Petrology of Moriyoshi volcano magma mixing event after caldera collapse Petrography and geochemistry of the volcanic rocks of Moriyoshi volcano, nort

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1 Petrology of Moriyoshi volcano magma mixing event after caldera collapse Petrography and geochemistry of the volcanic rocks of Moriyoshi volcano, northeastern Japan, reveals the mechanism which had produced the different chemical trends of the rocks between the earlier stage (pre-caldera activity) and the later one (post-caldera activity). In the later stage, phenocryst assemblage of basalt and andesite (SiO2=53-66%) is complex (olivine+orthopyroxene+hornblende+clinopyroxene+fe-ti oxide+quartz+ plagioclase). The compositions of phenocrystic minerals, clinopyroxene (Wo45 En40), orthopyroxene (Wo2 En60) and plagioclase (An 35-55), are nearly constant in spite of the wide variation of whole-rock chemistry. Magnesian olivine phenocrysts (Fo 78-71) are in disequilibrium with quartz, iron-rich orthopyrox ene and clinopyroxene. Compositional zonations of phenocrystic minerals are normal in olivine and reverse in clinopyroxene, orthopyroxene and plagioclase. These features cannot be explained in terms of simple crystallization differentiation model. The linear trends on variation diagrams indicate that two magmas, with different temperature and compositions, were mixed. Low temperature magma (SiO2=66%) would contain plagioclase, quartz, orthopyroxene, clinopyroxene and hornblende phenocrysts. This dacitic magma was mixed with basaltic magma, containing olivine phenocryst, to produce the calc-alkaline trend (low iron-enrichment on the SiO2-FeO / MgO diagram) in the later stage. In the earlier stage, the rocks consist of augite-hypersthene andesite to dacite, which are accompanied by a small amount of olivine-bearing augite-hypersthene andesite. The compositions of phenocrystic minerals gradually change according to whole-rock chemistry. The distinct disequilibrium petrographic features are not found in olivine free rocks. On the contrary, in olivine-bearing rocks, normally zoned olivine phenocryst (Fo87-73) is in disequilibrium with reversely zoned orthopyroxene (mg value 68-62) and clinopyroxene (72-67). The olivine-bearing rocks would be produced by magma mixing process, between basaltic magma and andesitic magma. But magma mixing process at the earlier stage is negligible, because the proportion of mixed magma to eruptives of the earlier stage is estimated to be less than 10%. Therefore, the tholeiitic trend (strong iron-enrichment on the SiO2-FeO /MgO diagram) of these rocks can be explained in terms of fractional crystallization mechanism. Basaltic magma would not have crystallized calcic plagioclase with olivine phenocryst (Fo87-71). This delay of crystallization of plagioclase does not depend on H20 content judging from F content. Crystallization of plagioclase is supressed by crystallization of basaltic magma at high pressure. So basaltic magma of Moriyoshi volcano had stopped at the deeper level (>25 km) and crystallized olivine phenocryst. This fractionated basaltic magma had rised rapidly to shallower level magma chamber to mix with andesitic or dacitic magma. Mixed magma effused mainly after the formation of caldera. In the earlier stage, which is the

2 stage of constructing a stratovolcano, if magma mixing process had occurred, mixed magma could not rise easily under the regional compressional stress field on the northeastern Japan. Hence evidence of magma mixing would not be clear. In the later stage, mixed magma would have rised easily through the crack formed by the caldera collapse. Fig. 1. Index map of the Moriyoshi volcano. Other areas represent the Quarternary volcanoes. The zonation of those volcanoes are foll owed by Takahashi and Fujinawa (1983) and Shimotori et al. (1984).

3 Table 1. Representative chemical compositions of olivine Fig. 2. Simplified geological map of the Moriyo shi volcano. Abbreviations: ph, phenocryst; mph, microphenocryst; c, core; r, rim; Fo, forsterite.

4 Fig. 3. Chemical compositions of pyroxenes and olivines of representative rocks (atomic ratio). Solid circles are the core of phenocryst, which is connected with the rim by the solid line. Open circles represent the core of microphenocryst or groundmass minerals (except for E-2-9 and L- 1). In L-1, open circles represent the core of microphenocryst and crosses are the core of groundmass minerals. Dotted line (in E-2-9 and L-1) connects between phenocryst and reaction rim. Sample numbers are the same as those in Nakagawa (1983).

