Detrital garnet provenance analysis was carried out on sandstones of the Cretaceous Yukawa Formation in the Shimanto belt of central Kii Peninsula, Southwest Japan. The Yukawa Formation is an upper … Expand. View 1 excerpt, cites background. Rb—Sr Geochronology of the Hida metamorphic belt, Japan. RbSr whole-rock and mineral isochron ages have been determined for metamorphic and granitic rocks of the Hida metamorphic belt.
The results indicate that an extensive metamorphic event together with … Expand. U-Th-Pb ages of three zircons of granitic and metamorphic rocks from Ryoke metamorphic zone in the Kinki district have been determined.
Rb-Sr whole-rock model age dates on Precambrian gneisses in South Korea have values that are greatly scattered owing to lower Mesozoic thermotectonic activity which caused an isotopic homogenization … Expand.
U-Th-Pb ages of sphene and zircon from the Hida metamorphic terrain, Japan. Abstract Four sphenes as well as six zircons, three of which coexist with sphene, from the igneous and metamorphic rocks of the Hida metamorphic terrain, Japan, were analyzed for U-Th-Pb ages.
The … Expand. Rb-Sr dating on the rocks in Japan I ,. Abstract: Geologic age measurements with the Rb-Sr method were made on micas and feldspars separated from granites, granite pegmatites, gneisses and schists of the South Western part of Japan.
And … Expand. On the pacific-type orogeny and its model — extension of the paired belts concept and possible origin of marginal seas. Abstract The Pacific-type orogenic zone consists of a pair of belts with contrasting nature; outer oceanward belt and, inner continentward belt.
The former belt is km or less in width and … Expand. Origin and development of marginal basins in the western Pacific. The semi-isolated basins and series of basins of intermediate to normal oceanic depths that lie behind island arc systems are termed marginal basins, and are believed to be of extensional origin. Convincing geological data indicate that the oceanic structure of the earth's crust is secondary and is formed as the result of the breakup and "basification" of the continental crust.
Small areas at altitudes of 2, feet west of Windy Creek and 5, feet southeast of Gold King Creek consist largely of boulders and blocks. Apparently derived from headwater regions of Nenana and Wood Rivers in Alaska Range and deposited by ancient glaciers that flowed north over former valley floors much higher than present river beds.
Ancient val- ley floor of Nenana River is feet above present river level at Rex and 1, feet above river level at Ferry Wahrhaftig, , p. Maximum thickness in Fair- banks quadrangle about 2, feet. West of California Creek includes several hundred feet of coarse sandstone at base; east of California Greek entire formation is con- glomerate.
Thickness and pebble size decrease northward; imbrication and crossbedding indicate deposition by north- flowing streams. West of Totatlanika River pebbles and boulders consist of sandstone and conglomerate from Cant- well Formation Lower Cretaceous , quartz, chert, quartz- ite, volcanic rocks, granite, and granodiorite from plutons in Alaska Range to the south; and dark-green altered ophitic ilmenite-bearing gabbro from belt of Triassic greenstone in southern part of central Alaska Range.
Unit peren- nially frozen, but contains little ground ice. According to Jack A. Structure contours on base of Nenana Gravel show the inferred configuration of the surface in part restored on which it was deposited. In constructing contours east of California Creek and south of Buzzard and Boulder Creeks, thickness of coal-bearing formation beneath Nenana Gravel was assumed to be to feet. A synclinal basin of coal-bearing rocks with maximum thickness of 1, feet is believed to havfe underlain Nenana Gravel in area immediately north of Rex Dome, as inferred from single patch of coal-bearing formation on ridgetop north of mouth of Rex Creek.
Tcb Coal-bearing formation. Pinches out north- ward and is overlapped unconformably by Nenana Gravel. Can be divided into five units, locally separated by un- conformities: 1 At the base, a discontinuous unit feet thick in Rex Creek and MacAdam Creek basins, feet thick at the head of Tatlanika Creek, and less than feet thick elsewhere, of interfingering lenticular poorly sorted clayey pebbly sandstone, sandy micaceous claystone, and lenticular and locally bony coal. Clastic rocks were derived locally, and unit was deposited on ir- regular land surface.
