Research ArticleGEOLOGY

Long-term magmatic evolution reveals the beginning of a new caldera cycle at Campi Flegrei

See allHide authors and affiliations

Science Advances  14 Nov 2018:
Vol. 4, no. 11, eaat9401
DOI: 10.1126/sciadv.aat9401
  • Fig. 1 Studied units and sampling localities.

    (A) Variation in time of magma DI (DI = Q + Ab + Or + Ne + Lc normative), crystallinity (% crystals), and eruption size for the sampled eruptions. The calculated crystallinity exclusively accounts for the amount of macrocrysts. The groundmass crystallinity was calculated and subtracted from the total crystallinity when microlites were observed (see Materials and Methods). Approximate ages and relative stratigraphic position of the sampled units were compiled using data from the literature (see the Supplementary Materials). About 200 and 40 km3 of magma dense rock equivalent (DRE) were erupted during the CI (15) and the NYT (21), respectively. The volume of the pre- and post-caldera eruptions is not very well constrained because of the paucity of preserved outcrops. The available field data and drill-hole observations suggest that the post-CI/pre-NYT activity mostly consisted of small-volume eruptions (69). During the post-NYT activity, the erupted volumes were generally less than 0.1 km3 (although some reached up to 1 km3 DRE). Bulk rock data are reported on anhydrous basis. Fe2O3 was converted to FeO (= Fe2O3 × 0.8998) to compare bulk rock data with the matrix glass compositions. Asterisks indicate the units with uncertain relative stratigraphic position (see the Supplementary Materials). In the legend, n denotes the number of bulk rock (x) and glass (y) analyses. (B) Shaded relief map of Campi Flegrei caldera and Campanian Plain showing the sampling localities (numbers correspond to the sites reported in the data file S1). The dashed lines indicate the reconstructed CI and NYT caldera rims (70). A simplified map shows the location of the study area in Southern Italy.

  • Fig. 2 Matrix glass compositions.

    Plot of Eu anomaly [Eu/Eu* = EuN/(SmN × GdN)1/2; trace element concentrations normalized to values from (71)] versus Ba content [in parts per million (ppm)] in matrix glasses from the sampled eruptions at Campi Flegrei. The low Ba-Eu/Eu* region of the plot is enlarged in the inset. In the CI and NYT, white-filled symbols refer to the most evolved compositions, whereas gray-filled symbols refer to the least evolved and predominantly late-erupted compositions (see Fig. 1). Note that the fractional crystallization of a feldspar-dominated mineral assemblage drives the residual liquid toward progressive depletion in Ba, Eu/Eu* (dashed arrow), and Sr. A combined effect of fractional crystallization and crystal-liquid separation produces extracted melts with much higher fractionated geochemical signatures compared to those obtained by simple fractional crystallization (27). This explains why the highly evolved matrix glass compositions (i.e., extracted melts) belong to the crystal-poor units (e.g., pre-CI, early phases of CI, pre-NYT, and Monte Nuovo). Matrix glasses displaying intermediate Ba (and Sr) together with positive Eu anomalies in the caldera-forming units are interpreted as representative of the liquids derived by remelting of a feldspar-dominated cumulate mush (i.e., remelted cumulates) (34). Typical uncertainty (1σ) is smaller than the size of symbols. In the legend, n denotes the number of glass analyses.

  • Fig. 3 Sanidine compositions.

    Ba content (in ppm) in sanidines and back-scattered images of the two types of crystals recognized in the studied units (asterisks indicate the units with uncertain relative stratigraphic position; see the Supplementary Materials). Solid symbols refer to crystal cores, whereas empty symbols refer to crystal rims. Type 1 crystals are zoned and show increasing Sr and Ba contents toward crystal rims (colored symbols). Type 2 crystals are unzoned and show low Sr and Ba contents (gray symbols). Dashed lines indicate the occurrence of type 1 (colored lines) and type 2 (gray lines) crystals in the studied units. Note that only the two caldera-forming eruptions contain both types of sanidine. Typical uncertainty (1σ) is smaller than the size of symbols. Number of sanidine analyses (n): 87 (pre-CI), 181 (CI), 141 (post-CI/pre-NYT), 71 (NYT), 85 (epoch 1), 37 (epoch 2), 44 (epoch 3a), 220 (epoch 3b), and 98 (Monte Nuovo).

  • Fig. 4 Variations of temperature and water content.

