scholarly journals Deformation of rhyolite lava crust associated with intermittent inner flow of lava: palaeomagnetic evidence

2019 ◽  
Vol 220 (1) ◽  
pp. 190-200
Author(s):  
Koji Uno ◽  
Kuniyuki Furukawa ◽  
Kotaro Nakai ◽  
Takuma Kamio ◽  
Tatsuo Kanamaru
Keyword(s):  
Curie Temperature ◽  
Remanent Magnetization ◽  
Deformation Analysis ◽  
Thermal Demagnetization ◽  
Primary Mode ◽  
Rhyolite Lava ◽  
Magnetization Component ◽  
Multiple Components ◽  
Mobile Part

SUMMARY A palaeomagnetic study has been conducted to examine the deformation of thick crusts of rhyolite lava while its inner portions continue to flow. The Sanukayama rhyolite lava, which erupted in the Pleistocene in Kozushima Island, Japan, was chosen as the investigation site because of its well-exposed vertical lithofacies variations classified into three distinct zones (pumiceous, obsidian and crystalline). The targets of this study are the pumiceous and obsidian zones, which constitute the crust of the lava. Thermal demagnetization reveals three remanent magnetization components from the pumiceous and obsidian samples but only a single magnetization component from the inner crystalline rhyolite samples. Alternating field demagnetization is ineffective in isolating the magnetization components in the pumiceous and obsidian samples. The multiple components of remanent magnetization of the crust are interpreted to have been acquired during cooling as thermoremanent magnetizations. We suspect intermittent lava transport of the inner portions, the primary mode of rhyolite lava advancement, to be responsible for the presence of multiple components in pumice and obsidian of the lava crust. When the inner portions of the lava retain mobility to flow out of the crust, the solidified crust of the lava surface below the magnetite Curie temperature remains susceptible to deformation. Analysis of palaeomagnetic directions from the crust allows the deformation of the crust to be described in terms of rotation. Although the mode of rhyolite lava advancement is not well understood, because of its infrequent occurrence, our observations offer an important insight on how the mobile part of the lava is associated with the deformation of the crust during continued lava advance.

scholarly journals Tracing of traffic-related pollution using magnetic properties of topsoils in Daejeon, Korea

2020 ◽  
Vol 79 (20) ◽  
Author(s):  
Seungwoo Lee ◽  
Seoyeon Kim ◽  
Hyeji Kim ◽  
Youlee Seo ◽  
Yeoncheol Ha ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Magnetic Susceptibility ◽  
Remanent Magnetization ◽  
Coarse Grained ◽  
Morphological Observation ◽  
Exhaust Emission ◽  
Thermal Demagnetization ◽  
Main Street ◽  
Traffic Related Pollution ◽  
The Difference

Abstract The present study was designed to explore the possibility of roadside pollution screening using magnetic properties of topsoil samples in Daejeon, South Korea. Low-field magnetic susceptibility, frequency dependence of magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, isothermal remanent magnetization (IRM) acquisition and demagnetization, back-field IRM treatment, and thermal demagnetization of composite IRM were determined for roadside topsoil samples. Magnetic susceptibility measured on 238 samples from the upper 5 cm of the topsoils ranged from 8.6 to 82.5 × 10–5 SI with a mean of 28.3 ± 10.8 × 10–5 SI. The proximal zone, 55 m wide area situated on either side of the main street, exhibited an enhancement of magnetic susceptibility. In areas distant from the main street, low magnetic susceptibility (< 50 × 10–5 SI) was observed. The topsoil samples exhibited significant susceptibility contrasts, suggesting that two dimensional magnetic mapping was effective in identifying traffic-related pollution. A few magnetic hotspots with intensities of magnetic susceptibility near or over 50 × 10–5 SI might reflect the difference in topographic elevation and surface morphology. Among various IRM-related parameters, remanence of coercivity was most significant statistically. In most samples, IRM component analysis provided dual coercivity components. Thermal demagnetization of composite IRM and morphological observation of magnetic separates suggest angular magnetite produced by vehicle non-exhaust emissions spherical magnetite derived from exhaust emission to be the dominant contributors to the magnetic signal. It is likely that lower- and higher-coercivity components represent the presence of coarse-grained angular magnetite and fine-grained spherical magnetite, respectively.

Paleomagnetism of the 1180 Ma Grenvillian Umfraville gabbro, Ontario

1978 ◽  
Vol 15 (6) ◽  
pp. 956-962 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Paleomagnetic Data ◽  
Grenville Province ◽  
Thermal Demagnetization ◽  
Before And After ◽  
Primary Origin

The 1180 ± 20 Ma Umfraville gabbro is a slightly metamorphosed stock in the Grenville Province. It was sampled at 17 sites (183 specimens). After alternating field and thermal demagnetization the gabbro retains the same very stable remanent magnetization of primary origin both before and after screening. The screened AF direction from 10 sites (96 specimens) gives a pole position of 166°E, 11°S (δp = 7°, δm = 10°). This position is ≈ 13° southeast of that originally reported for the gabbro by Hood. This pole position either does not fit or necessitates modifications to the four hypotheses that have been invoked to explain Grenville paleomagnetic data.

