Magnetic Fields of the Early Solar System Recorded in Chondrules and Meteorites: Insights from Magnetic Remanence and First-Order Reversal Curve (FORC) Measurements (original) (raw)
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Journal of Geophysical Research, 2007
1] Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are lognormal shaped, with Bjurbole distributions being bimodal or trimodal. The highest-coercivity mode in the Bjurbole chondrules is derived from tetrataenite, which interacts strongly with the lower-coercivity grains in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is <10 mT, low-coercivity magnetic overprints are common. Therefore paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early solar system, have a mean REMc paleointensity of 10.4 mT. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 mT, respectively. (2007), Micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system,
Magnetic properties and paleointensity determination of seven H-group chondrites
Physics of the Earth and Planetary Interiors, 1983
. Magnetic properties and paleointensity determination of seven H-group chondrites. Phys. Earth Planet. Inter., 31: 1-9. Seven H-group meteorites were studied for paleointensity determination. The method used was the Thellier and Thellier double step heating method. The reliability of the results was estimated from the demagnetization behaviour and from the shape of the pTRM/NRM curve. The best values are obtained for Prairie Dog Creek (H3:1.40e), Mooresfort (H5:0.70e) and Oakley Stone (H6:1.20e). Less reliable results are obtained for Bath (H4:1.70e), Ochansk (H4:1.30e), Pultnsk (HS: 0.50e) and Indio Rico (H6:0.80e).
Analyzing Micromagnetic Properties With FORCIT Software
Eos, Transactions American Geophysical Union, 2007
Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are lognormal shaped, with Bjurbole distributions being bimodal or trimodal. The highest-coercivity mode in the Bjurbole chondrules is derived from tetrataenite, which interacts strongly with the lower-coercivity grains in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is <10 mT, low-coercivity magnetic overprints are common. Therefore paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early solar system, have a mean REMc paleointensity of 10.4 mT. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 mT, respectively.
Micromagnetic and microstructural analyses in chondrules of the Allende meteorite
Revista Mexicana De Ciencias Geologicas, 2010
Results of micromagnetic and microstructural studies of individual chondrules from the Allende carbonaceous meteorite are presented. Allende is a member of the CV3 carbonaceous chondrites, and part of the oxidized meteorites with iron in silicates and oxides. Magnetic hysteresis data in terms of plots of parameter ratios give relationships with chondrule size and shape, in particular with magnetization ratio (Mr/Ms) and coercivity (Hc). Morphology, internal structure and elemental composition are investigated by scanning electron microscopy and spectrometric analyses. Chondrules show low ranges of magnetization ratios (Mr/Ms from 0 to 0.22) and coercivity (Hc from 3 to 24 mT). Low values suggest that chondrules are susceptible to alteration and re-magnetization, which affects paleointensity determinations for the early planetary magnetic fields A linear relation of Mr/Ms as a function of Hc is found up to values of 0.17 and 17 mT, respectively. This relation correlates with internal microstructure and composition, with compound chondrules showing higher hysteresis ratio and parameter values. Chondrules with hysteresis parameters falling outside the major trend show internal structures, composition and textures indicative of compound chondrules, and fragmentation and alteration processes. Microprobe analyses show distinct mineralogical assemblages with spatial compositional variation related to chondrule size, shape and microstructure.
Magnetic remanence in the Murchison meteorite
The Murchison meteorite is a carbonaceous chondrite containing a small amount of chondrules, various inclusions, and matrix with occasional porphyroblasts of olivine and/or pyroxene. It also contains amino acids that may have served as the necessary components for the origin of life. Magnetic analyses of Murchison identify an ultrasoft magnetic component due to superparamagnetism as a significant part of the magnetic remanence. The rest of the remanence may be due to electric discharge in the form of lightning bolts that may have formed the amino acids. The level of magnetic remanence does not support this possibility and points to a minimum ambient field of the remanence acquisition. We support our observation by showing that normalized mineral magnetic acquisition properties establish a calibration curve suitable for rough paleofield determination. When using this approach, 1-2% of the natural remanence left in terrestrial rocks with TRM and/or CRM determines the geomagnetic field intensity irrespective of grain size or type of magnetic mineral (with the exception of hematite). The same method is applied to the Murchison meteorite where the measured meteorite remanence determines the paleofield minimum intensity of 200-2000 nT during and/or after the formation of the parent body.
