Mantle and Recycled Oceanic Crustal Components in Mantle Xenoliths From Northeastern China and their Mantle Sources

Abstract

The subduction of the Paleo-Pacific plate is widely credited for the destruction of the eastern North China Craton. However, how the Pacific plate subduction has affected the off-craton lithospheric mantle in northeastern China is less clear, as few studies have focused on the lithospheric mantle-derived xenoliths in that region. We report petrography, mineral and rock chemistry, and in situ isotopic compositions of Sr in clinopyroxene and O in olivine for 20 peridotite and 11 pyroxenite xenoliths hosted by the Cenozoic volcanic rocks at Jiaohe and Shuangliao localities. The peridotites include lherzolites, harzburgites, and a wehrlite, many are metasomatized. Group 1 garnet pyroxenites have high Al 2 O 3 , Ni, and Mg#; positive Eu and Sr anomalies; and olivine δ 18 O values of 4.8-5.1‰, which we attribute to recycling of oceanic crustal components to the asthenosphere and their reactions with host peridotites. Groups 2 and 3 pyroxenites are garnet-free and contain peridotite-like pyroxenes; we argue that they were formed by reactions of lithospheric peridotites with evolved melts derived from recycled oceanic crust. In addition, one pyroxenite contains orthopyroxene surrounded by fine-grained olivine and clinopyroxene, while another pyroxenite and the wehrlite contain zoned clinopyroxene with gradual increases in Na 2 O, (La/Yb) N , Sr, and 87 Sr/ 86 Sr ratios and decreases in Ti/Eu from core to rim. These characteristics record infiltration of a carbonatite melt shortly before the transport of the xenoliths. The inferred carbonatite melt has 87 Sr/ 86 Sr ≥ 0.70415 and mantle-like olivine δ 18 O and originated from carbonated asthenosphere. Our results, together with previous studies on the host basalts, suggest that subducted crustal materials were initially transported to the asthenosphere beneath northeastern China to produce carbonate-bearing domains. Upwelling of the carbonated asthenosphere produced carbonatite melts that migrated upward and metasomatized the overlying lithospheric mantle.

Machine Learning Reveals Source Compositions of Intraplate Basaltic Rocks

“…(2010) and Guo et al. (2020) found a series of garnet pyroxenite xenoliths hosted by the Cenozoic basalt from Jiaohe, a location close to the east group basalt (Figure 5). These garnet pyroxenites exhibit trace elements and Sr‐Nd‐O isotopic features resembling those of altered lower oceanic gabbros and were suggested to have genetic links with the recycled oceanic crust in the mantle.…”

“…The values in brackets represent pyroxenite percentages in the mantle source of basaltic rocks predicted by the support vector machine model. The Jiaohe basalts (white dot) contain a series of garnet pyroxenite xenoliths (Guo et al., 2020; Yu et al., 2010).…”

“…Guo et al. (2020) observed the carrying of many mantle xenoliths by the Cenozoic basaltic rocks in Northeast China, suggesting that magma ascended quickly in crustal conduits and thus the magma evolution is very limited during its ascent in crustal conduits. Therefore, it may not be reasonable to use correction methods to gain high magnesian primary magmas that equilibrium with typical mantle peridotite.…”

“…Based on the consideration of FC3MS value (FeO/CaO−3 × MgO/SiO 2 ) versus La/Yb, Z. F. Yang and Zhou (2013) suggest that many low magnesian (MgO = 4-10 wt.%) Cenozoic basaltic rocks in eastern China represent primary pyroxenite melts, not highly evolved magmas from peridotite melts. Guo et al (2020) observed the carrying of many mantle xenoliths by the Cenozoic basaltic rocks in Northeast China, suggesting that magma ascended quickly in crustal conduits and thus the magma evolution is very limited during its ascent in crustal conduits. Therefore, it may not be reasonable to use correction methods to gain high magnesian primary magmas that equilibrium with typical mantle peridotite.…”

Petrogenetic Constraints of Early Cenozoic Mafic Rocks in the Southwest Songliao Basin, NE China: Implications for the Genesis of Sandstone-Hosted Qianjiadian Uranium Deposits

“…The chemical compositions of olivine from alkali basaltic rocks (sample BLS01-3) and tholeiitic basaltic rocks (sample BLS07-2) were presented in Table S4 and plotted in Figure 10. The olivine exhibits granular in texture ( Figure 10) and is characterized by higher CaO contents (> 0.26 wt.%), but lower NiO (< 0.23 wt.%) and Fo (<75.82) (Figure 11a,b) than the olivine xenocrysts of the peridotite xenoliths entrained from the Shuangliao basalts [61]. These characteristics are similar to magmatic phenocrysts, differing from fragmented mantle-derived xenocrysts.…”