About 1.1 billion years ago, the oldest and most structurally stable part of North America, called Laurentia – was rapidly heading south towards the equator. Laurentia eventually slammed into other lands on Earth during the Grenville orogeny, forming the supercontinent Rodynia.
Laurentia’s path during that period is known thanks to its paleomagnetic properties. By tracking the direction and magnetism of the rocks in the lithosphere, scientists can approximate the relative position and movement of Laurentia leading to the formation of Rodynia.
Rocks along Lake Superior in northern Wisconsin and Michigan are particularly important for tracking Laurentia’s movements. These rocks were dominated by red sandstone, siltstone, and mild conglomerates, but were deposited during extensive deposition caused by rifts in the central North American continent and are present in hematite-like iron oxides. Hematite can acquire magnetization when deposited. This records where the rocks were associated with the Earth’s poles at the time.
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Unfortunately, existing paleomagnetic records are undermined by gaps between 1075 million and 900 million years ago, limiting our understanding of how, when and where Rodynia was formed.
To fill this data gap, Fuentes et al. New samples were collected from the Freda Formation near Lake Superior. The authors combined these data with age modeling of stratigraphy to estimate the location of new sedimentary pale or geomagnetic poles at specific times in the past.
Previous studies have shown that for 30 million years, from 10 to 110 to 180 million years ago, Laurentia moved from about 60°N to 5°N at a rate of 30 cm (12 inches) per year. The study showed that over the next 30 million years, Laurentia’s progress slowed to 2.4 cm (1 inch) per year across the equator.
The slowing of aleocentinent during Freda formation deposition is consistent with the onset of the Grenville orogeny. The results confirm that at this interval a stagnant single lid regime was effective in which the lithosphere operates as a single continuous plate rather than as a multiple independent plate.
This article was originally published on eos.org. Please read the original article.
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