scholarly journals Fold pattern analysis around Kanjamalai Salem district Tamilnadu

2020 ◽  
Vol 2 (2) ◽  
pp. 74-32
Author(s):  
Thirukumaran V ◽  
Suresh R
Keyword(s):  
Interference Pattern ◽  
High Amplitude ◽  
Iron Formation ◽  
Amplitude Analysis ◽  
Banded Iron Formation ◽  
Rock Types ◽  
Folded Structure ◽  
History Of ◽  
Granulite Terrain ◽  
The Hill

Kanjamalai one of the fascinating location in Southern Granulite Terrain (SGT) for studying Archaean geology and structures as the entire hill is made up of variety of rock types like two pyroxene granulite, amphibolites, quartzo - feldsapthic gneisses, banded iron formation, and intrusive rocks like dunite, peridotite and pegmatite and beautifully carved structures. The entire hill resembles a canoe shape with doubly plunging fold structure with E-W elongation. The entire hillock seems to sit pretty on mylonitised hornblende biotite gneisses which also have a common N70-95 degree trend and sub vertical dip with NE plunge which is in contradiction to centrally plunging lineations of the hill. The SW part of Kanjamalai near Chinasrirangapadi was displaying beautiful fold structures, with interference pattern out of which six domains were selected for detailed study and analysis. The multiple generation folded structure will have a clue in reconstructing the deformation history of this Kanjamalai. The observed f1, f2 and f3 folds show significant Type III interference pattern as that of Ramsay and 01 and 03 type folds of Bernhard Grasemann.   Wavelength –amplitude analysis was made to generalize and regroup the observed folds in to high amplitude, high wavelength or open folds, low wavelength and Mesoscopic folds. And visual harmonic analysis was made to analyse the symmetry of the folds and analyze the geometry, symmetry and harmony and genesis of the fold in terms of relative timing of the events.

scholarly journals The early Archaean to Proterozoic history of the Isukasia area, southern West Greenland

1986 ◽  
Vol 154 ◽  
pp. 1-80
Author(s):  
A.P Nutman
Keyword(s):  
Volcanic Rocks ◽  
Amphibolite Facies ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Stratigraphic Sequence ◽  
Supracrustal Belt ◽  
History Of ◽  
High Grade Metamorphism ◽  
Polyphase Metamorphism ◽  
Chemical Sediments

The c. 3800 Ma Isua supracrustal belt and associated smaller bodies of supracrustal rocks are intruded by >3600 Ma orthogneisses. A coherent stratigraphic sequence is recognised consisting of interlayered metabasic rocks, metasediments derived from volcanic rocks, chemical sediments, and metabasic and ultramafic intrusions. Despite repeated deformation and high-grade metamorphism sedimentary structures are locally preserved. The depositional environment was probably an immersed volcanic region remote from areas of significantly older crust. Conglomeratic structures in a metachert and banded iron formation unit suggest shoaling and shallow water conditions. Felsic sediments locally preserve evidence of deposition from turbidite flows. The Isua supracrustal rocks are regarded as thin fragments of a thicker, more extensive sequence. The orthogneisses that intrude the supracrustal rocks consist of 3750-3700 Ma multiphase tonalites (the grey gneisses) which were first intruded by the basic Inaluk dykes, then by abundant shallow-dipping swarms of c. 3600 Ma granite sheets (the white gneisses) and finally by c. 3400 Ma pegmatitic gneiss sheets. These early Archaean rocks were metamorphosed under amphibolite facies conditions and repeatedly deformed prior to intrusion of the Tarssartôq basic dykes in the mid Archaean. In the late Archaean (3100-2500 Ma) there was polyphase metamorphism up to amphibolite facies grade and two or more stages of deformation and local intrusion of granitic gneiss sheets and pegmatites. However, despite general strong deformation there is a large augen of low deformation preserved within the arc of the Isua supracrustal belt. During the Proterozoic there was intrusion of basic dykes, major faulting with associated recrystallisation under uppermost greenschist to lowermost amphibolite facies conditions, followed by heating and intrusion of acid dykes at c. 1600 Ma. No profitable mineralisations have been located.