Early evolution of the solar accretion disk inferred from Cr-Ti-O isotopes in individual chondrules
Earth and Planetary Science Letters, 2020
Isotopic anomalies in chondrules hold important clues about the dynamics of mixing and transport processes in the solar accretion disk. The meaning of these anomalies is debated and they have been interpreted to indicate either disk-wide transport of chondrules or local heterogeneities of chondrule precursors. However, all previous studies relied on isotopic data for a single element (either Cr, Ti, or O), which does not allow distinguishing between source and precursor signatures as the cause of the chondrules' isotope anomalies. To overcome this problem, we obtained the first combined O, Ti, and Cr isotope data for individual chondrules from enstatite, ordinary, and carbonaceous chondrites. We find that chondrules from noncarbonaceous (NC) chondrites have relatively homogeneous ∆ 17 O, ε 50 Ti, and ε 54 Cr, which are similar to the compositions of their host chondrites. By contrast, chondrules from carbonaceous chondrites (CC) have more variable compositions, some of which differ from the host chondrite compositions. Although the compositions of the analyzed CC and NC chondrules may overlap for either ε 50 Ti, ε 54 Cr, or ∆ 17 O, in multi-isotope space none of the CC chondrules plot in the compositional field of NC chondrites, and no NC chondrule plots within the field of CC chondrites. As such, our data reveal a fundamental isotopic difference between NC and CC chondrules, which is inconsistent with a disk-wide transport of chondrules across and between the NC and CC reservoirs. Instead, the isotopic variations among CC chondrules reflect local precursor heterogeneities, which most likely result from mixing between NC-like dust and a chemically diverse dust component that was isotopically similar to CAIs and AOAs. The same mixing processes, but on a larger, disk-wide scale, were likely responsible for establishing the distinct isotopic compositions of the NC and CC reservoirs, which represent in inner and outer disk, respectively.
Geochimica et Cosmochimica Acta, 2009
We evaluate initial ( 26 Al/ 27 Al) I , ( 53 Mn/ 55 Mn) I , and ( 182 Hf/ 180 Hf) I ratios, together with 207 Pb/ 206 Pb ages for igneous differentiated meteorites and chondrules from ordinary chondrites for consistency with radioactive decay of the parent nuclides within a common, closed isotopic system, i.e., the early solar nebula. The relative initial isotopic abundances of 26 Al, 53 Mn, and 182 Hf in differentiated meteorites and chondrules are consistent with decay from common solar system initial values, here denoted by I(Al) SS , I(Mn) SS , and I(Hf) SS, respectively. I(Mn) SS and I(Hf) SS = 9.1 ± 1.7 Â 10 À6 and 1.07 ± 0.08 Â 10 À4 , respectively, correspond to ''canonical" I(Al) SS = 5.1 Â 10 À5 . I(Hf) SS so determined is consistent with I(Hf) SS = 9.72 ± 0.44 Â 10 À5 directly determined from an internal Hf-W isochron for CAI minerals. I(Mn) SS is within error of the lowest value directly measured for CAIs. We suggest that erratically higher values measured for CAIs in carbonaceous chondrites may reflect proton irradiation of unaccreted CAIs by the early Sun after other asteroids destined for melting by 26 Al decay had already accreted. The 53 Mn incorporated within such asteroids would have been shielded from further ''local" spallogenic contributions from within the solar system. The relative initial isotopic abundances of the short-lived nuclides are less consistent with the 207 Pb/ 206 Pb ages of the corresponding materials than with one another. The best consistency of shortand long-lived chronometers is obtained for ( 182 Hf/ 180 Hf) I and the 207 Pb/ 206 Pb ages of angrites. ( 182 Hf/ 180 Hf) I decreases with decreasing 207 Pb/ 206 Pb ages at the rate expected from the 8.90 ± 0.09 Ma half-life of 182 Hf. The model solar system age thus determined is T SS,Hf-W = 4568.3 ± 0.7 Ma. ( 26 Al/ 27 Al) I and ( 53 Mn/ 55 Mn) I are less consistent with 207 Pb/ 206 Pb ages of the corresponding meteorites, but yield T SS,Mn-Cr = 4568.2 ± 0.5 Ma relative to I(Al) SS = 5.1 Â 10 À5 and a 207 Pb/ 206 Pb age of 4558.55 ± 0.15 Ma for the LEW86010 angrite. The Mn-Cr method with I(Mn) SS = 9.1 ± 1.7 Â 10 À6 is useful for dating accretion (if identified with chondrule formation), primary igneous events, and secondary mineralization on asteroid parent bodies. All of these events appear to have occurred approximately contemporaneously on different asteroid parent bodies. For I(Mn) SS = 9.1 ± 1.7 Â 10 À6 , parent body differentiation is found to extend at least to 5Mapost−TSS,i.e.,untildifferentiationoftheangriteparentbody5 Ma post-T SS , i.e., until differentiation of the angrite parent body 5Mapost−TSS,i.e.,untildifferentiationoftheangriteparentbody4563.5 Ma ago, or 4564.5Maagousingthedirectlymeasured207Pb/206PbagesoftheD′Orbigny−clanangrites.The4564.5 Ma ago using the directly measured 207 Pb/ 206 Pb ages of the D'Orbigny-clan angrites. The 4564.5Maagousingthedirectlymeasured207Pb/206PbagesoftheD′Orbigny−clanangrites.The1 Ma difference is characteristic of a remaining inconsistency for the D'Orbigny-clan between the Al-Mg and Mn-Cr chronometers on one hand, and the 207 Pb/ 206 Pb chronometer on the other. Differentiation of the IIIAB iron meteorite and ureilite parent bodies probably occurred slightly later than for the angrite parent body, and at nearly the same time as one another as shown by the Mn-Cr ages of IIIAB irons and ureilites, respectively. The latest recorded epi-0016-7037/$ -see front matter Published by Elsevier Ltd. Geochimica et Cosmochimica Acta 73 (2009) 5115-5136 sodes of secondary mineralization are for carbonates on the CI carbonaceous chondrite parent body and fayalites on the CV carbonaceous chondrite parent body, both extending to $10 Ma post-T SS . Published by Elsevier Ltd.