Archean basin–craton complexes and the growth of Precambrian shields

1977 ◽  
Vol 14 (12) ◽  
pp. 2737-2759 ◽  
Author(s):  
Alan M. Goodwin
Keyword(s):  
Mantle Convection ◽  
Age Groups ◽  
Canadian Shield ◽  
Superior Province ◽  
Low Grade ◽  
Lower Grade ◽  
Metamorphic Terranes

Southern Superior Province of the Canadian Shield contains cratonic and basinal elements arranged in high- to low-grade metamorphic terranes such that higher grade gneissic cratons are interpreted to represent primary infrastructure to lower grade volcanic-rich (greenstone) basins. Ensimatic accumulation of volcanic components is favoured with derivation of gneissic (granitic) components by ensuing metamorphic differentiation and granitization processes. Such vertically reconstructed basin–craton complexes which are tentatively ascribed to initial Archean mantle convection, are viewed as building units of growing Precambrian shields.Globally, twenty-seven identified Archean cratons belong to three main age groups based on maximum recorded ages as follows: 3.5–3.8 Ga, 2.9–3.1 Ga, and 2.6–2.7 Ga. The three age groups that correspond to major periods of Archean orogeny may represent accretion superevents (after Moorbath).Most cratons as presently exposed display lithologic characteristics of lower superstructure–upper infrastructure of typical basin–craton complexes thereby suggesting a common degree of crustal buoyancy, hence level of erosion. Archean belts of southern Superior Province provide unique opportunity for reconstruction of the typical basin–craton complex.

A detailed 40Ar/39Ar age study of an Abitibi dike from the Canadian Superior Province

1979 ◽  
Vol 16 (5) ◽  
pp. 1060-1070 ◽  
Author(s):  
J. A. Hanes ◽  
Derek York
Keyword(s):  
Canadian Shield ◽  
Superior Province ◽  
Low Grade ◽  
Polar Wander ◽  
Mafic Mineral ◽  
Fine Grained ◽  
Apparent Polar Wander Path ◽  
Step Heating ◽  
Apparent Age ◽  
Hydrothermal Event

40Ar/39Ar step-heating analyses were performed on 11 felsic and mafic mineral separates from a 90 m wide Precambrian diabase dike of the Abitibi swarm in the Superior Province of the Canadian Shield. Deuterically altered minerals from the dike interior define a primary age of 2150 ± 25 Ma. Updated ages, obtained from felsic separates within 30, and mafic within 1.5 m of the dike border, are evidence of a previously undetected 'Hudsonian' (1.7–1.8 Ga) hydrothermal event in the area. It is possible to distinguish the deuteric from the later hydrothermal alteration by both dating and petrographic methods. The data from this study demonstrate the successful application of 40Ar/39Ar dating to early Proterozoic dikes which have suffered low grade metamorphism. The ages support a north to south sense of motion of the Track 5 apparent polar wander path (APWP). A monotonic decrease in apparent age of felsic spectra indicates reactor induced recoil effects which are correlated with the fine-grained saussurite in the feldspar.

Constraints from 40Ar/39Ar geochronology on the tectonothermal history of the Kapuskasing uplift in the Canadian Superior Province

1994 ◽  
Vol 31 (7) ◽  
pp. 1146-1171 ◽  
Author(s):  
J. A. Hanes ◽  
D. A. Archibald ◽  
M. Queen ◽  
E. Farrar
Keyword(s):  
Fault Zone ◽  
Age Groups ◽  
Fault Zones ◽  
Fault Reactivation ◽  
Superior Province ◽  
Lower Grade ◽  
Upper Limit ◽  
Step Heating ◽  
History Of ◽  
Structural Levels

