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The Macau Volcanic Field (MVF) in the Borborema Province, NE Brazil, contains multiple centres of volcanic activity of Early to Late Cenozoic ages. We present element and Sr–Nd–Pb isotope geochemical data for four of the few most prominent basalt types of this volcanic field: Serrote Preto-type, Serra Aguda-type, Pico do Cabugi-type and Serra Preta-type, in order to assess their magmatic history from source to crystallization and the evolution of the mantle beneath the Borborema Province. The basalts are basically sodic nephelinitic–basanitic–alkali olivine basalts enriched in LILE and in Nb–Ta. The Serra Preta, Cabugi and Serra Aguda types demonstrate compositions close to primitive characteristics with 10%

Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic–ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic–ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87 Sr/ 86 Sr i and 143 Nd/ 144 Nd i ratios (0.70432–0.70641 and 0.512216–0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87 Sr/ 86 Sr ratios (0.70422–0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to be responsible for the increse in the K 2 O/Na 2 O, Ba/Sr and Rb/Sr ratios. This enrichment was associated with the relevant role of biotite breakdown in the assimilated host rock partial melts. The petrological model for the Ponte Nova massif is explained as repeated influxes of antecryst-laden basanite magmas that deposited most of their suspended crystals on the floor of the upper-crust magma chamber. Each intrusion is representative of relatively primitive olivine- and clinopyroxene-phyric basanites that had assimilated different degrees of partial melts of heterogeneous host rocks. This study reveals the relevant role of crustal assimilation processes in the magmatic evolution of nepheline-normative rocks, especially in upper-crust chamber environments.

The first precise ID-TIMS U–Pb baddeleyite/zircon dating of dykes representative of the main activity in the Florianopolis Dyke Swarm (Parana–Etendeka Magmatic Province, south Brazil) reveals a restricted age range (134.7 ± 0.3 to 133.9 ± 0.7 Ma). This is at least 5 Ma older than indicated by previous 40 Ar/ 39 Ar stepwise heating dating, and precludes a direct relationship with syn-rifting magmatism connected with opening the south Atlantic Ocean. Instead, as indicated by their age and geochemical signature, these dykes are feeders to the nearby Urubici lavas (and coeval Khumib lavas in Etendeka). These new geochronological results also cast doubt on a large (> 10 Ma) time span for the emplacement of the Florianopolis Dyke Swarm implied by 40 Ar/ 39 Ar dates, but the determination of its upper age limit still requires accurate dating of younger, low-volume fine-grained dykes with distinct low-Ti chemistry; crystals suitable to U–Pb dating were not obtained thus far from these dykes.

The Late Cretaceous Búzios Island alkaline massif intrudes Precambrian charnockites and consists dominantly of syenitic rocks that are cut by a large number of dikes, mostly NE-trending, and representing two distinct suites, a felsic one and a mafic-ultramafic one. Alkali feldspar is the most abundant mineral; other constituents are clinopyroxene, commonly replaced by amphibole/biotite, and opaques. Accessory minerals include occasionally rare phases bearing Zr, Ti, Nb and Rare Earth Elements (REE). The felsic dikes may also have nepheline (sodalite). The mafic-ultramafic suite, in particular the lamprophyres, shows a primary mineral assemblage with olivine, clinopyroxene and amphibole in addition to a groundmass having glassy material and carbonates (ocelli). The Búzios rocks are chemically evolved, mostly of potassic affinity and mainly belong to the miaskitic series. Variation diagrams for major and trace elements show a bimodal distribution, suggesting an origin from different magmatic pulses. The rocks are interpreted as having been derived by fractional crystallization processes from a basanitic parental magma. The SiO2-undersaturated and SiO2-oversaturated associations present in the massif are apparently not linked to a single magmatic source, and in the petrogeny residual system two trends are evident: the first one towards the phonolitic minimum and the second one towards the rhyolitic minimum, possibly pointing to amphibole fractionation. RESUMO: O maciço alcalino da Ilha dos Búzios, do Cretáceo Superior, é intrusivo em charnockitos precambrianos e consiste predominantemente de rochas sieníticas cortadas por grande número de diques, orientados preferencialmente para NE, representando duas suítes distintas: félsica e máfica-ultramáfica. Feldspato alcalino é o mineral mais abundante; outros constituintes são clinopiroxênio, comumente substituído por anfibólio/biotita, e opacos. Minerais acessórios incluem ocasionalmente fases raras contendo Zr, Ti, Nb e elementos terras raras (ETR). Os diques félsicos podem possuir também nefelina (sodalita). A suíte máfica-ultramáfica, particularmente os lamprófiros, apresenta uma assembleia mineralógica primária com olivina, clinopiroxênio e anfibólio, além de massa fundamental com material vítreo e carbonatos (ocelli). As rochas de Búzios são quimicamente evoluídas, de filiação claramente potássica e pertencem sobretudo à série miaskítica. Diagramas de variação para elementos maiores e traços mostram distribuição bimodal, sugerindo a origem a partir de diferentes pulsos magmáticos. As rochas são interpretadas como derivadas por cristalização fracionada a partir de magma parental de composição basanítica. As associações insaturadas e supersaturadas em SiO2 presentes no maciço não estão aparentemente ligadas a uma fonte magmática única, sendo evidentes duas tendências distintas no sistema petrogenético residual: a primeira no sentido do mínimo fonolítico, e a segunda no do mínimo riolítico, possivelmente indicando fracionamento de anfibólio.

