Very low- and low-grade metamorphism in the Trinity Peninsula Group (Permo-Triassic) of northern Graham Land, Antarctic Peninsula

1996 ◽  
Vol 133 (5) ◽  
pp. 583-594 ◽  
Author(s):  
J. L. Smellie ◽  
B. Roberts ◽  
S. R. Hirons
Keyword(s):  
Antarctic Peninsula ◽  
Thermal Evolution ◽  
Accretionary Prism ◽  
White Mica ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Magmatic Arc ◽  
Optical Identifications ◽  
The Trinity ◽  
Pressure Series

AbstractThe Permo-Triassic Trinity Peninsula Group is a widespread, regionally metamorphosed metasedimentary sequence in northern Graham Land, Antarctica, which forms the local ‘basement’ to the mainly Jurassic–Cretaceous Antarctic Peninsula magmatic arc. The metamorphic grade, thermal evolution and pressure series of this major tectono-stratigraphical unit are largely unknown. Determining the nature of the metamorphism has relied hitherto on conventional optical identifications of the major phases, mainly in rare volcanic beds. However, diagnostic mineral parageneses are generally absent and the precise metamorphic grade is unknown or has to be inferred over large areas. Using white mica (illite) crystallinity of interbedded mudrocks, the Trinity Peninsula Group is now shown to have been pervasively altered mainly at anchizonal and epizonal grades. Conditions ranged from upper anchizonal in the northeast to thoroughly epizonal in the southwest. Outwith thermal aureoles near plutonic intrusions, the alteration temperatures ranged mainly from 250 to 325 °C, exceeding 300 °C in the highest-grade (epizone/greenschist facies) parts of the sequence. The facies series, K-white mica b cell dimension measurements and mineral phases present are characteristic of an intermediate pressure series altered under moderate geothermal gradients (<35 °C/km), corresponding to burial depths of c. 7–10 km. Unroofing and substantial erosion of the Trinity Peninsula Group took place during polyphasal vertical tectonic movements linked to the development of the magmatic arc in northern Graham Land. The geological setting of the Trinity Peninsula Group is ambiguous and could have been a foreland (or back-arc) basin or the mid- to upper levels of an accretionary prism.

The geology of Cape Dubouzet, northern Antarctic Peninsula: continental basement to the Trinity Peninsula Group?

1996 ◽  
Vol 8 (4) ◽  
pp. 407-414 ◽  
Author(s):  
Francisco Hervé ◽  
Jorge Lobato ◽  
Ignacio Ugalde ◽  
Robert J. Pankhurst
Keyword(s):  
Antarctic Peninsula ◽  
Late Jurassic ◽  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Metamorphic Complex ◽  
Calc Alkaline ◽  
Magmatic Arc ◽  
The Antarctic ◽  
The Trinity

Cape Dubouzet is mainly composed of a volcanic-subvolcanic complex of extrusive rhyolitic breccias, a banded rhyolite and a semi-annular body of dacite porphyry rich in xenoliths of metamorphic rocks. Major and REE geochemistry indicate that the volcanic rocks are calc-alkaline and that they are genetically related by fractional crystallization of a plagioclase-bearing assemblage from a common magma. Rb-Sr data suggest that the rhyolitic complex is of Middle-to-Late Jurassic age, and that it is intruded by Late Cretaceous stocks of banded diorite and gabbro. All these rocks are partially covered by moraines whose clasts are of local provenance. Xenoliths in the dacite porphyry suggest that the northern tip of the Antarctic Peninsula is underlain by a metamorphic complex composed of amphibolites, meta-tonalites and pelitic gneiss containing garnet, sillimanite, cordierite, hercynite, and andalucite. Such rocks are not known in the Scotia metamorphic complex, nor in the Trinity Peninsula Group and its low grade metamorphic derivatives, which also occur as rare xenoliths in the dacite. Previous dating of xenoliths collected from the moraines suggested a late Carboniferous age for this amphibolite-grade metamorphism. Both the Jurassic-Cenozoic magmatic arc of the Antarctic Peninsula and the accretionary complex rocks of the Trinity Peninsula Group were thus developed, at least in part, over pre-existing continental crust.