The Kapuskasing uplift (KU) in the Superior Province of the Canadian Shield has been interpreted as an oblique cross section through the Archean mid-crust. However, the time of juxtaposition of the granulites of the KU against the lower grade rocks of the Abitibi greenstone belt (AGB) along the Ivanhoe Lake fault zone is problematic. To constrain the postmetamorphic tectonothermal history of the KU, we have conducted 57 40Ar/39Ar step-heating analyses on mineral and rock samples collected in a transect across the southern KU and adjacent AGB. The age spectra record a complex thermal history. Amphiboles from the AGB in the footwall of the Ivanhoe Lake fault zone have ca. 2.66 Ga dates, similar to closure ages for amphiboles from farther east in the AGB. Amphibole dates of 2.46–2.52 Ga from the deepest structural levels of the KU place an upper limit on the time of major uplift of the granulites and their juxtaposition with the AGB. Biotite and muscovite dates from the transect cluster into three age groups. The presence in the deepest structural levels of the KU of biotite with 2.40–2.45 Ga dates indicates that significant uplift (15–20 km or more) of the granulites had occurred by this time. Micas with dates in the 2.25–2.30 Ga range are close to fault zones; these dates may indicate a ca. 2.30 Ga episode of fault reactivation. Feldspar, fault-related whole rocks, and some micas record events post 2.1 Ga. These correspond to the emplacement of mafic and lamprophyric dykes and fault reactivation.

scholarly journals Parosteal Osteosarcoma with Pancreatic Metastasis and Multiple Relapses: A Case Report and Review of the Literature

2021 ◽  
pp. 983-988
Author(s):  
Daniel Cirotski ◽  
Jyoti Panicker
Keyword(s):  
Age Groups ◽  
Bone Cancer ◽  
Pancreatic Metastasis ◽  
Low Grade ◽  
Parosteal Osteosarcoma ◽  
Disease Course ◽  
Review Of The Literature ◽  
Histologic Subtype ◽  
Primary Bone ◽  
Multiple Relapses

Osteosarcoma is the most common primary bone cancer in all age groups. Metastasis mostly occurs with high-grade tumors disseminating to the lungs and other bones. Spread to the pancreas is rare and undocumented in the low-grade subtypes. Additionally, it is uncommon for the disease course of low-grade subtypes to involve multiple relapses. We present a 35-year-old woman with parosteal osteosarcoma who has experienced an atypical metastasis to the pancreas as well as multiple local and pulmonary relapses. The lesion was identified incidentally on routine imaging, and the patient underwent resection. We compare our case to the other reports of pancreatic metastasis in the literature. Despite being especially rare, clinicians ought to be aware of pancreatic metastasis of osteosarcoma. Furthermore, despite parosteal osteosarcoma’s less aggressive disease course, it can uncommonly lead to multiple relapses. We present a rare case exemplifying these phenomena in the prognostically favorable histologic subtype of parosteal osteosarcoma.

scholarly journals Selection of Optimal Magnets for Traction Motors to Prevent Demagnetization

Machines ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 124
Author(s):  
Dantam Rao ◽  
Madhan Bagianathan
Keyword(s):  
Flux Density ◽  
Electric Vehicles ◽  
Parallel Line ◽  
Low Grade ◽  
Lower Grade ◽  
Worst Case ◽  
Traction Motors ◽  
Knee Point ◽  
Point Of Intersection ◽  
Selection Of

Currently, permanent-magnet-type traction motors drive most electric vehicles. However, the potential demagnetization of magnets in these motors limits the performance of an electric vehicle. It is well known that during severe duty, the magnets are demagnetized if they operate beyond a ‘knee point’ in the B(H) curve. We show herein that the classic knee point definition can degrade a magnet by up to 4 grades. To prevent consequent excessive loss in performance, this paper defines the knee point k as the point of intersection of the B(H) curve and a parallel line that limits the reduction in its residual flux density to 1%. We show that operating above such a knee point will not be demagnetizing the magnets. It will also prevent a magnet from degenerating to a lower grade. The flux density at such a knee point, termed demag flux density, characterizes the onset of demagnetization. It rightly reflects the value of a magnet, so can be used as a basis to price the magnets. Including such knee points in the purchase specifications also helps avoid the penalty of getting the performance of a low-grade magnet out of a high-grade magnet. It also facilitates an accurate demagnetization analysis of traction motors in the worst-case conditions.

