Volcano volcanic zones

Figure 1.167. Sulfur content vs. value for Quaternary volcanic rocks of Japan. Field bounded by solid lines show two volcanoes (AK and HK), two volcanic zones (NA and CH) in Northeast Japan, three volcanic belts (IM, SW and RY), alkaline rocks (AL) and volcanic rocks of unusually high values (HI) in Ryukyu belt. Symbols surrounded by small circles show S S values of Satsuma-Iwojima volcanic rocks in West Japan (Ueda and Sakai, 1984).

Three U-Th isochrons are available from the Nevados de Payachata volcano (Central Volcanic Zone of Chile) (Bourdon et al. 2000) one rhyolite sample gives an age similar to the eruption age, while two other give older ages, in particular a dacite whose crystallization age is 100 ka older than the eruption age. 

In contrast to the southern volcanic zone, Parinacota volcano lies on very thick continental crust (> 70 km) in the central volcanic zone of Chile. Bourdon et al. (2000a) showed that young Parinacota lavas encompass a wide range of U-Th disequilibria. excesses were attributed to fluid addition to the mantle wedge but °Th-excesses in lavas from the same volcano are more difficult to explain. The lavas with °Th-excesses also have low ( °Th/ Th) (< 0.6) characteristic of lower continental crust characterized by low Th/U and in their preferred model. Bourdon et al. (2000a) attributed the °Th-excesses to contamination by partial melts, formed in the presence of residual garnet, of old lower crustal materials. 

The volcanoes of the Roman Province developed in a region characterised by Late Miocene-Quaternary extensional tectonics related to the eastward migration of Apennine mountain range and to the contemporaneous opening of the Tyrrhenian Sea. The volcanic zone is characterised by a system of Upper Miocene to Pleistocene NW-SE basins, developed along normal faults and intersected by strike-slip NE-SW faults (Bartolini et al. 1982). Both fault systems represent zones of crustal weakness along which Roman potassic magmas were intruded. 

Hickey-Vargas R., Abdollahi M. J., Parada M. A., Lopezesco-bar L., and Frey F. A. (1995) Cmstal xenoliths from Calbuco volcano, Andean southern volcanic zone—implications for cmstal composition and magma-emst interaction. Contrib. Mineral. Petrol. 119(4), 331-344. 

Bourdon E., Eissen J.-P., Monzier M., Robin C., Martin H., Gotten J., and Hall M. L. (2002) Adakite-Uke lavas from Antisana Volcano (Ecuador) evidence from slab melt metasomatism beneath the Andean northern volcanic zone. J. Petrol. 192, 561-570. 

Feeley TC, Sharp ZD (1995) 0-18/0-16 isotope geochemistry of silicic lava flows erapted from volcano Hague, Andean central volcanic zone. Earth Planet Sci Letters 133 239-254 Fourcade S, Maury RC, Defant MJ, McDermott F (1994) Mantle metasomatic emichment versus arc crast contamination in the Philippines Oxygen isotope study of Batan ultramafic nodules and northern Luzon arc lavas. Chem Geol 114 199-215... 

Sarano F, Murphy RC, Houghton BF, Hedenquist JW (1989) Preliminary observations of submarine geothermal activity in the vicinity of White Island Volcano, Taupo Volcanic Zone, New Zealand. J Royal Soc New Zealand 19 449-459... 

Miyashita (1995) proposed that the epithermal mineralizations in Hokusatsu district (Kyushu) are related to strata volcanoes in the volcanic depression and not to caldera formation, hy compiling the data on the ages of mineralization and volcanic activities, gravity and geology. He considered that the Hokusatsu volcanic depression zone is an extension of the Okinawa Trough. This volcanic depression started from 5-6 Ma (Kamata and Watanabe, 1985), where bimodal volcanism is found. 

Sano and Williams (1996) calculated present-day volcanic carbon flux from subduction zones to be 3.1 x 10 mol/year based on He and C isotopes and C02/ He ratios of volcanic gases and fumaroles in circum-Pacific volcanic regions. Williams et al. (1992) and Brantley and Koepenich (1995) reported that the global CO2 flux by subaerial volcanoes is (0.5-2.0) x lO mol/m.y. and (2-3) x 10 mol/m.y. (maximum value), respectively. Le Guern (1982) has compiled several measurements from terrestrial individual volcanoes to derive a CO2 flux of ca. 2 x 10 mol/m.y. Le Cloarec and Marty (1991) and Marty and Jambon (1987) estimated a volcanic gas carbon flux of 3.3 X 10 mol/m.y. based on C/S ratio of volcanic gas and sulfur flux. Gerlach (1991) estimated about 1.8 x 10 mol/m.y. based on an extrapolation of measured flux. Thus, from previous estimates it is considered that the volcanic gas carbon flux from subduction zones is similar to or lower than that of hydrothermal solution from back-arc basins. 

The most important observations about U-series isotopes in arc lavas for this chapter are (1) the widespread excess of over °Th but deficit of with respect to Pa and (2) the extreme Ra enrichments in some arc lavas. We will explore the profound implications of these for magma genesis and transport at subduction zones. The conclusions apply most convincingly to the oceanic arcs where the observations are most extreme (the volcanic fronts of Tonga, Marianas, and eastern Sunda, and one or two volcanoes in some other arcs). Whether the conclusions apply elsewhere is harder to verify but there is no convincing reason with respect to U-series data to believe that they do not. 

The resulting CO2 gas is returned to the atmosphere by two means (1) volcanic emissions associated with eruptions near subduction zones, i.e., back-arc volcanoes or (2) diffusion through the sediments of the continental rise into the ocean, followed by gas exchange across the air-sea interfece. The combined production of CO2 from these two settings is thought to exceed that from the high-temperature hydrothermal reaction zones. 

Magma types 2006). A significant part in formation of magmatic complexes accompaning riftogenesis belongs to the sources of different nature and to characteristics of the continental crust contaminated by those complexes. These very data accounted for the formation of a contrasting volcanism which is widely developed in the zone of the Central-Asian fold belt. The paper considers a bimodal volcano-plutonic complex of the end of the Late Cretaceous. It is spatially located within the continuation of the formations with similar composition which compose the Central-Asian fold belt. 

Roccamonfina is an asymmetric truncated composite cone, with a base diameter of about 20 km and a 6 km wide, NW-SE-elongated summit caldera that is breached on the east side (Fig. 5.7). The caldera floor, sited at about 600 m above sea level, hosts several lava flows and domes which reach a maximum altitude of about 1000 m. The volcano is composed of alternating lava flows, domes and pyroclastic deposits which were emitted both from central and parasitic vents between about 0.6 and 0.1 Ma. As shown in Fig. 5.3, rock compositions range from mafic to felsic, and from subal-kaline to alkaline potassic and ultrapotassic (Appleton 1972 Giannetti and Ellam 1994). The volcanic activity took place in a zone of NW-SE trending extensional faults cut by younger N-S faulting (Chiesa et al. 1995 Fig. 5.1). 

Figure 9 Subduction zone statistics histograms of depths of (a) the slab surface below the volcanic front and (b) the width of volcanic arcs. The vertical axis denotes arc lengths in km measured at the trench. This is our own compilation (unpublished) based on locations of quaternary volcanoes and slab surfaces from tomography...

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