Chapter 23: Alteration, Mineralization, and Age Relationships at the Kışladağ Porphyry Gold Deposit, Turkey

2020 ◽  
pp. 467-495
Author(s):  
T. Baker ◽  
S. Mckinley ◽  
S. Juras ◽  
Y. Oztas ◽  
J. Hunt ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
White Mica ◽  
Western Anatolia ◽  
Low Grade ◽  
Porphyry Deposits ◽  
Magmatic Arc ◽  
Argillic Alteration ◽  
Metamorphic Basement ◽  
Slab Tear ◽  
Roll Back

Abstract The Miocene Kışladağ deposit (~17 Moz), located in western Anatolia, Turkey, is one of the few global examples of Au-only porphyry deposits. It occurs within the West Tethyan magmatic belt that can be divided into Cretaceous, Cu-dominant, subduction-related magmatic arc systems and the more widespread Au-rich Cenozoic magmatic belts. In western Anatolia, Miocene magmatism was postcollisional and was focused in extension-related volcanosedimentary basins that formed in response to slab roll back and a major north-south slab tear. Kışladağ formed within multiple monzonite porphyry stocks and dikes at the contact between Menderes massif metamorphic basement and volcanic rocks of the Beydağı stratovolcano in the Uşak-Güre basin. The mineralized magmatic-hydrothermal system formed rapidly (&lt;400 kyr) between ~14.75 and 14.36 Ma in a shallow (&lt;1 km) volcanic environment. Volcanism continued to at least 14.26 ± 0.09 Ma based on new age data from a latite lava flow at nearby Emiril Tepe. Intrusions 1 and 2 were the earliest (14.73 ± 0.05 and 14.76 ± 0.01 Ma, respectively) and best mineralized phases (average median grades of 0.64 and 0.51 g/t Au, respectively), whereas younger intrusions host progressively less Au (Intrusion 2A: 14.60 ± 0.06 Ma and 0.41 g/t Au; Intrusion 2 NW: 14.45 ± 0.08 Ma and 0.41 g/t Au; Intrusion 3: 14.39 ± 0.06 and 14.36 ± 0.13 Ma and 0.19 g/t Au). A new molybdenite age of 14.60 ± 0.07 Ma is within uncertainty of the previously published molybdenite age (14.49 ± 0.06 Ma), and supports field observations that the bulk of the mineralization formed prior to the emplacement of Intrusion 3. Intrusions 1 and 2 are altered to potassic (biotite-K-feldspar-quartz ± magnetite) and younger but deeper sodic-calcic (feldspar-amphibole-magnetite ± quartz ± carbonate) assemblages, both typically pervasive with disseminated to veinlet-hosted pyrite ± chalcopyrite ± molybdenite and localized quartz-feldspar stockwork veinlets and sodic-calcic breccias. Tourmaline-white mica-quartz-pyrite alteration surrounds the potassic core both within the intrusions and outboard in the volcanic rocks. Tourmaline was most strongly developed on the inner margins of the tourmaline-white mica zone, particularly along the Intrusion 1 volcanic contact where it formed breccias and veins, including Maricunga-style veinlets. Field relationships show that the early magmatic-hydrothermal events were cut by Intrusion 2A, which was then overprinted by Au-bearing argillic (kaolinite-pyrite ± quartz) alteration, followed by Intrusion 3 and late-stage, low-grade to barren argillic and advanced argillic alteration (quartz-pyrite ± alunite ± dickite ± pyrophyllite). Gold deportment changes with each successive hydrothermal event. The early potassic and sodic-calcic alteration controls much of the original Au distribution, with the Au dominantly deposited with feldspar and lesser quartz and pyrite. Tourmaline-white mica and argillic alteration events overprinted and altered the early Au-bearing feldspathic alteration and introduced additional Au that was dominantly associated with pyrite. Analogous Au-only deposits such as Maricunga, Chile, La Colosa, Colombia, and Biely Vrch, Slovakia, are characterized by similar alteration styles and Au deportment. The deportment of Au in these Au-only porphyry deposits differs markedly from that in Au-rich porphyry Cu deposits where Au is typically associated with Cu sulfides.

scholarly journals Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary domain (SW Iberian Variscides)

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 469-488 ◽  
Author(s):  
Irene Pérez-Cáceres ◽  
David Jesús Martínez Poyatos ◽  
Olivier Vidal ◽  
Olivier Beyssac ◽  
Fernando Nieto ◽  
...  
Keyword(s):  
B Cell ◽  
Microstructural Analysis ◽  
Carbonaceous Material ◽  
Accretionary Prism ◽  
Low Pressure ◽  
White Mica ◽  
Cell Dimension ◽  
Low Grade ◽  
The South ◽  
Metamorphic Evolution

