O Complexo Encantadas é uma unidade Paleoproterozóica constituída por gnaisses tonalíticos, trondhjemíticos e dioríticos com presença subordinada de anfibolitos e rochas metaultramáficas ricas em hornblenda. Este complexo é cortado por corpos tabulares de metagranitos porfiríticos e equigranulares que se encontram posicionados ao longo de uma zona de cisalhamento dúctil de disposição suborizontal. Esta estrutura define o contato entre os Complexos Encantadas e Porongos, respectivamente, infra e supra-estrutura do Domo de Santana da Boa Vista. Os metagranitos têm afinidade cálcico-alcalina médio a alto-K e caráter levemente peraluminoso. A evolução como termos independentes indica que os metagranitos representam unidades petrológicas distintas, sendo afetados por processos de fracionamento de plagioclásio, biotita, zircão e apatita. Os metagranitos apresentam enriquecimento em ETRL e empobrecimento em ETRP, com valores elevados de Ba, Rb, Sr, U e Th, anomalias negativas de Nb e Ti, dispondo-se no campo das rochas geradas em ambientes de arco magmático. Os dados estruturais indicam que os metagranitos tiveram uma evolução complexa, e sua colocação é contemporânea a D1 e, portanto, de acordo com os dados geocronológicos disponíveis, sua idade situa-se próxima de 2 Ga, que é a idade presumível do metamorfismo de facies anfibolito, interpretado aqui como um evento orogênico, provavelmente colisional. Os metagranitos porfiríticos e equigranulares juntamente com os gnaisses dioriticos, tonaliticos e trondhjemiticos do Complexo Encantadas constituem uma associação magmática de ambiente de margem continental ativa, cujo magmatismo está associado a fontes mantélicas metassomatisadas por fluídos derivados de subducção litosférica durante o Paleoproterozóico. / The Encantadas Complex is a Paleoproterozoic unit constituted by tonalitic, trondhjemitic and dioritic gneisses with rare presence of amphibolites and hornblende-rich metaultramafic rocks. This complex is cut by tabular bodies of porphyritic and equigranular metagranites which are emplaced along a ductile shear zone with suborizontal disposition. This structure defines the contact between the Encantadas and Porongos complexes, respectively, infrastructure and suprastructure of Santana da Boa Vista Dome. The metagranites have medium to high-K calc-alkaline affinity and slightly peraluminous character. The evolution as independent terms indicates The metagranites represent distinct petrologic units with independent evolution, that are affected by fractionating of plagioclase, biotite, zircon and apatite. The metagranites show enrichment in LRRE and depletion of HREE, with high values of Ba, Rb, Sr, U and Th and negative anomalies of Nb and Ti, like granites of magmatic arc. Structural data indicate that metagranites have had a complex evolution, and their emplacement was simultaneous with D1 event which, according to the available geochronological data, has age close to 2 Ga. This event is interpreted as a metamorphic one associated with a collisional orogeny. Porphyritic and equigranular metagranites together with gneisses of Encantadas Complex constitute an active continental margin arc association, whose magmatism is related to metasomatised-mantle sources affected by fluids derived from the subducted lithophere during the Paleoproterozoic times.