Prominent coal bed 24 feet in maximum thickness at top. Pebbles in sandstone are chiefly quartz, chert, and quartzite. Pebbles of granitic, gabbroic, and volcanic rocks are common to abundant. This unit grades northwestward into non-coal-bearing facies as much as 1, feet thick, consisting of sandstone and conglomerate; it overlaps units 1 to 3, apparently with local unconformity, and rests directly on schist west of California Creek and north of Buzzard and Hearst Creeks.
Near base of unit 5 on Tatlanika Creek are one or two discontinuous rhyolitic ash beds 0 to 25 feet thick. All units are peren- nially frozen to depths of 5 to feet and have low to moderate ice content. Units 1 to 4 are thicker and con- tain more coal in adjacent parts of Healy Quadrangle to south. Areas of outcrop of non-coal-bearing facies of unit 4 and all of unit 5 are shown by stipple pattern. Mt Totatlanika Schist. Contacts between the two facies are generally sharp.
Augen are locally deformed into spindles, parallel to schistosity, elsewhere original crystalline outlines are at a sharp angle to schis- tosity. Locally contains layers of black carbonaceous schist 10 to 20 feet thick. In mountains between the head of Buzzard Creek and Wood River, the coarse facies schist and gneiss is separated by a thrust fault from an underlying third facies consisting of pale-yellow quartz-feldspar gneiss, with infaulted and interbedded black carbonaceous schist and dark-green chloritic schist, Foliation of Totatlanika Schist is due to parallel orien- tation of mica and chlorite flakes and fine layers of dif- ferent mineral composition; lineation is commonly a linear streaking and elongation of some of the minerals, particularly the microcline augen, in a single direction in the plane of foliation.
The permafrost is cut by two or three sets of joints, trending roughly N to NW, NE, and due E, spaced 1 to 5 feet apart and perpendicular to foli- ation. Totatlanika Schist is considered to be Mississip- pian? DSt Tolovana? Forms prominent ridge in extreme northwest corner of quadrangle. Weathers buff to yellowish brown. Contains crushed zones recemented by white calcite and quartz.
Chert rare or absent. Correlated on basis of lithology and geographic trend with the Tolovana Lime- stone in the White Mountains 90 miles to the northeast, which is 4, feet thick at the type locality Church and Durfee, , and is Middle Silurian to Middle or early Late Devonian in age Mertie, , p.
Oliver, written communication, February 13, and July 6, Nilkoka Group. Interbedded siliceous shale is hard, thin bedded, medium light gray weathering1 to light yellowish gray. Color of fine-grained rocks predominantly green but mottled by red through pale olive green, dusky yellow, and light yellowish gray areas produced by leaching and oxidation along joints, on exposed surfaces, and in more porous parts. Siltstone green or tan; limestone medium gray to dark gray-brown, or creamy where weathered.
Grit is gray but stained rusty brown on weathered surfaces. Locally the rock is foliated, generally parallel to bedding. The fine-grained rocks range from shale and argillite to phyllite. In the Nilkoka Group the chert and shale nc alternate in bands several miles wide with grit and phyllite ng. The Nilkoka is the underlying bedrock in most of the area west of Tolovana River and north of the Tanana; type locality is west bank of Tanana downstream from mouth of Tolovana Brooks, , p. Unit nc is cor- related with Mertie's , p.
Age of Nilkoka un- certain, but is believed to be Precambrian or early Paleozoic. Includes muscovite-bio- tite schist, garnet-mica schist, calcite- and dolomite-bear- ing schist, dark-gray to black chloritic and graphitic schist, amphibolite, light-gray to white impure marble, and light- brown light-gray-weathering gneiss that has been af- fected by retrograde metamorphism. A small area of quartz-sericite schist and graphitic schist on upper Totatlanika River and Bonanza Creek at south border of area mapped as Birch Creek Schist, but may be younger.
