As intrusões Indaiá I e II (também referidas como Perdizes 3-A e 3-B) são corpos intrusivos hipoabissais ultrabásicos de pequeno porte, associados ao magmatismo cretácico da Província Alcalina Alto Paranaíba, oeste do Estado de Minas Gerais. Esta dissertação de mestrado objetivou compreender a gênese e processos de evolução relacionados a intrusão Indaiá II, cuja classificação ambígua entre kimberlito e kamafugito dividiu autores em trabalhos anteriores.. Também buscou-se discutir a possível vinculação genética com a intrusão vizinha, Indaiá I. Para tanto, foram realizadas novas análises petrográficas, geoquímicas e isotópicas de rocha total, e química mineral. A intrusão principal (Indaiá I) é classificada como um kimberlito do Grupo I. Já a intrusão satélite (Indaiá II) distingue-se quimicamente e petrograficamente, possuindo uma composição ultrapotássica, similar à kamafugítica, e apresenta menor concentração de macrocristais de olivina, diopsídio como o principal constituinte da matriz ( e não a monticellita como Indaiá I) e possui uma presença abundante de microenclaves félsicos. Estes enclaves apresentam estrutura estirada, e são constituídos principalmente por kalsilita/ nefelina, vidro devitrificado, diopsídio e flogopita. A presença de texturas sugestivas de desequilíbrio físico-químico como embayment e sieve em grãos de olivina e clinopiroxênio em Indaiá II são indicativas de processos de sistema aberto. A abundância de diopsídio na matriz e a substituição de olivina por clinopiroxênio nas bordas de macrocristais e microcristais apontam para um aumento da atividade de sílica no decorrer do processo de cristalização. A alta proporção de xenólitos crustais na rocha, totalmente transformados ou com evidências de fusão parcial, e a presença de apatitas aciculares nas suas cercanias, indicam a operação de um processo de contaminação crustal. Novos dados de química mineral e litogeoquímica de elementos maiores e traços corroboram esse processo. Os trends composicionais de minerais como espinélio e flogopita são bastante similares a ocorrências de kimberlitos contaminados registrados na literatura. Além disso, amostras de Indaiá II apresentam elevado C.I. (Contamination Index, 2,12-2,25), maior percentual de SiO2, K2O e maior razão Rb/Sr que a intrusão principal. Modelos de contaminação crustal foram efetuados a partir da mistura do fundido de Indaiá I e do fundido das rochas granitoides encaixantes. Os fundidos de Indaiá I e II foram obtidos pela extração do volume dos núcleos de macrocristais de olivina, considerados xenocristais em ambas as ocorrências, das análises de rocha total. A quantidade de olivina foi obtida através de análises modais, e a composição considerada foi obtida através de uma média das análises pontuais de microssonda eletrônica e LA-ICP-MS. O fundido da encaixante foi estimado utilizando-se as análises de rocha-total das encaixantes crustais da área e calculando-se um fundido parcial desta rocha a 750ºC e pressões entre 1-5Kbar com o software RhyoliteMelts (para elementos maiores). A composição de elementos-traço do fundido foi modelada por balanço de massa, a partir de coeficientes de partição compilados da literatura e a proporção de minerais no resíduo sólido obtida dos modelos por elementos maiores. Curvas de mistura entre elementos maiores e traços também parecem confirmar o processo. Novos dados isotópicos de 87Sr/86Sr e 143Nd/144Nd foram obtidos para estas intrusões, como também para a encaixante local. Curvas de mixing isotópico foram feitas para tentar estabelecer a quantidade de contribuição crustal nos magmas de Indaiá II. Nestes modelos, as amostras de Indaiá II ajustam-se concordantemente às curvas de mistura entre os polos de Indaiá I e da encaixante. Concluimos que: 1) a intrusão Indaiá II representaria uma intrusão kimberlítica altamente contaminada, 2) a contaminação provavelmente ocorreu pela assimilação de fundidos anatéticos oriundos das principais rochas encaixantes crustais da área, 3) que Indaiá I e Indaiá II poderiam ter um mesmo magma progenitor, mas com diferentes graus de contaminação crustal. / The intrusions Indaiá I and II (also referred as Perdizes 