Archean and Proterozoic tectono-magmatic activity along the southern margin of the Superior Province in northwestern Iowa, United States

1993 ◽  
Vol 30 (6) ◽  
pp. 1275-1285 ◽  
Author(s):  
Kenneth E. Windom ◽  
W. Randall Van Schmus ◽  
Karl E. Seifert ◽  
E. Timothy Wallin ◽  
Raymond R. Anderson
Keyword(s):  
United States ◽  
Iron Formation ◽  
Superior Province ◽  
Banded Iron Formation ◽  
Tectonic Zone ◽  
Minnesota River ◽  
Rock Types ◽  
Tectonic Environment ◽  
Juvenile Crust ◽  
Archean Greenstone Belt

A Precambrian igneous body of ultramafic and mafic rocks, named the Otter Creek layered igneous complex, occurs within the basement of northwestern Iowa, United States. It is marked by a circular magnetic anomaly, one of several that lie north and west of an inferred suture between the Archean Superior Province and Early Proterozoic juvenile crust. Sm–Nd whole-rock analyses for several rock types from the Otter Creek complex yield an isochron age of 2890 ± 90 Ma, with an εNd(t) of −0.9 ± 2.4. A block of older banded iron formation, itself intruded by lamprophyre dikes, is contained within the layered sequence. The iron formation – lamprophyre block has undergone high-temperature metamorphism followed by a retrograde event. A quartz monzodiorite gneiss, with a U–Pb age of 2523 ± 5 Ma, occurs near the layered complex, but the contact relations are not known. The layered series is overlain by Proterozoic keratophyre with a U–Pb age of 1782 ± 10 Ma. These felsic pyroclastic rocks are extremely depleted in K, Rb, Ba, and Cs. Our data are consistent with Archean greenstone-belt formation, including chemical sedimentation followed by mafic–ultramafic magmatism at approximately 2.9 Ga, followed by two later episodes of magmatism, one at approximately 2.5 Ga and the other at approximately 1.78 Ga. The Otter Creek complex is the first Archean greenstone reported south of the Great Lakes Tectonic Zone (GLTZ); its 2.9 Ga age is older than those reported for the granite–greenstone rocks north of the GLTZ. The southern portion of the Superior Province thus appears to have formed later, and in a different tectonic environment, than the high-grade gneisses of the Minnesota River Valley, but before the bulk of the granite–greenstone rocks exposed in northern Minnesota, Ontario, and eastern Manitoba.

scholarly journals O “QUADRO GEOGNÓSTICO DO BRASIL” DE WILHELM LUDWIG VON ESCHWEGE: BREVES COMENTÁRIOS À SUA VISÃO DA GEOLOGIA NO BRASIL

2013 ◽  
Author(s):  
Friedrich E. Renger
Keyword(s):  
Physical Geography ◽  
Iron Formation ◽  
Mica Schist ◽  
The Third ◽  
Rock Types ◽  
History Of Geology ◽  
Quadrilátero Ferrífero ◽  
History Of ◽  
First Time ◽  
East West

O trabalho apresenta uma resenha da obra “Geognostisches Gemälde von Brasilien und wahrscheinlichesMuttergestein der Diamanten “ de Wilhelm Ludwig von Eschwege por ocasião do sesquicentenário da suamorte em 1o de fevereiro de 2005. A obra foi publicada, em pequena tiragem, em 1822. Trata inicialmentedos grandes divisores de água: um de direção aproximada leste – oeste, separando a bacia do rio Amazonasdas dos rios Paraná e Paraguai, que Eschwege batiza de “Serra das Vertentes”, o outro divisor separa a baciado Rio São Francisco dos rios que correm diretamente ao Oceano Atlântico o qual chama de “Serra doEspinhaço”, incluindo nela a Serra da Mantiqueira. Em segundo lugar apresenta um esquema estratigráficobaseado nos modelos usados na Europa, como, por exemplo, aquele proposto em 1787 por AbrahamGottlieb Werner, professor da Academia de Minas de Freiberg na Alemanha. A Primeira FormaçãoPrimitiva é formada pelo embasamento cristalino, a Segunda Formação Primitiva corresponde às seqüênciassupracrustais dobradas (representadas pelos Supergrupos Rio das Velhas, Minas e Espinhaço), a Terceira oude Transição abrange essencialmente o atual Grupo Bambui e uma quarta subdivisão reúne depósitossuperficiais como aluviões e coberturas terciárias e quarternárias. Percebe-se que suas idéias a respeito dageologia do Brasil são fortemente influenciadas pela escola netunista de Werner. Descreve aindamacroscopicamente os principais tipos de rocha encontrados no Brasil, define os novos termos “itacolumito”e “itabirito” e introduz o termo “tapanhoacanga” na nomenclatura geológica, todos com suas localidadestipo.Tapanhoacanga, hoje reduzida para canga, é de origem indígena de tapanhu = escravo negro e acanga= cabeça (ou a = cabeça e canga = osso). A última parte do “Quadro geognóstico... “ trata da ocorrência dosdiamantes no Brasil e de sua possível rocha matriz, na sua opinião formados em concreções limoníticasoriginadas das rochas ferruginosas da Segunda Formação Primitiva.Palavras-chave: História da Geologia, Quadrilátero Ferrífero, Serra do Espinhaço, estratigrafia precambriana,itabirito, itacolumito, canga, diamantes ABSTRACT: ESCHWEGE’S “GEOGNOSTICAL SKETCH OF BRAZIL AND THE PROBABLE SOURCE ROCK OFDIAMONDS”: BRIEF COMMENTS ON HIS VISION OF BRAZILIAN GEOLOGY. This small brochure waspublished in 1822 by the German geologist Wilhem Ludwig von Eschwege (1777 – 1855) and is nowtranslated to Portuguese for the first time completely as a memorial of his passing away 150 years ago.Initially, Eschwege reports on the physical geography of Brazil and suggests the names “Serra das Vertentes”(Watershed Mountains) and “Serra do Espinhaço” (Backbone Ridge), running East – West the first and North– South the second, separating the great hydrographic basins in Brazil. A main chapter is dedicated to a veryfirst proposal of a stratigraphic scheme based on European models of the time and heavily influenced by A.G. Werner, the principal protagonist of the neptunism, which interpreted all rocks as being precipitated fromaqueous solutions. He distinguishes four stratigraphic divisions: the First Primitive Formation containinggranite, gneiss, and mica schist, corresponding in more modern terms to the crystalline basement; the SecondPrimitive Formation is formed by itacolumite (quartzite), itabirite (iron formation) and schist, representedby the Rio das Velhas, Minas, and Espinhaço supergroups. The third or Transitional Formation composed byslates, quartz schist, greywacke, and massive limestone corresponds to the Macaúbas and Bambui groups. Thefourth and uppermost formation encloses all superficial deposits, such as alluvial, river gravels and a peculiarferruginous conglomerate called by the native tapanhoacanga, which means Negro head. His argumentationis heavily influenced by neptunistic thinking. Eschwege still describes in great detail the principal rock types,as known at this time in Brazil and introduces the terms itacolumite, itabirite and (tapanhoa)canga into thegeological nomenclature. The second part is dedicated to the occurrence, distribution and origin of Braziliandiamonds. He considers that they are formed within any rock of his Second Primitive Formation, due to theoccasional founding of limonitic concretions with inclusions of diamonds.Keywords: History of geology, Quadril

