Rochas basálticas da formação serra geral no município de Araçatuba, estado de São Paulo

Pós-graduação em Geologia Regional - IGCE

The Early Cretaceous San Juan Plutonic Suite, Ecuador: A magma chamber in an oceanic plateau ?

Sections through an oceanic plateau are preserved in tectonic slices in the Western Cordillera of Ecuador (South America). The San Juan section is a sequence of mafic-ultramafic cumulates. To establish that these plutonic rocks formed in an oceanic plateau setting, we have developed criteria that discriminate intrusions of oceanic plateaus from those of other tectonic settings. The mineralogy and crystallization sequence of the cumulates are similar to those of intra-plate magmas. Clinopyroxene predominates throughout, and orthopyroxene is only a minor component. Rocks of intermediate composition are absent, and hornblende is restricted to the uppermost massive gabbros within the sequence. The ultramafic cumulates are very depleted in light rare-earth elements (LREE), whereas the gabbros have flat or slightly enriched LREE patterns. The composition of the basaltic liquid in equilibrium with the peridotite, calculated using olivine compositions and REE contents of clinopyroxene, contains between 16% and 8% MgO and has a flat REE pattern. This melt is geochemically similar to other accreted oceanic plateau basalts, isotropic gabbros, and differentiated sills in western Ecuador. The Ecuadorian intrusive and extrusive rocks have a narrow range of epsilonNd(i) (+8 to +5) and have a rather large range of Pb isotopic ratios. Pb isotope systematics of the San Juan plutonic rocks and mineral separates lie along a mixing line between the depleted mantle (DMM) and the enriched-plume end members. This suggests that the Ecuadorian plutonic rocks generated from the mixing of two mantle sources, a depleted mid-oceanic ridge basalt (MORB) source and an enriched one. The latter is characterized by high (Pb-207/Pb-204)(i) ratios and could reflect a contamination by recycled either lower continental crust or oceanic pelagic sediments and (or) altered oceanic crust (enriched mantle type I, EMI). These data suggest that the San Juan sequence represents the plutonic components of an Early Cretaceous oceanic plateau, which accreted in the Late Cretaceous to the Ecuadorian margin.

Petrology, geochemistry and geodynamic implications of Jurassic island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic low-grade sequence, eastern Rhodope, Bulgaria

In the eastern Bulgarian Rhodope, mafic extrusive rocks and underlying greenschists are found in the Mesozoic low-grade unit, which represents the northern extension of similar sequences including the Evros ophiolites in Thrace (Greece). Both rock types define a suite of low-Ti tholeiitic basalts to transitional boninitic basaltic andesites and andesites and associated metapyroclastites (greenschists), intruded at its base by diorite dikes of a boninitic affinity. Mafic lavas and greenschists display large ion lithophile element (LILE) enrichment relative to high-field strength elements (HFSE), flat REE patterns of a slight light REE depletion, a strong island arc tholeiite (IAT) and weak MORB-like signature. All these rocks are characterized by negative Nb anomalies ascribed to arc lavas. They have positive epsilon Nd(i) values in the range of +4.87 to +6.09, approaching the lower limit of MORB-like source, and relatively high ((207)Pb/(204)Pb)(i) (15.57-15.663) at low ((206)Pb/(204)Pb)(i) (18.13-18.54) ratios. The Nd isotopic compositions coupled with trace element data imply a dominantly depleted MORB-like mantle source and a contribution of subduction modified LILE-enriched component derived from the mantle wedge. The diorite dike has a low eNdi value of -2.61 and is slightly more Pb radiogenic ((207)Pb/(204)Pb)(i) (15.64) and ((206)Pb/(204)Pb)(i) (18.56), respectively, reflecting crustal contamination. Petrologic and geochemical data indicate that the greenschists and mafic extrusive rocks represent a magmatic assemblage formed in an island arc setting. The magmatic suite is interpreted as representing an island arc-accretionary complex related to the southward subduction of the Meliata-Maliac ocean under the supra-subduction back-arc Vardar ocean/island arc system. Magmatic activity appears to have initiated in the north during the inception of the island arc system by the Early-Middle Jurassic time in the eastern Rhodope that most likely graded to back-arc spreading southwards as represented by the Late Jurassic MORB-type Samothraki Island ophiolites. This tectonic scenario is further constrained by paleotectonic reconstructions. The arc-trench system collided with the Rhodope in the Late Jurassic times. (c) 2007 Elsevier B.V. All rights reserved.

