2 edition of Migmatites and the origin of granitic rocks found in the catalog.
Migmatites and the origin of granitic rocks
K. R. Mehnert
Bibliography: p. -388.
|Statement||by K. R. Mehnert.|
|LC Classifications||QE461 .M4913|
|The Physical Object|
|Pagination||x, 394 p. with illus.|
|Number of Pages||394|
|LC Control Number||68015620|
Get Permissions Field features and petrographic criteria for granitic rocks of magmatic origin are listed, and a brief discussion is presented concerning the mode of emplacement and the differentiation of intrusive masses. However, with pegmatites, large crystals are attributed to low-viscosity fluids that allow ions to be very mobile. Representative results are presented in Table 1. Eventually there is an overabundance of water, and pockets of water separate from the melt. Pre-migmatization structures are preserved only in enclaves, which are locally abundant.
The development of a hyperfeldspathic parent magma with the requisite geochemical features can be ascribed to hydrous partial melting of mafic to intermediate rocks at deep crustal or greater depths, leaving a garnetiferous residue. Malo migmatite belt of Brittany was chosen because melting there occurred predominantly in the stability field of biotite Brown, ; Weber etal. Migmatite is the penultimate member of a sequence of lithology transformations first identified by Lyell, Sederholm  called the migmatite-forming process palingenesis. Magmatic foliations and lineations in diatexite migmatites and granites, respectively, dip and plunge to the north or northeast Fig. These facies include replacement dikes, replacement breccias, and metamorphic migmatites.
The volcano-plutonic interface - not Read's hiatus. Mesocratic diatexite Diatexite that contains between 10 and 30 vol. More Rocks. In contrast to other Grenville anorthosites, primary magmatic features are largely preserved.
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He thought that the granitic partings in banded gneisses originated through the agency of either melt or a nebulous Migmatites and the origin of granitic rocks book, the ichor, both derived from nearby granites.
Thus, the modern view of migmatites corresponds closely to Holmquist's concept of ultrametamorphism, and to Sederholm's concept of anatexis, but is far from the concept of palingenesis, or the various metasomatic and subsolidus processes proposed during the granitization debate; Cliff section through near-vertically dipping ptgmatically folded migmatites see Read .
They are also compositionally different. Leucocratic diatexite Leucocratic diatexite Fig. The melt and residuum fraction in the magma can become separated if their flow velocities are different Sawyer, I can hardly aspire to convert my reader in so dramatic a way, yet this book is an attempt, however inadequate, to pass on the enthusiasm that I inherited, and which has been reinforced by innumerable discussions on the outcrop with granitologists of many nationalities and of many shades of opinion.
The ions in the water are much more mobile than ions in the melt. Migmatites and the origin of granitic rocks book facies of granitic rocks of metamorphic origin are described in detail. To be called a "pegmatite," a rock should be composed almost entirely of crystals that are at least one centimeter in diameter.
The type of melt—residuum separation process depends on the melt fraction present. Appinites, diatremes and granodiorites - the interaction of wet basalt with granite.
Malo anatectic region, and are associated with top-to-the-south kinematic indicators. Structure and intraplate deformation of the North-American craton Papers submitted to this volume have however all been collected in one part since all of them deal with different aspects of deformation of the continental basement.
However, the details of the petrogenetic relationship between diatexite migmatite and derivative granite magmas have not yet been investigated for other common protoliths, such as metasedimentary rocks. At higher melt fractions the physical nature of the partially molten rock changes from solid dominated to melt dominated.
Since the s, interest in granites has been greatly stimulated by the thesis that granites image their source rocks in the inaccessible deep crust, and that their diversity is the result of varying global tectonic context.
The name "pegmatite" has nothing to do with the mineral composition of the rock. Mechanisms of basement exhumation in the evolution of orogenic belts 4. It appears that calcic myrmekite has been frequently overlooked, and is a common accessory feature in these rock types.
Cooling due to surface exposure is conducted very slowly to deeper rocks so the deeper crust is slow to heat up and slow to cool. Uses of Pegmatite Pegmatite rock has very few uses. Open in new tab Download slide a Simplified geological map of the Armorican segment of the Cadomian belt showing the major tectonostratigraphic units.
Fibrolitic sillimanite is rare, and occurs either as small clots of fibres, or as scattered needles in other phases, such as plagioclase and muscovite. All have undergone a textural homogenization that has destroyed the primary centimetre-scale bedding typical of the metasedimentary rock and the metatexite.
Differentiation in granitic magmas: zoning as an example of multifactinal processes at work. The arc-related St. Rare elements concentrated in large crystals make pegmatite a potential source of valuable ore. Magmatic foliations and lineations in diatexite migmatites and granites, respectively, dip and plunge to the north or northeast Fig.
Away from the BMFZ, the regional metamorphic grade is low, suggesting that heat for the high-temperature deformation and metamorphism was supplied by the intrusions.
Etymology[ edit ] The Finnish petrologist Jakob Sederholm first used the term in for rocks within the Scandinavian craton in southern Finland. Rocks matching this description can also be found around igneous intrusive bodies in low-grade or unmetamorphosed country-rocks.
Their assistance is gratefully acknowledged. This allows them to move about freely and form crystals rapidly. A second part contains a complete list of all papers and posters presented at the meeting. Some melanocratic diatexite contains biotite augen, which are either individual biotite porphyroblasts or aggregates of biotite grains; in many cases the biotite is crenulated or kinked, indicating that folding and disruption of mafic schlieren occurred during diatexite formation.Aug 28, · For a long time, the origin of granitic rocks was debated by geologists.
Between the s and the s, many geologists argued that granites could form from sedimentary or other non-granitic rocks through chemical alteration caused by fluids. Gneiss, migmatite, and amphibolite (about Ma) - Quartzofeldspathic gneiss and less abundant amphibolite and migmatite.
Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a Migmatites and the origin of granitic rocks book zircon age of +/- 22 Ma (Sims and.
Migmatites form by partial melting (partial anatexis) of older rocks or by injection of granitic melt into the older rocks. The Odessadale migmatite typically con tains layers and pods of granitic material parallel to or cutting across the compositional layering of a con torted biotite granite gneiss matrix.Gneiss, migmatite, and amphibolite (about Ma) pdf Quartzofeldspathic gneiss and less abundant amphibolite pdf migmatite.
Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of +/- 22 Ma (Sims and.Many Precambrian migmatites were formed under such conditions.
Migmatites located near large intrusive bodies of granitoids arose when granitic melt was injected into adjacent metamorphic rocks (injection gneiss). Migmatite is commonly found in ancient granite-gneiss complexes.Ebook Classic is now deprecated. It will be completely retired in October Please redirect your searches to the new ADS modern form or the classic 42comusa.com info can be found on our blog.