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and Planetary Science Letters 487 (2018) 1–8

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Earth and Planetary Science Letters

www.elsevier.com/locate/epsl

Magnetization of Extraterrestrial Allende material may relate to terrestrial descend

Gunther Kletetschka a,b,c a Institute of Geology, Academy of Sciences of the Czech Republic, Czech Republic b Faculty of Science, Charles University, Czech Republic c Department of Geology and Geophysics, University of Alaska Fairbanks, USA a r t i c l e i n f o a b s t r a c t

Article history: The origin of magnetization in Allende may have significant implications for our understanding of Received 5 September 2017 core formation/differentiation/dynamo processes in parent bodies. The magnetic Allende data Received in revised form 4 January 2018 may contain information that could constrain the magnetic history of Allende. The measurements on Accepted 23 January 2018 Allende reveal an existence of magnetization component that was likely acquired during the Available online 3 February 2018 transit to terrestrial conditions. Both the pyrrhotite carrying magnetic remanence intensity Editor: J. Brodholt and direction of the chondrules change erratically when subjecting the Allende meteorite’s chondrules Keywords: to temperatures near 77 K and back to room temperature. Chondrules with more intense original Allende magnetization are denser and contain larger inverse thermoremanent magnetization (ITRM). Temperature magnetic dynamo dependent monitoring of ITRM revealed that magnetization was acquired at temperature near 270 K. paleomagnetism Such temperature is consistent with the condition when, in addition to temperature increase, the atmospheric uniaxial pressure applied during the meteorite entry on the porous material was responsible decelerating magnetization for meteorite break up in the atmosphere. During this process, collapse of the pore space in the matrix and some chondrules would generate crystalline anisotropy energy accumulation within pyrrhotite grains in form of parasitic magnetic transition. © 2018 Elsevier B.V. All rights reserved.

