Early Cretaceous gabbroic complex from Yinan, Shandong Province: petrogenesis and mantle domains beneath the North China Craton

Abstract

Sensitive high resolution ion microprobe (SHRIMP) zircon U-Pb ages, geochemical and Sr-NdPb isotopic data are reported for the gabbroic complex from Yinan (Shandong Province) with the aims of characterizing the nature of the Mesozoic mantle beneath the North China Craton. The Yinan gabbros contain alkali feldspar and biotite, and are characterized by moderate Mg#, high SiO 2 , low FeO and TiO 2 contents and a strong enrichment of light rare earth elements [(La/Yb) n =11-50], but no Eu anomaly. They have low Nb/La (0.07-0.29), radiogenic 87 Sr/ 86 Sr (0.710) and unradiogenic Nd (t) (À15 to À13). These ''crustal fingerprints'' cannot be attributed to crustal contamination, given the lack of correlation between isotopic ratios and differentiation indices and the unreasonably high proportion of crustal contaminant (>20%) required in modeling. Instead, compositional similarities to contemporaneous basalts from nearby regions imply that the Yinan gabbros were not significantly affected by crystal cumulation. Isotopic data available for the Mesozoic mafic magmas reveal two distinct mantle domains beneath Shandong. While the EM1-like domain (with low 87 Sr/ 86 Sr) is confined to western Shandong, the mantle beneath eastern Shandong is dominated by EM2-type (with high 87 Sr/ 86 Sr) affinities. This aerial distinction suggests that the EM2-like signature of the Yinan gabbros may have been inherited from westerlysubducted Yangtze crust during the Triassic North China-South China collision. Emplacement of the Yinan gabbros (127 Ma) is likely affiliated with the widespread and protracted extension during the late Mesozoic in this region.

Repeated modification of lithospheric mantle in the eastern North China Craton: Constraints from SHRIMP zircon U-Pb dating of dunite xenoliths in western Shandong

“…The weighted mean 206 Pb/ 238 U age of 139±4 Ma (MSWD = 0.75) for seven spots is consistent with timing of formation of the Tietonggou high-Mg diorites (131-135 Ma) [28,29] within error, suggesting that the zircons formed during a period of intensive interaction between delaminated lower continental crustderived melt and mantle peridotite. These ages also are consistent with the timing of large-scale mantle-and crustderived magmatism in the eastern NCC during the Early Cretaceous, such as the Jinling, Yi'nan (Shangyu), and Ji'nan intrusions in western Shandong (127-134 Ma) [29,[48][49][50]; the Liguo, Jiagou, Banjing, Fengshan, and Caishan intrusions in Xuzhou-Huaibei (127-132 Ma) [51,52]; and granitoids in eastern Shandong and eastern Liaodong (120-130 Ma) [53][54][55].…”

Two tales of the continental lithospheric mantle prior to the destruction of the North China Craton: Insights from Early Cretaceous mafic intrusions in western Shandong, East China

“…7b and c). (Xu et al, 2004b) are shown for comparison. Chondrite and PM normalization factors are from Taylor and McLennan (1985) and Sun and McDonough (1989), respectively.…”

“…There are two mantle domains (EM1-and EM2-like, respectively; Fig. 1b) beneath western Shandong Province (Xu et al, 2004b). If the EM1-type mantle domain represents the proto-lithospheric mantle beneath the NCC, and the EM2-type mantle domain represents the lithospheric mantle modified by the Yangtze crust and its derived melts/fluids Xu et al, 2004b), the spatial distribution of these two mantle domains may yield information on mechanisms of the cratonic destruction.…”

“…1b) beneath western Shandong Province (Xu et al, 2004b). If the EM1-type mantle domain represents the proto-lithospheric mantle beneath the NCC, and the EM2-type mantle domain represents the lithospheric mantle modified by the Yangtze crust and its derived melts/fluids Xu et al, 2004b), the spatial distribution of these two mantle domains may yield information on mechanisms of the cratonic destruction. The generation of the Yinan gabbro-diorite complex (Xu et al, 2004a(Xu et al, ,b, 2007b was probably related to reactivation of weakened lithospheric zones of the southeastern NCC along the DabieSulu orogenic belt and Tan-Lu fault zone ( Fig.…”

“…1. (a) Simplified tectonic framework and distribution of two Ordovician diamondifeous kimberlite (Mengyin and Feixian) and three granulite-xenolith locations (Nushan, Junan and Hannuoba) in eastern China; the North China Craton is cut by the Tan-Lu fault zone (TLFZ) to the east and the Daxinganling-Taihangshan Gravity Lineament (DTGL) to the west; (b) Distribution of the Mesozoic intrusive and eruptive rocks in Shandong Province and the locations of the Jinan and Zouping gabbros (modified after the geological maps of Shandong Province in 1/1,500,000 scale from the Geological Atlas of China); Dashed line denotes the possible boundary that separates two spatially decoupled mantle domains (EM1-and EM2-like, respectively) modified after Xu et al (2004b) and Yang et al (2012); (c) Geologic sketch map of the Jinan gabbro (after Yang et al, 2005) and sample locations; (d) Geologic sketch map of Zouping area (modified after the Zhangqiu geological map of 1/200,000 scale) and the sample locations. the lithospheric mantle beneath the southeastern NCC.…”