Πετρογραφική, ορυκτοχημική και γεωχημική διερεύνηση της γένεσης και της γεωτεκτονικής εξέλιξης των οφιολιθικών σχηματισμών στην περιοχή της Βάβδου (Δ. Χαλκιδική). Ιδιαίτερη έμφαση δώθηκε στη δημιουργία χρωμιτών και στη γεωχημεία των PGE ως πετρογενετικούς δείκτες / Petrographic, mineralogical and geochemical investigation of the genesis and geotectonic evolution of the ophiolitic formations in the area of Vavdos (W. Chalkidiki). Particular emphasis was given to the evolution of chromites and to the geochemistry of PGE as petrogenetic indicators

Η νήσος της Τήνου (εικόνα 1), με εμβαδό περίπου 200 km2, βρίσκεται στη δυτική Ελλάδα και είναι τρίτη σε έκταση μεταξύ των νήσων που συγκροτούν το σύμπλεγμα των Κυκλάδων, στο Αιγαίο πέλαγος. Από γεωτεκτονικής απόψεως υπάγεται στην γεωτεκτονική ενότητα, γνωστή ως ‘Αττικοκυκλαδική Κρυσταλλοσχιστώδης Μάζα’. Από διάφορες γεωλογικές μελέτες που έχουν συνταχθεί κατά καιρούς, έχει προκύψει ότι στην γεωλογική της δομή μετέχουν μεταμορφίτες, μαγματίτες και τεταρτογενή ιζήματα. Από τα πετρώματα αυτά οι μεν μεταμορφίτες καλύπτουν το 79%, τα δε υπόλοιπα το 17% και 4%, αντίστοιχα, της επιφάνειας της νήσου.Με βάση μελέτες που πραγματοποιήθηκαν στις οφιολιθικές εμφανήσεις της Τήνου, προέκυψε πως η σύσταση του μανδυακού περιδοτίτη είναι χαρζβουργιτική, μέσα στον οποίο υπήρχαν αρκετές μικρές εμφανήσεις χρωμίτη. Οι χαρακτήρες που έχουν μελετηθεί γεωχημικά και ορυκτολογικά-πετρογραφικά, αφορούν κυρίως τον διάσπαρτο τύπο σπινελλίου και τον τεκτονίτη-περιδοτίτη που είναι ο δυνητικός ξενιστής κοιτασμάτων χρωμίτη.Το ενδιαφέρον της νήσου της Τήνου από απόψεως οικονομικής γεωλογίας περιορίζεται – σύμφωνα τουλάχιστον με τα δεδομένα που έχουν προκύψει από τις μέχρι τώρα έρευνες – αποκλειστικά και μόνο στα μάρμαρα και στα βιομηχανικά ορυκτά και πετρώματα (τάλκης). Μεταλλικά ορυκτά απατώνται μεν, σε φυσικές όμως συγκεντρώσεις τέτοιες, ώστε ούτε οι διαστάσεις τους ούτε και η περιεκτικότητά τους σε μέταλλο να αφήνουν περιθώρια για θετικές εκτιμήσεις. Παλαιότερα, έγινε προσπάθεια εκμεταλλεύσεως, σε διάφορες θέσεις, χωρίς θετικά αποτελέσματα όμως. Τα μεταλλευτικά έργα είναι μικρών διαστάσεων, συνήθως εκσκαφές, και σε λίγες περιπτώσεις στοές και κεκλιμένα. Σημειώνεται ότι σε πολλές από τις εκσκαφές δεν υπάρχουν σήμερα ίχνη μεταλλεύματος, ούτε στα τοιχώματά τους, ούτε στα μπάζα. Η συγκέντρωση της ομάδας του λευκόχρυσου (PGE) και του χρυσού στους χρωμιτίτες των οφιολίθων της Τήνου είναι της τάξεως των εκατοντάδων ppb. Αυτά τα στοιχεία συγκεντρώνονται κυρίως θειούχα μεταλλικά ορυκτά (σουλφίδια), όπως ο χαλκοπυρίτης, και σχηματίζονται στο ορθομαγματικό στάδιο, σχηματίζοντας ομάδες, μέσα στους κόκκους του χρωμίτη. / Tinos island (picture 1), with an area of about 200 km2, is located in weastern Greece and is the third largest island of the Cyclades group of islands, in the Aegean Sea. Geologically, is regarded, to belong to the geotectonic unit, known as the ‘Atticocycladic Crystalline Massif’. As a result of many geological studies, it was found that the geological structure of the island is made up from metamorphic and magmatic rocks, as well as Quaternary sediments. These rocks cover an area of about 79%, 17% and 4%respectively of the island’s surface area. Based on studies performed in the Tinos ophiolitic complex, showed that the composition of the mantle peridotites is harzburgitic, in which there were several small commulations of chromite. The characters studied geochemical and mineralogical-petrographical, mainly concern the disseminated spinel type and the peridotite which is a potential host rock for chromite deposits. The interest of Tinos island in terms of economic geology is limited - at least according to the data derived from the surveys so far - to marbles and industrial minerals and rocks (talc). Metallic minerals are occured, but in natural concentrations such that neither the dimensions nor the content of metal allow for positive evaluations. Previously, an exploitation attempt was made, in various positions, but without positive results. Mining projects are small, usually excavations, and in a few cases tunnels and ramps. Note that in many of the excavation does not exist today mines traces neither in their walls, nor in the rubble. The concentration of platinum group (PGE) and gold in chromitites of serpentines of Tinos are about of hundreds of ppb. These components are mainly concentrated sulphurous metallic minerals (sulfides) such as chalcopyrite, and formed in orthomagmatic stage, forming groups within the granules of the chromite.

