1,721,172 research outputs found
Constraints and current problems for the Caribbean Plate margins evolution: the main results of the Italian-Caribbean research group (IGCP 433)
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A reappraisal of ultra-alkaline Intra-Apennine volcanism in central-southern Italy: evidence for subduction-modified mantle sources
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Petrogenesis and regional chemical correlations of the flood basalt sequence in the Central Deccan Traps, India
No full textFLOW DIRECTIONS FOR SOME RYODACITE IGNIMBRITES ESTIMATED BY ANISOTROPY OF MAGNETIC SUSCEPTIBILITY (AMS) MEASUREMENTS: CENTRAL WESTERN SARDINIA (ITALY)
No full textMiocene shoshonite volcanism in Sardinia: implications for magma sources and geodynamic evolution of the central-western Mediterranean
No full textIn this paper we document the existence of a Miocene shoshonite (SHO) volcanism in Northern Sardinia (Anglona). This occurrence completes the spectrum of orogenic magmas related to the subduction process which developed from the Eocene along the Palaeo-European continental margin, in concert with the opening of the Ligurian-Balearic back-arc basin and southeastward drift/rotation of the Sardinia-Corsica continental block. K-Ar ages show that the oldest volcanics of the area are calcalkaline (CA) basalts and andesites (~. 21. Ma), overlain by 19.7-18.4. Ma-old more potassic products such as high-potassium calcalkaline (HK-CA) and SHO lavas. CA, HK-CA and SHO suites include basalts and differentiated lavas of andesite and latite composition, respectively, that (according to the PELE software modelling) represent ~. 40-45% residual liquid fraction after shallow fractional crystallization. Application of the "Arc Magma Simulator" software suggests that the generation of primary melts of the distinct suites may occur at similar degrees of partial melting (5-8%) and melting pressures (2-2.2. GPa, ~. 60-70. km depth) in the mantle wedge. By contrast, the potassic character of parental melts of CA, HK-CA and SHO suites is controlled by 1) the amount of subducted continental components (possibly terrigenous sediments) and 2) the pressure (depth) at which these metasomatic agents are released from the slab. Results suggest that the slab depth beneath the volcanic district increased from ~. 80-100 to 100-120. km for CA and SHO magmas, respectively. Accordingly, the evolution from CA to SHO magmatism in the same plumbing system could be related to slab deepening and increase of the subduction angle of ~. 5-10° in the time span of 2-3. Ma. This tectono-magmatic scenario conforms to the major anticlockwise rotation (~. 30°) event of the Sardinia block (between 20.5 and 18. Ma). This geodynamic evolution preludes the development of the volcanism in the Apennine-Tyrrhenian domains, where the final collisional/post-collisional stages of subduction were characterized by accentuated slab retreat and roll back, inter-arc extension and eruption of highly potassic magmas in the frontal arc (Roman and Aeolian Provinces)
Petrological modelling of Albanian Ophiolites with particular regard to the Bulqiza Chromite ore deposits
No full textPetrogenesis and tectono-magmatic significance of basalts and mantle peridotites from the Albanian–Greek ophiolites and sub-ophiolitic mélanges. New constraints for the Triassic–Jurassic evolution of the Neo-Tethys in the Dinaride sector.
No full textPlume-related Paranà-Etendeka igneous province: An evolution from plateau to continental rifting and breakup
No full textA critical review of the available multidisciplinary data on the Paranà-Etendeka Province allows for the reconciliation of the controversial aspects of its origin in a coherent tectonomagmatic scenario, in which continental flood basalt (CFB) magmatism evolved from the Paranà plateau s.s. (Stage 1) to progressive continental rifting in Etendeka (Stage 2), and then opened to the South Atlantic at the same latitude; the CFB magmatism is triggered by the prolonged impingement of the proto Tristan plume on the western Gondwana lithosphere. The provinciality of the CFB is evidenced by the incompatible element distribution and Sr-Nd-Pb isotopic data, where the Paranà and Etendeka magmas are more akin to lithospheric and asthenospheric (plume-related) components, respectively. Stage 1 consisted of the rapid outpouring of the Paranà Plateau s.s. CFB (135–134 Ma, ~ 800,000 km3, and eruption rate ~0.8 km3/a) that was zonally arranged with prevailing high-TiO2 (HT) basalts in the central-northern part and low-TiO2 (LT) suites at the southern periphery. The differentiated nature (MgO = 8–4%) of these plateau magmas suggests the variable extent of fractional crystallisation during rise through a relatively thick lithosphere. Petrological modelling, isotopic signatures (87Sr/86Sr 0.70483–0.70620, and εNd(t) from −1.27 to −5.78), and incompatible element distributions approaching the EM1 mantle component suggest that the HT and LT Paranà basalts may be derived from mantle sources located in the lower lithosphere at P 3–4 GPa and a potential temperature (Tp) of 1500–1550 °C. The high Tp recorded (and the relative Texcess 250–300 °C thermal anomaly) can be attained after several million years of lithospheric heating, beginning from the first plume impact, which is represented by precursor alkaline events (145–138 Ma) at the westernmost border of the Paranà plateau. The subsequent rifting (Stage 2, mostly 134–128 Ma) developed SE of the Paranà plateau in relation to the NW drifting of the Gondwana plate over the rising plume and was accompanied by progressive lithospheric arching, thinning, and rifting, which culminated in continental breakup close to the Etendeka border. The concomitant and exclusive appearance, in both the HT and LT suites of this region, of the hottest and deepest (Tp up to ~1590 °C and P up to ~5 GPa) high-MgO sub-lithospheric magmas (87Sr/86Sr 0.70319–0.70533 and εNd(t) from 9.08 to 0.53) is consistent with their generation from the axial zone of the upwelling plume. The basic–acidic bimodal character of CFB magmatism, since the beginning of this stage, must be related to the intensive block faulting of the rifted margins that favoured magma trapping and crystal fractionation to trachydacite and dacite-rhyolite differentiates from the respective HT and LT basalts. Owing to the higher SiO2 and viscosity, the prevailing dacite-rhyolite magmas were more prone to pond in crustal magma chambers, where they experienced assimilation fractional crystallisation (87Sr/86Sr 0.71466–0.72558 and εNd(t) from −5.50 to −9.31) before erupting as extensive rheo-ignimbrites. During the final rifting stage, CFB activity continued until 128 Ma (with sporadic episodes until 122 Ma), and the plume dynamic support gradually vanished beneath the two conjugate South American/South African continental margins, up to the opening of the South Atlantic and hot-spot volcanism of the Rio Grande and Walvis Ridges
Phlegraean Fields volcanism revisited: A critical re-examination of deep eruptive systems and magma evolutionary processes.
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