O Complexo Encantadas é uma unidade Paleoproterozóica constituída por gnaisses tonalíticos, trondhjemíticos e dioríticos com presença subordinada de anfibolitos e rochas metaultramáficas ricas em hornblenda. Este complexo é cortado por corpos tabulares de metagranitos porfiríticos e equigranulares que se encontram posicionados ao longo de uma zona de cisalhamento dúctil de disposição suborizontal. Esta estrutura define o contato entre os Complexos Encantadas e Porongos, respectivamente, infra e supra-estrutura do Domo de Santana da Boa Vista. Os metagranitos têm afinidade cálcico-alcalina médio a alto-K e caráter levemente peraluminoso. A evolução como termos independentes indica que os metagranitos representam unidades petrológicas distintas, sendo afetados por processos de fracionamento de plagioclásio, biotita, zircão e apatita. Os metagranitos apresentam enriquecimento em ETRL e empobrecimento em ETRP, com valores elevados de Ba, Rb, Sr, U e Th, anomalias negativas de Nb e Ti, dispondo-se no campo das rochas geradas em ambientes de arco magmático. Os dados estruturais indicam que os metagranitos tiveram uma evolução complexa, e sua colocação é contemporânea a D1 e, portanto, de acordo com os dados geocronológicos disponíveis, sua idade situa-se próxima de 2 Ga, que é a idade presumível do metamorfismo de facies anfibolito, interpretado aqui como um evento orogênico, provavelmente colisional. Os metagranitos porfiríticos e equigranulares juntamente com os gnaisses dioriticos, tonaliticos e trondhjemiticos do Complexo Encantadas constituem uma associação magmática de ambiente de margem continental ativa, cujo magmatismo está associado a fontes mantélicas metassomatisadas por fluídos derivados de subducção litosférica durante o Paleoproterozóico. / The Encantadas Complex is a Paleoproterozoic unit constituted by tonalitic, trondhjemitic and dioritic gneisses with rare presence of amphibolites and hornblende-rich metaultramafic rocks. This complex is cut by tabular bodies of porphyritic and equigranular metagranites which are emplaced along a ductile shear zone with suborizontal disposition. This structure defines the contact between the Encantadas and Porongos complexes, respectively, infrastructure and suprastructure of Santana da Boa Vista Dome. The metagranites have medium to high-K calc-alkaline affinity and slightly peraluminous character. The evolution as independent terms indicates The metagranites represent distinct petrologic units with independent evolution, that are affected by fractionating of plagioclase, biotite, zircon and apatite. The metagranites show enrichment in LRRE and depletion of HREE, with high values of Ba, Rb, Sr, U and Th and negative anomalies of Nb and Ti, like granites of magmatic arc. Structural data indicate that metagranites have had a complex evolution, and their emplacement was simultaneous with D1 event which, according to the available geochronological data, has age close to 2 Ga. This event is interpreted as a metamorphic one associated with a collisional orogeny. Porphyritic and equigranular metagranites together with gneisses of Encantadas Complex constitute an active continental margin arc association, whose magmatism is related to metasomatised-mantle sources affected by fluids derived from the subducted lithophere during the Paleoproterozoic times.

O Complexo Encantadas é uma unidade Paleoproterozóica constituída por gnaisses tonalíticos, trondhjemíticos e dioríticos com presença subordinada de anfibolitos e rochas metaultramáficas ricas em hornblenda. Este complexo é cortado por corpos tabulares de metagranitos porfiríticos e equigranulares que se encontram posicionados ao longo de uma zona de cisalhamento dúctil de disposição suborizontal. Esta estrutura define o contato entre os Complexos Encantadas e Porongos, respectivamente, infra e supra-estrutura do Domo de Santana da Boa Vista. Os metagranitos têm afinidade cálcico-alcalina médio a alto-K e caráter levemente peraluminoso. A evolução como termos independentes indica que os metagranitos representam unidades petrológicas distintas, sendo afetados por processos de fracionamento de plagioclásio, biotita, zircão e apatita. Os metagranitos apresentam enriquecimento em ETRL e empobrecimento em ETRP, com valores elevados de Ba, Rb, Sr, U e Th, anomalias negativas de Nb e Ti, dispondo-se no campo das rochas geradas em ambientes de arco magmático. Os dados estruturais indicam que os metagranitos tiveram uma evolução complexa, e sua colocação é contemporânea a D1 e, portanto, de acordo com os dados geocronológicos disponíveis, sua idade situa-se próxima de 2 Ga, que é a idade presumível do metamorfismo de facies anfibolito, interpretado aqui como um evento orogênico, provavelmente