Big insights from tiny peridotites: Evidence for persistence of Precambrian lithosphere beneath the eastern North China Craton

Abstract

Previous studies have shown that the eastern North China Craton (NCC) lost its ancient lithospheric mantle root during the Phanerozoic. The temporal sequence, spatial extent, and cause of the lithospheric thinning, however, continue to be debated. Here we report olivine compositions, whole-rock Re-Os isotopic systematics, and platinum-group element abundances of small (b 2 cm in maximum dimension) mantle peridotite xenoliths from two basalt localities from the eastern NCC, Wudi (Cenozoic) and Fuxin (Cretaceous). These locations lie far (~150-200 km) from the Tan-Lu fault, which has been linked to lithospheric replacement in the eastern NCC. Peridotites at both locations have fertile to moderately refractory compositions (Fo b 91.5), while highly refractory (Fo N 92) lithospheric mantle is largely absent. Osmium isotopic data suggest the Wudi peridotites experienced melt depletion primarily during the Paleoproterozoic (~1.8 Ga), although an Archean Os model age for one xenolith indicates incorporation of a minor component of Archean lithospheric mantle. These data suggest that a previously unrecognized Paleoproterozoic orogenic event removed and replaced the original Archean lithospheric mantle beneath the sedimentary basin at the southern edge of the Bohai Sea. By contrast, the Fuxin peridotites, entrained in Cretaceous basalts that crop out along the northern edge of the eastern NCC, document the coexistence of both ancient (≥2.3 Ga) and modern lithospheric mantle components. Here, the original Late Archean-Early Paleoproterozoic lithospheric mantle was, at least partially, removed and replaced prior to 100 Ma. Combined with literature data, our results show that removal of the original Archean lithosphere occurred within Proterozoic collisional orogens, and that replacement of Precambrian lithosphere during the Mesozoic may have been spatially associated with the collisional boundaries and the strike-slip Tan-Lu fault, as well as the onset of Paleo-Pacific plate subduction.

Olivine and melt inclusion chemical constraints on the source of intracontinental basalts from the eastern North China Craton: Discrimination of contributions from the subducted Pacific slab

“…Because continental crust has a higher Th/Nb (0.70, Rudnick and Gao, 2003) than OIBs (0.08, Sun and McDonough, 1989), a negative correlation between Th/ Nb and e Nd values would be predicted if crustal contamination played an important role in basalt petrogenesis. However, the intraplate basalts of this study have nearly constant Th/Nb ratios (0.06-0.1), and e Nd from À1.4 to +5.9 (Tables 1 and S1), which together with their peridotite xenocryst-bearing charcteristics (Chu et al, 2009;Liu et al, 2015), rule out crustal contamination as a significant cause of geochemical differences among our samples.…”

“…2a). These olivines strongly resemble olivines from mantle xenoliths in Dashan and Changwei depression basalts (mostly with Fo > 89 and Ca < 715 ppm; Chu et al, 2009;Liu et al, 2015). BSE images show that the population II olivines in CZ typically have mantled cores (Fig.…”

“…The olivine crystals in GG16-2 show euhedral and subhedral shapes that differ from xenocrystic grains (e.g., Kamenetsky et al 2006). All the olivines in GG16-2 have Fo values lower than 89, lower limit of Fo for olivines from eastern NCC mantle xenoliths (e.g., Chu et al, 2009;Liu et al, 2015), which strongly suggests these olivines are cognate phenocrysts.…”

“…The last magmatic episode, 8.7-0.3 Ma, consists of scattered and isolated basaltic centers erupting mainly basanite and nephelinite, occurring as outcrops far from the TLFZ, such as Penglai and Qixia in the Jiaodong Peninsula and Wudi in the overlap region between the western Shandong and BBB (e.g., Zeng et al, 2010). Basalts from the latter two periods commonly contain mantle xenoliths (Chu et al, 2009;Liu et al, 2015).…”

Regional heterogeneity in the water content of the Cenozoic lithospheric mantle of Eastern China

“…Cenozoic volcanoes are widely distributed in Eastern China, extending from Heilongjiang province in the north to Hainan province in the south. In many localities, abundant mantle xenoliths are hosted in the alkali basalts, and they have attracted numerous studies of the characteristics of the lithospheric mantle [ Deng and Macdougall , ; Tatsumoto et al ., ; Qi et al ., ; Xu et al ., , , , X. S. Xu et al ., , ; Griffin et al ., ; Zheng et al ., , , , , , , ; Fan et al ., ; Xu et al ., , ; Chen et al ., ; Gao et al ., ; Chen et al ., ; Wu et al ., , ; Zhang et al ., , ; Rudnick et al ., ; Xu and Bodinier , ; Reisberg et al ., ; Ying et al ., ; Yu et al ., ; Choi et al ., ; Tang et al ., , , ; Chu et al ., ; Yu et al ., , ; J. G. Liu et al ., , ; Xiao et al ., ; Zhao and Fan , ; Hong et al ., ; Liu et al ., ; Zhang et al ., ; Lu et al ., ; Pan et al ., ; Xu et al ., ; Li et al ., ; Liu et al ., ]. Eastern China consists of three main blocks from south to north: the South China Block (SCB), North China Craton (NCC), and Northeast China (NEC, also named as Xing‐Meng orogenic belt), with the Qinling‐Dabie‐Sulu orogenic belt between the NCC and the SCB (Figure ).…”