EVOLUÇÃO PETROLÓGICA E ESTRUTURAL DA PORÇÃO ORIENTAL DO ESTADO DE MINAS GERAIS E SUAS IMPLICAÇÕES GEOTECTÔNICAS

A metamorphic terrain with high-grade rocks of the Atlantic Metamorphic Belt underlies the eastern part of Minas Gerais State, from south of the town of Manhuaçu to Caratinga. This terrain comprises peraluminous gneisses, igneous and meta-igneous rocks. Granulites occur as small nucleus and vary in composition between peraluminous and basic to intermediate, the latter represented by enderbitic mobilizate. Their formation, as well as that of migmatites of granitic composition, is considered to be related to mafic and ultramafic intrusions. In basic granulites, garnet-bearing mineral assemblages, with the development of corona textures, attest the effects of granulite facies metamorphism, although igneous assemblages and textures are still well preserved. Retrograde alteration assemblages are locally preserved. Despite of the diversity of metamorphic phenomena in this area, T and P calculations reveal consistent results. Temperature and pressure calculations were undertaken in basic granulites slightly affected by the retrograde process. Using Fe +²/Mg exchange between garnet and ortopyroxene as geothermometers and the exchange reaction: An +En = 2/3Pyr + 1/3Grs + Qz as geobarometers peak metamorphic temperatures in the range of 660 to 760°C, at 4,8 to 6,6 Kbar are obtained. Mineral, textural and geochemical evidences indicate that the metamorphic conditions have changed with time and suggest that the formation of the granulites is caused by the underplating of magmas, probably mantle-derived, at the base of the crust. Several rations between major, trace and rare earth elements have been employed. The basic rocks are similar in composition to tholeiites generated in within-plate tectonic settings. Positive correlations netween K2O and SiO2 and negative between MgO and SiO2 in fresh gabbro-noritic rocks and enderbites indicate magmatic differentiation. The geochemical character of altered basic rocks displays an unsystematic dispersion in correlations diagrams. This lack of correlation coupled with field and petrographic suggest the effects of a late metasomatic event on these rocks. This metasomatism comprises the dispersed development of charnockitic rocks with large K-feldspars and quartz crystals. Later dynamic processes gave place to subvertical shear zones with a well defined foliation.

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Relações morfométricas para Copaifera langsdorffii (Desf.) Kuntze na região norte de Minas Gerais, Brasil

Revista Ecologia e Nutrição Florestal - ENFLO ◽

10.5902/2316980x38551 ◽

2020 ◽

Vol 8 ◽

pp. 01

Author(s):

Caio Ferreira da Silva ◽

Drauzio Correia Gama ◽

Lais Almeida Araújo ◽

Jean Barcello Xavier Bahia ◽

Vinícius Orlandi Barbosa Lima

Keyword(s):

Minas Gerais ◽

Northern Region ◽

Economic Importance ◽

Crown Area ◽

Crown Diameter ◽

Breast Height ◽

Great Economic Importance ◽

Minas Gerais State ◽

Copaifera Langsdorffii ◽

Positive Correlations

Copaifera langsdorffii specie occurs throughout Brazil and is of great economic importance, mainly due to its production of oil-resin used for various pharmacological purposes. The objective of this study was to analyze the morphometric relationships in C. langsdorffii stand in northern region of Minas Gerais state, Brazil. Twenty trees were randomly sampled and were measured: stem circumference at 1.3 m height, total height (Ht) and crown diameter (CD). Morphometric indices were estimated. Correlations between dendrometric and morphometric variables were obtained through the Pearson matrix. The morphometric relations of crown proportion (CP), crown area (CA), formal of crown (FC), degree of slenderness (DS), salience index (SI), coverage index (CI) and vital space (VS) presented values of 15.26%, 25.06 m², 1.47, 16.35, 21.70, 0.47 and 7.01, respectively. Strong positive correlations were found in: diameter at breast height (DBH) in relation to CD and CA; Ht with crown proportion (CP) and DS; the formal of crown (FC) with the CI and VS, and between the CI and VS. The morphometric indices made it possible to understand the few magnitude of stand variation. The species can be characterized as facilitating management.