This work presents the preparation and physical properties of spinel nanoparticles and nanocomposites. All nanocomposites in diamagnetic matrix like chromites CoCr2O4, CuCr2O4, NiCr2O4, ZnCr2O4 and ferrite MgFe2O4 were prepared using sol-gel method. On the other hand, isolated nanoparticles such as MgCr2O4, MnCr2O4, CuCr2O4, NiCr2O4, and FeCr2O4, were prepared using autocombustion a co-precipitation methods. CoFe2O4 and MgFe2O4 were prepared by microemulsion alkoxide method. This microemulsion method was used for the spinel nanoparticles preparation for the first time. This work describes the influence of heat treatment temperature on the final particle size and influence of particle size on physical properties of material. The study of the influence of twovalent cationt in the spinel structure on the magnetic properties of chromites was also carried out. The final samples were characterized by XRD powder diffraction, Mössbauer spectroscopy, infrared and Raman spectroscopy, and HRTEM. The dependence of magnetization on applied magnetic field at constant temperature and ZFC (zero-field cooling) - FC (field cooling) measurement was carried out on the prepared sample.

O Ofiolito Arroio Grande, localizado no sudeste do Cinturão Dom Feliciano, próximo à fronteira Brasil/Uruguai, entre Arroio Grande e Jaguarão (RS), é uma associação metaultramáfica-máfica-sedimentar que representa fragmentos de uma mélange ofiolítica, relacionada à amalgamação do paleocontinente Gondwana Ocidental durante os estágios finais do ciclo orogênico Brasiliano-Panafricano. As rochas do Ofiolito Arroio Grande se encontram circundadas por rochas metassiliciclásticas do Complexo Arroio Grande, do qual o ofiolito faz parte, e também como xenólitos em meio a granitoides da Suíte Pinheiro Machado e do Granito Três Figueiras (os quais integram o Batólito Pelotas-Aiguá). A unidade metaultramáfica do ofiolito compreende serpentinitos e xistos magnesianos cromíferos. Sua unidade metamáfica é constituída por anfibolitos, metagabros e metadioritos. A unidade metassedimentar compreende mármores calcíticos, intrudidos por enxame de diques máficos. O Ofiolito Arroio Grande está posicionado ao longo da Zona de Cisalhamento Ayrosa Galvão-Arroio Grande (transcorrente, dúctil, alto ângulo), responsável pela milonitização da maioria das rochas dessa associação. As investigações desenvolvidas no ofiolito tiveram o objetivo de identificar as fontes magmáticas dos protólitos e os processos que ocorreram desde sua geração no manto/crosta oceânica até sua incorporação no continente, além de obter idades (absolutas e relativas) referentes a esses processos. Para os metaultramafitos, a geoquímica de rocha total (e.g. Ni >1000 ppm; Cr > 1500 ppm), em conjunto com a química mineral de cromitas (e.g. Cr# 0,6-0,8; TiO2 0,01-0,20 %peso; Fe2+/Fe3+ ± 0,9), sugeriu protólitos harzburgíticos mantélicos, cuja fonte é um manto depletado sob uma região de espalhamento oceânico de retroarco, que experimentou altas taxas de fusão parcial. Esses harzburgitos foram posteriormente serpentinizados em ambiente oceânico, sugerido pelas razões 87Sr/86Sr630 de um serpentinito (ca. 0,707). Para os metamafitos, a geoquímica de rocha total e isotópica sugeriram protólitos toleíticos oceânicos, gerados em um contexto de suprassubducção em ambiente de retroarco (e.g. Cr 260-600 ppm; Nb/Y 0,1-0,5; Ti/Y ± 500; La/Nb 2-5; Th/Yb 0,1-5 e Nb/Yb 1-5; padrões de REE; razões 87Sr/86Sr630 variando de MORB – 0,703 – a IAT – 0,705-0,707), cuja fonte magmática foi enriquecida por material crustal e fluidos relacionados à subducção. A idade mínima para a obducção e metamorfismo das unidades ofiolíticas foi estimada em 640 Ma, a partir da datação (U-Pb SHRIMP) de um quartzo sienito. Esse último é o resultado de fusões relacionadas a intrusões diorítico-tonalíticas, atribuídas ao magmatismo de arco continental da Suíte Pinheiro Machado. Essas intrusões afetaram os mármores e os anfibolitos (fragmentos dos enxames de diques máficos), de maneira que, em pelo menos 640 Ma, rochas da mélange ofiolítica (já metamorfizadas) estavam alojadas em ambiente continental. Um evento metassomático posterior (relacionado à intrusão do Granito Três Figueiras, sincinemática à zona de cisalhamento acima referida) afetou os serpentinitos, gerando zonas de talcificação, tremolitização e cloritização, essa última representando um blackwall que também envolveu unidades metassiliciclásticas do Complexo Arroio Grande. O Ofiolito Arroio Grande foi inserido no contexto geotectônico da bacia de retroarco Marmora, cujos fragmentos são encontrados na Namíbia (Terreno Marmora) e no Uruguai (Complexo Paso del Dragón e Bacia Rocha – Terreno Punta del Este). / The Arroio Grande Ophiolite, located in the southeastern region of the Dom Feliciano Belt, near the Brazil/Uruguay border, is a metaultramafic-mafic-sedimentary association which represents slices of an ophiolitic mélange, related to the Western Gondwana amalgamation during the late stages of the Brasiliano-Panafrican orogenic cycle. The Arroio Grande Ophiolite rocks are enveloped by metasiliciclastic units of the Arroio Grande Complex and occur as xenolyths within granitoids of the Pinheiro Machado Suite and within the Três Figueiras Granite (units of the Pelotas-Aiguá Batholith). The metaultramafites of the ophiolite comprise serpentinites and Cr-rich magnesian schists. The metamafites comprise amphibolites, metagabbros and metadiorites. The metasedimentary unit comprises calcitic marbles, which are intruded by mafic dykes. The ophiolite is found along the Ayrosa Galvão- Arroio Grande Shear Zone (transcurrent, ductile, high angle), responsible for the mylonitization of this association. The investigations developed in this ophiolite had the objective of identify the magmatic sources of the protoliths and the processes that occurred since their generation within the mantle/oceanic crust until their incorporation into the continental crust, including their absolute and relative ages. The bulk-rock chemistry of the metaultramafites (e.g. Ni >1000 ppm; Cr > 1500 ppm), together with the mineral chemistry of the chromites (e.g. Cr# 0.6-0.8; TiO2 0.01-0.20 wt%; Fe2+/Fe3+ ± 0.9), suggested harzburgitic protoliths, attributed to a depleted mantle source under a back-arc spreading region, which experienced high degrees of partial melting. These harzburgites were serpentinized in an oceanic setting, as suggested by the 87Sr/86Sr630 ratio of a serpentinite (ca. 0.707). The bulkrock chemistry of the metamafites suggested oceanic tholeiitic protoliths, generated in a supra-subduction setting in a back-arc environment (e.g. Cr 260-600 ppm; Nb/Y 0.1-0.5; Ti/Y ± 500; La/Nb 2-5; Th/Yb 0.1-5 and Nb/Yb 1-5; REE patterns; 87Sr/86Sr630 ratios ranging from MORB – 0.703 – to IAT – 0.705-0.707), whose magmatic source was contaminated by crustal material and subduction-related fluids. The minimum age for the obduction and metamorphism of the Arroio Grande Ophiolite rocks was estimated around 640 Ma from the U-Pb age of a quartz-syenite. The latter is the result of melting, related to dioritic-tonalitc intrusions, attributed to the continental magmatism of the Pinheiro Machado Suite. These intrusions affected both the marbles and the amphibolites (fragments of the mafic dykes), in order that, at least around 640 Ma, rocks of the ophiolitic mélange (already metamorphosed) were emplaced on the continent. A late metasomatic event (related to the emplacement of the Três Figueiras Granite, syn-kinematic to the abovementioned shear zone) affected the serpentinites, generating zones of talcification, tremolitization and chloritization, the latter representing a blackwall which also involved metasiliciclastic rocks of the Arroio Grande Complex. The Arroio Grande Ophiolite was inserted in the geotectonic context of the Marmora back-arc basin, whose fragments are found in Namibia (Marmora Terrane) and Uruguay (Paso del Dragón Complex and Rocha Basin – Punta del Este Terrane).

