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. The darkest parts of a migmatite, usually with prevailing dark minerals. Tonalite gneiss, migmatite bt gneiss, migmatite hbbt gneiss,migmatite quartz monzonite, monzodiorite granodiorite tonalite, trondjhemite gabbro peridotite, serpentinite volcanic sandstone conglomerate, sandstone iron formation rhyolite, dacite andesite, dacite basalt, basaltic andesite 330000 ross river pluton ogamarockland deposit 330000 o. Metamorphic gneiss has many uses as a building material such as flooring, ornamental stones, gravestones, facing stones on buildings and work surfaces. It occurs between two leucosomes or, if remnants of the more or less unmodified parent rock mesosome are still present, it is arranged in rims around these remnants.
The reservoir rocks are biotite plagiogneiss, mixed gneiss, mixed granite, cataclasite and graniteporphyry, dioritic porphyrite. Hornfels finegrained, granoblastic rock of any composition that was produced by contact metamorphism. This allows contractors to use gneiss as a crushed stone in road construction, building site preparation, and landscaping projects. Evolution of the migmatite dome on naxos hallenberger, maximilian matkovskiy, sachar introduction migmatites are a mixture of metamorphic and igneous rocks and form when a metamorphic rock partially melts and crystallizes into an igneous rock. The migmatite gneiss complex is the common est rock type in the nigerian basement complex. Geology of kennesaw mountain, migmatite, mcconnell.
The lithology of xinglongtai buried hill is the vein combination of regional metamorphic rock, migmatite, and igneous rock. If this is true, then the gneissic and migmatitic rocks in central wisconsin may represent an. Tonalite gneiss, migmatite bt gneiss, migmatite hbbt gneiss, migmatite quartz monzonite, monzodiorite granodiorite tonalite, trondjhemite gabbro peridotite, serpentinite volcanic sandstone conglomerate, sandstone iron formation rhyolite, dacite andesite, dacite basalt, basaltic andesite 330000 ross river pluton ogamarockland deposit 330000 o. The rock derived its name from a greek word which means mixed rock.
Migmatite definition of migmatite by the free dictionary. Commonly, migmatites occur below deformed metamorphic rocks that represent the base of eroded mountain chains, commonly within precambrian cratoni. N2 gneiss domes are ubiquitous structures in all exhumed orogens, and their formation represents a first order thermaltectonic process that has operated from the archean to the present. Gneiss usually does not split along planes of weakness like most other metamorphic rocks. To the northwest, the complex is separated from the rocks of the central. Gneiss and granofels range in composition from felsic to intermediate to mafic.
Only the massabesic gneiss complex has any evidence of prealleghanian metamorphism. Because metamorphic rocks form by recrystallizaton. Pdf evolution of a granite gneissmigmatite terrane in. Very widespread, the biotitic gneisses are normally finegrained with strong foliation caused by the parallel arrangement of alternating dark and light minerals. It typically consists of darker bands rich in mafic minerals and lighter quartzofeldspathic parts. Gneiss any rock possessing a gneissic foliation see above, in which individual grains are visible to the naked eye or easily seen at 10x magnification. Migmatitegneiss complexes, schist belts and the panafrican older granites. Migmatite definition is a gneiss produced by the injection of igneous material between the laminae of a schistose formation called also injection gneiss. A banded metamorphic rock, pervasively heterogeneous on a meso to megascopic scale. Compositional and petrogenetic features of schistose rocks of ibadan area, southwestern nigeria the crystalline basement is mainly composed of metamorphosed rocks and tectonically structured precambrian rocks schist, gneiss, migmatite, quartzite and granitic intrusions huhn et al. Many rocks were injected by a granitoid that has blue quartz and augen of potassic feldspar and are arteritic migmatites. Evolution of a granite gneissmigmatite terrane in rajasthan 485 the 1st one is primary biotite.
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. Formation of diatexite migmatite and granite magma during. Mechanical deformation and chemical recrystallization are the two processes that affect rock during metamorphism. Migmatites comprise leucosome bands, comprised largely of quartz and feldspar, which crystallised from partial melts or segregated. 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. A migmatite is a banded, granular metamorphic rock that contains light coloured bands with evidence for partial melting.
Please practice handwashing and social distancing, and check out our resources for adapting to these times. These temperatures cause the individual minerals to migrate, forming distinct bands through. Migmatite is a composite rock found in medium and highgrade metamorphic environments. The term migmatite was introduced by sederholm1908 to designate certain gneissic rocks which looked like mixed rock. Download highquality specimen natural rock stone migmatite migmatic images, illustrations and vectors perfectly priced to fit your projects budget. A user s guide to migmatites, report book 20 001 6. The darker parts usually exhibit features of metamorphic rocks eg. It was first discovered by jakob johannes sederholm in 1907. A characteristic feature of the gneiss is the numerous small xenoliths of psammitic gneiss.
