Geochemical Studies on volcanoes in the Canarian islands.

Research Project

Project/Area Number	07041095
Research Category	Grant-in-Aid for international Scientific Research
Allocation Type	Single-year Grants
Section	Field Research
Research Institution	University of Tokyo
Principal Investigator	WAKITA Hiroshi Laboratory for Earthquake Chemistry Faculty of Science, University of Tokyo Professor, 理学部, 教授 (40011689)
Co-Investigator(Kenkyū-buntansha)	PERES N.M カナリア火山観測所, 研究員 NAKAI Shunichi Laboratory for Earthquake Chemistry Faculty of Science, University of Tokyo Asso, 理学部, 助教授 (50188869) N.M Perez IPNAC-CSIC,Canary Islands
Project Period (FY)	1995
Project Status	Completed (Fiscal Year 1995)
Budget Amount *help	¥2,200,000 (Direct Cost: ¥2,200,000) Fiscal Year 1995: ¥2,200,000 (Direct Cost: ¥2,200,000)
Keywords	Canarian Islands / Helium Isotope Ratio / Hot Spot Volcanism / Lower Mantle / Oceanic Island
Research Abstract	Helium isotopic ratios in natural systems are a potential tool for detecting mantelic degassing from different tectonics settings such as mid-ocean ridge basalts, oceanic volcanic islands, are volcanism, and intraplate continental volcanism environments. Helium isotopic signature from mantle plume regions such as Hawaii, Iceland, and Yellowstone range from 9 to 30 Ra which indicates helium degassing from the lower mantle. Several hypothesis have been considered for the origin of the volcanic activity in the Canary Islands. Helium isotope systematics applied to the actual degassing will provide an additional insight to the discussion on whether the Canarian archipelago is indeed a hot spot. More than 40 gas samples have been collected from actual degassing sites at La Palma, Tenerife and Lanzarote islands. The observed ^3He/^4He ratios vary significantly from 1.02 to 9.63 Ra, being Ra (atmospheric ratio) =1.40*10^<-6>. Most of the samples show isotopic ratios higher than atmospheric value indicating a contribution of mantle-derived helium. The highest observed helium isotopic ratio, 9.63 Ra, was detected inside Taburiente caldera (La Palma Is.). This ^3He/^4He ratio is higher than the typical MORB-type helium 8(]SY.+-.])1 Ra and agrees well with a plume-type helium. Such evidence supports that the volcanic-hydrothermal discharge in La Palma island is related to magma derived from a rising hot zone. The geographical distribution of the ^3He/^4He ratios obtained in this Field Research shows the highest level of helium-3 emission on the westernmost zone of the Canarian archipelago. This ^3He/^4He ratio would imply the existence of a helium source degassing from the lower mantle. The result of this International Scientific Research Program add an additional insight to the controversy on the origin of the volcanic activity of the Canary islands which seems to be related to a hot spot model.