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Suzanne A Mcenroe - One of the best experts on this subject based on the ideXlab platform.
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Effect of magnetic anisotropy on the Natural Remanent Magnetization in the MCU IVe’ layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway
Journal of Geophysical Research: Solid Earth, 2017Co-Authors: Andrea R. Biedermann, Michael J Jackson, Dario Bilardello, Suzanne A McenroeAbstract:A strong negative magnetic anomaly, caused by an intense Natural Remanent Magnetization (NRM) approximately opposite today's geomagnetic field, is observed above the MCU IVe' unit of the Bjerkreim Sokndal Layered Intrusion. The anomaly is strongest in the east, close to Heskestad, and decreases when following the layer toward the north and west. This study investigates how the NRM changes along the layer and how its direction and intensity are affected by magnetic fabrics in the intrusion. NRM, low-field anisotropy of magnetic susceptibility, and anisotropy of anhysteretic remanence have been measured on 371 specimens from 46 sites. The orientation of both the magnetic fabrics and the NRM changes for different locations along the layer, and it appears that the NRM is tilted away from the mean paleofield and toward the direction of maximum susceptibility and maximum anhysteretic remanence. When NRM directions are corrected for magnetic fabrics, the angle between the NRM and mean paleofield direction generally decreases for specimens with a single-component NRM. No correlation was found between the NRM intensity and the directional relationship between NRM, magnetic fabric, and mean paleofield.
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Anorthosites as Sources of Magnetic Anomalies
The Earth's Magnetic Interior, 2011Co-Authors: Laurie L. Brown, Suzanne A Mcenroe, William H. Peck, Lars Petter NilssonAbstract:Magnetic anomalies provide information about location, size and composition of earth structures, ore bodies and tectonic features even in bodies containing only a few percent magnetic minerals. Here we investigate the magnetic properties and oxide mineralogy of anorthosites, rocks rich in plagioclase (>90%), and compare their magnetic signatures to aeromagnetic anomaly maps of the regions. Two of the anorthosite complexes have large negative anomalies associated with them; both have low susceptibility and high remanence related to hemo-ilmenite mineralogy and Remanent directions antiparallel to the present field. One complex has appreciable Natural Remanent Magnetization quasi-parallel to the present field, and strong susceptibility, creating an enhanced positive anomaly. The fourth anorthosite has little or no magnetic anomaly over much of its area, in accordance with the weak remanence, low susceptibility and variable magnetic mineralogy observed. The anorthosite samples producing significant anomalies, and maintaining strong and stable Natural Remanent Magnetization over geologic time all contain oxides of the hematite-ilmenite series. This study adds support to ‘lamellar Magnetization’ whereby exsolved phases in the ilmenite-hematite system produce strong and stable Magnetization with only minor amounts of oxide material.
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exchange bias identifies lamellar magnetism as the origin of the Natural Remanent Magnetization in titanohematite with ilmenite exsolution from modum norway
Earth and Planetary Science Letters, 2008Co-Authors: Karl Fabian, Suzanne A Mcenroe, Peter Robinson, Valera P ShcherbakovAbstract:Abstract Large and stable negative magnetic anomalies in southwestern Sweden, southern Norway, the Adirondacks, USA, and Quebec, Canada, are related to rock units with a magnetic fraction consisting primarily of ilmeno-hematite or hemo-ilmenite. It has been suggested that the unusual magnetic stability of these rocks results from lamellar magnetism. This is a type of magnetic remanence, carried by uncompensated magnetic layers at interfaces between nanoscale exsolution structures of antiferromagnetic (AFM) hematite and paramagnetic ilmenite. Here we present the first direct proof that this lamellar magnetism indeed is responsible for the Natural Remanent Magnetization (NRM) of a rock from Modum, Norway. Our argument expands a previous observation, that, in mineral grains from this rock, the cooling of a positive-induced remanence from room temperature to 5 K – which is well below the ordering temperature of ilmenite (57 K) – leads to a large negative shift of the low-temperature (LT) hysteresis loop. This can only be explained by exchange bias due to exchange coupling across the hematite–ilmenite interfaces. In a different experiment, we now have cooled the original NRM of untreated grains to 5 K, and then measured the hysteresis loop. Again, in several separate grains we observed large shifts of the hysteresis curves. This shows that exchange bias develops also from the untreated NRM. This observation proves that the moments, which carry the NRM, also participate in the exchange coupling at the hematite–ilmenite interfaces. Therefore, the NRM is not carried by defect moments or stress-induced moments, which occur in normal bulk hematite. A closer look at the NRM-induced LT loops shows that exchange bias acts in both field directions, though one direction is clearly predominant. This observation can be interpreted as a frozen equilibrium of different proportions of oppositely directed lamellar moments, a key feature of the original lamellar magnetism hypothesis. We discuss lamellar aggregation, and the formation of exchange-coupled clusters to explain the observed high efficiency of lamellar NRM. We also conclude that remanence carried by lamellar moments should not be used for paleointensity estimates of terrestrial or extraterrestrial material.