CASE STUDY ON CIRCUMSCRIBED GLIOMAS, THEIR CLINICOPATHOLOGICAL CORRELATION IN A TERTIARY CARE CENTER

2021 ◽  
pp. 42-45
Author(s):  
Esther Alffi Papang ◽  
K. Rama
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Tertiary Care ◽  
Biological Behavior ◽  
Low Grade ◽  
Lower Grade ◽  
Who Grade ◽  
Primary Tumors ◽  
Short Period ◽  
The Impact

The histogenesis and biological behavior of primary tumors of the central nervous system(CNS) are very diverse. The majority of present gliomas as benign, slow growing lesions classied as by the WHO classicati grade I or II (Low grade gliomas) on of CNS tumors. However, a signicant fraction of gliomas develop over a short period of time and progress rapidly and are therefore classied as WHO grade III or IV(High grade gliomas). Astrocytomas are primary central nervous system tumours that can develop in adults or in children. They arise from the Astrocytes. They can be divided into diffuse that generally have a higher grade and poorer prognosis and those that are localised that tend to be of a lower grade and have a better prognosis. In this study, we outline the basic histological spectrum and features, epidemiological aspects and grade of circumscribed gliomas (localised) or other Astrocytic tumours according to WHO classication . These are the Pilocytic Astrocytoma, Pilomyxoid Astrocytoma, Subependymal giant cell Astrocytoma, Pleomorphic xanthoastrocytoma and Anaplastic astrocytoma . The knowledge of these tumours are important as they are one of the commonest cause of mortality and morbidity in both the young and old, accounting for about 60% of the glial tumours. Therefore neuropathological diagnosis and tumour characteristics will therefore profoundly inuence the impact of treatment strategies.

scholarly journals High-risk HPV genotypes and cervical lesions association in postmenopausal women

2021 ◽  
Vol 31 (Supplement_2) ◽  
Author(s):  
Ana Rita Fernandes Miranda da Costa ◽  
Cláudia Sousa ◽  
Erica Isidoro ◽  
Regina Silva ◽  
Cristiana Mourato
Keyword(s):  
Cervical Cancer ◽  
High Risk ◽  
Postmenopausal Women ◽  
Age Groups ◽  
Low Grade ◽  
High Grade ◽  
Cervical Lesions ◽  
Intraepithelial Lesion ◽  
The Bethesda System ◽  
High Risk Hpv

Abstract Background Persistent infection by high-risk Human Papillomavirus (hrHPV) are the major cause of cervical cancer. Studies report disparities in the incidence of infection and the various genotypes of this virus in different age groups, suggesting a higher frequency of hrHPV in young women and low-risk subtypes being predominant in older women. This study aimed to investigate the incidence and distribution of hrHPV genotypes in postmenopausal women as well as the correlation with the cytological findings. Methods 16 859 women, aged 50–64 years, performed cervical cancer screening test in Friuri Venezia Giulia region, Italy. The infection was evaluated by the Polymerase Chain Reaction methodology and the positive samples were evaluated by Liquid Based Cytology according to the Bethesda System from 2014. A statistical analysis was performed to study the molecular and cytological data of this population. Results hrHPV infection were found in 5.8% of the women and 78.3% of these were caused by hrHPV other than HPV16 and HPV18 (). Also, 65.7% of the positive samples were negative for intraepithelial lesion or malignancy while low grade squamous intraepithelial lesion was the most frequent (22.4%). There was an increase in the number of high-grade intraepithelial lesions in the presence of HPV16 compared to that recorded when this genotype was absent (20.8% vs. 8.5%). No cervical cancers were detected. Conclusions Infection with hrHPV is uncommon in postmenopausal women and it is mostly caused by subtypes less associated with the development of cervical cancer. Yet, HPV16 infection triggers the development of high-grade lesions.

scholarly journals Development and Validation of an Efficient MRI Radiomics Signature for Improving the Predictive Performance of 1p/19q Co-Deletion in Lower-Grade Gliomas

Cancers ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 5398
Author(s):  
Quang-Hien Kha ◽  
Viet-Huan Le ◽  
Truong Nguyen Khanh Hung ◽  
Nguyen Quoc Khanh Le
Keyword(s):  
Gold Standard ◽  
Binary Classification ◽  
Predictive Performance ◽  
Deletion Mutation ◽  
Gradient Boosting ◽  
Low Grade ◽  
Lower Grade ◽  
Chromosome 1P ◽  
Extreme Gradient Boosting ◽  
External Test