Abstract. The Pulo do Lobo domain is one of the units exposed within the orogenic suture zone between the Ossa-Morena and the South Portuguese zones in the SW Iberian Variscides. This metasedimentary unit has been classically interpreted as a Rheic subduction-related accretionary prism formed during pre-Carboniferous convergence and eventual collision between the South Portuguese Zone (part of Avalonia) and the Ossa-Morena Zone (peri-Gondwanan terrane). Discrete mafic intrusions also occur within the dominant Pulo do Lobo metapelites, related to an intra-orogenic Mississippian transtensional and magmatic event that had a significant thermal input. Three different approaches have been applied to the Devonian–Carboniferous phyllites and slates of the Pulo do Lobo domain in order to study their poorly known low-grade metamorphic evolution. X-ray diffraction (XRD) was used to identify the mineralogy and measure crystallographic parameters (illite “crystallinity” and K-white mica b-cell dimension). Compositional maps of selected samples were obtained from electron probe microanalysis, which allowed for processing with XMapTools software, and chlorite semiempirical and thermodynamic geothermometry was performed. Thermometry based on Raman spectroscopy of carbonaceous material (RSCM) was used to obtain peak temperatures. The microstructural study shows the existence of two phyllosilicate growth events in the chlorite zone, the main one (M1) related to the development of a Devonian foliation S1 and a minor one (M2) associated with a crenulation cleavage (S2) developed in middle–upper Carboniferous times. M1 entered well into epizone (greenschist facies) conditions. M2 conditions were at lower temperature, reaching the anchizone–epizone boundary. These data accord well with the angular unconformity that separates the Devonian and Carboniferous formations of the Pulo do Lobo domain. The varied results obtained by the different approaches followed, combined with microstructural analysis, provide different snapshots of the metamorphic history. Thus, RSCM temperatures are higher in comparison with the other methods applied, which is interpreted to reflect a faster re-equilibration during the short-lived thermal Mississippian event. Regarding the metamorphic pressure, the data are very homogeneous: very low celadonite content (0 %–10 %) in muscovite (and low values of K-white mica b-cell dimension; 8.995 Å mean value), indicating a low pressure–temperature gradient, which is unexpected in a subduction-related accretionary prism. Highlights A multidisciplinary approach has been applied to study the metamorphism of the Pulo do Lobo metapelites. Devonian metamorphism entered epizone conditions. Carboniferous metamorphism reached the anchizone–epizone boundary. The inferred low-pressure gradient is incompatible with a subduction-related accretionary prism.

The influence of strain, lithology and stratigraphical depth on white mica (illite) crystallinity in mudrocks from the vicinity of the Corris Slate Belt, Wales: implications for the timing of metamorphism in the Welsh Basin

1991 ◽  
Vol 128 (6) ◽  
pp. 633-645 ◽  
Author(s):  
B. Roberts ◽  
R. J. Merriman ◽  
W. Pratt
Keyword(s):  
Strain Energy ◽  
Important Variable ◽  
White Mica ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Illite Crystallinity ◽  
Red Sandstone ◽  
Xrd Study ◽  
Profound Influence ◽  
Lower Palaeozoic

AbstractLow and very low grade metamorphism in a mudrock-dominated succession, ranging from Upper Cambrian to Wenlock, is characterized by the white mica (illite) crystallinity technique. Kubler indices indicate that grade ranges from late diagenetic to low epizonal. The prograde reaction most easily observed by XRD study is the progressive ordering of K/Na micas; diagnostic 2M1 polytypic reflections become recognizable at 0.4 Δ 2θ and strengthen as grade advances. Grade generally correlates with thickness of overburden in the > 9 km thick succession. However, strain exercises additionally a profound influence on grade, and the distribution of strain was related to décollement resulting from inhomogeneities and ductility contrasts within the succession. Strain energy is seen as an additional and important variable in the development of white mica crystallinity in slates. The distribution of metamorphic grade implies that the Lower Palaeozoic succession was augmented by several kilometres of Lower Devonian (Old Red Sandstone) strata at the metamorphic culmination. The culmination was syntectonic and represents an Acadian rather than an early diastathermal event. Subsequent dextral movement on the Bala Fault displaced the regional isocryst pattern by c. 4 km. Retrogressive smectite appears to be localized to the vicinity of the Bala Fault and is probably of Variscan age.

