scholarly journals Palaeomagnetism of the Mahatta Humaid Group (Cambrian – Early Ordovician, Oman), including a re-interpretation of previous Neoproterozoic palaeomagnetic data

GeoArabia ◽  
2009 ◽  
Vol 14 (2) ◽  
pp. 71-96
Author(s):  
Haroldo Vizán ◽  
Peter Turner ◽  
John A. Millson ◽  
Rob A. Ixer
Keyword(s):  
Remanent Magnetization ◽  
Sedimentary Basins ◽  
Vertical Axis ◽  
Petrographic Analysis ◽  
Polar Wander ◽  
Magnetic Carriers ◽  
Palaeomagnetic Data ◽  
Primary Origin ◽  
The Mean ◽  
Early Palaeozoic

ABSTRACT We carried out a palaeomagnetic study in the Al-Huqf region (Sultanate of Oman) on rocks that belong to different units of the Cambrian – Ordovician Mahatta Humaid Group. Thirty-nine samples were systematically collected from a succession ca. 520–495 Ma old. Seventeen samples showed characteristic remanent magnetization components with two antipodal polarities carried by hematite. Evidence suggests that these components have a primary origin. A detailed petrographic analysis revealed syntaxial overgrowths parallel to the easy plane of magnetization of the magnetic carriers that has probably enhanced and reinforced the primary magnetization. A palaeopole computed with the mean direction of the 17 characteristic remanent magnetization components was considered alongside previously published Neoproterozoic – early Palaeozoic palaeomagnetic data, which we placed in an updated chronostratigraphic framework for the Neoproterozoic – Cambrian Huqf Supergroup. Two interpretations were considered: (1) Oman was detached from the Arabian-Nubian craton until ca. 660 Ma, and it became attached (or was nearby) to it by ca. 630 Ma. In this interpretation, an apparent polar wander (APW) path of Arabia is proposed between ca. 630 and 500 Ma. The palaeomagnetic directions of Mirbat obtained by Killner et al. (2005) in rocks 720–660 Ma old are therefore assumed as primary, and taking into account that Oman was an independent block of the Arabian-Nubian craton, the corresponding palaeopole is not considered in the proposed segment of the Arabian APW path. (2) The Neoproterozoic data belong to two different tectonic blocks within the Arabian-Nubian craton and were involved in left-lateral, strike-slip movements along NW-trending faults. One block included the localities of Al Jabal al-Akhdar and Al-Huqf and may have rotated counter-clockwise c. 45° about a vertical axis between ca. 600 and 500 Ma. The other block included the locality of Mirbat and rotated counter-clockwise c. 25° about a vertical axis between ca. 600 and 550 Ma. These suggested block rotations may have played a role in generating the underlying fabrics for some of the sedimentary basins in Oman. In the second model, the rocks sampled by Killner et al. (2005) in Mirbat were re-magnetized during the intrusion of dike swarms at ca. 615–600 Ma.

PALAEOMAGNETISM OF DIABASE DYKES OF THE CANADIAN SHIELD

1965 ◽  
Vol 2 (4) ◽  
pp. 278-298 ◽  
Author(s):  
W. F. Fahrig ◽  
E. H. Gaucher ◽  
A. Larochelle
Keyword(s):  
Remanent Magnetization ◽  
Lake Superior ◽  
Canadian Shield ◽  
Igneous Rocks ◽  
Palaeomagnetic Data ◽  
The World ◽  
Oriented Samples ◽  
The Mean ◽  
The Individual ◽  
Dyke Swarms

