Johnson & Pollard (7) recognise that laccolith
formation is characterised by three distinct stages.
The 'bun' may be the result of what is known on Earth as a laccolith
, an intrusion formed by magma pushing up from below.
Whilst he was in fact describing an actual geological feature--a laccolith
which he saw as resembling a cactus --he was also, tongue-in-cheek, commenting on what he saw as an absurd number of "-lith" words in the field of Geology.
Some geologists believe Devils Tower began as a laccolith
, a buried intrusion of igneous rock; others say it is a volcanic plug, the leftover spout of an extinct volcano.
This mushroom shaped, shallow intrusive body is called a laccolith
Ongoing field mapping of Cretaceous sedimentary rocks has identified numerous intrusions that appear to be cross cut by Laramide and post-Laramide deformation in the South Persimmon Gap Laccolith
(SPGL) and Dagger Mountain areas.
Kelsey-Fry (still representing Fallon) observes that Murrihy "opined", a word that, along with rostral and laccolith
, you very rarely hear.
It was probably a laccolith
that was exposed by erosion and tectonic uplift, evidenced by the occurrence of a fault line a few kilometers from the site.
The rhyolite body is a mushroom-shaped laccolith
, slightly elongated northwest-southeast and dipping gently to the southwest.
The magmatic sequence led to the formation of a nested Christmas-tree laccolith
complex with a total thickness of about 2400 m of porphyritic rocks emplaced at depths of 2--3.
A locally sulfidic laccolith
intrusive of quartz-eye porphyry of the Caetano Tuff underlies the skarns, and this may have been the source of the IP anomaly.
Sills, dykes and related laccoliths
are the physical record of the transfer of magma through the upper crust.