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effects of nanoscale exsolution in hematite ilmenite on the acquisition of stable Natural Remanent Magnetization
Earth and Planetary Science Letters, 2004Co-Authors: Takeshi Kasama, Suzanne A Mcenroe, Noriaki Ozaki, Toshihiro Kogure, Andrew PutnisAbstract:Abstract To investigate the acquisition mechanism of high and stable Natural Remanent Magnetization (NRM) in rocks of the Russell Belt, Adirondack Mountains, New York, we examined the exsolution microstructures and compositions of magnetic minerals using three samples with different magnetic properties. The samples contain titanohematite with ilmenite lamellae, end-member hematite without lamellae and rare magnetite as potential carriers for the NRM. Transmission electron microscopy (TEM) observations and element mapping by energy-filtered TEM (EFTEM) of the titanohematite indicated that very fine ilmenite lamellae with a minimum thickness ∼2 nm are abundant between larger ilmenite lamellae a few hundreds of nanometers thick. The ilmenite lamellae and titanohematite hosts, with the compositions of Ilm 90–100 Hem 10–0 and Ilm 7–16 Hem 93–84 , respectively, share (001) planes, and the abundant fine ilmenite lamellae have coherent, sharp structural and compositional interfaces with their titanohematite hosts. Comparison between samples shows that the Magnetization is correlated with the amount of fine exsolution lamellae. These results are consistent with the lamellar magnetism hypothesis, suggesting that the acquisition of high and stable NRM is related to the interfacial area between fine ilmenite lamellae and their host titanohematite. End-member hematite with a multi-domain magnetic structure only contributes a minor amount to the NRM in these samples.
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Effects of nanoscale exsolution in hematite–ilmenite on the acquisition of stable Natural Remanent Magnetization
Earth and Planetary Science Letters, 2004Co-Authors: Takeshi Kasama, Suzanne A Mcenroe, Noriaki Ozaki, Toshihiro Kogure, Andrew PutnisAbstract:Abstract To investigate the acquisition mechanism of high and stable Natural Remanent Magnetization (NRM) in rocks of the Russell Belt, Adirondack Mountains, New York, we examined the exsolution microstructures and compositions of magnetic minerals using three samples with different magnetic properties. The samples contain titanohematite with ilmenite lamellae, end-member hematite without lamellae and rare magnetite as potential carriers for the NRM. Transmission electron microscopy (TEM) observations and element mapping by energy-filtered TEM (EFTEM) of the titanohematite indicated that very fine ilmenite lamellae with a minimum thickness ∼2 nm are abundant between larger ilmenite lamellae a few hundreds of nanometers thick. The ilmenite lamellae and titanohematite hosts, with the compositions of Ilm 90–100 Hem 10–0 and Ilm 7–16 Hem 93–84 , respectively, share (001) planes, and the abundant fine ilmenite lamellae have coherent, sharp structural and compositional interfaces with their titanohematite hosts. Comparison between samples shows that the Magnetization is correlated with the amount of fine exsolution lamellae. These results are consistent with the lamellar magnetism hypothesis, suggesting that the acquisition of high and stable NRM is related to the interfacial area between fine ilmenite lamellae and their host titanohematite. End-member hematite with a multi-domain magnetic structure only contributes a minor amount to the NRM in these samples.
Andrew Putnis - One of the best experts on this subject based on the ideXlab platform.