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U-Pb evidence for late Neoarchean crustal reworking in the Southern São Francisco Craton (Minas Gerais, Brazil)

Anais da Academia Brasileira de Ciências ◽

10.1590/s0001-37652003000400008 ◽

2003 ◽

Vol 75 (4) ◽

pp. 497-511 ◽

Cited By ~ 21

Author(s):

José C.S. Campos ◽

Maurício A. Carneiro ◽

Miguel A.S. Basei

Keyword(s):

Granulite Facies ◽

Minas Gerais ◽

Metamorphic Complex ◽

Granulite Facies Metamorphism ◽

Sialic Crust ◽

Facies Metamorphism ◽

Minimum Age ◽

Crustal Reworking ◽

Metamorphic Complexes

The Passa Tempo Metamorphic Complex is one of several metamorphic complexes that form the Archean sialic crust of the southern São Francisco Craton. It encompasses hypersthene-bearing gneissic rocks, with subordinateNW- or EW-trending mafic-ultramafic bodies and granodioritic to alkali-granitic, weakly foliated, and light-colored granitoids. These granitoids are the product of generalized migmatization that followed granulite-facies metamorphism. To determine the ages of the granulite-facies metamorphism and granitoid genesis, we obtained U-Pb ages on zircon extracted from the mesosome and leucosome of the migmatitic gneisses. For the mesosome, a discordia that intercepts Concordia at 2622 ± 18 Ma is interpreted as a minimum age for granulite-facies metamorphism. For the leucosome, the upper intercept of discordia at 2599 ± 45 Ma corresponds to migmatization and granitoid genesis. Contemporaneous metamorphism and magmatism have been documented elsewhere in the São Francisco Craton, especially in the southern portion, demonstrating vast and vigorous reworking of sialic crust by the end of the Neoarchean.

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Fluid inclusions in granulites and eclogites from the Bergen Arcs, Caledonides of W. Norway

Mineralogical Magazine ◽

10.1180/minmag.1990.054.375.02 ◽

1990 ◽

Vol 54 (375) ◽

pp. 145-158 ◽

Cited By ~ 43

Author(s):

T. Andersen ◽

H. Austrheim ◽

E. A. J. Burke

Keyword(s):

Fluid Inclusions ◽

Shear Zones ◽

Granulite Facies ◽

Mole Percent ◽

Molar Volumes ◽

Granulite Facies Metamorphism ◽

Laser Raman ◽

Granulite Metamorphism ◽

Facies Metamorphism ◽

Eclogite Facies

AbstractThe Grenvillian granulite-facies complex on Holsnøy island, Bergen Arcs, W. Norway, has been metamorphosed at eclogite-facies conditions during the Caledonian orogeny (ca. 425 Ma). The granulite-eclogite facies transition takes place along shear zones and fluid pathways. Mineral thermobarometry indicates PT conditions of 800–900°C and 8–10 kbar for the Proterozoic granulite facies metamorphism and 700–800°C and 16–19 kbar for the eclogite-forming event. Quartz in the granulite facies complex contains CO2 fluid inclusions with less than 2.5 mole percent N2; the molar volumes are compatible with the PT conditions of the Proterozoic granulite metamorphism. Quartz in pegmatitic quartz + omphacite and quartz + phengite/paragonite veins coeval with shear-zone eclogites contain N2 ± CO2 fluid inclusions. Combined laser Raman microanalysis and microthermometry show that the least disturbed inclusions have XCO2 = 0.1–0.3, and molar volumes less than 40 cm3/mole, which may agree with the PT conditions during Caledonian high-pressure metamorphism. Younger, low-density N2 and N2-H2O fluid inclusions are the results of decrepitation and redistribution of early inclusions during the retrograde PT evolution of the eclogites.