Sr-Nd-Pb isotopic constraints on the nature of the mantle sources involved in the genesis of the high-Ti tholeiites from northern Paraná Continental Flood Basalts (Brazil)

There has been little research on geochemistry and isotopic compositions in tholeiites of the Northern region from the Paraná Continental Flood Basalts (PCFB), one of the largest continental provinces of the world. In order to examine the mantle sources involved in the high-Ti (Pitanga and Paranapanema) basalt genesis, we studied Sr, Nd, and Pb isotopic systematics, and major, minor and incompatible trace element abundances. The REE patterns of the investigated samples (Pitanga and Paranapanema magma type) are similar (parallel to) to those of Island Arc Basalts' REE patterns. The high-Ti basalts investigated in this study have initial (133Ma) 87Sr/86Sr ratios of 0.70538-0.70642, 143Nd/144Nd of 0.51233-0.51218, 206Pb/204Pb of 17.74-18.25, 207Pb/204Pb of 15.51-15.57, and 208Pb/204Pb of 38.18-38.45. These isotopic compositions do not display any correlation with Nb/Th, Nb/La or P2O5/K2O ratios, which also reflect that these rocks were not significantly affected by low-pressure crustal contamination. The incompatible trace element ratios and Sr-Nd-Pb isotopic compositions of the PCFB tholeiites are different to those found in Tristan da Cunha ocean island rocks, showing that this plume did not play a substantial role in the PCFB genesis. This interpretation is corroborated by previously published osmium isotopic data (initial γOs values range from+1.0 to+2.0 for high-Ti basalts), which also preclude basalt generation by melting of ancient subcontinental lithospheric mantle. The geochemical composition of the northern PCFB may be explained through the involvement of fluids and/or small volume melts related to metasomatic processes. In this context, we propose that the source of these magmas is a mixture of sublithospheric peridotite veined and/or interlayered with mafic components (e.g., pyroxenites or eclogites). The sublithospheric mantle (dominating the osmium isotopic compositions) was very probably enriched by fluids and/or magmas related to the Neoproterozoic subduction processes. This sublithospheric mantle region may have been frozen and coupled to the base of the Parana basin lithospheric plate above which the Paleozoic subsidence and subsequent Early Cretaceous magmatism occurred. © 2013 Elsevier Ltd.

Chemical composition of basalts and andesites from the Sea of Japan

An investigation of uranium and thorium contents in extrusive rocks from underwater rises in the Sea of Japan demonstrates that concentrations of these radioactive elements can be used as indicators of geodynamic conditions. It is concluded that basalt volcanism of the Sea of Japan is of continental type.

Litogeoquímica E aspectos Petrogenéticos dos basaltos da Província Magmática do Paraná na porção centro-norte do Estado de São Paulo

The petrographic and geochemical characterization of flood basalts of Serra Geral Formation are here presented. The investigated areas are situated in four different regions of São Paulo state: Jaú, Ribeirão Preto, Franca and Fernandópolis. They represent almost the total area of outcrops of basalts in the São Paulo State. The petrographical data reveals that these rocks are constituted mainly by plagioclase (30-40%), pyroxenes, augite and pigeonita (20-30%) and magnetite (5-15%), and show a intergranular texture and its varieties intersertal, hialophitic and pilotaxitic. The geochemical data show a basic and tholeiitic affinity of the studied basalts, with high-Ti content (TiO2 > 1.8%), typical of the northern region of Paraná Basin. Three different magma-types were recognized: Paranapanema, Urubici and Pitanga. The first magma-type is concentrated in the Fernandópolis region, the second in the Franca region, and the Pitanga occurs in the Ribeirão Preto and Jaú regions. The distribution patterns of these magma-types and the detailed study of geochemical data showed that they are, probably, generated by a melting of a continental lithospheric mantle.

Appendix A. Whole-rock major, trace and rare earth element analyses of the Ulubey volcanics, Appendix B. Analytical standards and detection limits for analyses