The Monte de Trigo alkaline suite is a SiO2-undersaturated syenite-gabbroid association from the Serra do Mar alkaline province. Eudialyte-group minerals (EGMs) occur in one nepheline microsyenite dyke, associated with aegirine-augite, wöhlerite, låvenite, magnetite, zircon, titanite, britholite, and pyrochlore. Major compositional variations include Si (25.09- 25.57 apfu ), Nb (0.31- 0.76 apfu ), Fe (1.40-2.13 apfu ), and Mn (1.36- 2.08 apfu ). The EGMs also contain relatively high contents of Ca (6.13- 7.10 apfu ), moderate enrichment of rare earth elements (0.38-0.67 apfu ), and a relatively low Na content (11.02-12.28 apfu ), which can be correlated with their transitional agpaitic assemblage. EGM compositions indicate a complex solid solution that includes eudialyte, kentbrooksite, feklichevite, zirsilite-(Ce), georgbarsanovite, and manganoeudialyte components. EGM trace element analyses show low Sr and Ba contents and a negative Eu/Eu* anomaly, which are interpreted as characteristic of the parental magma due to the previous fractionation of plagioclase and/or alkali feldspar. The EGMs from the dyke border have higher contents of Fe, Sr (2,161-2,699 ppm), Mg (1,179-3,582 ppm), and Zn (732- 852 ppm) than those at the dyke center. These differences are related to the incorporation of xenoliths and xenocrysts of melatheralitic host rock into the nepheline-syenitic magma followed by crystal-melt diffusive exchange. RESUMO: A suíte alcalina do Monte de Trigo é uma associação sienítico-gabroide que pertence à província alcalina da Serra do Mar. Minerais do grupo da eudialita (EGMs) ocorrem em um dique de nefelina microssienito associados a egirina-augita, wöhlerita, lavenita, magnetita, zircão, titanita, britolita e pirocloro. As principais variações composicionais incluem Si (25,09-25,57 apfu ), Nb (0,31-0,76 apfu ), Fe (1,40-2,13 apfu ) e Mn (1,36-2,08 apfu ). Os EGMs também contêm concentrações relativamente altas de Ca (6,13-7,10 apfu ), enriquecimento moderado de elementos terras raras (0,38-0,67 apfu ) e concentrações relativamente baixas de Na (11,02-12,28 apfu ), o que pode ser correlacionado com uma assembleia agpaítica transicional. As composições dos EGMs indicam uma solução sólida complexa entre os componentes eudialita, kentbrooksita, feklichevita, zirsilita-(Ce), georgbarsanovita e manganoeudialita. Análises de elementos traços das EGMs mostram baixas concentrações de Sr e Ba e anomalia negativa de Eu/Eu*, que são interpretadas como uma característica do magma parental por conta do fracionamento de plagioclásio e/ou feldspato alcalino. Os EGMs da borda do dique possuem concentrações maiores de Fe, Sr (2.161-2.699 ppm), Mg (1.179-3.582 ppm) and Zn (732-852 ppm) que aqueles do centro do dique. Essas diferenças estão relacionadas com a incorporação de xenólitos e xenocristais da rocha encaixante melateralítica no magma nefelina-sienítico seguido de trocas difusivas entre os cristais e o líquido.

The Niquelândia Complex, Brazil, is one of the world's largest mafic–ultramafic plutonic complexes. Like the Mafic Complex of the Ivrea-Verbano Zone, it is affected by a pervasive high-T foliation and shows hypersolidus deformation structures, contains significant inclusions of country-rock paragneiss, and is subdivided into a Lower and an Upper Complex. In this paper, we present new SHRIMP U–Pb zircon ages that provide compelling evidence that the Upper and the Lower Niquelândia Complexes formed during the same igneous event at ca. 790 Ma. Coexistence of syn-magmatic and high-T subsolidus deformation structures indicates that both complexes grew incrementally as large crystal mush bodies which were continuously stretched while fed by pulses of fresh magma. Syn-magmatic recrystallization during this deformation resulted in textures and structures which, although appearing metamorphic, are not ascribable to post-magmatic metamorphic event(s), but are instead characteristic of the growth process in huge and deep mafic intrusions such as both the Niquelândia and Ivrea Complexes. Melting of incorporated country-rock paragneiss continued producing hybrid rocks during the last, vanishing stages of magmatic crystallization. This resulted in the formation of minor, late-stage hybrid rocks, whose presence obscures the record of the main processes of interaction between mantle magmas and crustal components, which may be active at the peak of the igneous events and lead to the generation of eruptible hybrid magmas.

