Добірка наукової літератури з теми "Co-magmatism"

The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.

AbstractAlkaline rock and carbonatite complexes, including the Prairie Lake complex (NW Ontario), are widely distributed in the Canadian region of the Midcontinent Rift in North America. It has been suggested that these complexes were emplaced during the main stage of rifting magmatism and are related to a mantle plume. The Prairie Lake complex is composed of carbonatite, ijolite and potassic nepheline syenite. Two samples of baddeleyite from the carbonatite yield U–Pb ages of 1157.2±2.3 and 1158.2±3.8 Ma, identical to the age of 1163.6±3.6 Ma obtained for baddeleyite from the ijolite. Apatite from the carbonatite yields the same U–Pb age of ~1160 Ma using TIMS, SIMS and laser ablation techniques. These ages indicate that the various rocks within the complex were synchronously emplaced at about 1160 Ma. The carbonatite, ijolite and syenite have identical Sr, Nd and Hf isotopic compositions with a 87Sr/86Sr ratio of ~0.70254, and positive εNd(t)1160 and εHf(t)1160 values of ~+3.5 and ~+4.6, respectively, indicating that the silicate and carbonatitic rocks are co-genetic and related by simple fractional crystallization from a magma derived from a weakly depleted mantle. These age determinations extend the period of magmatism in the Midcontinent Rift in the Lake Superior area to 1160 Ma, but do not indicate whether the magmatism is associated with passive continental rifting or the initial stages of plume-induced rifting.

Neogene basalts in the eastern of the Bureya massif and the adjacent Kursk-Komsomolskaya zone of the Sikhote-Alin fold system occur in the seismically and tectonically active area along the Khingan, Amgun and Tanlu-Kharpi deep faults. Analysis of age constraints on the timing of basaltoid magmatism in the Miocene suggests three phases of magmatism in the study areas: Early Miocene (Udurchukan Formation: 22,6–18,6 Ma); Middle Miocene (Ayakit Complex: 14,8–13,0 Ma), and Late Miocene (Ayakit Complex: 10,0–9,3 Ma). Rock studies have found that basalts (Ayakit plateau), basaltic andesites (Udurchukan plateau), and leucitites (Yadasen Island) are enriched in sodium oxides, potassium, titanium, iron, magnesium, and phosphorus. Two samples of alkaline olivine basalts from the Ayakit plateau yielded high KkTe (578,0) and Ag (172,7); elevated Kk in high field-strength Nb (6,2), Ta (3,4) and radioactive Th (2,7), U (2,4). The contents of Co, Ni, Zr, Mo, W, Zn, Sr, Ba, Hg, light and middle REE are 1,1–1,5 times or even higher than the clarke values for mafic rocks. There is a slight deficit of Sb, Cs, Bi, Cu, Li, Sc, Rb, Tm, Yb, Lu (Kk < 0,7). A similar chemical composition of the SASS basalts (Solnechny settlement and Yadasen Island) suggests that they have a common magma source.

The Murzinka granite area (Central Urals), which combines Murzinka granite pluton and underlying rocks of the Murzinka-Adui metamorphic complex, exhibits an evident wetrending geochemical zonation of magmatism with increasing of Rb, Li, Nb and Ta contents and decreasing ba and Sr contents and K/Rb, zr/Hf and Nb/Ta ratios from vein granites of the Yuzhakovo complex to granites of the Vatikha complex and further to granites of the Murzinka complex (Fershtater et al., 2019). To develop the ideas about geochemical zonation of the Murzinka granite magmatism, as well as about the role of gneisses of the Murzinka-Adui metamorphic complex in the formation of granites, we studied the distribution of trace elements in biotite and feldspars of gneisses and granites. Biotite shows an increase in Li, Rb, Cs, Nb, Ga, zn, Mn, Sc, Sn and Tl contents and a decrease in V, Cr, Co, Ni, Y, zr and ba contents from vein biotites of the Yuzhakovo granites to two-mica granites of the Murzinka complex. The composition of feldspars also changes in this direction: plagioclase is enriched in Li, Rb, Cs, be, zn and depleted in Sr, ba, Ga and Pb and K-feldspar is enriched in Rb and depleted in Sr and ba. The varying trace element composition of rock-forming minerals of gneisses and granites is explained by We-trending change in the composition of a crustal protolith, as well as the formation conditions of granites. Figures 6. Tables 4. References 17.

