- #How to read a ternary diagram plutonic rocks how to
- #How to read a ternary diagram plutonic rocks plus
These diagrams are used to illustrate interactions between parts within a system. There are 3 types of Interaction diagrams Sequence diagrams, communication diagrams, and timing diagrams.
#How to read a ternary diagram plutonic rocks how to
All three are without any quartz or feldspars (instead they have feldspathoid minerals), tephrite has less than 10 percent olivine, basanite has more, and foidite is predominantly feldspathoid.This sequence diagram tutorial is to help you understand sequence diagrams better to explain everything you need to know, from how to draw a sequence diagram to the common mistakes you should avoid when drawing one. The division between foidite, tephrite, and basanite is dashed because it takes more than just alkali versus silica to classify them. That determination requires studying thin sections. Trachyte has less than 20 percent Q, trachydacite has more. Trachyte and trachydacite are distinguished by their quartz content versus total feldspar. Basaltic trachyandesites are likewise divided into mugearite and shoshonite, and trachyandesites are divided into benmoreite and latite. Trachybasalts are subdivided by the alkalis into sodic and potassic types named hawaiite, if Na exceeds K by more than 2 percent, and potassic trachybasalt otherwise. As igneous rocks evolve during their time beneath the Earth's crust, their compositions tend to move upward and rightward on this diagram. Geologists usually use the TAS classification because it's more consistent.
#How to read a ternary diagram plutonic rocks plus
Total alkali (sodium plus potassium, expressed as oxides) is a fair proxy for the alkali or A-to-P modal dimension of the volcanic QAP diagram, and silica (total silicon as SiO 2) is a fair proxy for the quartz or Q direction. Volcanic rocks are usually analyzed with bulk chemistry methods and classified by their total alkalis (sodium and potassium) graphed versus silica, hence the total alkali silica or TAS diagram. Rare rocks including carbonatite, lamproite, keratophyre, and others that are "off the chart.".Rocks with isolated larger grains (phenocrysts) may yield distorted results.Gabbros, which can be further classified according to three modes (P/olivine/pyx+hbde).Rocks with M above 90: Ultramafic rocks have their own ternary diagram with three modes (olivine/pyroxene/hornblende).Rocks without enough silica to yield quartz: These instead contain feldspathoid minerals and have their own ternary diagram (F/A/P) if they are phaneritic.Aphanitic rocks: These are classified by chemical, not mineral content.A large proportion of igneous rocks aren't suited for this classification method: The corresponding volcanic rock types are called rhyolitoids, but not very often.
The middle three plutonic rock types - granite, granodiorite and tonalite - are together called granitoids.
For plutonic rocks, gabbro and diorite have plagioclase with a calcium percentage (anorthite or An number) above and below 50, respectively. Which name to use depends on the composition of the plagioclase. Notice that the rock names at the P vertex are ambiguous. That's the official definition of the fields, and you can calculate your rock's position that way too. Notice that the lines that fan downward from the Q vertex are based on values, expressed as percentage, of the expression P/(A + P), meaning that each point on the line, regardless of the quartz content, has the same proportions of A to P.(Naturally, the number for A will also be there.) Read its name from the field in the diagram. The point where the lines for Q and P meet is your rock.That will be a line parallel to the left side.
Measure along one of the sides, then draw a horizontal line at that point. Draw a line on the ternary diagram below to mark the value of Q, zero at the bottom and 100 at the top.Discard M and recalculate Q, A and P so that they add up to 100 - that is, normalize them.Determine the percentage, called the mode, of quartz (Q), alkali feldspar (A), plagioclase feldspar (P), and mafic minerals (M).In plutonic rocks, all of the minerals are crystallized into visible grains. The QAP ternary diagram is used to classify igneous rocks with visible mineral grains (phaneritic texture) from their feldspar and quartz content. (c) 2008 Andrew Alden, licensed to ( fair use policy) Igneous Rock Classification Diagrams Click the image for a larger version.
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