Geologie et pétrographie des roches sédimentaires et volcaniques kétilidiennes (Protérozoique inférieur) de la baignoire d'Arsuk, Groenland méridional

The Arsuk ø area is situated along the north-western border of the Early Proterozoic (> 1750 m.y.) mobile belt of South Greenland. Around Arsuk ø reactivated Archaean (> 2500 m.y.) basement is represented by gneiss, amphibolites and migmatites belonging to several lithological series. In the Arsuk basin Early Proterozoic (Ketilidian) supracrustals consist of a group of sedimentary rocks which is overlain by a group of volcanic rocks. The sedimentary Ikerasârssuk Group, with a thickness between 1000 and 1500 m, consists of semi-pelites and pelites with several zones of pyrite-bearing graphite schists and dolomitic limestones. There are also numerous sills of basic rocks which have the same age as the overlying group of volcanic rocks. In some localities the basal member of the group consists of feldspathic quartzites. The volcanic Arsuk Group, the upper part of which is eroded away, has a measured thickness of 4200 m. It consists of pillow lavas, basic massive lavas, volcanic breccias, lapillis and tuffites. There are also some ultrabasic rocks and thin horizons of pyrite-bearing graphite schists with chert. These supracrustal rocks underwent intense deformation at the close of the Early Proterozoic. Three phases can be recognised. The first phase produced N-S to NNE-SSW recumbent folds and the regional schistosity. Refolding during the second phase resulted in folds with E-W to ESE-trending axial planes and a strain slip cleavage. The last phase produced N-S trending structures. The grade of metamorphism during the first phase of deformation corresponds to greenschist facies. In the supracrustals close to the basement recrystallisation in amphibolite facies took place between the first and third phases of folding. This shows the existence of a gradient towards still higher grade metamorphic conditions in the underlying Archaean basement undergoing thorough reconstitution at the end of the Early Proterozoic. As a result of the deformation the stratigraphical unconformity between the Early Proterozoic (Ketilidian) supracrustals and the Archaean basement has been destroyed. During the Gardar period (Middle Proterozoic: > 950 m.y.) and again during the Mesozoic faulting and dyking occurred.

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Episodic Early Proterozoic granitoid plutonism in the Makkovik Province, Labrador: U–Pb geochronological data and geological implications

Canadian Journal of Earth Sciences ◽

10.1139/e92-094 ◽

1992 ◽

Vol 29 (6) ◽

pp. 1166-1179 ◽

Cited By ~ 35

Author(s):

A. Kerr ◽

T. E. Krogh ◽

F. Corfu ◽

U. Schärer ◽

S. S. Gandhi ◽

...

Keyword(s):

Volcanic Rocks ◽

Mobile Belt ◽

Trace Element Geochemistry ◽

Element Geochemistry ◽

Early Proterozoic ◽

Rock Types ◽

Layered Gabbro ◽

High Level ◽

Orogenic Belts ◽

Middle Proterozoic

Episodic granitoid plutonism in the Early Proterozoic Makkovik Province of the easternmost Canadian Shield is revealed by high-precision U–Pb zircon studies of a range of intrusive rock types. The oldest granites yield ages of 1893 ± 2 and 1891 ± 5 Ma and document a previously unrecognized event that may correlate with an early migmatization of reworked Archean basement. These dates also constrain early structural reworking of the basement, the earliest deformational event grouped as part of the Makkovikian orogeny. Four samples have essentially identical zircon ages of 1801 ± 2, 1802 ± 2, [Formula: see text], and 1825–1799 Ma, and a fifth is slightly older, at [Formula: see text]. These ages suggest correlation with local volcanic sequences, dated in part at 1807 ± 4 Ma. The plutonic suites include both syn- and posttectonic granitoid assemblages and define the main magmatic pulse associated with the Makkovikian orogeny and constrain its final deformational episode. Distinctive, fluorine-enriched "A-type" granites yield an age of 1719 ± 3 Ma and represent a previously unrecognized late postorogenic to anorogenic magmatism of regional significance. Two layered, gabbro–diorite–monzonite–syenite suites yield identical zircon ages of 1649 ± 1 and 1649 ± 3 Ma. A regionally extensive granodioritic unit gives an age of 1647 ± 2 Ma, and a high-level alaskitic granite is dated imprecisely at 1640–1650 Ma. These plutonic suites correlate with volcanic rocks previously dated at 1649 ± 1 Ma.These data show that the plutonic evolution of the Makkovik Province is significantly more complex than previously supposed. The clustering of ages suggests episodic, rather than continuous, magmatism. The different age groupings can, to some extent, be correlated with compositional associations defined by major- and trace-element geochemistry. The new data also raise questions about the regional configuration of Early and Middle Proterozoic orogenic belts in Labrador. Previous correlations between the Makkovik Province, the Ketilidian Mobile Belt of Greenland, and the Svecofennian and Trans-Scandinavian belts of Sweden are supported and expanded by these new results.

