Geochemical characteristics of basic intrusive rocks in the Yunkai uplift, Guangdong-Guangxi, China, and their tectonic significance.

The main types of basic intrusive rock in banded-augen (rapakivi) granitic rocks in the Xinyi-Gaozhou area, Yunkai uplift, Guangdong-Guangxi, are meta-norite-gabbros and meta-gabbros. They have the following geochemical characteristics: low TiO2 (0.24-0.53%), low total REE (18.64-78.30 μg/g). LREE enrichment (LREE/HREE=2.69-5.28), (La/ Yb)N=1.79-4.73, no pronounced Eu negative anomaly (δEu=0.81-1.16), pronounced Ta, Nb, P, Zr and Ti negative anomalies, La/Nb = 1.94-5.42 (1) ,Th/Ta=2.29-17.63 (averaging 10.75), Nb/Th7.4, eNd(0=-3.6 to -8.4 (averag-ing-5.9), higher Ti/Zr and Ti/Y, lower Rb/Ba and La/Yb showing the features of an enriched mantle source region. The meta-norite-gabbro has a whole rock-mineral Sm-Nd isochron age of 392±53 Ma, which suggesting that Caledonian basic intrusive rocks in the region formed in a tectonic setting of the volcanic arc at the continental margin of subduction-collision and are the product of the extension-delamination-underplating stage after subduction-collision.