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Fracturing and crystal plastic behaviour of garnet under seismic stress in the dry lower continental crust (Musgrave Ranges, Central Australia)

Solid Earth ◽

10.5194/se-10-1635-2019 ◽

2019 ◽

Vol 10 (5) ◽

pp. 1635-1649 ◽

Cited By ~ 2

Author(s):

Friedrich Hawemann ◽

Neil Mancktelow ◽

Sebastian Wex ◽

Giorgio Pennacchioni ◽

Alfredo Camacho

Keyword(s):

Plastic Deformation ◽

Continental Crust ◽

High Stress ◽

Shear Zones ◽

Granulite Facies ◽

Lower Continental Crust ◽

Granulite Facies Metamorphism ◽

High Calcium ◽

Central Australia ◽

Lower Crustal

Abstract. Garnet is a high-strength mineral compared to other common minerals such as quartz and feldspar in the felsic crust. In felsic mylonites, garnet typically occurs as porphyroclasts that mostly evade crystal plastic deformation, except under relatively high-temperature conditions. The microstructure of granulite facies garnet in felsic lower-crustal rocks of the Musgrave Ranges (Central Australia) records both fracturing and crystal plastic deformation. Granulite facies metamorphism at ∼1200 Ma generally dehydrated the rocks and produced millimetre-sized garnets in peraluminous gneisses. A later ∼550 Ma overprint under sub-eclogitic conditions (600–700 ∘C, 1.1–1.3 GPa) developed mylonitic shear zones and abundant pseudotachylyte, coeval with the neocrystallization of fine-grained, high-calcium garnet. In the mylonites, granulite facies garnet porphyroclasts are enriched in calcium along rims and fractures. However, these rims are locally narrower than otherwise comparable rims along original grain boundaries, indicating the contemporaneous diffusion and fracturing of garnet. The fractured garnets exhibit internal crystal plastic deformation, which coincides with areas of enhanced diffusion, usually along zones of crystal lattice distortion and dislocation walls associated with subgrain rotation recrystallization. The fracturing of garnet under dry lower-crustal conditions, in an otherwise viscously flowing matrix, requires transient high differential stress, most likely related to seismic rupture, consistent with the coeval development of abundant pseudotachylyte. Highlights. Garnet is deformed by fracturing and crystal plasticity under dry lower-crustal conditions. Ca diffusion profiles indicate multiple generations of fracturing. Diffusion is promoted along zones of higher dislocation density. Fracturing indicates transient high-stress (seismic) events in the lower continental crust.

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A mechanism for Nb incorporation in rutile and application of Zr-in-rutile thermometry: A case study from granulite facies paragneisses of the Mogok metamorphic belt, Myanmar

Mineralogical Magazine ◽

10.1180/minmag.2017.081.014 ◽

2017 ◽

Vol 81 (6) ◽

pp. 1503-1521 ◽

Cited By ~ 3

Author(s):

Maw Maw Win ◽

M. Enami ◽

T. Kato ◽

Ye Kyaw Thu

Keyword(s):

High Temperature ◽

Early Stage ◽

Granulite Facies ◽

Metamorphic Belt ◽

Fine Grained ◽

Coupled Substitution ◽

Trivalent Cations ◽

Positive Correlations ◽

Zr In Rutile

AbstractRutile grains occur extensively in host phases of biotite and quartz-feldspar aggregate in high-temperature paragneisses of the Mogok metamorphic belt of Myanmar. They occur as an isolated phase and sometimes show intergrowth texture with ilmenite. Most rutile grains contain up to 3.7 wt.% Nb2O5, which shows positive correlations with Fe and trivalent elements. Niobium substitutes for Ti by a coupled substitution with the trivalent cations (M3+) of Nb5+M3+Ti4+-2. Fine-grained rutile grains included in ilmenite are distinctly poor in Nb (<0.1 wt.% as Nb2O5) and contain Fe of 1.7–3.2 wt.% as Fe2O3, suggesting vacancybearing substitution of Fe3+4 Ti4+-3□–1, where □ indicates a vacancy. The rutile grains in the felsic phases contain high Zr contents of up to 4200 ppm, suggesting equilibrium temperatures over 800°C using the Ti-in-rutile geothermometer. These high-temperature conditions are consistent with those estimated by conventional methods reported in the literature and suggest widespread occurrences of the upperamphibolite and granulite facies metamorphic rocks in the middle segment of the Mogok metamorphic belt. In contrast, the Zr contents of rutile grains in biotite are usually <1000 ppm, implying equilibrium temperatures lower than 750°C. Most of the rutile grains poorer in Zr might have been included in biotite and were isolated from the zircon-bearing system during an early stage of prograde metamorphism. Some other rutile grains poorer in Zr might have been an exsolved phase from Ti-rich biotite during retrograde metamorphism, which was furthered by the infiltration of metamorphic fluid under lower-amphibolite facies conditions.

