Origin of early Cretaceous calc-alkaline lamprophyres from the Sulu orogen in eastern China: implications for enrichment processes beneath continental collisional belt

K-Ar dating, major- and trace-element and Sr-Nd isotopic analyses were carried out for early Cretaceous (122-127 Ma) lamprophyres from the Sulu orogen in eastern China. The results show strong fractionation in rare-earth elements with (LREE) >100 times chondrite, but HREE < 10 times chondrite, indicating the presence of residual garnet in the melting source. These rocks are characterized by significant LILE and LREE enrichment but Nb and Ta depletion with moderate Zr/Hf (39.8-50.8 with regard to 36 for primitive mantle) and Nb/Ta (17.8-23.0, compared with 17.5 for primitive mantle) fractionations, probably as a consequence of carbonate- and rutile-rich melt metasomatism induced by dehydration and/or melting of subducted continental slab at mantle depths. Age-correlated Sr-Nd isotope ratios show moderate ranges of Sr-87/Sr-86(i) from 0.70787 to 0.70934 and - 17.2 to - 11.6 Of epsilon(Nd)(t). The lamprophyres from the Sulu orogen were derived from decompression melting of such a metasomatized lithospheric mantle that was mainly composed of phlogophite garnet peridotites and experienced crystal fractionation of a mineral assemblage of olivine +/- clinopyroxene plagioclase en route to the Surface. Such geochemical and isotopic signatures are also prevalent in the contemporaneous basaltic lavas in the Dabie-Sulu belt, suggesting predominant enrichment processes by carbonate- and rutile-rich metasomatic assemblage beneath the continental collisional belt. (C) 2004 Elsevier B.V. All rights reserved.