Anomalously high delta D and micro-scale hydrogen isotope heterogeneities in the mantle: Ion microprobe analysis of amiboles from peridotite xenoliths at Nushan, eastern China

Citation
Q. Xia et al., Anomalously high delta D and micro-scale hydrogen isotope heterogeneities in the mantle: Ion microprobe analysis of amiboles from peridotite xenoliths at Nushan, eastern China, CHIN SCI B, 46(6), 2001, pp. 505-509
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Multidisciplinary
Journal title
CHINESE SCIENCE BULLETIN
ISSN journal
1001-6538 → ACNP
Volume
46
Issue
6
Year of publication
2001
Pages
505 - 509
Database
ISI
SICI code
1001-6538(200103)46:6<505:AHDDAM>2.0.ZU;2-6
Abstract
Hydrogen isotopic compositions of four amphibole grains from three pieces o f Iherzolite xenoliths in Cenozoic basanites of Nushan, eastern China have been analyzed by ion microprobe. deltaD values of all analyzed points range from -94 parts per thousand to +46 parts per thousand, some of which are m uch higher than the highest deltaD (+8 parts per thousand) reported previou sly for mantle materials. The heterogeneities of D/H ratios within single g rains have been observed, the variation of deltaD is up to 80 parts per tho usand on the scale of less than 400 mum. No correlation between hydrogen is otopic ratios and hydrogen contents can be found, implying that the scatter of deltaD values could not result from a late shallow process such as hydr ogen loss or hydrothermal alterations and should be considered as inherited from the source at depth. Chemical compositions of Nushan amphiboles are v ery homogeneous, excluding the fact that the scatter of deltaD values could arise from variable fractionation factors between a single fluid source an d minerals. Therefore, metasomatic fluids responsible for the formation of Nushan amphiboles should be heterogeneous and result in the observed large variable and anomalously high deltaD values of amphiboles, We suggested tha t such metasomatic fluids could be related to magma degassing in the mantle source. Based on the D-H diffusion data and the scale of hydrogen isotope heterogeneities, it was inferred that the mantle metasomatism took place so on before the eruption of host magma.