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Reproductive health among Venezuelan migrant women at the north western border of Brazil: A qualitative study

Journal of Migration and Health ◽

10.1016/j.jmh.2021.100060 ◽

2021 ◽

pp. 100060

Author(s):

Maria Y. Makuch ◽

Maria Jose D. Osis ◽

Cinthia Brasil ◽

Helder S.F. de Amorim ◽

Luis Bahamondes

Keyword(s):

Reproductive Health ◽

Qualitative Study ◽

Migrant Women ◽

The North ◽

Western Border ◽

North Western

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Three generations of stars: a possible case of triggered star formation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1543 ◽

2020 ◽

Vol 496 (1) ◽

pp. 870-874

Author(s):

M B Areal ◽

A Buccino ◽

S Paron ◽

C Fariña ◽

M E Ortega

Keyword(s):

Star Formation ◽

Young Stellar Objects ◽

H Ii Regions ◽

Stellar Objects ◽

Three Generations ◽

The North ◽

Western Border ◽

H Ii Region ◽

New Generation ◽

North Western

ABSTRACT Evidence for triggered star formation linking three generations of stars is difficult to assemble, as it requires convincingly associating evolved massive stars with H ii regions that, in turn, would need to present signs of active star formation. We present observational evidence for triggered star formation relating three generations of stars in the neighbourhood of the star LS II +26 8. We carried out new spectroscopic observations of LS II +26 8, revealing that it is a B0 III-type star. We note that LS II +26 8 is located exactly at the geometric centre of a semi-shell-like H ii region complex. The most conspicuous component of this complex is the H ii region Sh2-90, which is probably triggering a new generation of stars. The distances to LS II +26 8 and to Sh2-90 are in agreement (between 2.6 and 3 kpc). Analysis of the interstellar medium on a larger spatial scale shows that the H ii region complex lies on the north-western border of an extended H2 shell. The radius of this molecular shell is about 13 pc, which is in agreement with what an O9 V star (the probable initial spectral type of LS II +26 8 as inferred from evolutive tracks) can generate through its winds in the molecular environment. In conclusion, the spatial and temporal correspondences derived in our analysis enable us to propose a probable triggered star formation scenario initiated by the evolved massive star LS II +26 8 during its main-sequence stage, followed by stars exciting the H ii region complex formed in the molecular shell, and culminating in the birth of young stellar objects around Sh2-90.

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Petrogenesis and tectonic implications of Early Cretaceous volcanic rocks from the Shanghulin Basin within the north‐western Great Xing'an Range, NE China: Constraints from geochronology and geochemistry

Geological Journal ◽

10.1002/gj.3583 ◽

2019 ◽

Vol 55 (5) ◽

pp. 3476-3496 ◽

Cited By ~ 1

Author(s):

An‐Qi Mao ◽

De‐You Sun ◽

Dong‐Guang Yang ◽

Zong‐Yuan Tang ◽

Han Zheng

Keyword(s):

Early Cretaceous ◽

Volcanic Rocks ◽

Ne China ◽

The North ◽

Tectonic Implications ◽

Great Xing’An Range ◽

North Western

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The geology of the north-eastern corner of Greenland - photogeological studies and 1993 field work

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v161.8240 ◽

1994 ◽

Vol 161 ◽

pp. 21-33

Author(s):

H.F Jepsen ◽

J.C Escher ◽

J.D Friderichsen ◽

A.K Higgins

Keyword(s):

Field Work ◽

Tectonic Activity ◽

Mobile Belt ◽

North East ◽

The North ◽

Upper Proterozoic ◽

North Eastern ◽

Field Season ◽

Upper Boundary ◽

Middle Proterozoic

Late Archaean and Early Proterozoic crust-forming events in North-East and eastern North Greenland were succeeded by Middle Proterozoic sedimentation and volcanic activity; Late Proterozoic through Tertiary sedimentation was interrupted by several periods of tectonic activity, including the Caledonian orogeny in East Greenland and the Mesozoic deformation of the Wandel Hav mobile belt. Photogeological studies helped pinpoint areas of special interest which were investigated during the short 1993 field season. Insights gained during field work include: the nature of the crystalline basement terrain in the Caledonian fold belt, redefinition of the upper boundary of the Upper Proterozoic Rivieradal sandstones, revision of Caledonian nappe terminology, and the northern extension of the Caledonian Storstrømmen shear zone.

