Subduction-related origin of the 750 Ma Xuelongbao adakitic complex (Sichuan Province, China): Implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China

The Xuelongbao plutonic complex in the eastern margin of the Tibetan Plateau is dated at 748 ± 7 Ma using the SHRIMP zircon U-Pb method and represents part of the Neoproterozoic igneous assemblage of South China. Rocks in the complex include tonalite and granodiorite and have SiO 2 ranging from 62.0 to 74.8 wt.% and Al 2O 3 from 14.3 to 20.9 wt.%. Their Na 2O contents range from 4.2 to 6.7 wt.% and K 2O from 0.47 to 1.96 wt.%, indicating that they belong to the Na-series. These rocks show chondrite-normalized REE patterns depleted in HREE and variably enriched in LREE. They have positive Sr and negative Nb and Ti anomalies in the primitive mantle-normalized trace elemental spider diagram. Their Sr contents range from 320 to 780 ppm and Y contents are lower than 10 ppm, resulting in high Sr/Y ratios (52-320), characteristic of typical adakites. Their εNd (t) and initial Sr isotopic compositions range from + 0.36 to + 2.88 and from 0.7033 to 0.7054, respectively. The geochemical features of the Xuelongbao plutonic complex are consistent with an origin from adakitic magmas that were likely derived from partial melting of a subducted oceanic slab. Together with arc signatures of other granites and mafic intrusions in the region, the 750 Ma Xuelongbao adakitic complex provides evidence for a major, subduction-related Neoproterozoic magmatic event of South China. © 2006 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex