The Composition and Ages of Lower Crust along Ningde-Hukou Transect: Constraints from Geochemistry, Neody-mium Isotope and Detrital Zircon Ages

摘要

The transect runs from Ningde City of Fujian Province to Hukou City of Jiangxi Province and crosses the Huaxia Block in east and Yangtze Block in west bounded by Jiangshao Fault. The oldest basement along the transect is the Paleoproterozoic rocks with the ages of 2400-2000 Ma for Huaxia Block and 2200-2000 Ma for Yangtze Block. These rocks have been metamorphosed to amphibolite facies (Huaxia Block) or high-grade greenschist to low-grade amphibolite facies (Yangtze Block) , representing the characteristics of the middle crust along the transect. Most Tdm ages and detrital zircon ages in igneous rocks range from 2750 Ma to 2500 Ma and some are up to 3100 Ma, which give an age information of lower crust. A lot of the granitoids in Huaxia Block are S-type ones and have negative snh values, therefore it indicates that the composition of lower crust is composed mainly of felsic protoliths. The ?nj of Caledonian granitoids rang-ing from —11 to —8 and 6Nd of Yanahanian granitoids from —6 to —1 infer that the composition of the lower crust in Huaxia Block evoluted from granite-rich(" fertile") to granite-poor("sterile" ) that were caused either by crustal differentiation or by the addition of mantle components. The granitoids and acid volcanics from Yangtze. Block are. also peraluminous S-type ones mainly, whereas have ttu from —6 to 4-4, which suggest that the lower crust of Yangtze Block have been added by great amount of mantle com-ponents and the composition of the lower crust of Huaxia Block is more evolved than Yangtze Block.