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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: 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: Oregon State University http://volcano.oregonstate.edu/ophiolites. Accessed 30 Jan 2017.