Tholeiitic basaltic and basaltic andesite dikes of Brasiliano (or PanAfrican) age (≈ 600 Ma) intrude the basement of the Nico Perez region, Uruguay. Major and trace element geochemistry of the basalts indicates that they suffered fractionation in shallow magma chambers. The variation in element ratios, which remain virtually unchanged during fractionation (K/Rb, Rb/Ba, Ba/Nb, La/Nb, Zr/Nb and Ti/Zr), indicate that the dikes are not strictly comagmatic. However, they have certain features in common: LILE and LREE enrichment with respect to HFSE and HREE; high Rb/Ba (> 0.9) and Rb/Sr (> 0.08); low K/Rb ( 2; Ba/Nb > 22 Ti/Zr < 60).87Sr/86Sr and143Nd/144Nd at 665 Ma are in the range 0.7052 – 0.7119 and 0.51158 – 0.51177, respectively.

The nomenclature and classification of breccias of igneous origin has been, and still is, a subject of considerable debate, which reflects the ongoing discussions about their formation and emplacement. This is especially valid for those breccias emplaced in plutonic or subvolcanic environments. During field studies in the large alkaline massif of Pocos de Caldas, southern Brazil, the author was confronted by a seemingly bewildering variety of breccias and other pyroclastic rocks, thus providing the impetus for a revision of the subject and the proposal for simple ways of describing and classifying such breccias. Special emphasis was placed on the important group of breccias emplaced at depth ("subsurface breccias") which are notoriously difficult to catalogue and to interpret; subaqueous types are non-existent, or at least very rare, in Pocos de Caldas, and are not dealt with in the present discussion. Breccias should be clearly characterized borrowing terminology and methods from the field of study of fragmental supracrustal (epiclastic and pyroclastic) rocks, both for descriptive purposes (e.g., description of form, sorting, roundness, petrographic variety, etc.) as well as for size ranges; in addition, other textural terms, such as "clast-supported", "clast-matrix supported", and "matrix-supported", should be used to describe the clast-to-matrix relationship. A breccia of igneous origin is defined as a clastic rock with suitable amounts (>;25%) of (angular to rounded) fragments greater than 2 mm which originates as a direct response to igneous phenomena. Genetic aspects of breccia formation are not considered a satisfactory guideline for classification purposes, mostly because breccia-forming processes are still very poorly undeir stood. The mechanisms, which have been proposed in the literature, range from well- researched and qualified hypothesis (such as the "implosion-fluidization" model of Biondi, 1979) to highly unlikely speculations. Still lacking is the ability to take the guesswork out of interpretations of texture and structure of breccias. In the proposed classification, emphasis is placed on descriptive and geologic aspects, in order to define the geologic environment in which the breccia was emplaced. On the one hand, this procedure introduces a standard nomenclature, independent of any genetic meaning (or misconception); additionally, emphasis on detailed description of the geologic environment may ultimately lead to a sounder basis for interpretation. The simplest classification of breccias is therefore threefold, recognizing only "volcanic", " subvolcanic" and "plutonic breccias". The first group comprises all deposits related to volcanic supracrustal activity, including various types of autoclastic flow breccias (including rubble found on advancing block lavas, and talus deposits and collapse fragments shed during cooling and growth of subaerially exposed volcanic domes), tephra deposits, pyroclastic flows and epigenetic sheets formed as a direct response to volcanism (e.g., lahars). The second group, associated with subvolcanic phenomena, includes types found in small, more or less confined bodies (pipes, necks, dikes, sills, irregular bodies: "conduits" in the broadest sense). Among these are autoclastic (e.g.,"friction" breccias) and xenolithic varieties (fragments enclosed within a groundmass of non-fragmented volcanic rocks). The most significant types, the economically important conduit breccias associated with explosive activities, are subdivided, merely for descriptive purposes, into non-intrusive varieties ("shatter" breccias, with angular fragments; "cracked" or "craquelee" rock; collapse breccias, with fragments derived from nearby wall-rocks) and the clearly intrusive types (including both conduit breccias with more or less angular fragments, accompanied by varying but usually important amounts of matrix, and conduit agglomerates, with rounded fragments and little or no matrix). There has been wide speculation as to the proper generating mechanism, fluidization usually being advanced as the main emplacement cause (probably triggered by an initial "implosion"). In well-defined subvolcanic conduits, it is observed that shatter breccias, "cracked" rock, and conduit breccias are distributed in a roughly zoned pattern; the first two types are restricted to wall-rock areas and are probably formed as a response to explosion-related com pressions and decompressions, while the conduit breccias appear as centrally located bodies. The group of "plutonic breccias" are divided into border types (protoclastic and friction breccias marginal to plutons, which are, structurally, cataclasites or milonites), agmatites (fragments in a groundmass of plutonic rock), "metasomatic" substitution varieties, and plutonic conduit breccias (with features similar to those encountered in the equivalent subvolcanic types).