Collisional and post-collisional volcanic rocks in the Ulubey (Ordu) area at the western edge of the Eastern Pontide Tertiary Volcanic Province (EPTVP) in NE Turkey are divided into four suites; Middle Eocene (49.4-44.6 Ma) aged Andesite-Trachyandesite (AT), Trachyandesite-Trachydacite-Rhyolite (TTR), Trachydacite-Dacite (TD) suites, and Middle Miocene (15.1 Ma) aged Trachybasalt (TB) suite. Local stratigraphy in the Ulubey area starts with shallow marine environment sediments of the Paleocene-Eocene time and then continues extensively with sub-aerial andesitic to rhyolitic and rare basaltic volcanism during Eocene and Miocene time, respectively. Petrographically, the volcanic rocks are composed primarily of andesites/trachyandesites, with minor trachydacites/rhyolites, basalts/trachybasalts and pyroclastics, and show porphyric, hyalo-microlitic porphyric and rarely glomeroporphyric, intersertal, intergranular, fluidal and sieve textures. The Ulubey (Ordu) volcanic rocks indicate magma evolution from tholeiitic-alkaline to calc-alkaline with medium-K contents. Primitive mantle normalized trace element and chondrite normalized rare earth element (REE) patterns show that the volcanic rocks have moderate light rare earth element (LREE)/heavy rare earth element (HREE) ratios relative to E-Type MORB and depletion in Nb, Ta and Ti. High Th/Yb ratios indicate parental magma(s) derived from an enriched source formed by mixing of slab and asthenospheric melts previously modified by fluids and sediments from a subduction zone. All of the volcanic rocks share similar incompatible element ratios (e.g., La/Sm, Zr/Nb, La/Nb) and chondrite-normalized REE patterns, indicating that the basic to acidic rocks originated from the same source. The volcanic rocks were produced by the slab dehydration-induced melting of an existing metasomatized mantle source, and the fluids from the slab dehydration introduced significant large ion lithophile element (LILE) and LREE to the source, masking its inherent HFSE-enriched characteristics. The initial 87Sr/86Sr (0.7044-0.7050) and eNd (-0.3 to +3.4) ratios of the volcanics suggest that they originated from an enriched lithospheric mantle source with low Sm/Nd ratios. Integration of the geochemical, petrological and isotopical with regional and local geological data suggest that the Tertiary volcanic rocks from the Ulubey (Ordu) area were derived from an enriched mantle, which had been previously metasomatized by fluids derived from subducted slab during Eocene to Miocene in collisional and post-collisional extension-related geodynamic setting following Late Mesozoic continental collision between the Eurasian plate and the Tauride-Anatolide platform.

Geochemical composition of the Trincheira Complex in the southwestern Amazon craton, Brazil

We document the first-known Mesoproterozoic ophiolite from the southwestern part of the Amazon craton, corresponding to the Trincheira Complex of Calymmian age, and propose a tectonic model that explains many previously enigmatic features of the Precambrian history of this key craton, and discuss its role in the reconstruction of the Columbia supercontinent. The complex comprises extrusive rocks (fine-grained amphibolites derived from massive and pillowed basalts), mafic-ultramafic intrusive rocks, chert, banded iron formation (BIFs), pelites, psammitic and a smaller proportion of calc-silicate rocks. This sequence was deformed, metasomatized and metamorphosed during the development of the Alto Guaporé Belt, a Mesoproterozoic accretionary orogen. The rocks were deformed by a single tectonic event, which included isoclinal folding and metamorphism of the granulite-amphibolite facies. Layered magmatic structures were preserved in areas of low strain, including amygdaloidal and cumulate structures. Metamorphism was pervasive and reached temperatures of 780-853°C in mafic granulites and 680-720°C in amphibolites under an overall pressure of 6.8 kbar. The geochemical composition of the extrusive and intrusive rocks indicates that all noncumulus mafic-ultramafic rocks are tholeiitic basalts. The mafic-ultramafic rocks display moderately to strongly fractionation of light rare earth elements (LREE), near-flat heavy rare earth elements (HREE) patterns and moderate to strong negative high field strength elements (HFSE) anomalies (especially Nb), a geochemical signature typical of subduction zones. The lowest units of mafic granulites and porphyroblastic amphibolites in the Trincheira ophiolite are similar to the modern mid-ocean ridge basalt (MORB), although they locally display small Ta, Ti and Nb negative anomalies, indicating a small subduction influence. This behavior changes to an island arc tholeiites (IAT) signature in the upper units of fine-grained amphibolites and amphibole rich-amphibolites, characterized by progressive depletion in the incompatible elements and more pronounced negative Ta and Nb anomalies, as well as common Ti and Zr negative anomalies. Tectono-magmatic variation diagrams and chondrite-normalized REE and primitive mantle normalized patterns suggest a back-arc to intra-oceanic island arc tectonic regime for the eruption of these rocks. Therefore, the Trincheira ophiolite appears to have originated in an intraoceanic supra-subduction setting composed of an arc-back-arc system. Accordingly, the Trincheira Complex is a record of oceanic crust relics obducted during the collision of the Amazon craton and the Paraguá block during the Middle Mesoproterozoic. Thus, the recognition of the Trincheira ophiolite and suture significantly changes views on the evolution of the southern margin of the Amazon craton, and how it can influence the global tectonics and the reconstruction of the continents.

