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| Titel |
Gas Compositions and He-C Isotopic Ratios of Fumarolic Samples from Negros Island, Central Philippines |
| VerfasserIn |
Hsiao-Fen Lee, Tsanyao Frank Yang, Tefang Faith Lan, Yue-Gau Chen, Jaime S. Sincioco, Renato U. Jr. Solidum |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039661
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| Zusammenfassung |
| Four volcanoes that are distributed in the Negros Island, Central Philippines, include Kanlaon
Volcano which is considered as one of the most active volcanoes in Philippines. All of these
volcanoes are related to subduction system of Negros trench and form the Negros volcanic
arc. Besides Kanlaon, from north to south, the volcanoes in Negros Island are Silay Volcano,
Mandalagan Volcano and Cuernos de Negros Volcano. Although there is no eruption record
of these three volcanoes in last 10,000 years, due to the ongoing solfataric/fumarolic
activities, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) classifies
these as “potentially active” volcanoes. It means that there is still a considerable threat and
risk of eruption.
Fumarolic gas samples and bubbling gas samples of hot spring were collected in February
2007 and April 2008 to compare the compositions with others in the world. We
analyzed the gas composition, carbon isotopes of CO2, and helium isotopes of
these samples. The results of these samples show a similar composition as those of
low-temperature fumaroles in other parts of the world, i.e., temperature < 200 oC, and
H2S/SO2 >1. H2O is the major species of these gas samples, and CO2 is the
dominant component after de-watering. Minor components include H2S, N2 and CH4.
The gas composition of most of these samples falls in the range of affinity with
convergent plate gases associated with groundwater based on the plot of N2-He-Ar
diagram. The high 3He/4He ratios indicate a mantle-derived degassing source in
origin, i.e., magma chambers could still exist beneath these volcanoes. Helium
isotopes ratios show a decreasing trend from north to south, such distribution could be
due to more crustal contamination caused by the collision event which happened
in the northern part of the island. The carbon isotopic values of CO2 are far less
negative than the values from a magma source. There are other carbon sources of
CO2, most likely a thick sequence of limestone formation in Negros Island. When
CO2 rise from magma to surface, it reacts with the limestone formation so that
carbon isotopic values are changed. The outlet temperature of fumaroles and hot
springs ranged between 28 - and local boiling, and did not show significant variations
between 2007 and 2008, which implies the de-gassing systems might be quite steady. |
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