Hornblende Biotite Gneiss Research Articles

Rb-Sr ages of the gneiss and metamorphosed intrusive rocks of the Hida metamorphic belt in the Urushiyama area, Gifu Prefecture, central Japan.

Metamorphosed intrusive rocks (metagabbro and metatonalite), and nonmetamorphosed aplite dyke, all of which intrude into the coarse-grained biotite-hornblende gneiss, are exposed in the Urushiyama area along the Takahara River, the main part of the Hida metamorphic belt. RbSr mineral isochron ages of 216±10 Ma and 222±2 Ma are given for the coarse-grained biotitehornblende gneiss and metagabbro, respectively. On the contrary, the whole rock isochrons of the metagabbro and metatonalite show 415±144 Ma and 332±74 Ma, respectively. These whole rock ages correspond to the ages of intrusion of the gabbro and tonalite and they were re-equilibrated with respect to the Rb-Sr system approximately 220 Ma by the regional metamorphism. Whole rock samples of aplite dyke yield an isochron age of 172±7 Ma. The Hida gneiss in the Urushiyarna area seems to have been formed by the main stage of metamorphism and the deformation having been already finished before the intrusion of gabbro.

Archean and early proterozoic complexes of santa catarina, parana and sao paulo states, south-southeastern brazil : an outline of their geological evolution

The Luis Alves, Serra Negra and ltatins complexes are Arehean to early Proterozoic metamorphic units in the Brazilian States of Santa Catarina, Parana and Sao Paulo, south of the 24°S parallel. This paper summarizes their geological evolution based on petrographic, chemical, and mainly geochronological data. The three complexes consist of metamorphic rocks of the granulite facies, dominantly: norites, enderbites. charnoenderbites, ultramafites of granulite facies, kinzigites, quartzites, biotite-hornblende gneisses, meta-quartz diorites, metadiorites, metagabbros, serpentinites and talcites. Petrographic and chemical data support an igneous origin for most of these rocks. The radiometric age determinations made bythe Rb-Sr and the K-Ar methods on different materiais gave results related, for the most part, to the Pre-Jequie (about 3,100 m.y.), Jequie (2,600 ± 200 m.y.) and Transamazonico (2,000 ± 200 m.y.) events. Geochronological data suggest that the three complexes were formed predominantly by crustal accretion-differentiation processes.

The Malton Gneiss: Archean gneisses in British Columbia

Abstract Petrological and geochemical analyses of gneisses from the Malton Gneiss Complex (199°W 52°30′N, south of Valemount, B.C. and west of the Rocky Mountain trench) reveal four distinct mineralogical and geochemical groups, based on their petrology, Y and Nb contents and Fe Mg ratios. The Complex appears to be an Archean meta-igneous complex, which has been chemically modified, with alkali enrichment, during an Upper Proterozoic igneous event. Group 1, the most common rock type in the Complex, consists of mafic biotite—hornblende gneisses and amphibolites. They have low Y contents and the lowest Fe Mg ratios in the Complex. (Na2O + K2O) averages about 5%, K Rb ratios are between 200 and 400, K/Ba between 200 and 100 and Sr Ba ratios vary widely. The group 2 rocks are granitic and tonalitic gneisses characteristically garnetiferous and preserving their Archean age. They have Y Nb ratios of about 2 and low Y and Nb contents. Rb values are also low, but not exceptionally so, the range being 70–180 ppm. K Rb ratios lie between 20 and 400, K/Ba between 20 and 50 and Sr/Ba between 0.1 and 0.5. Groups 3 and 4 are alkali granitic gneisses generally occurring as intrusive sheets. Group 3 gneisses have Y Nb ratios of approximately 0.5 and have higher Nb contents than groups 1 or 2. Group 4 gneisses have Y Nb ratios of apporoximately 1 and both Y and Nb contents are higher than in groups 1 and 2. Parameters indicating an increase in differentiation are higher in groups 3 and 4 than in groups 1 and 2, but group 3 gneisses include some rocks with very high K Rb ratios, the range being 200–800 and the average above 400. The Malton Gneiss has no obvious analogues in the nearest surface Canadian Shield. It has geochemical similarities with the Grey Gneiss of the North Atlantic Craton and may be similar to the Archean of Western Montana.

