Geochemistry and origin of Mn-deposits in the Waziristan ophiolite complex, north Waziristan, Pakistan

1999 ◽  
Vol 34 (7) ◽  
pp. 697-704 ◽  
Author(s):  
M. T. Shah ◽  
A. Khan
Keyword(s):  
Ophiolite Complex

scholarly journals Investigations on a Fe–Ru–Os–Ir alloy inclusion found in a chromite-bearing ophiolite complex in SE Iran

2021 ◽  
Vol 6 (1) ◽  
pp. 50-54
Author(s):  
Jamal Tarrah ◽  
Kurt Mengel ◽  
Zahra Abedpour
Keyword(s):  
Ophiolite Complex

Nature and mechanism of ilmenite alteration: a Mössbauer and X-ray diffraction study of oxidized ilmenite from the Beja-Acebuches Ophiolite Complex (SE Portugal)

2002 ◽  
Vol 66 (3) ◽  
pp. 421-430 ◽  
Author(s):  
J. C. Waerenborgh ◽  
J. Figueiras ◽  
A. Mateus ◽  
M. Gonçalves
Keyword(s):  
Mössbauer Spectroscopy ◽  
Mossbauer Spectroscopy ◽  
X Ray Diffraction ◽  
Ophiolite Complex ◽  
Cation Site ◽  
X Ray ◽  
Mößbauer Spectroscopy ◽  
Ilmenite Structure ◽  
Optical Evidence ◽  
Excess Fe

AbstractIlmenites from the least-altered rocks of the Beja-Acebuches Ophiolite Complex (SE Portugal), with low Ti values and excess Fe, despite rare optical evidence of hematite exsolution, were studied by 57Fe Mössbauer spectroscopy and X-ray diffraction. According to single-crystal XRD the sequence of alternate layers characteristic of the ideal ilmenite structure is preserved, the excess Fe being accommodated in the Ti layers. No superparamagnetic oxides were detected by 57Fe Mössbauer spectroscopy. The typical spectra of bulk αFe2O3 and of Fe3+-containing ilmenite, in the paramagnetic state above 49 K and magnetically ordered at 6 K, are observed. The average degree of oxidation of the ilmenites, estimated from the chemical analysis assuming ideally stoichiometric full cation site occupancies, is also confirmed by 57Fe Mössbauer data. Since our crystal chemistry study gave no evidence of crypto-exsolution textures within the ilmenite with the observed compositions, fast cooling from magmatic temperatures and decomposition of ilmenite in supergene conditions is suggested.

Geochemical processes and petrogenetic evolution of rodingite dykes in the ophiolite complex of Othrys (Central Greece)

Lithos ◽  
2009 ◽  
Vol 113 (3-4) ◽  
pp. 540-554 ◽  
Author(s):  
Basilios Tsikouras ◽  
Sofia Karipi ◽  
Ioannis Rigopoulos ◽  
Maria Perraki ◽  
Panagiotis Pomonis ◽  
...  
Keyword(s):  
Geochemical Processes ◽  
Ophiolite Complex ◽  
Central Greece

Platinum-group mineral characterisation in concentrates from low-grade PGE chromitites from the Vourinos ophiolite complex, northern Greece

2006 ◽  
Vol 115 (2) ◽  
pp. 49-57 ◽  
Author(s):  
A. Kapsiotis ◽  
T. A. Grammatikopoulos ◽  
F. Zaccarini ◽  
B. Tsikouras ◽  
G. Garuti ◽  
...  
Keyword(s):  
Platinum Group Mineral ◽  
Low Grade ◽  
Northern Greece ◽  
Ophiolite Complex ◽  
Group Mineral ◽  
Platinum Group

The gabbro–dyke transition zone demonstrated on Tviberg, Solund–Stavfjord Ophiolite Complex

1996 ◽  
Vol 133 (5) ◽  
pp. 573-582 ◽  
Author(s):  
K. P. Skjerlie ◽  
H. Furnes
Keyword(s):  
Transition Zone ◽  
Basaltic Magma ◽  
Source Region ◽  
Geochemical Evolution ◽  
Dyke Swarm ◽  
Gradual Transition ◽  
Ophiolite Complex ◽  
Plutonic Complex ◽  
Plutonic Rocks ◽  
High Level