Essential min- erals in Birch Creek Schist are quartz, sericite, biotite, plagioclase commonly albite, some albite-oligoclase , po- tassium feldspar, graphite, calcite, dolomite, and amphi- boles actinolite and tremolite ; accessory minerals include chlorite, garnet, epidote, clinozoisite, hornblende, phlogo- pite, iron oxides and hydroxides, and rarely staurolite and andalusite. Birch Creek Schist formed by synkinematic metamorphism of shale, siltstone, sandstone, and lime- stone.
Age uncertain but considered to be early Precam- brian by Mertie , p. Recent isotopic measurements give dates ranging from m.
Wasserburg, Eberlein, and Lanphere, ; on basis of these dates, the age of the Birch Creek Schist is considered to be Precambrian or early Paleozoic. Be- cause of complicated structure and intermixed rock types, the gross thickness of the Birch Creek Schist is unknown, but must be many thousands of feet Mertie, , p. At least two stages of deformation and recrystallization are indicated, the first probably of higher metamorphic grade than the second. Metamorphic grade is middle biotite and garnet zones near Fairbanks, and decreases northwestward to lower chlorite zone.
Well-developed zones of contact metamorphism border intrusive bodies. Earliest folds appear to have northwesterly trend, but later structural trends northeasterly Forbes and Brown, , parallel to trends of younger rocks in Livengood quadrangle to north.
Mineralogic layering and planar parallelism of platy minerals, as well as rare relict bed- ding, folded into closely spaced isoclinal folds with ampli- tudes of tens of feet. Unconformably overlain in the Alaska Range by the coal- bearing formation.
Age probably Mesozoic, although some may be early Tertiary. Intrusive mass east of Fox is gray to yellowish-brown coarse porphyritic biotite granite or quartz monzonite with microcline phenocrysts. Intrusion northeast of Fort Wainwright Ladd Air Force Base is spheroidally weathering medium-grained hypid- iomorphic pyroxene-bearing granodiorite, gray where fresh and brown on weathered surfaces.
Dikes north and west of Fairbanks are gray to yellowish-brown medium- grained quartz-bearing porphyritic granitic rocks. Intrusion west of Totat- lanika River at south edge of map area is gray porphyritic dacite, intruded at shallow depth, with phenocrysts of beta-quartz, calcic andesine, biotite, and hornblende 0. This body has closely spaced nearly vertical joints. Dmu Mafic and ultramafic rocks.
Diorite contains 45 percent strongly zoned plagioclase laths 1 to 3 mm long and 0. Most augite occurs as cores in amphibole crystals. Mafic min- erals locally altered to chlorite? Ore minerals consti- tute about 5 percent of the diorite. Plagioclase-hornblende-garnet gneiss containing hornblende blades and garnet megacrysts. Hoosac Formation - Rusty-brown to dark-gray, albite-spotted muscovite-biotite schist or gneiss, with interlayered black garnet-biotite-albite-quartz schist near base; interfingers with Dalton Formation.
Hoosac Formation - Rusty, gray, quartz-albite-mica -chlorite schist and gneiss. Locally conglomeratic. Hoosac Formation - Undifferentiated Hoosac Formation. Intimately interfolded Littleton and Partridge Formations - In areas of poor exposure and incomplete mapping. Marlboro Formation - Thinly layered amphibolite, biotite schist and gneiss, minor calc-silicate granofels and felsic granofels.
Massabesic Gneiss Complex - Biotite-feldspar paragneiss of Proterozoic Z age intruded by potassium-feldspar-rich gneiss of Ordovician age. Monson Gneiss - Layered to massive biotite-plagioclase gneiss, amphibolite, microcline augen gneiss. Nashoba Formation - Sillimanite schist and gneiss, partly sulfidic, amphibolite, biotite gneiss, calc-silicate gneiss and marble. Nashoba Formation occurs in Nashoba zone of eastern MA.