REE distributions in a high-grade Archaean gneiss complex in Scotland: Implications for the genesis of ancient sialic crust

Seventeen rocks from the Lewisian Gneiss of the Inner Hebrides of Scotland, which represent three distinct lithological types at granulite to greenschist facies of metamorphism show rare-earth element patterns which seem not to have been disturbed by their complex metamorphic history. Some indication of their origin can be obtained by simple geochemical models. Three tonalitic pyroxene gneisses are characterized by: (1) light REE enrichment and heavy REE depletion; (2) low total REE contents; (3) moderate Eu enrichment. Their REE chemistry can be approximated by a model involving 10% partial melting of various garnet-bearing basaltic source materials. Alternatively, they may be some form of crystal cumulate, preserving their original anhydrous mineralogy, representing 30% crystallization of a parent tonalitic magma. Three tonalitic to granodioritic hornblende-biotite gneisses are characterized by: (1) light REE enrichment and heavy REE depletion; (2) significantly higher total REE contents than the pyroxene gneisses; (3) moderate Eu depletion. Their REE patterns can be approximated by a residual silicic melt in a model involving 30% fractional crystallization of solids with the modal mineralogy of the pyroxene gneisses or 40% removal of pure anorthosite from a parent dacitic magma. Two strongly metasomatised diopside-actinolite gneisses and one highly sheared epidote-chlorite gneiss have REE patterns which are not significantly different from the hornblende-biotite gneisses which were their precursors before metasomatism and late greenschist-facies shearing. This suggests that strong alteration has not enciphered the REE systematics of the gneisses. Basic gneisses of quartz tholeiite composition occurring as early dykes, which shared the same metamorphic history as the tonalitic to granodioritic gneisses, are characterised by: (1) slight enrichment in light REE relative to heavy REE; (2) variable total REE contents; (3) little difference between granulite and amphibolite facies types. Their REE patterns can be matched by models involving 5–15% partial melting of ultrabasic mantle with 3 times chondritic REE abundances, leaving a residue of olivine and orthopyroxene.

A Lewisian basement sheet within the Moine at Ribigill, north Sutherland

Synopsis A Lewisian basement sheet, consisting of hornblende and hornblende-biotite gneiss and amphibolite with a central zone of feldspathic migmatite, tectonically emplaced within the Moine is described using 98 major and trace element analyses of Lewisian and Moine rocks. The Lewisian rocks are quite distinct from the unmigmatized local Moine metasediments and can be distinguished from a Moine pre-metamorphic basic intrusion (the ‘Ben Hope Sill’) which forms part of the boundary of the Lewisian sheet. It is inferred, by comparison with published data, that the Ribigill Lewisian originally had a ‘Scourian-type’ geochemistry depleted in K, Rb, Pb, etc., during an early Lewisian high grade metamorphism. The rocks were retrogressed and migmatized during a later Lewisian event, with the introduction of Ce, Th, K, Rb, and possibly Na. The Ribigill migmatites differ from published accounts of Laxfordian migmatites in several respects most notably in having high K/Rb ratios.

Strata-bound scheelite mineralisation in skarns and gneisses from the Bindal area, Northern Norway

Scheelite in the Bindal area, Northern Norway, is developed in hornblende-biotite gneisses of volcano-sedimentary origin, especially in the zones of disseminated sulphides in the gneisses. Scheelite is present either in mobilised quartz veins or in skarnitised hornblende-biotite gneiss where limestone was in contact with these rocks. An exhalative-sedimentary origin of the mineralisation is proposed, on account of the strata-bound character and the lack of any direct relationship to the plutonic rocks of the Bindal massif.

Regional geology of early Precambrian high-grade metamorphic rocks in West Greenland. Part 1: Kângnaitsoq to Ameralik

Within this region three types of area are distinguished: 1. Amphibolite-grade areas which did not reach a granulite grade. 2. Granulite-grade areas. 3. Amphibolite-grade areas, many of which have been retrogressed from the earlier granulite grade. The main rocks are hypersthene-biotite gneisses, biotite-hornblende gneisses, amphibolites with or without orthopyroxene, sillimanite mica schists, rare marbles, skarns and quartzites, layered calcic anorthosites, a great variety of meta-ultramafic rocks including rare zoned talc lenses, abundant pegmatites, several generations of dolerite dykes locally amphibolitised by deep-seated fauIts. The fold structure of the region is characterised by abundant large-scale interference patterns. The history of the region is interpreted on the basis of a deformed cover/basement relationship, all major units being now mutually conformable.

