Potassium-argon age studies in West Greenland

1968 ◽  
Vol 5 (3) ◽  
pp. 683-691 ◽  
Author(s):  
Ole Larsen ◽  
Jørgen Møller
Keyword(s):  
Central Region ◽  
Shear Zones ◽  
Fold Belt ◽  
West Greenland ◽  
Basement Rocks ◽  
Igneous Activity ◽  
Basement Gneiss ◽  
Age Studies ◽  
North And South ◽  
Age Determinations

Geochronological units have been established in West Greenland partly on the basis of 34 new K–Ar age determinations, of which 32 were made on biotites.The central part of West Greenland belongs to a single basement gneiss unit more than 2700 m.y. old. Blocks of basement rocks are traversed by rectilinear shear zones tens of kilometers long and several kilometers wide. In these tectonic belts relic slices of supracrustal rocks occur within reworked basement gneisses. The latter give K–Ar ages of 2500–2700 m.y. Ages close to 1800 m.y. are found locally. North and south of the central region of old basement younger orogenic rocks are found: the Nagssutôqidian fold belt in northern West Greenland dated at approximately 1700 to 1750 m.y. and the Ketilidian fold belt in South Greenland of which the late- to post-kinematic granites are about 1500 to 1600 m.y. old. The Gardar non-orogenic igneous activity, 1000 to 1300 m.y., is found only in South Greenland.

scholarly journals Fission track dating of lower Tertiary rhyolitic glass rocks from Disko

1985 ◽  
Vol 125 ◽  
pp. 28-30
Author(s):  
K Hansen ◽  
A.K Pedersen
Keyword(s):  
Late Stage ◽  
Fission Track ◽  
Volcanic Rocks ◽  
Time Span ◽  
Fission Track Dating ◽  
West Greenland ◽  
Lower Tertiary ◽  
Igneous Activity ◽  
Geomagnetic Anomaly ◽  
Age Determinations

The Tertiary igneous activity in West Greenland has not been dated in detail. Sediments contemporaneous with, or slightly older than, the early volcanic rocks are assigned amiddle Paleocene age from palaeontological evidence (Henderson et al., 1981), and palaeomagnetic work by Athavale & Sharma (1975) indicates that the Vaigat Formation picrites and the lower 500 m or so of the overlying Maligât Formation (Hald & Pedersen, 1975) were erupted in the time span represented by geomagnetic anomaly 25 together with the long reversal period between anomalies 25 and 24. The age estimated for this period is 56 to 52 Ma (Butler & Coney, 1981). The late Stage lamprophyre magmatism on Ubekendt Ejland appears to be much younger, about 30 to 40 Ma (Parrott & Reynolds, 1975). No reliable radiometric age determinations have been published from the Disko-Nûgssuaq area.

scholarly journals Geology of the Ilímaussaq alkaline intrusion, South Greenland. Description of map and structure

1964 ◽  
Vol 39 ◽  
pp. 1-82
Author(s):  
J Ferguson
Keyword(s):  
Controlling Factor ◽  
Alkali Granite ◽  
Residual Liquid ◽  
Crystal Mush ◽  
Basement Rocks ◽  
Alkaline Intrusion ◽  
Igneous Activity ◽  
Differentiation Trend ◽  
Age Determinations

The Ilímaussaq Intrusion forms part of the alkaline province of South Greenland. It is thought that all the alkaline intrusions in South Greenland were emplaced in the basement rocks towards the dose of the Gardar period. Rb/Sr age determinations of the Kungnât and Ilímaussaq rocks give values of 1240 m.y. and 1086 m.y. respectively. The Ilímaussaq Intrusion intruded into the Julianehåb granite and the overlying sandstones, basalts and trachytes of the Gardar continental series. The trachytes probably represent an extrusive phase of the Ilímaussaq igneous activity. E.S.E. faulting, initiated in Ketilidian or early Kuanitic time, continued through the Sanerutian into the Gardar period and is thought to be the controlling factor of emplacement for the major alkaline centres. The earliest magma of the Ilímaussaq Intrusion had an augite syenitic composition. After emplacement this magma proceeded along an undersaturated differentiation trend. The in situ undersaturated differentiation was interrupted by an injection of alkali granite into the upper parts of the intrusion. Following this, in situ undersaturated differentiation was resumed, and, aided by volatiles, formed a magma of peralkaline composition (agpaitic). Crystallization took place from the roof downwards with simultaneous gravity accumulation on the floor of the intrusion. Finally, a residual liquid, rich in volatiles, was trapped between the downward crystallizing naujaite and the gravity accumulating kakortokites. As a result of faulting and/or slumping, the residual crystal mush was injected into the overlying brecciated rocks where it crystallized to form the fissile lujavrites. Minor syenitic intrusions in the complex probably mark the last phase of igneous activity.

scholarly journals Isotopic age determinations from South Greenland and their geological setting

1965 ◽  
Vol 53 ◽  
pp. 1-56
Author(s):  
D Bridgwater
Keyword(s):  
Biotite Granite ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Isotopic Age ◽  
Fold Belt ◽  
South West ◽  
Intrusive Rocks ◽  
Igneous Activity ◽  
Fold Belts ◽  
Age Determinations

