The role of melt‐rock interaction in the formation of Quaternary high‐MgO potassic basalt from the Greater Khingan Range, northeast China

Abstract

Melt‐rock interaction between ascending melt and peridotite results in mantle metasomatism and also leads to compositional modification of the primary melt. While this process is known to occur, it is less well understood how the reactions and the composition of the resulting magma temporally evolve. Here whole‐rock major and trace element, Sr‐Nd‐Pb‐Hf isotopes, and olivine major element composition of Quaternary Nuominhe basalts in the Greater Khingan Range of northeast China are presented to unravel how melt‐rock interaction modified the composition of the high‐MgO potassic basalts as time progressed. The Nuominhe basalts are predominantly basanite with high MgO (8.1–16.8 wt %) and high total alkali content (K2O + Na2O = 6.0–9.2 wt %). They have high K2O/Na2O ratios (K2O/Na2O = 0.77–1.24) and low SiO2 and Al2O3 content (SiO2 = 44.4–48.7 wt %, Al2O3 = 10.5–13.2 wt %). They are characterized by enrichment in strongly incompatible elements, positive Ba, K, and Sr and negative Th, U, Zr, Hf, and Ti anomalies, similar to the composition of enriched mantle (EM1)‐type oceanic island basalts (OIBs). Their isotopic composition also compares to that of EM1‐type OIBs (i.e., with 87Sr/86Sr = 0.70467–0.70483, εNd = −4.1 to −1.5, εHf = −0.3 to 2.3, 206Pb/204Pb = 17.03–17.36). These elemental and isotopic characteristics are consistent with the interpretation that the potassium‐rich melts were derived from recycled crustal materials with EM1 signature. Phlogopite‐bearing mantle xenoliths and zoned olivine xenocrysts with high Fo89–92 and low CaO (<0.1 wt %) core and low Fo75–86 and high CaO (>0.1 wt %) rim composition record interaction between the ascending melt and mantle peridotite. Basalts erupted during late stages (Late Pleistocene and Holocene) of activity at the Nuominhe volcanic field show notably higher SiO2 content, Rb/Nb, Ba/Nb, K/La, and Ba/La, and lower MgO content than early‐stage basalts (Early and Middle Pleistocene), which we infer to reflect a temporally decreasing extent of melt‐rock interaction. During early stages of melt ascent, a reaction zone between melt channels and unreacted peridotite formed; at later stages this reaction zone effectively sealed the ascending melt from further reaction, resulting in increasing Rb/Nb, Ba/Nb, K/La, and Ba/La signatures of the erupted lavas.

Light Mg Isotopic Composition in the Mantle Beyond the Big Mantle Wedge Beneath eastern Asia

“…Variation in the Sr, Nd, Pb, and Hf isotopic composition of the Huihe nephelinites. Data for Cenozoic basalts in Eastern China are shown for comparison (NE China: Basu et al, ; Chu et al, ; Kuritani et al, ; Liu, Chen, et al, ; Rasskazov et al, ; Sun, Teng, et al, ; Sun et al, ; Wang et al, ; Yan & Zhao, ; Yan et al, ; Zhang et al, ; Zhang et al, ; Zhao et al, ; Zou et al, ; Zou et al, . North China: Basu et al, ; Chen et al, ; Choi et al, ; Guo et al, ; Han et al, ; Ho et al, ; Li, Ma, et al, ; Wang et al, ; Xu et al, ; Yu et al, ; Zeng et al, ; Zhang et al, ; Zhang et al, ; Zou et al, .…”

“…Fractional crystallization and crustal contamination also have the potential to affect Mg isotopic compositions. Crustal contamination may be particularly important in the evolution of continental intraplate Basu et al, 1991;Chu et al, 2013;Kuritani et al, 2009;Liu, Chen, et al, 2017;Rasskazov et al, 2011;Sun, Teng, et al, 2017;Sun et al, 2014;Wang et al, 2017;Yan & Zhao, 2008;Yan et al, 2007;Zhang et al, 2016;Zhang et al, 1995;Zhao et al, 2014;Zou et al, 2008;Zou et al, 2003. North China: Basu et al, 1991Chen et al, 2009;Choi et al, 2008;Guo et al, 2016;Han et al, 1999;Ho et al, 2011;Li, Ma, et al, 2016;Wang et al, 2011;Xu et al, 2012;Yu et al, 2015;Zeng et al, 2013;Zhang et al, 2009;Zhang et al, 2012;Zou et al, 2000.…”

Hot, volatile‐poor, and oxidized magmatism above the stagnant Pacific plate in Eastern China in the Cenozoic

“…The dark yellow, dark blue, and dark red symbols highlight samples (five for each volcanic center) for which we have determined mineral compositions and estimated the equilibrium melt compositions. The Wuchagou whole‐rock compositions are from Lim et al (); the Xunke whole‐rock compositions are from J. Q. Liu et al (); the Menluhe whole‐rock compositions are our new data. Whole‐rock compositions of sodic basalts (Halaha, dark green crosses; data from Ho et al, ) and potassic basalts (Wudalinachi, light green crosses; data from Kuritani et al, ) and their modeled liquid lines of decent (green diamonds) shown for comparison.…”

“…We have characterized whole‐rock major‐element compositions for 23 samples from the Menluhe volcanic center and report those of the Xunke and the Wuchagou volcanic centers, which were previously determined by our group (Lim et al, ; J. Q. Liu et al, ) to infer possible source lithologies of the magmas. All whole‐rock compositions were determined at the State Key Laboratory for Mineral Deposits Research, Nanjing University, using a Thermo Scientific ARL 9900 X‐ray fluorescence spectrometer (XRF).…”

“…The largest volumes of the Cenozoic basaltic andesitic and andesitic magmas have erupted at the Menluhe, Xunke, and Wuchagou volcanic centers, which we have sampled (Figure a). The Menluhe and the Xunke lavas are ~1.3–1.0 Ma and <1.0 Ma old (J. Q. Liu et al, ; Zhao et al, ), while the Wuchagou andesites have ages of ~8.0 to 10.5 Ma (Ho et al, ). The three studied volcanic centers may have had a different location relative to the edge of the stagnant slab than at present (Figure a) when they were active, but we presume that the difference was minor, because the edge of the stagnant slab appears to have remained in approximately the same location beneath Eastern Asia, while Eastern Asia's lithosphere has moved in ~N‐S direction (Jolivet et al, ).…”