![igneous rock ternary diagram igneous rock ternary diagram](https://www.thoughtco.com/thmb/8rL1plDQ3b5g88OgAMg-zXG4-kI=/600x555/filters:no_upscale():max_bytes(150000):strip_icc()/600QAPvolcanic-56a367bb5f9b58b7d0d1c837.jpg)
The PCA analysis yields two principal components (PC1 and PC2), which capture 39.23% and 35.17% of total variability, respectively. To overcome this limitation, the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis (PCA) of a large dataset derived from unweathered igneous rocks and their weathering profiles. However, the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock. Finally, the MFW diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock.Ībstract = "Chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering. Third, the W index is applicable to a wide range of felsic, intermediate and mafic igneous rock types. Second, the W index provides robust results even for highly weathered sesquioxide-rich samples. First, the W index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides, whereas most conventional indices are defined by between two and four oxides. The W index has a number of significant properties that are not found in conventional weathering indices. The M and F vertices characterize mafic and felsic rock source, respectively, while the W vertex identifies the degree of weathering of these sources, independent of the chemistry of the unweathered parent rock. Subsequently, PC1 and PC2 were then mapped onto a ternary diagram (MFW diagram). In contrast, PC2 is the direction along which the projections of unweathered felsic, intermediate and mafic igneous rocks appear to be best discriminated therefore, PC1 and PC2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock. The extent of weathering is reflected by variation along PC1, primarily due to the loss of Na 2O and CaO during weathering.
![igneous rock ternary diagram igneous rock ternary diagram](https://images.slideplayer.com/14/4182083/slides/slide_6.jpg)
Chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering. The official field numbers and rock definitions can be found in the description of the figures below, or see Coarse-grained ("plutonic") crystalline igneous rock or Fine-grained ("volcanic") normal crystalline igneous rock. Some of the fields are assigned to 2 or 3 rock types, which are further distinguished by their mafic mineral content or plagioclase type ( calcic or sodic). They mostly have similar field divisions, so most volcanic rocks have a corresponding plutonic rock of equivalent mineralogy (for example, rhyolite and granite). There are 2 QAPF diagrams, one for coarse grained ( plutonic) or intrusive igneous rocks, one for fine grained ( volcanic) or extrusive igneous rocks. The QAPF diagram is divided into 15 basic fields that define ranges of mineral compositions for the different classes of rocks. The corners represent cases in which only one felsic component is present, effectively 100% of either quartz, alkali-feldspar, plagioclase or foid.īecause foids and quartz are mutually exclusive in an igneous rock, the QAPF classification is always based on a maximum of 3 components, either QAP or APF, and the compositions of the rocks are plotted in either the upper or lower triangle. It is made of two ternary diagrams with the corners Q, A, P and F, A, P, adjoined to each other along their A-P edge. The composition of the rocks are plotted into a diamond-shaped coordinate system, the QAPF diagram, also known as Streckeisen diagram (named after the author of the original article). Within the QAPFM classification scheme proposed by the IUGS, rocks with less than 90 vol-% mafic minerals are classified by their content (in volume-%) of: