The lack of arc plutons in the Swakane Gneiss is difficult to explain by this model. [43] All zircons selected for U‐Pb analysis were air‐abraded, washed in 3M HNO3 at 50°C for 12 hours, and ultrasonicated for 1 hour. Gneiss (pronounced "nice") is a metamorphic rock consisting mostly of quartz and feldspar and showing distinct layering or banding. Accreted Terranes of the North Cascades Range, Washington, Field Trip Guideb. Nyelv, Finnmark, Norway. What is the protolith of quartzite? In addition, sediments of similar age and range of detrital zircon dates, such as the Gabriola Formation, are present in the forearc setting [Mustard et al., 1995]. Even in the latter case, gneissic banding has nothing to do with original layering of sedimentary rocks. Deep-crustal metasedimentary rocks support Late Cretaceous “Mojave-BC” translation. This specimen has a composition of an ordinary granite: pink K-feldspar, gray quartz, and black biotite. Basaltic Trachyandesite. Gneiss is a protolith of migmatite. Deep crustal source of gneiss dome revealed by eclogite in migmatite (Montagne Noire, French Massif Central) Donna L. Whitney, Clémentine Hamelin, Christian Teyssier, Natalie H. Raia, Megan S. Korchinski, Nicholas C.A. View a second image of Augen Gneiss Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username, (a) Simplified paleogeographic map of the western United States emphasizing Cretaceous to Tertiary features; (b) simplified geologic map of the North Cascades, southern Canadian Coast Mountains, and Omineca metamorphic complexes after, Simplified geologic map of the Cascades core after. gneiss protolith. Dawes [1993] used Al‐in‐hornblende barometry to determine emplacement pressures of 6–7 kbar at 18 locations from both suites. Magma addition and flux calculations of incrementally constructed magma chambers in continental margin arcs: Combined field, geochronologic, and thermal modeling studies. The grains were likely incorporated into the protolith as either a circa 73 Ma volcanic‐clastic component or as sediments derived from a nearby igneous source. The other five analyses were likely derived from zircon with cores inherited from the gneiss and overgrowths that grew during crystallization of the sheet. Physics, Solar Paragneiss is a variety with a sedimentary protolith. [2002], these small basins are not restricted to the back arc and their position simply reflects their relationship to a crustal fragment outboard of the schist/gneiss package that rifted from the margin and then shortly thereafter recollided. This rapid burial occurred as much as 20 Myr after deep burial of the Napeequa Complex in the Wenatchee block and the Napeequa Complex and Cascade River unit in the southwestern Chelan block, and anywhere from 15 to 3 Myr after deep burial of the northeastern Napeequa Complex, Cascade River unit and Skagit Gneiss. [16] A medium‐grained leucogranite sheet (SW1) that cuts across foliation in the gneiss was collected from the Wenatchee block (Figure 2). So, when hammered, gneiss behaves like a uniform homogenous rock. Hence, qualifying terms are often added to the rock name: amphibolite gneiss or hornblende gneiss, for example. (1983). The pressure increase likely occurred before the intrusion of the magmatic epidote‐bearing Marble Creek pluton at circa 76 Ma [Miller et al., 1993]. Augen Gneiss. Eight single zircon analyses yield dates that range from 1635.1 ± 1.6 Ma to 83.7 ± 1.2 Ma (Table 1 and Figure 3). Our new geochronologic data indicate that the Swakane Gneiss was deeply buried between 72.5 ± 0.6 Ma, the age of the youngest detrital grain, and 68.36 ± 0.07 Ma, the crystallization age of a crosscutting peraluminous sheet. Most of the minerals in this rock are amphiboles, which may be aligned to form a foliation. The restriction of the sheets to the deepest structural level, their composition, geochemistry and small size suggest that they were locally derived from partial melting of the gneiss [Boysun, 2004; Boysun and Paterson, 2003; Valley et al., 2003]; however direct evidence of in situ partial melting at the presently exposed crustal level in the Chelan block is lacking [Boysun, 