ON THE RELATIVELY COMPOSITIONAL HOMOGENEITY OF ALBANIAN EASTERN OPHIOLITIC BELT

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.

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

Minerals ◽

10.3390/min9020120 ◽

2019 ◽

Vol 9 (2) ◽

pp. 120 ◽

Cited By ~ 6

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.

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

Scientific Reports ◽

10.1038/s41598-021-00837-y ◽

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.

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

Mineralogy and Petrology ◽

10.1007/s00710-021-00757-9 ◽

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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Experimental investigation of the composition of incipient melts in upper mantle peridotites in the presence of CO2 and H2O

Lithos ◽

10.1016/j.lithos.2021.106224 ◽

2021 ◽

pp. 106224

Author(s):

Zsanett Pintér ◽

Stephen F. Foley ◽

Gregory M. Yaxley ◽

Anja Rosenthal ◽

Robert P. Rapp ◽

...

Keyword(s):

Experimental Investigation ◽

Upper Mantle ◽

Mantle Peridotites

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Upper mantle peridotites in the Bay of Islands Ophiolite, Newfoundland: Formation during the final stages of a spreading centre?

Tectonophysics ◽

10.1016/0040-1951(92)90366-e ◽

1992 ◽

Vol 206 (1-2) ◽

pp. 31-53 ◽

Cited By ~ 19

Author(s):

Günter Suhr

Keyword(s):

Upper Mantle ◽

Mantle Peridotites

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The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽

10.2138/gselements.17.1.23 ◽

2021 ◽

Vol 17 (1) ◽

pp. 23-28 ◽

Cited By ~ 1

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.

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On the Vp/Vs–Mg# correlation in mantle peridotites: Implications for the identification of thermal and compositional anomalies in the upper mantle

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2009.12.005 ◽

2010 ◽

Vol 289 (3-4) ◽

pp. 606-618 ◽

Cited By ~ 52

Author(s):

Juan Carlos Afonso ◽

Giorgio Ranalli ◽

Manel Fernàndez ◽

William L. Griffin ◽

Suzanne Y. O'Reilly ◽

...

Keyword(s):

Upper Mantle ◽

Mantle Peridotites

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Ultramafic mantle xenoliths in the Late Cenozoic Volcanic rocks of the Antarctic Peninsula and Jones Mountains, West Antarctica

Geological Society London Memoirs ◽

10.1144/m56-2019-44 ◽

2021 ◽

pp. M56-2019-44

Author(s):

Philip T. Leat ◽

Aidan J. Ross ◽

Sally A. Gibson

Keyword(s):

Antarctic Peninsula ◽

Upper Mantle ◽

Lithospheric Mantle ◽

Volcanic Rocks ◽

Oceanic Lithosphere ◽

Incompatible Trace Element ◽

Mantle Xenoliths ◽

South Shetland Islands ◽

West Antarctica ◽

Gondwana Margin

AbstractAbundant mantle-derived ultramafic xenoliths occur in Cenozoic (7.7-1.5 Ma) mafic alkaline volcanic rocks along the former active margin of West Antarctica, that extends from the northern Antarctic Peninsula to Jones Mountains. The xenoliths are restricted to post-subduction volcanic rocks that were emplaced in fore-arc or back-arc positions relative to the Mesozoic-Cenozoic Antarctic Peninsula volcanic arc. The xenoliths are spinel-bearing, include harzburgites, lherzolites, wehrlites and pyroxenites, and provide the only direct evidence of the composition of the lithospheric mantle underlying most of the margin. The harzburgites may be residues of melt extraction from the upper mantle (in a mid-ocean ridge type setting), that accreted to form oceanic lithosphere, which was then subsequently tectonically emplaced along the active Gondwana margin. An exposed highly-depleted dunite-serpentinite upper mantle complex on Gibbs Island, South Shetland Islands, supports this interpretation. In contrast, pyroxenites, wehrlites and lherzolites reflect percolation of mafic alkaline melts through the lithospheric mantle. Volatile and incompatible trace element compositions imply that these interacting melts were related to the post-subduction magmatism which hosts the xenoliths. The scattered distribution of such magmatism and the history of accretion suggest that the dominant composition of sub-Antarctic Peninsula lithospheric mantle is likely to be harzburgitic.

