Earth's anomalous middle-age magmatism driven by plate slowdown
C O'Neill1,2, M Brown3, B Schaefer4
1Department of Earth and Environmental Science, Macquarie Planetary Research Centre, Macquarie University, Sydney, 2109, Australia. thecraigoneill@gmail.com.
Scientific Reports
|June 21, 2022
Summary
Plate tectonics slowed during the Proterozoic, causing environmental stability. This slowdown also led to higher mantle temperatures, influencing magmatism and extreme metamorphism.
Area of Science:
- Geology
- Geophysics
- Earth Science
Background:
- The mid-Proterozoic era, known as the "boring billion," featured stable environments with low oxygen fluctuations and mildly oxygenated oceans.
- Subdued tectonic activity, indicated by long-lived passive margins, is hypothesized as the cause of this environmental stability.
- The Proterozoic displays unique magmatic (anorthosites, Rapakivi granites) and metamorphic records, with peak thermobaric ratios during the Mesoproterozoic.
Purpose of the Study:
- To develop a method for calculating plate velocities from passive margin data.
- To quantitatively constrain Proterozoic plate velocities and test the hypothesis of a tectonic slowdown.
- To model the consequences of a Proterozoic plate slowdown on mantle temperatures, magmatism, and metamorphism.
Main Methods:
- Calculating plate velocities from passive margin records, benchmarked against Phanerozoic data.
- Applying this method to Proterozoic geological observations.
- Utilizing mantle evolution models to simulate the effects of slower plate tectonics.
Main Results:
- The study provides the first quantitative constraints on Proterozoic plate velocities, confirming a significant slowdown.
- Higher mantle temperatures are linked to the slower plate velocities during this period.
- Increased intrusive magmatism and extreme thermobaric ratios in metamorphism are associated with the slowest plate velocities.
Conclusions:
- The Proterozoic plate slowdown explains both environmental stability and unique geological features.
- Higher mantle temperatures resulting from the slowdown facilitated the formation of massif anorthosites and Rapakivi granites.
- Extreme crustal metamorphism conditions were a direct consequence of reduced plate tectonic rates during the Mesoproterozoic.
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