3-A and 3-B) are hypoabissal ultrabasic bodies of small size associated with the Cretaceous magmatism of the Alto Paranaiba Alkaline Province, west of the Minas Gerais state. This master\'s dissertation aimed a better understanding of the genesis and the evolution processes related to the Indaiá II intrusion, whose ambiguous classification between kimberlite and kamafugite divided the authors of former works. Also, it is discussed the possible genetic linkage of Indaiá II with the neighbor intrusion, Indaiá I. For this purpose, new petrographic, whole rock geochemical, isotopic and mineral chemistry analyses were made. The main intrusion (Indaiá I) was classified as a group-I kimberlite. The satellite intrusion, Indaiá II, is petrographically and chemically distinct of the main one, having a ultrapotassic composition, similar to those of kamafugites, and presenting lower volumes of olivine macrocrysts, diopside as the main matrix phase (instead of monticellite as found in Indaiá I), and an abundant presence of felsic microenclaves. These enclaves present elongated structure and they mainly have kalsilite, devitrified glass, diopside and phlogopite. The presence of textures indicative of physical-chemical disequilibrium, such as embayment and sieve in olivine and clinopyroxene grains from Indaiá II are indicative of an open system process. The high amounts of diopside in the matrix and the substitution of the rims of olivine macro- and microcrysts by clinopyroxene point to an increase in the silica activity during the crystallization. The high proportion of crustal xenoliths in the rocks, most of these totally transformed or with evidences with partial melt, and the presence of acicular apatite in their border regions, indicate the action of crustal contamination processes. New mineral chemistry and whole rock geochemical (major and trace elements) data corroborate this process. The spinel and phlogopite compositional trends are very similar with those from contaminated kimberlitic occurrences registered in the literature. Moreover, samples from Indaiá II have high Contamination Index (C.I., 2.12-2.25), greater amounts of SiO2, K2O and higher Rb/Sr ratios than those from the main intrusion. Crustal contamination models were developed considering a mixing between the melt of Indaiá I and the partial melt of the granitoid host rocks of the area. The composition of melts from Indaiá I and II were calculated by the extraction of the amount of the cores of olivine macrocrysts, considered xenocrysts in both occurrences, from the whole-rock compositions. The amount of olivines was taken from modal concentrations and the considered composition was obtained by the average of electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) analyses. The major element composition of the partial melt of the host rock was estimated using the algorithm RhyoliteMelts. For these models, we considered the whole-rock compositions of the main host rocks of the area and used 750ºC and 1-5Kbar. The trace element composition of the host rock partial melts was modeled by mass balance calculations, using partition coefficients from the literature and the proportion of minerals in the solid residue obtained for the major element models. After the calculation of these liquid compositions, mixing curve models using major and trace element compositions were made and they are concordant with the crustal contamination processes. New 87Sr/86Sr and 143Nd/144Nd isotopic data were obtained for Indaiá I and II intrusions, as well as for the local host rock. Isotopic mixing curves were also made trying to constrain the amount of crustal contribution in Indaiá II magmas. In these models, Indaiá II samples fit concordantly with the mixing curves having Indaiá I and the host rock ratios as the main poles. We conclude that 1) Indaiá II is representative of a highly contaminated kimberlitic intrusion, 2) the contamination possibly occurred by the assimilation of the anatetic melts from the main crustal host rocks of this area and 3) that Indaiá I and Indaiá II could have the same parent melt, but with different degrees of crustal contamination.