Consists of interlayered sillimanite-bearing, partly sulfidic schist and gneiss, calc-silicate gneiss, and subordinate quartzite and marble. Protoliths were probably volcanogenic sediments interlayered with limy marine sediments.
Bell and Alvord divided Nashoba into 10 members on basis of lithology. Amphibolite is most abundant near presumed base, namely in Boxford Member. Skehan and Abu-Moustafa divided Nashoba into 30 members based on section in Wachusett-Marlborough tunnel. Subdivision of Nashoba is conjectural south of Marlborough and Shrewsbury. On MA State bedrock map Zen and others, only Boxford Member is separated out from the rest of the Nashoba because this unit was the only member clearly recognized in several area.
A definite sequence of members probably does not exist anywhere in the Nashoba because of lenticularity of assemblages and repeated rock types, both of which could be accounted for by either sedimentary or tectonic processes.
Although Castle considered Fish Brook to be either a premetamorphic intrusive rock or a core gneiss of intrusive or sedimentary ancestry, Bell and Alvord considered it to be volcanic or volcaniclastic in origin. If the rock were a core gneiss, that date would apply only to the Fish Brook and not to surrounding rocks; but, Bell and Alvord believe Fish Brook to be part of the Marlboro Formation-Nashoba Formation sequence and therefore the date does apply to the sequence.
In addition, a Ma date for Shawsheen Gneiss [reference not given] helps bracket age of Marlboro-Nashoba sequence. Although age on MA State bedrock map is shown as Proterozoic Z or Ordovician due to uncertainty regarding actual rocks sampled by Olszewski and a strong belief that rocks of Nashoba zone correlated with Ordovician rocks to the west , author now feels that rocks of Nashoba zone except for Tadmuck Brook Schist are all Proterozoic, but that they are unlike the Proterozoic rocks of neighboring Milford-Dedham zone.
Quinebaug Gneiss - Amphibolite, biotite and hornblende gneiss, felsic gneiss, and calc-silicate gneiss. Shawsheen Gneiss - Sillimanite gneiss, sulfidic at base; minor amphibolite. Tatnic Hill Formation - Sulfidic sillimanite schist, sillimanite schist and gneiss, biotite gneiss; minor amphibolite, calc-silicate gneiss and marble. Baltimore Gneiss Precambrian Baltimore Gneiss - Biotite-quartz-feldspar gneiss and biotite-hornblende gneiss; amphibolite widespread but subordinate; texturally varied; granitic gneiss, veined gneiss, augen gneiss, banded gneiss, and migmatite, in places complexly intermingled; age 1, m.
Cockeysville Marble - Metadolomite, calc-schist, and calcite marble are predominant; calc-gneiss and calc-silicate marble widespread but minor; thickness about feet. James Run Gneiss - Thick-bedded, light gray biotite-quartz-plagioclase gneiss with thin interbeds of quartz amphibolite; grades downward into sharply layered, thin- to thick-bedded paragneiss composed of subequal amounts of biotite-quartz-plagioclase gneiss and quartz amphibolite; thickness unknown.
Setters Formation - Upper member: Feldspathic mica schist and mica gneiss; total thickness to feet. Middle member: Impure quartzite interstratified with thin beds of mica schist; total thickness to feet. And Lower member: Medium-grained, feldspathic mica schist; locally granitized; total thickness to feet.
Thick-bedded to massive, pebble- and boulder-bearing, arenaceous to pelitic metamorphic rock; typically a medium-grained, garnet-oligoclase-mica-quartz gneiss; locally an intensely foliated gneiss or schist; apparent thickness 15, feet.