Some areas of the Canadian Shield are profusely intruded by swarms of subparallel basaltic dykes. These typically have a diabasic texture and formerly were considered to be strictly the intrusive equivalents of tholeiitic flood basalt.About 650 oriented samples were collected from about 25 dyke swarms and preliminary palaeomagnetic data from six of them are presented here. The Mackenzie swarm has a K–Ar age of 1 295 million years, occurs throughout the western Canadian Shield, and is the most extensive swarm of basic dykes known anywhere in the world. The other swarms are the Molson dykes (1 445 m.y.) in northeastern Manitoba, the Marathon dykes (1 810 m.y.) just north of Lake Superior, the Sudbury dykes (1 285 m.y.) of southeastern Ontario, the Matachewan dykes (2 485 m.y.) of western Quebec and northeastern Ontario, and the Abitibi dykes (1 230 m.y.), which occur from Sault Ste. Marie, Ontario, to Lake Mistassini, Quebec.The palaeomagnetic virtual pole positions of six swarms were derived from the mean of their measured remanent magnetization directions. These directions of magnetization were determined from the samples after they were magnetically washed in an a-c. field of 80 or 130 oersteds. The reasons for the dispersion within the individual swarms are discussed. The pole positions of the Sudbury and Mackenzie dykes are almost identical and the two swarms are the same age within the limits of analytical uncertainty. However, basalt of the Sudbury swarm is alkalic and more undersaturated than basalt of the Mackenzie dykes.No evidence was found to contradict the usual assumption that unaltered basic igneous rocks of this type acquire and generally retain a stable magnetization which was parallel with the earth's magnetic field at the time of the dyke intrusion.

Paleomagnetism of fluorite veins in the Devonian St. Lawrence granite, Newfoundland, Canada

2008 ◽  
Vol 45 (9) ◽  
pp. 969-980 ◽  
Author(s):  
K. Kawasaki ◽  
D. T.A. Symons
Keyword(s):  
Vertical Axis ◽  
Zircon Age ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Vertical Vein ◽  
Significant Difference ◽  
Appalachian Orogen ◽  
The Mean ◽  
The Difference

Paleomagnetic results are reported from the Devonian St. Lawrence granite and the fluorite veins within the granite or its related porphyry dikes. Paleomagnetic analysis of 359 specimens from 29 sites shows that there is no statistically significant difference at 95% confidence between the site mean characteristic remanent magnetization (ChRM) directions carried by pyrrhotite and (or) magnetite of the granite and fluorite veins. No post-granite metamorphic event is known in the area. Thus, these concordant directions indicate that the granite and fluorite veins are coeval and retain a primary remanence. However, the mean ChRM direction of 25 vein and granite sites yields an Early Pennsylvanian paleopole of ∼316 Ma on the North American apparent polar wander path at 35.5°N, 129.2°E (A95 = 3.4°) that is younger than the 374 ± 2 Ma Devonian U–Pb zircon age for the granite. Two intersecting vertical vein sets indicate that the St. Lawrence granite has not been tilted since emplacement of the fluorite veins. Therefore, the difference between the measured and expected paleopoles is interpreted to result from a postemplacement counterclockwise rotation of ∼17° of the St. Lawrence granite region about a vertical axis. Analysis of Carboniferous paleopoles in the northern Appalachian orogen indicates the rotation at the St. Lawrence area is Late Devonian during the Acadian orogeny.

A Discussion on global tectonics in Proterozoic times - Palaeomagnetic evidence for a Proterozoic super-continent

1976 ◽  
Vol 280 (1298) ◽  
pp. 469-490 ◽  
Keyword(s):  
North American ◽  
Mantle Convection ◽  
Great Circle ◽  
Prominent Feature ◽  
Time Data ◽  
Polar Wander ◽  
Late Precambrian ◽  
Palaeomagnetic Data ◽  
The Baltic ◽  
Global Tectonics

