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Tectonic significance of Late Triassic post-collisional lamprophyre dykes from the Qinling Mountains (China)

Published online by Cambridge University Press:  12 July 2007

XIAOXIA WANG
Affiliation:
Key Laboratory of Lithospheric Tectonics and Exploration, China University of Geosciences, Ministry of Education, Beijing 10083, China Development and Research Center, China Geological Survey, Beijing 100037, China
TAO WANG
Affiliation:
Institute of Geology, Chinese Academy of Geological Science, Beijing 100037, China
BOR-MING JAHN
Affiliation:
Institute of Earth Sciences, Academia Sinica, Taipei, 115, Taiwan
NENGGAO HU
Affiliation:
Chang'an University, Xi'an 710054, Shaanxi, China
WEN CHEN
Affiliation:
Institute of Geology, Chinese Academy of Geological Science, Beijing 100037, China

Abstract

The Qinling–Dabie orogen in central China is one of the major orogenic belts in East Asia. In the eastern Dabie–Sulu region, mafic lamprophyres show the enriched signatures of old sub-continental lithospheric mantle. However, little is known about the mafic igneous rocks and their lithospheric mantle sources in the western Qinling Range. New 40Ar–39Ar age dating, major- and trace-element data, and isotopic analyses of Qinling lamprophyres reveal their differences from the Dabie Sulu lamprophyres. Biotite 40Ar–39Ar dating yielded a plateau age of 219±2 Ma, identical to the ages of rapakivi-textured granitoids in the area. The association of lamprophyre dykes and rapakivi-textured granitoids indicates that the Qinling region was a post-collisional setting at c. 220 Ma. The Qinling lamprophyres are calc-alkaline, and rich in large ion lithophile elements (e.g. Ba, K), but depleted in Nb, Ta and Ti. They show highly fractionated REE patterns with LaN>100 and HREE <10 times chondrite abundances. εNd (219 Ma) values range from −0.5 to −3.3 and initial Sr isotope values from 0.7036 to 0.7058. These features suggest generation of the lamprophyre by partial melting of a metasomatized, garnet peridotite mantle source. The Qinling lamprophyres are distinct from the Dabie–Sulu lamprophyres in emplacement age (c. 135 Ma for Dabie–Sulu) and isotopic composition, suggesting that the nature of the lithospheric mantle and geodynamic evolution of the Qinling region contrasts with that of the Dabie–Sulu region.

Type
Original Article
Copyright
© 2007 Cambridge University Press

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