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Granite and other intrusive rocks

Granite and Intrusives Map

The boundary between the western and central basement rocks is studded with granite plutons and other intrusions and many more occur throughout the West Coast.

These plutons formed from melts that ascended through the crust and pooled within several kilometres of the surface. Their large crystals were the result of very slow cooling compared to fine grained volcanic rocks.The heat of the plutons also metamorphosed the rocks they pooled against resulting in new minerals such as biotite and garnet.

Two major pulses of pluton intrusions are known; the first between 370 and 320 million years ago and another around 130 to 105 million years. Both of these pulses occurred as ancient plate boundary zones ceased activity or moved elsewhere.

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