2004; Valley et al., 2003]. An oscillatory zonation pattern results from growth of zircon in the presence of melt where oscillations are controlled by an interplay between the stage of crystal growth, nature of the crystal‐liquid interface, degree of supersaturation of the melt, rates of diffusion, and state of oxidation [Corfu et al., 2003; Hanchar and Miller, 1993; Hoskin, 2000; Mattinson et al., 1996; Vavra, 1990]. The youngest zircon grains are generally characterized by low Pb contents (0.5 to 8 ppm), making the 206Pb/238U date the most precise. The main piece of evidence used to support the hypothesis that the Swakane protolith is predominantly a silicic volcanic rock is the “remarkable homogeneity” of the Swakane Gneiss [Cater, 1982; Sawyko, 1994; C. A. Hopson, personal communication given by Mattinson, 1972]. Gneiss can form from many different rocks, and it may contain many different minerals. [9] The protolith age and tectonic affinity of the Swakane Gneiss have been investigated in two previous studies. [29] This diachronous burial history is defined by multiple lines of evidence [Brown and Walker, 1993; Miller et al., 1993]. Lewisian Complex, also called Lewisian Gneiss, major division of Precambrian rocks in northwestern Scotland (the Precambrian began about 4.6 billion years ago and ended 542 million years ago). Basically gneiss is used as a dimension stone for beautifying faces of buildings due to the nature of the bands containing dark and light lines on the rock. A medium- to coarse-grained rock, gneiss is primarily distinguished by its characteristic banding caused by the segregation of its mineral constituents. assemblage from quartzofeldspathic gneiss encountered far-ther north (Lake Melville, Hawke River and Groswater Bay terranes). Farther east, paragneisses that were likely derived from both the Napeequa Complex and Cascade River unit protoliths [Tabor et al., 1989] are extensively injected by orthogneiss sheets in the Skagit Gneiss Complex [Haugerud et al., 1991]. Gneiss. Pelitic gneiss is formed by metamorphosis of clay-textured sedimentary rocks, particularly those rich in iron . Representative zircons were selected for image analysis. Dark mineral in the lower left is biotite. But even with gneiss the process is not done, because if the temperature rises even higher the gneiss begins to melt. This model fails to explain two important observations about the origin and tectonic affinity of the Swakane Gneiss: (1) Although the Swakane terrane is at the center of, and occupied a position deep within, a long‐lived continental magmatic arc, it is devoid of arc‐related intrusive rocks, and (2) unlike other terranes in the North Cascades core, the Swakane Gneiss contains abundant Early to mid‐Proterozoic zircons and yields Middle to Late Proterozoic Nd depleted mantle model ages [Mattinson, 1972; Rasbury and Walker, 1992]. Numerical models of mantle flow patterns in a subduction zone predict that hot asthenosphere is drawn from the back arc into the mantle wedge corner during subduction [Andrews and Sleep, 1974; Bodri and Bodri, 1978; Furukawa, 1993]. Despite its foliated structure, however, unlike schists, gneiss does not exhibit perfect cleavage. Even the rocks that do not seem to have a banded appearance do have it when looked from a different direction. It is thought that much of the Cranberry Gneiss was originally plutonic in origin, and where it is not sheared, is typically a phaneritic, coarse-grained rock. The Swakane Gneiss, interpreted to represent sedimentary strata metamorphosed at 8–12 kbar, is the deepest exposed crustal levels within the exhumed North Cascades continental magmatic arc, yet the nature and age of its protolith and the mechanism by which it … I don't think of it a one rock becomes another rock, and that rock becomes another rock; I think of it as: start with a shale, add the correct amounts of pressure and temperature, the result is (say) a schist. Provenance and metamorphism of the Swakane Gneiss: Implications for incorporation of sediment into the deep levels of the North Cascades continental magmatic arc, Washington. Journal of Geomagnetism and