Pulsed LASER deposition (PLD) is widely recognized as excellent deposition technique owing to stoichiometric transfer of target material, easy preparation and high quality. Thin films from few nanometers to micrometer regime can be fabricated with equal ease. Although a batch process is not suitable for mass scale industrial production, PLD is a versatile technique, efficient and convenient for high quality basic research.  This thesis illustrates the use of PLD technique to study the emerging trends in tailoring multifunctional magnetic thin films both from basic nanoscience and device development point of view.      After a comprehensive review of magnetism in chapter 1: entitled ‘A journey through classical to modern trends in magnetism, and multifunctional thin film devices’ followed by a reasonably thorough discussion on Pulsed Laser thin film technique in Chapter 2, we present: Studies of tailoring composite high energy product permanent magnetic FePtB based thin films for applications in NEMS /MEMS, (Chapter 3). Study of search for new multiferroic materials by investigating the properties of Chromites. Crystalline Chromites are antiferromagnetic below 150oC.  However depositing thin films by PLD of the crystalline 95.5% dense targets produced by Surface Plasma Sintering, we discovered that the resulting films were amorphous and ferromagnetic beyond room temperature. Moreover advanced spectroscopic techniques revealed that the amorphized state is metallic with Cr in a mixed valence state.   An understanding of the underlying physics of the observed phenomenon has been carried out based on first principles calculations.  These results are now being considered for publication in a high profile journal.  Extensive studies on the films showing that these materials are ferromagnetic, but not ferroelectric are discussed in chapter 4. A preliminary presentation of these studies was pier reviewed and published in MRS symposium proceedings. Fabrication of Room temperature, Transparent, high moment soft ferromagnetic amorphous Bulk metallic glass based FeBNbY thin films by PLD, suitable for Nanolithography in NEMS/MEMS device development .  (Chapter 5) From a basic study point of view on new trends on magnetism we present: 4. The use of PLD technique to demonstrate room temperature ferromagnetism in undoped MgO, and V-doped MgO thin films.  Both of these oxides which do not contain any intrinsically magnetic elements and are diamagnetic in their bulk form belong to a new class of magnetic films, the so called d0magnets signifying that robust above room temperature ferromagnetism arising from defects and controlled carriers and no occupied d-states can be tailored in semiconductors and insulators.  These, mostly ZnO and MgO based thin films which may be classified as Dilute Magnetic Semiconductors, DMS, and Dilute Magnetic Insulators, DMI, are now the materials of active interest in future Electronics involving components which exploit both charge and spin of electrons in the arena of SPINTRONICS. Extensive characterization of magnetic, electrical, optical properties and microscopic structure has ensured development of high quality magnetic materials for future applications. Further research on these promising materials is expected to yield new generation spintronic devices for better performance in terms of efficiency, energy consumption and miniaturization of sizes. / QC 20120511

