Xu, S., Nakai, S., Wakita, H. and Wang, X.B. (2004) Carbon and noble gas isotopes in the Tengchong volcanic geothermal area, Yunnan, southwestern China. Acta Geologica Sinica: English Edition, 78(5), pp. 1122-1135.
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Abstract
Carbon and noble gas isotope analyses are reported for bubbling gas samples from the Tengchong volcanic geothermal area near the Indo-Eurasian suture zone. All samples contain a resolvable component of mantle-derived He-3. Occurrence of mantle-derived He-3 coincides with surface volcanism. However, He-3 occurs over a larger geographic area than do surface volcanics. delta(13)C values for CO2 and CH4 vary from -33.4parts per thousand to 1.6parts per thousand and from -52.8parts per thousand to -2.8parts per thousand, respectively. He and C isotope systematics indicate that CO2 and CH4 in the CO2-rich gases originated predominantly from magmatic component mixed with crustal CO2 produced from carbonate. However, breakdown of organic matter and near-surface processes accounts for the CH4 and CO2 in N-2-rich gases. He-3/He-4 ratio distribution pattern suggests that mantle-derived He and heat sources of high- temperature system in central Tengchong originate from a hidden magma reservoir at subsurface. CO2-rich gases with the highest He-3/He-4 ratio (5.2 Ra) may be representative of the Tengchong magmatic component. Compared with MORB, this relative low He- 3/He-4 ratio could be fully attributed to either deep crustal contamination, or radioactive aging, or past contamination of the local mantle by U- and Th-rich subducted crustal material. However, a combination of low He-3/He-4, high radiogenic He- 4/Ar-40 ratio and identical CO2/He-3 and delta(13)C(CO2) relative to MORB may suggest addition of prior subductedd crsustal material (ca 1%-2%) to the MORB reservoir around 1.3 Ga ago, which is essentially compatible with the LIL-elements, and Sr-Nd-Pb isotopes of volcanic rocks.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Xu, Dr Sheng |
Authors: | Xu, S., Nakai, S., Wakita, H., and Wang, X.B. |
Subjects: | Q Science > QE Geology |
College/School: | College of Science and Engineering > Scottish Universities Environmental Research Centre |
Journal Name: | Acta Geologica Sinica: English Edition |
ISSN: | 1000-9515 |
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