I'm studying Plutonic (Intrusive) rocks and I really don't understand the difference between Plutonic Rocks that form in Sills and Dikes from the so called subvolcanic rocks, also known as a hypabyssal rocks. Aren't they the same? Why?


1 Answer 1


Main difference between a subvolcanic verses a plutonic is depth at which the rock solidified at from its molten state. Plutonic implies a depth greater than subvolcanic by definition but I am sure there is some overlap between shallow end of plutonic and subvolcanic. Depth of emplacement for plutonic would mostly be much greater than 2 km.

Plutonic is an igneous rock formed by solidification at considerable depth beneath the earth's surface.

Subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at medium to shallow depths (<2 km) within the crust.

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    $\begingroup$ Interesting, I had no idea. But in the last line shouldn't it be "(<2 km)"? $\endgroup$ Jan 26, 2019 at 15:39
  • $\begingroup$ What confuses me is that dikes and sills are by deffinition plutonic structuctures ( at least from where i am studying; Tarbuck). And it says that they DO form at shallow depths. So, they should be subvolcanics. $\endgroup$
    – Karl
    Jan 26, 2019 at 17:06

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