A new furnace for improving thermal demagnetization in paleomagnetism

2020 ◽  
Author(s):  
Huafeng Qin ◽  
Xiang Zhao ◽  
Shuangchi Liu ◽  
Greig Paterson ◽  
Zhaoxia Jiang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Curie Temperature ◽  
High Performance ◽  
Thermal Treatments ◽  
Thermal Demagnetization ◽  
Heating Wire ◽  
Low Magnetic Field ◽  
Detrimental Impact ◽  
The Magnetic Field ◽  
The Ideal

&lt;p&gt;Thermal demagnetization furnaces are routine facilities for paleomagnetic studies. The ideal thermal demagnetizer should maintain &amp;#8220;zero&amp;#8221; magnetic field during thermal treatments. However, magnetic field noises, including residual magnetic fields of material and induced fields caused by the heating current in the furnace are always present. The key to making high-performance demagnetization furnace is to reduce the magnetic field noises. By combining efficient demagnetization of shielding and a new structure of heating wire, we have developed a new demagnetization furnace with low magnetic field noises. Repeated progressive thermal demagnetization experiments using specimens that were previously completely thermal demagnetized above their Curie temperature were carry out to explore the effects of field within various types of furnace during demagnetization. These experiment confirm that magnetic field noises in the furnace can have an observable and detrimental impact on demagnetization behavior. Comparison between commercial furnaces and our new design show a notable reduction in the impacts of on thermal demagnetization behavior. The new heating element design and procedure for reducing magnetic&amp;#160;field&amp;#160;noises represent a significant improvement in the design of thermal demagnetizers and allows for extremely weak specimens to be successfully measured.&lt;/p&gt;

Paleomagnetism of late Paleozoic rocks in the northern Cache Creek terrane near Atlin, British Columbia

1992 ◽  
Vol 29 (3) ◽  
pp. 486-498 ◽  
Author(s):  
F. Cole ◽  
R. F. Butler ◽  
G. E. Gehrels
Keyword(s):  
British Columbia ◽  
Remanent Magnetization ◽  
Volcanic Rocks ◽  
Principal Component ◽  
Late Triassic ◽  
Relative Age ◽  
Thermal Demagnetization ◽  
Northern Portion ◽  
Paleozoic Rocks ◽  
Tectonic Interpretation

The Cache Creek terrane is exposed along the length of the Canadian Cordillera and is composed of oceanic strata that are probably, at least in part, exotic to North America. In the northern portion of the Cache Creek terrane near Atlin, British Columbia, paleomagnetic samples were collected from layered Paleozoic rocks at 22 sites (≥ 6 samples/site) on Alfred Butte. Principal component analysis of detailed thermal demagnetization data allowed clear isolation of a characteristic remanent magnetization (ChRM) from 17 of these sites. Blocking temperatures to 680 °C indicate that this magnetization is carried by hematite, and site-mean ChRM directions are determined with α95 < 10° for the majority of sites. On Sentinel Mountain, samples were collected from 16 sites in layered Paleozoic volcanic and chert rocks and from a diabase sill. Thermal demagnetization revealed a ChRM in the chert and volcanic rocks with blocking temperatures to 680 °C, whereas alternating-field demagnetization to 40 mT successfully isolated ChRM in the diabase sill. ChRM directions from four sites involved in a mesoscopic S-fold at Alfred Butte fail the fold test, indicating that the ChRM is a postfolding secondary remagnetization. Tests for relative age of structural tilting and remagnetization are ambiguous, with attendant uncertainties in tectonic interpretations. However, rock-magnetic and geologic constraints argue for a chemical remagnetization of these Paleozoic rocks in Late Triassic to Middle Jurassic time, possibly associated with structural juxtaposition of the Cache Creek and Stikine terranes along the Nahlin fault zone. Although certainly nonunique and speculative, the simplest tectonic interpretation of these paleomagnetic data involves postfolding and posttilting remagnetization during the Early Jurassic in a paleolatitudinal position that approximately agrees with predicted North American paleolatitudes for this time.

