Search results for "mantle"
showing 10 items of 322 documents
Lower Cretaceous tholeiitic dyke swarms from the Ponta Grossa Arch (southeast Brazil): Petrology, Sr-Nd isotopes and genetic relationships with the P…
1990
The Lower Cretaceous dykes of the Ponta Grossa Arch, the most important dyke swarms in Brazil, are associated with the flood basalts and rare acid flows of the northern Parana basin. The Ponta Grossa (PG) dykes are formed by two-pyroxene tholeiites and rare acid rocks. The basaltic dykes may be distinguished into two main groups: a dominant, high-TiO2 (> 2 wt.%; HTi) group and a subordinate, low-TiO2 (< 2 wt.%; LTi) group, characterized, for similar MgO content, by high and low incompatible-element contents, respectively. Most PG dykes do not show chemical and isotope evidence supporting important crustal contamination. PG dykes with (87Sr86Sr)0 < 0.7060 plot in the mantle array (ϵSr ≈ + 17…
Basalt magmatism along the passive continental margin of SE Brazil (Campos basin)
1992
The SE-Brazil passive continental margin is characterized by tholeiitic magmatism that is particularly widespread in the marginal Campos basin, facing the inland flood basalts of the adjacent Parana basin. Campos magmatism is represented by Early Cretaceous (EC; 134–122 Ma) flood basalts and minor Upper Cretaceous-Early Tertiary basalt flows and intrusives, which were emplaced in a basin with attenuated crustal thickness (20 km). Petrography, mineral chemistry, wholerock geochemistry and Sr−Nd isotope composition emphasize that the EC-Campos basalts have suffered extensive seawater interaction which caused enrichment in MgO, FeO total, K2O, Rb and Ba, and depletion in SiO2 and CaO, while Zr…
Sr-Nd-Pb isotope ratios, geochemical compositions, and40Ar/39Ar data of lavas from San Felix Island (Southeast Pacific): Implications for magma genes…
2000
We present the first trace element and age data combined with new Sr, Nd, and Pb isotope ratios on lavas from San Felix Island in the Southeast Pacific. A 40Ar/39Ar plateau age of 421 ± 18 ka implies young intraplate volcanic activity in this region relative to the ∼22 Ma old volcanism on the neighbouring Easter seamount chain (ESC). The incompatible element compositions of the San Felix magmas are similar to those of EM1-type basalts from Gough, although the isotopic compositions differ. San Felix formed some 20 Ma after the ESC plume affected the plate in this region but no chemical signature of the ESC material is observed in the young volcanic rocks. The composition of the San Felix bas…
Evidence of magmatic activity related to Middle Jurassic and Lower Cretaceous rifting from northeastern Brazil (Ceará-Mirim): K/Ar age, palaeomagneti…
1992
The Mesozoic magmatic activity in the easternmost part of NE Brazil (Ceara-Mirim) is mainly represented by two-pyroxene tholeiitic dykes; only few dykes have alkaline character. K/Ar ages and palaeomagnetism data indicate that Ceara-Mirim dykes are of Middle Jurassic (175-160 Ma) and Early Cretaceous (140-130 Ma) age. Both Middle Jurassic and Lower Cretaceous dykes have high incompatible-element concentrations and TiO2 with the lower contents generally confined to the Middle Jurassic dykes; rare tholeiitic dykes low in TiO2 and incompatible elements are present. Sr/1bNd isotopic and other chemical data do not support appreciable crustal contamination and in a 87Sr86Sr vs. 143Nd144Nd diagram…
Composition and provenance analysis of beach sands in an almost isolated sedimentary system – A field study of the Galápagos Archipelago
2021
The Galapagos Archipelago is the surface expression of an active hotspot or long-lived mantle plume. The Archipelago consists of a group of 13 main islands which are located in the eastern central Pacific Ocean about 1,000 km west of the northern edge of the South American continent, east of the East Pacific Rise and south of the Galapagos spreading center. Because of the large distance to the nearest continental land mass, Galapagos can be seen as an almost isolated sedimentary system. A provenance study conducted on samples collected from seventeen beaches on eleven islands, demonstrates that mineral grains and particles were derived from weathering of predominantly basaltic rocks and wer…
