In situ strength measurements on natural upper-mantle minerals

2008 ◽  
Vol 35 (5) ◽  
pp. 249-257 ◽  
Author(s):  
Junji Yamamoto ◽  
Jun-ichi Ando ◽  
Hiroyuki Kagi ◽  
Toru Inoue ◽  
Akihiro Yamada ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Mantle Minerals

scholarly journals Seismic anisotropy: an original tool to understand the geodynamic evolution of the Italian peninsula

1997 ◽  
Vol 40 (3) ◽  
Author(s):  
L. Margheriti ◽  
C. Nostro ◽  
A. Amato ◽  
M. Cocco
Keyword(s):  
Upper Mantle ◽  
Common Property ◽  
Seismic Waves ◽  
Seismic Anisotropy ◽  
Structural Features ◽  
Relative Strength ◽  
Plate Motion ◽  
Mantle Minerals ◽  
Anisotropic Bodies ◽  
Shallow Crust

Anisotropy is a common property of the Earth's crust and the upper mantle; it is related to the strain field of the medium and therefore to geodynamics. In this paper we describe the different possible origins of anisotropic behavior of the seismic waves and the seismological techniques used to define anisotropic bodies. In general it is found that the fast polarization direction is parallel to the absolute plate motion in cratonic areas, to the spreading direction near rifts or extensional zones, and to the main structural features in transpressive regimes. The delay times between fast and slow waves reflect the relative strength and penetration at depth of the deformation field. The correspondence between surface structural trends and anisotropy in the upper mantle, found in many regions of the world, strongly suggest that orogenic processes involve not only the shallow crust but the entire lithosphere. Recently in Italy both shear wave splitting analysis and Pn inversion were applied to define the trend of seismic anisotropy. Along the Northern Appeninic arc fast directions follow the strike of the arc (i.e., parallel to the strike of the Miocene-Pleistocene compressional features), whereas in the Tyrrhenian zone fast directions are about E-W SW-NE; parallel to the post-Miocene extension that is thought to have reoriented the mantle minerals fabric in the astenosphere.

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

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.

The distribution and abundance of halogens in eclogites: An in situ SIMS perspective of the Raspas Complex (Ecuador)

2020 ◽  
Vol 105 (3) ◽  
pp. 307-318 ◽  
Author(s):  
Benjamin M. Urann ◽  
Véronique Le Roux ◽  
Timm John ◽  
Grace M. Beaudoin ◽  
Jaime D. Barnes
Keyword(s):  
Upper Mantle ◽  
Subduction Zones ◽  
Secondary Ion Mass Spectrometry ◽  
Bulk Rock ◽  
Ocean Island Basalts ◽  
High Pressure Metamorphism ◽  
Southern Ecuador ◽  
And Behavior ◽  
Secondary Ion

Abstract We present in situ secondary ion mass spectrometry (SIMS) and electron microprobe analyses of coexisting garnet, omphacite, phengite, amphibole, and apatite, combined with pyrohydrolysis bulk-rock analyses to constrain the distribution, abundance, and behavior of halogens (F and Cl) in six MORB-like eclogites from the Raspas Complex (Southern Ecuador). In all cases concerning lattice-hosted halogens, F compatibility decreases from apatite (1.47–3.25 wt%), to amphibole (563–4727 μg/g), phengite (610–1822 μg/g), omphacite (6.5–54.1 μg/g), and garnet (1.7–8.9 μg/g). The relative compatibility of Cl in the assemblage is greatest for apatite (192–515 μg/g), followed by amphibole (0.64–82.7 μg/g), phengite (1.2–2.1 μg/g), omphacite (<0.05–1.0 μg/g), and garnet (<0.05 μg/g). Congruence between SIMS-reconstructed F bulk abundances and yield-corrected bulk pyrohydrolysis analyses indicates that F is primarily hosted within the crystal lattice of eclogitic minerals. However, SIMS-reconstructed Cl abundances are a factor of five lower, on average, than pyrohydrolysis-derived bulk concentrations. This discrepancy results from the contribution of fluid inclusions, which may host at least 80% of the bulk rock Cl. The combination of SIMS and pyrohydrolysis is highly complementary. Whereas SIMS is well suited to determine bulk F abundances, pyrohydrolysis better quantifies bulk Cl concentrations, which include the contribution of fluid inclusion-hosted Cl. Raspas eclogites contain 145–258 μg/g F and at least 7–11 μg/g Cl. We estimate that ~95% of F is retained in the slab through eclogitization and returned to the upper mantle during subduction, whereas at least 95% of subducted Cl is removed from the rock by the time the slab equilibrates at eclogite facies conditions. Our calculations provide further evidence for the fractionation of F from Cl during high-pressure metamorphism in subduction zones. Although the HIMU (high U/Pb) mantle source (dehydrated oceanic crust) is often associated with enrichments in Cl/K and F/Nd, Raspas eclogites show relatively low halogen ratios identical within uncertainty to depleted MORB mantle (DMM). Thus, the observed halogen enrichments in HIMU ocean island basalts require either further fractionation during mantle processing or recycling of a halogen-enriched carrier lithology such as serpentinite into the mantle.

scholarly journals New SIMS reference materials for measuring water in upper mantle minerals

2017 ◽  
Vol 102 (3) ◽  
pp. 537-547 ◽  
Author(s):  
Kathryn M. Kumamoto ◽  
Jessica M. Warren ◽  
Erik H. Hauri
Keyword(s):  
Reference Materials ◽  
Upper Mantle ◽  
Mantle Minerals