Major oxides, trace elements and rare earth elements of selected basalt samples at DSDP Hole 83-504B

DSDP Hole 504B is the deepest section drilled into oceanic basement, penetrating through a 571.5-m lava pile and a 209-m transition zone of lavas and dikes into 295 m of a sheeted dike complex. To define the basement composition 194 samples of least altered basalts, representing all lithologic units, were analyzed for their major and 26 trace elements. As is evident from the alteration-sensitive indicators H2O+, CO2, S, K, Mn, Zn, Cu, and the iron oxidation ratio, all rocks recovered are chemically altered to some extent. Downhole variation in these parameters enables us to distinguish five depth-related alteration zones that closely correlate with changes in alteration mineralogy. Alteration in the uppermost basement portion is characterized by pronounced K-uptake, sulfur loss, and iron oxidation and clearly demonstrates low-temperature seawater interaction. A very spectacular type of alteration is confined to the depth range from 910 to 1059 m below seafloor (BSF). Rocks from this basement portion exhibit the lowest iron oxidation, the highest H2O+ contents, and a considerable enrichment in Mn, S, Zn, and Cu. At the top of this zone a stockwork-like sulfide mineralization occurs. The chemical data suggest that this basement portion was at one time within a hydrothermal upflow zone. The steep gradient in alteration chemistry above this zone and the ore precipitation are interpreted as the result of mixing of the upflowing hydrothermal fluids with lower-temperature solutions circulating in the lava pile. Despite the chemical alteration the primary composition and variation of the rocks can be reliably established. All data demonstrate that the pillow lavas and the dikes are remarkably uniform and display almost the same range of variation. A general characteristic of the rocks that classify as olivine tholeiites is their high MgO contents (up to 10.5 wt.%) and their low K abundances (-200 ppm). According to their mg-values, which range from 0.60 to 0.74, most basalts appear to have undergone some high-level crystal fractionation. Despite the overall similarity in composition, there are two major basalt groups that have significantly different abundances and ratios of incompatible elements at similar mg-values. The majority of the basalts from the pillow lava and dike sections are chemically closely related, and most probably represent differentiation products of a common parental magma. They are low in Na2O, TiO2, and P2O5, and very low in the more hygromagmaphile elements. Interdigitated with this basalt group is a very rarely occurring basalt that is higher in Na2O, TiO2, P2O5, much less depleted in hygromagmaphile elements, and similar to normal mid-ocean ridge basalt (MORB). The latter is restricted to Lithologic Units 5 and 36 of the pillow lava section and Lithologic Unit 83 of the dike section. The two basalt groups cannot be related by differentiation processes but have to be regarded as products of two different parental magmas. The compositional uniformity of the majority of the basalts suggests that the magma chamber beneath the Costa Rica Rift reached nearly steady-state conditions. However, the presence of lavas and dikes that crystallized from a different parental magma requires the existence of a separate conduit-magma chamber system for these melts. Occasionally mixing between the two magma types appears to have occurred. The chemical characteristics of the two magma types imply some heterogeneity in the mantle source underlying the Costa Rica Rift. The predominant magma type represents an extremely depleted source, whereas the rare magma type presumably originated from regions of less depleted mantle material (relict or affected by metasomatism).

Geochemistry of basalts at DSDP Leg 73 Holes

During Deep Sea Drilling Project Leg 73 (South Atlantic), basaltic pillow lava, flows, and sills were encountered in Holes 519A, 520, 522B, and 524. Paleomagnetic data indicate that the basalts from Holes 519A (magnetic Anomaly 51) and 522B (Anomaly 16) have ages of about 12 m.y. and about 38 m.y., respectively. The major- and trace- (including rare-earth-) element characteristics of the Hole 519A basalts (a total of 27 m) demonstrate that these basalts are typical normal-type mid-ocean-ridge basalts (N-type MORB). In composition the basalts overlap olivine tholeiites from other normal Mid-Atlantic Ridge segments. Both the spectra of incompatible, or less-hygromagmatophile elements (such as Ti, V, Y, and Zr) and REE abundances indicate that these basalts are the result of a low-pressure fractionation of olivine, spinel, and Plagioclase prior to eruption. In Hole 520 only 1.7 m of basalt were recovered from a total drilling depth of 10.5 m. These pillow basalts crystallized from fairly evolved (N-type MORB) tholeiitic melts. In total, 19 m of basaltic pillow lavas and flows were penetrated in Hole 522B. Thirteen cooling units were distinguished on the basis of glassy margins and fine quench textures. In contrast to Holes 519A and 520, the basalts of the Hole 522B ridge section can be divided into two major groups of tholeiites: (1) Cooling Units 1 through 12 and (2) Cooling Unit 13. The basalts in this ridge section are also N-type MORBs but are generally more differentiated than those of Holes 519A and 520. The lowermost basalts (Cooling Unit 13) have the most primitive composition and make up a compositional group distinct from the more evolved basalts in the twelve units above it. Hole 524 was drilled on the south flank of the Walvis Ridge and thus provided samples from a more complex part of the South Atlantic seafloor. Three different basaltic rock suites, interlayered with volcanic detrital sediments, were encountered. The rock suites are, from top to bottom, an alkali basaltic pillow lava; a 16-m-thick alkaline diabase sill with an age of about 65 m.y. (according to K-Ar dating and planktonic foraminifers); and a second sill that is approximately 9 m thick, about 74 m.y. in age, and tholeiitic in composition, thus contrasting strongly with the overlying alkaline rocks. The alkali basalts of Hole 524 show chemical characteristics that are very similar to the basaltic lavas of the Tristan da Cunha group volcanoes, which are located approximately 400 km east of the Mid-Atlantic Ridge crest. Thus, the Walvis Ridge may plausibly be interpreted as a line of hot-spot alkaline volcanoes.

