How North America Almost Separated Into Two Pieces
SciShow・9 minutes read
1.1 billion years ago, Laurentia experienced the Midcontinent Rift, where volcanic rocks formed from massive magma eruptions, leading to many unanswered questions about its formation. Geologists believe the rift was influenced by the breakup of Amazonia, eventually ceasing due to the separation of the continents and resulting in the Grenville orogeny.
Insights
- The Midcontinent Rift, occurring 1.1 billion years ago, was a geological event where massive magma eruptions led to the formation of flood basalts in central North America, indicating a rift zone where tectonic plates thinned and split.
- The Wilson Cycle, explaining the cyclical process of continents breaking apart to form oceans, sheds light on the Midcontinent Rift's formation as influenced by the breakup of Amazonia from Laurentia, resulting in passive rifting and the eventual cessation of the rift due to stress relief on Laurentia post-breakup.
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Recent questions
How old are the rocks found in Laurentia?
1.1 billion years old
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Summary
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1.1 Billion Years Ago: Midcontinent Rift Formation
- 1.1 billion years ago, Laurentia, which later became central North America, was undergoing a significant geological event known as the Midcontinent Rift.
- Geophysicists in the 1940s discovered anomalies in gravity maps across the U.S., leading to the identification of the Midcontinent Gravity High and dense volcanic rocks connected to it.
- The rocks found were 1.1-billion-year-old flood basalts, formed from massive magma eruptions that cooled into basalt.
- Geologists have theorized that the Midcontinent Rift was a rift zone where tectonic plates thinned and began to split, but many questions remain about its formation and cessation.
- The Wilson Cycle explains the predictable pattern of continents breaking up to form oceans, with the continents at the end of this cycle 1.1 billion years ago.
- The Midcontinent Rift's formation was influenced by the breakup of Amazonia from Laurentia, causing passive rifting and the creation of microplates.
- The flood basalts in the Midcontinent Rift were remnants of an active rift, where a mantle plume caused the crust to thin, break, and fill with magma.
- The rift eventually ceased due to the relief of stress on Laurentia when Amazonia broke away, leading to the compression of the area and the formation of the Grenville orogeny.
