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.

scholarly journals Early (3700 Ma) Archaean rocks of the Isua supracrustal belt and adjacent gneisses

1983 ◽  
Vol 112 ◽  
pp. 5-22
Author(s):  
A.P Nutman ◽  
D Bridgwater ◽  
E Dimroth ◽  
R.C.O Gill ◽  
M Rosing
Keyword(s):  
Amphibolite Facies ◽  
Iron Formation ◽  
Ultramafic Rocks ◽  
Banded Iron Formation ◽  
Sedimentary Structures ◽  
The North ◽  
Gneiss Complex ◽  
Supracrustal Belt ◽  
Silicate Rocks

A coherent stratigraphy is recognised in the highly deformed, amphibolite facies early Archaean Isua supracrustal belt. The supracrustal belt consists of layered rocks (in which sedimentary structures are locally preserved), ultramafic rocks and units of garbenschiefer (a massive Mg-Al rich, leucoamphibolite). The layered supracrustal rocks form two sequences, which are separated from each other tectonically. When folding is taken into account, these sequences are now less than 200 m thick. Sequence A forms most of the belt. In it there is a transition upwards from predominantly layered amphibolites with banded iron formation horizons to calc-silicate rocks, carbonates and layered felsic metasediments. Sequence B is restricted to the western edge of the eastern part of the supracrustal belt. It changes upwards from predominantly layered felsic metasediments to ferromagnesian mica schists. The supracrustal belt is regarded as a thin fragment from a thicker, more extensive volcanosedimentary pile. The early Archaean gneisses adjacent to the supracrustal belt consist of early multiphase tonalites which were first intruded by mafic dioritic dykes and then by granitic sheets. The granitic sheets were originaIly horizontal to gently inciined and form up to 40 per cent of the gneiss complex. Interdigitation of supracrustal rocks and gneisses in the Isukasia area is due to both the style of intrusion ofthe gneisses and to tectonic intercalation. Archaean basic dykes that cut the supracrustal belt and adjacent gneisses are ofseveral generations. Within and south of the supracrustal belt they are generally strongly deformed and have been recrystallised under amphibolite facies conditions; but in the north of the area they are generally better preserved. The dykes cut across several generations of structures in the supracrustal belt and the adjacent gneisses.

The early Archaean Nulliak (supracrustal) assemblage, northern Labrador

1989 ◽  
Vol 26 (10) ◽  
pp. 2159-2168 ◽  
Author(s):  
A. P. Nutman ◽  
B. J. Fryer ◽  
D. Bridgwater
Keyword(s):  
Water Environment ◽  
Volcanic Rocks ◽  
Granulite Facies ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Shallow Water Environment ◽  
Scale Down ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks ◽  
Chemical Sediments

The Nulliak (supracrustal) assemblage, the remains of ca. 3800 Ma succession of volcanic and sedimentary rocks, was broken up by intrusion of the protoliths of the early Archaean Uivak orthogneisses and then deformed, metamorphosed, and variably metasomatised several times under upper amphibolite to granulite facies conditions in the Archaean. Amphibolites of "komatiitic basalt" and tholeiitic chemical affinity are the most important Nulliak assemblage lithologies. High Al2O3 metagabbroic rocks and anorthosites also occur. Interlayered with the amphibolites are marbles, calc-silicate rocks, and banded iron formation, interpreted as chemical sediments that were probably laid down in a shallow-water environment. Also found are felsic rocks probably derived by reworking of penecontemporaneous felsic volcanic rocks, and garnet- and sillimanite-bearing paragneisses derived from pelites. All these lithologies are randomly interlayered on a scale down to 1 m or less. The occurrence of 3850 – 3900 Ma cores for zircons in the surrounding polyphase Uivak gneisses suggests there may be an ancient sialic component in them, which could possibly represent basement upon which at least part of the Nulliak assemblage formed.

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.

Occurrence and genetic implications of hyalophane in manganese-rich iron-formation, Cuyuna Iron Range, Minnesota, USA

1994 ◽  
Vol 58 (392) ◽  
pp. 387-399 ◽  
Author(s):  
Peter L. McSwiggen ◽  
G. B. Morey ◽  
Jane M. Cleland
Keyword(s):  
Depositional Environment ◽  
Iron Formation ◽  
East Central ◽  
Early Proterozoic ◽  
Iron Range ◽  
The North ◽  
History Of ◽  
Ferromanganese Deposits ◽  
Iron Formations ◽  
Chemical Sediments

AbstractThe recent discovery of hyalophane [(K,Ba)Al1−2Si3−2O8] on the North range segment of the Early Proterozoic Cuyuna Iron Range of east-central Minnesota has shed new light on the depositional environment of these rocks. This Ba-feldspar occurs in a 10 m thick interval within the main iron-formation and typically contains between 8 and 26 mol.% celsian (BaAl2Si2O8). Its occurrence in several textural settings suggests that barium was being deposited at various stages in the paragenetic history of the iron-formation. Some of the hyalophane grains occur as the cores of micronodules, which are structurally similar to oolites or oncolites, but mineralogically are very complex. The hyalophane also occurs as rims on core grains of diverse mineral composition and as discrete phases in late crosscutting veins.Hyalophane, like other Ba-silicates, has a very restricted paragenesis. They are associated typically either with sedimentary manganese and ferromanganese deposits, or with Cu-Pb-Zn-Ba deposits. The presence of hyalophane in the Early Proterozoic manganiferous iron ores of east-central Minnesota casts doubt on the historic interpretation of these deposits as typical Superior-type sedimentary iron-formations and instead supports the view that these deposits, at least in part, consist of chemical sediments from a hydrothermal fumarolic system. The suggested involvement of a hydrothermal system is also supported by the occurrence of aegirine within the hyalophane-rich layer, and the occurrence of tourmalinites and Sr-rich baryte veins elsewhere in the Cuyuna North range.