Knowledge of the provenance of crustal volatiles and the processes by which they are released is extremely important for the dynamics of magmatic systems. Presented here are the results of multiple investigations, which aim to understand magmatic volatile contamination from contrasting but complementary perspectives. The main methodologies used include He and C isotope values and CO2/3He ratios of volcanic gases and fluids; simulation of magma-carbonate interaction using high-pressure high-temperature experimental petrology; X-ray microtomography of vesiculated xenoliths and computer modeling. Findings show that the contribution from upper crustal volatiles can be substantial, and is dependant on the upper crustal lithology on which a volcano lies, as well as the composition of the magma supplied. Carbonate dissolution in particular is strongly controlled by the viscosity of the host magma. The details of the breakdown of vesiculated xenoliths is complex but has wide reaching implications, ranging from the dissemination of crustally derived materials through a magma body to highlighting that crustal volatiles are largely unaccounted for in both individual volcano and global volatile budgets. In synthesizing the conclusions from each of the individual perspectives presented, I propose the contribution of volatiles from crustal sources to play a significant role in many geological systems. This volatile component should be taken into consideration in future research efforts.

A-type granites form in anorogenic settings and typically have high REE concentrations, K2O, Na2O, SiO2, FeOtotal, but low contents of Al2O3, MgO, CaO compared to other granite types. They have been divided in two groups according to their geochemical characteristics: differentiates of mantle-derived magmas (A1), and granites that are the result of melting depleted, lower crust (A2). The two largest A-type granites of the Mesozoic White Mountain Batholith of New Hampshire are the Mount Osceola and Conway granites. Electron microprobe analyses of biotite and amphibole in both granites are similar to those in other A-type granites: Fe-rich, but low MgO, and Al2O3. Whole-rock major and trace elements compositions of the Mount Osceola and the Conway granites are similar; both have high contents of REE, Zr, Nb, high Nb/Y ratios, and low CaO, Eu, and Sr and other compatible elements. Based on their high Nb/Y ratios, both granites are classified as mantle-derived magmas (A1). Microanalyses of ẟ18O and ƐHf of zircon show significant crustal contamination in both granites. The ẟ18O values for zircons from the Mount Osceola are between 7.4-8.9‰, and for the Conway Granite are 7.0-8.1‰. These values are distinct from mantle zircon (ẟ18O 5.3±0.3‰), which indicates large degrees of crustal contamination in both granites. Additionally, ƐHf (188Ma) for the Mount Osceola zircon ranges from -1.1 to +3.4, and those from the Conway Granite range from -2.1 to +4.6, indicating magma derivation in depleted mantle (ƐHf > 0) along with a crustal component. Although both granites have A1 compositions suggesting a mantle-derivation, this simple process is not recorded by the zircons. These zircons crystallized after considerable crustal contamination of mantle-derived A1 magmas and missed capturing the signature of that mantle component.

The assemblage of ca. 6–4 Ma volcanic rocks exposed at the Sagehen Research station in the Truckee-Tahoe region of the northern Sierra Nevada, United States, is interpreted to be, within the Ancestral Cascades volcanic arc, a Lassen-type stratovolcano complex. Sagehen is of particular importance because it is one of the few Tertiary arc volcanic centres in California which has not been heavily glaciated during the Pleistocene. The volcanic rocks are variably porphyritic or aphanitic, including abundant plagioclase with clinopyroxene and amphibole. The rocks range from basalt to basaltic-andesite to andesite in composition. Basalts are olivineand clinopyroxene-bearing with minor phenocrysts of plagioclase. The basaltic-andesites are primarily pyroxene bearing while the andesites contain pyroxene-, plagioclase- and hornblende porphyritic phases. Sagehen arc lavas are calc-alkaline and enriched in the large ion lithophile elements and depleted in High Field Strength Elements. The basalts are depleted in Zr and Hf while the andesites are enriched with Zr and Hf relative to the middle rare earth elements. Compared to previously studied Ancestral Cascade arc samples, Sagehen region basalts have lower 143Nd/144Nd isotopic values that do not correspond to proposed mantle-lithosphere mixing lines, while the andesite samples appear to represent the interplay of these two components on a 87Sr/86Sr vs. 143Nd/144Nd. The trace element data and isotopic plots suggest that the melts that produced the basalts are from subduction modified mantle wedge peridotites that ponded near the base of the lithosphere similar to the generation of other subduction related calc-alkaline lavas along convergent continental margins. The andesitic samples appear to be the result of further modification through crustal assimilation as seen in the higher isotopic Sr contents in the andesites and Ce/Smpmn vs. Tb/Ybpmn plots. Finally, the proposed map units from Sylvester & Raines (2007) were found to contain various geochemical facies based on the samples collected indicating that some map units may have to be redefined or sub-divided.

