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

Formation of mafic magmas through lower crustal AFC processes — An example from the Jinan gabbroic intrusion in the North China Block

“…The Jinan gabbros have moderately radiogenic Sr and unradiogenic Nd and Hf isotopic compositions (Table 2) and are similar to an EM1-like mantle reservoir (Guo et al, 2001;Huang et al, 2012;Yang et al, 2012a;Zhang et al, 2004 Sr(i) ratios from 0.7046 to 0.7059, ε Nd (t) values from −13.9 to −9.5 and Fig. 5.…”

“…In order to better characterize the whole-rock geochemistry of the Jinan mafic intrusion, we compile our new geochemical data with the published data by Huang et al (2012) and Yang et al (2012a). The rocks from the Jinan gabbroic intrusion can be divided into two groups: Group 1 with low positive to negative Eu-anomalies (i.e., Eu/Eu* b 1.2); and Group 2 with high positive Eu-anomalies (i.e., Eu/Eu* > 1.2).…”

“…The gabbros contain both baddeleyite and zircon as accessories, providing an opportunity to unravel a complete magma differentiation processes and the nature of mantle source. Previous whole-rock geochemical data show that the gabbros exhibit an EM1-like isotopic features (e.g., Guo et al, 2001;Huang et al, 2012;Yang et al, 2012a;Zhang et al, 2004). A compilation of published data of the Mesozoic mafic intrusions with such EM1-like Sr-Nd-Pb isotopic signatures in NCB also indicates addition of lower continental crustal materials either during magmatic evolution (as assimilants or contaminants) or in the formation of the mantle source (as recycled crustal components through lithospheric delamination and/or slab subduction), or both (See Appendix 1).…”

“…A compilation of published data of the Mesozoic mafic intrusions with such EM1-like Sr-Nd-Pb isotopic signatures in NCB also indicates addition of lower continental crustal materials either during magmatic evolution (as assimilants or contaminants) or in the formation of the mantle source (as recycled crustal components through lithospheric delamination and/or slab subduction), or both (See Appendix 1). Based on these observations, the formation of the Jinan gabbros and the related Mesozoic mafic rocks in NCB are considered to be either melts derived from enriched lithospheric mantle that had been hybridized by melts derived from the delaminated NCB lower mafic crust (e.g., Gao et al, 2008;Huang et al, 2012), or magmas contaminated by lower crustal rocks during magmatic evolution (e.g., Chen et al, 2004).…”

Mesoproterozoic high Fe–Ti mafic magmatism in western Shandong, North China Craton: Petrogenesis and implications for the final breakup of the Columbia supercontinent

“…Moreover, their low FeOt contents and depleted ε Nd (t = 1.84 Ga) values are distinctly different from the latter, which display enriched characteristics and mostly have a Fe-Ti-rich affinity (Wang et al, 2004. Additionally, Mesozoic basic magmatism also occurred in the area, including gabbroic intrusions (Huang et al, 2012) and diabase dykes , both of which do not possess high Fe-Ti abundances.…”