5 Fig. 4. Ti, Al, Mn and Ca contents of the core of orthopyroxene phenocryst Vertical axes represent the cation numbers based on pyroxene formula (0=6). Horizontal axes represent the atomic ratio..

6 Table 2. Representative chemical compositions of orthopyroxene Abbreviations: gm, groundmass; Wo, wollastonite; En, enstatite; Fs, ferrosilite; mg., 100 ~Mg/(Mg+Fe); others are the same as those in Table 1.

7 Table 3. Representative chemical compositions of clinopyroxene Abbreviations: gm, groundmass; others are the same as those in Table 2. Fig. 5. Ti, Al, Mn and Ca contents of the core of clinopyroxene phenocrysts. Vertical and horizontal axes are the same as those in Fig. 4.

8 Table 4. Representative chemical compositions of hornblende Abbreviations are the same as those in Table 1.

9 Table 5. Representative chemical compositions of Fe-Ti oxides Recalculated methods are followed by Carmichael (1967). Abbreviations are the same as those in Table 2 (ulvo., ulvospinel). Table 6. Representative chemical compositions of plagioclase Abbreviations: An, anorthite; Ab, albite; Or, orthoclase; others are the same as those in Table 2.

10 Fig. 6. Chemical compositions of plagioclase of representative rocks (atomic ratio). Sample numbers are the same as those in Nakagawa (1983).

Fig. 7. "Banded lava" (Ishimoriyama lava). Dark color band is basic andesite (Si02= 55%), containing olivine phenocryst. Light color band is hornblende dacite (SiOz=66%, L-7). Boundaries of both Fig.

11 Fig. 7. "Banded lava" (Ishimoriyama lava). Dark color band is basic andesite (Si02= 55%), containing olivine phenocryst. Light color band is hornblende dacite (SiOz=66%, L-7). Boundaries of both Fig. 8. Chemical compositions of mafic minerals bands are not sharp. (L-6) plotted in terms of Ca, Mg and Fe (atomic %). Closed circle are the core of phenocrysts, which is connected with the rim by the solid line. Open circles are the core of microphenocryst. Open triangles represent the core of pyroxenes in "basaltic groundmass".

12 Table 7. Data sources of Fig. 9 Akita-komagatake volcano (Nakagawa unpublished data) Rabaul caldera (Herring, 1977) Jeju volcanic island ( Lee, 1983 ) Myoko and Kurohime volcanoes ( Sakuyama, 1981 ) Higashi-Izu monogenetic volcanoes ( Miyajima, 1983 ) Funagata volcano ( Fujinawa, 1982 ) Fig. 9. Fe2+-Mg partitioning between clinopyroxene and olivine phenocrysts. Shaded area is compositional range in the rocks of L-stage (except for L-7). Closed cir cles are the rocks, containing normally zoned olivine and clinopyroxene phenocrysts (Table 7). Fig. 10. Compositional ranges (vertical bars) of phenocrystic minerals (L-stage) plotted on whole-rock SiO2 wt% (water free). Closed circles are average compositions. Abbreviations are following: OPX, orthopyroxene; CPX, clinopyroxene; PL, plagioclase; An, anorthite.

13 Fig. 12. The Si02-FeOt/MgO diagram (Fe0t, total iron as FeO). Open triangles are the rocks of E-1 stage. Open circles and squears represent the rocks from E-2 and E-3 stages, respectively. Closed circles are the rocks of L-stage. Solid line shows the boundary between the CA and TH series (after Miyashiro, 1974). Fig. 11. Variation diagram of rocks from L- stage (water free, data from Nakagawa (1983) and Nakagawa et al. (1984)).

14 Fig. 13. Compositional ranges (vertical bars) of phenocrystic minerals (E-2 and E-3 stages) plotted on whole-rock SiO2 wt% (water free). Closed circles are the average chemical compositions in respective rocks. * are olivine-bearing rocks. Abbreviations are the same as those in Fig. 10.

16 Fig. 14. The F-SiO2 diagram of the Quarternary volcanic rocks from northeastern Japan. Open circles are the tholeiitic rocks from the Sekiryou volcanic zone (after Ishikawa et al., 1980). Open triangles are the hornblende-free calc-alkaline rocks from Chokai volcano (after Ishikawa et al., 1980). Closed circles represent the hornblende-free rocks from Moriyoshi volcano (Nakagawa unpublished data).

contrasts between Atlantic and Pacific spread ing axes. J. Geol. Soc. London, 138, 695-712. Fujimaki, H. and Aoki, K.

