To the northwest, the complex is separated from the rocks of the central. The morton gneiss in the minnesota river valley, southwestern minnesota, consists of an older metamorphic complex of tonalitic gneisses and. His 2009 book on the subject, stories in stone, tours rocks in new york, morton, boston. From mcdonalds bathrooms to art deco, the morton gneiss has a colorful history of use in architecture. Minnesota river valleys and the history of their formation. The second major deformation affected the granitic phases as well as the older tonalitic gneissamphibolite complex and was responsible for the highly contorted structure of the morton gneiss. Two major mineralogic types of mafic enclaves amphibolite and pyroxeneamphibolite have been characterized in the morton quartzofeldspathic gneiss at morton, minnesota. The paleosome consists of tonalitic to granodioritic gneisses and. Minnesotas morton gneiss is one nicelooking stone minnpost.
Gneiss is formed by high temperature and highpressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss displays distinct foliation, representing alternating layers composed of different minerals. Her essay genome tome, which appeared in our summer 2005 issue, won the. The morton gneiss of southwestern minnesota is a migmatitic hybrid rock.
The fact that it is a a crystalline rock with large visible grains foliation indicates that. Courtesy mark ryan i recently attended a geology seminar sponsored by the geological society of minnesota. The composition of the earth reflects the continuum of processes that produced a suite of terrestrial planets in our solar system. The microadamellite porphyry at morton chemically resembles a phase of the sacred heart granite, but the gneissic adamellite to the northwest resembles in composition some of the aplite dikes that traverse the structure of the morton gneiss. The texture and mineral composition of the morton gneiss gives clues as to how the rock was formed. A similar origin as a synkinematic intrusion of granite is favored to explain the gneiss at montevideo. More recently, goldsmith 1991, pouliot 1994, larson 1999, and larson and others 1999 interpreted the contact to be a ductile fault. There are areas where the sandstone, shale petrified clay and limestone occur in the exchange. These rocks are mostly gneisses of various compositions along with other igneous and metamorphic rocks. Gneiss definition of gneiss by the free dictionary. Its hybrid nature is in part the result of litparlit injection, but more important is the strewing out of numerous basic inclusions by the magma. The bestknown units are the morton gneiss and the montevideo gneiss.
The layering of a gneiss may be weak or welldeveloped and consists of varying concentrations of biotite, garnet, hornblende, mica, and other minerals. The morton gneiss was formed by synkinematic intrusions of trondhjemitic and granitic magmas, and the structure dates back to the time of the intrusions, 3550 m. Paul, and was led by jeff thole, laboratory supervisor and instructor in the colleges geology department. Effects of weathering on the upb ages of zircon from the. The intersections of the chord with the concordia curve in fig. The term gneiss is not only the name of a particular kind of metamorphic rock, but also, in a wider sense, it is used as an expression of a certain texture. Along with the nearby montevideo gneiss, it is the oldest intact continental crust rock in the united states. Granitegneiss definition is a rock consisting of an orthogneiss or paragneiss having the composition of a granite.
Orthogneiss is gneiss derived from igneous rock such as granite. Peter sandstone, one of the purest sandstones in the world. Sometimes gneiss is what we call a band appearance, ie it consists of layers with slightly different color and composition. In the region where they occur, lewisian rocks form the basement, or lowermost, rocks. Contorted hornblendebiotitegneiss railway cut at morton, 150 feet long. Rainbow gneiss gc4ddnk was created by just4cache on 6220. It is characterized by alternating light and dark bands differing in mineral composition coarser grained than schist. Morton gneiss the morton gneiss has been quarried since the 19th century into the late 20th century for building and monument stone.
By 1980, the age of the morton had dropped back to 3. Sedimentary layers are formed by layers of clay, sand, gravel or limestone, when deposited in oceans, rivers and lakes. In the morton area a complex migmatite morton gneiss is composed of a paleosome of tonalitic to granodioritic gneiss and amphibolite and a neosome of granodiorite, adamellite, and granite pegmatite. In the laboratory, rock samples are crushed and the zircon grains are separated from the other minerals by heavy liquid and other mineral separation techniques. Actually the rock is a migmatite a mixed metamorphic rock consisting of a schist or gneissose component, and a granitic component forming layers or pods. Composed of archeanage migmatitic gneiss, it has been dated to 3. It is known for its beauty as an ornamental stone in buildings and monuments.