colisional. Os metagranitos porfiríticos e equigranulares juntamente com os gnaisses dioriticos, tonaliticos e trondhjemiticos do Complexo Encantadas constituem uma associação magmática de ambiente de margem continental ativa, cujo magmatismo está associado a fontes mantélicas metassomatisadas por fluídos derivados de subducção litosférica durante o Paleoproterozóico. / The Encantadas Complex is a Paleoproterozoic unit constituted by tonalitic, trondhjemitic and dioritic gneisses with rare presence of amphibolites and hornblende-rich metaultramafic rocks. This complex is cut by tabular bodies of porphyritic and equigranular metagranites which are emplaced along a ductile shear zone with suborizontal disposition. This structure defines the contact between the Encantadas and Porongos complexes, respectively, infrastructure and suprastructure of Santana da Boa Vista Dome. The metagranites have medium to high-K calc-alkaline affinity and slightly peraluminous character. The evolution as independent terms indicates The metagranites represent distinct petrologic units with independent evolution, that are affected by fractionating of plagioclase, biotite, zircon and apatite. The metagranites show enrichment in LRRE and depletion of HREE, with high values of Ba, Rb, Sr, U and Th and negative anomalies of Nb and Ti, like granites of magmatic arc. Structural data indicate that metagranites have had a complex evolution, and their emplacement was simultaneous with D1 event which, according to the available geochronological data, has age close to 2 Ga. This event is interpreted as a metamorphic one associated with a collisional orogeny. Porphyritic and equigranular metagranites together with gneisses of Encantadas Complex constitute an active continental margin arc association, whose magmatism is related to metasomatised-mantle sources affected by fluids derived from the subducted lithophere during the Paleoproterozoic times.

The Nahlin ophiolite represents one of the largest (~80 km long) and best-preserved ophiolites in the Cordillera of British Columbia and Yukon, Canada, yet it has been understudied compared to other ophiolites worldwide. Bedrock mapping at 1:20,000 scale in the Menatatuline Range area shows that the ophiolite is structurally disrupted with mantle bodies divisible into two massifs: Hardluck and Menatatuline. Studies of 30 samples show that both massifs consist of spinel harzburgites and minor lherzolites that have been strongly depleted by melt extraction (<2 wt % Al2O3 and ~45 wt % MgO). Clinopyroxene REE abundances determined by LA-ICP-MS illustrate different extents of depletion between the two massifs, with YbN varying from 2.3 – 5.0 and 1.7 – 2.2 in the Hardluck and Menatatuline massifs, respectively. Inversion modelling of the clinopyroxene REE abundances yields ~10 – 16% melting in the Hardluck massif and ~16 – 20% melting in the Menatatuline massif, with melt compositions that are compositionally similar to the gabbros and basalts proximal to the mantle rocks. All these extrusive and intrusive rocks in the ophiolite have an arc-signature, implying that the Nahlin ophiolite formed in a supra-subduction zone (SSZ) environment. The Nahlin peridotites document a two-stage evolution: depletion of a locally heterogeneous mantle source by hydrous fractional melting, followed by refertilization of the refractory harzburgite in the mantle wedge evidenced by LREE enrichment in clinopyroxene and whole-rock chemistry. This two-stage evolution is also recorded by the thermal history of the harzburgites. The REE-in-two-pyroxene thermometry has been reset following cryptic and modal metasomatism and relatively slow cooling, whereas major element two pyroxene geothermometry records temperatures varying from near solidus (~1290 °C) to ~800 °C, with the highest temperatures recorded in samples from the Menatatuline massif. The refractory nature of the Menatatuline harzburgites in combination with the arc-influenced volcanic geochemistry provides overwhelming evidence for a SSZ origin. Peridotite from the Hardluck massif displays characteristics of both abyssal and SSZ peridotites. These geochemical and geothermometric constraints can be reconciled by evolution of the Hardluck and Menatatuline massifs as two separate segments along a backarc ridge system, later juxtaposed by dextral strike-slip faulting. Alternatively, the Nahlin ophiolite may represent proto-forearc seafloor spreading associated with subduction initiation akin to the proposed origins of the Izu-Bonin-Mariana arc (Stern et al. 2012; Maffione et al. 2015). In any case, the geochemical data for peridotites and magmatic rocks herein require that the SSZ-type Nahlin ophiolite reside in the upper plate at an intraoceanic convergent margin. This interpretation has strong implications for models of northern Cordilleran tectonics, where the Cache Creek terrane is typically shown as a subducting ocean basin during Cordilleran orogenesis. / Graduate

