Oxygen isotope geochemistry of the potassic igneous rocks from the Roccamonfina volcano, Roman comagmatic region, Italy

https://doi.org/10.1016/0012-821X(79)90067-0Get rights and content

Abstract

18O/16O measurements were made on 80 samples of lavas, pyroclastics, and xenolithic nodules from the 0.05- to 1.54-m.y.-old Roccamonfina volcano. The δ18O values of these magmas varied from +5.6 to +10.1 in the High-K Series (HKS) and +6.6 to +8.8 in the Low-K Series (LKS). The xenolithic nodules, many of which are HKS cumulates, crystallized from magmas with δ18O= +7.8to+10.3. These data indicate that assimilation of high-18O country rocks (pelitic schists, flysch, and some carbonates) was an important petrologic process during fractional crystallization of both the early, HKS magmas (leucite-bearing tephrites, leucitites, and phonolites) and the later, LKS magmas (trachybasalts, trachyandesites, and trachytes). Combined with87Sr/86Sr, Pb isotope, and143Nd/144Nd data obtained by other workers from the same outcrop localities, the18O/16O data prove that:

  • (1)|

    The assimilated country rocks had relatively high87Sr/86Sr values (0.710–0.720), low143Nd/144Nd values (εNd ≈ −10to−15), and206Pb/204Pb values of about 18.70.

  • (2)|

    The HKS and LKS represent completely separate trends of magmatic differentiation and different parent magmas.

  • (3)|

    The HKS parent magma (leucite basanite?) probably had δ18O≈ +6.0and87Sr/86Sr≈ 0.708, while the LKS parent magma (trachybasalt?) had δ18O≈ 6.5and87Sr/86Sr≈ 0.706.

  • (4)|

    The HKS and LKS parent magmas are only indirectly related genetically, perhpps in their source regions in the upper mantle, or during an earlier episode of wall rock-magma interaction in the lower crust.

  • (5)|

    Although wall rock assimilation has played an important role in determining the isotopic and trace element characteristics of these magmas, the liquid line-of-descent and the changes in major element chemistry were dominated by fractional crystallization.

  • (6)|

    The energy required to heat up and dissolve the assimilated rocks was provided by the latent heat associated with concurrent fractional crystallization of the cumulates (as represented by some of the plutonic nodules).

  • (7)|

    The oxygen and strontium isotopic changes at Roccamonfina, although very significant, are much less than in the undersaturated magmas of the Roman Province further to the north. This is apparently because during and prior to the Quaternary potassic vulcanism, the latter terrane was invaded and heated by anatectic magmas associated with the Tuscan rhyolitic event, thus creating conditions favorable for much greater crustal assimilation.

Reference (51)

  • GiannettiB.

    Nuove ricerche petrografiche e petrogenetiche sulle lave fonolitiche della caldera vulcanica di Roccamonfina

    Atti Soc. Tosc. Sci. Nat., Mem.

    (1974)
  • TedescoC.

    Main lines of the history of the Roccamonfina volcano

    Bull. Volcanol.

    (1965)
  • GiannettiB.

    Studio geologico-petrografico della caldera del vulcano di Roccamonfina

    Boll. Serv. Geol. Ital.

    (1978)
  • CoxK.G. et al.

    Isotopic evidence for the derivation of some Roman Region volcanics from anomalously enriched mantle

    Contrib. Mineral. Petrol.

    (1976)
  • ArévaloC.P. et al.

    Zur Petrochemie des Roccamonfina-Vulkans (Prov. Caserta, Italien)

    Schweiz. Mineral. Petrogr. Mitt.

    (1962)
  • B. Turi, H.P. Taylor, Jr., P. Di Girolamo and M. Preite Martinez,18O/16O ratios of the volcanic rocks from the Pontine...
  • EverndenJ.F. et al.

    The potassium-argon dating of late Cenozoic rocks in East Africa and Italy

    Current Anthropol.

    (1965)
  • GaspariniP. et al.

    K-Ar dating of Italian Plio-Pleistocene volcanic rocks

    Earth Planet. Sci. Lett.

    (1967)
  • CortiniM. et al.

    Geocronologia e paleomagnetismo del vulcano Roccamonfina

    Ann. Geofis.

    (1975)
  • GiannettiB. et al.

    Datazioni K-Ar di lave leucitiche dello strato-vulcano di Roccamonfina

    Soc. Ital. Mineral. Petrol.

    (1979)
  • BarberiF. et al.

    The Campanian Ignimbrite: a major prehistoric eruption in the Neapolitan area (Italy)

    Bull. Volcanol.

    (1978)
  • Di GirolamoP. et al.

    Zur Stellung des grauen Campanichen Tuffs, innerhalb des quartären Vulkanismus Campaniens (Süd Italien)

    Ber. Naturforsch. Ges. Freiburg im Breisgau

    (1972)
  • B. Giannetti and D. Cozzupoli, The geology of Roccamonfina caldera (Campanian Province, Italy), unpublished...
  • GiannettiB.

    Petrografia del monte Tuororame (Vulcano di Roccamonfina)

    Atti. Acc. Sci. Torino

    (1972–1973)
  • Di GirolamoP.

    Rilevamento petrografico nel settore SW (Sessa Aurunca) del Vulcano di Roccamonfina

    Rend. Acc. Sci. Fis. Mat.

    (1968)
  • Cited by (74)

    • A metasomatized <sup>18</sup>O-rich veined lithospheric mantle source for ultrapotassic magmas

      2021, Lithos
      Citation Excerpt :

      The strongly 18O-enriched character of the Italian UPRs has been long recognized and remains a hotly debated topic. Holm and Munksgaard (1986) considered that the high δ18O values were inherited from a metasomatized parental mantle, whereas others have argued that they most likely resulted from crustal contamination (Peccerillo et al., 2010; Taylor Jr. et al., 1979; Turi et al., 1986). The Himalayan UPRs also have high bulk rock δ18O values of 7.6–11.0‰ (Miller et al., 1999; Zhao et al., 2009).

    • Mineralogical, geochemical and isotopic features of tuffs from the CFDDP drill hole: Hydrothermal activity in the eastern side of the Campi Flegrei volcano (southern Italy)

      2015, Journal of Volcanology and Geothermal Research
      Citation Excerpt :

      The radiogenic isotope values of the Phlegraean bulk pumice sample (shoshonite to trachy-phonolite) are well-known as they are measured on a large dataset: 87Sr/86Sr varies between 0.7068 and 0.7086, 143Nd/144Nd between 0.51236 and 0.51252, 206Pb/204Pb between 18.85 and 19.25 and δ11B between − 6.8 and − 10.6‰ (see Pappalardo et al., 2002; Tonarini et al., 2009; Di Renzo et al., 2011). Few δ18O measurements have been published and range from 6.97 to 8.28‰ (Turi and Taylor, 1976; Taylor et al., 1979). The Sr-isotope ratios are generally higher than those measured in the rocks from the nearby volcanic fields of Ischia and Procida, with the exception of products older than the Campanian Ignimbrite (De Astis et al., 2004), which overlap in terms of Sr-isotope geochemistry (e.g., De Vivo et al., 1989; Caprarelli et al., 1997).

    View all citing articles on Scopus
    View full text