A paleomagnetic test for northward tectonic transport of the eastern Selwyn Basin, northern Canadian Cordillera: data from the mid-Cretaceous Ragged Pluton

2008 ◽  
Vol 45 (7) ◽  
pp. 860-869 ◽  
Author(s):  
D. T.A. Symons ◽  
K. Kawasaki ◽  
C. J.R. Hart ◽  
M. J. Harris
Keyword(s):  
North America ◽  
Lower Cambrian ◽  
Remanent Magnetization ◽  
Canadian Cordillera ◽  
Thermal Demagnetization ◽  
Granitic Pluton ◽  
Tectonic Transport ◽  
Paleomagnetic Result ◽  
Stable Characteristic ◽  
Saturation Remanence

Ragged Pluton is a member of the Tungsten Plutonic Suite in the eastern Selwyn Basin. This circular massive 97 Ma granitic pluton is ∼5 km in diameter. It intrudes deformed and metamorphosed clastic strata of the Neoproterozoic to Lower Cambrian Vampire Formation. Thermal and alternating field step demagnetization data for 216 specimens from 21 plutonic sites isolated a stable characteristic remanent magnetization (ChRM) direction at 20 sites of declination D = 325.9°, inclination I = 80.4° (α95 = 2.7°, k = 142). Thermal demagnetization and saturation remanence analysis show that the ChRM is carried by both single-domain pyrrhotite and magnetite. Ragged Pluton’s paleopole at 73.9°N latitude, 191.4°E longitude (dp = 5.0°, dm = 5.2°) is concordant with its co-eval 97 Ma North American reference paleopole, showing at 95% confidence that the pluton has not been significantly rotated or translated relative to North America. This paleomagnetic result favours tectonic models in which the eastern Selwyn Basin is autochthonous, or nearly so, since the mid Cretaceous.

scholarly journals Remagnetization of Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania): tectonic implications

2012 ◽  
Vol 63 (6) ◽  
pp. 453-461 ◽  
Author(s):  
Panaiotu Cristian G. ◽  
Panaiotu Cristina E. ◽  
Lazăr Iuliana
Keyword(s):  
Remanent Magnetization ◽  
Upper Jurassic ◽  
Relative Rotation ◽  
Clockwise Rotation ◽  
Magnetization Component ◽  
Diagenetic Processes ◽  
Tectonic Implications ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Southern Carpathians

Abstract We present a pioneering paleomagnetic study on Upper Jurassic limestones from the Danubian Unit (Southern Carpathians, Romania). Thermal and alternating field demagnetizations were applied to define the characteristic remanent magnetization component in all six localities (81 samples). All samples have a normal polarity characteristic remanent magnetization. Negative regional and local fold tests suggest that this remanent magnetization is in fact a remagnetization produced by late diagenetic processes. The studied limestones were probably remagnetized during the collision of the Getic Unit and Danubian Unit which took place during the long normal polarity Chron C34 (82-118 Ma). The area mean direction (D = 75.5°, I = 50.0°, α95 = 10.2°, k = 44) implies about 75° clockwise rotation post remagnetization. Our paleomagnetic results further indicate the absence of significant relative rotation between the Getic Unit and the Danubian Unit during the Cenozoic.

Cretaceous remagnetization in the Sylvester Allochthon: limits to post-105 Ma northward displacement of north-central British Columbia

1988 ◽  
Vol 25 (8) ◽  
pp. 1316-1322 ◽  
Author(s):  
R. F. Butler ◽  
T. A. Harms ◽  
H. Gabrielse
Keyword(s):  
British Columbia ◽  
Confidence Level ◽  
Remanent Magnetization ◽  
Rocky Mountain ◽  
Natural Remanent Magnetization ◽  
Late Triassic ◽  
Geological Evidence ◽  
North Central ◽  
Thermal Demagnetization ◽  
Pole Location

The Sylvester Allochthon of the Slide Mountain Terrane in northern British Columbia is a structurally interleaved assemblage of ocean-floor lithologies ranging in age from Late Devonian to Late Triassic. It is the most inboard of oceanic suspect terranes and rests as a vast klippe on miogeoclinal strata of the Cassiar Terrane. The Sylvester Allochton and the Cassiar Terrane lie west of the Northern Rocky Mountain Trench Fault. Both the Sylvester Allochthon and the Cassiar Terrane are intruded by mid-Cretaceous (105 Ma) granite of the Cassiar Batholith. Six oriented cores were collected at each of 12 sites in Guadalupian Parafusulina-bearing limestone of the Sylvester Allochthon at a location 4 km from the batholith. Isothermal remanent magnetization (IRM) acquisition and subsequent thermal demagnetization indicate that pyrrhotite is the dominant ferrimagnetic mineral. Least-squares line fitting to four thermal demagnetization steps between 150 and 310 °C was used to determine the characteristic natural remanent magnetization (NRM) directions that fail the fold test at the 99.5% confidence level. We interpret these observations as indicating that the NRM is a thermoremanent or thermochemical remanent magnetism associated with intrusion of the Cassiar Batholith. The resulting paleomagnetic pole location is latitude = 75.7°N, longitude = 171.7°E, α95 = 8.5°. When compared with the mid-Cretaceous pole for cratonic North America, a small but significant clockwise rotation (R ± ΔR = 23.9 ± 18.1 °) is evident, but poleward translation (p ± Δp = 5.3 ± 9.2°) is not significant at the 95% confidence level. The paleomagnetic results are consistent with geological evidence for moderate (700 km) northward transport of the Cassiar Terrane (along with the previously emplaced overlying Sylvester Allochthon) during mid-Cretaceous to Tertiary dextral transcurrent faulting.

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