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Paleomagnetism of the Lawrenceton Formation volcanic rocks, Silurian Botwood Group, Change Islands, Newfoundland

Canadian Journal of Earth Sciences ◽

10.1139/e89-024 ◽

1989 ◽

Vol 26 (2) ◽

pp. 296-304 ◽

Cited By ~ 10

Author(s):

Julie E. Gales ◽

Ben A. van der Pluijm ◽

Rob Van der Voo

Keyword(s):

North American ◽

Volcanic Rocks ◽

Mobile Belt ◽

Structural Mapping ◽

Polar Wander ◽

The North ◽

Apparent Polar Wander Path ◽

Paleomagnetic Study ◽

North American Craton

Paleomagnetic sampling of the Lawrenceton Formation of the Silurian Botwood Group in northeastern Newfoundland was combined with detailed structural mapping of the area in order to determine the deformation history and make adequate structural corrections to the paleomagnetic data.Structural analysis indicates that the Lawrenceton Formation experienced at least two folding events: (i) a regional northeast–southwest-trending, Siluro-Devonian folding episode that produced a well-developed axial-plane cleavage; and (ii) an episode of local north-trending folding. Bedding – regional cleavage relationships indicate that the latter event is older than the regional folding.Thermal demagnetization of the Lawrenceton Formation yielded univectorial southerly and shallow directions (in situ). A fold test on an early mesoscale fold indicates that the magnetization of the Botwood postdates this folding event. However, our results, combined with an earlier paleomagnetic study of nearby Lawrenceton Formation rocks, demonstrate that the magnetization predates the regional folding. Therefore, we conclude that the magnetization occurred subsequent to the local folding but prior to the period of regional folding.While a tectonic origin for local folding cannot be entirely excluded, the subaerial nature of these volcanics, the isolated occurrence of these folds, and the absence of similar north-trending folds in other areas of eastern Notre Dame Bay suggest a syndepositional origin. Consequently, the magnetization may be nearly primary. Our study yields a characteristic direction of D = 175°, I = +43°, with a paleopole (16°N, 131 °E) that plots near the mid-Silurian track of the North American apparent polar wander path. This result is consistent with an early origin for the magnetization and supports the notion that the Central Mobile Belt of Newfoundland was adjacent to the North American craton, in its present-day position, since the Silurian.

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Aeolian Environments

The Physical Geography of Western Europe ◽

10.1093/oso/9780199277759.003.0017 ◽

2005 ◽

Author(s):

Eduard Koster

Keyword(s):

Sand Dunes ◽

Ural Mountain ◽

Aeolian Processes ◽

The North ◽

Aeolian Deposits ◽

The World ◽

Western Border ◽

Late Weichselian ◽

The Baltic ◽

North Western

The literature on aeolian processes and on aeolian morphological and sedimentological features has shown a dramatic increase during the last decade. A variety of textbooks, extensive reviews, and special issues of journal volumes devoted to aeolian research have been published (Nordstrom et al. 1990; Pye and Tsoar 1990; Kozarski 1991; Pye 1993; Pye and Lancaster 1993; Cooke et al. 1993; Lancaster 1995; Tchakerian 1995; Livingstone and Warren 1996; Goudie et al. 1999). However, not surprisingly the majority of these studies discuss aeolian processes and phenomena in the extensive warm arid regions of the world. The results of aeolian research in the less extensive, but still impressive, cold arid environments of the world are only available in a diversity of articles. At best they are only briefly mentioned in textbooks on aeolian geomorphology (Koster 1988, 1995; McKenna-Neuman 1993). Likewise, the literature with respect to wind-driven deposits in western Europe is scattered and not easily accessible. The aeolian geological record for Europe, as reflected in the ‘European sand belt’ in the north-western and central European Lowlands, which extends from Britain to the Polish–Russian border, is known in great detail (Koster 1988; van Geel et al. 1989; Böse 1991). Zeeberg (1998) showed that extensive aeolian deposits progress with two separate arms into the Baltic Region, and into Belorussia and northernmost Ukraine. Recently, Mangerud et al. (1999) concluded that the sand belt extends even to the Pechora lowlands close to the north-western border of the Ural mountain range in Russia. Sand dunes and cover sands are widespread and well developed in this easternmost extension of the European sand belt. The northerly edges of this sand belt more or less coincide with the maximal position of the Late Weichselian (Devensian, Vistulian) ice sheet, while the southern edges grade into coverloams or sandy loess and loess (Mücher 1986; Siebertz 1988; Antoine et al. 1999). However, along these southern edges the dune fields and sand sheets regionally are derived from different sources, such as the sands of the Keuper Formation or the floodplains of the Rhine and Main rivers.

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