scholarly journals Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary belt (SW Iberian Variscides)

2019 ◽  
Author(s):  
Irene Pérez-Cáceres ◽  
David Jesús Martínez Poyatos ◽  
Olivier Vidal ◽  
Olivier Beyssac ◽  
Fernando Nieto ◽  
...  
Keyword(s):  
B Cell ◽  
Microstructural Analysis ◽  
Carbonaceous Material ◽  
Accretionary Prism ◽  
White Mica ◽  
Cell Dimension ◽  
Low Grade ◽  
The South ◽  
Metamorphic Evolution ◽  
Mafic Intrusions

Abstract. The Pulo do Lobo belt is one of the units related to the orogenic suture between the Ossa-Morena and the South Portuguese zones in the SW Iberian Variscides. This metasedimentary unit has been classically interpreted as a Rheic subduction-related accretionary prism formed during the pre-Carboniferous convergence and eventual collision between the South Portuguese Zone (part of Avalonia) and the Ossa-Morena Zone (peri-Gondwanan terrane). Discrete mafic intrusions also occur in the dominant Pulo do Lobo metapelites, related to an intraorogenic Mississippian transtensional and magmatic event that had a significant thermal input. Three different approaches have been applied to the Devonian/Carboniferous phyllites and slates of the Pulo do Lobo belt in order to study their poorly known low-grade metamorphic evolution. X-Ray diffraction (XRD) was used to unravel the mineralogy and measure crystallographic parameters (illite crystallinity and K-white mica b-cell dimension). Compositional maps of selected samples were obtained from electron probe microanalysis, which allowed processing with XmapTools software, and chlorite semi-empirical and thermodynamic geothermometry was performed. Thermometry based on Raman spectroscopy of carbonaceous material (RSCM) was used to obtain peak temperatures. The microstructural study shows the existence of two phyllosilicate growth events at the chlorite zone, the main one (M1) related to the development of a Devonian foliation S1, and a minor one (M2) associated with a crenulation cleavage (S2) developed at middle/upper Carboniferous time. M1 entered well into epizone (greenschist facies) conditions. M2 conditions were at lower temperature, reaching the anchizone/epizone boundary. These data accord well with the unconformity that separates the Devonian and Carboniferous formations of the Pulo do Lobo belt. The varied results obtained by the different approaches followed, combined with microstructural analysis, are indicative of different snapshots of the metamorphic history. Thus, RSCM temperatures are higher in comparison with the other methods applied, which is interpreted as reflecting a faster reequilibration during the short-lived thermal Mississippian event. Regarding the metamorphic pressure, the data are very homogeneous (very low celadonite content in muscovite and low values of K-white mica b-cell dimension), indicating a low-pressure gradient, which is unexpected in a subduction-related accretionary prism.

Geology of new localities on Tabarin Peninsula, northern Antarctic Peninsula

2001 ◽  
Vol 13 (3) ◽  
pp. 323-328 ◽  
Author(s):  
Rodolfo A. Del Valle ◽  
Jorge R. Morelli ◽  
Carlos A. Rinaldi
Keyword(s):  
Antarctic Peninsula ◽  
New Record ◽  
Sedimentary Rocks ◽  
Low Grade ◽  
Magmatic Arc ◽  
Metasedimentary Rocks ◽  
New Localities ◽  
Ice Retreat ◽  
The Antarctic ◽  
Hope Bay

New outcrops of Hope Bay Formation and Larsen Basin rocks have been exposed by recent ice-retreat on Tabarin Peninsula, northern Antarctic Peninsula. Quartzose, very low-grade metasedimentary rocks, cropping out at Balegno Nunatak (63°28′53″S, 57°00′31″W) are assigned to the Permian–Triassic Hope Bay Formation, and dioritic rocks are assigned to the Antarctic Peninsula batholith. Sedimentary rocks exposed at Rubulis Nunatak (63°30′52″S, 57°07′29′W) closely resemble Lower Cretaceous sedimentary rocks cropping out at nearby Troilo Nunatak, western Tabarin Peninsula. These rocks are correlated with the lower Gustav Group (?Barremian–Coniacian) of the Larsen Basin. This new record confirs that the Larsen Basin extends over southern Tabarin Peninsula, where basin sediments are thought to be faulted against sediments of the Antarctic Peninsula magmatic arc.

