Geochronology of the Laoshan granitic complex in eastern China and its tectonic implications

During one orogenic cycle, orogenic belts around the world usually experience a transition from compression to extension, with the initiation of extension signalling the end of the compressional process or the beginning of the post-collisional setting. Igneous rocks in many orogenic belts preserve the record of the transition. For example, igneous (I)-type and sedimentary (S)-type granites are closely related to an overall compressional setting, and A-type granites mainly occur in a post-collisional extensional setting. Fortunately, I-type and S-type granites often juxtapose tectonically with A-type granites in many orogenic belts in the world, for example, eastern China. High-precision dating works on these rocks will be helpful to constrain the duration of transition from compression to extension. This study presents zircon U-Pb ages of I-type and A-type granites from the Laoshan granitic complex in eastern China, determined through the laser ablation-inductively coupled plasma mass spectrometry dating method. The new ages for the I-type and A-types granites are 123.4 and 116Ma, respectively, and these are interpreted to represent the respective emplacement ages for these two types of granites. Our new results, combined with the previously reported 145Ma for the I-type granites (determined by the Rb-Sr isotopic dating method) and 113-110.8Ma for A-type alkali granites (determined by isotope dilution dating method), indicate that the ages for I-type granites in the Laoshan granitic complex range from 145 to 123.4Ma, and those for A-type in the complex range from 116 to 110.8Ma. In general, granites in the Laoshan granitic complex record the relatively short-period tectonic transition process from compression to extension in this region, and the tectonic transition occurred in the whole eastern China margin during the Mesozoic era. Copyright (c) 2016 John Wiley & Sons, Ltd.