Late Precambrian Rocks of Eastern Avalon Peninsula, Newfoundland–A Volcanic Island Complex: Reply

1972 ◽  
Vol 9 (8) ◽  
pp. 1059-1060 ◽  
Author(s):  
C. J. Hughes ◽  
W. D. Brückner
Keyword(s):  
Volcanic Island ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Avalon Peninsula

Late Precambrian Rocks of Eastern Avalon Peninsula, Newfoundland — A Volcanic Island Complex

1971 ◽  
Vol 8 (8) ◽  
pp. 899-915 ◽  
Author(s):  
C. J. Hughes ◽  
W. D. Brückner
Keyword(s):  
Volcanic Rocks ◽  
Main Group ◽  
Volcanic Island ◽  
Precambrian Rocks ◽  
Crustal Movements ◽  
Late Precambrian ◽  
Isostatic Adjustment ◽  
Avalon Peninsula ◽  
Vertical Crustal Movements

A model of island volcanism is presented in which rocks are referred to (1) a "syn-volcanic" constructional phase represented by rocks of four penecontemporaneous facies—vent, alluvial, marine, and plutonic—whose interrelationships are discussed and (2) a "post-volcanic" destructional phase of erosion and sedimentation accompanied by isostatic adjustment resulting in the spreading of an apron of volcanic sediments around a slowly rising and eroding island core.The late Precambrian rocks of the eastern part of the Avalon Peninsula, southeasternmost Newfoundland, are shown to fit this model rather closely, both petrographically and in their distribution and field relationships. The Harbour Main Group of volcanic rocks, the Conception Group of marine volcanic sediments and tuffs, and the Holyrood Plutonic Series, dated at 574 ± 11 m.y., were all formed during the syn-volcanic constructional phase. Their apparently conflicting age relationships can be reconciled to the view that they are penecontemporaneous facies. The Cabot and Hodgewater Groups of marine and alluvial volcanic sediments were formed during the post-volcanic destructional phase. Apart from vertical crustal movements, only minor diastrophic deformation appears to have occurred during these two phases.This model of volcanic island environment may help in interpreting the geology of several other belts in eastern and central Newfoundland comprising late Precambrian and Paleozoic volcanic rocks and sediments.

Pre-Katangan geochronology of Zambia and adjacent parts of Central Africa

1968 ◽  
Vol 5 (3) ◽  
pp. 621-628 ◽  
Author(s):  
J. R. Vail ◽  
N. J. Snelling ◽  
D. C. Rex
Keyword(s):  
Lake Tanganyika ◽  
Central Africa ◽  
New Age ◽  
Orogenic Belt ◽  
Eastern Africa ◽  
Sedimentary Sequence ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Orogenic Belts ◽  
Age Determinations

The significance of new age determinations on pre-Katangan (Late Precambrian) rocks and minerals from Zambia and adjacent parts of Tanzania and Rhodesia is discussed. In northwestern Rhodesia, the Lomagundi-Piriwiri sediments were deposited between 2500 and 2000 m.y. ago and were folded along meridional trends at circa 1940 m.y. A later episode of folding and metamorphism along similar trends occurred about 1700 m.y. ago, but only affected the western part of the sedimentary sequence (the Piriwiri Series). This latter date is comparable to that which appears to characterize the Tumbide trend, a N- to NE-trending fold system, in Zambia.In Zambia the Tumbide trend is the oldest tectonic episode preserved in the basement and is found only in isolated blocks and cores into which later tectonisms have not penetrated. The dominant pre-Katangan tectonism is represented by the NE to ENE Irumide trend. Such tectonic trends are particularly well developed in the Irumide Orogenic Belt of northern Zambia and adjacent Tanzania. Age determinations set a younger limit of circa 900 m.y. to this trend and the existence of an Irumide Cycle between about 1600 and 900 m.y. is suggested. The possibility that the relatively unmetamorphosed sediments of the Upper Plateau Series and Abercorn Sandstones at the southern end of Lake Tanganyika, the Mafingi Series of northern Malawi, and the Konse Series of Tanzania, represent near-contemporaneous platform deposition associated with the Irumide belt is considered.From this and other recent studies the distribution of orogenic belts in central and eastern Africa can be revised and a number of features of their pattern and inter-relationships noted.

