Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: Partial melting of delaminated lower continental crust?

Research Article| December 01, 2002 Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: Partial melting of delaminated lower continental crust? Ji-Feng Xu; Ji-Feng Xu 1Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, People's Republic of China Search for other works by this author on: GSW Google Scholar Ryuichi Shinjo; Ryuichi Shinjo 2Department of Physics and Earth Sciences, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan Search for other works by this author on: GSW Google Scholar Marc J. Defant; Marc J. Defant 3Department of Geology, University of South Florida, Tampa, Florida 33620, USA Search for other works by this author on: GSW Google Scholar Qiang Wang; Qiang Wang 4Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, People's Republic of China Search for other works by this author on: GSW Google Scholar Robert P. Rapp Robert P. Rapp 5Department of Geosciences and Mineral Physics Institute, State University of New York, Stony Brook, New York 11794-2100, USA Search for other works by this author on: GSW Google Scholar Geology (2002) 30 (12): 1111–1114. https://doi.org/10.1130/0091-7613(2002)030<1111:OOMAIR>2.0.CO;2 Article history received: 15 May 2002 rev-recd: 14 Aug 2002 accepted: 15 Aug 2002 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ji-Feng Xu, Ryuichi Shinjo, Marc J. Defant, Qiang Wang, Robert P. Rapp; Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: Partial melting of delaminated lower continental crust?. Geology 2002;; 30 (12): 1111–1114. doi: https://doi.org/10.1130/0091-7613(2002)030<1111:OOMAIR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 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 ϵNd(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. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.