scholarly journals Oceanic lithosphere heterogeneity in the eastern Paleo-Tethys revealed by PGE and ReOs isotopes of mantle peridotites in the Jinshajiang ophiolite

2020 ◽  
Author(s):  
Yan-Jun Wang ◽  
Wen-Jun Hu ◽  
Hong Zhong ◽  
Wei-Guang Zhu ◽  
Zhong-Jie Bai
Keyword(s):  
Oceanic Lithosphere ◽  
Mantle Peridotites

The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 23-28 ◽  
Author(s):  
Elisabetta Rampone ◽  
Alessio Sanfilippo
Keyword(s):  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Crustal Material ◽  
Crustal Accretion ◽  
Mantle Dynamics ◽  
Western Tethys ◽  
Mantle Peridotites ◽  
Slow Spreading ◽  
Tethys Ocean ◽  
Basaltic Crust

The Alpine–Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys.

scholarly journals Mineralogical Evidence for Partial Melting and Melt-Rock Interaction Processes in the Mantle Peridotites of Edessa Ophiolite (North Greece)

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 120 ◽  
Author(s):  
Aikaterini Rogkala ◽  
Petros Petrounias ◽  
Basilios Tsikouras ◽  
Panagiota Giannakopoulou ◽  
Konstantin Hatzipanagiotou
Keyword(s):  
Partial Melting ◽  
Mantle Wedge ◽  
Oceanic Lithosphere ◽  
Upper Jurassic ◽  
Northern Greece ◽  
Rock Interaction ◽  
Oceanic Spreading ◽  
Mantle Peridotites ◽  
Mineral Compositions ◽  
Ocean Ridge

The Edessa ophiolite complex of northern Greece consists of remnants of oceanic lithosphere emplaced during the Upper Jurassic-Lower Cretaceous onto the Palaeozoic-Mesozoic continental margin of Eurasia. This study presents new data on mineral compositions of mantle peridotites from this ophiolite, especially serpentinised harzburgite and minor lherzolite. Lherzolite formed by low to moderate degrees of partial melting and subsequent melt-rock reaction in an oceanic spreading setting. On the other hand, refractory harzburgite formed by high degrees of partial melting in a supra-subduction zone (SSZ) setting. These SSZ mantle peridotites contain Cr-rich spinel residual after partial melting of more fertile (abyssal) lherzolite with Al-rich spinel. Chromite with Cr# > 60 in harzburgite resulted from chemical modification of residual Cr-spinel and, along with the presence of euhedral chromite, is indicative of late melt-peridotite interaction in the mantle wedge. Mineral compositions suggest that the Edessa oceanic mantle evolved from a typical mid-ocean ridge (MOR) oceanic basin to the mantle wedge of a SSZ. This scenario explains the higher degrees of partial melting recorded in harzburgite, as well as the overprint of primary mineralogical characteristics in the Edessa peridotites.

Unravelling the Remagnetization of the Oman Ophiolite

2020 ◽  
Author(s):  
Louise Koornneef ◽  
Antony Morris ◽  
Michelle Harris ◽  
Christopher MacLeod
Keyword(s):  
Subduction Zone ◽  
Large Scale ◽  
Oceanic Lithosphere ◽  
Magnetic Fabric ◽  
Oman Ophiolite ◽  
Mantle Peridotites ◽  
Important Exception ◽  
Magnetic Techniques ◽  
Tectonic Rotation ◽  
Lower Crustal

<p>The Oman ophiolite is a natural laboratory for the study of processes operating above a nascent subduction zone. It formed in the Late Cretaceous by supra-subduction zone spreading and shortly afterwards was emplaced onto the Arabian continental margin. Twelve massifs in the ophiolite expose complete sections of the Neotethyan oceanic lithosphere, including upper mantle peridotites, lower crustal gabbros, and upper crustal sheeted dykes and lava flows.</p><p> </p><p>Previous palaeomagnetic studies have suggested that the southern massifs of the ophiolite were affected by a large-scale remagnetization event during emplacement, that completely replaced original remanences acquired during crustal accretion. In contrast, primary magnetizations are preserved throughout the northern massifs. This study aimed to: (i) apply palaeomagnetic, magnetic fabric and rock magnetic techniques to analyse crustal sections through the southern massifs of the Oman ophiolite to investigate further the extent and nature of this remagnetization event; and (ii) use any primary magnetizations that survived this event to document intraoceanic rotation of the ophiolite prior to emplacement.</p><p> </p><p>Our new data confirms that remagnetization appears to have been pervasive throughout the southern massifs, resulting in presence of shallowly-inclined NNW directions of magnetization at all localities. An important exception is the crustal section exposed in Wadi Abyad (Rustaq massif) where directions of magnetization change systematically through the gabbro-sheeted dyke transition. Demagnetization characteristics are shown to be consistent with acquisition of a chemical remanent overprint that decreased in intensity from the base of the ophiolite upwards. The top of the exposed Wadi Abyad section (in the sheeted dyke complex) appears to preserve original SE-directed remanences that are interpreted as primary seafloor magnetizations. Similar SE primary remanences were also isolated at a control locality in the Salahi massif, outside of the region of remagnetization. Net tectonic rotation analysis at these non-remagnetised sites shows an initial NNE-SSW strike for the supra-subduction zone ridge during spreading, comparable with recently published models for the regional evolution of the ophiolite.</p>

