Petrogenesis of Early Cretaceous low-Mg adakitic rocks along the southernmost margin of the North China Craton: implications for late Mesozoic crustal evolution

作者：Chen, Longyao^*; Qu, Wei; Liu, Shuwen

来源：International Geology Review, 2017, 59(8): 996-1014.

DOI：10.1080/00206814.2016.1242094

• Low-Mg adakitic rocks
• petrogenesis
• crustal evolution
• North China Craton

This article reports systematic zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotopic data for the Early Cretaceous Jialou granitoids along the southernmost margin of the North China Craton (NCC), adjacent to the Tongbai Orogen. These results will provide significant constrains on the crustal evolution of the southern margin of the NCC. Zircon U-Pb analyses, using laser ablation-multicollector-inductively coupled plasma-mass spectrometry, indicate that the Jialou granitoids were emplaced at similar to 130Ma. The granitoids have high SiO2, K2O, Al2O3, Sr, and Ba contents, high Sr/Y and (La/Yb)N ratios, and low concentrations of MgO, Y, and heavy rare earth elements, indicating a low-Mg adakitic affinity. They have relatively high initial Sr-87/Sr-86 ratios (0.707464-0.708190) and negative epsilon Nd(t) values (-11.8 to -15.2), similar to those of the Palaeoproterozoic lower crust in the NCC. These geochemical and isotopic features indicate that the Jialou low-Mg adakitic rocks were derived by partial melting of mafic Palaeoproterozoic lower crust of the NCC at >50km depth, leaving behind a garnet amphibolite residue. The petrogenesis of the Jialou low-Mg adakitic rocks, plus the petrogenesis of Mesozoic granitoids and lower crustal xenoliths entrained in the Late Jurassic Xinyang volcaniclastic diatreme, suggests that the continental crust along the southern margin of the NCC was thickened during the Middle Jurassic to Early Cretaceous, but thinned after 130Ma. We propose that crustal thickening was caused by a late Middle Jurassic to Early Cretaceous intra-continental orogeny, rather than continent-continent collision between the NCC and the Yangtze Craton. We also suggest that crustal thinning and Early Cretaceous magmatism were related to subduction of the palaeo-Pacific plate, rather than post-orogenic collapse of the Qinling-Tongbai-Dabie Orogen.

• 出版日期2017-6
• 单位北京大学; 中国地质科学院地质力学研究所