Approaches to the Low Grade Metamorphic History of the Karakaya Complex by Chlorite Mineralogy and Geochemistry

The tectono-metamorphic history of the late Archean (2800–2600 Ma) Hemlo – Heron Bay greenstone belt in the Superior Province has been delineated from textural relationships, mineral chemistry, and P–T paths in metapelites, cordierite–orthoamphibole rocks, and metabasites from the White River exploration property, Hemlo area, Ontario. An early low-temperature, medium-pressure metamorphism (about 500 °C and 6–6.5 kbar (1 kbar = 100 MPa)) is indicated by the occurrence of relict kyanite and staurolite porphyroblasts and zoned garnet porphyroblasts in metapelites and the presence of zoned calcic amphiboles in metabasites. This early metamorphism appears to have been coeval with the previously documented D1 deformation that is associated with, for example, low-angle thrusts. A second regional metamorphism predominates in the Hemlo – Heron Bay greenstone belt and is generally of relatively low grade, at about 510–530 °C and 3.2–3.5 kbar, over most of the study area and increases to medium grade (550–650 °C and 4–5 kbar) towards the southern margin with the Pukaskwa Gneissic Complex and along the central axis enclosing the Hemlo Shear Zone. The second regional metamorphism was contemporaneous with the D3 deformation and was probably related to plutonism. This type of polymetamorphism in the Hemlo – Heron Bay greenstone belt may be equivalent to those in Phanerozoic subduction complexes and therefore supports the arc–arc accretion model for the development of the southern Superior Province. Although the Hemlo – Heron Bay greenstone belt most likely represents a single tectonic environment (an oceanic island arc), the restricted occurrence of the relict kyanite and staurolite indicates that the central portion of this Archean greenstone belt probably was at a deeper crustal level at the time of the first metamorphic event.

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Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway

10.5194/egusphere-egu21-7179 ◽

2021 ◽

Author(s):

Stephan Höpfl ◽

Jiří Konopásek ◽

Holger Stünitz ◽

Steffen G. Bergh

Keyword(s):

The Arctic ◽

Low Grade ◽

Prograde Metamorphism ◽

Northern Norway ◽

Metamorphic History ◽

Scandinavian Caledonides ◽

Nappe Complex ◽

History Of ◽

Peak Metamorphism ◽

Metamorphic Gradient

Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern NorwayH&#246;pfl Stephan1, Konop&#225;sek Ji&#345;&#237;1, St&#252;nitz Holger1,2 Bergh G., Steffen1UiT Norges arktiske universitet, Institutt for geovitenskap, [email protected]&#160;1Department of Geosciences, UiT The Arctic University of Norway, Troms&#248; 9037, Norway2Institut des Sciences de la Terre (ISTO), Universit&#233; d&#8217;Orleans, Orleans 45100, France&#160;The Balsfjord Series is located in the central part of Troms&#8211;Finnmark County, northern Norway, and is part of the upper allochthon of the Scandinavian Caledonides. It consists of an Ordovician&#8211;Silurian metsedimentary sequence lying on top of the mostly gabbroic Lyngen Magmatic Complex (LMC). The unit exhibits an inverted metamorphic gradient, where the metamorphic conditions increase from the base to the top, from very low grade in the southeast to medium grade in the west and northwest. The Balsfjord Series is sandwiched between two high-grade units, the Nakkedal + Troms&#248; Nappe Complex in the hanging wall and the Nordmannvik Nappe as the top part of the Reisa Nappe Complex (RNC) in the footwall. The Nakkedal + Troms&#248; Nappe Complex features metamorphic peak ages of ca. 455&#8211;450 Ma and the Nordmannvik Nappe of ca. 430 Ma. The peak metamorphism of the Balsfjord Series has never been dated and the role of the inverted metamorphic gradient is not yet understood. One of the main motivations in this project is to resolve the Caledonian deformation history in the Balsfjord Series, ideally leading to a regional tectonic model explaining the tectonostratigraphic and metamorphic relationships between the abovementioned units.The Balsfjord Series features two main discernible folding phases. The earlier phase displays tight to isoclinal folds with flat lying axial surfaces parallel to the penetrative foliation. Observed fold axes are parallel with the stretching lineation. These folds are best preserved in the northwestern, upper part of the unit and are syn-metamorphic in certain areas, as they fold original bedding (transposed foliation). A later folding phase is represented by mainly open folds with inclined to steep axial surfaces. Their fold axes are gently plunging with a predominant NE&#8211;SW orientation. We interpret these two folding events to be genetically related but slightly diachronous. The earlier folding phase with flat lying axial surfaces was likely generated during nappe thrusting and peak metamorphism of the Balsfjord Series. The subsequent open folding with inclined to steep axial surfaces is explained as a result of continued shearing and shortening of the weaker metapelitic Balsfjord Series against the more rigid gabbroic part of the LMC during the late stages of the Caledonian nappe thrusting.&#160;&#160;&#160;&#160;&#160;&#160;Observed thrust kinematics and penetrative retrogression at the bottom of the Nakkedal + Troms&#248; Nappe Complex suggest that its final exhumation took place during prograde metamorphism of the underlying Balsfjord Series. The ongoing dating of the prograde metamorphism in the Balsfjord series will provide important information about a possible continuity between the timing of peak metamorphism in the Nakkedal + Troms&#248; Nappe Complex, the Balsfjord series and the underlying RNC.