Chemical data on some rock-forming minerals from high-grade gneisses, amphibolites and anorthosites from the Fiskenæsset area

The area mapped by the writer is situated to the west of Fiskenæsset and lies in the boundary zone between granulite and amphibolite facies rocks (see Kalsbeek, this report). In the north a creamy- to pink-weathering gneiss, commonly containing hypersthene and biotite is the chief rock type. In the south small-folded, pale-grey weathering biotite-hornblende gneisses are predominant. Amphibolite is of common occurrence in layers, pods and agmatite. The areal extent of the anorthosite-pyribolite complex as previously outlined by reconnaissance mapping (Ghisler & Windley, 1967) was confirmed in general but modified in detail. Additional occurrences of rocks belonging to the complex were found.

The chemistry and origin of some basement amphibolites between Ivigtut and Frederikshåb, South-West Greenland

Chemical and modal analyses of 54 amphibolites, 5 biotite gneisses and 5 hornblende-biotite gneisses, into which the amphibolites grade, confirm the field and petrographic evidence that the amphibolites were probably basic tuffs and lavas which, when mixed with varying amounts of quartzo-feldspathic sediment, gave rise to the hornblende-biotite gneisses on metamorphism. Plotted in an alkali-silica diagram 34 samples fall in the field of tholeiite basalt and 20 in the field of alkali basalt while traces of normative nepheline, never exceeding 4 %, occur in only 10 samples. It is shown that the sporadic occurrence of garnet and diopside and the occurrence of up to 15 % quartz are primarily controlled by the original composition of the samples. Garnet is entirely found in amphibolites with low Niggli mg values (0.36-0.45), diopside in samples with relatively high CaO, while modal quartz increases as mg falls. It is therefore possible that the more quartzose and garnetiferous amphibolites formed from late differentiates of the original basaltic magma, but the possibility cannot be excluded that contamination with sedimentary material has played a role, especially in increasing the modal quartz.

The petrography and origin of gneisses, amphibolites and migmatites in the Qasigialik area, South-West Greenland

The migmatites from a small area (approx. 200 km2) in SW Greenland are described with special attention to the modal composition of the different rock types. After a general introduction a description of the field relationships of the rocks is given. The leucosome of the migmatites consists of leucocratic veins which mostly have a quartz-dioritic to granodioritic composition; a typical melanosome has rarely been found. The paleosome consists of banded biotite gneisses, hornblende-biotite gneisses and amphibolites. In subordinate quantities occur anorthositic gneisses and garnet-rich gneisses and amphibolites. Spread throughout the area, homogeneous biotite gneisses occur, which locally form large masses, but generally occur as minor outcrops full of inclusions of banded gneisses and amphibolites. These homogeneous gneisses are generally hardly migmatized. The different rock types are petrographically described. Histograms of measured An contents of plagioclase in the different rocks are given. It is shown from a large number of modal analyses that there is a gradual change in plagioclase and quartz content from the banded biotite gneisses via the hornblende-biotite gneisses to the amphibolites (in part). Some of the amphibolites do not fit into this pattern, these amphibolites are also in other respects difierent from the others, among others through the presence of garnet and/or diopside. The homogeneous biotite gneisses may have a granodioritic composition, but the majority of the samples contain hardly any alkali feldspar and agree in modal composition with the banded biotite gneisses, but for a slightly higher amount of biotite in the latter. The leucocratic veins also have often a quartz-dioritic composition which agrees with most of the gneisses, but with a much lower content of dark minerals. The paper is concluded with a discussion of the origin of the difierent rock types, based on the data collected. Most of the rocks are thought to be formed by isochemical metamorphism of geosynclinal sediments. The banded biotite gneisses probably represent original sediments of greywacke to arkose type. Part of the amphibolites probably represent original basic volcanic and tufiaceous rocks, which may have undergone erosion, transport and sedimentation. The hornblende-biotite gneisses are thought to derive from mixtures of normal sediment with varying amounts of tufiaceous material. Alternative interpretations of the gneisses and amphibolites are discussed. The homogeneous gneisses may have formed from the metasediments by a process of homogenization and mobilization. The origin of the leucocratic veins is discussed. The mineralogical composition of the veins and the An content of the plagioclase seem to exclude an origin by anatexis in situ of the gneisses, but the evidence is not conclusive.