A química mineral e de rocha e determinações de susceptibilidade magnética (SM) de granitóides sin- e tardi orogênicos (610- 600 Ma) localizados na porção oriental do batólito Agudos Grandes (porção central do Cinturão Ribeira, SE do Brasil) foram utilizadas para determinar as condições de cristalização e as implicações em sua petrogênese. Os granitos sin-orogênicos são metaluminosos e têm índice de cor (IC) entre 8 e 15, dado por hornblenda, biotita, titanita e magnetita (unidade HBgd). As temperaturas liquidus obtidas pelo geotermômetro de saturação em apatita decrescem de 1000 a 950º C com o fracionamento. As temperaturas solidus obtidas pelo geotermômetro hornblenda-plagioclásio, variam de 720 a 800º C e mostram aumento sistemático em direção a leste, refletindo diminuição da a(H2O) dos magmas. As pressões obtidas por geobarometria de Al em hornblenda variam muito pouco (3,6 a 4,5 kbar) mostrando não haver variações significativas no nível de exposição do batólito. Esses granitos cristalizaram sob condições fortemente oxidantes (DNNO ³ + 2), como revelado pela alta SM, pelas composições da biotita e da ilmenita reliquiar e pelo consumo da ilmenita sob fO2 acima do buffer TMQA. Os granitóides tardi-orogênicos (maciço Piedade) variam de metaluminosos a marginalmente peraluminosos. A unidade metaluminosa portadora de titanita e magnetita (BmgT; IC=8) cristalizou sob condições comparáveis às dos granitos sin-orogênicos. As demais unidades são formadas por granitos com biotita e ilmenita (± muscovita e magnetita) e IC variável entre 15 e 5. Essas rochas em geral cristalizaram sob condições mais reduzidas (QFM a DNNO = + 2), como revelado pela SM mais baixa e pela composição de biotita e ilmenita, mas localmente foram afetadas por processos de oxidação pós-magmática. As temperaturas liquidus obtidas a partir do geotermômetro de saturação em apatita para todas as rochas do maciço Piedade são tão elevadas quanto as dos granitos sin-orogênicos. Estimativas de pressão são precárias, mas as composições de muscovitas sugerem valores da ordem de 4 kbar. Os dados obtidos no presente trabalho são consistentes com modelos que admitem um vínculo genético entre os granitos sin- e tardi-orogênicos do batólito Agudos Grandes. Em particular as tendências de variação química contínua das biotitas, com aumento progressivo do componente siderofilita para os granitos com muscovita, paralelas com a diminuição de SM e diminuição de fO2, podem sugerir que diferenças observadas refletem processos de contaminação de magmas metaluminosos por rochas metassedimentares mais reduzidas. / Magnetic susceptibility (MS) measurements and mineral and rock chemistry were used to infer crystallization conditions of syn- to late-orogenic (610-600 Ma) granites of the eastern portion of the Agudos Grandes batholith (central Ribeira Belt, SE Brazil). The syn-orogenic granites are metaluminous and have color indices (IC) of 8 to 15 given by hornblende, biotite, titanite and magnetite (unit HBgd). Liquidus temperatures obtained by apatite saturation thermometry decrease slighlty, from 1000 to 950°C with fractionation. Solidus temperatures, derived from hornblende-plagioclase thermometry, raise eastwards in the batholith from 720 to 800° C, reflecting decreasing a(H2O) of the magmas. Pressures derived from Al-in-hornblende barometry are nearly invariable (3.6 to 4.5 kbar), showing that the batholith is exposed at approximately the same level of intrusion along the studied section. These granites crystallized under strongly oxidizing conditions (DNNO ³ + 2), as revealed by high MS, by the compositions of biotite and relict ilmenite, and by ilmenite consumption due to fO2 above the TMQA buffer. The late-orogenic granites (Piedade massif) are metaluminous to marginally peraluminous. The metaluminous unit (BmgT; IC=8) bears titanite and magnetite, and crystalized under conditions comparable to those shown by the syn-orogenic massifs. The remaining units are made up of biotite + ilmenite (± muscovite and magnetite) granites with variable IC (15 to 5). These rocks crystallized mostly under more reduced conditions (QFM to DNNO = + 2), as revealed by