Granulite

About: Granulite is a research topic. Over the lifetime, 6763 publications have been published within this topic receiving 268925 citations.

Problems with inferring P–T–t paths in low‐P granulite facies rocks

Abstract: Microstructural evidence commonly is used to infer metamorphic reactions, which are used to infer pressure–temperature–time (P–T–t) paths However, this approach in low-P/high-T (LPHT) granulite facies metamorphic terranes has two main problems (1) Microstructural evidence may be inconclusive, so that reactions cannot be inferred with confidence In particular, relative timing of mineral growth inferred from inclusions, moulding relationships and foliation–porphyroblast relationships is commonly ambiguous or invalid The most reliable indicators of metamorphic reactions are partial pseudomorphs and corona structures, especially if symplectic intergrowths (indicating simultaneous growth of two or more minerals) are involved (2) Even reactions that can be inferred with confidence do not indicate unique P–T trends, owing to P–T slopes of reaction curves Where successive reactions can be shown to have occurred in the same rock, a line or curve joining reaction-curve intersections gives an apparent single-event path However, isotopic evidence is needed to prove that polymetamorphism (involving more complex paths making fortuitous intersections with the apparent single-event path) did not occur Although these problems are well known, their importance is not always emphasized in metamorphic investigations The difficulties are illustrated by published work on P–T–t paths for Proterozoic LPHT granulite facies rocks of central Australia and Antarctica Recent work in Antarctica has shown that P–T–t paths may be episodic and more complex than the simple, single-event paths commonly inferred from microstructural evidence alone

Whole-rock, Phosphate, and Silicate Compositional Trends across an Amphibolite- to Granulite-facies Transition, Tamil Nadu, India

Abstract: Chemical trends from north (amphibolite facies) to south (granulite facies) along a 95 km traverse in Tamil Nadu, Southern India, include: whole-rock depletion of Rb, Cs, Th and U, enrichment in Ti and F, and depletion in Fe and Mn in biotite and amphibole; increases in Al and decreases in Mn in orthopyroxene; enrichment of fluorapatite in F. K-feldspar blebs are widespread along quartz^ plagioclase grain boundaries, and could indicate either partial melting or metasomatism. In the northernmost portion of the traverse the principal rare earth element (REE)-bearing minerals are allanite and titanite. South of a clinopyroxene isograd, monazite grains independent of fluorapatite are the major REE- and Th-bearing phase. Further south independent monazite is rare but Th-free monazite inclusions are common in fluorapatite. During prograde metamorphism, independent monazite was replaced by REE-rich fluorapatite in which the monazite inclusions later formed. The loss of independent monazite was accompanied by a loss of whole-rock Th and possibly a small depletion in light REE. Most mineralogical features along the traverse can be accounted for by progressive dehydration and oxidation reactions. Trace-element depletion is best explained by the action of an externally derived low H2O activity brine migrating from a source at greater depth, possibly preceded or accompanied by partial melting.