Earth’s Middle Ages: What Came after the GOE

2017 ◽  
Author(s):  
Donald Eugene Canfield
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Middle Ages ◽  
Atmospheric Oxygen ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Dissolved Iron ◽  
Great Oxidation Event ◽  
Low Levels ◽  
Substantial Rise

This chapter considers the aftermath of the great oxidation event (GOE). It suggests that there was a substantial rise in oxygen defining the GOE, which may, in turn have led to the Lomagundi isotope excursion, which was associated with high rates of organic matter burial and perhaps even higher concentrations of oxygen. This excursion was soon followed by a crash in oxygen to very low levels and a return to banded iron formation deposition. When the massive amounts of organic carbon buried during the excursion were brought into the weathering environment, they would have represented a huge oxygen sink, drawing down levels of atmospheric oxygen. There appeared to be a veritable seesaw in oxygen concentrations, apparently triggered initially by the GOE. The GOE did not produce enough oxygen to oxygenate the oceans. Dissolved iron was removed from the oceans not by reaction with oxygen but rather by reaction with sulfide. Thus, the deep oceans remained anoxic and became rich in sulfide, instead of becoming well oxygenated.

A new volcanic province: evidence from glacial erratics in western North Greenland

2000 ◽  
pp. 35-41 ◽  
Author(s):  
Peter R. Dawes ◽  
Bjørn Thomassen ◽  
T.I. Hauge Andersson
Keyword(s):  
Volcanic Rocks ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Common Component ◽  
Volcanic Province ◽  
North West ◽  
North East ◽  
The North ◽  
Surficial Deposits ◽  
North Greenland

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Dawes, P. R., Thomassen, B., & Andersson, T. H. (2000). A new volcanic province: evidence from glacial erratics in western North Greenland. Geology of Greenland Survey Bulletin, 186, 35-41. https://doi.org/10.34194/ggub.v186.5213 _______________ Mapping and regional geological studies in northern Greenland were carried out during the project Kane Basin 1999 (see Dawes et al. 2000, this volume). During ore geological studies in Washington Land by one of us (B.T.), finds of erratics of banded iron formation (BIF) directed special attention to the till, glaciofluvial and fluvial sediments. This led to the discovery that in certain parts of Daugaard-Jensen Land and Washington Land volcanic rocks form a common component of the surficial deposits, with particularly colourful, red porphyries catching the eye. The presence of BIF is interesting but not altogether unexpected since BIF erratics have been reported from southern Hall Land just to the north-east (Kelly & Bennike 1992) and such rocks crop out in the Precambrian shield of North-West Greenland to the south (Fig. 1; Dawes 1991). On the other hand, the presence of volcanic erratics was unexpected and stimulated the work reported on here.

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