O Ofiolito Arroio Grande, localizado no sudeste do Cinturão Dom Feliciano, próximo à fronteira Brasil/Uruguai, entre Arroio Grande e Jaguarão (RS), é uma associação metaultramáfica-máfica-sedimentar que representa fragmentos de uma mélange ofiolítica, relacionada à amalgamação do paleocontinente Gondwana Ocidental durante os estágios finais do ciclo orogênico Brasiliano-Panafricano. As rochas do Ofiolito Arroio Grande se encontram circundadas por rochas metassiliciclásticas do Complexo Arroio Grande, do qual o ofiolito faz parte, e também como xenólitos em meio a granitoides da Suíte Pinheiro Machado e do Granito Três Figueiras (os quais integram o Batólito Pelotas-Aiguá). A unidade metaultramáfica do ofiolito compreende serpentinitos e xistos magnesianos cromíferos. Sua unidade metamáfica é constituída por anfibolitos, metagabros e metadioritos. A unidade metassedimentar compreende mármores calcíticos, intrudidos por enxame de diques máficos. O Ofiolito Arroio Grande está posicionado ao longo da Zona de Cisalhamento Ayrosa Galvão-Arroio Grande (transcorrente, dúctil, alto ângulo), responsável pela milonitização da maioria das rochas dessa associação. As investigações desenvolvidas no ofiolito tiveram o objetivo de identificar as fontes magmáticas dos protólitos e os processos que ocorreram desde sua geração no manto/crosta oceânica até sua incorporação no continente, além de obter idades (absolutas e relativas) referentes a esses processos. Para os metaultramafitos, a geoquímica de rocha total (e.g. Ni >1000 ppm; Cr > 1500 ppm), em conjunto com a química mineral de cromitas (e.g. Cr# 0,6-0,8; TiO2 0,01-0,20 %peso; Fe2+/Fe3+ ± 0,9), sugeriu protólitos harzburgíticos mantélicos, cuja fonte é um manto depletado sob uma região de espalhamento oceânico de retroarco, que experimentou altas taxas de fusão parcial. Esses harzburgitos foram posteriormente serpentinizados em ambiente oceânico, sugerido pelas razões 87Sr/86Sr630 de um serpentinito (ca. 0,707). Para os metamafitos, a geoquímica de rocha total e isotópica sugeriram protólitos toleíticos oceânicos, gerados em um contexto de suprassubducção em ambiente de retroarco (e.g. Cr 260-600 ppm; Nb/Y 0,1-0,5; Ti/Y ± 500; La/Nb 2-5; Th/Yb 0,1-5 e Nb/Yb 1-5; padrões de REE; razões 87Sr/86Sr630 variando de MORB – 0,703 – a IAT – 0,705-0,707), cuja fonte magmática foi enriquecida por material crustal e fluidos relacionados à subducção. A idade mínima para a obducção e metamorfismo das unidades ofiolíticas foi estimada em 640 Ma, a partir da datação (U-Pb SHRIMP) de um quartzo sienito. Esse último é o resultado de fusões relacionadas a intrusões diorítico-tonalíticas, atribuídas ao magmatismo de arco continental da Suíte Pinheiro Machado. Essas intrusões afetaram os mármores e os anfibolitos (fragmentos dos enxames de diques máficos), de maneira que, em pelo menos 640 Ma, rochas da mélange ofiolítica (já metamorfizadas) estavam alojadas em ambiente continental. Um evento metassomático posterior (relacionado à intrusão do Granito Três Figueiras, sincinemática à zona de cisalhamento acima referida) afetou os serpentinitos, gerando zonas de talcificação, tremolitização e cloritização, essa última representando um blackwall que também envolveu unidades metassiliciclásticas do Complexo Arroio Grande. O Ofiolito Arroio Grande foi inserido no contexto geotectônico da bacia de retroarco Marmora, cujos fragmentos são encontrados na Namíbia (Terreno Marmora) e no Uruguai (Complexo Paso del Dragón e Bacia Rocha – Terreno Punta del Este). / The Arroio Grande Ophiolite, located in the southeastern region of the Dom Feliciano Belt, near the Brazil/Uruguay border, is a metaultramafic-mafic-sedimentary association which represents slices of an ophiolitic mélange, related to the Western Gondwana amalgamation during the late stages of the Brasiliano-Panafrican orogenic cycle. The Arroio Grande Ophiolite rocks are enveloped by metasiliciclastic units of the Arroio Grande Complex and occur as xenolyths within granitoids of the Pinheiro Machado Suite and within the Três Figueiras Granite (units of the Pelotas-Aiguá Batholith). The metaultramafites of the ophiolite comprise serpentinites and Cr-rich magnesian schists. The metamafites comprise amphibolites, metagabbros and metadiorites. The metasedimentary unit comprises calcitic marbles, which are intruded by mafic dykes. The ophiolite is found along the Ayrosa Galvão- Arroio Grande Shear Zone (transcurrent, ductile, high angle), responsible for the mylonitization of this