AbstractThe transition zone between 100 % dykes and high-level plutonic rocks of the Solund-Stavfjord Ophiolite Complex is complex due to the existence of many lithologies with different and variable contact relationships. The rocks of the plutonic complex vary in composition from FeTi basaltic to quartz dioritic, and the grain sizes vary from fine to pegmatitic. Felsic varieties are produced by fractional crystallization of basaltic magma as demonstrated by geochemical evolution and by gradual transition from gabbro to quartz diorite. Patches of fractionated dioritic rocks may show both gradual and intrusive relationships with the surrounding host gabbro. This demonstrates that late-stage liquids commonly left the source region and locally intruded the surrounding parent rocks. The high-level plutonic rocks are thoroughly epidotized and are cut by dykes consisting of granoblastic epidote and quartz. The high-level plutonic complex is associated with irregular bodies of fine- to medium-grained plagioclase-porphyritic diabase of high MgO content. These diabase bodies are intruded by dykes that become progressively more regular in shape. The plutonic complex locally shows intrusive relationships with the overlying 100% dyke complex, but is itself cut by two dyke swarms. The dykes of the first swarm formed while the plutonic complex experienced sinistral shear strain, and the dykes are generally less regular and thinner than the dykes of the second swarm. This indicates that the dykes of the first swarm intruded while the rocks of the plutonic complex were still hot, while the next dyke swarm intruded later when the rock complex was colder. Dykes of both swarms range in composition from slightly to strongly fractionated, suggesting that the magma chambers they were expelled from underwent significant fractionation in between magma replenishment. Numerous dykes of both swarms carry large quantities of glomeroporphyritic aggregates of plagioclase and altered clinopyroxene, indicating that the source area to the dykes very often was a crystal mush.

Melt Percolation, Melt-Rock Reaction and Oxygen Fugacity in Supra-Subduction Zone Mantle and Lower Crust from the Leka Ophiolite Complex, Norway

2021 ◽  
Author(s):  
Brian O’Driscoll ◽  
Julien Leuthold ◽  
Davide Lenaz ◽  
Henrik Skogby ◽  
James M D Day ◽  
...  
Keyword(s):  
Single Crystal ◽  
Subduction Zone ◽  
Oxygen Fugacity ◽  
Lower Crust ◽  
Oceanic Lithosphere ◽  
Ophiolite Complex ◽  
Global Comparison ◽  
Oceanic Spreading ◽  
Melt Percolation ◽  
Lower Crustal

Abstract Samples of peridotites and pyroxenites from the mantle and lower crustal sections of the Leka Ophiolite Complex (LOC; Norway) are examined to investigate the effects of melt-rock reaction and oxygen fugacity variations in the sub-arc oceanic lithosphere. The LOC is considered to represent supra-subduction zone (SSZ) oceanic lithosphere, but also preserves evidence of pre-SSZ magmatic processes. Here we combine field and microstructural observations with mineral chemical and structural analyses of different minerals from the major lithologies of the LOC. Wehrlite and websterite bodies in both the mantle and lower crust contain clinopyroxene likely formed at a pre-SSZ stage, characterised by high Al, high Cr, low Mg crystal cores. These clinopyroxenes also exhibit low Al, low Cr, high Mg outer rims and intracrystalline dissolution surfaces, indicative of reactive melt percolation during intrusion and disruption of these lithologies by later, SSZ-related, dunite-forming magmas. Chromian-spinel compositional variations correlate with lithology; dunite-chromitite Cr-spinels are characterised by relatively uniform and high TiO2 and Al2O3, indicating formation by melt-rock reaction associated with SSZ processes. Harzburgite Cr-spinel compositions are more variable but preserve a relatively high Al2O3, low TiO2 endmember that may reflect crystallisation in a pre-SSZ oceanic spreading centre setting. An important finding of this study is that the LOC potentially preserves the petrological signature of a transition between oceanic spreading centre processes and subsequent supra-subduction zone magmatism. Single crystal Cr-spinel Fe3+/ΣFe ratios calculated on the basis of stoichiometry (from electron microprobe [EPMA] and crystal structural [X-ray diffraction; XRD] measurements) correlate variably with those calculated by point-source (single crystal) Mössbauer spectroscopy. Average sample EPMA Fe3+/ΣFe ratios overestimate or underestimate the Mössbauer-derived values for harzburgites, and always overestimate the Mössbauer Fe3+/ΣFe ratios for dunites and chromitites. The highest Fe3+/ΣFe ratios, irrespective of method of measurement, are therefore generally associated with dunites and chromitites, and yield calculated log(fO2)FMQ values of up to ~+1.8. While this lends support to the formation of the dunites and chromitites during SSZ-related melt percolation in the lower part of the LOC, it also suggests that these melts were not highly oxidised, compared to typical arc basalts (fO2FMQ of >+2). This may in turn reflect the early (forearc) stage of subduction zone activity preserved by the LOC and implies that some of the arc tholeiitic and boninitic lava compositions preserved in the upper portion of the ophiolite are not genetically related to the mantle and lower crustal rocks, against which they exhibit tectonic contacts. Our new data also have implications for the use of ophiolite chromitites as recorders of mantle oxidation state through time; a global comparison suggests that the Fe3+/ΣFe signatures of ophiolite chromitites are likely to have more to do with local environmental petrogenetic conditions in sub-arc systems than large length-scale mantle chemical evolution.

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