scholarly journals Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin

2011 ◽  
Vol 38 (2) ◽  
pp. 284
Author(s):  
Gilda Collo ◽  
Margarita Do Campo ◽  
Fernando Nieto
Keyword(s):  
Low Pressure ◽  
Central Andes ◽  
White Mica ◽  
Metamorphic Grade ◽  
Metamorphic Event ◽  
Low Grade ◽  
Middle Ordovician ◽  
Upper Cambrian ◽  
Intermediate Pressure ◽  
Gondwana Margin

The metamorphic P-T conditions of low-grade units from the Famatina belt, Central Andes of Ar¬gentina, were estimated through petrography, X-ray diffraction, and electron microscopy. For the Middle-Upper Cambrian Negro Peinado Formation a tectono-metamorphic event associated with intense intrafoliar folding, with estimated temperatures between 290 and 400°C (KICIS: 0.16-0.27Δº2θ, biotite blastesis and compositional homo¬geneity in dioctahedral micas) and intermediate pressure conditions (white mica b parameter: 9.010Å-9.035Å), was recognized. The Achavil Formation (Middle-Upper Cambrian) presents a main metamorphic event associated with temperatures between 200 and 290°C (KICIS: 0.26-0.41Δº2θ) and intermediate- to low-pressure conditions (white mica b parameter values: 8.972Å-9.017Å). Some illitic substitution in dioctahedral micas also indicates lower metamorphic grade than the Negro Peinado Formation. For Upper Cambrian to Middle Ordovician sequences a burial metamorphic pattern, with a progressive decrease in metamorphic grade from Volcancito Formation to Cerro Morado Group (ca. 490-465 Ma; KICIS: 0.31-0.69Δº2θ) and absence of tendency changes linked to strati¬graphic discontinuities was proposed. Mica and chlorite are the main phyllosilicates in the oldest units, while Ilt/Sme (R3) mixed-layer is almost the only one in the youngest. White mica b parameter indicates intermediate- to low-pressure conditions for all these sequences. This burial metamorphic pattern presents a marked break as the youngest Ordovician unit (La Aguadita Formation, after ca. 452 Ma) records higher metamorphic conditions (IKCIS: 0.28-0.19Δº2θ) than units from the Ordovician arc, with estimated temperatures between 270 and 330ºC and intermediate-pressure conditions. Our results indicate that basin contraction and inversion processes related to the Ordovician Ocloyic Orogeny involved at least two well-discriminated and not superposed metamorphic episodes in this region.

Barrovian-type metamorphism in the western domain of the Cordillera Darwin Metamorphic Complex, Fuegian Andes

2021 ◽  
Author(s):  
Mauricio Calderon ◽  
Catalina Zúñiga ◽  
Francisco Hervé ◽  
Thomas Theye ◽  
Gonzalo Galaz ◽  
...  
Keyword(s):  
Geothermal Gradient ◽  
White Mica ◽  
Burial Depth ◽  
Metamorphic Complex ◽  
Constant Composition ◽  
Magmatic Arc ◽  
Garnet Core ◽  
Late Generation ◽  
Si Content ◽  
Two Stages

