Origin of podiform chromitite, a new model based on the Luobusa ophiolite, Tibet

Xiong, Fahui; Yang, Jingsui; Robinson, Paul T.; Xu, Xing; Liu, Zhao; Li, Yuan; Li, Jinyang; Chen, Songyong

doi:10.1016/j.gr.2014.04.008

Cited by 128 publications

(78 citation statements)

References 42 publications

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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%

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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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Section: Introductionmentioning

confidence: 99%

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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“…The origin of podiform chromitite has diverse hypotheses, including fractional crystallization from ultramafic melts [ Dickey , ; Lago et al ., ; Leblanc and Ceuleneer , ], mixing or mingling of melts within dunite channels [ Arai and Abe , ; Arai , ; Zhou et al ., ], and residue of partial melting [ Dick and Bullen , ; Yang et al ., ; Yamamoto et al ., ]. However, none of these hypotheses yet provides convincing explanation for the chemical features of chromite and associated olivine in chromitites such as the extremely high chromite Cr# (up to 83) and olivine Fo (up to 98) [ Zhou et al ., ; Xiong et al ., ]. In addition, highly variable Mg# (49–71) with constant Cr# (76–83) of chromite in different types of ores [ Xiong et al ., ] indicates more heterogeneous distribution of Fe and Mg relative to Cr and Al in chromite.…”

Section: Introductionmentioning

confidence: 99%

Iron and magnesium isotopic constraints on the origin of chemical heterogeneity in podiform chromitite from the Luobusa ophiolite, Tibet

Xiao

Teng

et al. 2016

Geochem Geophys Geosyst

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We present high‐precision measurements of iron (Fe) and magnesium (Mg) isotopic compositions of olivine, orthopyroxene, and chromite separates from harzburgites, dunites, and chromitites in the mantle section of the Luobusa ophiolite, southern Tibet, to investigate the origins of podiform chromitite. Two harzburgites in the Zedong ophiolite, southern Tibet, are also reported for comparison. The olivine and orthopyroxene in the Luobusa and Zedong harzburgites have similar Fe and Mg isotopic compositions, with δ56Fe values ranging from 0‰ to +0.083‰ in olivine, from −0.034‰ to +0.081‰ in orthopyroxene and δ26Mg values ranging from −0.25‰ to −0.20‰ in olivine, from −0.29‰ to −0.26‰ in orthopyroxene, respectively. The olivines of two dunites from the Luobusa display small Fe and Mg isotopic variations, with δ56Fe values of +0.014‰ and +0.116‰ and δ26Mg values of −0.21‰ and −0.29‰. All chromites in the Luobusa chromitites have lighter Fe isotopic compositions than the coexisting olivines, with δ56Fe values ranging from −0.247‰ to +0.043‰ in chromite and from −0.146‰ to +0.215‰ in olivine (Δ56FeChr‐Ol = −0.294 to −0.101‰). The chromite δ26Mg values span a significant range from −0.41‰ to +0.14‰. Large disequilibrium Fe and Mg isotope fractionation between chromite and olivine, as well as positive correlation of chromite δ56Fe values with their MgO contents, could be attributed to Fe‐Mg exchange between chromite and olivine. In the disseminated chromitites, the higher modal abundances of olivine than chromite would result in a more extensive Fe‐Mg exchange, whereas chromite in the massive chromitite where olivine is rare could not be affected by this process.

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“…Because light and heavy REE cannot be easily fractionated during the differentiation of mantle-derived magmas (Ariskin et al, 1993;Hanson, 1980), the REE patterns of chromitites are theoretically effective in restoring the features of their parental magmas. During the formation of chromitites, dunites can be produced through melt-harzburgite interaction or magmatic accumulation (Arai and Yurimoto, 1994;Proenza et al, 1999;Rollinson, 2008;Xiong et al, 2015;Zhou et al, 1994. Given this genetic relationship, the geochemical features of dunites provide another important mean of exploring the relationship between high-Cr chromitite and magmatism during the initial stage of subduction.…”

Section: Introductionmentioning

confidence: 99%

Subduction initiation for the formation of high-Cr chromitites in the Kop ophiolite, NE Turkey

Zhang

Uysal

Zhou

et al. 2016

Lithos

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The Kop ophiolite in NE Turkey is a forearc fragment of Neo-Tethys ocean, consisting mainly of a paleo-Moho transition zone (MTZ) and a harzburgitic upper mantle unit. Locally, the Kop MTZ contains cumulate dunites and high-Cr chromitites (Cr# up to ca. 79), which are cut by pyroxenites. Dunites and chromitites in the MTZ have REE concentrations that are 1-2 orders of magnitude lower than those of chondrite; they are either depleted in LREE or have concave REE shapes. The LREE depleted patterns are interpreted to reflect production of cumulate rocks by magmas derived from a depleted mantle, the concave patterns the modification of these rocks by LREEenriched fluids. Clinopyroxenes from pyroxenites are diopsidic and characterized by high Mg#s (ca. 92-96) and high CaO contents (ca. 24-25 wt.%); their Al 2 O 3 contents (1.0-3.0 wt.%) fall between those of clinopyroxenes in N-MORB and komatiite/boninite, suggesting that the parental melts originated from more refractory mantle than abyssal lherzolites. However, these clinopyroxenes display LREE depleted patterns consistent with those of clinopyroxenes in abyssal lherzolites, indicating their genetic connection with decompression melting of asthenosphere. The cross-cutting relationship between pyroxenite veins and chromitiferous rocks suggests that depleted mantle remained beneath the proto-forearc after chromitite formation; it had not been significantly modified by slab-derived components and continued interacting with the upwelling asthenosphere until pyroxenite crystallization. This study provides a temporal constraint on the formation of high-Cr chromitites; they possibly began to be produced during the transition between early and late proto-forearc spreading, during which subduction dehydration had not well developed.

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Origin of podiform chromitite, a new model based on the Luobusa ophiolite, Tibet

Cited by 128 publications

References 42 publications

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

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

Iron and magnesium isotopic constraints on the origin of chemical heterogeneity in podiform chromitite from the Luobusa ophiolite, Tibet

Subduction initiation for the formation of high-Cr chromitites in the Kop ophiolite, NE Turkey

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