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Metamorphism of the Sierra de Maz and implications for the tectonic evolution of the MARA terrane

Geosphere ◽

10.1130/ges02268.1 ◽

2021 ◽

Author(s):

Andrew Tholt ◽

Sean R. Mulcahy ◽

William C. McClelland ◽

Sarah M. Roeske ◽

Vinícius T. Meira ◽

...

Keyword(s):

Tectonic Evolution ◽

Shear Zones ◽

Granulite Facies ◽

Metamorphic Petrology ◽

Granulite Facies Metamorphism ◽

Northwest Argentina ◽

Sufficient Detail ◽

Ductile Shear Zones ◽

Gondwana Margin ◽

Lower Crustal

The Mesoproterozoic MARA terrane of western South America is a composite igneous-metamorphic complex that is important for Paleozoic paleogeographic reconstructions and the relative positions of Laurentia and Gondwana. The magmatic and detrital records of the MARA terrane are consistent with a Laurentian origin; however, the metamorphic and deformation records lack sufficient detail to constrain the correlation of units within the MARA terrane and the timing and mechanisms of accretion to the Gondwana margin. Combined regional mapping, metamorphic petrology, and garnet and monazite geochronology from the Sierra de Maz of northwest Argentina sug- gest that the region preserves four distinct litho-tectonic units of varying age and metamorphic conditions that are separated by middle- to lower-crustal ductile shear zones. The Zaino and Maz Complexes preserve Barrovian metamorphism and ages that are distinct from other units within the region. The Zaino and Maz Complexes both record metamorphism ca. 430–410 Ma and show no evidence of the regional Famatinian orogeny (ca. 490–455 Ma). In addition, the Maz Complex records an earlier granulite facies event at ca. 1.2 Ga. The Taco and Ramaditas Complexes, in contrast, experienced medium- and low-pressure upper amphibolite to granulite facies metamorphism, respectively, between ca. 470–460 Ma and were later deformed at ca. 440–420 Ma. The Maz shear zone that bounds the Zaino and Maz Complexes records sinistral oblique to sinistral deformation between ca. 430–410 Ma. The data suggest that at least some units in the MARA terrane were accreted by translation, and the Gondwana margin of northwest Argentina transitioned from a dominantly convergent margin to a highly oblique margin in the Silurian.

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GEOLOGIA DA REGIÃO DE JEQUERI-VIÇOSA (MG), ORÓGENO ARAÇUAÍ MERIDIONAL

Revista Geonomos ◽

10.18285/geonomos.v19i2.47 ◽

2013 ◽

Author(s):

Daniel Tavares Gradim ◽

Gláucia Nascimento Queiroga ◽

Tiago Amâncio Novo ◽

Carlos Maurício Noce ◽

Antônio Carlos Pedrosa-Soares ◽

...

Keyword(s):