A brief geological review of the area between Sermiligârssuk and Kap Farvel is given using the following five main divisions of the Precambrian of South Greenland: 1) pre-Ketilidian (? 2000-2700 m. y.) 2) Ketilidian (? 1700-2000 m. y.) 3) post-Ketilidian = Kuanitic (? 1650-1700 m. y.) 4) Sanerutian (? 1500-1650 m. y.) 5) Gardar (1020-?1500 m.y.). In the area described these divisions are characterized by: 1) gneisses, 2) geosynclinal sedimentation and lava extrusion, metamorphism and plutonism, 3) basic and intermediate dyking, 4) renewed plutonism, and emplacement of synplutonic basic, intermediate and granitic rocks, 5) post-orogenic sedimentation, lava extrusion and a predominantly alkali suite of intrusive rocks. Isotopic age determinations are available from the two youngest of the above divisions in South Greenland; dates for the three older divisions are suggested by comparison of the development of South Greenland with other fold belts together with sparse data from elsewhere in Greenland. It is suggested that the pre-Ketilidian gneisses represent the remnant of an old fold belt formed approximately 2400-2700 m. y. ago which has been reactivated during the Ketilidian and Sanerutian plutonic episodes in South Greenland. It is further suggested that the Ketilidian, post-Ketilidian and Sanerutian episodes are phases in the evolution of one fold belt which started at approximately 2000 m. y. ago and represents the beginning of the Svecofennid chelogenic cycle in South Greenland. The Gardar magmatism is regarded as a typical post-orogenic alkali suite and it is thought that the Gardar activity at about 1200 m. y. may represent compensatory tensional conditions on the margins of the developing Grenville fold belt which probably passed south of Greenland. Eight K/Ar age determinations (Geochron Laboratories) give the following results: Sanerutian hypersthene gabbro, 1645 m. y. (biotite) and 1700 m. y. (augite); Sanerutian granite, 1620 m. y. (biotite) ; early Gardar dolerite, 1435 m. y. (augite); Gardar syenite, 1128 m. y. (biotite) and 1355 m. y. (augite); inclusion of anorthosite fragment in a Gardar dyke, 1025 m. y. (biotite) and 1075 m. y. (augite). Four Rb/Sr age determinations (Moorbath) give the following results: Ketilidian pegmatite affected by Sanerutian metamorphism, 1630 m. y; Sanerutian granite, 1615 m. y.; Sanerutian granite probably affected by Gardar event, 1220 m. y.; Gardar biotite granite, 1150 m. y. Results from other areas in Greenland are discussed and it is suggested that a large part of the south-west coastal strip is pre-Ketilidian in age and that the Nagssugtoqidian fold belt was formed at approximately the same time as the Ketilidian-Sanerutian fold belt in South Greenland, that is at the beginning of the Svecofennid chelogenic cycle. It is suggested that the main episodes described from South Greenland correspond to events in the Canadian shield as follows: pre-Ketilidian plutonism = Kenoran; Ketilidian-Sanerutian and Nagssugtoqidian = Hudsonian; Gardar = post-Hudsonian, pre-Grenville igneous activity. Tectono-igneous cycles are used in conjunction with basic dykes and age determinations as a method of dividing the Precambrian.

The Laurentia – West Greenland connection at 1.9 Ga: New insights from the Rinkian fold belt

2017 ◽  
Vol 51 ◽  
pp. 289-309 ◽  
Author(s):  
Mary Sanborn-Barrie ◽  
Kristine Thrane ◽  
Natasha Wodicka ◽  
Nicole Rayner
Keyword(s):  
Fold Belt ◽  
West Greenland

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

scholarly journals New hornblende and muscovite 40Ar/39Ar cooling ages in the central Rinkian fold belt, West Greenland

2006 ◽  
Vol 11 ◽  
pp. 115-124 ◽  
Author(s):  
Ann-Sofie Sidgren ◽  
Laurence Page ◽  
Adam A. Garde
Keyword(s):  
Metamorphic Grade ◽  
Fold Belt ◽  
The South ◽  
Igneous Complex ◽  
West Greenland ◽  
Structural History

The Palaeoproterozoic Rinkian fold belt in West Greenland consists of reworked Archaean basement, mainly orthogneiss, and the unconformably overlying Palaeoproterozoic Karrat Group. Both parts were intensely deformed and metamorphosed at around 1.87 Ga, at which time the crustal anatectic Prøven igneous complex was emplaced into the northern part of the belt. Seven new hornblende and muscovite 40Ar/39Ar cooling ages are presented from the central–northern parts of the Rinkian fold belt. Four 40Ar/39Ar hornblende ages ranging from 1795 ± 3 to 1782 ± 3 Ma were obtained from amphibolite and hornblendite enclaves in the Archaean orthogneiss, and two from relict dyke fragments in the latter that may be of Palaeoproterozoic age. Three 40Ar/39Ar muscovite ages of 1681 ± 6 Ma, 1686 ± 3 Ma and 1676 ± 3 Ma were obtained from samples of Karrat Group metagreywacke, andalusite schist and metasiltstone. The new 40Ar/39Ar ages, from hornblende and muscovite respectively, are very uniform and probably unrelated to local metamorphic grade and structural history, and are interpreted as regional late orogenic cooling ages. The new hornblende ages are significantly older than those previously obtained from the central and northern parts of the adjacent Nagssugtoqidian orogen to the south, and point to different uplift histories, which may suggest that the orogeny was not synchronous in the two regions.