The late Precambrian mafic dikes of the southern Tobacco Root Mountains, Montana: geochemistry, Rb–Sr geochronology and relationship to belt tectonics

1978 ◽  
Vol 15 (4) ◽  
pp. 467-479 ◽  
Author(s):  
Joseph L. Wooden ◽  
Charles J. Vitaliano ◽  
Steven W. Koehler ◽  
Paul C. Ragland
Keyword(s):  
Mantle Material ◽  
Mountain Area ◽  
Precambrian Rocks ◽  
Southwestern Montana ◽  
Late Precambrian ◽  
High K ◽  
Major Period ◽  
Tobacco Root Mountains ◽  
Low K ◽  
East West

During late Precambrian time three sets of mafic dikes were emplaced in southwestern Montana south of the east–west Helena embayment of the Belt Basin. The oldest dikes, intruded approximately 1455 Ma ago into both the southern Tobacco Root Mountains and the adjoining Ruby Range, are low K tholeiite in composition. The two other sets of dikes were intruded at approximately the same time, about 1120–1130 Ma ago. Both are high K quartz normative types: one is strongly enriched in Fe and is most similar to ferrobasalt or ferrogabbro in composition, the other is low in iron and differentiated along strong alkali and silica enrichment trends. The 1455 Ma old dikes and the iron-enriched 1120 Ma dikes have initial Sr ratios in the range 0.7020–0.7030 that indicate probable derivation from mantle material that has maintained a low Rb–Sr ratio (0.024) for much of the Earth's history. This mantle source is much lower in Rb–Sr ratio than that proposed for the source of dikes in the Beartooth–Bighorn Mountain area to the southeast. The iron-poor 1130 Ma old magma has an initial ratio of 0.709, which suggests contamination by crustal Sr.A strong correlation appears to exist between the timing of mafic intrusive events in the older Precambrian rocks to the south of the Belt Basin and tectonic-intrusive events within the basin. Intrusive events are recorded at 1455–1430 Ma ago both inside and outside the basin. A 1330 Ma old mafic intrusive event in the Beartooth Mountains is associated with a period of metamorphism and (or) a period of deposition in the basin. The 1120–1130 Ma old dikes are correlated with mafic flows and sills and another major period of deposition within the Belt Basin.

On the position of the Variscan front in southern New Brunswick and its relation to Precambrian basement

1976 ◽  
Vol 13 (1) ◽  
pp. 194-196 ◽  
Author(s):  
N. Rast ◽  
K. L. Currie
Keyword(s):  
New Brunswick ◽  
Precambrian Basement ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Mylonite Zone

The Variscan front is marked by a zone of cataclasis that generally follows an older and larger mylonite zone, but locally cuts across relatively undeformed Precambrian rocks. The older mylonite zone probably developed in Late Precambrian (Avalonian) time. Correlative Precambrian rocks extend across both the Variscan front, and the Bellisle fault to the northwest.

Volcanogenic cherts in the late Precambrian Conception Group, Avalon Peninsula, Newfoundland

1976 ◽  
Vol 13 (4) ◽  
pp. 512-519 ◽  
Author(s):  
Charles J. Hughes
Keyword(s):  
Sea Water ◽  
Chemical Data ◽  
Pyroclastic Material ◽  
Late Precambrian ◽  
Avalon Peninsula ◽  
Bedded Rocks

Bedded rocks of cherty appearance are locally abundant and conspicuous in the late Precambrian Conception Group of the Avalon Peninsula, southeast Newfoundland. Structural, petrographical, and chemical data from a well exposed locality near St. John's indicate that these beds are tuffaceous, predominantly of acid vitric composition, formed by pyroclastic material derived from contemporaneously active subaerial volcanic sources accumulating in sea water, and subjected to submarine transport. Appreciable quantities of acid material were thus erupted in 'Conception time.'

scholarly journals A Brief Summary of the Late Precambrian Rocks in the Caledonia Highlands of Southeastern New Brunswick

10.4138/1437 ◽  
1973 ◽  
Vol 9 (3) ◽  
Author(s):  
A. A. Ruitenberg ◽  
P. S. Giles ◽  
D. V. Venugopal ◽  
S. R. McCutcheon
Keyword(s):  
New Brunswick ◽  
Precambrian Rocks ◽  
Late Precambrian
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