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Proterozoic Time Stitch Large Quilt

Tectonic elements of North America, with the sedimentary cover removed.

Back to building the really old, central parts of Canada! Now, the old cratons get stitched together into a giant quilt which will cover much of the continent.
When the old microcontinents collided, they pushed all that had been between them together into collisional orogens, including newly formed magmatic material (called "juvenile" rocks) and accreted oceanic terranes, such as islands and groups of islands.

Take a look, for example, at the northwestern corner of North America. The ancient Slave geological province is surrounded by three different domains called Wopmay (in the west), Taltson (to the south), and Thelon (on its east side). What are they?

The Wopmay terrane was already over the hump at about 2,400 to 2,000 Ma years when it was attached or "accreted" to the Archean Slave protocraton between 1,900 and 1,700 Ma, forming the Wopmay orogen. The Taltson terrane, on the other hand, is a magmatic arc and relative youngster, whose plutons are 1,990 to 1,950 Ma. The Thelon terrane also is an orogen, i.e. a mountain belt. It was formed through an oblique collision between the Slave and Rae provinces. This happened 1,970 to 1,920 Ma. It is the oldest orogen along which Archean provinces were welded to each other.

The Superior Province is the largest component of the old continent, a typical part of the Canadian Shield. The Superior province collided with the Hearne and Rae Provinces to the north and northwest, which also are of Archean age, at about 1,900 to 1,800 Ma.

This collision formed the Trans-Hudson Orogen. It extends from the central United States across Manitoba and Saskatchewan. Then, it turns east and northeast across the Hudson Bay to northern Quebec and Ungava Bay, where the orogen is named New Quebec Orogen, completing the long weld or stitch between the Superior, Hearne and Rae Archean provinces.

To the northeast, the Nain Province includes rocks older than 3,800 Ma, which have been highly metamorphosed. By 2,600 Ma, Nain province was complete, including its eastern extension into Greenland (and beyond, to Europe). Remember how we can tell the ages of rock formations? By looking at the earth scientists' reliable atomic clock — by measuring the known rate of decay of radioactive isotopes.

Look again at our map, the "Tectonic elements of North America," this time at the northeast corner, where the northeastern edge of the Superior Province juxtaposes the southwestern one of the Nain Province. One would have been ill advised to stand between them, because these two old cratons did what eventually they seem destined to do, squeeze and crunch together what lies between them, compressing wide regions, oceans, and so on, into relatively narrow mountain belts or orogens.

In this case, it happened to include an eastern extension of the Rae province which, we saw earlier, was involved in squeezing the Trans-Hudson Orogen against the Superior province, creating in this region the New Quebec Orogen, an easterly relation of the Trans-Hudson Orogen.

On the other side of the Rae Province (also known as Eastern Churchill Province here) the crunch from the Nain Province created the Torngat Orogen. Perhaps, we should switch to a detailed sketch of this area.

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