17 contrasts between Atlantic and Pacific spread ing axes. J. Geol. Soc. London, 138, Fujimaki, H. and Aoki, K. (1980), Quantitative microanalyses of silicates, oxides and sulfides using an energy-dispersive type electron probe. Sci. Reb. Tohoku Univ., Ser Gerlach, D.C. and Grove, T.L. (1982), Petrology of Medicine Highland volcanics: characteriza tion of end members of magma mixing. Contrib. Mineral. Petrol., 80, Grove, T.L., Gerlach, D.C. and Sando, T.W. (1982), Origin of calc-alkaline series lavas at Medicine Lake volcano by fractionation, assimilation Aoki, K., Ishikawa, K. and Kanisawa, S. (1981), and mixing. Contrib. Mineral. Petrol., 80,160 Fluorine geochemistry of basaltic rocks from continental and oceanic regions and Hashizume, M., Oike, K., Asano, S., Hamaguchi, H., petrogenetic application. Contrib. Mineral. Okada, A., Murauchi, S., Shima, E. and Nogo Petrol., 76, shi, M. (1968), Crustal structure in the profile Aoki, K. and Fujimaki, H. (1982), Petrology and geochemistry of calc-alkaline andesite of presumed upper mantle origin from Itinome gata, Japan. Amer. Mineral., 67, Buddington, A.F. and Lindsley, D.H. (1964), Iron titanium oxide minerals and synthetic equiva lents. J. Petrol., 5, , Carmichael, I.S.E. (1967), The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesian silicates. Contrib. Mineral. Petrol., 14, Choen, L.H., Ito, K. and Kennedy, G.C. (1967), Melting and phase relations in an anhydrous basalt to 40 kilobars. Amer. J. Sci., 265, Eggler, D.H. (1972), Water-saturated and under saturated melting relations in Paricutin an desite and an estimate of water content in the natural magma. Contrib. Mineral. Petrol., 34, Eggler, D.H. and Burnham, C.W. (1973), Crystallization and fractionation trends in the system andesite-h2o-co2-02 at pressures to 10 kb. Geol. Soc. Amer. Bull., 84, Eichelberger, J.C. (1975), Origin of andesite and dacite: evidence of mixing at Glass Mountain in California and at other circum-pacific vol canoes. Geol. Soc. Amer. Bull., 86, Eichelberger, J.C. (1978), Andesites in island arcs and continental margins: relationship to crus tal evolution. Bull. Volcanol., 41, Flower, M.F.J. (1981), Thermal and kinematic control on ocean-ridge magma fractionation: across the northeastern part of Honshu, Japan, as derived from exprosion seismic observa tions. Part 2. Crustal structure. Bull. Earthq. Res. Inst., 46, Herring, R.E. (1977), Mineralogy and proposed P- T paths of basaltic lavas from Rabaul caldera, Papua New Guinea. Contrib. Mineral. Petrol., 61, Ishikawa, K., Kanisawa, S. and Aoki, K. (1980), Content and behavior of fluorine in Japanese Quarternary volcanic rocks and petrogenetic application. J. Volcanol. Geotherm. Res., 8, Jakes, P. and White, A.J.R. (1972), Hornblendes from calc-alkaline volcanic rocks island arcs and continental margins. Amer. Mineral., 57, Kawano, Y., Yagi, K. and Aoki, K. (1961), Petro graphy and petrochemistry of the volcanic rocks of Quaternary volcanoes of northeastern Japan. Sci. Rep. Tohoku Univ., Ser. 3,7,1-46. Kouchi, A. and Sunagawa, 1. (1982), Experimental study of mixing of basaltic and dacitic mag mas. Sci. Rep. Tohoku Univ., Ser. 3, 15, Kuno, H. (1960), High-alumina basalt. J. Petrol., 1, Kuno, H. (1966), Lateral variation of basalt magma type across continental margins and island

arcs, Bull. Volcanol., 29, 195-222. Kuno, H. (1968), Differentiation of basalt magmas. In : Hess, H.H. and Poldervaart, A. (eds.) Basalts, vol 2, Willey, New York, 624-688. Leake, B.E.