We investigated hellandite-group mineral phases from the Roman Region, alkali syenite ejecta, by multimethod analyses. They show a complex crystallisation history including co-precipitation of hellandite-(Ce) with brockite, resorption, sub-solidus substitution with mottanaite-(Ce), exsolution of perthite-like ferri-mottanaite-(Ce), overgrowth of an oscillatory-zoned euhedral shell of ferri-mottanaite-(Ce) and late, secondary precipitation of pyrochlore in the cribrose hellandite-(Ce) core. LREE/HREE crossover and a negative Eu anomaly in hellandite-group minerals follows fO2 increase during magma cooling. The distinction among the hellandite-group minerals is based on the element distribution in the M1, M2, M3, M4 and T sites. Additional information on miscibility relationship among the hellandite sensu strictu, tadzhikite, mottanaite, ferri-mottanaite and ciprianiite endmembers derives from molar fraction calculation. We observed that change in composition of hellandite-group minerals mimic the ligands activity in carbothermal-hydrothermal fluids related to carbonatitic magmatism.

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The Ayyarmalai A-type charnockite and A-type alkali granite lies on the south-eastern margin of the Palghat-Cauvery Shear System and provides an example of co-magmatism that was later overprinted with granulite facies metamorphism at ~2.45-2.5Ga. The Palghat-Cauvery Shear System represents an intriguing zone with Neoproterozoic aged granulites (~800-500 Ma) to the south and Archaean granulites (~3000-2500 Ma) to the north; the origins of which are still often disputed. This study presents whole rock major and trace element compositions, mineral chemistry, pressure-temperature estimates and whole rock Sm-Nd, Rb-Sr, Pb-Pb and δ18O isotopic compositions of this A-type charnockite-granite association found at Ayyarmalai, Tamil Nadu, Southern India. The subsequent data from this study suggests that: (1) the Ayyarmalai charnockites from the Palghat-Cauvery Shear System have zircon ages that are synchronous with events in the Northern Granulite Terrain; (2) The Dharwar Craton is a strong candidate for the protolith of these rocks; (3) Evidence of a Neoproterozoic-Cambrian granulite metamorphic event (~520 Ma) appears to be absent in these rocks questioning the existence or location of a Neoproterozoic - Cambrian suture zone proposed for the Palghat-Cauvery Shear System recently. U-Pb zircon ages show zoned igneous cores ~2.65-2.68 Ga ages in both rock types defining the crystallisation age, while the large metamorphic rim overgrowths date the Archaean granulite metamorphic event at ~2.45 - 2.5 Ga. Geochemical data of the Ayyarmalai charnockites reveal a very primitive, unfractionated REE pattern with no Eu-anomaly, ferroan, high K-calc-alkaline, with moderate enrichment of LREE with respect to HREE and fall within the field of high Ba-Sr type granitoids. Extraction of Pyroxene- Hornblende rich cumulates resulted in an intermediate charnockites driving the crystallisation towards the final A-type alkali granite. The A-type alkali granites show a more fractionated REE pattern with a significant Eu-anomaly, ferroan, high-K- calc-alkaline, with enrichment of LREE and depletion in the low Ba-Sr type granitoids. εNd and Nd model ages indicate a highly evolved protolith (εNd(0) =-25.15 to -33.14) that encountered a crustal Archaean source (2.89-3.09 Ga) causing contamination as the magmas ascended. Harker diagrams, Nd data (isochron age, ~2519 Ma) and U-Pb zircon crystallisation ages suggest a co-magmatic relationship between the charnockite and alkali granite. Conventional geothermometry/barometry suggest minimum pressure-temperature conditions existed at 740 – 750°C and P=5.61 – 5.84 kbar. The data presented from this study is consistent with a magmatic origin of these charnockites favouring the early crystallisation of orthopyroxene. The correlation with the data from the Dharwar Craton suggest that the study region may have encountered Dharwar Craton on magmatic ascent causing crustal contamination
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010

