Protolith ages and timing of peak and retrograde metamorphism of the high-pressure granulites in the Shandong Peninsula, eastern North China Craton

摘要

High-pressure (HP) granulites widely occur as enclaves within tonalite-trondhjemite-granodiorite (TTG) gneisses of the Early Precambrian metamorphic basement in the Shandong Peninsula, southeast part of the North China Craton (NCC). Based on cathodoluminescence (CL), laser Raman spectroscopy and in-situ U-Pb dating, we characterize the zircons from the HP granulites and group them into three main types: inherited (magmatic) zircon, HP metamorphic zircon and retrograde zircon. The inherited zircons with clear or weakly defined magmatic zoning contain inclusions of apatites, and 207 Pb/ 206 Pb ages of 2915–2890?Ma and 2763–2510?Ma, correlating with two magmatic events in the Archaean basement. The homogeneous HP metamorphic zircons contain index minerals of high-pressure metamorphism including garnet, clinopyroxene, plagioclase, quartz, rutile and apatite, and yield 207 Pb/ 206 Pb ages between 1900 and 1850?Ma, marking the timing of peak HP granulite facies metamorphism. The retrograde zircons contain inclusions of orthopyroxene, plagioclase, quartz, apatite and amphibole, and yield the youngest 207 Pb/ 206 Pb ages of 1840–1820?Ma among the three groups, which we correlate to the medium to low-pressure granulite facies retrograde metamorphism. The data presented in this study suggest subduction of Meso- and Neoarchean magmatic protoliths to lower crust depths where they were subjected to HP granulite facies metamorphism during Palaeoproterozoic (1900–1850?Ma). Subsequently, the HP granulites were exhumated to upper crust levels, and were overprinted by medium to low-pressure granulite and amphibolite facies retrograde event at ca. 1840–820?Ma. Graphical abstract Display Omitted Highlights ? HP granulite facies mineral inclusions identified in metamorphic zircons. ? U-Pb ages of zircon domains with HP granulite facies inclusions range from 1925 ± 27 to 1853 ± 21. ? The ages represent the timing of peak HP granulite facies metamorphism in the basement of Shandong Peninsula.