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effects of nanoscale exsolution in hematite ilmenite on the acquisition of stable Natural Remanent Magnetization
Earth and Planetary Science Letters, 2004Co-Authors: Takeshi Kasama, Suzanne A Mcenroe, Noriaki Ozaki, Toshihiro Kogure, Andrew PutnisAbstract:Abstract To investigate the acquisition mechanism of high and stable Natural Remanent Magnetization (NRM) in rocks of the Russell Belt, Adirondack Mountains, New York, we examined the exsolution microstructures and compositions of magnetic minerals using three samples with different magnetic properties. The samples contain titanohematite with ilmenite lamellae, end-member hematite without lamellae and rare magnetite as potential carriers for the NRM. Transmission electron microscopy (TEM) observations and element mapping by energy-filtered TEM (EFTEM) of the titanohematite indicated that very fine ilmenite lamellae with a minimum thickness ∼2 nm are abundant between larger ilmenite lamellae a few hundreds of nanometers thick. The ilmenite lamellae and titanohematite hosts, with the compositions of Ilm 90–100 Hem 10–0 and Ilm 7–16 Hem 93–84 , respectively, share (001) planes, and the abundant fine ilmenite lamellae have coherent, sharp structural and compositional interfaces with their titanohematite hosts. Comparison between samples shows that the Magnetization is correlated with the amount of fine exsolution lamellae. These results are consistent with the lamellar magnetism hypothesis, suggesting that the acquisition of high and stable NRM is related to the interfacial area between fine ilmenite lamellae and their host titanohematite. End-member hematite with a multi-domain magnetic structure only contributes a minor amount to the NRM in these samples.
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Effects of nanoscale exsolution in hematite–ilmenite on the acquisition of stable Natural Remanent Magnetization
Earth and Planetary Science Letters, 2004Co-Authors: Takeshi Kasama, Suzanne A Mcenroe, Noriaki Ozaki, Toshihiro Kogure, Andrew PutnisAbstract:Abstract To investigate the acquisition mechanism of high and stable Natural Remanent Magnetization (NRM) in rocks of the Russell Belt, Adirondack Mountains, New York, we examined the exsolution microstructures and compositions of magnetic minerals using three samples with different magnetic properties. The samples contain titanohematite with ilmenite lamellae, end-member hematite without lamellae and rare magnetite as potential carriers for the NRM. Transmission electron microscopy (TEM) observations and element mapping by energy-filtered TEM (EFTEM) of the titanohematite indicated that very fine ilmenite lamellae with a minimum thickness ∼2 nm are abundant between larger ilmenite lamellae a few hundreds of nanometers thick. The ilmenite lamellae and titanohematite hosts, with the compositions of Ilm 90–100 Hem 10–0 and Ilm 7–16 Hem 93–84 , respectively, share (001) planes, and the abundant fine ilmenite lamellae have coherent, sharp structural and compositional interfaces with their titanohematite hosts. Comparison between samples shows that the Magnetization is correlated with the amount of fine exsolution lamellae. These results are consistent with the lamellar magnetism hypothesis, suggesting that the acquisition of high and stable NRM is related to the interfacial area between fine ilmenite lamellae and their host titanohematite. End-member hematite with a multi-domain magnetic structure only contributes a minor amount to the NRM in these samples.
Takeshi Kasama - One of the best experts on this subject based on the ideXlab platform.
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effects of nanoscale exsolution in hematite ilmenite on the acquisition of stable Natural Remanent Magnetization
Earth and Planetary Science Letters, 2004Co-Authors: Takeshi Kasama, Suzanne A Mcenroe, Noriaki Ozaki, Toshihiro Kogure, Andrew PutnisAbstract:Abstract To investigate the acquisition mechanism of high and stable Natural Remanent Magnetization (NRM) in rocks of the Russell Belt, Adirondack Mountains, New York, we examined the exsolution microstructures and compositions of magnetic minerals using three samples with different magnetic properties. The samples contain titanohematite with ilmenite lamellae, end-member hematite without lamellae and rare magnetite as potential carriers for the NRM. Transmission electron microscopy (TEM) observations and element mapping by energy-filtered TEM (EFTEM) of the titanohematite indicated that very fine ilmenite lamellae with a minimum thickness ∼2 nm are abundant between larger ilmenite lamellae a few hundreds of nanometers thick. The ilmenite lamellae and titanohematite hosts, with the compositions of Ilm 90–100 Hem 10–0 and Ilm 7–16 Hem 93–84 , respectively, share (001) planes, and the abundant fine ilmenite lamellae have coherent, sharp structural and compositional interfaces with their titanohematite hosts. Comparison between samples shows that the Magnetization is correlated with the amount of fine exsolution lamellae. These results are consistent with the lamellar magnetism hypothesis, suggesting that the acquisition of high and stable NRM is related to the interfacial area between fine ilmenite lamellae and their host titanohematite. End-member hematite with a multi-domain magnetic structure only contributes a minor amount to the NRM in these samples.