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Deformational behaviour of migmatites and problems of structural analysis in migmatite terrains

Geological Magazine ◽

10.1017/s001675680002923x ◽

1984 ◽

Vol 121 (4) ◽

pp. 339-345 ◽

Cited By ~ 31

Author(s):

Eileen McLellan

Keyword(s):

Structural Analysis ◽

Low Grade ◽

High Grade ◽

Metamorphic History ◽

Fold Type ◽

History Of ◽

Deformation Processes ◽

Geometrically Complex ◽

Fold Formation ◽

Very High

AbstractAn understanding of the response of migmatites to deformation is crucial to an interpretation of their structures, and in anatectic and intrusive migmatite terrains due consideration must be given to the modification of deformation processes imposed by melts. In partially molten systems containing more than 30% melt the classical theories of fold formation are inapplicable; the folds produced are of the ‘viscous fold’ type. Their geometry is unpredictable and may mimic structures due to refolding; this is particularly true at very high degrees of melting where flow of melt carrying rafts of solids begins. Failure to distinguish ‘viscous folds’ from the products of refolding will lead to errors in interpreting the structural and metamorphic history of an area, and to consequent misinterpretation of the true structural relations between geometrically complex high-grade and more regularly deformed low-grade areas.

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Thermal metamorphic history of Antarctic CV3 and CO3 chondrites inferred from the first and second order Raman peaks of polyaromatic organic carbon

American Mineralogist ◽

10.2138/am-2021-7507 ◽

2020 ◽

Keyword(s):

Organic Carbon ◽

Second Order ◽

Metamorphic History ◽

History Of

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Primary acquired melanosis (PAM) without atypia/WHO low-grade conjunctival melanocytic intraepithelial lesion over areas of oculodermal melanocytosis

BMJ Case Reports ◽

10.1136/bcr-2020-236741 ◽

2020 ◽

Vol 13 (10) ◽

pp. e236741

Author(s):

Bashar M Bata ◽

Sachin M Salvi ◽

Hardeep Singh Mudhar

Keyword(s):

Bulbar Conjunctiva ◽

Low Grade ◽

Primary Acquired Melanosis ◽

Conjunctival Biopsy ◽

History Of ◽

Intraepithelial Lesion ◽

The Relationship ◽

Oculodermal Melanocytosis ◽

Substantia Propria ◽

New Onset

An elderly white man with a history of left oculodermal melanocytosis presented with new onset brown pigmentation of the left bulbar and inferior tarsal conjunctiva. The bulbar conjunctival pigmentation was at the level of the conjunctival epithelium and was overlying areas of typical slate-grey scleral pigmentation characteristic of oculodermal melanocytosis. Both areas of new pigmentation were biopsied. The bulbar conjunctiva revealed primary acquired melanosis (PAM) without atypia with increased melanin production and the tarsal conjunctival biopsy showed PAM without atypia sine pigmentio overlying areas of substantia propria spindle-shaped heavily pigmented melanocytes of oculodermal melanocytosis. The case report examines the relationship between the epithelial and substantia propria melanocytes and correlates the findings with what is known about this association from the dermatopathology literature.

