Tectonic significance of Late Triassic post-collisional lamprophyre dykes from the Qinling Mountains (China)
Journal
Geological Magazine
Journal Volume
144
Journal Issue
5
Pages
837-848
Date Issued
2007
Author(s)
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. © 2007 Cambridge University Press.
SDGs
Type
journal article