scholarly journals ON THE RELATIVELY COMPOSITIONAL HOMOGENEITY OF ALBANIAN EASTERN OPHIOLITIC BELT

2017 ◽  
Vol 50 (4) ◽  
pp. 1789
Author(s):  
Α. Çina
Keyword(s):  
Upper Mantle ◽  
Oceanic Lithosphere ◽  
Upper Jurassic ◽  
Sharp Separation ◽  
Mantle Peridotites ◽  
Compositional Homogeneity ◽  
Ophiolitic Belt ◽  
Mirdita Zone ◽  
Geological Units ◽  
Shed Light

Ophiolitic formation of Albanides, named as Mirdita zone, represents a compactsegment of oceanic lithosphere of Middle-Upper Jurassic. Based on petrographic,geochemical and metalogenical features two types of belts are distinguished: westernMORB and eastern SSZ types. In fact, structural and geological units as well as manyother elements have shed light on lack of a sharp separation between the two belts.Recent investigations have evidenced that different ultramafic massifs of westernophiolitic formation, represent an evident variation of their composition fromharzburgite to lherzolitic -types. This composition reflects a different grade of partialmelting of upper mantle. Peridotites show a high variability, from 0.3 - 3.8 wt.%Al2O3, varying from small to highly extreme depleted peridotite.On the contrary, Albanian eastern belt, it seems to be formed by a more homogeneoushartzburgitic mantle.Detailed petrologic and metallogenic investigations have evidenced that this beltchanges also from one massif to another, naturally at a smaller level, therefore it iseasier to be named relatively homogeneous. It is distinguished by a higher meltingdegree, chiefly of hartzburgitic-type, characterized by whole and thick ultramaficsection, as well as by metalogenic variety, mostly of metallurgic-type of chromitemineralization. It is supposed that rock-forming and mineraluzation processes havebeen developed not uniformly along the ophiolitic belt.

scholarly journals Depletion of the upper mantle by convergent tectonics in the Early Earth

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. L. Perchuk ◽  
T. V. Gerya ◽  
V. S. Zakharov ◽  
W. L. Griffin
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Upper Mantle ◽  
Subduction Zones ◽  
Convergence Rates ◽  
Oceanic Lithosphere ◽  
Early Earth ◽  
Plate Convergence ◽  
Depleted Mantle ◽  
Mantle Peridotites

AbstractPartial melting of mantle peridotites at spreading ridges is a continuous global process that forms the oceanic crust and refractory, positively buoyant residues (melt-depleted mantle peridotites). In the modern Earth, these rocks enter subduction zones as part of the oceanic lithosphere. However, in the early Earth, the melt-depleted peridotites were 2–3 times more voluminous and their role in controlling subduction regimes and the composition of the upper mantle remains poorly constrained. Here, we investigate styles of lithospheric tectonics, and related dynamics of the depleted mantle, using 2-D geodynamic models of converging oceanic plates over the range of mantle potential temperatures (Tp = 1300–1550 °C, ∆T = T − Tmodern = 0–250 °C) from the Archean to the present. Numerical modeling using prescribed plate convergence rates reveals that oceanic subduction can operate over this whole range of temperatures but changes from a two-sided regime at ∆T = 250 °C to one-sided at lower mantle temperatures. Two-sided subduction creates V-shaped accretionary terrains up to 180 km thick, composed mainly of highly hydrated metabasic rocks of the subducted oceanic crust, decoupled from the mantle. Partial melting of the metabasic rocks and related formation of sodic granitoids (Tonalite–Trondhjemite–Granodiorite suites, TTGs) does not occur until subduction ceases. In contrast, one sided-subduction leads to volcanic arcs with or without back-arc basins. Both subduction regimes produce over-thickened depleted upper mantle that cannot subduct and thus delaminates from the slab and accumulates under the oceanic lithosphere. The higher the mantle temperature, the larger the volume of depleted peridotites stored in the upper mantle. Extrapolation of the modeling results reveals that oceanic plate convergence at ∆T = 200–250 °C might create depleted peridotites (melt extraction of > 20%) constituting more than half of the upper mantle over relatively short geological times (~ 100–200 million years). This contrasts with the modeling results at modern mantle temperatures, where the amount of depleted peridotites in the upper mantle does not increase significantly with time. We therefore suggest that the bulk chemical composition of upper mantle in the Archean was much more depleted than the present mantle, which is consistent with the composition of the most ancient lithospheric mantle preserved in cratonic keels.

