Plutonic Igneous Rocks

	Poorna's Physical Geology Pages	Updated on 05.05.15
	Plutonic Igneous Rocks

Welcome! Thanks for visiting the home page of Poorna Pal's Geology-101 (Physical Geology) class at the Glendale Community College. This is a 3-unit lecture class that satisfies the GE Physical Science requirement and therefore transfers to UC, CSU, USC and all other North American universities/colleges for the baccalaureate degree. This page describes the organization of the course, the schedules for broadcasts, class meetings, Tests and Final Examination, grading scheme etc., and provides links to some sites of interest, including Poorna's web-notes and hand-outs.

"Rock Cycle" ― a theoretical concept that relates tectonism, erosion, and the various rock forming processes to the common rock types ― plausibly began with the formation of granitic crust and granite, the most common plutonic rock is also what the "Rock Cycle" ends with.

Try the following links for interesting "Rock Cycle" presentations:

http://www.bbc.co.uk/education/rocks/rockcycle.shtml http://www.intel.com/education/unitplans/rockcycle/rock.htm

http://www.moorlandschool.co.uk/earth/rockcycle.htm

About Plutonic Igneous Rocks

How Igneous Rocks Form?

Visit the URL:
http://www.fi.edu/fellows/fellow1/
oct98/create/igneous.htm
for the animation of igneous rocks and for more information on the igneous rocks.

Igneous rocks are primary rocks in the rock cycle and form by solidifying from molten condition.

There are two kinds of igneous rocks: plutonic and volcanic.

Intrusive or plutonic rocks form from the slow cooling and solidification of magma.

These intrusive bodies can form either near-surface (volcanic necks or plugs, dikes and sills) or be deep-seated (plutons like stocks and batholiths).

The intrusive igneous rocks have phaneritic (or coarse grained) to porphyritic textures, compared to the porphyritic to aphinitic textures of extrusive igneous rocks.

Felsic (60-75% silica, with “free” quartz) composition dominates the intrusive or plutonic rocks (e.g., granites and grano-diorites), compared to the mafic (with ~50% silica, no “free” quartz) basalts in the case of extrusive or volcanic rocks. Gabbro, the plutonic equivalent of basalt, is mafic and diorite, the plutonic equivalent of andesite, is of intermediate composition.

The red and pink shaded regions in this geological map of California are intrusive igneous bodies. This map can be accessed at the California Geological Survey website http://www.consrv.ca.gov/cgs/information/geologic_
mapping/index.htm#Related%20Links.
These igneous intrusives form the bulk of the Sierra Nevada Ranges. Contrasted with these large batholiths are such more common though shallow or near-surface features as dikes and sills.

Granites and granitization complete the “rock cycle” as granite batholiths, the most common plutonics, often form in the core zones of folded mountain belts through the process of dynamothermal metamorphism. But then, note that the primordial crust too is likely to have been granitic.

Want to take a self-test on igneous rocks and processes? Try North Dakota State University’s Geoscience website at the URL: http://www.ndsu.nodak.edu/instruct/schwert/geosci/g120/igneous.htm	To view the samples of different igneous rocks, try the URL: http://www.dc.peachnet.edu/ ~pgore/geology/geo101/igneous.htm
For a plutonic rocks exercise using Bowen's reaction series, try the URL: http://web.clas.ufl.edu/users/phiggins/BowensRSEx.html