association. The investigations developed in this ophiolite had the objective of identify the magmatic sources of the protoliths and the processes that occurred since their generation within the mantle/oceanic crust until their incorporation into the continental crust, including their absolute and relative ages. The bulk-rock chemistry of the metaultramafites (e.g. Ni >1000 ppm; Cr > 1500 ppm), together with the mineral chemistry of the chromites (e.g. Cr# 0.6-0.8; TiO2 0.01-0.20 wt%; Fe2+/Fe3+ ± 0.9), suggested harzburgitic protoliths, attributed to a depleted mantle source under a back-arc spreading region, which experienced high degrees of partial melting. These harzburgites were serpentinized in an oceanic setting, as suggested by the 87Sr/86Sr630 ratio of a serpentinite (ca. 0.707). The bulkrock chemistry of the metamafites suggested oceanic tholeiitic protoliths, generated in a supra-subduction setting in a back-arc environment (e.g. Cr 260-600 ppm; Nb/Y 0.1-0.5; Ti/Y ± 500; La/Nb 2-5; Th/Yb 0.1-5 and Nb/Yb 1-5; REE patterns; 87Sr/86Sr630 ratios ranging from MORB – 0.703 – to IAT – 0.705-0.707), whose magmatic source was contaminated by crustal material and subduction-related fluids. The minimum age for the obduction and metamorphism of the Arroio Grande Ophiolite rocks was estimated around 640 Ma from the U-Pb age of a quartz-syenite. The latter is the result of melting, related to dioritic-tonalitc intrusions, attributed to the continental magmatism of the Pinheiro Machado Suite. These intrusions affected both the marbles and the amphibolites (fragments of the mafic dykes), in order that, at least around 640 Ma, rocks of the ophiolitic mélange (already metamorphosed) were emplaced on the continent. A late metasomatic event (related to the emplacement of the Três Figueiras Granite, syn-kinematic to the abovementioned shear zone) affected the serpentinites, generating zones of talcification, tremolitization and chloritization, the latter representing a blackwall which also involved metasiliciclastic rocks of the Arroio Grande Complex. The Arroio Grande Ophiolite was inserted in the geotectonic context of the Marmora back-arc basin, whose fragments are found in Namibia (Marmora Terrane) and Uruguay (Paso del Dragón Complex and Rocha Basin – Punta del Este Terrane).

Made available in DSpace on 2014-10-09T12:49:48Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:15Z (GMT). No. of bitstreams: 1 10384.pdf: 9700840 bytes, checksum: b2fbf22494ca3f10b89bc09793b74be1 (MD5) / Dissertacao (Mestrado) / IPEN/D / Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP

O Ofiolito Arroio Grande, localizado no sudeste do Cinturão Dom Feliciano, próximo à fronteira Brasil/Uruguai, entre Arroio Grande e Jaguarão (RS), é uma associação metaultramáfica-máfica-sedimentar que representa fragmentos de uma mélange ofiolítica, relacionada à amalgamação do paleocontinente Gondwana Ocidental durante os estágios finais do ciclo orogênico Brasiliano-Panafricano. As rochas do Ofiolito Arroio Grande se encontram circundadas por rochas metassiliciclásticas do Complexo Arroio Grande, do qual o ofiolito faz parte, e também como xenólitos em meio a granitoides da Suíte Pinheiro Machado e do Granito Três Figueiras (os quais integram o Batólito Pelotas-Aiguá). A unidade metaultramáfica do ofiolito compreende serpentinitos e xistos magnesianos cromíferos. Sua unidade metamáfica é constituída por anfibolitos, metagabros e metadioritos. A unidade metassedimentar compreende mármores calcíticos, intrudidos por enxame de diques máficos. O Ofiolito Arroio Grande está posicionado ao longo da Zona de Cisalhamento Ayrosa Galvão-Arroio Grande (transcorrente, dúctil, alto ângulo), responsável pela milonitização da maioria das rochas dessa associação. As investigações desenvolvidas no ofiolito tiveram o objetivo de identificar as fontes magmáticas dos protólitos e os processos que ocorreram desde sua geração no manto/crosta oceânica até sua incorporação