Mesozoic felsic dikes in the Jiaobei Terrane, southeastern North China Craton: Constraints from zircon geochronology and geochemistry, and implications for gold metallogeny

Abstract

The Jiaobei Terrane in the southeastern North China Craton (NCC) witnessed intense magmatic pulses during Mesozoic in response to lithospheric thinning. These include sporadic felsic-porphyritic dikes which preserve important information on the magmatic processes and of its implications on lithospheric thinning. Here we present a detailed investigation of representative felsic-porphyritic dikes based on whole-rock geochemical analysis, zircon LA-ICPMS U-Pb geochronology, trace elements and hafnium isotopic compositions. Our results identify stages of felsic dikes in the Jiaobei Terrane with ages in the range of 131–127 Ma and 123–116 Ma. The early stage felsic dikes (ESFDs) have negative zircon ɛHf(t) (−22.4 to −11.1), high zircon EuN/EuN* (0.41–0.92) and Ce4+/Ce3+ (62–944), low Ti-in-zircon crystallization temperatures (524–738 °C), and are geochemically comparable to the coexisting Guojialing granodiorite. Abundant inherited zircons and scattered zircon Hf, Yb/Gd, Th/U, and Ce/Sm values suggest that the magmas from which the dikes formed involved crustal contamination. They are interpreted to be the hypabyssal phase of the Guojialing suite sourced from the Paleoproterozoic lower crust of the eastern NCC with input of mantle components, associated with extensive crust-mantle interaction during the peak lithospheric thinning. The late stage felsic dikes (LSFDs) are characterized by variable zircon ɛHf(t), EuN/EuN* and Ce4+/Ce3+ values (−20.1 to −12.2, 0.38–0.88 and 64–956 for the granodiorite- and quartz-porphyritic dikes; −27.6 to −16.2, 0.17–0.75 and 22–503 for the monzogranite-porphyritic dikes), low Ti-in-zircon crystallization temperatures (562 to 774 °C), and display geochemical similarity with the Aishan granitoids. Systematic variations of zircon Hf, Yb/Gd, Th/U and Ce/Sm suggest that fractional crystallization of hornblende played a significant role in the formation of the late dikes. The LSFDs originated from the Neoarchean-Paleoproterozoic lower crust of the NCC with heterogeneous involvement of lesser amounts of mantle materials than the early dikes, consistent with weak crust-mantle interaction during the waning stage of lithospheric thinning. In the LSFDs, the granodiorite and monzogranite porphyries are broadly coeval (123–118 Ma) with large scale gold mineralization in the area as also favored by the high zircon Ce4+/Ce3+ ratios. Our study also provides new insights into the formation of gold deposits.