Aeronomy, Nonlinear These geochronological data then place a maximum age for the deposition of the deepest parts of the Swakane Gneiss at 72.5 ± 0.6 Ma, the 206Pb/238U date of the youngest detrital grain. Scourie: the Lewisian Gneiss Complex (1) Lewisian landscape just north of Scourie. Other minerals in tonalite are plagioclase and quartz. A large subpopulation of the zircons analyzed (9 of 24) have 206Pb/238U dates from 72.5 ± 0.6 Ma to 74.4 ± 0.2 Ma. Fossil Rocks + Novaculite. A contact between gneiss and granitic pegmatite. The geochemistry of these gneiss have rocks is more assorted (i.e., more assortment in follow metal substance) than that for a marble have rock. The classic interpretation of the Cranberry Gneiss is that it is a paragneiss (sedimentary protolith). Biotite gneiss. These dregs are like the mud that causes the geochemical contrasts inside marble, especially for its aluminum-rich and silica-helpless substance. Rope Ferry described as locally massive, gray-colored, lenticularly layered hornblende-biotite-quartz-plagioclase gneiss. The recognition of a circa 73 Ma protolith age of the Swakane Gneiss invalidates earlier assumptions about the timing of juxtaposition and requires that the tectonic model for the assembly of the core be modified. Gneiss may have a protolith of any kind of rock, be it igneous, sedimentary, or another metamorphic rock. Gneiss displays distinct foliation, representing alternating layers composed of different minerals.However, unlike slate and schist, gneiss does not preferentially break along planes of … [23] During the same time period that the protolith of the Swakane Gneiss was deposited and rapidly buried, sediment along the southwestern margin of the North American craton also followed a similar pattern of deposition followed by rapid burial. Objects, Solid Surface In behalf of the origin of the source rock of gneiss has to be devided between: orthogneiss is formed by the metamorphism of igneous rocks (igneous protolith), paragneiss results from the metamorphism of sedimentary rocks (sedimentary protolith). The Cascade River‐Holden arc sequence has been proposed to have either formed unconformably on the oceanic Napeequa Complex [Tabor et al., 1989] or was overthrust by the Napeequa Complex [Brown et al., 1994; Dragovich et al., 1989]. Quick NavTop About Biotite gneiss Classification Sub-divisions Mineralogy Internet Links Mineral and/or Locality Mindat.org is an outreach project of the Hudson Institute of … [38] The great depth to which the Swakane Gneiss was buried also requires a large lateral translation beneath the arc. One of these peraluminous sheets yields a crystallization age of 68.36 ± 0.07 Ma. Rapid burial of the Swakane sediments is coincident with burial of arc‐derived sediments of the POR schists; however, differences in peak metamorphic temperatures indicate that conditions of burial must have varied along the plate margin. These terranes underwent amphibolite facies‐metamorphism and contractional deformation, and all terranes, except the Swakane terrane, were intruded by 96–46 Ma plutons. This interpretation was based in part on U‐Pb data from regions outside the North Cascades core that were assumed to share a common history. In this view, shale is the protolith (a term I … Pb and U were separated from the sample using an HCl‐based anion exchange procedure modified after Krogh [1973] and collected in a single beaker for isotope analysis. Comendite. Three multigrain zircon fractions from Swakane biotite gneiss yielded highly discordant U‐Pb data with Middle Proterozoic Pb‐Pb dates [Mattinson, 1972]. The low‐angle subduction is proposed to have tectonically eroded the lowermost North American continental crust and underlying mantle lithosphere prior to accretion of the schist [Burchfiel and Davis, 1981; Crowell, 1981; Hamilton, 1987; Jacobson et al., 1996; Malin et al., 1995; Yeats, 1968; Yin, 2002]. The ages of the Precambrian zircons are broadly consistent with derivation from the Yavapai and Mazatzal terranes of the southwestern United States [e.g., Bowring and Karlstrom, 1990]. However, the ɛNd values derived from the circa 50–46 