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Tectono-metamorphic history of the ophiolitic Lento unit (northern Corsica): evidences for the complexity of accretion-exhumation processes in a fossil subduction system

Geodinamica Acta ◽

10.3166/ga.20.99-118 ◽

2007 ◽

Vol 20 (1-2) ◽

pp. 99-118 ◽

Cited By ~ 12

Author(s):

Nicola Levi ◽

Alessandro Malasoma ◽

Michele Marroni ◽

Luca Pandolfi ◽

Matteo Paperini

Keyword(s):

Metamorphic History ◽

History Of ◽

Subduction System

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Solitary Paraganglioma of the Hypoglossal Nerve: Case Report

Neurosurgery ◽

10.1227/neu.0b013e31820a16b5 ◽

2011 ◽

Vol 68 (4) ◽

pp. E1170-E1174 ◽

Cited By ~ 5

Author(s):

Kazim Raza ◽

Chandrasekaran Kaliaperumal ◽

Michael Farrell ◽

John A. O'Dwyer ◽

Christopher Pidgeon

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Resonance ◽

Hypoglossal Nerve ◽

Jugular Foramen ◽

Low Grade ◽

Resonance Imaging ◽

Stereotactic Radiation ◽

Hypoglossal Canal ◽

Suboccipital Craniotomy ◽

History Of

Abstract BACKGROUND AND IMPORTANCE: We report the case history of solitary hypoglossal paraganglioma in a 64-year-old woman. The surgical difficulties encountered in the removal of this challenging tumor are discussed and as a literature review provided. CLINICAL PRESENTATION: A 64-year-old woman presented with a short history of dysphonia, occasional dysphagia, tinnitus, altered taste, and unilateral left-sided tongue wasting. On examination, there was left lower motor hypoglossal paralysis. Imaging showed a discrete enhancing lobulated mass, measuring 2 × 2 cm, in the region of the hypoglossal nerve extending into the hypoglossal canal suggestive of hypoglossal paraganglioma. A left dorsolateral suboccipital craniotomy was performed with the patient in the sitting position. The hypoglossal nerve appeared to be enlarged, and the jugular foramen was normal. Complete surgical debulking of the tumor was not attempted because of its vascular nature. The nerve was decompressed, and neuropathology confirmed a low-grade paraganglioma arising from the hypoglossal nerve. The patient was scheduled to receive stereotactic radiation for further management. CONCLUSION: When a case of solitary hypoglossal paraganglioma is encountered in clinical practice, the aim of management should be mainly focused on achieving a diagnosis and preserving the hypoglossal nerve function. If there is evidence of vascularity in the lesion noted on magnetic resonance imaging, a preoperative angiogram should be obtained with a view for embolization. We decompressed the hypoglossal canal and achieved good improvement in the patient's symptoms. We recommend stereotactic radiosurgery for remnant and small hypoglossal tumors and regular follow-up with magnetic resonance imaging scans.

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Pressure, temperature, and composition history of syntectonic fluids in a low-grade metamorphic terrane

Geology ◽

10.1130/g21143.1 ◽

2005 ◽

Vol 33 (5) ◽

pp. 421 ◽

Cited By ~ 13

Author(s):

Arthur Goldstein ◽

Bruce Selleck ◽

John W. Valley

Keyword(s):

Low Grade ◽

History Of ◽

Metamorphic Terrane ◽

Composition History

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Atypical Presentation of Atypical Teratoid Rhabdoid Tumor in a Child

Case Reports in Oncological Medicine ◽

10.1155/2013/815923 ◽

2013 ◽

Vol 2013 ◽

pp. 1-4 ◽

Cited By ~ 1

Author(s):

Y. T. Udaka ◽

K. Shayan ◽

N. A. Chuang ◽

J. R. Crawford

Keyword(s):

Rhabdoid Tumor ◽

Low Grade Glioma ◽

Low Grade ◽

Atypical Presentation ◽

Atypical Teratoid Rhabdoid Tumor ◽

Resonance Imaging ◽

Atypical Teratoid ◽

History Of ◽

Progressive Weight Loss ◽

Intracranial Neoplasm

Atypical Teratoid Rhabdoid Tumor (ATRT) is a rare malignant intracranial neoplasm more commonly diagnosed in young children. The authors report the case of an 11-year-old boy with a long standing history of slowly progressive weight loss, fatigue, and weakness over 1.5 years whose magnetic resonance imaging revealed a large heterogeneous enhancing dorsally exophytic lower brainstem mass. Examination revealed extreme cachexia, gaze-evoked nystagmus, dysphagia, dysarthria, bilateral dysmetria, and global weakness without ambulation. The protracted history and neuroimaging features were most suggestive of a low grade glioma. However, pathology revealed a hypercellular tumor with large hyperchromatic nucleoli and loss of INI-1 staining on immunohistochemistry consistent with a diagnosis of an ATRT. The child died shortly after surgery due to complications from his brainstem infiltrative disease. This case illustrates the diverse presentation of ATRT in childhood that can clinically and radiographically mimic that of low grade glioma.

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