Observations on the geology of an area near lakes Thomson and Hankinson, Fiordland

Abstract The physiography of the area is dominated by glaciated landforms carved in gneiss of the Fiordland Complex.The gneiss is generally dioritic, with gradations to quartzo-feldspathic and amphibolitic varieties, and is cut by mainly barren pegmatite veins; epidote is abundant.The rocks commonly show signs of post-consolidational shearing and crushing. There is a well defined zone of strongly crushed rocks, trending approximately north, which cuts obliquely across the northern end of Lake Han-kinson.In general the rocks are petrographically similar to those near Lake Manapouri.Chemical analyses of a microcline-bearing gneiss, a hornblende-biotite gneiss, and an amphibolite are compatible with derivation of these from acid and intermediate volcanic or tuffaceous sedimentary rocks and mildly alkaline olivine basalts respectively.Geometric analysis of foliation attitudes, lineations, and minor fold axes, shows that there is a statistical fold axis plunging gently to the south-west.

Contribuição ao conhecimento de Estruturas Migmatíticas no Complexo Brasileiro

It is the purpose of this paper to present briefly the results of a study of the genetic relations of the migmatite structures- of the area named Praia do Tombo, ilha Santo Amaro, State of Sao Paulo, Brazil. The migmatites in the area in question present the following petrographic features: the old rock, a biotite-hornblende gneiss, was intruded by granitic material whose main constituent is microclne. The illustrations give an idea of forming process. Pegmatite dikes cutting through the migmatite rock has provoked the formation of a characteristic greisening zone by a process of metasomatic alteration

PETROGRAPHY, STRUCTURES, AND PETROFABRICS OF THE PINCKNEYVILLE QUARTZ DIORITE, ALABAMA

The Pinckneyville quartz diorite complex underlies an area in eastern Alabama extending from the Coosa River in northwest Elmore County northeast through Coosa and Tallapoosa counties into Clay County. Dark-gray, coarse-grained quartz diorite gneiss constitutes the major part of the complex, but there are smaller amounts of granodiorite and granite gneiss. Hornblende-biotite gneisses also occur and are considered to represent metamorphosed basic sills and dikes intruded before the quartz diorite complex. Schist septa lie within the complex and are usually parallel to the regional strike. The sequence of intrusion as interpreted from inclusions and petrographic data is (1) quartz diorite, (2) granodiorite, (3) granite. Small but persistent amounts of allanite and epidote are characteristic of the rocks of the complex. The texture is subporphyritic and shows evidence of protoclastic deformation. A northeast-southwest trend of inclusions, foliation, lineation, and contacts dominates. Primary flow structures are shown in the orientation of inclusions and micas. Secondary structures were superposed on the original flow structures shortly after intrusion and prior to complete consolidation. A prominent secondary structure is a lineation in b. Stretching in b is indicated by boudinage structures, the lineation, and small displacements of dikes. The intensity of the planar structures in the gneiss grades from strong to indistinct or lacking from east to west. Structures in schist inclusions indicate that some folding had taken place prior to intrusion. Thin pegmatite, granodiorite, and granite dikes are common. Most of them are essentially parallel to the regional strike. The petrographic boundary between gneiss and schist is always sharp. On a large scale, the gneiss structures are essentially parallel to the contacts, but slight to marked discordant relations occur at many localities. The schist structures usually parallel the contacts. Petrofabric analysis confirms the structural field observations. The mica fabrics are ac -girdles and are most complete where the foliation is weakest. Microscopic s -planes do not always coincide with the observed foliation. The quartz fabrics are also ac -girdles but are not so well developed as the mica girdles. Quartz orientations cannot always be related to known s -planes. It is concluded that the Pinckneyville quartz diorite complex represents a syntectonic intrusion—that is, that intrusion took place while external or regional forces were still active. The shape of the intrusion was controlled largely by the wall-rock structures which had developed earlier. The rocks show both igneous and metamorphic characteristics because the intrusion took place under regional metamorphic conditions.

