Anatomy of a middle Miocene Valles-type caldera cluster: Geology of the Okueyama volcano-plutonic complex, southwest Japan

Takahashi, Masaki

doi:10.1016/0377-0273(86)90039-9

Cited by 39 publications

(23 citation statements)

References 32 publications

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“…The Okueyama granitic body is vertically zoned being granodiorite at the lowest part and changing its composition upward to monzogranite, then aplitic granite containing pegmatite at the top 200 m, and thus differentiated vertically (Takahashi, 1986). They are composed of quartz-oversaturated rocks, except for a small part at 680 m above sea level, which is composed of monzonite (MT680, see Appendix I of Ishihara and Chappell, 2010).…”

Section: Genetic Consideration On the Cape Ashizuri Plutonmentioning

confidence: 99%

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Zircon and REE-rich alkaline plutonic rocks intruded into the accretionary prism at the Cape Ashizuri, Shikoku Island, Japan

Ishihara¹,

Hoshino²

2013

Bull. Geol. Surv. Japan

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Abstract:The Cape Ashizuri body is a small, 12 km 2 , Miocene plutonic complex having gabbroids, syenite, quartz syenite to syenogranite in its southern half and biotite monzogranite in its northern half, right next to the Shimanto accretionary sediments. Chemical analyses indicate that the granitoids have mostly meta-aluminous value of A/CNK<1.0, except for three monzogranite. The granitoids are rich in K 2 O, plotted in the shoshonite-high K fields. The granitoids are also rich in Na 2 O and Rb. Ga content is higher than 18 ppm, indicating characteristics of the A-type granitoids. A distinct characteristic of the Cape Ashizuri granitoids is predominance of HFSE (high-field-strength-element), such as Zr (<1,220 ppm), Hf (25.6 ppm), Nb (<202 ppm), Ta (<14 ppm), LREE (<1002 ppm), HREE (<50.5 ppm), Y (<74 ppm), Th (74.2 ppm). Fluorine is also enriched up to 0.43 wt.%.These HFSE are contained in such common accessory minerals as zircon, ilmenite, allanite and titanite, and rare minerals of fergusonite, chevkinite and others. Zircon is the most common and visible rarely by naked eyes. Zircon in the highest Zr rock, 58A142 sample, contains the maximum values of 2.4 wt.% HfO 2 and 1.0 wt.% Y 2 O 3 . Ilmenite in the 58A142 sample shows 4.3-5.7 wt.% MnO, but that in other quartz syenite shows lower values as 1.7-1.8 wt.% MnO, while its niobium content, up to 3.8 wt.% Nb 2 O 5 , is seen along the rim, indicating the niobium concentrated at the latest magmatic stage. Allanite shows Mn-poor character of the magnetite series (0.44 wt.% MnO), and contains 24.6-25.8 wt.% LREE. The most mafic phase of the gabbroids is 47.0 wt.% SiO 2 and 12.5 wt.% MgO, indicating its origin of the upper mantle. Quartz syenitic rocks have 55-60 wt.% SiO 2 and low Sr 0 ratio of 0.7035, implying a small degree of the partial melting of mafic igneous source rocks in the lower crust for the alkaline rocks. The high contents of HFSE and F were caused by this small degree of the partial melting. The biotite monzogranite in the northern part is considered as a mixed magma generated from the lower igneous crust and overlying accreted sediments of the Shimanto Supergroup. It is interesting to explore hydrothermal REE concentration related to these plutonic and subvolcanic activities.

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Section: Genetic Consideration On the Cape Ashizuri Plutonmentioning

confidence: 99%

“…The data are compared with the I-type ilmenite-series chemistry of the Okueyama pluton (Ishihara and Chappell, 2010), which is vertically zoned calc-alkaline pluton (Takahashi, 1986), occurring in the same Outer Zone of Southwest Japan.…”

Section: Introductionmentioning

confidence: 99%

Zircon and REE-rich alkaline plutonic rocks intruded into the accretionary prism at the Cape Ashizuri, Shikoku Island, Japan

Ishihara¹,

Hoshino²

2013

Bull. Geol. Surv. Japan

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“…Many granite plutons are believed to have approximately fiat roofs [Pitcher, 1978' Lipman, 1984Takahashi, 1986' Lipman et al, 1993' Fiske and Tobbish, 1994' John, 1995. In the 3-D experiments we first used cylindrical reservoirs with fiat roofs; we subsequently investigated collapse into reservoirs of more complex geometry.…”

Section: Experimental Methodsmentioning

confidence: 99%

Experimental study of caldera formation

Roche¹,

Druitt²,

Merle³

2000

J. Geophys. Res.

290

265

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Abstract. Scaled experiments have been carried out on caldera collapse mechanisms, using silicone as analogue magma and dry sand as analogue rock. Experiments were carried out in two and three dimensions using a range of roof aspect ratios (thickness/width 0.2 to 4.5) appropriate for caldera collapse. They reveal a g•neral mechanism of collapse, only weakly dependent on the shape of the reservoir. For low roof aspect ratios (_<1), subsidence starts by flexure of the roof and the formation of outward dipping, reverse ring faults, which in turn trigger formation of peripheral inward dipping, normal ring faults. The subsidence always occurs asymmetrically. In cross section the reverse faults delimit a coherent piston, bounded on each side by an annular zone of inwardly tilted strata located between the reverse and normal ring fault sets. The surface depression consists of a nondeformed area (piston) surrounded by an annular extensional zone (tilted strata). For high aspect ratios (> 1), multiple reverse faults break up the roof into large pieces, and subsidence occurred as a series of nested wedges (2-D) or cones (3-D). The extensional zone dominates the surface depression. In the case where preexisting regional faults do not play a major role, the collapse mechanics of calderas probably depends strongly on the roof aspect ratio. Calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults. The annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias. Collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant.

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“…Both petrography and bulk chemistry imply that 1) the chemical variation of the Toki granite is not solely due to fractional crystallization, and 2) assimilation of crustal host rocks or simultaneous intrusion of diŠer-ent magmas has played a signiˆcant role during the emplacement process. (Mazurek, 2000千木良， 2002Mazurek et al, 2003;Jakob et al, 2003;Bahat et al, 2003; Takahashi, 1986;Nishimura andYanagi, 2000細野・牧野， 2002;Wu et al, 2005) Tuttle and Bowen, 1958;Luth et al, 1964;Luth, 1969)。土岐花崗岩体の貫入定置の際の圧力，水蒸気相の条件にふさわしい花崗岩最小メルト組成として， (Fig. 14) …”

mentioning

confidence: 99%

Zoning of rock facies and chemical composition in the Toki granitic body, Central Japan

Yuguchi¹,

Tsuruta²,

Nishiyama³

2010

Japanese Magazine of Mineralogical and Petrological Sciences

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Anatomy of a middle Miocene Valles-type caldera cluster: Geology of the Okueyama volcano-plutonic complex, southwest Japan

Cited by 39 publications

References 32 publications

Zircon and REE-rich alkaline plutonic rocks intruded into the accretionary prism at the Cape Ashizuri, Shikoku Island, Japan

Zircon and REE-rich alkaline plutonic rocks intruded into the accretionary prism at the Cape Ashizuri, Shikoku Island, Japan

Experimental study of caldera formation

Zoning of rock facies and chemical composition in the Toki granitic body, Central Japan

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