| Abstract: | The petrogenesis and geodynamic setting of the Late Jurassic Baita porphyry quartz monzodiorite in Xingcheng--Liaoxi area provide information for understanding the Mesozoic tectonic evolution of the northeastern North China Craton. In this paper, geochronological, whole-rock geochemical, and in-situ zircon Hf isotopic analyses of Baita porphyry quartz monzodiorite were investigated to constrain the crystallization age and petro-genesis . Zircons exhibit typical oscillatory zoning in cathodoluminescence images and show relatively high Th/U ratios (0. 78--1. 62), and U-Pb analyses indicate that these rocks were crystallized during the Late Jurassic (159 ± 1 Ma). Geochemically, they are characterized by high contents of SiO2 (65. 21wt％--65. 31wt％), Al2O3(16.29wt％--16.31wt％),Sr(521×10-6-539×10-6),andSr/Yratio(45.1--47.8)butlowY(10.9× 10 -6 -12. 0 × 10 -6), with obvious adakitic geochemical affinities. These above-mentioned findings, combined with their negative εHf(t) values ( -21. 7 to -20. 2), corresponding two-stage model age (TDM2) of 2579--2484 Ma, as well as low MgO (1.38wt％--1.39wt％), Cr (18.5×10-6-19.5×10-6) and Ni (9.45×10-6 -9. 46 × 10 -6 ) values, indicate that Baita porphyry quartz monzodiorite may be generated by partial melting of the Neoarchean-Paleoproterozoic thickened basaltic lower crust. Based on the results from this study and pre-vious regional studies, it is concluded that Baita porphyry quartz monzodiorite was spatially related to the west-ward subduction of the Paleo-Pacific plate. |
