Download English 301 definitions assignment

Assignment 1:3 Definitions
Introduction:
The objective of this assignment is to explore how to define a technical term to a non-technical
reader. We will describe our term as a parenthetical definition, a sentence definition and an
expanded definition. The definition that each reader chooses to study will depend on the
amount of detail they are wanting, as each type of definition provides a different level of detail.
Definition of “Opheolite”
Parenthetical definition:
An ophiolite (sequence of igneous rocks) is formed from the submarine eruption of magma
which is then exposed above sea level and thrusted onto continental rocks.
Sentence definition:
An ophiolite is a sequence of igneous rocks that are produced as a result of parts of the upper
mantle and crust being erupted in a submarine environment and then are later exposed above
sea level as a part of continental rock.
Expanded definition:
An ophiolite is an igneous rock that is was produced in a submarine environment and was then
thrusted onto a continental plate. Ophiolites are used as models for us to understand what
processes occur at mid-ocean ridges and how much of the ocean floor is formed. At mid-ocean
ridges, magma is erupted underwater and is mixed with the
sediments on the ocean floor which creates layers in the
rock (figure 1) throughout the eruption and deposition
stages. The base of the ophiolite consists of sediments
(carbonates) that were already on the sea floor. Following
a sediment layer, there is a layer of peridotites, which are
course-grained igneous rocks composed of large minerals
(mostly olivine and pyroxene). The peridotites originate
from the mantle magma that was sitting under the midocean ridge crest. There is then a layer of igneous rock,
mainly composed of the minerals plagioclase and
clinopyroxene, called gabbro. This gabbro layer is formed
as a result of crystallization and settling out of certain
minerals in the magma chamber. Above the gabbro layer,
there is a layer of dikes, which fed magma upward, as well
as a layer of volcanic rocks (pillow basalts). Pillow basalts
form when magma is erupted from the mid-ocean ridge and then cools very quickly in the
ocean water, this process produces a “pillow” look. Often there will also be another layer of
sediment on top of the layers of igneous rock that were deposited proceeding the formation of
the igneous rock. As a result of tectonic activity, the ophiolite structure is thrust up on the edge
of a continent where it becomes exposed above sea level. This process allows geologists to be
able to study them and better understand what processes occur at mid-ocean ridges.
Works Cited:
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Peters, Tj. Ophiolite Genesis and Evolution of the Oceanic Lithosphere Proceedings of the
Ophiolite Conference, Held in Muscat, Oman, 7-18 January 1990. Springer Netherlands,
1991. Web. 31 Jan. 2017.
Oregon State University
http://volcano.oregonstate.edu/ophiolites. Accessed 30 Jan 2017.
U.S. Geological Survey
https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=ORJu;0. Acessed 30 Jan
2017.
Visual:
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Oregon State University
http://volcano.oregonstate.edu/ophiolites. Accessed 30 Jan 2017.