Chemical characteristics of chromian spinel in plutonic rocks: Implications for deep magma processes and discrimination of tectonic setting

Arai, Shoji; Okamura, Hidenobu; Kadoshima, K.; Tanaka, Chima; Suzuki, Kenji; Ishimaru, Satoko

doi:10.1111/j.1440-1738.2010.00747.x

Cited by 134 publications

(74 citation statements)

References 81 publications

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“…Alternated formation of olivine-oversaturated and clinopyroxene-oversaturated magmas would be required, and a kind of supersaturation of magma with olivine or clinopyroxene around the olivine-clinopyroxene cotectic boundary is potentially capable of accumulating such series of rocks, although this model is very speculative. The concerned magma for the Takashima cumulates is of arc affinity based on high Cr# and low TiO 2 content of the chromian spinel (Table 1) (Arai et al, 2011); these data are consistent with their mode of occurrence as xenoliths on the Southwest Japan arc (cf., Arai et al, 2000). A much more detailed examination is possible on the Moho transition zone of ophiolites of arc origin such as Turkish ones (e.g., Parlak et al, 2002), in which the spatial relation of individual rocks is much clearer on outcrops.…”

Section: Discussionsupporting

confidence: 73%

Formation process of olivine–clinopyroxene cumulates inferred from Takashima xenoliths, Southwest Japan arc

Muroi

Arai

2014

Journal of Mineralogical and Petrological Sciences

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Rocks of the dunite-clinopyroxenite series (dunite, wehrlite, olivine clinopyroxenite, and clinopyroxenite) are common as cumulates formed around Moho in arc-related environments, but their formation processes remain unclear. They are common as xenoliths of Group I from Takashima in the Southwest Japan arc, and a description of their formation process is provided here. The rocks vary from dunite to clinopyroxenite via wehrlite and olivine clinopyroxenite, and all showing mosaic equigranular to weakly porphyroclastic textures. The rocks are completely free from plagioclase, and they contain <3 vol% chromian spinel. Some of them contain up to 3 vol% orthopyroxene; these are approximate mixtures of olivine and clinopyroxene. As the dunites change to clinopyroxenites, the Mg# [= Mg/(Mg + total Fe) atomic ratio] varies from 0.93 to 0.84 in olivine, and from 0.92 to 0.87 in clinopyroxene. The Cr# [= Cr/(Cr + Al) atomic ratio] of the chromian spinel varies from 0.8 to 0.2 with decreases in the Mg# of olivine and clinopyroxene. The Mg-Fe distribution relation between olivine and clinopyroxene suggests their subsolidus equilibration is around 800-900°C. Initial Mg#s expected at a magmatic temperature indicate that their formation proceeded from magma in the order of Mg-rich dunites followed by clinopyroxenites and then less Mg-rich dunite-wehrlite-olivine clinopyroxenite. This suggests a zigzag liquid path, starting from a mantle-derived olivine-oversaturated magma, around the olivine-clinopyroxene cotectic boundary. Continuous crystallization of olivine or clinopyroxene due to supersaturation could have enabled the magma to straddle the cotectic boundary to form alternately clinopyroxene-and olivineoversaturated magmas.

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Section: Discussionsupporting

confidence: 73%

Formation process of olivine–clinopyroxene cumulates inferred from Takashima xenoliths, Southwest Japan arc

Muroi

Arai

2014

Journal of Mineralogical and Petrological Sciences

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“…1c). The characteristics of spinels from the chromitite and dunite are beyond the compositional range of MORB -related spinels, while within the compositional range of arc -related plutonic rocks (Arai et al, 2011) (Fig. 3).…”

Section: Boninite Magmatismmentioning

confidence: 99%

“…3). The spinel chemistry of chromitite and surrounding peridotites indicates that the magma involved in discordant chromitite formation was arcrelated magma, such as boninite (Arai et al, 2011;Miura et al, 2012) (Fig. 3).…”

Section: Boninite Magmatismmentioning

confidence: 99%

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Formation of discordant chromitite at the initiation of sub-arc mantle processes: Observations from the northern Oman ophiolite

Miura

Arai

Tamura

2014

Journal of Mineralogical and Petrological Sciences

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Discordant chromitite, one of the structural types of ophiolitic chromitite, and surrounding peridotites, were examined in the mantle section of the northern Oman ophiolite along Wadi Hilti, to constrain its origin. Spinels from chromitite and adjacent peridotites show high Cr# (= Cr/(Cr + Al) atomic ratio), around 0.65 to 0.75, indicating an arc -related feature. Clinopyroxenes from adjacent harzburgites show low HREE contents, indicating a highly depleted character. The calculated melt composition in equilibrium with clinopyroxene in the dunite envelope indicates that the chromitite and surrounding peridotites were derived from arc -related magma, such as boninite. The arc -related magma was probably generated by the flux melting of depleted mantle harzburgite on the subducted slab, in terms of incompatible element enrichment in clinopyroxene from dunite and harzburgite. The highly depleted harzburgite surrounding discordant dunite and chromitite shows transitional changes in spinel and REE chemistry toward the surrounding oceanic harzburgites. This feature indicates that pre -existing oceanic harzburgite was partially modified by arc -related magma. Discordant chromitite, dunite, and highly depleted harzburgites are probably formed at the supra -subduction zone environment just before ophiolite obduction. Such arc -related features in mantle peridotite may be produced at a young sub -arc mantle.

