Roque Nublo (RN) volcanic complex represent the second magmatic cycle of Gran Canaria subaerial volcanic activity and it’s one of the most distinctive of the island for foids appearance and encompassing a large degree of evolution. However, it was so far somewhat neglected. Geochemical and magmatological features of rocks from RN have been analysed using different methods and investigated basing on both major and trace elements. The Roque Nublo products mainly consist of alkaline rocks with a concentration of SiO2 that ranges from 42.60 wt% to 56.10 wt%. These rocks can be semi-modally classified as tephri-phonolites while TAS diagrams inconsistently classify the samples in a wider range that goes from alkali-basalts to phonolites. Mg# values vs major oxides -diagrams show two different trends, while Cr+Ni distribution is consistent with magmatic differentiation by crystal settling. Further details on magma evolution are given by multielement diagrams using HFSE and LILE. The diagrams show an enrichment in LILE, a characteristics concentration in Zr and negative peaks for U and Rb. LREE/HREE ratios suggest a low degree of partial-melting of the magmatic source and parallel REE pattern highlight the co-magmatic relationship between the rocks of the RN association. On this base is also possible to determine evolutionary sequence of the RN suite. Comparing this sequence with the depositional model from literature and filed survey it’s apparent that the sequence shows an inverse order that can be justified assuming the existence of a zoned magma chamber or multiple chambers in a different state of evolution. Explosivity associated with mafic alkaline magmas requires additional juvenile propellant such as CO2 whose virtual presence needs a re-examination of emplacement mechanism and magma-coolant interaction.

Geo-petrological study of the Roque Nublo cycle (Gran Canaria, Spain)

STOPPA, Francesco
2010

Abstract

Roque Nublo (RN) volcanic complex represent the second magmatic cycle of Gran Canaria subaerial volcanic activity and it’s one of the most distinctive of the island for foids appearance and encompassing a large degree of evolution. However, it was so far somewhat neglected. Geochemical and magmatological features of rocks from RN have been analysed using different methods and investigated basing on both major and trace elements. The Roque Nublo products mainly consist of alkaline rocks with a concentration of SiO2 that ranges from 42.60 wt% to 56.10 wt%. These rocks can be semi-modally classified as tephri-phonolites while TAS diagrams inconsistently classify the samples in a wider range that goes from alkali-basalts to phonolites. Mg# values vs major oxides -diagrams show two different trends, while Cr+Ni distribution is consistent with magmatic differentiation by crystal settling. Further details on magma evolution are given by multielement diagrams using HFSE and LILE. The diagrams show an enrichment in LILE, a characteristics concentration in Zr and negative peaks for U and Rb. LREE/HREE ratios suggest a low degree of partial-melting of the magmatic source and parallel REE pattern highlight the co-magmatic relationship between the rocks of the RN association. On this base is also possible to determine evolutionary sequence of the RN suite. Comparing this sequence with the depositional model from literature and filed survey it’s apparent that the sequence shows an inverse order that can be justified assuming the existence of a zoned magma chamber or multiple chambers in a different state of evolution. Explosivity associated with mafic alkaline magmas requires additional juvenile propellant such as CO2 whose virtual presence needs a re-examination of emplacement mechanism and magma-coolant interaction.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11564/410483
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