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Effects of nanoscale exsolution in hematite–ilmenite on the acquisition of stable Natural Remanent Magnetization
Earth and Planetary Science Letters, 2004Co-Authors: Takeshi Kasama, Suzanne A Mcenroe, Noriaki Ozaki, Toshihiro Kogure, Andrew PutnisAbstract:Abstract To investigate the acquisition mechanism of high and stable Natural Remanent Magnetization (NRM) in rocks of the Russell Belt, Adirondack Mountains, New York, we examined the exsolution microstructures and compositions of magnetic minerals using three samples with different magnetic properties. The samples contain titanohematite with ilmenite lamellae, end-member hematite without lamellae and rare magnetite as potential carriers for the NRM. Transmission electron microscopy (TEM) observations and element mapping by energy-filtered TEM (EFTEM) of the titanohematite indicated that very fine ilmenite lamellae with a minimum thickness ∼2 nm are abundant between larger ilmenite lamellae a few hundreds of nanometers thick. The ilmenite lamellae and titanohematite hosts, with the compositions of Ilm 90–100 Hem 10–0 and Ilm 7–16 Hem 93–84 , respectively, share (001) planes, and the abundant fine ilmenite lamellae have coherent, sharp structural and compositional interfaces with their titanohematite hosts. Comparison between samples shows that the Magnetization is correlated with the amount of fine exsolution lamellae. These results are consistent with the lamellar magnetism hypothesis, suggesting that the acquisition of high and stable NRM is related to the interfacial area between fine ilmenite lamellae and their host titanohematite. End-member hematite with a multi-domain magnetic structure only contributes a minor amount to the NRM in these samples.
Almqvist Bjarne - One of the best experts on this subject based on the ideXlab platform.
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Palaeomagnetic data of sediment core SWERUS-C3-L2-13-PC
PANGAEA, 2020Co-Authors: Wiers Steffen, Snowball Ian, O'regan Matthew, Pearce Christof, Almqvist BjarneAbstract:Natural Remanent Magnetization and deMagnetization data of SWERUS-C3-L2-13-PC. Dataset also includes derived parameters
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Natural Remanent Magnetization data and derived parameters of sediment core PS92/054-1
PANGAEA, 2019Co-Authors: Wiers Steffen, Snowball Ian, O'regan Matthew, Almqvist BjarneAbstract:Natural Remanent Magnetization data and derived parameters
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Natural Remanent Magnetization data and derived parameters of sediment core PS92/039-2
PANGAEA, 2019Co-Authors: Wiers Steffen, Snowball Ian, O'regan Matthew, Almqvist BjarneAbstract:Natural Remanent Magnetization data and derived parameters
Qingsong Liu - One of the best experts on this subject based on the ideXlab platform.