The Glacier Creek volcanogenic massive sulfide (VMS) deposit is hosted within Late Triassic, oceanic back-arc or intra-arc, rift-related, bimodal volcanic rocks (Hyd or Tats Group) of the allochthonous Alexander terrane known as the Alexander Triassic Metallogenic Belt (ATMB). The deposit presently consists of four tabular massive sulfide lenses with a resource of 4.75 Mt. at 1.84% Cu, 4.57% Zn, 0.15% Pb, 0.28 g/t Au and 29.07 g/t Ag. A deposit-scale thrust fault offsets stratigraphy along the axial surface of a deposit-scale anticline. The massive sulfide lenses are barite-rich and are divided into 6 main ore-types based on mineral assemblages. There is a large range of sphalerite compositions, with low-Fe sphalerite dominant throughout the lenses and high-Fe sphalerite at the top and bottom of the lenses in pyrrhotite-rich zones. Lenses contain anomalous Sb, Hg and Tl. Gangue minerals include barite, quartz, barian-muscovite, calcite, albite, highly subordinate chlorite and locally hyalophane and celsian. Overlying massive sulfide is a tuffaceous hydrothermal sediment with anomalous REE patterns and local hyalophane. The general footwall to all four lenses is a thick unit of coherent to volcaniclastic feldspar-phyric basalt containing extensive lateral alteration. Four alteration facies are recognized based on mineral assemblages. Mass balance calculations for the footwall indicate general gains of S, Fe, Si and K with coincident loss of Ca, Na and Mg, along with trace element gains of Tl, Sb, Hg, Ba, Zn, Cu, As and loss of Sr with increased alteration intensity. Short wavelength infrared (SWIR) spectroscopy shows a general decrease in Na, K and Al content of muscovite and increase of Fe+Mg and Ba content towards ore. Integrated petrographic, mineral, chemical and sulfur-isotope data suggest a transition during deposit formation, from high-temperature, acidic, reduced hydrothermal fluids mixing with oxidized, SO4-rich seawater, to later cooler, low fO2-fS2 conditions of formation and a lack of SO4 in seawater.

>Magister Scientiae - MSc / A magmatic Ni-Cu (±Co-Zn) sulphide deposit, named the Hondekloof prospect, is present in the Kliprand area at the border between the Northern Cape and Western Cape Provinces of South Africa. The deposit occurs in the central part of the polyphase deformed and highly metamorphosed Garies Terrane, in the Namaqua Sector, along the south-western margin of the Mesoproterozoic Namaqua-Natal Metamorphic Province. Given the sub-economic concentrations yielded from evaluation of three of its known massive-sulphide lenses evaluated, the Hondekloof prospect has received relatively little consideration in terms of ongoing scientific research. Consequently, many aspects related to the genesis, classification and tectonic evolution of the deposit, to date, remain relatively unclear and unknown. The present contribution has therefore been geared to addressing some of those issues in view of the new data obtained on the country rocks and host rocks to the mineralization.Six exploration boreholes were logged, sampled and examined at the deposit site in Kliprand. A total of seven host rocks, namely meta-gabbronorite, biotite gneiss, feldspathic-biotite-garnet gneiss, pink gneiss, meta-syenite as well as enderbite along with a garnetiferous quartzofeldspathic rock occur in association with the sulphide mineralization. The origin, protoliths and tectonic settings of the host lithological units were determined and discussed in terms of modern plate tectonic principles. The meta-gabbronorite (the actual ore host), which had a magmatic protolith and forms part of the pre- to syn-tectonic Oorkraal Suite, displays the chemical characteristics of a depleted mantle origin (source of MORB-like melt), generated within a continental tectonic rift environment. Country rocks with sedimentary protoliths have chemical characteristics indicating a psammitic, felsic to intermediate provenance deposited within a regional subduction-related tectonic setting. A number of geochemical indices, of which the combination of element-ratios (such as Fe2O3/Al2O3 vs. TiO2/Al2O3, as well as Cr vs. Ni, amongst others) created as exploration vectors towards mineralisation, have shown potential for pointing towards the direction of the mineralization. Based on classification schemes of magmatic Ni sulphide deposits, it is has been suggested that the Hondekloof prospect could be classified as a low MgO, conduit-type, disseminated magmatic nickel sulphide deposit.