Partial Melting ◽

Shear Zone ◽

Granulite Facies ◽

Minas Gerais ◽

Amphibolite Facies ◽

Ultramafic Rocks ◽

Metamorphic Rocks ◽

The West ◽

Minas Gerais State ◽

Araçuaí Orogen

RESUMO: A característica fundamental da região de Jequeri-Viçosa, situada no extremo sul do Orógeno Araçuaí, é a abundância de rochas metamórficas, ortoderivadas e paraderivadas, de fácies anfibolito alto e granulito. O embasamento paleoproterozóico é representado, a oeste, por ortognaisses tonalíticos a graníticos do Complexo Mantiqueira e, a leste, por ortognaisses charno-enderbíticos do Complexo Juiz de Fora. Ambos os complexos incluem anfibolitos e exibem intensidades variáveis de migmatização. O contato entre eles é marcado pela zona de cisalhamento transpressiva destral de Abre Campo, interpretada como uma sutura paleoproterozóica reativada no Neoproterozóico. O Anfibolito Santo Antônio do Grama e rochas meta-ultramáficas associadas (Córrego do Pimenta) representam restos ofiolíticos ediacaranos, colocados ao longo da Zona de Cisalhamento de Abre Campo. Assentada sobre o embasamento, na parte oeste da área, ocorre uma associação metavulcano-sedimentar neoproterozóica do Grupo Dom Silvério, composta por xistos diversos e quartzito. Na porção leste da área mapeada, a cobertura metassedimentar neoproterozóica é atribuída ao Grupo Andrelândia que inclui paragnaisse migmatítico e raro quartzito. Corpos de hidrotermalito quartzoso, indiscriminadamente associados às unidades do embasamento e da cobertura neoproterozóica, ocorrem ao longo de zonas de cisalhamento. Hidrotermalitos ferruginosos associam-se ao Complexo Mantiqueira na Zona de Cisalhamento de Ponte Nova. O granito foliado a milonitizado da Serra dos Vieiras parece ser um produto de fusão parcial do paragnaisse Andrelândia. Completam o quadro geológico os pegmatitos da Suíte Paula Cândico e diques de diabásio mesozóicos.Palavras-chave: Paleoproterozóico, Neoproterozóico, Orógeno AraçuaíABSTRACT: GEOLOGY OF THE JEQUERI-VIÇOSA REGION, MINAS GERAIS STATE, SOUTHERN ARAÇUAÍ OROGEN. This paper focuses on the southwestern sector of the Araçuaí orogen in a region located close to the boundary with the northern Ribeira orogen. This region is rich in ortho- and para-derived metamorphic rocks of the high amphibolite and granulite facies. The Paleoproterozoic basement includes, to the west, tonalitic to granitic orthogneisses of the Mantiqueira Complex and, to the east, enderbitic to charnockitic orthogneisses of the Juiz de Fora Complex. Both complexes also include amphibolite enclaves and show several rates of partial melting. The contact between them is marked by the dextral transpressional Abre Campo shear zone, considered to be a Paleoproterozoic suture reactivated during the Neoproterozoic Era. The Santo Antônio do Grama Amphibolite and associated meta-ultramafic rocks (Córrego do Pimenta) are Ediacaran ophiolite slivers emplaced along the Abre Campo shear zone. In the western part of the region, the Paleoproterozoic basement is locally covered by a metavolcano-sedimentary assemblage composed of amphibolite facies schist and quartzite of the Neoproterozoic Dom Silvério Group. To the east, the Neoproterozoic cover comprises the migmatized paragneiss and rare quartzite of the Andrelândia Group. The Serra dos Vieiras foliated to mylonitic granite seems to be formed from the partial melting of the Andrelândia paragneiss. Pegmatites of the Paula Cândido Suite and Mesosozic diabase dikes complete the geologic framework of the mapped area.Keywords: Paleoproterozoic, Neoproterozoic, Araçuaí Orogen

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Field work on marble and calc-silicate rocks in the Nordre Strømfjord region

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v28.7225 ◽

1970 ◽

Vol 28 ◽

pp. 19-20

Author(s):

P.B Sørensen

Keyword(s):

Personal Communication ◽

Granulite Facies ◽

Field Work ◽

Fold Belt ◽

Granulite Facies Metamorphism ◽

The North ◽

Facies Metamorphism ◽

Basic Rocks ◽

Metamorphic Gradient ◽

Silicate Rocks

As a member of the group working in the Agto-Nordre Strømfjord area (see Bondesen, this report) the writer studied and collected from the extensive outcrops of marble and associated calc-silicate rocks which occur in the region, especially around Nordre Strømfjord. Ramberg (1949) divided the Nagssugtoqidian fold belt in this region into the Isortoq Complex and the Egedesminde Complex, the first characterised by granulite facies metamorphism and the latter by amphibolite facies. K. Sørensen (personal communication) has indicated that a metamorphic gradient exists in the Isortoq Complex from the north to the south in the western part of the Agto sheet area, as seen by the increasing amount of orthopyroxene in the basic rocks. The field data obtained on the calcareous rocks can be correlated with this scheme although a detailed study is necessary.