Correlation of some metamorphic rocks in the Central Carolina Piedmont

A belt of the Piedmont between Lincolnton, North Carolina, and Gaffney, South Carolina, is underlain by metamorphic country rocks, granitic rocks and albitic pegmatite, and Triassic diabase. The country rocks comprise quartzite, variably micaceous crystalline limestone and dolomite, impure limestone or carbonate-silicate rocks, fine-grained mica schists and gneisses, hornblende and hornblende-biotite gneisses, and scarce pyroxene, amphibole, quartz-tourmaline, and chlorite rocks. The noncarbonate rocks, except quartzite, have been mapped as pre-Cambrian (the Carolina and Roan formations). The quartzite, carbonate-silicate rocks, and crystalline limestone have been mapped as Cambrian (the Kings Mountain, Blacksburg, and Gaffney formations). Textures are for the most part crystalloblastic, but some varieties, particularly the carbonate-silicate, show definite evidence of sequential rather than simultaneous crystallization of the minerals; cataclastic texture is but slightly developed. The silicate minerals in the carbonate-silicate rocks are mineralogically and texturally identical with those in the closely associated silicate rocks. Those in the carbonate-silicate rocks clearly have not been formed by the recrystallization of minerals previously granulated, and it is therefore concluded that those in the silicate rocks have not had such an origin. The genetic relation between the carbonate and noncarbonate rocks thus implied was clarified by large-scale mapping near Kings Mountain. There, the quartzite occurs interbedded with west-dipping rocks of the other types but is most abundant in two distinct zones within the limestone. The upper or western limit of the limestone throughout the area is about equidistant from the irregular eastern margin of a large granitic body and occurs at some places above the upper quartzite zone and at other places below it. The carbonate-silicate rocks, largely equivalent to the Blacksburg schist, have been found throughout the limestone as sporadic layers and bodies of indefinite outline, but they are most abundant near the irregular upper limit of the limestone—the lower limit of conformably overlying hornblende gneiss sharply interlayered with mica schist. The upper quartzite is thus in a zone of transition from carbonate to silicate rocks, and the relation of this zone to the margin of the granite indicates that the transition is of metamorphic origin. The layers of hornblende gneiss immediately above the limestone are strongly metamorphosed beds of the limestone series, but it is not known whether they originally contained all the elements necessary to form the silicate minerals. Evidence for the chemical transfer of material is the presence of hornblende, tremolite, and microcline porphyroblasts in the limestone and of tourmaline, albite, microcline, and spodumene in the silicate rocks only near pegmatite and granite. It is believed that the granite was the source of aqueous solutions that invaded the sedimentary rocks and effected their recrystallization or reconstitution. The granite is apparently of late Carboniferous age; the country rocks are older, but no evidence could be found for determining their actual age. Thus, near Kings Mountain, mica schists and gneisses previously mapped as Carolina gneiss, and hornblende gneisses previously mapped as Roan gneiss, actually constitute the metamorphosed upper part of the Gaffney. Similar rocks in the Beaverdam Creek area apparently are stratigraphically higher. The micaceous rocks were derived by the metamorphism of shaly rocks, and the hornblendic rocks by the metamorphism of pure or impure calcareous rocks, regardless of the stratigraphic position of either type. Evidence in other parts of the Carolina Piedmont, according to the literature as well as reconnaissance observations by the writer, indicates that intrusive diorite and possibly recrystallized mafic volcanic rocks have been included in the Roan, and possibly recrystallized felsic volcanic rocks in the Carolina. The names Carolina and Roan, therefore, have lithologic but not stratigraphic significance, and the rocks associated with them probably will be divided eventually into formations on the basis of comparative genetic history rather than physical appearance.

A syntectonic intrusion in eastern Alabama

The Pinckneyville quartz‐diorite complex underlies an area in eastern Alabama extending from the Coosa River in northwest Elmore County northeast through Coosa and Tallapoosa counties into Clay County.Dark‐gray, coarse‐grained quartz‐diorite gneiss constitutes the major part of the complex, but there are smaller amounts of granodiorite and granite gneiss. Hornblende biotite gneiss also occurs and is considered to represent either metamorphosed basic sills and dikes intruded earlier than the quartz‐diorite complex or possibly original sediments. Schist septa lie within the complex and are usually parallel to the regional strike. The sequence of intrusion as interpreted from inclusions and petrographic data is quartz‐diorite—granodiorite—granite. Small but persistent amounts of allanite and epidote are characteristic of the rocks of the complex. The texture is subporphyritic and shows evidence of protoclastic deformation.