The Precambrian apparent polar wander (a.p.w.) curve for Africa is now defined in a general way from ca . 2700 million years (Ma) to Palaeozoic times, and is compared here with palaeomagnetic results from other Precambrian regions. Loops present in the African and North American a.p.w. curves between 2000 and 1000 Ma can be matched in size and shape, and when superimposed show that the AfroArabian and North American regions were in continuity at this time. Data from other Gondwanaland continents are reviewed and seem to be consistent with the SmithHallam reconstruction to ca . 2100 Ma for South America, to ca . 1800 Ma for India, and possibly for Australia back to ca . 2100 Ma. The a.p.w. curve from the Baltic and Ukrainian Shields can be matched with that from Africa and North America such that there was crustal continuity prior to 1000 Ma with the Gothide and Grenville mobile belts in great-circle alignment. The limited palaeomagnetic data from the Siberian Shield do not allow it to be placed uniquely with respect to the other land masses but are consistent with a position in juxtaposition with the Baltic-Ukrainian Shields such that massive anorthosites and ca . 1000 Ma mobile belts are in alignment with those from elsewhere. The palaeomagnetic evidence is consistent with a model in which the bulk of the Precambrian shields were aggregated together as a single super-continent during much of Proterozoic times, the most prominent feature of which is a great circle alignment of massive anorthosites (2250-1000 Ma) along a belt which also became a concentrated zone of igneous intrusion by rapakivi granites and alkaline intrusions, and culminated in generation of long linear mobile belts at 1150 ± 200 Ma and thick graben sedimentation. The predominance of this feature during much of the Proterozoic suggests that a simple mantle convection system pertained during this time. The proposed super-continent is not greatly different in form from the later shortlived super-continent Pangaea, formation of which may have involved relatively minor redistribution of the sialic regions in late Precambrian (probably post-800 Ma) and Palaeozoic times.

Drift Forces on a Floating Body of Simple Geometry Due to Second Order Interactions Between Pairs of Harmonics With Different Frequencies

2009 ◽  
Author(s):  
Joa˜o Pessoa ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Vertical Cylinder ◽  
Vertical Axis ◽  
Second Order ◽  
The Body ◽  
Floating Body ◽  
Order Problem ◽  
Simple Geometry ◽  
The Mean ◽  
Order Quantities ◽  
Drift Forces

The paper presents an investigation of the slowly varying second order drift forces on a floating body of simple geometry. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom and a ratio of diameter to draft of 3.25. The hydrodynamic problem is solved with a second order boundary element method. The second order problem is due to interactions between pairs of incident harmonic waves with different frequencies, therefore the calculations are carried out for several difference frequencies with the mean frequency covering the whole frequency range of interest. Results include the surge drift force and pitch drift moment. The results are presented in several stages in order to assess the influence of different phenomena contributing to the global second order responses. Firstly the body is restrained and secondly it is free to move at the wave frequency. The second order results include the contribution associated with quadratic products of first order quantities, the total second order force, and the contribution associated to the free surface forcing.

Comparative Analysis of the Exposure and Surgical Freedom of the Endoscopic Extended Minipterional Craniotomy and the Transorbital Endoscopic Approach to the Anterior and Middle Cranial Fossae

2018 ◽  
Vol 17 (2) ◽  
pp. 174-181 ◽  
Author(s):  
Raywat Noiphithak ◽  
Juan C Yanez-Siller ◽  
Juan M Revuelta Barbero ◽  
Raymond I Cho ◽  
Bradley A Otto ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Standard Deviation ◽  
Minimally Invasive ◽  
Vertical Axis ◽  
Endoscopic Approach ◽  
Extended Version ◽  
Specific Approach ◽  
Significant Difference ◽  
Surgical Application ◽  
The Mean

AbstractBACKGROUNDNumerous minimally invasive approaches to the skull base have been successively developed. Knowledge of the surgical nuances of a specific approach may facilitate approach selection. This study sought to compare the nuances of an extended version of the minipterional craniotomy (EMPT) with those of the transorbital endoscopic approach (TOEA) to the anterior and middle cranial fossae (ACF and MCF, respectively).OBJECTIVETo quantitatively analyze and compare the area of exposure and surgical freedom between EMPT and TOEA to the ACF and MCF.METHODSEMPT and TOEA were carried out in 5 latex-injected cadaveric heads, bilaterally (10 sides). For each approach, the area of exposure, surgical freedom, and angle of attack were obtained with neuronavigation and statistically compared.RESULTSNo significant difference was found between the mean area of exposure of EMPT and TOEA at the ACF and MCF (P = .709 and .317, respectively). The mean exposure area at the ACF was of 13.4 ± 2.6 cm2 (mean ± standard deviation) and 13.0 ± 1.9 cm2 for EMPT and TOEA, respectively. Except for the crista galli, EMPT afforded a larger area of surgical freedom at all targets. EMPT also achieved significantly greater attack angles in vertical axis except to the crista galli. The horizontal attack angles to all targets were similar between approaches.CONCLUSIONEMPT and TOEA offer a comparable area of exposure at the ACF and MCF in the cadaver; however, the instrument maneuverability afforded by EMPT is superior. Further studies are necessary to better define their precise surgical application.

