Discovery of in situ super-reducing, ultrahigh-pressure phases in the Luobusa ophiolitic chromitites, Tibet: New insights into the deep upper mantle and mantle transition zone

2016 ◽  
Vol 101 (6) ◽  
pp. 1285-1294 ◽  
Author(s):  
Ru Y. Zhang ◽  
Jing-Sui Yang ◽  
W.G. Ernst ◽  
Bor-Ming Jahn ◽  
Yoshiyuki Iizuka ◽  
...  
Keyword(s):  
Transition Zone ◽  
Upper Mantle ◽  
Ultrahigh Pressure ◽  
Mantle Transition Zone

Origin of the Indus ophiolite linked to the mantle transition zone (410–660 km)

2021 ◽  
Author(s):  
Souvik Das ◽  
Asish R. Basu
Keyword(s):  
Transition Zone ◽  
Plate Tectonics ◽  
Tectonic Setting ◽  
Ultrahigh Pressure ◽  
Historical Contingency ◽  
Mantle Transition Zone ◽  
Contingency Model ◽  
Mid Ocean Ridge ◽  
Consistent Change ◽  
Ocean Ridge

ABSTRACT The southeast Ladakh (India) area displays one of the best-preserved ophiolite sections in this planet, in places up to 10 km thick, along the southern bank of the Indus River. Recently, in situ, ultrahigh-pressure (UHP) mineralogical evidence from the mantle transition zone (MTZ; ∼410–660 km) with diamond and reduced fluids were discovered from two peridotite bodies in the basal mantle part of this Indus ophiolite. Ultrahigh-pressure phases were also found by early workers from podiform chromitites of another coeval Neo-Tethyan ophiolite in southern Tibet. However, the MTZ phases in the Indus ophiolite are found in silicate peridotites, but not in metallic chromitites, and the peridotitic UHP phases show systematic and contiguous phase transitions from the MTZ to shallower depth, unlike the discrete UHP inclusions, all in Tibetan chromitites. We observe consistent change in oxygen fugacity (fO2) and fluid composition from (C-H + H2) to (CO2 + H2O) in the upwelling peridotitic mantle, causing melting to produce mid-ocean-ridge basalt (MORB). At shallow depths (<100 km) the free water stabilizes into hydrous phases, such as pargasitic amphibole, capable of storing water and preventing melting. Our discoveries provide unique insights into deep sub-oceanic-mantle processes, and link deep-mantle upwelling and MORB genesis. Moreover, the tectonic setting of Neo-Tethyan ophiolites has been a difficult problem since the birth of the plate-tectonics concept. This problem for the origin of ophiolites in mid-ocean-ridge versus supra-subduction zone settings clearly confused the findings from Indus ophiolites. However, in this contribution, we provide arguments in favor of mid-ocean-ridge origin for Indus ophiolite. In addition, we venture to revisit the “historical contingency” model of E.M. Moores and others for Neo-Tethyan ophiolite genesis based on the available evidence and have found that our new results strongly support the “historical contingency” model.

scholarly journals Seismic waveform tomography of the central and eastern Mediterranean upper mantle

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 669-690 ◽  
Author(s):  
Nienke Blom ◽  
Alexey Gokhberg ◽  
Andreas Fichtner
Keyword(s):  
Subduction Zone ◽  
Transition Zone ◽  
Upper Mantle ◽  
High Velocity ◽  
Eastern Mediterranean ◽  
Crust And Upper Mantle ◽  
Mantle Transition Zone ◽  
Seismic Waveform ◽  
Waveform Tomography ◽  
Seismic Waveform Tomography

Abstract. We present a seismic waveform tomography of the upper mantle beneath the central and eastern Mediterranean down to the mantle transition zone. Our methodology incorporates in a consistent manner the information from body and multimode surface waves, source effects, frequency dependence, wavefront healing, anisotropy and attenuation. This allows us to jointly image multiple parameters of the crust and upper mantle. Based on the data from ∼ 17 000 unique source–receiver pairs, gathered from 80 earthquakes, we image radially anisotropic S velocity, P velocity and density. We use a multi-scale approach in which the longest periods (100–150 s) are inverted first, broadening to a period band of 28–150 s. Thanks to a strategy that combines long-period signals and a separation of body and surface wave signals, we are able to image down to the mantle transition zone in most of the model domain. Our model shows considerable detail in especially the northern part of the domain, where data coverage is very dense, and displays a number of clear and coherent high-velocity structures across the domain that can be linked to episodes of current and past subduction. These include the Hellenic subduction zone, the Cyprus subduction zone and high-velocity anomalies beneath the Italian peninsula and the Dinarides. This model is able to explain data from new events that were not included in the inversion.

scholarly journals Mantle transition zone thickness beneath Cameroon: evidence for an upper mantle origin for the Cameroon Volcanic Line

2011 ◽  
Vol 187 (3) ◽  
pp. 1146-1150 ◽  
Author(s):  
Angela Marie Reusch ◽  
Andrew A. Nyblade ◽  
Rigobert Tibi ◽  
Douglas A. Wiens ◽  
Patrick J. Shore ◽  
...  
Keyword(s):  
Transition Zone ◽  
Upper Mantle ◽  
Mantle Transition Zone ◽  
Cameroon Volcanic Line ◽  
Mantle Origin
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