&lt;p&gt;The Cordillera de Darwin Metamorphic Complex (CDMC) comprise metamorphosed supracrustal rocks and metaplutonic suites which records a unique tectonic evolution among the metamorphic complexes of the southernmost Andes. The pressure (P) and temperature (T) conditions determined in garnet-bearing schists in the Central Domain of the CDMC indicate a clockwise P-T path of metamorphism reaching burial depth as high as 12 kbar at ca. 620&amp;#176;C. This metamorphic event has been related to the closure of a marginal back-arc basin (Rocas Verdes Basin) and collision of an ensialic magmatic arc with the continent in the late Cretaceous. We focus on garnet-biotite schists intercalated within a huge block consisting of repeated sequences of metabasalts and amphibolites (Rocas Verdes Ophiolites), located in the Western Domain of the CDMC, at Seno Mart&amp;#237;nez. The chemical zonation of small garnet porphyroblasts (diameter of ca. 300 um) record two stages of metamorphism. Garnet is almost almandine in composition with lesser amounts of Ca, Mn and Mg. &amp;#160;The concentric zonation is characterized by relatively lower contents of Fe-Mg and higher contents of Ca-Mn in the core. Garnet bear tiny inclusions of clinozoisite, which is also present as isolated grains in the foliated matrix. Laths of biotite define the main foliation and have a nearly constant composition characterized by X&lt;sub&gt;Fe&lt;/sub&gt; of ca. 0.6. Two generations of phengitic white mica are identified on basis of Si content (a.pf.u.) varying between 3.20-3.30 (early generation) and of ca. 3.15 (late generation). To reconstruct the P-T conditions of metamorphism through thermodynamic modeling using the Perple_X software package, the bulk rock and mineral composition were considered. Using compositional isopleths of X&lt;sub&gt;Fe&lt;/sub&gt;, X&lt;sub&gt;Mg&lt;/sub&gt;, X&lt;sub&gt;Ca&lt;/sub&gt; and X&lt;sub&gt;Mn&lt;/sub&gt; in zoned garnet, Si content in white mica and X&lt;sub&gt;Fe&lt;/sub&gt; in biotite allow the constrain two stages of metamorphism (M1 and M2). The P-T conditions of M1, represented by the composition of the garnet core, are restricted to ca. 8 kbar and 400&amp;#176;C. M2 is restricted to ca. 7.5 kbar at 480&amp;#176;C, determined with the composition of the garnet rim, X&lt;sub&gt;Fe&lt;/sub&gt; in biotite and Si content in late phengitic white mica. Our preliminary results indicate that ophiolitic rocks and interleaved garnet-bearing schists were tectonically buried and metamorphosed in a relatively hot subduction interface characterized by a geothermal gradient of ca. 16&amp;#176;C/km, prior to the collision of the ensialic magmatic arc. Acknowledgements. This study was supported by the Fondecyt grant 1161818.&lt;/p&gt;

scholarly journals The thrust contact between the Canastra and Vazante groups in the Southern Brasília Belt: structural evolution, white mica crystallinity and implications for the Brasiliano orogeny

2016 ◽  
Vol 46 (4) ◽  
pp. 567-583 ◽  
Author(s):  
Manuela de Oliveira Carvalho ◽  
◽  
Claudio de Morisson Valeriano ◽  
Pamela Alejandra Aparicio González ◽  
Gustavo Diniz Oliveira ◽  
...  
Keyword(s):  
Structural Evolution ◽  
White Mica ◽  
Low Grade ◽  
Kink Bands ◽  
Metasedimentary Rocks ◽  
Kübler Index ◽  
Crenulation Cleavage ◽  
Thrust Sheets ◽  
Brasiliano Orogeny ◽  
Carbonaceous Phyllite

ABSTRACT: Two regional thrust-sheets of Neoproterozoic metasedimentary rocks occur in the Southern Brasília Belt, northwest Minas Gerais. The lower one comprises the Vazante Group, that is formed in the studied area, from base to top, by the Serra do Garrote (metapelites interlayered with carbonaceous phyllite), Serra do Poço Verde (beige to pink stromatolitic metadolomite with interlayered greenish slates), Morro do Calcário (gray stromatolitic metadolomite interlayered with gray slates) and Serra da Lapa (phyllite with dolarenitic lenses interlayered with slates) formations. The upper thrust sheet consists of the Canastra Group (Paracatu formation): laminated sericite phyllites and carbonaceous phyllites interlayered with quartzite. The Braziliano orogeny resulted in four phases of contractional deformation, associated with low-grade metamorphism. The first two (D1 and D2) are ductile, while the third and fourth ones (D3 and D4) are brittle-ductile. D1 developed a slaty S1 cleavage subparallel to the primary layering, with shallow to steep dips to NW. D2 developed a crenulation cleavage (S2) that dips moderately to NW and is associated with tight to isoclinal folds. D3 and D4 phases developed crenulations and open folds and kink bands. S3 dips steeply to NW, while S4 has moderate to steep dips to NE and SW. White mica crystallinity (Kübler index) measurements in metapelites indicate that both the Canastra and Vazante groups reached anchizone/epizone conditions, and metamorphic discontinuities along thrusts indicate that the peak of metamorphism is pre or syn-thrusting.

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