The geochemical characteristics of the Jurassic plume magmatism within Ahlmannryggen massif (Queen Maud Land, East Antarctica)

2019 ◽  
Vol 486 (1) ◽  
pp. 98-102
Author(s):  
N. M. Sushchevskaya ◽  
B. V. Belyatsky ◽  
G. L. Leitchenkov ◽  
V. G. Batanova ◽  
A. V. Sobolev
Keyword(s):  
Mantle Peridotite ◽  
Oceanic Lithosphere ◽  
East Antarctica ◽  
Geochemical Characteristics ◽  
Mantle Melting ◽  
Plume Magmatism

Mesozoic dikes associated with the Karoo plume were studied within the East Antarctica where at Queen Maud Land on the Almannryggen massif high-Ti magnesian Fe-basalts were found. It is assumed that such basalts originate by means of the pyroxenite-containing mantle melting. The isotopic characteristics of the studied dolerites reflect the composition of the pyroxenite source - the ancient oceanic lithosphere (ЕМI), submerged at the mantle depths of 150-170 km in the paleosubduction zone of the Gondwanian continent and transformed 180 m.y. ago into the pyroxenite melt when interacting with the plume mantle peridotite.

THE TECTONIC SIGNIFICANCE OF (OLD) ZIRCON IN OCEANIC MANTLE PERIDOTITES AND CHROMITITES

2017 ◽  
Author(s):  
Paul T. Robinson ◽  
◽  
Jingsui Yang ◽  
Jianwei Li ◽  
Zhang Duan ◽  
...  
Keyword(s):  
Mantle Peridotites ◽  
Tectonic Significance

scholarly journals Water contents of nominally anhydrous orthopyroxenes from oceanic peridotites determined by SIMS and FTIR

2021 ◽  
Author(s):  
Kirsten T. Wenzel ◽  
Michael Wiedenbeck ◽  
Jürgen Gose ◽  
Alexander Rocholl ◽  
Esther Schmädicke
Keyword(s):  
Upper Mantle ◽  
Secondary Ion Mass Spectrometry ◽  
Spinel Peridotite ◽  
Structural Water ◽  
Major Element Composition ◽  
Mantle Peridotites ◽  
History Of ◽  
Polarized Ftir ◽  
Water Contents ◽  
Forearc Region

AbstractThis study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic reference orthopyroxenes from spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al2O3 ranges between 4.02 and 5.56 wt%, and Cr2O3 ranges between 0.21 and 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the water contents of the eleven reference orthopyroxenes vary from dry to 249 ± 6 µg/g H2O. Using these reference grains, a set of orthopyroxene samples obtained from variably altered abyssal spinel peridotites from the Atlantic and Arctic Ridges as well as from the Izu-Bonin-Mariana forearc region was analyzed by SIMS and FTIR regarding their incorporation of water. The major element composition of the sample orthopyroxenes is typical of spinel peridotites from the upper mantle, characterized by Mg#s between 0.90 and 0.92, Al2O3 between 1.66 and 5.34 wt%, and Cr2O3 between 0.62 and 0.96 wt%. Water contents as measured by SIMS range from 68 ± 7 to 261 ± 11 µg/g H2O and correlate well with Al2O3 contents (r = 0.80) and Cr#s (r. = -0.89). We also describe in detail an optimized strategy, employing both SIMS and FTIR, for quantifying structural water in highly altered samples such as abyssal peridotite. This approach first analyzes individual oriented grains by polarized FTIR, which provides an overview of alteration. Subsequently, the same grain along with others of the same sample is measured using SIMS, thereby gaining information about homogeneity at the hand sample scale, which is key for understanding the geological history of these rocks.

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