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

Abstract

The major and trace elements and H2O contents of minerals in peridotite xenoliths hosted by the Cenozoic basalts in Northeast China (NEC) were evaluated using electron microprobe, laser‐ablation inductively coupled plasma–mass spectrometry and Fourier transform infrared spectroscopy, respectively. Although a potential loss of H during the xenoliths' ascent cannot be excluded for olivine, orthopyroxene (opx) and clinopyroxene (cpx) largely preserved the H2O contents of their mantle source in all of the samples, as inferred from (1) the homogenous H2O contents within single pyroxene grains and (2) the equilibrium H2O partitioning between cpx and opx. No OH was detected for pyroxenes of peridotite xenoliths from the north part of NEC (NNEC). Combined with previously published data from the North China Craton (NCC) and the South China Block (SCB), the regional heterogeneity in the water contents in the Cenozoic lithospheric mantle beneath the whole Eastern China has been revealed. The lithospheric mantle beneath the NNEC is completely dry. The “bulk” water contents of the lithospheric mantle of the south part of NEC and the NCC have similar ranges and average values, whereas those of the SCB are much higher (12–195 ppm, average 90 ± 45 ppm for whole rock). The regional variations in the H2O content of the Cenozoic lithospheric mantle of Eastern China cannot be caused by partial melting, mantle metasomatism, or variations in redox state. We propose that the lithospheric mantle beneath the different regions of Eastern China may have distinct origins and may have undergone distinct geodynamic processes.

Variations in the H2O Content and H2O/Ce Ratio of Mantle Pyroxenites: Implications for Enriched Components in the Mantle

“…Several absorption bands between 2,800 and 3,700 cm −1 are observed for both the cpx and opx grains in the pyroxenite xenoliths as display in Figure . The IR absorption bands are characteristic of pyroxenes, similar to those reported by Bell and Rossman (), Hao et al (, ), and Warren and Hauri (). In contrast, the rare coexisting olivines show no detectable OH peak, similar to the olivines in peridotites from NCC (Xia et al, ; Yang et al, ).…”

“…(a) SiO 2 versus H 2 O; (b) TiO 2 versus H 2 O; (c) Al 2 O 3 versus H 2 O; (d) Na 2 O versus H 2 O; (e) Cr 2 O 3 versus H 2 O; (f) Mg# versus H 2 O. Data of Hannuoba peridotites (Hao et al, ) are shown for comparison.…”

“…Two samples (H16 and DM9843) show a slight LREE-enriched pattern, with a (La/Yb) n ratio of~2. The Al-pyroxenites show a convex-upward REE pattern, which is typical for a cumulitic origin, with much higher LREE and middle REE contents compared to those of Hannuoba peridotite (represented by peridotite P12 from Hao et al, 2016) and the other pyroxenite groups. The clinopyroxenite sample DMP6 is distinct within the Al-pyroxenite for its higher LREE concentration and LREE/HREE ratio.…”

“…The dash line indicates REE content calculated from whole rock data, with experiment D values and mineral modal. A peridotite sample P12 with depleted pattern is also shown for comparison (Hao et al, 2016). range from 44 to 208 ppm in cpx and from 5 to 22 ppm in opx.…”

Water contents of clinopyroxenes from sub‐arc mantle peridotites

“…(b) Comparison of inferred water contents in different upper mantle reservoirs. Data: mid-ocean ridge basalt sources (Michael, 1988;Saal, Hauri, Langmuir, & Perfit, 2002); ocean island basalt sources (Dixon, Clague, Wallace, & Poreda, 1997, 2002Hauri, 2002;Jamtveit, Brooker, Brooks, Larsen, & Pedersen, 2001;Nichols, Carroll, & Hoskuldsson, 2002;Seaman et al, 2004;Wallace, Frey, Weis, & Coffin, 2002); arc lava sources (Plank, Kelley, Zimmer, Hauri, & Wallace, 2013); sub-continental lithospheric mantle (Bonadiman et al, 2009;Hao et al, 2016;Li, Lee, Peslier, Lenardic, & Mackwell, 2008;Xia et al, 2010;Yang et al, 2008); sub-arc mantle (this study) Plot of H 2 O versus IV Al 3+ for the sub-arc and intra-plate clinopyroxenes for which Al IV data were obtained (cf. Table 2).…”