The St. Cyr klippe hosts well preserved to variably retrogressed eclogites found as sub-meter to hundreds of meter scale lenses within quartzofeldspathic schists in the Yukon-Tanana terrane, Canadian Cordillera. The St. Cyr area consists of structurally imbricated, polydeformed, and polymetamorphosed units of continental arc and oceanic crust. The eclogite-bearing quartzofeldspathic schists form a 30 by 6 kilometer thick, northwest-striking, coherent package. The schists consist of metasediments and felsic intrusives that are intercalated on the tens of meter scale. The presence of phengite and Permian age zircon crystallized under eclogite facies metamorphic conditions indicates that the eclogite was metamorphosed in situ with its quartzofeldspathic host. I investigated the metamorphic evolution of the eclogite-facies rocks in the St. Cyr klippe using isochemical phase equilibrium thermodynamic (pseudosection) modeling. I constructed P-T pseudosections in the system Na2O-K2O-CaO-FeO-O2-MnO-MgO-Al2O3-SiO2-TiO2-H2O for the bulk-rock composition of an eclogite and a host metatonalite. In combination with petrology and mineral compositions, St. Cyr eclogites followed a five-stage clockwise P-T path. Peak pressure conditions for the eclogites and metatonalites reached up to 3.2 GPa, well within the coesite stability field, indicating the eclogites reached ultrahigh-pressure conditions. Decompression during exhumation occurred with a corresponding temperature increase. SHRIMP-RG zircon dating shows that the protolith of the eclogites formed within the Yukon-Tanana terrane during early, continental arc activity, between 364 and 380 Ma, while the metatonalite protolith formed at approximately 334 Ma, during the Little Salmon Cycle of the Klinkit phase of Yukon-Tanana arc activity. Both the eclogites and the metatonalites were then subducted to mantle depths and metamorphosed to ultrahigh-pressure conditions during the late Permian, between 266 and 271 Ma. The results of our study suggest portions of the Yukon-Tanana terrane were subducted to high-pressure and ultrahigh-pressure conditions. This is the first report of ultrahigh-pressure metamorphism in the accreted terranes of the North American Cordillera. Petrological, geochemical, geochronological, and structural relationships link the eclogites at St. Cyr to other eclogite localities in Yukon, indicating the high-pressure assemblages form a larger lithotectonic unit within the Yukon-Tanana terrane.

The North Caribou Terrane forms the core of Superior Province and records a protracted history of crustal growth and modification. At the centre of the North Caribou Terrane, lies the North Caribou greenstone belt, which is surrounded by granitoids of diverse compositions and ages. This study reports whole-rock geochemistry, zircon and titanite geochronology, and hornblende geobarometry on these plutonic rocks. Although zircons as old as 3132 ± 7 Ma were found, the main magmatic pulse occurred between 2880 and 2830 Ma, and geobarometry indicates tectonic thickening during this period. This was followed by widespread hydrothermal alteration and limited magmatism from 2760 to 2680 Ma, and shallow, brittle-ductile intrusions at circa 2630 Ma. From 2730 to 2630 Ma, intrusions were emplaced at increasingly shallow crustal levels. All of the rocks, except for the youngest pegmatitic intrusions, show similar patterns in major and trace elements, with a general trend toward more evolved compositions through time. These patterns indicate that the granitoids record mostly reworking of early intrusions, which is also consistent with patterns observed in the geochronology.