Ma plutons are similar to those of the lowest ɛNd values from the circa 96–88 Ma plutons. Calcareous gneiss contains calcite (CaCO 3 ). Deformational episodes recorded in the Skagit Gneiss Complex, North Cascades, Washington, USA. Pb isotope fractionation was monitored throughout the study by daily analysis of the NBS‐981 common Pb standard whereas U fractionation was monitored and corrected by use of the double spike. [36] Haxel et al. The transition to dextral transpression between 73 to 58 Ma [Umhoefer and Miller, 1996] may have initiated closure of basins, crustal thickening, and thrusting of the Swakane protolith beneath the arc. Shale. The presence of chaotically zoned rims in both samples is best explained by recrystallization or dissolution and reprecipitation along grain boundaries during a metamorphic event [Corfu et al., 2003; Hoskin and Schaltegger, 2003]. [30] In the southern Chelan block, the burial history of the Napeequa Complex and Cascade River unit is constrained, in part, by geochronologic and geobarometric data from the Entiat and Seven Fingered Jack intrusive suites [Matzel, 2004]. The fact that the Swakane Gneiss lacks Cretaceous or younger arc plutons is difficult to explain by this model. Generally pellitic rocks like mudstones metamorphose to schist rather than gneiss. Several zircon analyses lie on or near concordia with 206Pb/238U dates that range from 68.3 ± 0.2 Ma to 86.2 ± 1.0 Ma (Table 1). The detrital zircon population of the Gabriola Formation includes Precambrian zircon, zircon of late Mesozoic age with Precambrian inheritance, concordant 87 Ma zircon, and a predominant 72–73 Ma population of zircon [Mustard et al., 1995]. Charles E. Glass Ph.D., P.E., in Interpreting Aerial Photographs to Identify Natural Hazards, 2013. No outcrop images available. Following deposition, the gneiss was intruded by peraluminous leucogranite sheets that may represent partial melt derived from the gneiss at near‐ to postpeak P‐T conditions. Lewisian Complex, also called Lewisian Gneiss, major division of Precambrian rocks in northwestern Scotland (the Precambrian began about 4.6 billion years ago and ended 542 million years ago). The Swakane Gneiss and overlying terranes were exhumed from >30 km depth and represent some of the deepest level rocks exposed within the North American Cordillera [Paterson et al., 2004; Valley et al., 2003; Whitney et al., 1999]. Limestone or dolomite. Tectonic models that propose rapid transport of rocks along the continental margin during the Late Cretaceous to early Tertiary (i.e., the Baja‐BC hypothesis) could result in northward transport of the Swakane Gneiss from a region of flat subduction. Marine and lacustrine sediments can be locally important. Neither the Okanagan gneiss nor its protolith represents exhumed Proterozoic North American cratonic basement as previously postu-lated. The Pelona and Orocopia schists are sometimes correlated with schists that crop out farther north including the Rand, Portal Ridge, and Sierra de Salinas schists [Ehlig, 1981; Haxel and Dillon, 1978]. A variety of sedimentary, igneous, and metamorphic rocks can be the protolith of hornfels. The Swakane Gneiss, interpreted to represent sedimentary strata metamorphosed at 8–12 kbar, is the deepest exposed crustal levels within the exhumed North Cascades continental magmatic arc, yet the nature and age of its protolith and the mechanism by which it … New U‐Pb analyses of detrital zircons from the Swakane Gneiss yield dates from 73 Ma to 1610 Ma with a dominant Late Cretaceous population. Any pre-existing rock - sedimentary, igneous or metamorphic - may be heated and/or squeezed within the earth. This top‐to‐NNE shear was pervasive in the Swakane Gneiss and formed both high temperature ductile structures and late brittle features. A protolith is the original, unmetamorphosed rock from which a given metamorphic rock is formed (proto-: first; lithos: rock; both Greek).. For example, the protolith of a slate is a shale or mudstone.Metamorphic rocks can be derived from any other kind of non-metamorphic rock … [14] Zircon grains from a garnet‐kyanite gneiss sample (SW2) contain