ESCI 111 Exam 1

what is magma? what is in magma?
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Terms in this set (19)
intrusive: aka plutonic rocks; form when magma crystallizes at depth; observes at Earth's surface in locations where uplifting and erosion have stripped away the overlying rocks; occur in the White Mountains, New Hampshire; Stone Mountain, Georgia; Mount Rushmore in the Black Hills of South Dakota; and Yosemite National Park, California

extrusive: aka volcanic rocks; form when molten rock solidifies at the surface; when lava solidifies of when erupted volcanic debris fall to Earth's surface; abundant in western portions of the Americas, where they make up the volcanic peaks of the Cascade Range and the Andes Mountains; also many oceanic islands, including the Hawaiian chain and Alaska's Aleutian Islands
Aphanitic; fine-grained; small crystals; light, intermediate, or dark in color
Phaneritic: coarse-grained; can distinguish the individual minerals without a microscope
Porphyritic: large crystals embedded in a matrix of smaller crystals
Vesicular: nearly spherical voids are left by gas bubbles;
Pyroclastic: fragmental; formed from the consolidation of individual rock fragments ejected during explosive volcanic eruptions; particles may be very fine ash, molten blobs, or large angular blocks torn from the walls of a vent during eruption
Pegmatitic: coarse-grained; crystals larger than one centimeter in diameter; most occur as small masses or thin veins within or around the margins of large intrusive igneous bodies
sills: horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds or other rock structures
laccoliths: igneous intrusions that can lift the sedimentary strata they penetrate, so as to arch the beds above while leaving those below relatively flat
dikes: discordant bodies that form when magma is forcibly injected into fractures and cut across bedding surfaces and other structures in the host rock
batholiths: the largest intrusive igneous plutons; occur as mammoth linear structures several hundred kilometers long and up to 100 kilometers wide; can find them in Sierra Nevada, California: Coast Mountains of western Canada into southern Alaska, Peru; produced by hundreds of discrete injections of magma that form smaller plutons that intimately crowd against or penetrate one another