Tese de doutoramento (co-tutela), Ciências Geofísicas e da Geoinformação (Geofísica), Université de Toulouse, Universidade de Lisboa, 2013
The Jurassic-Cretaceous Iberian kinematics is still not well understood, mainly due to limitations on reconstructions based on marine magnetic anomalies (uncertainties about the nature of the crust and presence of the Cretaceous Normal Superchron) and on paleomagnetic data (insu cient and sometimes low-quality data, low age resolution, tectonic in uences and remagnetizations). In this thesis, we rst provide new high-quality paleomagnetic poles for the Late Cretaceous of Iberia, calculated from two ma c sills (Foz da Fonte, 88 Ma et Pa co de Ilhas, 94 Ma), which enable better calibrating the Iberian apparent polar wander path (APWP) at the Late Cretaceous. A detailed study of magnetic mineralogy and microscopic observations (electronic and optic) con rm a primary magnetization carried by titanomagnetite. We then present a new compilation of the published paleomagnetic data for the Late Jurassic-Cretaceous of Iberia from which we calculate mean poles for six time periods. By rotating these mean poles to the African frame using Euler rotation poles from kinematic models we evaluate their position with respect to the global APWP in African coordinates. We verify that while post-rift mean poles (from 70 to 120 Ma) are in agreement with the APWP, poles corresponding to pre-rift times (older than 120 Ma) do not t the APWP, revealing an incompatibility between the di erent types of data. We next seek for the cause of this incompatibility, which may be due to the APWP (we show that this is unlikely since di erences between di erent APWPs are not signi cative), euler poles (we show that a discard is veri ed using both end-member models of Olivet [1996] and Vissers & Meijer [2012]) and/or paleomagnetic data. We solve the inverse problem of nding the Euler poles that t the pre-rift mean paleomagnetic poles with the GAPWP and then test their implications on Iberian reconstructions. We nd that Iberian poles from the Early Cretaceous (mean poles for 123 and 130 Ma) are incompatible with the GAPWP, bringing into question their validity. Contrarily, Late Jurassic data (mean pole at 151 Ma) are compatible with the GAPWP and thus can be considered reliable. These results enable us to constrain a reconstruction of Iberia and surrounding plates at 150 Ma. These results highlight that more high-quality paleomagnetic data are needed for the Iberian plate particularly at the Early Cretaceous, and that kinematic models based on the interpretation of marine magnetic anomalies should be reviewed. In the last part of this thesis we present a study of the anisotropy of magnetic susceptibility of the Foz da Fonte sill, 7-8 m width. A detailed vertical sampling of the sill allowed us to distinguish three domains with respect to the magnetic fabric, which we relate with distinct regimes of magma ow. The chilled margins, 50 cm apart from the margins, where low anisotropies suggest low velocity gradients and heterogeneous ow paths during initial emplacement stages; in the center of the sill, where undisturbed magma ow is expected, low anisotropies suggest low shear gradients and magma displacement close to pure translation; and intermediate zones, where high anisotropy values are ascribed to maximum shear gradient zones. A mean orientation at N310 of the magnetic lineation agrees with the direction of elongation of vesicles and is interpreted as magma ow direction. In addition, a sense of ow toward the southeast is inferred from the mirror imbrication of the magnetic foliation and lineation at the borders. Implications of these results are discussed with respect to the West Iberian Late Cretaceous magmatism, by integrating magnetic anomalies, isotope chronology and tectonics. The Cabo Raso anomaly is proposed as the magmatic source of the Foz da Fonte sill, and a 350 km long magmatic structure is proposed to connect the region of Sintra-Cabo Raso to the Tore seamount.
Fundação para a Ciência e a Tecnologia (FCT, projetos PEst-OE/CTE/LA0019/2013, PTDC/CTE-GIX/117298/2010, PTDC/CTEGIN/68462/2006); TOPOMED (TOPOEUROPE/0001/2007); Prémio Fundação Calouste Gulbenkian