1. Introduction the meteorite entry into the Earth atmosphere the meteorite in- terior would warm from temperatures near 150 K (Johnson et 1.1. characteristic al., 1979) (disk-averaged (main Belt) equilibrium black- body temperature is greater than 120 K (Carporzen et al., 2011)) to about 300 K not only in the presence of geomagnetic field Chondrite are undifferentiated conglomerates of but also experiencing structural changes due to bolide’s decel- primitive material, containing intermixed grains of , py- eration, heating, deformation, and breaking up prior to descent. roxene, feldspar and metallic Fe–Ni compounds. While ordinary Warming from temperatures below room temperature occurred chondrites are the materials most likely matched with the S- at the same time when meteorite was breaking up in the atmo- type , carbonaceous chondrites match C-, P-, and D-type sphere while experiencing the maximum break up pressure in the asteroids (Krot, 2011). Magnetism of carbonaceous (C) and or- range of pressures observed during breaking up of the Chelyabinsk dinary (L, LL, HH) chondrites is due to Fe–Ni compounds, pri- meteorite (18 MPa) (Borovicka et al., 2013). At that time, the marily α-kamacite (<7% Ni), γ -taenite (>7% Ni), γ -tetrataenite meteorite interior temperature is rising due to compression but (43–52% Ni), pyrrhotite, troilite, and magnetite (Fu et al., 2014; probably does not exceed the 270 K as Tagish meteorite inte- Wasilewski and Dickinson, 2000). rior did not show such signs after the atmospheric descend and breaking up and landing on the lake ice surface (Brown et al., 1.2. Transit to geomagnetic environment 2000). Deformation associated with this process may lead to crys- talline anisotropy energy accumulation and significant changes in One needs to understand how laboratory meteorite magnetism its magnetic record (Nagata et al., 1963). Magnetic minerals, when research relates to the magnetic record of the asteroids. During warmed from low temperatures, acquire Inverse Thermo-Remanent Magnetization (ITRM). This remanence usually relates to magnetic transitions (e.g., Verwey transition at 120 K or pyrrhotite transition E-mail address: [email protected]. near 35 K) (Dunlop, 2006; Nagata et al., 1963) and is identified https://doi.org/10.1016/j.epsl.2018.01.020 0012-821X/© 2018 Elsevier B.V. All rights reserved. 2 G. Kletetschka / Earth and Planetary Science Letters 487 (2018) 1–8 by acquisition of magnetic remanence during the heating from were accounted for compaction during the deformational event low temperatures primarily across the specific magnetic anisotropy on the Allende’s . The prior observation illuminated transition. However, accumulation in crystalline anisotropy energy difference between matrix and chondrules in terms of Allende’s (Kletetschka et al., 2000b) could be triggered by deformation event physical response to external pressures during the uniaxial defor- at temperature other than phase transition temperatures, such as mation (Tait et al., 2016; Watt et al., 2006). Verwey or pyrrhotite transitions (Nagata et al., 1963). This pro- When descending on Earth’s surface, overall uniaxial pressures cess may have contributed to the deformational events of the that lead to Allende bolide disintegration were in the range 18 MPa fluffy type Ca–Al-rich inclusions (CAIs) (Katayama et al., 2012; comparable to friable chondrite meteorites (Borovicka et al., 2013). MacPherson and Grossman, 1984), matrix material, and chondrules For the case of chondrite meteorite, the individual chondrules that were identified with the deformational events on the Allende translate the overall uniaxial pressure to the mineral surfaces and parent body (Tait et al., 2016). pore spaces. These may generate local anisotropy related imperfec- tions in the compensation of the two constituent sublattices of the 1.3. Allende chondrite antiferromagnetism of pyrrhotite and thus generate parasitic mag- netism. For the purpose of this paper, parasitic magnetic transition, Allende fall occurred on February 8, 1969 at 1:05 am near generated by translation of decelerating uniaxial pressure, would Pueblito de Allende, in Chihuahua, Mexican state. Allende broke be called decelerating parasitic magnetic transition (DPMT). Edges up due to deformation during the descent in the atmosphere and of mineral surfaces may serve as pressure point resulting from produced thousands of fragments of fusion-crusted individuals. Al- the overall uniaxial pressure. The magnetic is inferred lende meteorite belongs to a group of CV3 carbonaceous chon- to be due to pyrrhotite, , and magnetite (Fu et al., 2014; drites. These are grouped according to distinctive composition, re- Muxworthy et al., 2017). Allende also contains troilite (Haggerty flecting the type of parent body from which they originated. Dom- and McMahon, 1979). It has been shown that sulfide minerals have inant minerals are olivine and . Allende contains mostly compromised sensitivity to pressure compared to other common chondrules of various size and composition that are in average magnetic minerals like magnetite or hematite (Gilder et al., 2011; about order of magnitude magnetically weaker than matrix ma- Louzada et al., 2010). In fact the pressure required to completely terial (Fu et al., 2014). reset pyrrhotite’s magnetization is within the S1 shock classifica- tion for Allende meteorite (<5GPa (Rochette et al., 2001)). The 1.4. Allende’s magnetism phase transformation pressure (i.e., the complete magnetic reset pressure) for pyrrhotite is 2.8 GPa which is much higher than 1.4.1. Magnetic petrology 18 MPa. Several shock remanent magnetization and pressure re- Major ferromagnetic phases in chondrules are mixtures of sul- manent magnetization studies have been conducted on the Allende phides, and magnetite. Prior work suggested that mixture meteorite (Carporzen et al., 2011; Tikoo et al., 2015). They find that of sulphides, magnetite and metals were unstable when demagne- extremely strong background fields (600–700 μT) are required to tized by alternating magnetic field (AF), producing erratic jumps reproduce the NRM intensity of Allende for shock remanent mag- in direction and amplitudes while sulphide dominated fragments netization (SRM) and/or pressure remanent magnetization (PRM) were AF stable (Wasilewski and Saralker, 1981). acquired at pressures >2GPa. 18 MPa pressures applied during the Recent paleointensity procedures were severely modified when in the terrestrial field would therefore impart discovered that mixtures of minerals that were heated/cooled only minimal pressure-induced remanence that would not be com- brought erroneous directions and intensities (Finn and Coe, 2016). parable in intensity to the observed magnetization components. The extension of this effect to meteorites brings concerns when However, any deformational process, either from the parent looking back on the paleomagnetic studies of Allende meteorites body event or from the atmosphere descent, would be less effi- that involved heating (Carporzen et al., 2011; Fu et al., 2014; O’Brien and Tarduno, 2016; Tarduno et al., 2017). cient on chondrules than in matrix. This is because the spherical shape of the chondrules prevents deformation of their interior. 1.4.2. Induced magnetic properties Both Allende matrix and chondrules have evidence of anisotropy Recent magnetic analysis exercised magnetic hysteresis proper- which is thought to originate on Allende’s parent body (Tait et ties of Allende and indicated that magnetic interaction may have al., 2016). There is detectable preferred orientation emphasized taken place (Wang and Salveson, 2005). However, hysteresis inter- by the observation that all Allende material, including the chon- action properties do not necessarily resolve magnetic remanence drules, have shortening in one direction as the grains have been interactions. This is because all magnetic carriers are being mag- pushed together along one axis and pushed further apart perpen- netized homogeneously by hysteresis, while magnetic remanence dicular to that shortening axis (Tait et al., 2016). This indicates an signature has contrasting remanence acquisition values for differ- exposure to a uniform stress field. The microscopic fabrics have ent magnetic grains (Kletetschka et al., 2000a, 2006). forms of compressive flattening flows in the matrix of Allende Another study proposed evidence for an impact-induced mag- forming “sigmoidal structure” around chondrules as a result of de- netic fabric in Allende (Muxworthy et al., 2017). The evidence was formation event that involved both matrix and chondrules after based on the thermal history of Allende, differential porosity of their accretion together (Watt et al., 2006). The amount of strain matrix and chondrules, and the magnetic remanence record of Al- recorded in the matrix changes based on the distance to more re- lende chondrules and matrix. Impact pressures up to 2GPa would sistant particles. This indicates that the amount of strain is not generate large heating in porosity rich matrix and acquire matrix homogeneously expressed in Allende material. The apparent order magnetization while exposed to an ambient magnetic field while to the amount of deformation; CAIs (64.5%) > matrix (21.5%) > less porous chondrules would not reach such high temperatures chondrules (17.6%) (Tait et al., 2016) relates to porosities prior to and stayed un-magnetized (Muxworthy et al., 2017). deformation. In addition to the deformation that was recognized to occur on 1.5. Anisotropy of Allende Allende’s parent body, additional deformation occurred during the Allende’s descend within the terrestrial atmosphere as evidenced Anisotropy features were identified within both the Allende by the bolide’s break up associated with significant uniaxial pres- matrix and chondrules (Tait et al., 2016; Watt et al., 2006) and sures (Borovicka et al., 2013). Download English Version: https://daneshyari.com/en/article/8907061

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