geology of the Thelon River drainage basin in Northern Canada. The average bedrock age, weighted according to area of lithologic units, is 2.3 billion years. It is one of the oldest large river basins on Earth. Lithologic units are color coded: blue: marine sediments (33.5%), yellow: continental sediments (1.3%), tan: intercalated sediments and volcanics (1%), light gray: felsic volcanic rocks, dark gray: basic volcanic rocks (3.7%), orange: intermediate intrusive rocks (0.7%), red: felsic intrusive rocks (21.3%), pink: metamorphic rocks (32%). The 87Sr/86Sr isotope composition of dissolved strontium in the Thelon river is fairly radiogenic (about 0.718) and typical of runoff from old shield areas. (Mark Miller)

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