Geochemistry of basalts from the Caribbean Large Igneous Province

Oceanic flood basalts are poorly understood, short-term expressions of highly increased heat flux and mass flow within the convecting mantle. The uniqueness of the Caribbean Large Igneous Province (CLIP, 92-74 Ma) with respect to other Cretaceous oceanic plateaus is its extensive sub-aerial exposures, providing an excellent basis to investigate the temporal and compositional relationships within a starting plume head. We present major element, trace element and initial Sr-Nd-Pb isotope composition of 40 extrusive rocks from the Caribbean Plateau, including onland sections in Costa Rica, Colombia and Curaçao as well as DSDP Sites in the Central Caribbean. Even though the lavas were erupted over an area of ~3*10**6 km**2, the majority have strikingly uniform incompatible element patterns (La/Yb=0.96+/-0.16, n=64 out of 79 samples, 2sigma) and initial Nd-Pb isotopic compositions (e.g. 143Nd/144Ndin=0.51291+/-3, epsilon-Nd i=7.3+/-0.6, 206Pb/204Pbin=18.86+/-0.12, n=54 out of 66, 2sigma). Lavas with endmember compositions have only been sampled at the DSDP Sites, Gorgona Island (Colombia) and the 65-60 Ma accreted Quepos and Osa igneous complexes (Costa Rica) of the subsequent hotspot track. Despite the relatively uniform composition of most lavas, linear correlations exist between isotope ratios and between isotope and highly incompatible trace element ratios. The Sr-Nd-Pb isotope and trace element signatures of the chemically enriched lavas are compatible with derivation from recycled oceanic crust, while the depleted lavas are derived from a highly residual source. This source could represent either oceanic lithospheric mantle left after ocean crust formation or gabbros with interlayered ultramafic cumulates of the lower oceanic crust. High 3He/4He in olivines of enriched picrites at Quepos are ~12 times higher than the atmospheric ratio suggesting that the enriched component may have once resided in the lower mantle. Evaluation of the Sm-Nd and U-Pb isotope systematics on isochron diagrams suggests that the age of separation of enriched and depleted components from the depleted MORB source mantle could have been <=500 Ma before CLIP formation and interpreted to reflect the recycling time of the CLIP source. Mantle plume heads may provide a mechanism for transporting large volumes of possibly young recycled oceanic lithosphere residing in the lower mantle back into the shallow MORB source mantle.

Petrografia, geoquímica e geocronologia das rochas metavulcânicas e metaplutônicas dos Greenstone Belts faina e Serra de Santa Rita : implicações para o ambiente tectônico

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Pós-Graduação em Geologia, 2016.

Multiple plume events in the genesis of the peri-Caribbean Cretaceous oceanic plateau province

The oceanic crust fragments exposed in central America, in north-western South America, and in the Caribbean islands have been considered to represent accreted remnants of the Caribbean-Colombian Oceanic Plateau (CCOP). On the basis of trace element and Nd, Sr, and Pb isotopic compositions we infer that cumulate rocks, basalts, and diabases from coastal Ecuador have a different source than the basalts from the Dominican Republic. The latter suite includes the 86 Ma basalts of the Duarte Complex which are light rare earth element (REE) -enriched and display (relative to normal mid-ocean ridge basalts, NMORB) moderate enrichments in large ion lithophile elements, together with high Nb, Ta, Pb, and low Th contents. Moreover, they exhibit a rather restricted range of Nd and Pb isotopic ratios consistent with their derivation from an ocean island-type mantle source, the composition of which includes the HIMU (high U-238/Pb-204) component characteristic of the Galapagos hotspot. In contrast, the 123 Ma Ecuadorian oceanic rocks have flat REE patterns and (relative to NMORB) are depleted in Zr, Hf, Th, and U. Moreover, they show a wide range of Nd and Pb isotopic ratios intermediate between those of ocean island basalts and NMORB. It is unlikely, on geochemical grounds, that the plume source of the Ecuadorian fragments was similar to that of the Galapagos. In addition, because of the NNE motion of the Farallon plate during the Early Cretaceous, the Ecuadorian oceanic plateau fragments could not have been derived from the Galapagos hotspot but were likely formed at a ridge-centered or near-ridge hotspot somewhere in the SE Pacific.

