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A new model for chromitite formation in ophiolites: Fluid immiscibility.

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Title: A new model for chromitite formation in ophiolites: Fluid immiscibility.
Authors: Su, Benxun1,2,3 (AUTHOR) subenxun@mail.igcas.ac.cn, Liu, Xia1,2,3 (AUTHOR), Chen, Chen1,2,3 (AUTHOR), Robinson, Paul T.1 (AUTHOR), Xiao, Yan2 (AUTHOR), Zhou, Meifu4 (AUTHOR), Bai, Yang1,2,3 (AUTHOR), Uysal, Ibrahim5 (AUTHOR), Zhang, Pengfei4 (AUTHOR)
Source: SCIENCE CHINA Earth Sciences. 2021, Vol. 64 Issue 2, p220-230. 11p.
Subjects: Ophiolites, Immiscibility, Dunite, Fluids, Magmas, Electric conduits, Droplets
Abstract: Although the involvement of hydrous fluids has been widely invoked in formation of podiform chromitites in ophiolites, there is lack of natural evidence to signify the role and mechanism of fluids. In this study, a new model for the genesis of podiform chromitite is proposed on basis of revisits of comprehensive petrological, mineralogical and geochemical results of the well-preserved Kızıldağ ophiolite and the well-characterized Luobusa chromite deposit. In this model, ascending magmas intruding oceanic lithospheric mantle would presumably form a series of small magma chambers continuously connected by conduits. Tiny chromite nuclei would collect fluids dispersed in such magmas to form nascent droplets. They tend to float upward in the magma chamber and would be easily transported upward by flowing magmas. Chromite-rich droplets would be enlarged via coalescence of dispersed droplets during mingling and circulation in the magma chamber and/or transport in magma conduits. Crystallization of the chromite-rich liquid droplets would proceed from the margin of the droplet inward, leaving liquid entrapped within grains as precursor of mineral inclusions. With preferential upward transportation, immiscible chromite-rich liquids would coalesce to a large pool in a magma chamber. Large volumes of chromite would crystallize in situ, forming podiform chromitite and resulting in fluid enrichment in the chamber. The fluids would penetrate and compositionally modify ambient dunite and harzburgite, leading to significant fractionations of elemental and isotopic compositions between melts and fluids from which dunite and chromitite respectively formed. Therefore, fluid immiscibility during basaltic magma ascent plays a vital role in chromitite formation. [ABSTRACT FROM AUTHOR]
Copyright of SCIENCE CHINA Earth Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: A new model for chromitite formation in ophiolites: Fluid immiscibility.
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  Data: <searchLink fieldCode="AR" term="%22Su%2C+Benxun%22">Su, Benxun</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<i> subenxun@mail.igcas.ac.cn</i><br /><searchLink fieldCode="AR" term="%22Liu%2C+Xia%22">Liu, Xia</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Chen%2C+Chen%22">Chen, Chen</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Robinson%2C+Paul+T%2E%22">Robinson, Paul T.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Xiao%2C+Yan%22">Xiao, Yan</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Zhou%2C+Meifu%22">Zhou, Meifu</searchLink><relatesTo>4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Bai%2C+Yang%22">Bai, Yang</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Uysal%2C+Ibrahim%22">Uysal, Ibrahim</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Zhang%2C+Pengfei%22">Zhang, Pengfei</searchLink><relatesTo>4</relatesTo> (AUTHOR)
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  Data: Although the involvement of hydrous fluids has been widely invoked in formation of podiform chromitites in ophiolites, there is lack of natural evidence to signify the role and mechanism of fluids. In this study, a new model for the genesis of podiform chromitite is proposed on basis of revisits of comprehensive petrological, mineralogical and geochemical results of the well-preserved Kızıldağ ophiolite and the well-characterized Luobusa chromite deposit. In this model, ascending magmas intruding oceanic lithospheric mantle would presumably form a series of small magma chambers continuously connected by conduits. Tiny chromite nuclei would collect fluids dispersed in such magmas to form nascent droplets. They tend to float upward in the magma chamber and would be easily transported upward by flowing magmas. Chromite-rich droplets would be enlarged via coalescence of dispersed droplets during mingling and circulation in the magma chamber and/or transport in magma conduits. Crystallization of the chromite-rich liquid droplets would proceed from the margin of the droplet inward, leaving liquid entrapped within grains as precursor of mineral inclusions. With preferential upward transportation, immiscible chromite-rich liquids would coalesce to a large pool in a magma chamber. Large volumes of chromite would crystallize in situ, forming podiform chromitite and resulting in fluid enrichment in the chamber. The fluids would penetrate and compositionally modify ambient dunite and harzburgite, leading to significant fractionations of elemental and isotopic compositions between melts and fluids from which dunite and chromitite respectively formed. Therefore, fluid immiscibility during basaltic magma ascent plays a vital role in chromitite formation. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of SCIENCE CHINA Earth Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1007/s11430-020-9690-4
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        Text: English
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        PageCount: 11
        StartPage: 220
    Subjects:
      – SubjectFull: Ophiolites
        Type: general
      – SubjectFull: Immiscibility
        Type: general
      – SubjectFull: Dunite
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      – SubjectFull: Magmas
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      – SubjectFull: Electric conduits
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      – SubjectFull: Droplets
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