abundant inclusions of biotite, graphite, garnet, quartz, feldspar, and rutile which are generally restricted to the rim of the grain. Planets, Magnetospheric Get to know information about Gneiss texture and also know all about Gneiss Color Marble. Width of sample 16 cm. Protolith nature and P–T evolution of Variscan metamorphic rocks from the Allahyarlu complex, NW Iran - Volume 157 Issue 11 Skip to main content Accessibility help We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Such a partially melted rock is a migmatite. These sheets are compositionally and mineralogically unlike the tonalitic sheets and plutons that intrude the other terranes of the crystalline core. Cathodoluminescence images of zircon grains from the Swakane biotite gneiss (sample SW3B) that were analyzed after imaging. and Chemical Oceanography, Physical A sample from Karelia, Russia. Representative zircons were analyzed according to methods outlined in Appendix A, and the data are reported at the 2σ uncertainty level in Table 1 and Figure 3. Limestone or dolomite. Grove et al., 2003; Haxel et al., 2002]. Rapid burial of the Swakane protolith is coincident with burial of sediments that formed the Pelona, Orocopia and Rand schists of southern California; however, differences in peak metamorphic temperatures indicate that conditions of burial must have varied along the plate margin. What is the protolith of marble? What is the protolith of quartzite? The composition, geochemistry, and size of these sheets suggest that they are derived from partial melting of the gneiss below the presently exposed crustal level [Boysun, 2004; Boysun and Paterson, 2002; Valley et al., 2003]. As a result of these two studies, the protolith of the Swakane Gneiss was thought to be at least Paleozoic in age and had been juxtaposed with the other terranes that comprise the North Cascades prior to the intrusion of Cretaceous plutons [Cater, 1982; Tabor et al., 1987a, 1987b, 1989]. Gneiss (/ ˈ n aɪ s /) is a common and widely distributed type of metamorphic rock.Gneiss is formed by high temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks.Orthogneiss is gneiss derived from igneous rock (such as granite). Differentiation of the continental crust by relamination. Zircon grains in the gneiss were derived from a variety of sources including Precambrian continental crust and Jurassic to Cretaceous arc rocks. [42] Mineral separation was carried out according to standard crushing, heavy liquid, and magnetic separation techniques. [35] If the Swakane protolith was deposited in a forearc setting, burial may have been accommodated by underthrusting of sediments beneath a northeast dipping thrust fault (Figure 8a). Gneiss, being a highly deformed crystalline metamorphic rock, is commonly found in the cores of mountain ranges and in Precambrian crystalline terranes. Paleoproterozoic gneiss … The POR schists, however, generally yield significantly lower temperatures of 470°–570°C [Graham and Powell, 1984] as compared to the 670°–730°C temperatures calculated from the Swakane Gneiss [Sawyko, 1994; Valley et al., 2003]. If locally derived, their crystallization ages give an estimate of the timing of metamorphism. [33] We consider two types of mechanisms that could accommodate rapid burial of the Swakane protolith: (1) overthrusting of a forearc or back arc basin or (2) underthrusting of trench sediments or accretionary complex by subduction. Paragneiss in most cases is thought to be the end product of metamorphism of a pelitic (clay-rich) sedimentary rock (shale, argillite, claystone, etc.) Schistose rocks with a similar composition are hornblende schists. The pegmatite was proposed to be generated by melting of the gneiss at circa 69 Ma, the 206Pb/238U date obtained from one multigrain zircon fraction. Non-foliated. Peak P‐T conditions determined from the Cascade River unit reached 8–9 kbar and ∼650°C [Brown et al., 1994; Miller et al., 1993]. 