Late Mesozoic magmatism and sedimentation in the Jiaodong Peninsula: new constraints on lithospheric thinning of the North China Craton

Abstract

Intense magmatism and voluminous sedimentation occurred in the Jiaodong Peninsula during Mesozoic in response to the lithospheric thinning in eastern North China Craton (NCC). Here we report the results from an integrated geochemical and Sr-Nd-Pb-Hf isotopic study on granitoids and UPb and LuHf isotopes of the detrital zircons from Mesozoic sediments in the Jiaodong Peninsula to provide new constraints on the crustal response to the lithospheric thinning. Geochronologic data reveal three distinct magmatic pulses at 170-140 Ma, 140-125 Ma and 125-105 Ma in this region. The Sr-Nd-Pb isotope data (0.7080–0.7139 for ⁸⁷Sr/⁸⁶Sr, −22.3--10.8 for ɛNd(t), 16.97-17.47 for ²⁰⁶Pb/²⁰⁴Pb, 15.42-15.55 for ²⁰⁷Pb/²⁰⁴Pb, 37.36–38.34 for ²⁰⁸Pb/²⁰⁴Pb) and zircon ɛHf(t) values (−29--10) for the Mesozoic plutons show more similarities with those of the lower crust of the Yangtze Craton (YC) wedged beneath the NCC, than those of the NCC. The Sr/Y, (La/Yb)N and Nb/Ta ratios for the three episodes of granitic magmatism show a gradual decrease, which is interpreted to reflect upward migration of the depth of partial melting from ~170 Ma to ~105 Ma. The dominant detrital zircon population in the sediments deposited during ca. 125–105 Ma was derived from pre-Jurassic sources in the NCC and YC basement whereas the Cretaceous population was derived from volcanic rocks in the interior of the craton. The alternating sequence suggests episodic uplift of the NCC and YC basements during this period. The data obtained in this study allow us to summarize the crustal evolution of this region into three phases. (1) During 170–140 Ma, partial melting of wedged YC lower crust resulted in high magmatic flux. (2) During 140–125 Ma, intense magmatism continued, accompanied by uplift and erosion of basement, and initiation of basin filling. (3) During 125–105 Ma, the source depth of granitoid magma became shallower associated with continuing episodic basement uplift, representing the peak of lithospheric thinning.