no continente, além de obter idades (absolutas e relativas) referentes a esses processos. Para os metaultramafitos, a geoquímica de rocha total (e.g. Ni >1000 ppm; Cr > 1500 ppm), em conjunto com a química mineral de cromitas (e.g. Cr# 0,6-0,8; TiO2 0,01-0,20 %peso; Fe2+/Fe3+ ± 0,9), sugeriu protólitos harzburgíticos mantélicos, cuja fonte é um manto depletado sob uma região de espalhamento oceânico de retroarco, que experimentou altas taxas de fusão parcial. Esses harzburgitos foram posteriormente serpentinizados em ambiente oceânico, sugerido pelas razões 87Sr/86Sr630 de um serpentinito (ca. 0,707). Para os metamafitos, a geoquímica de rocha total e isotópica sugeriram protólitos toleíticos oceânicos, gerados em um contexto de suprassubducção em ambiente de retroarco (e.g. Cr 260-600 ppm; Nb/Y 0,1-0,5; Ti/Y ± 500; La/Nb 2-5; Th/Yb 0,1-5 e Nb/Yb 1-5; padrões de REE; razões 87Sr/86Sr630 variando de MORB – 0,703 – a IAT – 0,705-0,707), cuja fonte magmática foi enriquecida por material crustal e fluidos relacionados à subducção. A idade mínima para a obducção e metamorfismo das unidades ofiolíticas foi estimada em 640 Ma, a partir da datação (U-Pb SHRIMP) de um quartzo sienito. Esse último é o resultado de fusões relacionadas a intrusões diorítico-tonalíticas, atribuídas ao magmatismo de arco continental da Suíte Pinheiro Machado. Essas intrusões afetaram os mármores e os anfibolitos (fragmentos dos enxames de diques máficos), de maneira que, em pelo menos 640 Ma, rochas da mélange ofiolítica (já metamorfizadas) estavam alojadas em ambiente continental. Um evento metassomático posterior (relacionado à intrusão do Granito Três Figueiras, sincinemática à zona de cisalhamento acima referida) afetou os serpentinitos, gerando zonas de talcificação, tremolitização e cloritização, essa última representando um blackwall que também envolveu unidades metassiliciclásticas do Complexo Arroio Grande. O Ofiolito Arroio Grande foi inserido no contexto geotectônico da bacia de retroarco Marmora, cujos fragmentos são encontrados na Namíbia (Terreno Marmora) e no Uruguai (Complexo Paso del Dragón e Bacia Rocha – Terreno Punta del Este). / The Arroio Grande Ophiolite, located in the southeastern region of the Dom Feliciano Belt, near the Brazil/Uruguay border, is a metaultramafic-mafic-sedimentary association which represents slices of an ophiolitic mélange, related to the Western Gondwana amalgamation during the late stages of the Brasiliano-Panafrican orogenic cycle. The Arroio Grande Ophiolite rocks are enveloped by metasiliciclastic units of the Arroio Grande Complex and occur as xenolyths within granitoids of the Pinheiro Machado Suite and within the Três Figueiras Granite (units of the Pelotas-Aiguá Batholith). The metaultramafites of the ophiolite comprise serpentinites and Cr-rich magnesian schists. The metamafites comprise amphibolites, metagabbros and metadiorites. The metasedimentary unit comprises calcitic marbles, which are intruded by mafic dykes. The ophiolite is found along the Ayrosa Galvão- Arroio Grande Shear Zone (transcurrent, ductile, high angle), responsible for the mylonitization of this association. The investigations developed in this ophiolite had the objective of identify the magmatic sources of the protoliths and the processes that occurred since their generation within the mantle/oceanic crust until their incorporation into the continental crust, including their absolute and relative ages. The bulk-rock chemistry of the metaultramafites (e.g. Ni >1000 ppm; Cr > 1500 ppm), together with the mineral chemistry of the chromites (e.g. Cr# 0.6-0.8; TiO2 0.01-0.20 wt%; Fe2+/Fe3+ ± 0.9), suggested harzburgitic protoliths, attributed to a depleted mantle source under a back-arc spreading region, which experienced high degrees of partial melting. These harzburgites were serpentinized in an oceanic setting, as suggested by the 87Sr/86Sr630 ratio of a serpentinite (ca. 0.707). The bulkrock chemistry of the