Open AccessPetrogenesis and magma residence time of lavas from Tengchong volcanic field (China): Evidence from U series disequilibria and 40 Ar/ 39 Ar dating
Author(s) -
Wang Fei,
Peng Zicheng,
Zhu Rixiang,
He Huaiyu,
Yang Liekun
Publication year - 2006
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2005gc001023
Subject(s) - geology , geochemistry , lile , isochron dating , volcanic rock , petrogenesis , partial melting , trace element , magma , mantle (geology) , basalt , volcano , isochron
We present U‐Th disequilibria measurements as well as radiogenic and trace element data for volcanic rocks erupted over the past ∼200,000 years at Tengchong volcano field (TVF), near the collisional belt of India‐Asia, southwestern China. Mineral separates, matrix, and whole rock were analyzed separately by mass spectrometry for 230 Th‐ 238 U disequilibria. Whole rocks are characterized by either 230 Th enrichment or depletion relative to 238 U. Three mineral internal 230 Th age isochrons and a CO 2 laser 40 Ar/ 39 Ar age were determined. A difference of ∼40 ka between the 230 Th age and the 40 Ar/ 39 Ar age can be interpreted as the residence time of the associated magma. Large variations in Sr, Nd, and Pb isotopic compositions and trace element ratios suggest more than one source for the TVF lavas. High Th contents, Th/U ratios and LILE element abundances, as well as their large variations can be attributed to partial melting of mantle previously metasomatized by subduction‐derived components. Excesses of 238 U in some lavas could be the feature of another end‐member, an arc‐type melt, in the source. Fast extraction of the melts may result in the observed chemical disequilibrium.