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. Massabesic gneiss complex as a migmatized equivalent of the berwick formation bothner and others, 1984. A migmatite, or mixed rock in greek, is a banded, heterogenous rock composed of intermingled metamorphic and igneous components. The authors suggest that migmatites in this region have resulted from partial melting and metasomatism. Migmatite a rock consisting of metamorphic enclosing material with veins of granite. The rocks that form gneiss are exposed to extreme pressures and temperatures of between 600 and 700 degrees celsius.
The dynamics of migmatite domes in extending orogens. The country rock is a paragneiss composed of thin, alternating fine and coarsegrained layers. These are, without exception, perfectly aligned and very much flattened in the plane of foliation of the gneiss fig. 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. Migmatites and related rocks british geological survey. 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. The name can be prefixed by the dominant andor porphyroblastic minerals present, e. Both domes are exposed in cordilleranstyle metamorphic core complexes that developed during extension of previously thickened crust and contain a core of anatectic migmatite. 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. Malo anatectic region, and are associated with toptothe.
More than 50 complexes occur in nigeria obaje, 2009. 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. Gneiss granofels and migmatite gneiss and granofels range in composition from felsic to intermediate to mafic. Pdf tectonic and structural analysis of the migmatite. Geological mapping in the migmatite complex near lyngdal has demon strated the significance of major rock units, designated lithostructural forma tions, as principal divisions of the complex. A heterogeneous silicate rock with properties of both igneous and metamorphic rocks. From this description of rocks units and also the younger granite intrusion. Gneiss and migmatite of archean age in the precambrian. Metamorphic rocks in which minerals are brought into line or layers due to heat and pressure, common for regoinal metamorphism, type of foliation. Migmatite is a rock composed of both igneous and metamorphic rocks.
Migmatite kennesaw gneiss qte mig or 00 0 0 00 or 0 or gms ms 60 55 qie. Gneiss 1b gneiss is a high grade metamorphic rock it shows separate bands of minerals the bands can be flat or wavy it is largely made of the minerals feldspar, mica and quartz its original parent rock can be granite type rocks it is a durable rock, used for. Migmatite article about migmatite by the free dictionary. 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. This research involves investigation of the role of partial melting in the tectonic development of orogens, including continental arcs and collisional belts. Contains a wide variety of rock types including graphitic schist and marble. Gneiss is very common and actually forms the majority of the earths lower crust, so any deep tunneling encounters gneiss. Gneiss is formed from the hightemperature metamorphism of existing igneous rocks, generally granite or diorite.
Gneiss gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. The outer parts consist mostly of metatexite migmatite, and the inner part principally of diatexite migmatite brown, 1979. 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. Major rocks in nigeria migmatite, gneiss, migmatite gneiss. Origin of migmatite granite and its relations to iron. Migmatite definition of migmatite by merriamwebster. The vanduzi migmatite gneiss occurs between the messica granite gneiss in the west and the nhansipfe granitic orthogneiss in the east fig. Jun 12, 2017 the term migmatite was introduced by sederholm1908 to designate certain gneissic rocks which looked like mixed rock.
Conformable granitic gneisses and banded gneiss series form the oldest part, in which augen gneisses ap parently developed by partial anatexis and. Here is a thorough, if tortured, description of migmatite, with words not defined in the text asterisked and defined below. More recently, goldsmith 1991, pouliot 1994, larson 1999, and larson and others 1999 interpreted the contact to be a ductile fault. Gneiss, migmatite, and amphibolite about 2800 ma quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Aug 25, 20 heavily folded migmatite or migmatitic gneiss, like my rock from dulsnibba, norway above geirangerfjord stay safe and healthy. Some gneiss is durable enough to perform well as a dimension stone. For schist, complete the diagram describing the types of metamorphism it undergoes. Gneiss displays distinct foliation, representing alternating layers composed of different minerals.
Plan map of the southeast portion of the rice lake belt. 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. Metamorphism involves changes in mineral assemblage and rock texture and occurs in the solid state as a result of changes in temperature and pressure. The younger granites the mesozoic younger granite ring complexes of nigeria form part of a wider province of alkaline anorogenic magmatism extending from northern niger republic to south central nigeria. Muscovitebiotite gneiss, andor by the word augen when appropriate. The foliation is parallel to that of the psammitic gneiss. Magmatic foliations and lineations in diatexite migmatites and granites, respectively, dip and plunge to the north or northeast fig. The rock contains alternating layers of lightcolored bands, known as leucosomes, and darkcolored bands, known as melanosomes. However, unlike slate and schist, gneiss does not preferentially break along. 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. Such rocks are usually gneissic banded and felsic rather than mafic in composition. The older metasediments were also among the earliest rocks to form on the nigerian basement complex. 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.