the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A discovery of nanoscale sulfide droplets in MORB glasses: Implications for the immiscibility of sulfide melt and silicate melt
Lei Zuo
Peng Zhang
Rui Liu
Dongping Tao
Xiang Liu
Genwen Chen
Kun Wang
Gang Tao
Abstract. Sulfur forms an immiscible liquid upon saturation in magma, and sulfide droplets were commonly found in fresh mid-ocean ridge basalt (MORB) magmas. In this paper, scanning electron microscopy (SEM) determined that MORB samples were primarily fine-grained and weakly phyric, with hypocrystalline to vitreous textures. A focused ion beam cut from the MORB glasses examined by transmission electron microscopy (TEM) revealed a range of nanoscale sulfide droplets (10–15 nm), featuring rounded shapes and smooth edges. Texturally, the droplets were crystalline and homogeneous in composition. Elemental S, Na, Fe, Cu, and Ni were evenly distributed within the droplets, while the content of element Si, Al and O are less in the droplets. Previous reports have elucidated the immiscibility between sulfide and silicate melts, and the structure of the silicate melt also affects the size distribution of sulfide droplets. This is the first report on nanoscale sulfide droplets within MORB glasses, and those results indicated that nanoscale sulfide droplets were the initial phase of sulfide saturation; such insight may prove useful in understanding how siderophile and chalcophile elements behaved during sulfide crystallization. In addition, this study determined the immiscibility of sulfides and silicate melts occurred in the early nanometer stage, the immiscibility of sulfides in magmatic Ni-Cu sulfide deposits was the key to the formation of magmatic Ni-Cu sulfide deposits. Therefore, all immiscibility phenomena may occur in the nanometer stage during magma evolution.
Lei Zuo et al.
Status: open (until 14 Jun 2023)
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RC1: 'Comment on egusphere-2023-213', Anonymous Referee #1, 11 May 2023
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This paper aims at ”a deeper understanding of the initial solidification of sulfide-oxide liquids” (line 70-71) using an example from MORB-type glasses. Although the paper reports nanoscale sulphide globules two main conclusions that “nanoscale sulfide droplets were the initial phase of sulfide saturation” and “all immiscibility phenomena may occur in the nanometer stage during magma evolution” remain unsupported. Clearly, liquid immiscibility occurs on all scales, including nanoscale, which follows from results of numerous experimental and melt inclusion studies. Therefore, the results by Lei Zuo et al. are neither novel nor particularly significant. This study does not contribute to “understanding how siderophile and chalcophile elements behaved during sulfide crystallization” (line 35) and has nothing to do with identifying “the key to the formation of magmatic Ni-Cu sulphide deposits” through the study of sulphide unmixing in MORB magmas. The 4. RESULTS section is only 7 lines long!!!!!
The manuscript is sprinkled with the statements that are awkward and often wrong. Just a few examples are given below
lins 24 fresh mid-ocean ridge basalt (MORB) magmas
lines 29-31 Elemental S, Na, Fe, Cu, and Ni were evenly distributed within the droplets, while the content of element Si, Al and O are in the droplets.
lines 39-40 all immiscibility phenomena may occur in the nanometer stage during magma evolution.
lines 46 with liquid immiscibility the more important for magma evolution
lines 58 The sulfur in MORB magma is saturated before magma eruption…
lines 65-66 the sulfide droplet sizes influence the physical behavior of the separate sulfide phases
lines 66-67 the different of sulfide droplets 67 also plays an important role in partitioning the siderophile and cupolophile elements ….
lines 95-97 As determined by SEM, the MORB samples were primarily fine-grained and weakly phyric with hypocrystalline to vitreous textures (Fig. 2a). Some phenocrysts were 1-10 μm and relatively rich in Si and O (Figs. 2b-f, 3a-c).
Please note that surfaces shown on Figs. 2 and 3 are dusted, but reported as “weakly phyric”)))
lines 158-159 In this study, nanoscale sulfide droplets in natural MORB glass are reported for the first time, thus demonstrating S-saturated fractionation in another way.
lines 186-187 The experimental results show that when the composition of silicate melt becomes immiscible, two-phase nanoscale droplets will soon appear
lines 212-213 chalcophile elements appeared to enter the sulfide droplets and distribute evenly within the sulfide globule in the early stage
lines 218 5.4 Implications of sulfide droplets on magmatic evolution and formation of sulfide deposits
lines 222-223 The earlier immiscibility begins during magmatic evolution, the better its influence on magmatic evolution, and the better its geochemical and petrological significance
lines 226-227 As one of the immiscible two phases, the immiscibility of sulfide droplets and silicate melt plays an important role in magma evolution
lines 232-234 The study shows that the formation of magmatic Ni-Cu sulfide deposits is related to the separation and enrichment of sulfur saturated and immiscible sulfide liquids in mantle-derived basic and ultrabasic magmas (Arndt et al., 2005)
lines 245-247 this new understanding of sulfide and silicate melt immiscibility, which occurs during the early nanometer stage provides a new idea for further study of the immiscibility stage during magma evolution.
lines 72-82 the whole paragraph, and in particular, “Hawkings et al (2020) reported that Greenland Ice Sheet meltwaters may provide biolabile particulate Fe that fuels the large summer phytoplankton bloom in the Labrador Sea (Hawkings et al., 2018)” is irrelevant to this study.
Citation: https://doi.org/10.5194/egusphere-2023-213-RC1
Lei Zuo et al.
Lei Zuo et al.
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