All lithographic and geochemical data show that Harris granite rocks are of A-type nature. Negative anomalies of Ba, Nb, Ti, Sr and Eu and enrichment in LILEs, especially Rb and Th, indicate the crustal origin of these rocks. The negative anomaly of Eu in the trace element pattern can be attributed to the separation of feldspar during crystallization or the presence of feldspar as a residual phase in the origin and the anomaly of P and Ti to iron-titanium and apatite oxides. Enrichment in LILE and HFSE elements with negative anomalies of Nb and Ti is a characteristic of subduction-dependent granites, usually attributed to the mantle origin, previously due to the metamorphic activity of fluids from sediments deposited by LILE and HFSE elements (Pearce, 1984), or may be the nature of magmas rooted from a subcontinent meteorite mantle formed during early subduction. In addition, enrichment at Th, Rb, and depletion at Sr, Eu, Ba, Nb, and Ti indicate that the granites are rooted in crustal lavas (Zhao and Zhou., 2007).All lithographic and geochemical data show that Harris granite rocks are of A-type nature. Negative anomalies of Ba, Nb, Ti, Sr and Eu and enrichment in LILEs, especially Rb and Th, indicate the crustal origin of these rocks. The negative anomaly of Eu in the trace element pattern can be attributed to the separation of feldspar during crystallization or the presence of feldspar as a residual phase in the origin and the anomaly of P and Ti to iron-titanium and apatite oxides. Enrichment in LILE and HFSE elements with negative anomalies of Nb and Ti is a characteristic of subduction-dependent granites, usually attributed to the mantle origin, previously due to the metamorphic activity of fluids from sediments deposited by LILE and HFSE elements (Pearce, 1984), or may be the nature of magmas rooted from a subcontinent meteorite mantle formed during early subduction. In addition, enrichment at Th, Rb, and depletion at Sr, Eu, Ba, Nb, and Ti indicate that the granites are rooted in crustal lavas (Zhao and Zhou., 2007).
please find the paper published in "Lithos 46 1999. 605–626" titled as "A review of the relationships between granitoid types..."
One warning about granite classification: There are many variables for origin, including depth of partial melt origination (P,T), fluid presence in the source and above, the composition of the protolith (s), age/maturity of crust and upper mantle, and many variations in tectonic mechanisms. "A'-types are by definition anorogenic, generated in extensional or certainly not compressional terranes. However, there are still diverse products possible from non-orogenic conditions. 'S' types, 'M' types, and "I" types can occur under varying tectonic conditions. The original classes were developed from a restricted region's evidence. It is best to specify each of the influential factors involved in granite generation, as opposed to simply providing a simplified class designation.
Typically, when we talk about A-type granites, we refer to granitoids that are Anorogenic in origin/emplacement and characterized by low water content. The are emplaced more frequently within intraplate continental rifting settings. In terms of geochemical compositional characteristics, high silica and alkalis and enriched specific REE composition including gallium, yttrium and cerium, typically, Ga/Al is high while Ba, P, Ti and Eu are generally depleted. The paper recommended by Hemayat Jamali is very useful for this subject matter and associated granitoids.
A-type granites are a type of igneous rock that form from the solidification of magma or lava. They are characterized by their high silica content, which gives them a felsic composition, and by their relatively low levels of iron and magnesium. A-type granites are typically light in color and may have a pink, red, or white hue.
Other characteristics of A-type granites include:
Coarse-grained texture: A-type granites tend to have large, easily visible mineral grains.
High potassium content: A-type granites often have high levels of potassium, which gives them a distinctive geochemical signature.
Low levels of mafic minerals: A-type granites typically have low levels of mafic minerals, such as biotite and hornblende, which are commonly found in other types of granites.
High levels of quartz: A-type granites often have high levels of quartz, which gives them a shiny appearance.
High levels of alkali feldspar: A-type granites tend to have high levels of alkali feldspar, which gives them a light color.
A-type granites are thought to form in a variety of tectonic settings, including within the continental crust and in island arcs. They are often associated with regional metamorphism and may be found in metamorphic belts.
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