Silurian - Precambrian Z Berwick Formation. Gneiss and amphibolite Late Archean, 2. Protoliths are bimodal intermediate and mafic volcanic rocks Sims and others, Migmatitic gneiss and amphibolite Late to Early Archean - Varied gneisses of mostly unknown age in cores of gneiss domes and fault-bounded uplifts Archean gneiss terranes. Includes granite of Late Archean age that transgresses gneisses and amphibolite.
Granite-rich migmatite Late Archean Granite-rich migmatite - Granitic gneiss, paragneiss, schist, and migmatite in the Vermillion Granitic Complex, and other parts of extreme northern Minnesota. Grades into granitoid rocks.
Migmatitic gneiss, amphibolite, and granite - Montevideo and Morton Gneisses m. Inferred to include various younger rocks, including granitoid intrusions in the Hillman Migmatite and pillowed basalt in poorly exposed areas of southwestern Minnesota. North Carolina. Alligator Back Formation; Gneiss Late Proterozoic Gneiss - finely laminated to thin layered; locally contains massive gneiss and micaceous granule conglomerate; includes schist, phyllite, and amphibolite.
Mica schist and phyllite - laminated to thin layered; interlayered with minor biotite-muscovite gneiss and amphibolite. Amphibolite - metamorphosed mafic extrusive and intrusive rock; includes hornblende gneiss, thin layers of mica schist, and small nonlayered masses of metadiorite and metagabbro.
Amphibolite and Biotite Gneiss - interlayered; minor layers and lenses of hornblende gneiss, metagabbro, mica schist, and granitic rock. Metagraywacke - foliated to massive, locally conglomeratic; interlayered and gradational with mica schist, muscovite-biotite gneiss, and rare graphitic schist.
Mica schist - locally sulfidic and graphitic; minor interlayered mica gneiss and amphibolite. Muscovite-biotite gneiss - locally sulfidic; interlayered and gradational with mica schist, minor amphibolite, and hornblende gneiss. Banded Gneiss - interlayered with calc-silicate rock, metaconglomerate, amphibolite, sillimanite-mica schist, and granitic rock.
Biotite Granitic Gneiss my - unconformity; contains paragneiss and granitic to quartz monzonitic orthogneiss; locally schistose and mylonitic. Locally includes tectonic slices, infolded remnants, or recrystallized equivalents of the Grandfather Mountain Formation.
Equivalent to the Wilson Creek Gneiss. Blowing Rock Gneiss my - unconformity; abundant white potassic feldspar megacrysts in finely banded biotite schist, locally calcareous; interlayered with quartz-feldspar schist, calcareous biotite schist, phyllite, black slate, calcareous quartzite, sulfidic greenstone, and siliceous tuff.
Coweeta Group - quartz dioritic gneiss, feldspar-quartz-biotite gneiss, metasandstone and quartzite, alumino-silicate schist, garnetiferous biotite gneiss, and minor amphibolite.
Quartz dioritic gneiss predominant. Felsic Mica Gneiss - interlayered with biotite and hornblende gneiss and schist. Felsic Mica Gneiss - interlayered with graphitic mica schist and mica-garnet schist, commonly with kyanite; minor hornblende gneiss.
Henderson Gneiss my - monzonitic to granodioritic; inequigranular. Injected Gneiss - biotite gneiss and schist intruded by numerous sills and dikes of granite, pegmatite, and aplite; minor hornblende gneiss. Lineated Felsic Mica Gneiss - white to pink, with strong lineation of muscovite-biotite streaks and prismatic quartz aggregates; planar foliation and layering weak; minor mica schist and hornblende gneiss.
Mica Schist - contains garnet, staurolite, kyanite, or sillimanite; includes lenses and layers of quartz schist, micaceous quartzite, biotite gneiss, amphibolite, and phyllite. Mica Schist - Garnet, staurolite, kyanite, or sillimanite occur locally; lenses and layers of quartz schist, micaceous quartzite, calc-silicate rock, biotite gneiss, amphibolite, and phyllite. Migmatitic Biotite-Hornblende Gneisses my - unconformity; layered biotite-granite gneiss, biotite-hornblende gneiss, amphibolite, calc-silicate rock; locally contains relict granulite facies rock.
