Effects of shock pressure and temperature on titanomagnetite from ICDP cores and target rocks of the El’gygytgyn impact structure, Russia

Kontny, Agnes; Grothaus, Lea

doi:10.1007/s11200-016-0819-3

Cited by 19 publications

(31 citation statements)

References 33 publications

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“…In Reznik et al (2016) we already suspected that the faint second T V at around 100 K (Figure 4) might be related to some degree of distortion in the magnetite lattice. T V s around 100 K has also been observed in shocked magnetite from impacted rocks (e.g., Kontny & Grothaus, 2017; and are suggested to indicate a small amount of vacancies and increased Fe 31 concentration in surface layers of magnetite grains. The heated shocked 10, 20 and 30 GPa samples show an even stronger irreversibility below T V .…”

Section: Discussionmentioning

confidence: 76%

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

Kontny

Резник

Boubnov

et al. 2018

Geochem Geophys Geosyst

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We studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite‐bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature‐dependent magnetic susceptibility, magnetic hysteresis and low‐temperature saturation isothermal remanent magnetization. Structural properties of magnetite were analyzed using X‐ray diffraction, high‐resolution scanning electron microscopy and synchrotron‐assisted X‐ray absorption spectroscopy. The shock‐induced changes include magnetic domain size reduction due to brittle and ductile deformation features and an increase in Verwey transition temperature due to lattice distortion. After heating, the crystal lattice is relaxed and apparent crystallite size is increased suggesting a recovery of lattice defects documented by a mosaic recrystallization texture. The structural changes correlate with modifications in magnetic domain state recorded by temperature‐dependent magnetic susceptibility, hysteresis properties and low‐temperature saturation isothermal remanent magnetization. These alterations in both, magnetic and structural properties of magnetite can be used to assess impact‐related magnetic anomalies in impact structures with a high temperature overprint.

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Section: Discussionmentioning

confidence: 76%

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

Kontny

Резник

Boubnov

et al. 2018

Geochem Geophys Geosyst

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“…The initial increase in K from room temperature in Figs. 9C and D is a common feature of maghemite and has been explained as the thermally-prompted relaxation of lattice stresses at the contact between maghemite rims and magnetite cores ('maghemite bump'; Kontny and Grothaus, 2017;Liu et al, 2004;Velzen and Zijderveld, 1992). Maghemite (γ-Fe2O3) is a typical oxidation product of magnetite which retains the cubic spinel structure and much of the magnetism of its precursor magnetite (Clark, 1997).…”

Section: Magnetic Mineralogical Resultsmentioning

confidence: 99%

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

Belgrano¹,

Diamond²,

Vogt³

et al. 2019

Preprint

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Abstract. Recent studies have revealed genetic similarities between Tethyan ophiolites and oceanic proto-arc sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction-initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in submarine fore-arcs. In contrast, the Semail ophiolite, in which the 3–5 km thick upper-crustal succession is exposed in an oblique cross-section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the protoarc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulphide (VMS) deposits that they host, we have re-mapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses and geophysical interpretations with pre-existing geological maps. By linking the major element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes) through to axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley) and finally boninites (Boninitic Alley). Geotimes (Phase 1) axial dykes and lavas make up ~55 vol% of the Semail upper crust, whereas post-axial (Phase 2) lavas constitute the remaining ~ 45 vol % and ubiquitously cover the underlying axial crust. The Semail boninites occur as discontinuous accumulations up to 2 km thick at the top of the sequence and constitute ~ 15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

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“…This is contradictory to previous reports. At higher shock pressures >5 GPa, the ferrimagnetic susceptibility decreases with increasing shock pressure (e.g., Kontny & Grothaus, 2017;Nishioka et al, 2007;Reznik et al, 2016). Reznik et al (2016) owe the decrease in susceptibility to fracturing (~5 GPa) and plastic deformation (>10 GPa).…”

Section: Effect Of Shock Waves On Magnetic Propertiesmentioning

confidence: 99%

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

et al. 2019

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Magnetic fabrics provide important clues for understanding impact cratering processes. However, only a few magnetic fabric studies for experimentally shocked material have been reported so far. In the framework of MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network), we conducted two impact experiments on blocks of Maggia gneiss with the foliation oriented perpendicular (A38) and parallel (A37) to the target surface. Maggia gneiss has plenty of biotite bands forming a strong rock foliation. The bulk magnetic susceptibility varies from 0.376 × 10−3 to 1.298 × 10−3 SI in unshocked and from 0.443 × 10−3 to 3.940 × 10−3 SI in shocked gneiss. The thermomagnetic curves reveal a Verwey transition at −147 °C and a Curie temperature between 576 and 579 °C in unshocked and shocked samples, indicating nearly pure magnetite, which carries the magnetic fabrics. In A37 and A38 kinking is prominent from the point source down to a depth of 2 and 4.2 dp (projectile diameter) or 1 and 2.1 cm, respectively. Kinking, folding, and fracturing changed the position of magnetite grains with respect to each other to reorient the magnetic fabrics. Reorientation of magnetic fabrics is conspicuous down to 20 dp (10 cm) in A38, where no other impact‐related deformation is visible. The reorientation of magnetic fabrics may, therefore, aid in identifying impact processes at very low pressures, starting at 0.1 GPa, when other common indicators are absent.

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Effects of shock pressure and temperature on titanomagnetite from ICDP cores and target rocks of the El’gygytgyn impact structure, Russia

Cited by 19 publications

References 33 publications

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

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