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Radial Anisotropy and it's Relation to Fast and Slow Moving Tectonic Plates

10.5194/egusphere-egu21-13788 ◽

2021 ◽

Author(s):

Tak Ho ◽

Keith Priestley ◽

Eric Debayle

Keyword(s):

Upper Mantle ◽

Large Scale ◽

Oceanic Lithosphere ◽

Azimuthal Anisotropy ◽

Plate Motion ◽

Moho Depth ◽

Dispersion Characteristics ◽

Anisotropic Models ◽

Ocean Ridges ◽

Average Dispersion

We present a new radially anisotropic (&#958;)&#160;tomographic model for the upper mantle to transition zone depths derived from a large Rayleigh (~4.5 x 106&#160;paths) and Love (~0.7 x 106&#160;paths) wave path average dispersion curves with periods of 50-250 s and up to the fifth overtone. We first extract the path average dispersion characteristics from the waveforms. Dispersion characteristics for common paths (~0.3 x 106&#160;paths) are taken from the Love and Rayleigh datasets and jointly inverted for isotropic Vs&#160;and&#160;&#958;. CRUST1.0 is used for crustal corrections and a model similar to PREM is used as a starting model. Vs&#160;and&#160;&#958;&#160;are regionalised for a 3D model. The effects of azimuthal anisotropy are accounted for during the regionalisation. Our model confirms large-scale upper mantle features seen in previously published models, but a number of these features are better resolved because of the increased data density of the fundamental and higher modes coverage from which our&#160;&#958;(z) was derived. Synthetic tests show structures with radii of 400 km can be distinguished easily. Crustal perturbations of +/-10% to Vp, Vs&#160;and density, or perturbations to Moho depth of +/-10 km over regions of 400 km do not significantly change the model. The global average decreases from&#160;&#958;~1.06 below the Moho to&#160;&#958;~1 at ~275 km depth. At shallow depths beneath the oceans&#160;&#958;>1 as is seen in previously published global mantle radially anisotropic models. The thickness of this layer increases slightly with the increasing age of the oceanic lithosphere. At ~200 km and deeper depths below the fast-spreading East Pacific Rise and starting at somewhat greater depths beneath the slower spreading ridges,&#160;&#958;<1. At depths &#8805;200 km and deeper depths below most of the backarc basins of the western Pacific&#160;&#958;<1. The signature of mid-ocean ridges vanishes at about 150 km depth in Vs&#160;while it extends much deeper in the&#160;&#958;&#160;model suggesting that upwelling beneath mid-ocean ridges could be more deeply rooted than previously believed. The pattern of radially anisotropy we observe, when compared with the pattern of azimuthal anisotropy determined from Rayleigh waves, suggests that the shearing at the bottom of the plates is only sufficiently strong to cause large-scale preferential alignment of the crystals when the plate motion exceeds some critical value which Debayle and Ricard (2013) suggest is about 4 cm/yr.

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Internal lithospheric rotation at the initiation of intra-oceanic rift-drift: An example of proto-transform tectonics from the Vourinos Ophiolite, Greece

10.1130/2021.2552(04) ◽

2021 ◽

Author(s):

Anne Ewing Rassios ◽

Dina Ghikas ◽

Anna Batsi ◽

Petros Koutsovitis ◽

Evangelos Tzamos ◽

...

Keyword(s):

Upper Mantle ◽

Oceanic Lithosphere ◽

Ductile Deformation ◽

New Paradigm ◽

Crustal Rocks ◽

Mantle Boundary ◽

Ridge Crest ◽

Transition Area ◽

The 1960S

ABSTRACT The “petrological Moho” recognized in the Jurassic Vourinos Ophiolite (northern Greece) was the first “crust-mantle” boundary described within a fossil oceanic lithosphere. Early observations suggested a Cenozoic brittle-field block rotation of the petrological Moho transition area resulting in an oblique clockwise rotation of ∼100°, but a brittle fault system responsible for the mechanism of this rotation was never located. A modern interpretation of research dating from the 1960s to the present documents the occurrence of a diverse set of ductile structures overprinting this primary intra-oceanic feature. The following observations from our original “Moho” studies in the Vourinos complex are still pertinent: the contact between the upper mantle units and the magmatic crustal sequence is in situ and intrusional in nature; high-temperature intragranular ductile deformation (mantle creep at temperatures from around 1200 °C down to ∼900 °C) fabrics terminate at the crust-mantle boundary; the overlying oceanic crustal rocks display geochemical fractionation patterns analogous to crustal rocks in the in situ oceanic lithosphere. Since these original studies, however, understanding the mechanisms of ductile deformation and ridge crest processes have advanced, and hence we can now interpret the older data and recent observations in a new paradigm of oceanic lithosphere formation. Our major interpretational breakthrough includes the following phenomena: lower temperature, intergranular deformation of ∼900 °C to 700 °C extends from the upper mantle tectonites up into the lower crustal cumulate section; the origin of mineral lineations within adcumulate crustal rocks as remnants of ductile deformation during early phases of magmatic crystallization; syn-magmatic folding and rotation of the cumulate section; the tectonic significance of flaser gabbro and late gabbroic intrusions in the crustal sequence; and the relevance and significance of a cumulate troctolite unit within the crustal sequence. These observations collectively point to an important process of a ductile-field, syn-magmatic rotation of the Moho transition area. The most plausible mechanism explaining such a rotation is proto-transform faulting deformation near the ridge crest. By recognizing and distinguishing structures that resulted from such initial rotational deformation in the upper mantle peridotites of ophiolites, future field-based structural, petrographic, and petrological studies can better document the mode of the initiation of oceanic transform faults.

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