lower MS and by the compositions of biotite and ilmenite, but were locally affected by post-magmatic oxidation processes. The liquidus temperatures obtained from apatite saturation thermometry in all granites from the Piedade massif are as high as those of the syn-orogenic massifs. Pressure estimates, based on muscovite compositions, are less reliable, but yield values around 4 kbar. The data obtained in this work are consistent with models which admit a genetic link between the syn-orogenic and the late-orogenic granites of the Agudos Grandes batholith. Continuous chemical variation of biotites, with the siderophyllite component increasing steadily towards the muscovite-bearing granites, and parallel decreasing of MS and fO2 suggest that contamination of metaluminous magmas by more reduced metasediments could explain most of the variation observed.

A química mineral e de rocha e determinações de susceptibilidade magnética (SM) de granitóides sin- e tardi orogênicos (610- 600 Ma) localizados na porção oriental do batólito Agudos Grandes (porção central do Cinturão Ribeira, SE do Brasil) foram utilizadas para determinar as condições de cristalização e as implicações em sua petrogênese. Os granitos sin-orogênicos são metaluminosos e têm índice de cor (IC) entre 8 e 15, dado por hornblenda, biotita, titanita e magnetita (unidade HBgd). As temperaturas liquidus obtidas pelo geotermômetro de saturação em apatita decrescem de 1000 a 950º C com o fracionamento. As temperaturas solidus obtidas pelo geotermômetro hornblenda-plagioclásio, variam de 720 a 800º C e mostram aumento sistemático em direção a leste, refletindo diminuição da a(H2O) dos magmas. As pressões obtidas por geobarometria de Al em hornblenda variam muito pouco (3,6 a 4,5 kbar) mostrando não haver variações significativas no nível de exposição do batólito. Esses granitos cristalizaram sob condições fortemente oxidantes (DNNO ³ + 2), como revelado pela alta SM, pelas composições da biotita e da ilmenita reliquiar e pelo consumo da ilmenita sob fO2 acima do buffer TMQA. Os granitóides tardi-orogênicos (maciço Piedade) variam de metaluminosos a marginalmente peraluminosos. A unidade metaluminosa portadora de titanita e magnetita (BmgT; IC=8) cristalizou sob condições comparáveis às dos granitos sin-orogênicos. As demais unidades são formadas por granitos com biotita e ilmenita (± muscovita e magnetita) e IC variável entre 15 e 5. Essas rochas em geral cristalizaram sob condições mais reduzidas (QFM a DNNO = + 2), como revelado pela SM mais baixa e pela composição de biotita e ilmenita, mas localmente foram afetadas por processos de oxidação pós-magmática. As temperaturas liquidus obtidas a partir do geotermômetro de saturação em apatita para todas as rochas do maciço Piedade são tão elevadas quanto as dos granitos sin-orogênicos. Estimativas de pressão são precárias, mas as composições de muscovitas sugerem valores da ordem de 4 kbar. Os dados obtidos no presente trabalho são consistentes com modelos que admitem um vínculo genético entre os granitos sin- e tardi-orogênicos do batólito Agudos Grandes. Em particular as tendências de variação química contínua das biotitas, com aumento progressivo do componente siderofilita para os granitos com muscovita, paralelas com a diminuição de SM e diminuição de fO2, podem sugerir que diferenças observadas refletem processos de contaminação de magmas metaluminosos por rochas metassedimentares mais reduzidas. / Magnetic susceptibility (MS) measurements and mineral and rock chemistry were used to infer crystallization conditions of syn- to late-orogenic (610-600 Ma) granites of the eastern portion of the Agudos Grandes batholith (central Ribeira Belt, SE Brazil). The syn-orogenic granites are metaluminous and have color indices (IC) of 8 to 15 given by hornblende, biotite, titanite and magnetite (unit HBgd). Liquidus temperatures obtained by apatite saturation thermometry decrease slighlty, from 1000 to 950°C with fractionation. Solidus temperatures, derived from hornblende-plagioclase thermometry, raise eastwards in the batholith from 720 to 800° C, reflecting decreasing a(H2O) of the magmas. Pressures