Chapter 9: Problem 8

Are the rocks that become ophiolites within a mountain chain older or younger than molasse deposits that form along the mountain chain?

Short Answer

Expert verified

Ophiolites, which form during the early stages of the orogenic process, are older than molasse deposits that form during the late stages of the process. Therefore, rocks that become ophiolites within a mountain chain are older than molasse deposits that form along the mountain chain.

Step by step solution

Understand ophiolites

Ophiolites are slices of oceanic lithosphere, which predominantly consist of ultramafic and mafic rocks such as peridotite, gabbro, and basalt, that have been thrust onto the edge of a continental plate during the process of plate tectonics. Their formation is commonly associated with the early stages of the collision of two tectonic plates, one oceanic and one continental, causing the heavier oceanic plate to subduct beneath the lighter continental plate. As this subduction occurs, a portion of the oceanic plate is scraped onto the continent, resulting in the formation of an ophiolite.

Understand molasse deposits

Molasse deposits are conglomerates, sandstones, and shales deposited along a mountain chain due to erosion. They typically originate from a rising mountain range, near the end of the orogenic process (mountain building). As a mountain range forms, erosion removes sediments from the mountain chain, and these sediments are transported by rivers, streams, and other means to low-lying areas, where they accumulate to form molasse deposits.

Compare the formation processes of ophiolites and molasse deposits

To determine whether ophiolites or molasse deposits are older, we need to compare their formation processes. Ophiolites form during the early stages of the collision of two tectonic plates, which marks the beginning of the orogenic process. On the other hand, molasse deposits are associated with the late stages of the orogenic process, as they form due to the erosion of a rising mountain range.

Determine the relative ages of ophiolites and molasse deposits

Based on the comparison of the formation processes, we can conclude that ophiolites are older than molasse deposits. This is because ophiolites form during the early stages of the orogenic process, whereas molasse deposits form during the late stages of the process. As a result, rocks that become ophiolites within a mountain chain are older than molasse deposits that form along the mountain chain.

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Are the rocks that become ophiolites within a mountain chain older or younger than molasse deposits that form along the mountain chain?

Short Answer

Step by step solution

Understand ophiolites

Understand molasse deposits

Compare the formation processes of ophiolites and molasse deposits

Determine the relative ages of ophiolites and molasse deposits

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