Whole-rock and zircon evidence for evolution of the Late Jurassic high-Sr ∕ Y Zhoujiapuzi granite, Liaodong Peninsula, North China Craton

Abstract

Middle–Late Jurassic high-Sr/Y granitic intrusions are extensively exposed in the Liaodong Peninsula in the eastern part of the North China Craton (NCC). However, the genesis of the high Sr/Y signature in these intrusions has not been studied in detail. In this study, we report results of zircon U–Pb dating, Hf isotopic analysis, and zircon and whole-rock geochemical data for the Late Jurassic Zhoujiapuzi granite in the middle part of the Liaodong Peninsula. The Zhoujiapuzi granite is high-K (calc–alkaline) and peraluminous in nature, with high SiO2 (68.1 wt %–73.0 wt %) and Al2O3 (14.5 wt %–16.8 wt %), low TFe2O3 (1.10 wt %–2.49 wt %) and MgO (0.10 wt %–0.44 wt %), and high Sr/Y (19.9–102.0) and LaN/YbN (14.59–80.40), which is characteristic of high-Sr/Y I-type granite. The geochemical signatures, in combination with the presence of a large number of Paleoproterozoic inherited zircons, indicate that the Zhoujiapuzi granite was most likely derived from partial melting of the basement in the region, specifically the Liaoji granites. The high Sr/Y signature is inherited from these source rocks. Laser ablation–inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon U–Pb dating of the autocryst zircons from two samples (from different localities) yielded consistent weighted average ages of 160.7 ± 1.1 Ma (mean squared weighted deviation – MSWD = 1.3) and 159.6 ± 1.1 Ma (MSWD = 1.2), with εHf(t) values in the range of −26.6 to −22.8. Morphological and chemical studies on autocrystic zircon grains show that there are two stages of zircon growth, interpreted as magmatic evolution in two distinct stages. The light-cathodoluminescence (light-CL) core reflects a crystallization environment of low oxygen fugacity and high TZr–Ti; the dark-CL rim formed with high oxygen fugacity and lower TZr–Ti. Based on the geochemical features and regional geological data, we propose that the Liaodong Peninsula in the Late Jurassic was part of a mature continental arc, with extensive melting of thick crust above the Paleo-Pacific subduction zone.