derived from Al-in-hornblende barometry are nearly invariable (3.6 to 4.5 kbar), showing that the batholith is exposed at approximately the same level of intrusion along the studied section. These granites crystallized under strongly oxidizing conditions (DNNO ³ + 2), as revealed by high MS, by the compositions of biotite and relict ilmenite, and by ilmenite consumption due to fO2 above the TMQA buffer. The late-orogenic granites (Piedade massif) are metaluminous to marginally peraluminous. The metaluminous unit (BmgT; IC=8) bears titanite and magnetite, and crystalized under conditions comparable to those shown by the syn-orogenic massifs. The remaining units are made up of biotite + ilmenite (± muscovite and magnetite) granites with variable IC (15 to 5). These rocks crystallized mostly under more reduced conditions (QFM to DNNO = + 2), as revealed by lower MS and by the compositions of biotite and ilmenite, but were locally affected by post-magmatic oxidation processes. The liquidus temperatures obtained from apatite saturation thermometry in all granites from the Piedade massif are as high as those of the syn-orogenic massifs. Pressure estimates, based on muscovite compositions, are less reliable, but yield values around 4 kbar. The data obtained in this work are consistent with models which admit a genetic link between the syn-orogenic and the late-orogenic granites of the Agudos Grandes batholith. Continuous chemical variation of biotites, with the siderophyllite component increasing steadily towards the muscovite-bearing granites, and parallel decreasing of MS and fO2 suggest that contamination of metaluminous magmas by more reduced metasediments could explain most of the variation observed.

The assemblage of ca. 6–4 Ma volcanic rocks exposed at the Sagehen Research station in the Truckee-Tahoe region of the northern Sierra Nevada, United States, is interpreted to be, within the Ancestral Cascades volcanic arc, a Lassen-type stratovolcano complex. Sagehen is of particular importance because it is one of the few Tertiary arc volcanic centres in California which has not been heavily glaciated during the Pleistocene. The volcanic rocks are variably porphyritic or aphanitic, including abundant plagioclase with clinopyroxene and amphibole. The rocks range from basalt to basaltic-andesite to andesite in composition. Basalts are olivineand clinopyroxene-bearing with minor phenocrysts of plagioclase. The basaltic-andesites are primarily pyroxene bearing while the andesites contain pyroxene-, plagioclase- and hornblende porphyritic phases. Sagehen arc lavas are calc-alkaline and enriched in the large ion lithophile elements and depleted in High Field Strength Elements. The basalts are depleted in Zr and Hf while the andesites are enriched with Zr and Hf relative to the middle rare earth elements. Compared to previously studied Ancestral Cascade arc samples, Sagehen region basalts have lower 143Nd/144Nd isotopic values that do not correspond to proposed mantle-lithosphere mixing lines, while the andesite samples appear to represent the interplay of these two components on a 87Sr/86Sr vs. 143Nd/144Nd. The trace element data and isotopic plots suggest that the melts that produced the basalts are from subduction modified mantle wedge peridotites that ponded near the base of the lithosphere similar to the generation of other subduction related calc-alkaline lavas along convergent continental margins. The andesitic samples appear to be the result of further modification through crustal assimilation as seen in the higher isotopic Sr contents in the andesites and Ce/Smpmn vs. Tb/Ybpmn plots. Finally, the proposed map units from Sylvester & Raines (2007) were found to contain various geochemical facies based on the samples collected indicating that some map units may have to be redefined or sub-divided.