ZI Feng1, 2，WANG Qiang2，LIU Xin-hua1，QIU Hua-ning2
(1. Institute of Geology, Hunan University of Sciences and Technology, Xiangtan 411201, China;
2. State Key Laboratory of Isotopic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China)
Fig. Microscopic photos of the Yeshan and Shanlichen intrusive rocks.
Abstract：The Yeshan and Shanlichen plutons are tectonically located in the Eastern Yangtze Block and to the east of the Tan-Lu Fault Belt (TLFB). The Yeshan and Shanlichen intrusive rocks mainly consist of quartz diorite porphyries. They have hornblende and biotite with 40Ar/39Ar plateau ages of 131.22 ± 0.77 Ma and 130.07 ± 0.48 Ma, respectively. These intrusive rocks are geochemically similar to adakites, e.g., w(SiO2)>56%, high Al2O3 [w(Al2O3) = 14.95%～17.67%], Sr [w(Sr) = 495×10-6～2086×10-6], Sr/Y = 44～159,and La/Yb=26～68, but low heavy rare earth element contents, e.g., w(Yb) = 0.82×10-6～1.56×10-6 and w(Y) = 9.14×10-6～20.32×10-6, with negligible to positive Eu anomalies (δEu = 0.90～1.11). Moreover, most samples have relatively high MgO [w(MgO) = 2.01%～4.98%], IMg (45～71), Cr [w(Cr) = 19.2×10-6～199×10-6] and Ni [w(Ni) = 13.8×10-6～58.8×10-6] values. They also exhibit the similar Sr-Nd-Pb isotope compositions, (87Sr/86Sr)i= 0.7059 ~ 0.7062, εNd(t) = -14.75～-12.15, (206Pb/204Pb)t= 16.082～16.847, (207Pb/204Pb)t= 15.303～15.461, and(208Pb/204Pb)t= 35.889～36.919. The Yeshan and Shanlichen adakitic magmas were most likely generated by partial melting of delaminated lower crust and subsequently interacted with mantle peridotites at different percentage during their ascent. The crust may be thickened bythe collision orogenic processes between the Yangtze Block and the Northern China Block in Triassic and later crustal detachment of the Eastern Yangtze Block. Chronological data indicate that the Cretaceous adakitic magmatism occurring along both sides of the TLFB may be closely related to the transitions from left-lateral strike-slip to extensional movement of the TLFB due to the subduction of Paleo-Pacific Plate.
Key words：adakitic rocks; delamination; crustal detachment; Tan-Lu Fault Belt; Yeshan; Shanlichen; Yangtze Block
E-mail: zifeng@hnust.edu.cn
ACTA MINERALOGICA SINICA Vol. 31, No. 2, 2011, Page 185-200