The prognosis and treatment plans for patients diagnosed with low-grade gliomas (LGGs) may significantly be improved if there is evidence of chromosome 1p/19q co-deletion mutation. Many studies proved that the codeletion status of 1p/19q enhances the sensitivity of the tumor to different types of therapeutics. However, the current clinical gold standard of detecting this chromosomal mutation remains invasive and poses implicit risks to patients. Radiomics features derived from medical images have been used as a new approach for non-invasive diagnosis and clinical decisions. This study proposed an eXtreme Gradient Boosting (XGBoost)-based model to predict the 1p/19q codeletion status in a binary classification task. We trained our model on the public database extracted from The Cancer Imaging Archive (TCIA), including 159 LGG patients with 1p/19q co-deletion mutation status. The XGBoost was the baseline algorithm, and we combined the SHapley Additive exPlanations (SHAP) analysis to select the seven most optimal radiomics features to build the final predictive model. Our final model achieved an accuracy of 87% and 82.8% on the training set and external test set, respectively. With seven wavelet radiomics features, our XGBoost-based model can identify the 1p/19q codeletion status in LGG-diagnosed patients for better management and address the drawbacks of invasive gold-standard tests in clinical practice.

scholarly journals EPID-13. A POPULATION-BASED ANALYSIS OF CNS TUMOR DIAGNOSES, TREATMENT, AND SURVIVAL IN CONGENITAL AND INFANT AGE GROUPS

2020 ◽  
Vol 22 (Supplement_3) ◽  
pp. iii321-iii321
Author(s):  
Muriel Hart ◽  
Amy Mellies ◽  
Alina Beltrami ◽  
Ahmed Gilani ◽  
Adam Green
Keyword(s):  
Age Groups ◽  
Young Patients ◽  
High Grade Glioma ◽  
Population Based ◽  
Cns Tumors ◽  
Low Grade ◽  
Tumor Type ◽  
Older Children ◽  
Embryonal Tumors ◽  
Chi Square

Abstract BACKGROUND Congenital (<3 months) and infant (3 to 11 months) brain tumors are biologically different from tumors in older children, but epidemiology of these tumors has not been studied comprehensively. Insight into epidemiological differences could help tailor treatment recommendations by age and increase overall survival (OS). METHODS Population-based data from the SEER 18 registries was obtained for 14,493 0-19-year-olds diagnosed with CNS tumors between 1990 and 2015. Incidence, treatment, and survival were analyzed using Chi-square and Kaplan-Meier analyses. RESULTS Between the <3 month, 3–5 month, 6–11 month, and 1–19 year age groups, tumor type distribution differed significantly (p<0.001); high-grade glioma (HGG) was most common in the <3-month-olds, while low-grade glioma (LGG) was most common in the other groups. 5-year OS for all tumors was 36.7% (<3 months), 56.0% (<3–5 months), 63.8% (6–11 months), and 74.7% (1–19 years) (log rank p<0.001). OS by tumor type was worst for <3-month-olds with LGG, medulloblastoma, and other embryonal tumors; OS was worst for 3-5-month-olds with ependymoma, <1-year-olds collectively with atypical teratoid-rhabdoid tumor, and 1-19-year-olds with HGG (log rank p<0.02 for all tumor types). <3-month-olds were least likely to receive any treatment for each tumor type and least likely to undergo surgery for all except HGG. <1-year-olds were far less likely than 1-19-year-olds to undergo radiation for embryonal tumors, as expected, but were also less likely to undergo chemotherapy. CONCLUSIONS Congenital/infant CNS tumors differ pathologically, therapeutically, and prognostically from those in older children. Treatment changes could help address poorer outcomes for these young patients.

Some new measurements of heat flow in the Superior Province of the Canadian Shield

1987 ◽  
Vol 24 (7) ◽  
pp. 1486-1489 ◽  
Author(s):  
Malcolm Drury ◽  
Alan Taylor
Keyword(s):  
Standard Deviation ◽  
Heat Flow ◽  
Canadian Shield ◽  
Superior Province ◽  
Flow Measurements ◽  
Radiogenic Heat ◽  
Radiogenic Heat Production ◽  
Climatic Variations ◽  
The Mean ◽  
A Site

Borehole heat-flow measurements are reported from six new sites in the Superior Province of the Canadian Shield. Values adjusted for glaciation effects, but not for Holocene climatic variations, range from 42 to 56 mW/m2. When these new values are combined with 21 previously published borehole values the mean is 42 mW/m2 with a standard deviation of 11 mW/m2. The data for a site on the Lac du Bonnet batholith suggest that the batholith has a thin veneer, less than 3 km, of rock of high radiogenic heat production at the surface.

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