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Schlieren textures are a particularly common example of granite formation in migmatites, and are often seen in restite xenoliths and around the margins of S-type granites. Ptygmatic folds are formed by highly plastic ductile deformation of the gneissic banding, and thus have little or no relationship to a defined foliation , unlike most regular ...
For example, Coastal Batholith of Peru consists of 7–16% gabbro and diorite, 48–60% tonalite (including trondhjemite), and 20–30% granodiorite, with 1–4% granite. [22] These TTG rocks in continental arc batholiths may partially originate from the magma differentiation (i.e. fractional crystallisation ) of the subduction induced mantle ...
Migmatite featuring felsic minerals, at Morton Gneiss Complex Granitization is an old, and largely discounted, hypothesis that granite is formed in place through extreme metasomatism . The idea behind granitization was that fluids would supposedly bring in elements such as potassium, and remove others, such as calcium, to transform a ...
Many of the minerals of these rocks are schillerized, as they contain minute platy or rod-shaped inclusions, disposed parallel to certain crystallographic planes or axes. The reflection of light from the surfaces of these inclusions gives the minerals often a peculiar appearance, e.g. the quartz is blue and opalescent, the feldspar has a milky ...
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock.
Metamorphism of crustal rocks in which peak temperature exceeds 900 °C, recognized either by robust thermobarometry or by the presence of a diagnostic mineral assemblage in an appropriate bulk composition and oxidation state, such as assemblages with orthopyroxene + sillimanite + quartz, sapphirine + quartz or spinel + quartz, generally at pressure conditions of sillimanite stability in ...
Most of the mineral evolution papers have looked at the first appearance of minerals, but one can also look at the age distribution of a given mineral. Millions of zircon crystals have been dated, and the age distributions are nearly independent of where the crystals are found (e.g., igneous rocks, sedimentary or metasedimentary rocks or modern ...
The resulting skarn may consist of a variety of different minerals which are highly dependent on both the original composition of the hydrothermal fluid and the original composition of the protolith. [4] If a skarn has a respectable amount of ore mineralization that can be mined for a profit, it can be classified as a skarn deposit. [2] [3] [4]