metamafites suggested oceanic tholeiitic protoliths, generated in a supra-subduction setting in a back-arc environment (e.g. Cr 260-600 ppm; Nb/Y 0.1-0.5; Ti/Y ± 500; La/Nb 2-5; Th/Yb 0.1-5 and Nb/Yb 1-5; REE patterns; 87Sr/86Sr630 ratios ranging from MORB – 0.703 – to IAT – 0.705-0.707), whose magmatic source was contaminated by crustal material and subduction-related fluids. The minimum age for the obduction and metamorphism of the Arroio Grande Ophiolite rocks was estimated around 640 Ma from the U-Pb age of a quartz-syenite. The latter is the result of melting, related to dioritic-tonalitc intrusions, attributed to the continental magmatism of the Pinheiro Machado Suite. These intrusions affected both the marbles and the amphibolites (fragments of the mafic dykes), in order that, at least around 640 Ma, rocks of the ophiolitic mélange (already metamorphosed) were emplaced on the continent. A late metasomatic event (related to the emplacement of the Três Figueiras Granite, syn-kinematic to the abovementioned shear zone) affected the serpentinites, generating zones of talcification, tremolitization and chloritization, the latter representing a blackwall which also involved metasiliciclastic rocks of the Arroio Grande Complex. The Arroio Grande Ophiolite was inserted in the geotectonic context of the Marmora back-arc basin, whose fragments are found in Namibia (Marmora Terrane) and Uruguay (Paso del Dragón Complex and Rocha Basin – Punta del Este Terrane).

Made available in DSpace on 2014-10-09T12:49:48Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:15Z (GMT). No. of bitstreams: 1 10384.pdf: 9700840 bytes, checksum: b2fbf22494ca3f10b89bc09793b74be1 (MD5) / Dissertacao (Mestrado) / IPEN/D / Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP

La croûte intra-océanique du sud-Kohistan comprend les complexes de Spat et Jijal, les amphibolites de Kamila et le complexe de Chilas. Le complexe de Jijal est une intrusion litée constituée de dunite, clinopyroxénite à olivine, websterite, webstérite à grenat et de gabbro à grenat. Mis en place à l'interface manteau croûte, il résulte de la cristallisation fractionnée sous haute pression et haute température (10-12 Kbars; 800- 1100°C) d'un liquide tholéiitique d'arc intra-océanique hautement magnésien. Les roches de Thak Gah (complexe de Chilas) ont cristallisé sous plus faible pression et température (5 - 6 kbars, 800 à 950°C) dans un réservoir magmatique plus superficiel. Les métaplutonites de Chilas et Kamila présentent également des signatures géochimiques analogues à des tholéiites d'arc insulaire. Au contraire, les amphibolites à grains fins du Groupe de Kamila apparaissent comme des métavolcanites de type N-MORB, elles représentent des reliques de croûte océanique et le substratum de l'arc du Kohistan. Plusieurs horizons enrichis en PGE caractérisent le complexe de Jijal. Des enrichissements en Ir,Ru, Ni corrélés au Cr dans les dunites, indiquent que l'irridium et le ruthénium précipitent précocément avec la chromite sous haute fugacité d'oxygène. Des enrichissements en Ir et Ru du même type caractérisent les dunites chromifères des complexes de Thak Gah et de Spat. Dans les webstérites à grenat de Jijal, des sulfures disséminés (chalcopyrite, pentlandite, pyrrhotite± pyrite) et des minéraux du Groupe du platine (témagamite, monchéite, mérenskyite et sperrylite) correspondent à des enrichissements en Ir, Ru, Pt, Pd, Au, Ni et Cu. Ils résultent de la formation d'un liquide sulfuré consécutif à la baisse de f02. Dans les gabbros à grenats, des enrichissements en Pt, Pd et Cu traduisent l'action de fluides hydrothermaux tardi-magmatiques. Ces minéralisations diffèrent de celles du Bushveld. La saturation en soufre induite par les processus de cristallisation sous haute pression apparaît le moteur essentiel des dépôts observés dans les webstérites à grenats. De telles minéralisations représentent un exemple type de dépôts de PGE associés aux arcs insulaires.