Phanerozoic magma underplating and crustal growth beneath the North China Craton

Abstract

Evidence for post‐Archaean crustal growth via magma underplating is largely based on U–Pb dating of zircons from granulite‐facies xenoliths. However, whether the young zircons from such xenoliths are genetically related to magma underplating or to anatexis remains controversial. The lower‐crustal xenoliths carried by igneous rocks in the Chifeng and Ningcheng (North China Craton) have low SiO2 and high MgO, indicating that parental melts of their protoliths were of unambiguous mantle origin. The xenoliths contain abundant magmatic zircons with late‐Palaeozoic ages, and have more radiogenic zircon Hf‐isotope compositions and hence younger model ages than ancient crustal magmas and the “reworking array” of the basement rocks. Our data suggest that the granulites represent episodic magmatic underplating to the lower crust of this craton in Phanerozoic time. Considering the observation that regional lowermost crust (~5 km) is mafic and characterized by Phanerozoic zircons, this work reports an example of post‐Archaean crustal growth via magma underplating.

Rock probes and seismic methods to constrain the structure, composition and evolution of the deep crust beneath North China Block

“…Ga [37] . [56] )中发现的二辉石麻粒岩及少量单斜辉 石麻粒岩、紫苏辉石麻粒岩和斜长角闪岩 [56,70] , 阜新 晚中生代玄武岩(100~92 Ma)中发现的麻粒岩、二长 岩 [37,71] , 四子王旗玄武岩(128~108 Ma)中含有的二辉 麻粒岩 [72] . 南缘及东南缘捕虏体在数量和种类上更加 丰富, 包括信阳晚中生代火山岩中的榴辉岩、麻粒 岩、变辉长岩和辉石岩 [34] , 徐淮闪长岩中麻粒岩、角 闪岩、辉石岩及榴辉岩 [59,60,73] , 青岛、莒南晚中生代晚 期火山岩中携带的麻粒岩、辉石岩 [61,62,74] .…”

Geochronology and Geochemistry of Late Triassic Intrusive Rocks in the Xiuyan Area, Liaodong Peninsula, Eastern North China Craton: Petrogenesis and Implications for Lithospheric Thinning

“…Low Rb/Sr values (0.069-0.172) and high Nb/Ta values (19.67-24.78) suggest that the pluton did not experience significant crystallization and differentiation (Duan et al, 2014). High MgO, Cr, and Ni contents, combined with low SiO 2 contents, are distinctive features of any crust-derived melt (Gao et al, 2016;Ma et al, 2017). Considering that the gabbro also has Hf isotopic compositions similar to Late Triassic lamprophyres that were derived from enriched mantle (Duan et al, 2014), it is possible that the Hedong gabbro was derived from a similar enriched mantle source.…”