Structure and Geographical Extent
The Blake River Megacaldera Complex consists of mainly mafic to intermediate volcanic flows and less abundant felsic volcanic flows and intercalated pyroclastic rocks, which underwent three stages of major volcanic activity.
- The first phase resulted in the creation of the 40–80 km in diameter, eastwest striking Misema Caldera which has been dated to 2704-2707 Ma. It is a coalescence of at least two large mafic shield volcanoes that formed more than 2703 million years ago.
- The second phase resulted in the creation of the 15–30 km in diameter, northwest-southeast New Senator Caldera which formed 2701-2704 Ma. Its formation consists of thick massive mafic sequences which has inferred to be a subaqueous lava lake during the early stages of the caldera's development.
- The third phase of activity constructed the classic east-northeast striking 2696 Ma Noranda Caldera which contains a 7-to-9-km-thick succession of mafic and felsic rocks erupted during five major series of activity.
The Blake River Megacaldera Complex is considered a supervolcano due to its great size and its multiple dikes and vents. The Misema Caldera is in the order of 3500 to 4000 km2, making the complex similar to the Yellowstone Caldera in Wyoming, Lake Toba in Indonesia and strikingly similar in structure to the Olympus Mons caldera on Mars. As a result, the Blake River Group is best categorized as a meganested caldera complex.
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