Hydrogen partitioning between nominally anhydrous upper mantle minerals and melt between 3 and 5 GPa and applications to hydrous peridotite partial melting

2009 ◽  
Vol 262 (1-2) ◽  
pp. 42-56 ◽  
Author(s):  
Travis J. Tenner ◽  
Marc M. Hirschmann ◽  
Anthony C. Withers ◽  
Richard L. Hervig
Keyword(s):  
Partial Melting ◽  
Upper Mantle ◽  
Mantle Minerals

Age constraints for rare felsic mantle xenoliths from Elie Ness, Scottish Midland Valley

2020 ◽  
Author(s):  
Eszter Badenszki ◽  
J. Stephen Daly ◽  
Martin J. Whitehouse ◽  
Brian G. J. Upton
Keyword(s):  
Upper Mantle ◽  
Solid Phase ◽  
Mantle Xenoliths ◽  
Solid Phase Reaction ◽  
Phase Reaction ◽  
Magma Intrusion ◽  
Accessory Zircon ◽  
Complex Source ◽  
Age Constraints

<p>EN-101, a rare albitite [Pl +Fe-Ti oxide +Ap +Zrn] xenolith from Elie Ness, Scottish Midland Valley, is hosted by a c. 290 Ma old alkali basaltic diatreme [1, 2].  EN-101 is considered to belong to the Scottish “anorthoclasite suite” comprising xenoliths and megacrysts of various compositions which are interpreted as samples from the upper mantle – lower crust where they form (syenitic) vein or dyke-like bodies e.g., [3, 4, 5]. The “anorthoclasite suite” has been found in all Scottish terranes suggesting that the presumed dyke system must be extensive.</p><p>Xenoliths of the “anorthoclasite suite” primarily consist of Na-rich and Ca-poor feldspar megacrysts, with generally high Na/K ratios [3] that are typically accompanied by accessory zircon, apatite, biotite, magnetite and Fe-rich pyroxene whereas garnet and corundum with Nb-rich oxides are only occasionally present [3, 4, 5]. Upton et al. [4, 5] argued that the parental melt of the “anorthoclasite suite” formed though small–fraction melting of metasomatized mantle and subsequent melt–solid phase reaction was also involved.  Upton et al. [5] proposed that crystallization of the anorthoclasite suite samples occurred shortly prior to- or contemporaneously with their entrainment. However so far no in-situ dating has been carried out on these samples.</p><p>Early attempts to date the anorthoclasite suite using zircon and feldspar megacrysts from Elie Ness suggested at least a two-stage formation mechanism, where zircon megacrysts yielded a U-Pb age of c. 318 Ma, while euhedral feldspar xenocrysts are significantly younger and roughly coeval with the host volcanism yielding a K-Ar whole-rock age of c. 294 Ma [6].  In this study we present the first in situ U-Pb dating of zircon, which yielded a concordia age of 328 ± 2 Ma (MSWD=0.19; n=12) for EN-101. Zircons εHf<sub>328</sub> values range from +5.2 to +7.5 consistent with a mildly depleted source refreshed by metasomatism. These results may indicate that the proposed extensive syenitic veining within the Scottish upper mantle not only has a complex source [5], but is possibly the result of repeated episodes of magma intrusion.</p><p>References:</p><ol><li>Gernon, T.M. et al. 2013 Bulletin of Volcanology. 75:1-20.</li> <li>Gernon, T.M. et al. 2016 Lithos. 264:70-85.</li> <li>Aspen, P. et al. 1990 European Journal of Mineralogy 2:503-17.</li> <li>Upton, B.G.J. et al. 1990 Journal of Petrology.40:935-56.</li> <li>Upton, B.G.J. et al. 2009 Mineral Mag. 73:943-56.</li> <li>Macintyre, R.M. et al. 1981 Transactions of the Royal Society of Edinburgh: Earth Sciences. 72:1-7.</li> </ol>

scholarly journals Single-crystal elasticity of iron-bearing phase E and seismic detection of water in Earth's upper mantle

2019 ◽  
Vol 104 (10) ◽  
pp. 1526-1529 ◽  
Author(s):  
Niccolò Satta ◽  
Hauke Marquardt ◽  
Alexander Kurnosov ◽  
Johannes Buchen ◽  
Takaaki Kawazoe ◽  
...  
Keyword(s):  
Sound Wave ◽  
Upper Mantle ◽  
Stiffness Tensor ◽  
Ambient Conditions ◽  
Brillouin Spectroscopy ◽  
Shear Moduli ◽  
Mantle Minerals ◽  
Wave Velocities ◽  
Seismic Detection ◽  
Iron Bearing

Abstract The elastic properties of Mg2.12(2)Fe0.21(2)Ni0.01Si1.15(1)O6H2.67(8) phase E single crystals with Fe3+/ΣFe = 0.25(3) have been determined by Brillouin spectroscopy at ambient conditions. We find that that the elasticity of iron-bearing phase E is described by the six independent stiffness tensor components (all in units of GPa): C11 = 192.2(6), C12 = 56.4(8), C13 = 43.5(8), C14 = –4.3(3), C33 = 192.1(7), C44 = 46.4(3). The Voigt-Reuss-Hill averages of bulk and shear moduli are 95.9(4) and 59.6(2) GPa, respectively. The aggregate velocities of iron-bearing phase E are νP = 7.60(2) and νS = 4.43(1) km/s, markedly lower than those of major mantle minerals at ambient conditions. Modeling based on our results suggests that the presence of iron-bearing phase E may reduce the sound wave velocities in upper mantle and transition zone rocks, making it a possible target for future seismological investigations aiming to map hydration in subducting slabs.

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