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An integrated Natural Remanent Magnetization acquisition model for the Matuyama-Brunhes reversal recorded by the Chinese loess
'Wiley', 2018Co-Authors: Jin Chunsheng, Qingsong Liu, Hu Pengxiang, Jiang Zhaoxia, Li C, Han Peng, Yang Huihui, Liang WentianAbstract:Geomagnetic polarity reversal boundaries are key isochronous chronological controls for the long Chinese loess sequences, and further facilitate paleoclimatic correlation between Chinese loess and marine sediments. However, owing to complexity of postdepositional Remanent Magnetization (pDRM) acquisition processes related to variable dust sedimentary environments on the Chinese Loess Plateau (CLP), there is a long-standing dispute concerning the downward shift of the pDRM recorded in Chinese loess. In this study, after careful stratigraphic correlation of representative climatic tie points and the Matuyama-Brunhes boundaries (MBB) in the Xifeng, Luochuan, and Mangshan loess sections with different pedogenic environments, the downward shift of the pDRM is semiquantitatively estimated and the acquisition model for the loess Natural Remanent Magnetization (NRM) is discussed. The measured MB transition zone has been affected by the surficial mixing layer (SML) and reMagnetization. Paleoprecipitation is suggested to be the dominant factor controlling the pDRM acquisition processes. Rainfall-controlled leaching would restrict the efficiency of the characterized Remanent Magnetization carriers aligning along the ancient geomagnetic field. We conclude that the MBB in the central CLP with moderate paleoprecipitation could be considered as an isochronous chronological control after moderate upward adjustment. A convincing case can then be made to correlate L8/S8 to MIS 18/1
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Reliability of the Natural Remanent Magnetization recorded in Chinese loess
Journal of Geophysical Research, 2010Co-Authors: Chunsheng Jin, Qingsong LiuAbstract:[1] Chinese loess-paleosol sequences undoubtedly have recorded geomagnetic events (both polarity reversals and excursions). However, the fidelity of the rapid paleomagnetic field oscillations during a polarity reversal remains uncertain. To test the reliability and consistency of the Natural Remanent Magnetization records in Chinese loess, 10 subsets of parallel samples across the Matuyama-Brunhes (MB) reversal boundary were obtained from the Luochuan region in the hinterland of the Chinese Loess Plateau. Our paleomagnetic results show diversified virtual geomagnetic poles (VGPs) during the MB transition but consistent VGPs outside of the transitional zone. The anisotropy of magnetic susceptibility and rock magnetism results indicate that the sampled interval is rather uniform and undisturbed. The discrepancies of the characteristic Remanent Magnetization within the MB transition are probably due to the low efficiency in aligning magnetic grains, mainly pseudo-single-domain magnetite, associated with the low field intensity. Nevertheless, the stratigraphic location of the MB boundary can be confidently defined. Therefore, we conclude that Chinese loess-paleosol sequences can record geomagnetic reversal events, but the morphology within the polarity transition is rather questionable.
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Chemical overprint on the Natural Remanent Magnetization of a subtropical red soil sequence in the Bose Basin, southern China
Geophysical Research Letters, 2007Co-Authors: Chenglong Deng, Qingsong Liu, Wei Wang, Caicai LiuAbstract:[1] We present a high-resolution paleomagnetic investigation of the subtropical red soil sequence at the Damei section, Bose Basin, southern China. Maghemite with low coercivities and fine-grained hematite with high coercivities but relatively low unblocking temperatures were identified as main carriers of the Natural Remanent Magnetization (NRM). Strong chemical weathering occurring under subtropical climatic conditions in southern China led to a chemical Remanent Magnetization (CRM) overprint that is sufficiently strong to mask the primary NRM. Analysis of the Bose Basin soil sequence indicates that the CRM has a large lock-in depth (>4 m). This example shows that magnetostratigraphic studies on red soil sequences in subtropical-tropical southern China should be interpreted with caution.
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Effects of low-temperature oxidation on Natural Remanent Magnetization of Chinese loess
Chinese Science Bulletin, 2002Co-Authors: Qingsong Liu, Subir K. Banerjee, Michael J Jackson, Rixiang Zhu, Yongxin PanAbstract:This study systematically investigates changes in both compositions and grain-sizes of magnetic minerals in the Chinese loess/paleosol samples (Yichuan, China) during thermal deMagnetization processes. Between 100 and 200°C, (1) H c and H cx significantly decrease while M rs and M s remain stable; (2) concentration of the multi-domain (MD) grains increases while that of superparamagnetic (SP) grains decreases; and (3) there exists the abnormal behavior of the thermal deMagnetization in the Natural Remanent Magnetization (NRM). In addition, the corresponding changes in all these parameters are gradually muted with the increase of the pedogenesis degree. The results indicate that the observed alteration probably relates to reducing processes caused by the burning of the organic matter in samples. Before the thermal treatment, the MD grains in loess samples had been partially altered in nature by low-temperature oxidization (LTO). This CRM can be sufficiently attenuated or even removed by the reducing process between 100 and 200°C during the thermal treatment and has no apparent harmful effects on the characteristic Remanent Magnetization (ChRM) between 300 and 500°C.