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the Canindé Domain, Northern portion of Sergipano Fold Belt, NE-Brazil, occur an association of metamorfized mafic igneous rocks from the Novo Gosto and Gentileza units.Those rocks represent important pieces in the Sergipano Fold Belt geological evolution. The Canindé Domain has been scenario of several interpretations about the tectonic and petrogenetic settings, due to intense deformation and metamorphism that obliterated much of the Canindé Domain rocks original features. Petrographic and geochemical data from the ortho-amphibolites of the Novo Gosto and Gentileza units showed this work contribute to discuss the igneous processes involved in the protoliths genesis, therefore building up to the Canindé Domain tectonic model definition and the major evolutionary aspects. The petrographic data indicate that the studied rocks show Amphibolite Facies paragenesis, marked by hornblende and plagioclase, with retrometamorphic transformations to Greenschist Facies, defined by biotite, epidote, chlorite and sericite paragenesis. These transformations, which were more intense in areas with shear zones concentrations, are probably, the result of hydrothermal fluid action. In spite of the superimposed metamorphic processes, it was possible to observe igneous relicts features, such as blast-glomeroporphiritic, blast- intergranular and blast-subophytic textures. The chemical data suggest that the protoliths of the studied rocks of the Novo Gosto and Gentileza units correspond to basalts with tholeiitic affinity. These basalts are divided into high-Ti (> 2 % TiO 2 ) and low-Ti (< 1,19 % TiO 2 ). Gentileza Unit rocks correspond to andesites and basaltic andesites with tholeiitic to calc- alkaline affinity. The geochemical data interpretation suggest that the igneous protoliths of the studied rocks of the Novo Gosto and Gentileza units were formed in a continental rift environment, derived from magmas generated in different proportions of mixtures between enriched and depleted reservoirs, with OIB-type components contribution. Ratios and correlations among incompatible elements indicate crustal contamination participation in the igneous protoliths generation of both units. / No Domínio Canindé, porção norte da Faixa de Dobramentos Sergipana, NE-Brasil, ocorrem rochas ígneas máficas metamorfizadas das unidades Novo Gosto e Gentileza. Estas rochas representam peças importantes na evolução geológica da faixa. O Domínio Canindé foi palco de diversas interpretações quanto ao ambiente geotectônico e petrogenético, devido à intensa deformação e metamorfismo, que obliteraram boa parte das feições originais das rochas do domínio. Neste trabalho são apresentados e discutidos dados petrográficos e geoquímicos dos ortoanfibolitos das unidades Novo Gosto e Gentileza, com o intuito de discorrer sobre os processos ígneos envolvidos na gênese dos protólitos, de forma a contribuir com a definição do ambiente tectônico de formação e dos principais aspectos evolutivos do Domínio Canindé. Os dados petrográficos indicam que as rochas estudadas possuem uma paragênese estabelecida no Fácies Anfibolito, marcada por hornblenda e plagioclásio, com transformações retrometamórficas para o Fácies Xisto Verde, definidas por biotita, epídoto, clorita e sericita. Essas transformações, que são mais intensas em áreas com concentrações de zonas de cisalhamento, são possivelmente o resultado da ação de fluidos hidrotermais. Apesar dos processos metamórficos superimpostos, foi possível observar feições ígneas reliquiares, marcadas por texturas blasto-glomeroporfirítica, blasto-intergranular e blasto-subofítica. Os dados químicos indicam, que os protólitos das rochas estudadas da Unidade Novo Gosto, correspondem à basaltos de afinidade toleítica, que podem ser divididos em alto-Ti (> 2% TiO 2 ) e baixo-Ti (< 1,19% TiO 2 ). As rochas da Unidade Gentileza correspondem, em sua maioria, à andesitos e andesitos basálticos de afinidade toleítica a cálcio-alcalina. A interpretação dos dados geoquímicos sugere que os protólitos ígneos das rochas estudadas foram formados em um ambiente de rifte continental, derivados de magmas gerados a partir de diferentes proporções de misturas entre reservatórios enriquecidos e empobrecidos, com contribuição de componentes tipo-OIB. Razões e correlações entre elementos incompatíveis sugerem a participação de contaminação crustal na geração dos protólitos ígneos das duas unidades.

