Abstract
A rare massive yellowish-green serpentinized dunite, covering a minimum area up to ~50 m2, has been found in Ji’an County, Jilin Province, Northeast China. It contains primary olivine and secondary serpentine (antigorite) and brucite. Other primary minerals like orthopyroxene, clinopyroxene, and aluminum-rich phase (such as garnet, spinel, and plagioclase), frequently appearing in ultramafic rocks, have not been identified. The olivine is essentially pure forsterite, with an Mg# (100 × Mg/(Mg + Fe)) of ~99.6–99.7. Due to these distinct features, we especially name the protolith of this dunite as jianite (集安岩). The forsterite grains range up to ~2 mm, show clear equilibrium textures such as nearly straight grain boundaries and ~120° dihedral angles at their triple junctions, and display no intragranular or intergranular composition variations. They are extensively ruptured and hydrated (i.e., serpentinized), with the fractures (and the grain boundaries as well) filled by fine-grained antigorite (ideally Mg6(Si4O10)(OH)8) and brucite (ideally Mg(OH)2). These secondary phases are also extremely poor in Fe, indicating a good chemical equilibrium with the forsterite. The serpentinization reaction may have proceeded as forsterite + fluid = antigorite + brucite at temperatures of ~425(25) °C and at relatively low but undetermined pressures. The fluid was likely a B-rich, but Si-poor dilute aqueous fluid, as implied by the trace element characteristics and water-related infrared features of the forsterites in equilibrium. The petrogenesis of the jianite is presently unclear.
Highlights
The ultramafic peridotitic upper mantle generally consists of olivine (Ol; (Mg,Fe)2SiO4), orthopyroxene, clinopyroxene, and an aluminous phase
The hydration zones along the grain boundaries of the olivines, with coarser serpentine and brucite grains, are wider than those in the fractures within the olivine grains, indicating a hierarchic fluid-transport system operating in the hydration process (Figure 4)
Both along the grain boundaries and in the fractures of the olivine grains, the serpentine aggregates, appearing as layers, often locate themselves next to the olivines and sandwich the layers of the brucite aggregates. This phenomenon might imply that, if both the Mg cations and the Si cations contained by the serpentines and brucites were from the olivines, the Mg cations would have diffused much faster than the Si cations in the fluid, leading to the crystallization of the serpentines near the olivines and the crystallization of the brucites slightly farther away
Summary
The ultramafic peridotitic upper mantle generally consists of olivine (Ol; (Mg,Fe)2SiO4), orthopyroxene, clinopyroxene, and an aluminous phase (plagioclase, spinel or garnet, depending on pressure). The Mayihe formation, a boron-bearing sequence with a deposition age of ~M2in1er2al6s –201290,4100, 2M20 a [26], contains various altered felsic and granitic rocks, dolom3iotifc18marble, serpentinized olivine marble, and boron- and iron-bearing serpentinite, and amphibolite [24,27]. It has been prTohpeorsoecdk dtohcautmseonmteed mheeretaevxpoolcseasniinctrhoecMksayoihfethfoermJia’atinongorfotuhepJif'oanrmgreodupa,tw~h2ic1h8l9o–c2at1e5s6inMa and experienthceeLdiaaon-Jai Pmroptheriobzooliicteriffat czioense.mTehteaMmaoyrihpehfiocremvaetinotna, at ~bo1r8o8n1-–be1a8r7in0gMseaqu[2e4n]c.e Ewxitihstaindgeppoestitrioocnhemical and geoasecgrhepeoemnf t~ii2cn1aiz2le6ad–n1o9al4ilvy0isnMeesamo[a2fr6b]t,lhece,oanantldatiebnroserdvoanvr-iooanulcdsaainrloitcenr-rebodecafkreislnsgischsaeonrwpdengttrhianeniticeti,hcaarnrodacckatmse, rpdihsoitlbiocomsliittoeicf[2mt4h,a2er7b]c.laeIt,lc-alkali volcanicharsocbkeesnopf rioslpaonseddatrhca,tinsodmiceamtinetgavtohlecapnoicssroibckles ionfvthoelvJei'manegnrtooupf afnormanecdieant t~2s1u8b9d–2u1c5t6ioMnaparnodcess [28]. 7500 Ce laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) hosted by the MOE. The data were processed by using the OMNIC8 software and PeakFit V4.12 software
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
