Both Uses

intrusion
in
A Prayer for Owen Meany
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Owen Meany used to say that we residents of Gravesend were sitting over a bona fide outcrop of intrusive igneous rock; he would say this with an implied reverence—as if the consensus of the Gravesend community was that the Exeter Pluton was as valuable as a mother lode of gold.†
p. 14.1

intrusive = unwelcome involvement
And it turned out that Owen Meany didn't know a metamorphic schist from an igneous intrusion—unless the latter was granite.†
p. 447.8 *

intrusion = an interruption or involvement that is unwelcome

Definitions:

(1) (intrusion)
an involvement or interruption that is unwelcome
(2) (meaning too rare to warrant focus)
In geology, intrusion can reference the forcing of molten rock into fissures or between strata of an earlier rock formation.