Hydrogen isotope fractionations between amphiboles, micas, and fluids in alkaline igneous intrusions

RÉSUMÉ DE LA THÈSE Les teneurs des amphiboles en éléments majeurs et en isotopes stables ont été analysées dans plusieurs complexes ignés alcalins et hyperalcalins, dans le but de déterminer l'importance des variations de composition des minéraux pour le fractionnement isotopique de l'hydrogène dans un système naturel minéral-magma-fluide. Cette étude se concentre principalement sur les syénites néphéliniques de complexes intrusifs alcalins bien connus mais à chimie variable, dont les amphiboles, ainsi que d'autres silicates hydratés tels que micas et eudialytes, lorsque cela était possible, ont été séparés. L'intérêt principal s'est porté sur le complexe alcalin d'Ilímaussaq de la Province du Gardar, au Sud du Groenland. Dans une optique de comparaison, nous avons collecté et analysé d'autres échantillons provenant du complexe de Tugtutôq (Sud Groenland), des complexes de Khibina et Lovozero (Péninsule de Kola, Russie), du Mont St-Hilaire et du Mont Royal (Canada) et de 6 autres du nord-ouest de la Namibie (Cape Cross, Okenyenya, Messum, Etaneno, Kalkfeld,et Okorusu). Les compositions isotopiques de l'hydrogène des amphiboles des ces différentes zones présentent de grandes variations (-227 à -700/00), ce qui est atypique pour des magmas d'origine mantellique. Les valeurs comprises entre -80 et -400/00 indiquent une provenance du manteau. Ces larges variations de compositions ainsi que l'extrême appauvrissement en isotope lourd de l'hydrogène (D), en comparaison avec d'autres roches ignées, semblent être propres.aux roches alcalines et hyperalcalines de ce type, ce qui indiquerait un processus commun. Les différents complexes alcalins choisis présentent un large intervalle de composition chimique des amphiboles. La caractérisation des amphiboles par microscopie électronique et par spectroscopie Mössbauer contribuent à observer le contrôle du Fe sur le fractionnement des isotopes de l'hydrogène. En effet, cela a mis en évidence un contrôle du Fe sur le fractionnement et même, dans le cas du complexe hyperalcalin d'Ilímaussaq, une relation entre le rapport Fei3+/FeT et les variations du rapport D/H. Les complexes étudiés diffèrent de par leur index agpaïtique (Na+K/Al) et également de par leur contenu en fer. Les plus hautes valeurs en Fe (27-35 wt%) et en éléments alcalins dans les amphiboles, ainsi que les teneurs de D/H les plus basses et leur grande variation, sont celles du complexe d'Ilímaussaq. Les amphiboles de la Péninsule de Kola et du Canada sont similaires, mais toutefois moins appauvries en D. En ce qui concerne les amphiboles des complexes du NO de la Namibie, elles présentent des compositions isotopiques de l'hydrogène magmatiques normales (-73 à -100 0/00), contiennent moins de Fe (15-17 wt%) et sont fortement enrichies en Ca et moins en Na. Dans ce cas, l'alcalinité est moins importante en comparaison des autres complexes étudiés. En dehors des teneurs en éléments alcalins des amphiboles, l'alcalinité des fluides s'avère également un facteur important, ce qui est cohérent avec certaines suggestions à partir de systèmes expérimentaux. Afin de mieux contraindre ce facteur, des expériences d'échanges hydrothermaux entre les amphiboles et les fluides de salinité différente ont été effectuées en simulant des conditions naturelles. L'approximation d'amphiboles naturelles de complexes ignés alcalins, couplée aux expériences d'échange, aide à préciser les facteurs contrôlant le fractionnement des isotopes de l'hydrogène dans les roches alcalines. Les valeurs extrêmement basses de 3D des amphiboles de ces complexes alcalins peuvent être dues à une combinaison de différents facteurs, telles qu'une haute alcalinité, une haute teneur en Fe et une faible profondeur d'intrusion. Les grandes variations ainsi que les faibles valeurs de SD des amphiboles étudiées peuvent résulter d'un processus magmatique interne et il est peu probable que de l'eau météorique soit impliquée et/ou que le dégazage magmatique ait joué un rôle. THESIS ABSTRACT Major element and stable isotope compositions of amphiboles were analyzed from a number of alkaline and peralkaline igneous complexes in order to determine the importance of compositional variations in minerals to hydrogen isotope fractionations in natural mineral-melt-fluid systems. The thesis mainly focuses on nepheline syenites of well-studied, but chemically variable alkaline intrusive rocks, from which amphiboles and, if possible, other hydrous silicates such as micas and eudialytes were separated. The system of primary interest was the alkaline Ilímaussaq Complex of the Gardar Province of South Greenland. For the purpose of comparison additional samples were collected and examined from the Tugtutôq Complex (South Greenland), the Khibina and Lovozero Complexes (Kola Peninsular, Russia), Mount St-Hilaire and Mount Royal (Canada) and six further complexes from NW Namibia (Cape Cross, Okenyenya, Messum, Etaneno, Kalkfeld, and Okorusu). The hydrogen isotope compositions of amphiboles from the localities studied differ greatly, which is atypical for amphiboles from mantle, range between - 227 and - 700/00 (latter compatible with a simple mantle origin). As this wide range in compositions and the extreme depletion in the heavy hydrogen isotope (D) content relative to other igneous rocks appear to be unique to alkaline to peralkaline rocks of this type, a common process is indicated. The different alkaline complexes chosen cover a wide range of amphibole chemical compositions. Detailed chemical characterization of amphiboles by electron microprobe and Mössbauer spectroscopy analyses helped to constrain the control of Fe on the H-isotope fractionations. Complete characterization of the chemical compositions of the amphiboles support Fe-control on fractionations and at least for the peralkaline Ilímaussaq complex a relationship between Fe3+/FeT