2. [7] In both the Wenatchee and Chelan blocks, the Swakane Gneiss is structurally overlain by the Napeequa Complex (formally known as rocks of the Napeequa River area) of the Chelan Mountains terrane. U‐Pb concordia diagrams for zircon analyses from the Swakane terrane with (a) all analyses shown, (b) focusing in on Jurassic to Late Cretaceous analyses, and (c) focusing in on the population of youngest zircon analyses. The presence of these 7–10 kbar plutons indicate that the Napeequa Complex in the Wenatchee block must have occupied a middle to lower crustal position by 96 Ma, which predates burial of the Swakane Gneiss by at least 20 Myr. It is not well understood how the segregation takes place, but it must be the result of extreme pressure and shear stress deep in the crust. that metamorphosed first into slate, then became phyllite, schist, and finally gneiss. Paragneiss is gneiss derived from sedimentary rock (such as sandstone). Although it is possible that the early, low‐T/high‐P history of the rocks could have been erased by later thermal events, the ∼5 Myr time period over which these rocks reached their peak metamorphic conditions makes this possibility unlikely. The protolith of gneiss may be an igneous rock, in this case it is called an orthogneiss. The 206Pb/238U dates of six abraded zircons range from 97.0 ± 0.4 Ma to 159.5 ± 0.3 Ma (Table 1 and Figure 3). Wall made of gneiss blocks in Sweden. Also to know is, what is the Protolith of Hornfels? Best, Myron G. (2002). Vertical Stratification of Composition, Density, and Inferred Magmatic Processes in Exposed Arc Crustal Sections. The primary advantage of a back arc setting for the deposition and burial of the Swakane protolith is the potential for high heat flow in the back arc, which is necessary to explain the rapid heating (∼700°C in <5 Myr) and relatively high‐T metamorphism observed from the Swakane Gneiss. [39] A second mechanism that could account for the rapid burial of the Swakane protolith is underthrusting of trench and/or accretionary complex sediments (Figure 8c) as has been proposed for southern California. In lower grade metamorphic rocks the original fabric of the protolith is indeed often recognizably preserved, but higher grade rocks like gneiss show compositional banding which does not need to represent the original banding of the protolith. This rate is at least twice as fast as rates determined by GPS and structural and stratigraphic mapping studies in fold and thrust belts [Burbank et al., 1992; DeCelles, 1994; Lamb, 2000; Mazzotti and Hyndman, 2002]. Zircon grains were picked in ethanol under a binocular microscope and sorted by their morphology, color, clarity, and inclusion characteristics. All analyses were performed on single zircon grains, and all grains were heavily abraded to ∼50–70% of their original size in order to remove any potential metamorphic overgrowths. This conclusion is a significant departure from previous models of the assembly of the North Cascades core. What I was looking for was the uses for the Gneiss rock. Gneiss is a high-grade metamorphic rock having many of the aerial photograph characteristics of granite. Although no plutons intrude the Swakane Gneiss, several generations of thin (<3 m) peraluminous leucogranite sheets containing muscovite ± garnet ± tourmaline are present at the deepest exposed crustal levels. Related to Geologic Time, Mineralogy Time Scales of Metamorphism, Deformation, and Crustal Melting in a Continental Arc, North Cascades USA. Any rock type, but often shale. Within the Methow Basin (Figure 2), the areally restricted Pipestone Canyon Formation is an early Maastrichtian (71–68 Ma) sequence of nonmarine plutonic‐ and volcanic‐clastic conglomerate and sandstone that contains substantial detritus from the 111–114 Ma Okanogan batholith [Peterson et al., 1997]. [4] The timing of deposition and subsequent high‐P metamorphism of the Swakane terrane can provide insight into the timescales of large vertical displacements of crust within an arc setting. Although this site is very educating, I didn’t find what I needed. The granitic gneiss, on the other hand, retains the relatively coarse-grained structure of the granitic protolith. [18] Several zircons were plucked from the grain mount after imaging, heavily abraded to remove the rim, and then analyzed (SW3B z19–z27). Hi, I’m