Pdf evolution of a granite gneissmigmatite terrane in. Geology of kennesaw mountain, migmatite, mcconnell. Metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite facies zones of the higo low. No locality information or originating geologic unit is provided. Migmatites are highly heterogeneous rocks found in highgrade metamorphic environments. Within these crustalscale structures, detachment zones record significant amounts of localized extension and preserve an interface between cool upper crust and hot. Malo anatectic region, and are associated with toptothe. Local geological setting the lithologies in the study areas include porphyritic granites, schists, biotite. The migmatite gneiss complex is the oldest basement rock, and is believed to be of sedimentary origin but was later profoundly altered into metamorphic and granite conditions. Massabesic gneiss complex as a migmatized equivalent of the berwick formation bothner and others, 1984. If this is true, then the gneissic and migmatitic rocks in central wisconsin may represent an.
Gneiss and migmatite of archean age in the precambrian. Rbsr data for the migmatite and gneiss indicate elevated initial 87 sr 86 sr ratios, suggesting that the migmatite and gneiss formed from crustal rocks of intermediate to granitic composition which were themselves formed more than 3. This type of metamorphic was created by regional metamorphism, in which a sedimentary or igneous rock has been deeply buried and subjected to high temperatures and pressures. Pdf petrography and structural features of migmatites, granites. Metamorphic gneiss has many uses as a building material such as flooring, ornamental stones, gravestones, facing stones on buildings and work surfaces. Migmatite article about migmatite by the free dictionary. The migmatite gneiss complex is the common est rock type in the nigerian basement complex. Many rocks were injected by a granitoid that has blue quartz and augen of potassic feldspar and are arteritic migmatites. This title provides genetically based definitions and a system of nomenclature with which it is be possible to describe and map migmatites effectively. The country rock is a paragneiss composed of thin, alternat ing fine and coarsegrained layers. More recently, goldsmith 1991, pouliot 1994, larson 1999, and larson and others 1999 interpreted the contact to be a ductile fault. In addition, the laguigangri group containing schist, gneiss, and migmatite units crops out in the core of the yelaxiangbo dome figure 1b, as well as some quaternary sediments composed of gravel, sand gravel.
Transition from gneiss to migmatite and the relationship of. Migmatite definition of migmatite by merriamwebster. Some gneiss is durable enough to perform well as a dimension stone. Migmatites comprise leucosome bands, comprised largely of quartz and feldspar, which crystallised from partial melts or segregated metamorphic fluids. Such rocks are usually gneissic banded and felsic rather than mafic in composition. Gneiss, metamorphic rock that has a distinct banding, which is apparent in hand specimen or on a microscopic scale.
Veins, contorted layers, and irregular pods of silicarich granite occur within the structure of foliated iron and magnesiumrich metamorphic rocks like gneiss, schist and amphibolite. The migmatitegneiss complex covers half of nigerias surface area and encompasses archean gray gneisses, with tonalite and granodiorite consistencies. The development of a stromatic migmatite exposed east and southeast of arvika western sweden is described in four stages beginning with the country rock and following evolution through three areas characterized by low, medium and high amounts of leucosomes areas l, m, and h, respectively. The migmatitegneiss complex mgn, the schist belts sb and the older granites og modi. The highestgrade, nonmigmatitic rocks are gneisses and granofelses of the andalusitekfeldspar zone fig. Here is a thorough, if tortured, description of migmatite, with words not defined in the text asterisked and defined below. The rock derived its name from a greek word which means mixed rock. Paragneiss is gneiss derived from sedimentary rock. The oldest rocks yet found are gneiss, with the oldest dated to over 4 billion years old, older than most estimates of the beginnings of life on earth. Gneiss domes occur in a wide variety of orogenic and anorogenic domains of the continental crust, and play a major role in lithosphere dynamics by allowing upwards transfer of heat and mass. Migmatite is a rock composed of both igneous and metamorphic rocks. A migmatite, or mixed rock in greek, is a banded, heterogenous rock composed of intermingled metamorphic and igneous components. Gneiss gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist.
A migmatite is a banded, granular metamorphic rock that contains light coloured bands with evidence for partial melting. Rock melting experiments show that the initial melting temperatures of phyllite, biotite plagioclase gneiss and migmatite granite range from 630 to 640c, but those of bif and plagioclase amphibolite are 150200 c higher. Migmatite with diffuse relics of preexisting rocks or rock structures. Compositional characteristics of the migmatite gneiss around. Origin of migmatites by deformationenhanced melt infiltration of. Origin of migmatite granite and its relations to iron. The dynamics of migmatite domes in extending orogens. Migmatite definition is a gneiss produced by the injection of igneous material between the laminae of a schistose formation called also injection gneiss. Includes granite of late archean age that transgresses gneisses and amphibolite. The nigeria basement complex have been conformed to comprise of three major rock units of which are. It is created when a metamorphic rock such as gneiss partially melts, and then that melt recrystallises into an igneous rock, creating a mixture of the unmelted metamorphic part with the recrystallised igneous part. The older metasediments were also among the earliest rocks to form on the nigerian basement complex. For the casual student, it is convenient to think of a gneiss as a rock with parallel, somewhat irregular. Typically, the rock contains alternating lighter layers leucosomes, comprised of lightcolored minerals such as quartz, feldspar, and muscovite and darker layers melanosomes, comprised of darkcolored minerals such as amphibole and biotite.