Rb–Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith Fold Belt, Quebec

1987 ◽  
Vol 24 (4) ◽  
pp. 813-825 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Fold Belt ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
The North ◽  
Basement Rocks ◽  
History Of ◽  
Wide Zone

The Churchill Province north of the Proterozoic Cape Smith volcanic fold belt of Quebec may be divided into two parts. The first is a broad antiform of migmatitic gneisses (Deception gneisses) extending north from the fold belt ~50 km to Sugluk Inlet. The second is a 20 km wide zone of high-grade metasedimentary rocks northwest of Sugluk Inlet. The Deception gneisses yield Rb–Sr isochron ages of 2600–2900 Ma and initial ratios of 0.701–0.703, showing that they are Archean basement to the Cape Smith Belt. The evidence that the basement rocks have been isoclinally refolded in the Proterozoic is clear at the contact with the fold belt. However, the gneisses also contain ubiquitous synclinal keels of metasiltstone with minor metapelite and marble that give isochron ages less than 2150 Ma. These ages, combined with low initial ratios of 0.7036, show that they are not part of the basement, as the average 87Sr/86Sr ratio for the basement rocks was about 0.718 at that time.The rocks west of Sugluk Inlet consist mainly of quartzo-feldspathic sediments, quartzites, para-amphibolites, marbles, and some pelite and iron formation. In contrast to the Proterozoic sediments in the Deception gneisses, these rocks yield dates of 3000–3200 Ma, with high initial ratios of 0.707–0.714. These initial ratios point to an age (or a provenance) much greater than that of the Archean Deception gneisses. The rocks of the Sugluk terrain are intruded by highly deformed sills of granitic rocks with ages of about 1830 Ma, demonstrating again the extent and severity of the Proterozoic overprint. The eastern margin of this possibly early Archean Sugluk block is a discontinuity in age, lithology, and geophysical character that could be a suture between two Archean cratons. It is not known if such a suturing event is of Archean age, or if it is related to the deformation of the Cape Smith Fold Belt.Models of evolution incorporating both the Cape Smith Belt and the Archean rocks to the north need to account for the internal structure of the fold belt, the continental affinity of many of the volcanic rocks, the continuity of basement around the eastern end of the belt, and the increase in metamorphism through the northern part of the belt into a broad area to the north. The Cape Smith volcanic rocks may have been extruded along a continental rift, parallel to a continental margin at Sugluk. Continental collison at Sugluk would have thrust the older and higher grade Sugluk rocks over the Deception gneisses, produced the broad Deception antiform, and displaced the Cape Smith rocks to the south in a series of north-dipping thrust slices.

History of Field Observations on Volcanic Rocks of Western Mexico, Pre-Columbian to Recent

2011 ◽  
Vol 30 (1) ◽  
pp. 106-134 ◽  
Author(s):  
Eric Swanson
Keyword(s):  
World War Ii ◽  
Volcanic Rocks ◽  
Mining Industry ◽  
Colonial Period ◽  
Field Observations ◽  
Stratigraphic Sequence ◽  
Spanish Colonial ◽  
Volcanic Origin ◽  
Western Mexico ◽  
History Of

By the time the first detailed reports on western Mexico's volcanic rocks had begun to appear in the 1970s, most of the earlier observations on these rocks and most knowledge of those who made these observations were all but forgotten. A review of previous field observations in this region shows, however, a long history of geologic discovery reflecting or even preceding developments elsewhere.Ethnological studies suggest that the Pre-Columbian inhabitants of the Sierra Madre Occidental (SMO) observed the characteristics of rock formations in their sierra homeland and understood something of the regional stratigraphic relationships. Late sixteenth and early seventeenth century explorers of the Spanish Colonial Period singled out volcanic rock known to them as piedra de malpaís for special recognition, and Padre Kino and his fellow explorers clearly recognized the volcanic origin of piedra de malpaís decades prior to similar observations in Europe. As the Spanish Colonial Period came to a close, Andrés Manuel del Río help organize a state-of-theart mining college in Mexico City where students were instructed in Werner's geognosy prior to their taking positions in Mexico's mining industry, most of it located in western Mexico's volcanic rocks.Although the first part of the tumultuous period between Mexico's revolutions of 1810 and 1910 saw few advances in geological knowledge, the reign of President Porfirio Díaz produced a geologic map of Mexico, the founding of the Instituto de Geología, and an ‘American invasion’ of geologists and mining engineers who locally gathered information on the nature of volcanic rocks of western Mexico. During the same period, Instituto geologist Ezequiel Ordóñez established the general stratigraphic sequence in the SMO, recognized the widespread occurrence of rhyolite there, and applied the petrographic microscope to the study of SMO volcanic rocks. The first identification of ignimbrites in the SMO came as a result of the World War II-era search for strategic minerals, and NASA's push to put a man on the Moon supported a series of student mapping projects producing the SMO's first geologic maps showing individual ignimbrite units and calderas.

Biological Fe oxidation controlled deposition of banded iron formation in the ca. 3770Ma Isua Supracrustal Belt (West Greenland)

2013 ◽  
Vol 363 ◽  
pp. 192-203 ◽  
Author(s):  
Andrew D. Czaja ◽  
Clark M. Johnson ◽  
Brian L. Beard ◽  
Eric E. Roden ◽  
Weiqiang Li ◽  
...  
Keyword(s):  
Iron Formation ◽  
Banded Iron Formation ◽  
West Greenland ◽  
Fe Oxidation ◽  
Supracrustal Belt ◽  
Controlled Deposition
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