scholarly journals Multi-stage fluid infiltration and metasomatism in supra-subduction zone mantle: evidence from halogens and noble gases in the Leka Ophiolite Complex, Norway

2021 ◽  
Author(s):  
Elliot Carter ◽  
Brian O'Driscoll ◽  
Ray Burgess ◽  
Patricia Clay
Keyword(s):  
Subduction Zone ◽  
Noble Gases ◽  
Ophiolite Complex ◽  
Fluid Infiltration ◽  
Multi Stage

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.

Magnetite Redistribution during Multi-stage Serpentinization: Evidence from the Taishir massif, the Khantaishir Ophiolite, Western Mongolia

2021 ◽  
Author(s):  
Otgonbayar Dandar ◽  
Atsushi Okamoto ◽  
Masaoki Uno ◽  
Noriyoshi Tsuchiya
Keyword(s):  
Hydrogen Generation ◽  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
Ultramafic Rocks ◽  
Western Mongolia ◽  
Fluid Infiltration ◽  
Multi Stage ◽  
Fe Content ◽  
Coarse Grains ◽  
Modal Abundance

<p>Magnetite commonly forms during serpentinization of mantle peridotite, involving the hydrogen generation within the oceanic lithosphere. Although magnetite is concentrated in veins, the mobility of iron during serpentinization is still poorly understood. The completely serpentinized ultramafic rocks (originally dunite) within the Taishir massif in the Khantaishir ophiolite, western Mongolia, include abundant magnetite + antigorite veins, which manifest novel distribution of magnetite. The serpentinite records the multi-stage serpentinization, in order of (1) Al-rich antigorite + lizardite mixture with hourglass texture (Al<sub>2</sub>O<sub>3</sub> = 0.46-0.69 wt%; Atg+Lz), (2) Al-poor antigorite composed of thick veins and their branches (Atg), and (3) chrysotile that cut all previous textures. The Mg# (= Mg/ (Mg + Fe<sub>total</sub>)) of Atg+Lz (0.94-0.96) is lower than Atg (0.99) and chrysotile (0.98). In the region of Atg+Lz, magnetite occurs as the arrays of fine grains (<50 μm) around the hourglass texture. In the Atg veins replacing Atg+Lz, magnetite disappears and re-precipitated as coarse grains (100-250 μm) in the center of some veins. As the extent of replacement of Atg+Lz by Atg veins increases, both modal abundance of magnetite and the bulk Fe content decrease. These characteristics indicate that hydrogen generation mainly occurred at the stage of Atg+Lz formation, and magnetite distribution was largely modified via dissolution and precipitation in response to later fluid infiltration associated with the Atg veins. This also indicates the high iron mobility within the serpentinized peridotites even after the primary stage of magnetite formation.</p>

Paleomagnetic results from the western Himalaya indicate multi-stage India-Eurasia collision

2021 ◽  
Author(s):  
Craig R Martin ◽  
Oliver Jagoutz ◽  
Rajeev Upadhyay ◽  
Leigh H Royden ◽  
Michael P Eddy ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Classical Model ◽  
Western Himalaya ◽  
Paleomagnetic Data ◽  
Northwestern Part ◽  
Himalayan Orogeny ◽  
The North ◽  
Multi Stage ◽  
Early Paleocene ◽  
Stage Process

<p>The classical model for the collision between India and Eurasia, which resulted in the formation of the Himalayan orogeny, is a single-stage continent-continent collision event at around 55 – 50 Ma. However, it has also been proposed that the India-Eurasia collision was a multi-stage process involving an intra-oceanic Trans-Tethyan subduction zone south of the Eurasian margin. We present paleomagnetic data constraining the location the Kohistan-Ladakh arc, a remnant of this intra-oceanic subduction zone, to a paleolatitude of 8.1 ± 5.6 °N between 66 – 62 Ma. Comparing this result with new paleomagnetic data from the Eurasian Karakoram terrane, and previous paleomagnetic reconstructions of the Lhasa terrane reveals that the Trans-Tethyan Subduction zone was situated 600 – 2,300 km south of the contemporaneous Eurasian margin at the same time as the first ophiolite obduction event onto the northern Indian margin. Our results confirm that the collision was a multistage process involving at least two subduction systems. Collision began with docking between India and the Trans-Tethyan subduction zone in the Late Cretaceous and Early Paleocene, followed by the India-Eurasia collision in the mid-Eocene. The final stage of India-Eurasia collision occurred along the Shyok-Tsangpo suture zone, rather than the Indus-Tsangpo. The addition of the Kshiroda oceanic plate, north of India after the Paleocene reconciles the amount of convergence between India and Eurasia with the observed shortening across the India–Eurasia collision system. Our results constrain the total post-collisional convergence accommodated by crustal deformation in the Himalaya to 1,350 – 2,150 km, and the north-south extent of the northwestern part of Greater India to < 900 km.</p>

scholarly journals Recycling of nitrogen and light noble gases in the Central American subduction zone: Constraints from 15N15N

2021 ◽  
Vol 571 ◽  
pp. 117112
Author(s):  
J. Labidi ◽  
E.D. Young ◽  
T.P. Fischer ◽  
P.H. Barry ◽  
C.J. Ballentine ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Noble Gases ◽  
Central American ◽  
Central American Subduction Zone

scholarly journals Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia

2021 ◽  
Vol 26 (53) ◽  
pp. 1-17
Author(s):  
Nomuulin Amarbayar ◽  
Noriyoshi Tsuchiya ◽  
Otgonbayar Dandar ◽  
Atsushi Okamoto ◽  
Masaoki Uno ◽  
...  
Keyword(s):  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
Bulk Rock ◽  
Fluid Infiltration ◽  
Multi Stage ◽  
Central Asian ◽  
Bulk Rock Chemistry ◽  
Three Stages ◽  
Arc Setting ◽  
Global Cycle

Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si < 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (<300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.

scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
Vol 2(11)2011 (2(11)) ◽  
pp. 269-271
Author(s):  
A.G. Rodnikov ◽  
◽  
L. Zabarinskaya ◽  
N. Sergeyeva ◽  
◽  
...  
Keyword(s):  
Subduction Zone ◽  
Sedimentary Basin ◽  
Deep Structure ◽  
Deryugin Basin ◽  
Ophiolite Complex ◽  
The North ◽  
Deep Faults

The constructed model for a deep structure of the lithospere under the Neftegorsk earthquake region shows that North Sakhalin consists of the North Sakhalin sedimentary basin, the Deryugin basin and the ophiolite complex located between them. The ophiolite complex composed of the the ultrabasic rocks, fixes the position of the ancient subduction zone which was active about 100-60 million years ago. On a surface the subduction zone manifests itself as deep faults running along Sakhalin. The center of the Neftegorsk earthquake was directly formed by burst of activity of this ancient subduction zone.

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