The Keweenawan sequence is a failed rift or aulacogen.
True
False
The correct answer and explanation is:
Answer: True
Explanation:
The Keweenawan sequence refers to a major geological event involving extensive volcanic and sedimentary rock formations primarily found in the Lake Superior region of North America. This sequence is part of the Keweenawan Rift, which formed approximately 1.1 billion years ago during the Proterozoic Eon.
The Keweenawan Rift is classified as a failed rift or aulacogen. But what does that mean?
- Rift: A rift forms when the Earth’s crust begins to pull apart due to tectonic forces, causing thinning and the development of a valley-like structure.
- Failed rift (aulacogen): Sometimes, a rift begins to form but never fully develops into a new ocean basin or divergent plate boundary. Instead, it “fails” and remains as a geological scar or basin filled with sedimentary and volcanic rocks. This leftover feature is called an aulacogen.
Why is the Keweenawan Rift considered a failed rift?
- Initial Rifting: The Keweenawan Rift formed as a continental rift, part of an attempt to split the ancient supercontinent Rodinia.
- Volcanism and Sedimentation: The rifting produced massive basaltic lava flows and thick sedimentary sequences—the Keweenawan sequence—preserved today in the Lake Superior region.
- Failure to Progress: The rift never succeeded in splitting the continent fully to create a new ocean basin. Instead, the rift “failed,” becoming a structurally weakened zone filled with the Keweenawan volcanic and sedimentary deposits.
- Modern Geology: Today, the Keweenawan Rift stands as evidence of this failed attempt at continental breakup and is studied for its economic mineral deposits (like copper and nickel) often associated with such rift systems.
Summary:
The Keweenawan sequence is part of the Keweenawan Rift system, which is a classic example of a failed rift or aulacogen — an aborted attempt at continental rifting that resulted in a geological basin filled with volcanic and sedimentary rocks rather than a new ocean basin. Therefore, the statement is True.