New insights into the mantle source of a large igneous province from highly siderophile element and Sr-Nd-Os isotope compositions of carbonate-rich ultramafic lamprophyres

Hydrogen Concentrations and He Isotopes in Olivine From Ultramafic Lamprophyres Provide New Constraints on a Wet Tarim Plume and Earth's Deep Water Cycle

“…Additionally, the 3 He/ 4 He ratios (5.31–5.84 Ra) of primitive high‐Ni olivines are slightly lower than the range of MORBs (i.e., depleted upper mantle). In combination with depleted Sr‐Nd isotopes of primary apatite and perovskite, and moderately radiogenic Pb and Os isotopes of bulk samples (C. H. Wang et al., 2022), these new results suggest that water in the aillikites was mainly sourced from a plume contaminated by deeply recycled (U‐bearing) hydrated crustal material. This study reinforces the view that the Tarim plume was wet (Xia et al., 2016), but clarifies that much of this water was stored in deeply subducted material that polluted the plume source in the lowermost mantle.…”

“…Based on Os isotope mass balance calculations, C. H. Wang et al. (2022) suggested that less than one third of recycled oceanic crustal material can occur in the Tarim plume. If we assume that 30% of water in the mantle plume source originated from deeply subducted oceanic material and the remaining 70% from a depleted mantle source containing 200 ppm H 2 O, the recycled oceanic crust should contain ca.…”

“…To constrain how much water was retained in the subducted crustal component, we here employ the approximate H 2 O contents (i.e., 520 ppm) of the mantle plume source of the Wajilitag aillikites. Based on Os isotope mass balance calculations, C. H. Wang et al (2022) suggested that less than one third of recycled oceanic crustal material can occur in the Tarim plume. If we assume that 30% of water in the mantle plume source originated from deeply subducted oceanic material and the remaining 70% from a depleted mantle source containing 200 ppm H 2 O, the recycled oceanic crust should contain ca.…”

“…The occurrence of fresh, olivine‐rich aillikites (or carbonate‐rich UMLs) in the northwest Tarim large igneous province (LIP) (Figure 1a) provides an ideal opportunity to examine Earth's deep water cycle because these magmas are probably genetically linked to the Tarim plume (C. H. Wang, Zhang, Giuliani, et al., 2021; D. Y. Zhang et al., 2013). Based on detailed bulk‐rock major‐element and trace‐element and Sr‐Nd‐Os isotope, olivine major‐element and trace‐element and oxygen isotope, and bulk‐carbonate C‐O isotope analyses, it was previously suggested that these rocks originated from a moderately depleted sub‐lithospheric (plume) source which was marginally contaminated by deeply subducted oceanic crustal components based on radiogenic Os isotopes (C. H. Wang, Zhang, Giuliani, et al., 2021; C. H. Wang et al., 2022). In this work, we combine new H 2 O content and He isotope data for olivine with new and existing olivine major‐ and trace‐element composition and bulk‐rock Sr‐Nd‐Os isotope results (C. H. Wang, Zhang, Giuliani, et al., 2021; C. H. Wang, Zhang, Xie, et al., 2021; C. H. Wang et al., 2022), including newly acquired bulk‐rock Pb isotope data, to constrain the source of water in these rocks.…”

“…In this work, we combine new H 2 O content and He isotope data for olivine with new and existing olivine major-and trace-element composition and bulk-rock Sr-Nd-Os isotope results (C. H. Wang, Zhang, Giuliani, et al, 2021;C. H. Wang, Zhang, Xie, et al, 2021;C. H. Wang et al, 2022), including newly acquired bulk-rock Pb isotope data, to constrain the source of water in these rocks.…”