ratios and variations in D/H. The studied complexes differ in their agpaitic index (Na+K/Al) and also in their Fe-content. The most iron (27-35 wt. %) and alkaline element rich amphiboles, with the lowermost D/H ratio, as well with very wide range, are the ones from Ilímaussaq complex. Similar, but less D depleted amphiboles are from the Kola Peninsula and the Canadian localities. The complexes described from NW Namibia have amphiboles with normal magmatic hydrogen isotope composition (-730/00 to -1000/00), and have less Fe-content (15-17 wt. %), and are more Ca-and less Na-rich. In this case alkalinity is not that important in comparison to the other studied complexes. Beside the alkaline element contents in the amphiboles, the alkalinity of the fluids has been found to be an important factor, in conjunction with earlier suggestions from experimental systems. To further constrain this factor, hydrothermal exchange experiments between amphiboles and fluids of different salinity simulating natural conditions were performed. The approach of examining natural amphiboles from alkaline igneous complexes in parallel to performing exchange experiments - helped to further constrain the factors controlling the H-isotope fractionations in alkaline rocks. The observed changes between the hydrogen and oxygen isotope compositions of amphiboles and fluids before and after the experiments suggest that another phase was produced during the experiments, which influenced the final hydrogen isotope composition of the system. This presumably hydrous phase has also influenced the Fe3 +/Fe2+ ratio of the amphiboles, which became more oxidized. The extremely low SD values of amphiboles in these alkaline complexes may be due to a combination of different factors such as high alkalinity, high Fe-content, and shallow intrusion depths. This wide range and the low SD values of the amphiboles studied might be a result of internal, magmatic processes and it is unlikely that meteoric water was involved and/or magmatic degassing played an important role. RÉSUMÉ DE LA THÈSE (pour le grand public) Fractionnement isotopique de l'hydrogène entre amphiboles, micas et fluides dans des intrusions alcalines Zsófia Wáczek Directeur de thèse, Prof. Torsten W. Vennemann Institut de Minéralogie et Géochimie, Université de Lausanne Les roches alcalines et celles qui leurs sont associées sont des sources importantes de nombreux minéraux et minerais, tels l'apatite, le niobium, le diamant et autres pierres précieuses. Cette étude se concentre sur des complexes alcalins localisés dans le sud du Groenland, au Canada, dans la péninsule de Kola en Russie et au nord-ouest de la Namibie. Ces complexes sont composés de roches ayant cristallisé à partir de magmas et de fluides très enrichis en alcalins. Cet enrichissement permet la précipitation de minéraux inhabituels riches en potassium et/ou sodium, telles les amphiboles sodiques, également enrichies en fer. Les amphiboles étudiées ont des compositions calciques, sodi-calciques et sodiques, qui reflètent leurs différents environnements de formation. Des études précédentes ont révélé une large gamme de rapports isotopiques de l'hydrogène dans les amphiboles de roches hyperalcalines, dont certains extrêmement bas. Cette variation importante est très intrigante, sachant que des valeurs entre -40 et -800/00 correspondent à des silicates ignés hydratés et non altérés, alors que des valeurs descendant jusqu'a -1500/00 nécessiteraient une altération par de l'eau météorique et/ou une contamination par les roches environnantes ou des sédiments riches en matière organique. Dans lé cas précis du complexe d'Ilímaussaq (sud du Groenland), aucune de ces explications n'a pu être démontrée et des valeurs encore plus faibles ont été trouvées. Le complexe d'Ilímaussaq présente des valeurs de rapport isotopique de l'hydrogène entre -227 et -500/00 dans les amphiboles. Une origine mantellique permet d'expliquer les valeurs élevées, mais d'autres processus doivent entrer en jeu pour engendrer les valeurs les plus négatives. C'est à l'identification de ces processus que nous nous sommes attachés dans ce travail. Les grandes variations observées dans les teneurs en fer et dans le rapport Fe3+/FeT des roches et des minéraux de ces complexes sont corrélées avec d'autres paramètres chimiques, tels que la composition isotopique de l'hydrogène dans les amphiboles. Nous avons dès lors abordé les questions suivantes: quelle est la relation entre la teneur en fer des amphiboles et leur composition isotopique? Que nous apprennent les changements de la teneur en fer et les changements dans le rapport Fe3+/FeT sur les processus pétrologiques dans ces roches? Pour répondre à ces questions, nous avons analysé les compositions isotopiques de l'oxygène et de l'hydrogène dans les amphiboles et d'autres silicates hydratés. La composition chimique et le rapport Fe3+/FeT des amphiboles ont également été déterminés. Des expériences hydrothermales simulant des conditions naturelles ont été entreprises afin de mieux comprendre les processus de fractionnement isotopiques dans ces systèmes très alcalins. Nos conclusions sont les suivantes: (1) Les valeurs extrêmement faibles ainsi que les larges variations des rapports isotopiques de l'hydrogène des amphiboles de ces complexes alcalins sont dues à une combinaison de facteurs tels que la forte alcalinité, la haute teneur en fer et la profondeur très faible de l'intrusion. (2) Ces valeurs sont probablement le résultat de processus magmatiques internes. (3) Il est peu probable que les eaux météoriques et/ou le dégazage magmatique aient joué un rôle lors de la formation de ces amphiboles. (4) Certaines corrélations, en accord avec les études précédentes, ont pu être trouvées au niveau des concentrations en fer. (5) Dans le cas du complexe d'Ilímaussaq exclusivement, une relation a été trouvée entre le rapport Fe3+/FeT et la composition isotopique de l'hydrogène des amphiboles.