scholarly journals Differences in Demographic and Radiographic Characteristics between Patients with Visible and Invisible T1 Slopes on Lateral Cervical Radiographic Images

2022 ◽  
Vol 11 (2) ◽  
pp. 411
Author(s):  
Sadayuki Ito ◽  
Hiroaki Nakashima ◽  
Akiyuki Matsumoto ◽  
Kei Ando ◽  
Masaaki Machino ◽  
...  
Keyword(s):  
Pilot Study ◽  
Surgical Planning ◽  
Vertical Axis ◽  
Sagittal Vertical Axis ◽  
Radiographic Images ◽  
T1 Slope ◽  
Group I ◽  
Significant Difference ◽  
The Mean ◽  
Flexion And Extension

Introduction: The T1 slope is important for cervical surgical planning, and it may be invisible on radiographic images. The prevalence of T1 invisible cases and the differences in demographic and radiographic characteristics between patients whose T1 slopes are visible or invisible remains unexplored. Methods: This pilot study aimed to evaluate the differences in these characteristics between outpatients whose T1 slopes were visible or invisible on radiographic images. Patients (n = 60) who underwent cervical radiography, whose T1 slope was confirmed clearly, were divided into the visible (V) group and invisible (I) group. The following radiographic parameters were measured: (1) C2-7 sagittal vertical axis (SVA), (2) C2-7 angle in neutral, flexion, and extension positions. Results: Based on the T1 slope visibility, 46.7% of patients were included in group I. The I group had significantly larger C2-7 SVA than the V group for males (p < 0.05). The C2-7 SVA tended to be larger in the I group, without significant difference for females (p = 0.362). Discussion: The mean C2-7 angle in neutral and flexion positions was not significantly different between the V and I groups for either sex. The mean C2-7 angle in the extension position was greater in the V group. The T1 slope was invisible in males with high C2-7 SVA.

Palaeomagnetic results from the middle Tertiary Meander Intrusives of northern Victoria Land, East Antarctica

1996 ◽  
Vol 8 (1) ◽  
pp. 61-72 ◽  
Author(s):  
Elena Belluso ◽  
Roberto Lanza
Keyword(s):  
Remanent Magnetization ◽  
Ross Sea ◽  
East Antarctica ◽  
Magnetic Mineralogy ◽  
Tilt Correction ◽  
Palaeomagnetic Data ◽  
Victoria Land ◽  
Geological Models ◽  
Laboratory Investigations ◽  
The Antarctic

The Tertiary stocks (Meander Intrusives) cropping out along the coasts of the Ross Sea were sampled for a palaeomagnetic study during the sixth Italian expedition to northern Victoria Land. Laboratory investigations concerned magnetic mineralogy and remanent magnetization. Minerals of the magnetiteulvöspinel series occur in the rocks from all stocks, with low-Ti titanomagnetite usually prevalent. Haematite and goethite occur in small amounts as alteration products. Large secondary components commonly screen the characteristic remanent magnetization and were removed by thermal or AF demagnetization at temperatures or peak-fields higher than 360°C and 20 mT respectively. A total of 10 VGPs were obtained from radiometrically dated rocks (42–22 Ma); the averaged position (69°S, 334°E; α95=9.9°) is the first middle Tertiary palaeomagnetic pole for East Antarctica, and gives evidence for a reversal in the course of the APW path. This evidence is not substantially altered by a supposed tilt-correction consistent with geophysical and geological models for the uplift of the Transantarctic Mountains. No definite conclusion about relative movements between East Antarctica and the Antarctic Peninsula can be drawn from the existing palaeomagnetic data.

