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1 Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, People's Republic of China
2 Department of Physics and Earth Sciences, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
3 Department of Geology, University of South Florida, Tampa, Florida 33620, USA
4 Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, People's Republic of China
5 Department of Geosciences and Mineral Physics Institute, State University of New York, Stony Brook, New York 11794-2100, USA
To the best of our knowledge, modern adakites have not been documented in a nonarc environment. We report geochemical and isotopic data for Early Cretaceous Anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction. The Anjishan adakitic intrusive rocks, which are exposed in the Ningzhen area of east China, have high Sr/Y and La/Yb ratios coupled with low Yb and Y as well as relatively high MgO contents and Mg numbers (Mg#; 0.4–0.6), similar to products from slab melting. However, low 
Nd(t) values (–6.8 to–9.7) and high (87Sr/86Sr)i (0.7053–0.7066) are inconsistent with an origin by slab melting. The tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust. High Sr/Y and La/Yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting, implying that the crustal thickness exceeded 40 km in the Early Cretaceous. The present thickness of the crust in the Ningzhen area is only 30 km, and therefore the crust appears to have been thinned by at least 
10 km since the Early Cretaceous. The relatively high MgO contents and Mg# of the Anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks, possibly coinciding with lower-crustal delamination, which would also account for the observed thinning.
Key Words: adakite • lower-crustal melting • delamination • continental crust • slab melting • east China
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