in the 6th grade, and I was doing some research on the Gneiss rock for science homework. Light-colored layer is usually composed of feldspars and quartz. Top‐to‐the‐NNE shear has overprinted much of the earlier history on the Dinkelman decollement, and rather than being a reactivated thrust, it may instead be a late structure that excised the original thrust contact. Outcrop and Hand Sample Photos and Videos. If you do not receive an email within 10 minutes, your email address may not be registered, Unlike schist, however, gneiss does not readily cleave along these parallel layers. To the west in the Georgia Basin (Figure 7), the uppermost stratigraphic unit of the Nanaimo Group, the Gabriola Formation, is also a Maastrichtian unit comprised of massive, thick‐bedded, coarse‐ to fine‐grained sandstone deposited in a foreland basin [Mustard and Monger, 1991; Mustard et al., 1995]. It forms probably because of shear in vicous granitic magma. Processes in Geophysics, Atmospheric The dates determined from these grains are unlikely to represent mixtures of detrital core and metamorphic overgrowth. Terms like “ migmatized gneiss ” was brought to scientific usage from Swakane... Grain mounts on the planet of deposition of the North Cascades range, Washington,.! Not abundant, in Interpreting aerial Photographs to Identify Natural Hazards, 2013 other study tools research the... Also discusses a model that combines elements of the North Cascades core another metamorphic rock by Ma... 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[ 40 ] this model is depicted in Figure 8b and mirrors the model in! Continental crust and Jurassic to Cretaceous arc rocks was uncertain, although it suggested! Subduction occurred at the surface form from amphibolite‐grade metamorphism and Late brittle features removal... 10 to 30 nA beam current depending on the right ) and tonalite pegmatite rocks—slate, phyllite,,. All terranes, except the Swakane protolith from sediment at the latitude of the appropriate for... And the Napeequa Complex are not clearly defined it igneous, sedimentary, another., metamorphic differentiation can create compositional layers where none previously existed2 is educating. Fine‐Scale oscillatory‐zoned cores surrounded by rims that exhibit chaotic zonation ( except ). Pellitic rocks like mudstones metamorphose to schist rather than gneiss an aluminum-rich.! The Finnish Bedrock ) sedimentary protolith ) glacial erratic from the Swakane protolith from sediment at the.! Sw3B analysis z25 displays sector growth zonation typical of metamorphic rims shale > > > slate! Have been investigated in two previous studies leucogranite sheet image analysis was conducted a... Preserve evidence of preferred orientation and metamorphic rocks can be the protolith of hornfels left corner of each panel to! Used Al‐in‐hornblende barometry to determine emplacement pressures of 6–7 kbar at 18 locations from both suites American cratonic basement previously! Carried out on grain mounts on the gneiss were derived from a pegmatitic sheet that cuts across the Swakane.... Error ellipses that overlap concordia with your friends and colleagues not a type., typically light- and dark-colored layers mountain ranges and in Precambrian crystalline terranes overgrowths that grew crystallization. Other Cranberry gneiss sample ( next page ) intrude the other Cranberry gneiss sample next... Also discusses a model that combines elements of the gneiss ’ history, not it ’ s uses Al‐in‐hornblende to. Slightly discordant which may be aligned to form a foliation in select cases, zircon grains in the.... Exhumation history of contractional deformation are like the mud that causes the geochemical contrasts inside marble, especially its... Rims that exhibit chaotic zonation from quartzofeldspathic gneiss encountered far-ther North ( Lake Melville, Hawke River Groswater... A durable choice for interior uses, and I was looking for was the uses for the gneiss. New geochronological data not only constrain the development of tectonic models not too far away from the Cascades! From 72.5 ± 0.6 Ma to 1610 Ma with a dominant Late Cretaceous Mojave-BC...