Geometries of sills intruded into the lava pile of the Faroe Island Basalt Group (FIBG), which were targeted in this study, were mostly recorded by conventional mapping methods where measured distances and positions were plotted onto accurate topographic maps aided by the use of high-quality photos of relevant outcrops. These data were subsequently used to manually plot 2D profiles along selected tracks and to produce electronic 3D maps using ArcGIS software. The general geometries of the investigated sills, measured at lateral scales ranging from a few metres to a few kilometres and at vertical scales ranging from a few metres to a few hundred metres, differ somewhat from typical sill geometries reported previously for sills intruded into sedimentary successions. The ubiquitous saucer-shapes of the sills from this study, which generally curve upwards in a gradual manner from inner sub-horizontal sections to steeper outer margins, contrast with the common angular transitions from inner sub-horizontal to outer steeper sections of sills reported from sedimentary host-rocks. In this thesis we explore possible alternatives to already existing theories on sill emplacement in sedimentary successions. Major and trace element compositions for samples representing most of the sills exposed in the Faroe Islands have been determined by means of XRF and ICP-MS analyses. Geochemically most of these sills can be grouped into two main categories characterised either by high or by low TiO2 contents. Different sorts/types of metasomatism of source rocks to high-TiO2 versus low-TiO2 sills are indicated by different Nb and Ta anomalies. Modelling by means of REE and other trace elements suggest that much of the compositional differences between these two main categories can be explained by various degrees of partial melting of broadly similar mantle sources. Additional fractionation and accumulation of plagioclase modified some of the melts that gave rise to the actual sills. The initial partial melting event probably occurred at depths slightly shallower than the lower limit of the garnet stability field at ~85 km while plagioclase crystallisation/accumulation most likely occurred at depths shallower than ~18 km. Isotopic compositions may point to very slight contamination of some sills with crustal material.

The assemblage of ca. 6–4 Ma volcanic rocks exposed at the Sagehen Research station in the Truckee-Tahoe region of the northern Sierra Nevada, United States, is interpreted to be, within the Ancestral Cascades volcanic arc, a Lassen-type stratovolcano complex. Sagehen is of particular importance because it is one of the few Tertiary arc volcanic centres in California which has not been heavily glaciated during the Pleistocene. The volcanic rocks are variably porphyritic or aphanitic, including abundant plagioclase with clinopyroxene and amphibole. The rocks range from basalt to basaltic-andesite to andesite in composition. Basalts are olivineand clinopyroxene-bearing with minor phenocrysts of plagioclase. The basaltic-andesites are primarily pyroxene bearing while the andesites contain pyroxene-, plagioclase- and hornblende porphyritic phases. Sagehen arc lavas are calc-alkaline and enriched in the large ion lithophile elements and depleted in High Field Strength Elements. The basalts are depleted in Zr and Hf while the andesites are enriched with Zr and Hf relative to the middle rare earth elements. Compared to previously studied Ancestral Cascade arc samples, Sagehen region basalts have lower 143Nd/144Nd isotopic values that do not correspond to proposed mantle-lithosphere mixing lines, while the andesite samples appear to represent the interplay of these two components on a 87Sr/86Sr vs. 143Nd/144Nd. The trace element data and isotopic plots suggest that the melts that produced the basalts are from subduction modified mantle wedge peridotites that ponded near the base of the lithosphere similar to the generation of other subduction related calc-alkaline lavas along convergent continental margins. The andesitic samples appear to be the result of further modification through crustal assimilation as seen in the higher isotopic Sr contents in the andesites and Ce/Smpmn vs. Tb/Ybpmn plots. Finally, the proposed map units from Sylvester & Raines (2007) were found to contain various geochemical facies based on the samples collected indicating that some map units may have to be redefined or sub-divided.