The Blake River Megacaldera Complex, also called the Blake River Group, is a giant subaqueous caldera cluster or a nested caldera system that spans across the Ontario-Quebec border in Canada.
The caldera complex is around 2700 million years old, consisting of a series of overlapping calderas of various ages and sizes. It lies within the southern zone of the Abitibi greenstone belt of the Superior craton and has an area of 3,000 km2.
The Blake River Megacaldera Complex has been a center of major interest since 2006 with numerous excursions at the international, national and local level.[1] It is a world-class metallotect with respect to both hydrothermal Cu-Zn massive sulfides and gold-rich massive sulfides.
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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 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.[2] As a result, the Blake River Group is best categorized as a meganested caldera complex.[3]
Calderas are usually collapsed structures between 2–100 km in diameter derived from either a single massive eruption, or as a result of a series of eruptions. Fractures will form around the edge of the chamber, usually in a roughly circular shape. These ring fractures may in fact serve as volcanic vents.
If the magma is rich in silica, the caldera is often filled in with ignimbrite, tuff, rhyolite, and other igneous rocks. Silica-rich magma is slow flowing, having high viscosity. As a result, gases tend to become trapped at high pressure within the magma.
When the magma gets near the surface of the Earth, the reduction in pressure causes the gas to expand quickly, resulting in explosions and the spread of volcanic ash over wide areas.
A silicic or rhyolitic caldera may erupt hundreds or even thousands of cubic kilometers of material in a single event. The pre-caldera structure can be either a stratovolcano or a shield volcano.