18 arcs, Bull. Volcanol., 29, Kuno, H. (1968), Differentiation of basalt magmas. In : Hess, H.H. and Poldervaart, A. (eds.) Basalts, vol 2, Willey, New York, Leake, B.E. (1978), Normenclature of amphiboles. Can. Mineral., 16, Lee, M.W. (1983), Petrology and geochemistry of Jeju volcanic island, Korea. Sci. Rep. Tohoku Univ., Ser. 3, 16, (1981), Petrology of rhyolite and dacite erupt ed in last 300 years from Usu volcano, Japan. Abstract, 1981 IAVCEI Symposium, Volc. Soc. Japan, Presnall, D.C., Dixon, S.A., Dixon, J.R., O'Donnell, T.H., Brenner, N.L., Schrock, R.L. and Dycus, D.W. (1978), Liquidus phase ralations on the Lofgren, G. (1980), Experimental studies on the join diopside-frosterite-anorthite from 1 atm dynamic crystallization of silicate melts. In: to 20 kb: their bearing on the generation and Hargraves, R.B. (ed.) Physics of magmatic crystallization of basaltic magma. Contrib. processes. Princeton. 585p Mineral. Petrol., 66, Loomis, T.P. (1981), An investigation of disequili Rhodes, J.M., Dungan, M.A., Blanchard, D.P. and brium growth processes of plagioclase in the Long, P.E. (1979), Magma mixing at Mid system anorthite-albite-water by methods of - Ocean Ridges: evidence from basalts drilled numerical simulation. Contrib. Mineral. Pet near 22N on the Mid-Atlantic Ridge. rol., 76, Tectonophysics, 55, MacDonald, G.A. and Katsura, T. (1965), Eruption Sakuyama, M. (1979a), Evidence of magma mix of Lassen Peak, Cascade range, California, in ing: petrological study of Shirouma-Oike 1915: example of mixed magmas. Geol. Soc. calc-alkaline andesite volcano, Japan. J. Amer. Bull., 76, Volcanol. Geotherm. Res., 5, Matsui, Y. and Nishizawa,O. (1974), Iron (II)- Sakuyama, M. (1979b), Lateral variations of H2O magnesium exchange equilibrium between contents in Quaternary magmas of northeast olivine and calcium-free pyroxene over a tem ern Japan. Earth Planet. Sci. Lett., 43, perature range 800 Ž to 1300 Ž. Bull. Soc. Fr. Sakuyama, M. (1981), Petrological study of the Mineral. Crystallogr., 97, Myoko and Kurohime volcanoes, Japan: crys tallization sequence and evidence for magma mixing. J. Petrol., 22, Sakuyama, M. (1983), Petrology of arc volcanic rocks and their origin by mantle diapirs. J. Volcanol. Geotherm. Res., 18, Sakuyama, M. and Koyaguchi, T., (1984), Magma mixing in mantle xenolith-bearing calc-alkalic ejecta, Ichinomegata volcano, northeastern Japan. J. Volcanol. Geotherm. Res., 22, Sigurdsson, H. and Sparks, R.S.J. (1981), Petrology of rhyolitic and mixed magma ejecta from the Nakamura, K. (1977), Volcanoes as possible indica 1875 eruption of Askja, Iceland. J. Petrol., 22, tors of tectonic stress orientation-principle and proposal. J. Volcanol. Geotherm. Res., 2, Nakamura, K. and Uyeda, S. (1980), Stress gradi ent in arc-back arc regions and plate subduc tion. J. Geophys. Res., 85, Obata, M., Banno, S. and Mori, T. (1974), The iron magnesium partitioning between naturally oc curring coexisting olivine and Ca-rich clinopy roxene: an application of the simple mixture model to olivine solid solution. Bull. Soc. Fr. Yanagi, T. and Ishizaka, K. (1978), Batch Mineral. Crystallogr., 97, fractionation model for the evolution of vol Okumura, K., Soya, T., Ono, K. and Satoh, H. canic rocks in island arc: an example from

19 central Japan. Earth Planet. Sci. Lett., 40, Yoder, H.S. and Tilley, C.E. (1962), Origin of basalt magmas: an experimental study of natural and synthetic rock systems. J. Petrol., 3, Worner, G. and Wright, T.L. (1984), Evidence for magma mixing within the Laacher See magma chamber (east Fifel, Germany), J. Volcanol. Geotherm. Res., 22,

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