However, unlike slate and schist, gneiss does not preferentially break along planes of. Pdf the osokom area is made up dominantly of varieties of. Gneiss usually is distinguished from schist by its foliation and schistosity. If a 390 ma zircon in an amphibolite aleinikoff and others, 1995 proves to be metamorphic, then the massabesic gneiss complex may have a more complicated acadian metamorphic history than its sibling avalonian. Gneiss is formed by high temperature and highpressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. A general impression of the pink gneiss formation is that of a very homo genous series of granitic biotite gneisses where transition between several types has been. Migmatitic gneiss and amphibolite late to early archean. An example of a diatexite migmatite from the birksgate gneiss, musgrave prov ince. Two migmatite domes, the okanogan dome washington state and the naxos dome cyclades, greece record the dynamics of migmatite dome formation in extending orogens. The rare earth element geochemistry of granite, gneiss, and. Melt transport and magma accumulation in a migmatitecored.
Currently only the basic nebulae generation function work. It was first discovered by jakob johannes sederholm in 1907. Expansive cliffface exposures in the fosdick mountains antarctica migmatite cored gneiss dome enabled the documentation of suprasolidus deformation and melt migration structures in middle to lower crustal rocks at a scale significant for continental differentiation and crustal flow. Both domes are exposed in cordilleranstyle metamorphic core complexes that developed during extension of previously thickened crust and contain a core of anatectic migmatite. Migmatite definition of migmatite by the free dictionary. Major rocks in nigeria migmatite, gneiss, migmatite gneiss. Gneiss is very common and actually forms the majority of the earths lower crust, so any deep tunneling encounters gneiss. Migmatite gneiss within the precambrian basement rocks around awo, southwestern nigeria were stud ied with a view to determine origin and compositional.
Paragneiss is gneiss derived from sedimentary rock such as sandstone. This allows contractors to use gneiss as a crushed stone in road construction, building site preparation, and landscaping projects. Jun 12, 2017 the term migmatite was introduced by sederholm1908 to designate certain gneissic rocks which looked like mixed rock. Contains a wide variety of rock types including graphitic schist and marble.
The term migmatite was introduced by sederholm1908 to designate certain gneissic rocks which looked like mixed rock. Gneiss nice is a rock of great variety with large mineral grains arranged in wide bands. Petrogenesis of metatexite and diatexite migmatites. A heterogeneous silicate rock with properties of both igneous and metamorphic rocks. Gneiss and granofels range in composition from felsic to intermediate to mafic. The presence of two generations of granitic rocks in the gneiss domes he examined led eskola to suggest that the general condition for gneissdome formation is the superposition of two orogenic events. Gneiss, migmatite, and amphibolite about 2800 ma quartzofeldspathic gneiss and less abundant amphibolite and migmatite. The country rock is a paragneiss composed of thin, alternating fine and coarsegrained layers. Except for the watersmeet dome late to early archean. Very widespread, the biotitic gneisses are normally finegrained with strong foliation caused by the parallel arrangement of alternating dark and light minerals. Structure in a migmatite or granitised rock that can be recognised as premigmatitic or pregranitic. Expansive cliffface exposures in the fosdick mountains antarctica migmatitecored gneiss dome enabled the documentation of suprasolidus deformation and melt migration structures in middle to lower crustal rocks at a scale significant for continental differentiation and crustal flow. Separated granitic and biotitic portions of a migmatite from the western.
Ebook atlas of migmatites as pdf download portable. This results in me being very conversant and visually familiar with the rocks of the atlanta area. Ebook atlas of migmatites as pdf download portable document. Within this complex are occurrences of schist, migmatite, garnet, sillimanite, kyanite and staurolite, which together indicate highgrade metamorphism up to the level of amphibolite on the. The accompanying museum signage identifies the rock as a 3.
The vanduzi migmatite gneiss occurs between the messica granite gneiss in the west and the nhansipfe granitic orthogneiss in the east fig. A banded metamorphic rock, pervasively heterogeneous on a meso to megascopic scale. Migmatite, in geology, rock composed of a metamorphic altered host material that is streaked or veined with granite rock. The darker parts usually exhibit features of metamorphic rocks eg. To the northwest, the complex is separated from the rocks of the central.
The outer parts consist mostly of metatexite migmatite, and the inner part principally of diatexite migmatite brown, 1979. Migmatite gneiss da 28 chlorite schist da 29 tourmaline schist da 2140 from gy 303 at university of south alabama. Gneiss granofels and migmatite gneiss and granofels range in composition from felsic to intermediate to mafic. It consists of two or more constituents often layered repetitively. Gneiss usually does not split along planes of weakness like most other metamorphic rocks. Orthogneiss is gneiss derived from igneous rock such as granite. Pdf transition from gneiss to migmatite and the relationship of. Composition of the layers varies from granitic fine to tonalitic. Metamorphic migmatite varied gneisses of mostly unknown age in cores of gneiss domes and faultbounded uplifts archean gneiss terranes. Because metamorphic rocks form by recrystallizaton of minerals.
Extension of thickened and hot crust commonly leads to the formation of migmatitecored metamorphic core complexes mcc coney and harms, 1984, lister and davis, 1989, whitney et al. It typically consists of darker bands rich in mafic minerals and lighter quartzofeldspathic parts. Magmatic foliations and lineations in diatexite migmatites and granites, respectively, dip and plunge to the north or northeast fig. It means a type of rock texture, not a composition. Hornblendebiotite granite with amphibolitefacies enclaves of metamafic and calcsilicate gneisses constitute the cratonic foreland. The rock shown above is an archeanaged migmatite from minnesota. The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of wellequilibrated banded microstructure by crystallization of new. From this description of rocks units and also the younger granite intrusion. Conformable granitic gneisses and banded gneiss series form the oldest part, in which augen gneisses ap parently developed by partial anatexis and. Here, we report data from an outcrop in the highest grade part of the granulite facies zone, in which diatexite occurs as a 3 m thick layer between 2 m thick layers of stromatic.
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