Petrology and geochemistry of submarine volcanism in the Sicily Channel Rift
2006
Submarine magmatism in the Sicily Channel Rift began in the early Pliocene and lasted until almost 200 yr ago. We present here petrological and geochemical data on volcanic rocks dredged from Graham and Nameless banks and Pantelleria seamounts in the Pelagian sector of the Sicily Channel Rift. Petrological evidence suggests that the ascent of magmas to the surface was relatively rapid, probably through channels superimposed over the major tectonic discontinuities of the Rift. Major and trace element data indicate an ocean island basalt affinity for Graham and Nameless bank alkaline lavas and a depleted tholeiitic signature for one Pantelleria seamount, which had a shallower mantle source. S…
Halogens in Mafic and Intermediate-Silica Content Magmas
2018
As volatile and variably mobile components, halogens play key roles in magmatic, metasomatic, mineralizing, and volcanic processes by influencing the physical and chemical properties of melts, fluids, and minerals. Volcanic emission of halogens to the atmosphere leads to long- and short-term impacts on atmospheric chemistry that range from global perturbation of the stratospheric O3 budget to more localized life-threatening contamination of soils and fresh water. The concentrations of F, Cl, Br, and I in melts, fluids, and minerals provide crucial geochemical information and insights into magmatic processes ranging from partial melting to volcanic eruptions. Halogen research is useful for e…
Chemo-probe into the mantle origin of the NW Anatolia Eocene to Miocene volcanic rocks: Implications for the role of, crustal accretion, subduction, …
2017
Post-collisional Cenozoic magmatic activity in NW Anatolia produced widespread volcanism across the region. In the Biga Peninsula, in the west, medium-K calc-alkaline to ultra-K rocks with orogenic geochemical signature were emplaced at similar to 43-15 Ma (Biga orogenic volcanic rocks; BOVR). Volcanic activity in the Central Sakarya region, to the east, is mainly restricted to-53-38 Ma, but also continued during the Early Miocene with small basaltic extrusives (Sakarya orogenic volcanic rocks; SOVR). This study presents a new set of geochemical data (whole rock major and trace elements and Sr-Nd-Pb isotopic compositions), obtained from the Cenozoic calc-alkaline volcanic rocks from these t…
The Nevados de Payachata volcanic region (18�S/69�W, N. Chile) II. Evidence for widespread crustal involvement in Andean magmatism
1990
Volcanism extending over 11 Ma is represented in the rocks of the Nevados de Payachata region, culminating in the formation of two large composite stratocones within the last 500 000 years. Chemically distinct mafic magmas are erupted at a number of parasitic centers. These cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones. Two distinct trends are defined by the intermediate and evolved rocks; a high LILE (large ion lithophile element), TiO2 and Ce/Yb lineage among the youngest rocks (including the two major stratocones), and a more typical calc-alkaline trend among the older (>1 Ma) rock type…
Petrological and structural significance of the Santa Elena-Nicoya ophiolitic complex in Costa Rica and geodynamic implications
1999
Detailed structural and petrological investigations were carried out on the Santa Elena-Nicoya ophiolitic complex in Costa Rica, which is represented by a classic association of mantle tectonites (Santa Elena Peninsula), a cumulitic gabbroic-plagiogranite sequence, and basaltic volcanics and sills (Matapalo and Esperanza Units of the Nicoya Peninsula), with discontinuous radiolarian covers. Despite biostratigraphically different ages (Late Jurassic for Matapalo and Mid-Late Cretaceous for Esperanza) in both units, the major and trace element data, Sr-Nd isotope systematics, and mineral phase crystallization order show identical tholeiitic fractionation trends, where the marked Fe-Ti enrichm…