This thesis presents a 40Ar/39Ar geochronological analyses of biotite from thin ductile shear zones in Paleoproterozoic granulite-facies gneisses from the Ellesmere-Devon crystalline terrane, Nunavut, Canada. The gneisses are part of the Paleoproterozoic Thelon tectonic zone. U-Pb dates of zircon show that the gneisses have magmatic protolith ages ranging from 2007–1958 Ma. The quartzofeldspathic gneisses in southeast Ellesmere Island display centimeter-scale E- to NE-striking sinistral and dextral mylonite zones offsetting pegmatitic dikes that are the last stage of ductile deformation of the basement rocks. Samples were taken from nearshore outcrops at Hayes Fiord, Pim Island, NE of the Leffert Glacier and NW of Cape Isabella. Biotite clusters replace orthopyroxene as the result of post-granulite facies metamorphism in the gneisses. Biotite in mylonitic and ultramylonitic fabrics is found as flattened clusters and also as individual crystals defining shear bands related to mylonitization. Eight samples were dated, including biotite from five mylonites, one deformed pegmatite, one tonalite and muscovite from a pegmatite. Major element X-ray maps demonstrate that the biotite is chemically homogenous. Backscattered electron images and electron dispersive spectroscopy via scanning electron microscopy confirm that biotite lacks intercrystalline layering with other K phases. Step-heating analysis of mica at the University of Vermont yielded Paleoproterozoic 40Ar/39Ar ages. The apparent age spectra form plateau ages in all but one mylonite sample. Biotite from a protomylonite was 2051 ± 26 Ma, older than the protolith ages obtained from U-Pb zircon geochronology, and most likely indicates excess Ar. Pegmatitic muscovite was 1977 ± 35 Ma. Biotite dates range from 1874 ± 13 Ma to 1838 ± 14 Ma for the five mylonites without excess Ar. Biotite dated from ductile shear zones signals the latest deformation in the basement, which was active as early as 1887 Ma.

Indiana University-Purdue University Indianapolis (IUPUI) / The Tso Morari terrane within the Himalayan orogenic belt underwent ultrahigh-pressure (UHP) coesite-eclogite metamorphism due to northward subduction of the Indian continent under the Eurasian continent during the early Eocene. In this study we optimized a best protocol for thermodynamically modelling pressure-temperature (P-T) paths of high-grade metabasites using the Tso Morari eclogite as a case study through evaluating the effects of employing commonly used thermodynamic modeling techniques (e.g., programs, thermodynamic datasets, a-X relations). A “fishhook” shaped clockwise P-T path was obtained with a peak pressure of ~28.5 kbar at ~563 °C, followed by a peak temperature of ~613 °C at ~24.5 kbar. The peak pressures predicted by modelling protocols are consistent with the conventional thermobarometry results and petrographic observations from the Tso Morari eclogites. Secondly, thermodynamic modelling using P-M(H2O) pseudosections on Tso Morari UHP rocks indicates three distinct fluid events during the prograde and retrograde metamorphism. Fluid Event 1 caused the fluid-assisted homogenization of prograde garnet cores in eclogite at ~18.5 kbar and ~555 °C; Fluid Event 2 is evidenced by the formation of poikiloblastic epidote (~23.5 kbar and ~610 °C, at the expense of lawsonite) and amphibole (from ~19.0 to ~14.5 kbar at ~610 °C, at the expense of omphacite and talc), and symplectite association (~8.7 kbar and ~625 °C) in the eclogite matrix without external fluid supply. Fluid Event 3 was determined through modelling the amphibolitization of eclogites with external fluid infiltration at ~9.0–12.5 kbar and ~608 °C. This fluid phase most likely derived from the mixing of dehydrated host orthogneiss and/or metasediments during exhumation through the amphibolite-facies zone in the subduction channel. This study demonstrates the need for using careful petrographic observations in parallel with thermodynamic modelling to achieve realistic results. / 2023-12-02