The origin and significance of crustal minerals in ophiolitic chromitites and peridotites

Robinson, Paul T.; Trumbull, Robert B.; Schmitt, Axel K.; Yang, Jingsui; Li, Jianwei; Zhou, Mei‐Fu; Erzinger, J.; Dare, Sarah A. S.; Xiong, Fahui

doi:10.1016/j.gr.2014.06.003

Cited by 163 publications

(85 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…They are neither prismatic nor rounded and appear practically featureless in CL images, lacking any pre-existing texture relics (i.e., oscillatory zoning; Figure 8). Zircons are entirely absent from the mesh-textured serpentinized groundmass; possibly entrapment of old inherited zircons in olivine could effectively protect them from the ambient environment [22]. The zircon-pargasite intergrowths in Cr-spinel are anhedral with a granular texture (Figure 6a) unlike those described by [68].…”

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 94%

“…Three main scenarios have been proposed to explain the 'paradoxical' finding of Zr-rich phases in ophiolitic chromitites: (i) incorporation of ancient zircons in the sub-oceanic mantle by ascending fluids/melts as a result of deep subduction [22]; (ii) precipitation of Zr-dominant phases by rich-in-fluid melts related to mantle metasomatism (e.g., [64,65]) and (iii) introduction of zircon in chromitites through (a network of) intergranular fluids representing late fractions of igneous intrusions in the upper mantle [27,28].…”

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 99%

“…Xenocrystic zircons have been described from several chromitite occurrences over the globe [21][22][23][24][25][26]. We note that recycled zircons from the Tibetan (Luobusa, Dongqiao), Semail (Oman) and Ray-Iz (Urals) chromitites have complex internal structures and co-occur with various combinations of super-reducing ultrahigh-pressure (SuR-UHP) minerals without showing resetting of their U-Pb ages [22,26]. However, a SuR-UHP mineral assemblage is missing from the Ayios Stefanos chromitites and the studied zircons show metamictization at variable degrees.…”

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 99%

See 2 more Smart Citations

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

et al. 2016

View full text Add to dashboard Cite

Several small chromium (Cr) ore bodies are hosted within a unit of tectonically thinned dunite in the retired Ayios Stefanos mine of the western Othris ophiolite complex in Greece. Chromium ores consist of tectonically imprinted bodies of semi-massive to massive, podiform and lenticular chromitites composed of chromian spinel [Cr-spinel] and mid-ocean ridge basalts (MORBs). Several Cr-spinel crystals in these ores exhibit imperfect zones made up of spinel hosting oriented lamellae of Mg-silicates (mostly chlorite) locally overgrown by porous domains along grain boundaries and fractures. From the Cr-spinel core to the lamellae-rich rim Cr#, Mg# and Fe 3+ # generally increase (0.68-0.87, 0.78-0.88 and 0.55-0.80, respectively), whereas from the core or the spinel zones with oriented lamellae to the porous domains Mg# and Fe 3+ # generally decrease (0.45-0.74 and ≤0.51, correspondingly). The lamellae-rich rims formed at oxidizing conditions, whereas the porous rims resulted from a later reducing event. Several tiny (≤30 µm), subhedral to anhedral and elongated Zr-bearing silicate mineral grains were discovered mainly along open and healed fractures cutting Cr-spinel. Most of the Zr-bearing silicate minerals (30 out of 35 grains) were found in a chromitite boulder vastly intruded by a complex network of gabbroic dykes. The dominant Zr-bearing silicate phase is by far zircon displaying a homogeneous internal texture in cathodoluminescence (CL) images. Raman spectroscopy data indicate that zircons have experienced structural damage due to self-irradiation. Their trace-element contents suggest derivation from a plagioclase-bearing, low-SiO 2 intermediate to mafic source. Combined micro-textural and minerochemical data repeat the possibility of zircon derivation from limited volumes of high-T fluids emanating from the gabbroic intrusions. Once zircon is precipitated in cracks, it may be altered to Ca-rich Zr-bearing silicate phases (i.e., armstrongite, calciocatapleiite). Almost all zircons in these samples show evidence of gains in solvent compounds (CaO, Al 2 O 3 and FeO) possibly due to re-equilibration with late deuteric fluids.

show abstract

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 94%

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 99%

Section: An Inductive Reasoning Approach To the Potential Origin Of Zmentioning

confidence: 99%

See 1 more Smart Citation

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Very recently this has all changed and a series of newly published studies have extended our knowledge of the Earth's hidden depths enormously and have brought with them some great surprises. These results were presented by Jing-sui Yang, Paul Robinson and colleagues of the Chinese Academy of Geological Sciences in Beijing and Bill Griffin and colleagues at Macquarie University, Australia at a scientific meeting in Beijing in 2014 and more recently the details of their work have been published (Yang et al, 2014Robinson et al, 2015;McGowan et al, 2015).…”

mentioning

confidence: 89%

Surprises from the top of the mantle transition zone

Rollinson

2016

Geology Today

View full text Add to dashboard Cite

Recent studies of chromite deposits from the mantle section of ophiolites have revealed a most unusual collection of minerals present as inclusions within the chromite. The initial discoveries were of diamonds from the Luobosa ophiolite in Tibet. Further work has shown that mantle chromitites from ophiolites in Tibet, the Russian Urals and Oman contain a range of crustal minerals including zircon, and a suite of highly reducing minerals including carbides, nitrides and metal alloys. Some of the minerals found represent very high pressure phases indicating that their likely minimum depth is close to the top of the mantle transition zone. These new results suggest that crustal materials may be subducted to mantle transition zone depths and subsequently exhumed during the initiation of new subduction zones—the most likely environment for the formation of their host ophiolites. The presence of highly reducing phases indicates that at mantle transition zone depths the Earth's mantle is ‘super’‐reducing.

show abstract

“…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%

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

Guo

et al. 2018

Minerals

View full text Add to dashboard Cite

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.

show abstract

The origin and significance of crustal minerals in ophiolitic chromitites and peridotites

Cited by 163 publications

References 59 publications

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

Surprises from the top of the mantle transition zone

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

Contact Info

Product

Resources

About