Trace element and Sr isotope records of multi‐episode carbonatite metasomatism on the eastern margin of the North China Craton

Abstract

Lherzolite xenoliths entrained in the Changle Cenozoic basalts were analyzed to infer mantle process beneath the eastern block of the North China Craton. These xenoliths were classified into two types. Clinopyroxenes (Cpx) in the type-1 xenoliths are strongly enriched in large ion lithophile elements and light rare earth elements (LREE) but depleted in high field-strength elements and heavy rare earth elements, and show high Ca/Al, Zr/Hf, and (La/Yb) N ratios but low Ti/Eu ratios. These features indicate that they were crystallized from a carbonatitic melt. Cpx in the type-2 xenoliths are mostly characterized by a chemical zonation, that is, LREE and Sr contents and (La/Yb) N and Eu/Ti ratios gradually increase from the cores to the rims. Some fresh cores preserve the original signatures of the depleted mantle. These observations indicate partial modification of pre-existing Cpx by carbonatite metasomatism. Two episodes of metasomatism were identified based on Sr isotopic compositions of Cpx and carbonate inclusions within olivines. Both the carbonate inclusions and Cpx cores in the type-2 xenoliths have relatively high 87 Sr/ 86 Sr ratios (>0.7033), suggesting metasomatism due to CO 2 -rich silicate melt derived from the recycled oceanic crust. However, low 87 Sr/ 86 Sr ratios of Cpx rims in the type-2 xenoliths suggest a late stage of metasomatism by a low-87 Sr/ 86 Sr carbonatitic melt (<0.7024), which might have been caused by upwelling of the asthenosphere mantle. Such multiple metasomatism could have played an important role in changing the chemical composition of mantle from refractory and depleted to fertile and enriched.

Zircon Xenocrysts from Cenozoic Alkaline Basalts of the Ratanakiri Volcanic Province (Cambodia), Southeast Asia—Trace Element Geochemistry, O-Hf Isotopic Composition, U-Pb and (U-Th)/He Geochronology—Revelations into the Underlying Lithospheric Mantle

“…Several types of continental carbonatitic-influenced mantle sources are known to have the potential to generate zircon megacrysts of an RVP type. Asian examples include: (1) stratified mantle deduced from ultramafic xenoliths that show initial silicate and then carbonatitic metasomatism in kamafugites from Western Qinlan, Central China [115], and (2) Pacific slab-induced carbonatitic metasomatism in garnet-bearing lherzolite xenoliths from Cenozoic basalts in NE China [116][117][118]. The latter is related to alkali basalts at Changle where zircon megacrysts have Hf-Y ranges similar to those in RVP zircons and the carbonatitic-modified mantle is recognized [13].…”

Natural Clinopyroxene Reference Materials for in situ Sr Isotopic Analysis via LA-MC-ICP-MS

“…There is still lack of accessible clinopyroxene reference material for Sr isotope microanalysis. Despite a few published papers about in situ Sr analysis of clinopyroxene, the shortage of reference materials hinders the development of in situ Sr isotope measurements for clinopyroxene (Waight et al, 2002 ; Bizzarro et al, 2003 ; Schmidberger et al, 2003 ; Hart et al, 2005 ; Sun et al, 2012 ; Xu et al, 2013 ; Su et al, 2015 ; Tong et al, 2016 ; Deng et al, 2017 ; Tang et al, 2019 ).…”

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

“…Several publications (e.g., Deng et al, 2017; Xu, Pei, et al, 2013) proposed that melts/fluids were transported to the base of the CLM directly from the Pacific slab and tried to link the metasomatism in the peridotites to the subduction. Their inferences were based on relatively high 87 Sr/ 86 Sr ratios (0.7033–0.7055) in the peridotites that overlap the values of subducted oceanic components (Staudigel et al, 1995).…”