    Time paths of equilibrium temperature (°C) and magma water content (wt %) estimated for the studied units (asterisks indicate the units with uncertain relative stratigraphic position; see the Supplementary Materials) using clinopyroxene-liquid thermometry (24) and K-feldspar–liquid hygrometry (25). n indicates the number of mineral-liquid equilibrium couples. Note that no clinopyroxene-liquid equilibrium pairs were obtained for S. Severino 2, Belvedere Miliscola 1, and Verdolino and that no K-feldspars–liquid equilibrium pairs were obtained for Minopoli 1 and 2. Water contents obtained via melt inclusion analyses from the literature (dashed bars) are reported for these two units [1 to 3.5 ± 0.4 wt % (55) and 0.2 to 3 ± 0.5 wt % (56), respectively]. The gray area includes the errors of estimate associated with the clinopyroxene-liquid thermometer (±20°C) and K-feldspar–liquid hygrometer (±0.7 wt %). See Materials and Methods.

  • Fig. 5 Phases of a caldera cycle.

    (A) The caldera stage is characterized by large volume magma withdrawal involving the crystal-poor cap and part of the cumulate mush remobilized after more mafic recharge. This represents the main mechanisms responsible for the generation of gradients in the pyroclastic sequences of caldera-forming eruptions at Campi Flegrei (27, 28). (B) The early post-caldera stage is associated with frequent injections of more mafic magmas of deeper origin into the upper crustal reservoir. Magmas can be erupted along the caldera ring faults or stall into the crust where they interact with the residual cumulate mush triggering remobilization and eruption of crystal-rich material. During this stage, eruption frequency is high and concentrates within the caldera. (C) The transition to the late post-caldera/pre-caldera stage is marked by a decrease of the eruption frequency, which allows magmas to stall in the crust and evolve via fractional crystallization. When the crystallinity of the system reaches ~50 to 70%, melt can be efficiently extracted from the crystal mush forming a crystal-poor and water-rich cap in the upper part of the reservoir (32). Modified after (1).

  • Fig. 6 Thermomechanical model.

    Variations of (A) overpressure (in MPa), (B) reservoir volume (in km3), (C) temperature (in°C), and (D) water content (in wt %) over the past 15 ka at Campi Flegrei caldera obtained using thermomechanical modeling (26). In (A), eruption occurs when the critical overpressure reaches 40 MPa (60) and the magma is mobile [<50% crystals (72)]. The modeled number of eruptions and accumulated volumes (in km3) are indicated for each eruptive epoch (see run no. 1 in table S1). In (B), the crystallinity window suitable for melt extraction is between 50 and 70% crystals (32). In (C) and (D), the equilibrium temperatures and magma water contents obtained by means of clinopyroxene-liquid thermometry and K-feldspar–liquid hygrometry, respectively (Fig. 4), are juxtaposed to the modeled curves for comparison. In (D), the gray curve refers to the H2O saturation limit calculated on the basis of our refined solubility curve for alkaline compositions (fig. S7). See table S1 and figs. S8 and S9 for a comparison with other model results.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/11/eaat9401/DC1

    Fig. S1. Variation of the DI (DI = Q + Ab + Or + Ne + Lc normative) with time at Campi Flegrei.

    Fig. S2. Geochemistry of volcanic rocks from Campi Flegrei.

    Fig. S3. Clinopyroxene compositions.

    Fig. S4. Plagioclase compositions.

    Fig. S5. Biotite compositions.

    Fig. S6. Melting curve.

    Fig. S7. Solubility curve.

    Fig. S8. Effect of varying critical overpressure on the model results.

    Fig. S9. Effect of varying recharge rate on the model results.

    Table S1. Compilation of literature data and model runs.

    Data file S1. Tables reporting sample list, bulk rock and matrix glass analyses, mineral chemistry, and crystallinity of the sampled units.

    References (73100)

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Variation of the DI (DI = Q + Ab + Or + Ne + Lc normative) with time at Campi Flegrei.
    • Fig. S2. Geochemistry of volcanic rocks from Campi Flegrei.
    • Fig. S3. Clinopyroxene compositions.
    • Fig. S4. Plagioclase compositions.
    • Fig. S5. Biotite compositions.
    • Fig. S6. Melting curve.
    • Fig. S7. Solubility curve.
    • Fig. S8. Effect of varying critical overpressure on the model results.
    • Fig. S9. Effect of varying recharge rate on the model results.
    • Table S1. Compilation of literature data and model runs.
    • References (73100)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Data file S1 (Microsoft Excel format). Tables reporting sample list, bulk rock and matrix glass analyses, mineral chemistry, and crystallinity of the sampled units.

    Files in this Data Supplement:

Stay Connected to Science Advances


Editor's Blog

Navigate This Article