Unexpectedly high-PGE chromitite from the deeper mantle section of the northern Oman ophiolite and its tectonic implications

Ahmed, Abdulhakim; Arai, Shoji

doi:10.1007/s00410-002-0347-8

Cited by 243 publications

(154 citation statements)

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“…Pos sibly, ol iv ine (Fo 95-96 ) co ex ist ing with chro mite in the mas sive BBM gives a hint of com po si tion of "du nite en ve lope". Its compo si tion is sim i lar to that of olivines from Oman (Ahmed and Arai, 2002).…”

Section: Discussionmentioning

confidence: 68%

“…Cr sol u bil ity in ba saltic melt is low (of the or der of a few hundred ppm; Roeder and Reynolds, 1991), and oversaturation in Cr is reached readily, trig ger ing the pre cip i ta tion of chromitites (Ahmed and Arai, 2002). The sil i cate phase in clu sions (crys tallised from the melt) oc cur typ i cally in this type of chro mite (Borisova et al, 2012).…”

Section: Discussionmentioning

confidence: 99%

“…In Oman, the high-Al chromitites con tain 33-92 ppb to tal PGEs (Ahmed and Arai, 2002), whereas those from Lower Silesia con tain 42-79 ppb (GJSM) and 65-166 ppb (BBM). The Moho Tran si tion Zone (MTZ) in ophiolites com prises a dunitic layer with gab bro sills/lenses, con cor dant wehrlite sills/lenses, and chro mite pods, lo cated at the con tact be tween the up per most man tle harzburgites and the mas sive lay ered gab bro of the lower crust (Boudier and Nicolas, 1995;Koga et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

“…5) which suggests that no sig nif i cant frac tion ation of PGE-bear ing min er als af fected the magma from which chromitite crys tal lised. The Pd con tent in the stud ied chromitites is mostly be low the de tec tion limit, which could be ex plained by high mo bil ity of this el e ment dur ing the al ter ation pro cesses (Ahmed and Arai, 2002;Prichard and Brough, 2009).…”

Section: Discussionmentioning

confidence: 99%

“…The low PGE con tent in the stud ied chromitites and the Cr# of chro mite close to 0.50 cor re spond to chromitites from the Oman Ophiolite Moho Tran si tion Zone (MTZ) and their chromite (Ahmed and Arai, 2002;Page et al, 1982). In Oman, the high-Al chromitites con tain 33-92 ppb to tal PGEs (Ahmed and Arai, 2002), whereas those from Lower Silesia con tain 42-79 ppb (GJSM) and 65-166 ppb (BBM).…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 68%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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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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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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Distribution and Mobility of Platinum-Group Elements in the Late Cretaceous Ni-laterite in the Northern Oman Mountains

Al-Khirbash

Ahmed²

2021

Preprint

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Unexpectedly high-PGE chromitite from the deeper mantle section of the northern Oman ophiolite and its tectonic implications

Cited by 243 publications

References 44 publications

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

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

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

Distribution and Mobility of Platinum-Group Elements in the Late Cretaceous Ni-laterite in the Northern Oman Mountains

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