In 2006, pat bickford, emeritus professor of petrology at syracuse university, led a team of researchers who obtained the morton s most up to date age of 3,524 million years. The average chemical composition of the earths crust has been determined from tens of thousands of chemical analyses of rocks and minerals taken from the surface or drill holes. Age of the morton and montevideo gneisses and related. Gneiss pronounced nice is a metamorphic rock consisting mostly of quartz and feldspar and showing distinct layering or banding. It is formed by the metamorphosis of granite, or sedimentary rock. Roadside geology of minnesota steers you over glacial moraines and till plains to some of the states unparalleled geologic features, such as the morton gneiss, once thought to be the oldest rock on earth. A sample of this was used in construction of the fountain of freedom in independence mall. They were heated and squeezed, and the minerals recrystallized. Quick navtop about augen gneiss classification subdivisions mineralogy pronounciation internet links mineral andor locality is an outreach project of the hudson institute of mineralogy, a 501c3 notforprofit organization. Gc4ddnk rainbow gneiss earthcache in minnesota, united. Paragneiss is gneiss derived from sedimentary rock such as sandstone. These temperatures cause the individual minerals to migrate, forming distinct bands through the rock. Morton gneiss is a minnesota rock, not a rock star. Origin of the morton gneiss, southwestern minnesota.
Choose from 10 different sets of gneiss flashcards on quizlet. Mineral and rock compositions of mafic enclaves in the. Hanson geological society of america, 1980 science 175 pages. One indication of compositional equilibration of the amphibolite with host gneiss is the. Geochemistry of the archean rocks in the morton and. The morton gneiss, one of a number of granites and granite gneisses referred to the minnesota valley granite series, is a hybrid gneiss with complexly contorted structure and variable color. Molten rock cooled slowly, forming grains granite comes from granum, the latin word for grain of crystallized minerals. The latter is similar to the morton gneiss in mineralogical composition but is characterized by straight banding in contrast to the convoluted and contorted structure of the morton gneiss.
The molten rock cooled slowly, forming grains of crystallized minerals. Some amphibolite contains plagioclase megacrysts with an 66 cores and an 43 rims. The most common elements in the crust by weight are oxygen 46. The most famous rock is a migmatite commonly designated as the morton gneiss, from the name of the town where it has been quarried since the 19th century. Morton gneiss is one of the oldest rocks in minnesota at about 3. The tradename rainbow granite has been applied because of the striking color bands and patterns in the rock. Gneiss is a medium to coarsegrained, semischistose metamorphic rock. However, unlike slate and schist, gneiss does not preferentially break along planes of. Thus when we use gneiss as a name in the limited sense, we mean a rock which has the composition of granite quartz, feldspar, and mica with a certain foliated texture. The rocks that form gneiss are exposed to extreme pressures and temperatures of between 600 and 700 degrees celsius.
I was struck by the mortons popularity in the 1930s and specifically in art deco or moderne style projects, where the gneiss was. Morton gneiss, also known as rainbow gneiss, is an archeanage gneiss found in the minnesota river valley of southwestern minnesota, united states. It outcrops around morton, minnesota and has been dated to 3. The gneiss family of rocks varieties, uses and mineral. Of a similar age and appearance to the acasta gneiss, this another ancient rock that once formed the surface of ancient north america. The minerals in gneiss may come from rocks which were originally either igneous or sedimentary. Selected studies of archean gneisses and lower proterozoic. Selected studies of archean gneisses and lower proterozoic rocks, southern canadian shield, issues 179181 g. The morton gneiss is a archean migmatitic gneiss that is the oldest rock in the united states.
Lewisian complex, also called lewisian gneiss, major division of precambrian rocks in northwestern scotland the precambrian began about 4. Morton gneiss oldest earth rocks aonline science mall. Gneiss gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. Carver wrote an exceedingly interesting book, but he said very little on the geology of the. The leucotonalitic gneiss in the paleosome is trondhjemitic, with potassium largely in biotite. Perhaps the most popular and highly regarded radioisotopic dating method currently in use is the uthpb dating of grains of zircon zrsio4, baddeleyite zro2, titanite catisio5 andor monazite thpo4. Ships with certificate of authenticity, tag, information and perky display case. A banded or foliated metamorphic rock, usually of the same composition as granite. Morton gneiss, also known as rainbow gneiss, is an archeanage gneiss found in the. The lighter bands contain mostly quartz and feldspar, the darker often contain biotite, hornblende, garnet or graphite. The rocks included in adamellite2 are least deformed, and these appear to have been emplaced in the late stages of the second major deformation.
I discovered this during my research for stories in stone, when i began to develop a list of buildings built with the 3. Morton gneiss pronounced nice, named for the town in renville county where it has been quarried, is one of the oldest stones on the planet. Gneiss simple english wikipedia, the free encyclopedia. The second major deformation affected the granitic phases as well as the older tonalitic gneiss amphibolite complex and was responsible for the highly contorted structure of the morton gneiss. Granitegneiss definition of granitegneiss by merriam. Massabesic gneiss complex as a migmatized equivalent of the berwick formation bothner and others, 1984.
Whitney editor, christian teyssier editor, christine s. Dubious radiogenic pb places uthpb mineral dating in doubt. Discover delightful childrens books with prime book box, a subscription that. These structures do not record a layered deposition process but arise from preferential recrystallization. Morton gneiss is the oldest rock unit in the united states and this great, large specimen is available from sciencemallusa.
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