scholarly journals Mapping in the Fiskefjord area, southern West Greenland

1982 ◽  
Vol 110 ◽  
pp. 55-57
Author(s):  
A.A Garde ◽  
V.R McGregor
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Isotopic Age ◽  
Supracrustal Rock ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Geological Work ◽  
Age Determinations

Previous geological work on the 1:100000 map sheet 64 V.l N (fig. 15) includes published maps of smaller areas by Berthelsen (1960, 1962) and Lauerma (1964), mapping by Kryolitselskabet Øresund A/S (Bridgwater et al., 1976) and mapping by GGU geologists for the 1:500000 map sheet Frederikshåb Isblink - Søndre Strømfjord (Allaart et al., 1977, 1978). The Amltsoq and Niik gneisses and Malene supracrustal rock units south and east of Godthåbsfjord have not so far been correlated with rocks in the Fiskefjord area. Godthåbsfjord separates the granulite facies gneisses in Nordlandet from amphibolite facies Nûk gneisses on Sadelø and Bjørneøen; the granulite facies metamorphism occurred at about 2850 m.y. (Black et al., 1973), while no published isotopic age determinations from the Fiskefjord area itself are available.

scholarly journals Outline of the Nagssugtoqidian mobile belt of East Greenland

1979 ◽  
Vol 89 ◽  
pp. 9-18
Author(s):  
D Bridgwater ◽  
J.S Myers
Keyword(s):  
Shear Zones ◽  
Granulite Facies ◽  
Tectonic Activity ◽  
Mobile Belt ◽  
East Greenland ◽  
The North ◽  
Marginal Areas ◽  
High Level ◽  
North And South ◽  
Wide Zone

The Nagssugtoqidian mobile belt is a 240 km wide zone of deformation and plutonic activity which cuts across the Archaean craton of East Greenland. The belt was established 2600 m.y. ago by the formation of vertical E-W shear zones and the syntectonic intrusion of basic dykes. Tectonic activity along the E-W shear zones was followed by the emplacement of tonalitic intrusions, the Blokken gneisses, 2350 m.y. ago in the central parts of the mobile belt. The emplacement of the Blokken gneisses was accompanied and followed by further emplacement of basic dykes. These are synplutonic in the centre of the mobile belt but are emplaced into more rigid crust in the marginal areas of the belt and in the Archaean craton to the north and south. During a second major tectonic and thermal episode circa 1900 m.y. ago, the region was deformed by thrusting from the north. In the southem part of the mobile belt the earlier steep shear zones are cut by shear zones dipping gently northwards in which rocks are downgraded to greenschist facies. The grade of metamorphism increases northwards and shear zones are replaced by open folds with axial surfaces which dip gently northwards. The increasing ductility in the centre of and northem part of the belt is associated with the intrusion of charnockitic plutons and their granulite facies aureoles. Regional uplift occurred before the intrusion of high level post-tectonic plutons of diorite and granite 1550 m.y. ago.

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.

scholarly journals Attenuation of Coda Waves in the Central Region of the Gulf of California, México

2017 ◽  
Vol 56 (2) ◽  
Author(s):  
Héctor E. Rodríguez-Lozoya ◽  
Tonatiuh Domínguez R. ◽  
Luis Quintanar Robles ◽  
Armando Aguilar Meléndez ◽  
Héctor E. Rodríguez-Leyva ◽  
...  
Keyword(s):  
Central Region ◽  
Gulf Of California ◽  
Single Scattering ◽  
Coda Waves ◽  
Tectonic Activity ◽  
S Wave ◽  
A Value ◽  
Wave Travel ◽  
Coda Attenuation ◽  
North And South

Coda waves were analyzed from events recorded by NARS seismic network deployed along both margins of the Gulf of California, Mexico, to estimate coda attenuation Qc. Sato’s (1977) single scattering model was used for a coda window of 20 to 25 s beginning at twice the S-wave travel time. Events recorded from 2003 to 2007 located in the central region of the Gulf of California were analyzed. Source-to-receiver distances are between 40 and 500 km. Assuming a power law of the form QC (f) = QO f a, QC values were averaged and a value of QO = 83±3 and a frequency-dependence α value of 1.06±0.03 in the frequency range from 1 to 7 Hz was obtained. QO value and the high frequency dependency agree with the values of other regions characterized by a high tectonic activity. Based on source-station distribution two subregions (north and south) were defined. QC values were calculated and correlated with tectonics and morphology of each area. The observed higher attenuation in the south region can be attributed to the fact that south region is more fractured since the greater earthquakes occur in central to south Gulf of California and the oceanic crust is reported to be thinner in the southern region.

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