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“…The low TiO 2 con tent and aluminous na ture of the GJSM and BBM chro mites are typ i cal for MORB or arc ba salt (Arai et al, 2011;Ghosh et al, 2013), and we sug gest that these are the pos si ble tec tonic set tings of the Lower Silesian chromitites (Fig. 7).…”

Section: Discussionmentioning

confidence: 97%

Podiform chromitites from the Variscan ophiolite serpentinites of Lower Silesia (SW Poland) - petrologic and tectonic setting implications

Wojtulek

Puziewicz

Ntaflos

et al. 2015

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1 Uni ver sity of Wroc³aw, In sti tute of Geo log i cal Sci ences, pl. M. Borna 9, 50-204 Wroc³aw, Po land 2 Uni ver sity of Vi enna, De part ment of Lithospheric Re search, Althanstrasse 14, 1090 Vi enna, Aus tria Wojtulek, P.M., Puziewicz, J., Ntaflos, T., Buka³a, M., 2016. Podiform chromitites from the Variscan ophiolite serpentinites of Lower Silesia (SW Po land) -pet ro logic and tec tonic set ting im pli ca tions. Geo log i cal Quar terly, 60 (1): 56-66, doi: 10.7306/gq.1238The Gogo³ów-Jordanów Ser pen tin ite Mas sif (GJSM) and the Braszowice-BrzeŸnica Mas sif (BBM) are the larg est ser pentin ite out crops in the Fore-Sudetic Block (NE part of the Bo he mian Mas sif, Cen tral Eu rope). The GJSM is a peridotitic member of the Variscan OElê¿a Ophiolite (SW Po land). Podiform bod ies (veins and pock ets) of chromitite are found on the Czernica Hill (GJSM) and on the Grochowiec Hill (BBM) within strongly serpentinised harzburgites which oc cur sev eral hundred metres be low Palaeo-Moho. Chromitites con sist of rounded chro mite grains up to 3 cm across, and of chlorite fill ing the in ter stices. The veins are em bed ded in serpentine-olivine-chlorite ag gre gates. Rel ics of Mg-rich ol iv ine (Fo 95-96 ) oc cur in mas sive chromitite in the BBM. The bulk-rock to tal PGEs con tent is very low (42-166 ppm) and the PGE pat tern is neg a tively sloped to wards Pt and Pd and de pleted rel a tive to chondrite. The pri mary chro mite I is aluminous (Cr# 0.50-0.52, Mg# 0.60-0.70). The highly aluminous and magnesian (Cr# 0.38, Mg# 0.80) chro mite Ia oc curs lo cally in the BBM. The sec ond ary chro mite II is en riched in Cr and im pov er ished in Al (Cr# 0.57-0.69), it re places chro mite I. Both chro mite I and II con tain small amounts of Ti (<0.14 wt.% TiO 2 ). Sil i cate in clu sions in chro mite are scarce. The com po si tion and mode of oc cur rence of both the GJSM and the BBM chromitites are sim i lar, thus they were formed prob a bly un der the same con di tions. Tex tures of the chromitites sug gest their mag matic or i gin. Their cur rent geo log i cal po si tion in di cates their em place ment and crys tal lisa tion in the up per most man tle harzburgites oc cur ring be low the Moho Tran si tion Zone. The chromitites and host ing harzburgites were sub jected to the greenschist-fa cies meta mor phic over print. The mod er ate Cr# and low PGEs con tents sug gest that the chromitites orig i nated in the arc set ting, thus their host ophiolite is of su pra-subduction type.

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Chemical characteristics of chromian spinel in plutonic rocks: Implications for deep magma processes and discrimination of tectonic setting

Cited by 134 publications

References 81 publications

Formation process of olivine–clinopyroxene cumulates inferred from Takashima xenoliths, Southwest Japan arc

Formation process of olivine–clinopyroxene cumulates inferred from Takashima xenoliths, Southwest Japan arc

Formation of discordant chromitite at the initiation of sub-arc mantle processes: Observations from the northern Oman ophiolite

Podiform chromitites from the Variscan ophiolite serpentinites of Lower Silesia (SW Poland) - petrologic and tectonic setting implications

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