Diamonds, native elements and metal alloys from chromitites of the Ray-Iz ophiolite of the Polar Urals

Yang, Jingsui; Meng, Fanwei; Xu, Xing; Robinson, Paul T.; Dilek, Yıldırım; Makeyev, A. B.; Wirth, Richard; Wiedenbeck, Michael; Cliff, John

doi:10.1016/j.gr.2014.07.004

Cited by 167 publications

(92 citation statements)

References 114 publications

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“…In natural diamonds and carbides of ophiolites the carbon source may be roots and soils. Indeed, diamonds and carbides from ophiolites have rather light and variable ∂ 13 C (Trumbull et al, 2009;Yang et al, 2015) and highly positive ∂ 15 N ratios (Howell et al, 2015), matching in principle the respective isotope ratios of extant plant materials (Evans, 2001;Bowling et al, 2008). In the Luobusa diamonds, nitrogen is not aggregated (type 1B) unlike in diamonds with long residence times in the mantle (Cartigny et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

“…The identification of ultra-high pressure (UHP) phases in chromitites and harzburgites of ophiolite complexes (Robinson et al, 2004;Yang et al, 2014Yang et al, , 2015 appears to be changing that view. It is now being argued that mantle sections of ophiolites either originate in, or were processed within, the Earth's mantle at depths as great as 600 km Xu et al, 2015;Griffin et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes

Ballhaus¹,

Wirth²,

Fonseca³

et al. 2017

Geochem. Persp. Let.

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Since ultra-high pressure (UHP) minerals have been discovered in ophiolites from Tibet and the Polar Urals, it is speculated that the mantle sections of ophiolites may originate deep within the mantle. The UHP minerals are frequently found together with ultra-reduced silicides, carbides, and nitrides. Consequently, it is argued that the deep mantle, or at least domains within it, must be highly reduced, so reduced that practically all transition elements at depth are present in the metallic state. We find it problematic to rewrite the history of ophiolite complexes based on these observations and suggest we should search for alternative and more realistic modes of origin. Electric discharge experiments at >6000 K reported here show that the UHP and highly reduced phase assemblages may precipitate from plasmas. We argue that the mineral assemblages may originate by lightning strikes. As such, they may not record the origin and emplacement history of the mantle lithologies within which they occur.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes

Ballhaus¹,

Wirth²,

Fonseca³

et al. 2017

Geochem. Persp. Let.

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“…These studies include: major and trace elemental and/or isotopic compositions of different textural chromitites and their host peridotites (e.g., [1][2][3][4][5][6][7][8]), and unusual ultrahigh-pressure (UHP), highly reduced and crustally derived minerals found either in situ or as separates in the chromitites and peridotites (e.g., [9][10][11][12][13][14][15][16][17][18][19][20][21]). [42]), and the distribution of magmatism on the Lhasa terrane (modified from Chung et al [43]).…”

Section: Introductionmentioning

confidence: 99%

“…The Luobusa ophiolite originated at a mid-ocean ridge spreading center at 177 ± 31 Ma and was later modified by supra-subduction zone (SSZ) magmatism at 120 ± 10 Ma involving an intra-oceanic subduction system [5][6][7]41,53,54]. However, the presence of ultrahigh-pressure (UHP) and highly reduced minerals such as diamond, coesite, and native elements, initially found in the chromitites but more recently also in their host peridotites, requires additional processes or models to outline the genesis of the chromitites (e.g., [4,10,11,13,[17][18][19][20][55][56][57]). …”

Section: Introductionmentioning

confidence: 99%

Timing of Secondary Hydrothermal Alteration of the Luobusa Chromitites Constrained by Ar/Ar Dating of Chrome Chlorites

Guo

et al. 2018

Minerals

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Chrome chlorites are usually found as secondary phases formed by hydrothermal alteration of chromite deposits and associated mafic/ultramafic rocks. Here, we report the 40 Ar/ 39 Ar age of chrome chlorites separated from the Luobusa massive chromitites which have undergone secondary alteration by CO 2 -rich hydrothermal fluids. The dating results reveal that the intermediate heating steps (from 4 to 10) of sample L7 generate an age plateau of 29.88 ± 0.42 Ma (MSWD = 0.12, plateau 39 Ar = 74.6%), and the plateau data points define a concordant inverse isochron age of 30.15 ± 1.05 Ma (MSWD = 0.08, initial 40 Ar/ 36 Ar = 295.8 ± 9.7). The Ar release pattern shows no evidence of later degassing or inherited radiogenic component indicated by an atmospheric intercept, thus representing the age of the hydrothermal activity. Based on the agreement of this hydrothermal age with the~30 Ma adakitic plutons exposed in nearby regions (the Zedong area, tens of kilometers west Luobusa) and the extensive late Oligocene plutonism distributed along the southeastern Gangdese magmatic belt, it is suggested that the hydrothermal fluids are likely related to the~30 Ma magmatism. The hydrothermal fluid circulation could be launched either by remote plutons (such as the Sangri granodiorite, the nearest~30 Ma pluton west Luobusa) or by a similar coeval pluton in the local Luobusa area (inferred, not found or reported so far). Our results provide important clues for when the listwanites in Luobusa were formed.

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“…(2) Although lightning strikes can produce SuR minerals such as silicon carbide (moissanite), native metals and metal silicides (e.g., Essene and Fisher, 1986;Rodgers et al, 1989;Sheffer et al, 2003), no UHP minerals have been reported from fulgurites; yet both moissanite and diamond grains occur together in ophiolite samples (Yang et al, , 2015aZhang et al, 2016). These grains are mostly 200-300 μm in size and typically have euhedral to subhedral morphologies, whereas the experiments by Ballhaus et al (2017) produced SiC crystals 100 times smaller, all of which are anhedral.…”

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confidence: 99%

Comment 2 on “Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes”

Yang¹,

Trumbull²,

Robinson³

et al. 2018

Geochem. Persp. Let.

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We read with great interest the paper by C. Ballhaus and coauthors (2017) reporting on electrical discharge experiments that showed how SiC and other phases found in mantle-derived rocks can potentially form by lightning strikes (Ballhaus et al., 2017). The experiments are technically innovative and challenging and the results make fascinating reading. In a comment paper, Griffin et al. (2018) noted several lines of evidence that ultra-high pressure (UHP) and super reduced (SuR) minerals in ophiolites do not form by lightning strikes. Here, we add additional comments relating to the geological and mineralogical data from ophiolites that are not compatible with the model of Ballhaus et al. (2017).(1) Not all of the samples of podiform chromitite and peridotite hosting UHP and SuR minerals were collected from surface outcrops exposed to lightning; many come from active mines 30-50 m below the surface, from the interiors of large blocks of ore, and/or from deep drill cores (Zhang et al., 2016(Zhang et al., , 2017. Fulgurites are near-surface features, typically consisting of highly shattered and brecciated rock, which rarely extend more than a few meters below the surface. Furthermore, many of the same UHP and SuR minerals are routinely found in kimberlites sampled by deep mining operations (Shiryaev et al. 2011) leaving no question of their presence in the deeper mantle.

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Diamonds, native elements and metal alloys from chromitites of the Ray-Iz ophiolite of the Polar Urals

Cited by 167 publications

References 114 publications

Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes

Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes

Timing of Secondary Hydrothermal Alteration of the Luobusa Chromitites Constrained by Ar/Ar Dating of Chrome Chlorites

Comment 2 on “Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes”

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