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Answers to How Granite Would Evolve on a Ternary DiagramLook at apexes of the ternary diagram to the right. Note quartz is at the top, but feldspar and lithics are combined in the lower left; this is because both of these weather into something else - matrix. So, matrix is in the lower right.
Question: >>>>> Now, assume a granite has 25% quartz and the rest feldspar and lithics (mafic minerals). Where would you plot it on the diagram?
Question 2: >>>>> Now assume the granite is going to weather, but not be transported or sorted. How would the composition change on the diagram?
Question 3: >>>>> Now transport and sort the sediment. What paths would the components take on the diagram?
Analysis: A granite is an igneous rock, and therefore has no matrix. If it has 25% quartz then we plot granite on the left side at the 25% level.
As the granite weathers, feldspar/lithics turn into matrix, so the composition moves toward the right side, the matrix side. Since there is no sorting, the feldspar/lithics and their weathering product, matrix, remain mixed with the quartz. And since quartz does not weather, its abundance must remain at 25%. Thus the evolution line can only move horizontally, and the farther it moves to the right the less feldspar/lithics there is and the more matrix, until on the right line all feldspar/lithics would be turned into matrix.
Finally, we transport and sort the sediment, such as at the shore, where quartz remains on the beach while the matrix (shale) drifts off shore to the shelf.
The point is, everything we have learned about sedimentary rocks over the past pages and pages of text and diagrams can all be summarized in this one simple diagram - if you understand and know how to read it. Such diagrams are quick, easy, and slick, and tell a geologist at a glance a world of information - without getting mired in all the technical details.
|Last Update: 10/26/00||