Development of hypogene and supergene alteration and copper mineralization patterns, Sar Cheshmeh porphyry copper deposits, Iran /

The formation of the Sar Cheshmeh porphyry Cu-Mo deposit is related to the culmination of calc-alkaline igneous activity in the Kerman region. The deposit comprises a suite of Late Cenozoic intrusive sub-volcanic and extrusive rocks emplaced into a folded series of Eocene andesitic lavas and pyroclastic sediments. The earliest stage of magmatism was emplacement of a large granodiorite stock about 29 m.y.b.p. This was followed by intrusion of two separate porphyritic bodies at 15 (Sar Cheshrneh porphyry) and 12 m.y.b.p. (Late porphyry) and a series of sub-volcanic dikes between 12 and 9 m.y.b.p. Magmatic activity terminated with multi-phase extrusion of a Pelean dacitic dome complex between 10 and 2.8 m.y.b.p. The country rocks and the earlier porphyritic intrusions are pervasively altered to biotite-rich potassium silicate (metasomatic and hydrothermal) sericite-clay, phyllic and chlorite-clay, argillic assemblages. These grade outwards to an extensive propylitic zone. Within the ore body, the later intra-. and post-mineral dikes only reach the propylitic grade. At least three different sets of quartz veins are present, including a sericite-chlorite-quartz set which locally retrogrades pervasive secondary biotite to sericite. In the hypogene zone, metasomatic and hydrothermal alteration is related to all stages of magmatism but copper mineralization and veining are restricted to a period of 15 to 9 m.y.b.p.related to the early intrusive phases. The copper mineralization and silicate alteration do not fit a simple annular ring model but have been greatly modified by, 1. The existence of an ititial, outer ring, of metasomatic alteration overprinted by an inner.ring of hydrothermal alteration and, 2. later extensive dilating effects of intra- and post-mineral dikes. The hydrothermal clay mineral assemblage in the hypogene zone is illite-chlorite-kaolinite-smectite (beidellite). Preliminary studies indicate that the amount of each of these clays varies vertically and that hydrothermal zonation of clay minerals is possible. However, these minerals alter to illite-kaolinite assemblages in the supergene sulfide zone and to more kaolinite-rich assemblages in the supergene leached zone. Hydrothermal biotite breaks down readily in the supergene zone and is not well preserved in surface outcrops. The distribution of copper minerals in the supergene sulfide enrichment zone is only partly related to rock type being more dependent on topography and the availability of fractures.