Zircon U-Pb geochronological and geochemical constraints on the petrogenesis of the Taishan sanukitoids (Shandong): Implications for Neoarchean subduction in the Eastern Block, North China Craton

Abstract

Elemental, Sr-Nd-Pb isotopic and geochronological data are presented for the Taishan high-mg dioritic rocks (western Shandong) from the Eastern Block of the North China Craton in order to better understand the Archean tectonic evolution and crustal growth of the Craton. The rocks gave the zircon U-Pb age of 2536-2540 Ma. They show low SiO 2 and Al 2O 3 contents, high MgO, mg-number, Cr, Ni, Y, Yb, Sr and Ba, enriched LILEs and LREEs, depleted HFSEs and HREEs with (Nb/La) N of 0.07-0.12. They exhibit ε Nd(t) values of 1.53-3.30, ( 206Pb/ 204Pb) i of 11.20-15.30, ( 207Pb/ 204Pb) i of 14.14-14.83 and ( 208Pb/ 204Pb) I of 31.10-33.93. Such geochemical features with an affinity to both a mantle- and crust-like source for the Taishan dioritic rocks are similar to those of the typical Archean sanukitoids, suggesting an origination from a sub-arc mantle wedge variably metasomatized by the slab-derived dehydration fluids and melts before ∼50-100 Ma of the emplacement of the Taishan sanukitoid plutons. It is proposed that the Taishan sanukitoids resulted from the sudden change of the downgoing slab from a flat subduction to subsequently steeper subduction in an active continental margin regime during Neoarchean time. © 2009 Elsevier B.V. All rights reserved.