Phyllite and Schist - includes phyllonite and interlayered biotite gneiss. Porphyroblastic Gneiss - massive to foliated, granodioritic, migmatitic.
New Hampshire. Rye Complex Ordovician? Rye Complex - Light-colored to gray schists and gneisses, quartzites, and amphibolites. Variably migmatized and mylonized. Contact with Kittery Formation on west is the Portsmouth Fault. New Jersey. Biotite-Plagioclase Gneiss Middle Proterozoic Biotite-Plagioclase Gneiss - White- to light-gray weathering, greenish-gray, medium-grained, moderately well layered gneiss composed of biotite, plagioclase and accessory amounts of hornblende, clinopyroxene, and, locally, garnet.
Biotite-quartz-oligoclase gneiss - White- to light-gray-weathering, light- to medium-gray or greenish-gray, fine- to coarse-grained, massive to moderately well layered, foliated gneiss composed of oligoclase or andesine, quartz, biotite, and, locally, garnet. Commonly interlayered with amphibolite. Gneiss granofels and Migmatite - Gneiss and granofels range in composition from felsic to intermediate to mafic; intermediate compositions predominate. Contains a wide variety of rock types including graphitic schist and marble.
Many rocks were injected by a granitoid that has blue quartz and augen of potassic feldspar and are arteritic migmatites. One body of gneiss contains a 1 m by 0.
Unit probably represents a sequence of meta-sedimentary and metavolcanic rocks that have been heavily injected and migmatized by felsic magma. Hornblende-Plagioclase Gneiss - White- to gray-weathering, greenish-gray, medium-grained, moderately well foliated gneiss containing hornblende, clinopyroxene, plagioclase and trace amounts of apatite, titanite and opaque minerals.
Hypersthene-Quartz-Oligoclase Gneiss - Gray- to tan-weathering, greenish-gray to greenish-brown, medium-grained, moderately well layered and foliated, greasy-lustered gneiss of charnockitic affinity composed of andesine or oligoclase, quartz, clinopyroxene, hornblende, hypersthene, and sparse amounts of biotite.
Commonly interlayered with amphibolite and mafic-rich quartz-plagioclase gneiss. Manhattan Schist Hall, in press - Medium-dark gray, medium- to coarse-grained schist and gneiss composed of biotite, muscovite, quartz, and plagioclase, and local accessory minerals sillimanite, kyanite, tourmaline, and garnet.
Contains some interlayered amphibolite. Unit is not exposed in the map area, but is present in boring logs. Monazite Gneiss - Buff-weathering, light-greenish-gray to greenish-buff, fine- to medium-grained, moderately well-foliated, well-lineated gneiss composed of microcline microperthite, quartz, oligoclase, biotite, and monazite. Accessory minerals include hornblende, zircon and opaque minerals.
Mapped in Fox Hill Range area. Quartz-Oligoclase Gneiss - White-weathering, light-greenish-gray, medium- to coarse-grained, moderately layered to indistinctly foliated gneiss and lesser amounts of granofels composed of quartz, oligoclase or andesine, and, locally, biotite, hornblende and or clinopyroxene. Contains thin amphibolite layers. Wissahickon Formation - Fine- to medium-grained biotite-quartz-plagioclase schist and gneiss that contains thin amphibolite layers. Schist and gneiss in alternating layers suggest a turbidite sequence of shale and graywacke.
The rocks are at high metamorphic grade, and, in places, the more pelitic parts have partly melted forming veins of migmatite. Some exposures show evidence of polymetamorphism as micaceous minerals occur both within the schistosity and as static porphyroblasts. New Mexico. Considered to be Mesozoic igneous complex intruding lower Paleozoic and possibly Precambrian Z sedimentary rocks.
Grades into units shown on map as lower Paleozoic. New York. Bedford Gneiss Ordovician? Bedford Gneiss - biotite-quartz-plagioclase gneiss and interlayered amphibolite; in part with augen of andesine and microcline. Biotite-quartz-plagioclase gneiss - with subordinate biotite granitic gneiss, amphibolite, calcsilicate rock. Biotite-quartz-plagioclase gneiss - commonly very low in biotite content, with interbedded feldspathic and biotitic quartzite and amphibolite; sillimanite and garnet common, graphite sporadic.
Biotite-quartz-plagioclase gneiss, amphibolite, and related migmatite - locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.
Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure. Charnockite, mangerite, pyroxene-quartz syenite gneiss - overprint signifies inequigranular texture. Cheshire Quartzite and Dalton Formation.
Dolomitic and calcitic marbles interlayered with significant amounts of calcsilicate rock - metasedimentary amphibolite, pyroxene granulite, and various gneisses; includes interlayered diopsidic and tremolitic marble and quartzite, and talc-tremolite rock mined in Balmat-Edwards belt, northwest Adirondacks. Fordham Gneiss A member - fa: garnet-biotite-quartz-plagioclase gneiss, amphibolite, biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar granulite. Fordham Gneiss E member - fe: garnet-biotite-quartz-plagioclase gneiss, and amphibolite.
Garnet-bearing gneiss and interlayered quartzite - contains varying amounts of biotite, garnet, sillimanite; minor marble, amphibolite, rusty paragneiss. Garnet-biotite-quartz-feldspar gneiss - quartzite, quartz-feldspar gneiss, calcsilicate rock. Harrison Gneiss - in New York and Connecticut, Brookfield diorite gneiss in Connecticut, and Ravenswood Gneiss in Brooklyn - biotite-hornblende-quartz- plagioclase gneiss with accessory garnet and sphene; plagioclase commonly occurs as augen.
Hornblende-quartz syenite gneiss - overprint signifies inequigranular texture. Hornblende syenite gneiss - overprint signifies inequigranular texture. Hybrid rock: mangeritic to charnockitic gneiss - with xenocrysts of calcic andesine and, locally, xenoliths of anorthosite; with increasing percentage of anorthosite component, passes gradationally into anorthositic rocks.
Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss. Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss. Manhattan Formation, undivided - pelitic schists, amphibolite; Units?
Omc, and? Omd may be Cambrian eugeosynclinal rocks thrust upon Oma;? Omd - sillimanite-garnet-muscovite-biotite-plagioclase-quartz gneiss;?
Omc - sillimanite-garnet-muscovite-biotite-quartz-plagioclase schistose gneiss, sillimanite nodules, local quartz-rich layers;? Omb - discontinous unit of amphibolite and? Omc-type schist. Quartz-plagioclase gneiss - may contain pyroxenes, hornblende, biotite; locally interlayered with amphibolite; subordinate biotite mesoperthite gneiss.
Rusty and gray biotite-quartz-feldspar gneiss - rusty facies contains variable amounts of garnet, sillimanite, cordierite, graphite, sulfides; minor marble and calcsilicate rock. Sillimanite-cordierite-almandine-biotite-quartz-feldspar gneiss. Consists of amphibolite, micaceous quartzite, quartz schist, and recrystallized manganiferous chert.
Includes structurally complex amphibole schist and quartz-rich hornblende gneiss of unknown age exposed at and near Chetco Peak west of Cave Junction Smith and others, Felsic and intermediate gneiss Precambrian Felsic and intermediate gneiss - Light, medium grained; includes rocks of probable sedimentary origin. Felsic and intermediate gneiss - Medium grained, light pink to greenish gray; largely quartz, feldspar, and mica; commonly gneissic, containing alteration minerals; interfingers with gabbroic gneiss.
Felsic to mafic gneiss - Light, medium grained; predominantly quartz and feldspar of igneous origin.
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