scholarly journals Characterizing Human Cell Types and Tissue Origin Using the Benford Law

Cells ◽  
2019 ◽  
Vol 8 (9) ◽  
pp. 1004 ◽  
Author(s):  
Sne Morag ◽  
Mali Salmon-Divon
Keyword(s):  
Feature Selection Method ◽  
Cell Types ◽  
Machine Learning Algorithms ◽  
Unknown Primary ◽  
Rna Seq ◽  
Cancer Subtypes ◽  
Interdisciplinary Approaches ◽  
Primary Origin ◽  
The Mean ◽  
Benford Law

Processing massive transcriptomic datasets in a meaningful manner requires novel, possibly interdisciplinary, approaches. One principle that can address this challenge is the Benford law (BL), which posits that the occurrence probability of a leading digit in a large numerical dataset decreases as its value increases. Here, we analyzed large single-cell and bulk RNA-seq datasets to test whether cell types and tissue origins can be differentiated based on the adherence of specific genes to the BL. Then, we used the Benford adherence scores of these genes as inputs to machine-learning algorithms and tested their separation accuracy. We found that genes selected based on their first-digit distributions can distinguish between cell types and tissue origins. Moreover, despite the simplicity of this novel feature-selection method, its separation accuracy is higher than that of the mean-expression level approach and is similar to that of the differential expression approach. Thus, the BL can be used to obtain biological insights from massive amounts of numerical genomics data—a capability that could be utilized in various biomedical applications, e.g., to resolve samples of unknown primary origin, identify possible sample contaminations, and provide insights into the molecular basis of cancer subtypes.

New palaeomagnetic, petrographic and 40Ar/39Ar data to test palaeogeographic reconstructions of Caledonide Svalbard

2011 ◽  
Vol 149 (4) ◽  
pp. 696-721 ◽  
Author(s):  
KRZYSZTOF MICHALSKI ◽  
MAREK LEWANDOWSKI ◽  
GEOFF MANBY
Keyword(s):  
Remanent Magnetization ◽  
Large Scale ◽  
Age Determination ◽  
Late Ordovician ◽  
Polar Wander ◽  
Close Proximity ◽  
Lateral Displacements ◽  
First Time ◽  
Geographical Locations ◽  
Middle Proterozoic

AbstractNew palaeomagnetic and petrographic data are presented from Cambrian rocks of SW Svalbard to test, for the first time, Palaeozoic reconstructions of the major terranes of Svalbard. In the course of thermal demagnetization three ChRM (characteristic remanent magnetization) components were identified, which were labelled HORNL, HORNM and HORNH, respectively, on the basis of their different unblocking temperatures. The HORNM magnetization is related to the Late Ordovician–Silurian formation of the synmetamorphic S1 foliation. The HORNM palaeopole (Φ = −18.5°, Λ = 359°, Dp/Dm = 5.8°/11.4°, Plat = 6°N) matches exactly the Silurian sectors of the Baltica–Laurentia apparent polar wander paths after the closure of Iapetus (455–415 Ma). The 450 Ma 40Ar–39Ar age determination from mica ages obtained from the broad zone of mylonites along the Billefjorden Fault Zone which separates the Central and Eastern terranes, also suggests that the two terranes were eventually amalgamated by 450 Ma. The HORNMVGP also lies very near the palaeopole derived from the Middle Proterozoic rocks of the Eastern Terrane (Ny Friesland), metamorphosed during Caledonian time, suggesting its close proximity to the study area (Central Terrane). The present study has shown that at least two of the major terranes of Svalbard, as defined by previous authors, occupied similar geographical locations by Silurian time, and the previously proposed large-scale Late Devonian left lateral displacements are not supported.

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