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Fracturing and crystal plastic behavior of garnet under seismic stress in the dry lower continental crust (Musgrave Ranges, Central Australia)

10.5194/se-2019-110 ◽

2019 ◽

Author(s):

Friedrich Hawemann ◽

Neil Mancktelow ◽

Sebastian Wex ◽

Giorgio Pennacchioni ◽

Alfredo Camacho

Keyword(s):

Plastic Deformation ◽

High Strength ◽

Calcium Content ◽

Shear Zones ◽

Granulite Facies ◽

Plastic Behavior ◽

Granulite Facies Metamorphism ◽

High Calcium ◽

Central Australia ◽

Lower Crustal

Abstract. Garnet is a high strength mineral compared to other common minerals such as quartz and feldspar in the felsic crust. In felsic mylonites, garnet typically occurs as porphyroclasts that mostly evade deformation, except under relatively high temperature conditions. The microstructure of granulite facies garnet in felsic lower-crustal rocks of the Musgrave Ranges (Central Australia) records both fracturing and crystal-plastic deformation. Granulite facies metamorphism at ~ 1200 Ma generally dehydrated the rocks and produced mm-sized garnets in peraluminous gneisses. A later ~ 550 Ma overprint under sub-eclogitic conditions (600–700 °C, 1.1–1.3 GPa) developed shear zones and with abundant pseudotachylyte, coeval with the neocrystallization of fine-grained, high-calcium garnet. The granulitic fractured garnet porphyroclasts in mylonites show high calcium content along rims and fractures. However, in certain cases, these rims are narrower than equivalent rims along original grain boundaries, indicating contemporaneous diffusion and fracturing of garnet. The fractured garnets exhibit internal crystal-plastic deformation, that coincide with areas of enhanced diffusion, usually along zones of crystal lattice distortions and dislocation walls and by subgrain rotation recrystallization. Fracturing of garnet under dry lower crustal conditions, in an otherwise viscously flowing matrix, requires transient high differential stress, most likely related to seismic rupture, consistent with the coeval development of abundant pseudotachylyte.

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Exhumation of high-grade terranes—a review

Canadian Journal of Earth Sciences ◽

10.1139/e92-063 ◽

1992 ◽

Vol 29 (4) ◽

pp. 737-745 ◽

Cited By ~ 7

Author(s):

Jacques Martignole

Keyword(s):

High Temperature ◽

Shear Zones ◽

Granulite Facies ◽

High Grade ◽

Granulite Facies Metamorphism ◽

Magmatic Underplating ◽

Show Evidence ◽

Juvenile Crust ◽

Uplift And Erosion ◽

Lower Crustal

High-grade (granulite-facies) terranes are brought to the surface by a combination of uplift and erosion (exhumation). The reported mechanisms and durations of exhumation are variable and depend partly on the mode of formation of a given high-grade terrane. In this paper, we consider the case of granulite-facies conditions that are attained (i) in juvenile crust, in the roots of magmatic arcs (e.g., Kohistan, Fiordland), (ii) around deep-seated high-temperature plutonic complexes, and (iii) in the lower parts of thickened continental crust. In the case of the roots of magmatic arcs, Phanerozoic examples suggest that they are exhumed along shallow-dipping contraction faults or shear zones that developed during continental obduction in a convergent tectonic regime. This process is not fundamentally different from processes leading to the exhumation of high-pressure (blueschist, eclogite) terranes. In contrast, deep-seated high-temperature plutonic complexes are thermostructural domes, analogous to the lower levels of core complexes, which may also have contributed to the uprise of high-grade terranes. Such domes should be sought for around anorthositic or mafic plutons, where their ascent may also have been favoured by continental extension. These modes of exhumation are compatible with a monocyclic evolution. However, many high-grade terranes show evidence of a polycyclic evolution and, in such cases, the nature of the thermal perturbation responsible for granulite-facies metamorphism is still debated. Thermal modelling based on heat conduction in collision orogens shows that granulites cannot form at mid-cristal levels, namely those exposed after isostatically driven denudation. Thus, magmatic underplating and crustal extension have been suggested as causes of steepened geotherms. Underplating (or intraplating) supplies the heat and thickens the crust from below. Postcollisional extension has also been considered as a mechanism providing a heat pulse emanating from the asthenosphere, probably after the "detachment" of a relatively cold thermal boundary layer. Finally, isolated crustal-scale intracratonic thrusting may favour the rise of intermediate to lower crustal wedges (e.g., the Kapuskasing wedge, uplifted prior to the trans-Hudson collision).

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