Lithology of EM1 Reservoir Revealed by Fe Isotopes of Continental Potassic Basalts

Abstract

The origin of EM1 (Enriched Mantle 1) reservoir, initially defined by the ocean island basalts (OIBs) with extremely low 143Nd/144Nd and 206Pb/204Pb, has been long debated, because melting of the ambient refractory peridotite along with the EM1 component will dilute the “EM1 fingerprints” recorded in these rocks. Comparing to the OIBs, Cenozoic potassic basalts from northeast China, the typical EM1‐type basalts in continental region, are formed at a lower‐degree melting, and therefore have the chance to preserve more information of the EM1 component. Here high‐precision Fe isotopes of these potassic basalts are reported to constrain the source lithology. Their δ57Fe (0.15–0.28‰) are positively correlated with the K2O, SiO2, K/U, and Rb/Y, and negatively correlated with the εNd and δ26Mg, forming binary mixing arrays. One endmember is the inferred EM1 reservoir, whereas the other is the local lithospheric mantle. Major elemental compositions of the melts released from the EM1 component resemble those sediment‐derived experimental melts. Combining with their heavier Fe isotopes and higher Zn/Fe ratios relative to those mid‐ocean ridge basalts (MORBs), an eclogitic source of these potassic basalts is therefore proposed to account for these features. Differing from the most conventional thinking of the metasomatized, phlogopite‐bearing lithospheric mantle, we argue that the EM1 component in the source of continental potassic basalts are composed of ancient subducted crustal materials (i.e., recycled sediment ± oceanic crust). This deep EM1 component will transform into eclogite and release high‐SiO2 potassic melts when ascending to the shallow asthenosphere.

Stable Zirconium Isotopic Compositions of the Metasomatized Mantle

“…The subduction process initially had low angles and created a small mantle wedge (Inglis et al, 2019). The ranges for experiment data are from Zhang et al (2020), Shi et al (2023) and references therein. Compositions of melt inclusions are from Qian et al (2015).…”

“…(2020), Shi et al. (2023) and references therein. Compositions of melt inclusions are from Qian et al.…”

Generation of LOMU type alkali basalts in East Asia by melting and melt metasomatism of the asthenospheric mantle by a Paleoproterozoic subducted slab component

“…Intraplate Cenozoic volcanism in northeast China and Korea comprising of ultrapotassic to alkaline basalts has been extensively studied and show ocean island basalt (OIB) like trace element patterns and an enriched mantle (EM 1), or LOMU [low-µ;Douglass et al, (1999)] like radiogenic isotope ratios (Basu et al, 1991;Menzies, 1995;Chen et al, 2017;Sun et al, 2017;Wang et al, 2017;Choi et al, 2020). However, the origin of this signature is still ambiguous and thought to contain material from multiple components such as recycled sediments, oceanic crust, metasomatised asthenospheric mantle and the subcontinental lithospheric mantle (Choi et al, 2006(Choi et al, , 2020Chen et al, 2007;Kuritani et al, 2009Kuritani et al, , 2011Sun et al, 2017;Wang et al, 2017;Shi et al, 2023). Some Cenozoic alkali basalts from southwest Japan showing OIB like trace element patterns have also been reported to contain low radiogenic Pb compared to arc basalts (Tatsumoto, 1969) and later linked to the enriched mantle 1 or EM 1 (Zindler and Hart, 1986) type mantle component (Tatsumoto and Nakamura, 1991).…”

“…Contribution from enriched mantle components (both EM 1 and EM 2) to the basalts of southwest Japan have been proposed in the past based on their radiogenic isotope geochemistry (Tatsumoto and Nakamura, 1991;Uto, 2003, 2006). The source of the EM 1 or LOMU signature in East Asia has been suggested to originate from ancient subducted sediments based on Pb-Sr-Nd radiogenic and Mg-Ca-Zn stable isotope ratios (Eisele et al, 2002;Kuritani et al, 2011;Wang et al, 2017;Choi and Liu, 2022;Shi et al, 2023). Recent research suggests deep subduction of ancient carbonate sediments contributing to the time integrated low U/Pb bearing LOMU signature from northeast China, correlated to low  26 Mg,  44/40 Ca and high  57 Fe,  66 Zn (Li et al, 2017;Sun et al, 2017;Wang et al, 2017;Liu and Li, 2019;Wei et al, 2021;Shi et al, 2023).…”

“…The source of the EM 1 or LOMU signature in East Asia has been suggested to originate from ancient subducted sediments based on Pb-Sr-Nd radiogenic and Mg-Ca-Zn stable isotope ratios (Eisele et al, 2002;Kuritani et al, 2011;Wang et al, 2017;Choi and Liu, 2022;Shi et al, 2023). Recent research suggests deep subduction of ancient carbonate sediments contributing to the time integrated low U/Pb bearing LOMU signature from northeast China, correlated to low  26 Mg,  44/40 Ca and high  57 Fe,  66 Zn (Li et al, 2017;Sun et al, 2017;Wang et al, 2017;Liu and Li, 2019;Wei et al, 2021;Shi et al, 2023). However Choi and Liu (2022) argue for a Paleoproterozoic siliciclastic source for the EM 1 component in Changbaishan basalts, based on Pb-Mg-Zn isotope systematics with contribution from carbonated eclogite from the stagnant Pacific plate.…”