Burial Metamorphism of Late Precambrian Sediments near St. John's, Newfoundland

1972 ◽  
Vol 9 (11) ◽  
pp. 1568-1572 ◽  
Author(s):  
V. S. Papezik
Keyword(s):  
Mineral Assemblage ◽  
Tectonic Stresses ◽  
Late Precambrian ◽  
Maximum Thickness ◽  
Mineral Characteristics ◽  
Avalon Peninsula

The lowest member of the Late Precambrian Signal Hill Formation (a massive, gray, lithic sandstone), exposed at the eastern extremity of the Avalon Peninsula near St. John's, Newfoundland, is cut by a system of thin veins containing quartz, calcite, and whitish prehnite. The veins, confined to a narrow stratigraphic horizon, have been found, so far, along a strike distance of 4 km. Prehnite also forms small diffuse patches in the rock, producing a distinctive mottling effect; it is associated with authigenic quartz, sericite, chlorite, and small amounts of possibly metasomatic calcite.The prehnite-bearing mineral assemblage is consistent with mineral characteristics of the prehnite–pumpellyite facies, usually considered to be the result of burial metamorphism. The patchy interstitial prehnite is believed to have been formed by a reaction between authigenic laumontite and calcite. The prehnite-bearing assemblage may have been formed under a lithostatic load not greatly exceeding the present maximum thickness of the overlying part of the Cabot Group – about 4.5 km. The formation of both the interstitial prehnite and the prehnite-bearing veins was contemporaneous with the tectonic stresses responsible for the open folding of the Cabot Group.

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.'

A Possible Time Span for the Late Precambrian of the Avalon Peninsula, Southeastern Newfoundland in the Light of Worldwide Correlation of Fossils, Tillites, and Rock Units within the Succession

1972 ◽  
Vol 9 (12) ◽  
pp. 1710-1726 ◽  
Author(s):  
M. M. Anderson
Keyword(s):  
Time Span ◽  
Ice Age ◽  
Long Distance ◽  
Cape Breton Island ◽  
Late Precambrian ◽  
Cape Breton ◽  
The World ◽  
Absolute Age ◽  
Age Range ◽  
Avalon Peninsula

Since too few absolute age determinations have been carried out on late Precambrian rocks of the Avalon Peninsula, southeastern Newfoundland, a stratigraphic approach has been adopted to obtain the necessary dates on which to base a possible time-span for the whole succession. The correlatable 'features' of the Avalon Peninsula late Precambrian—fossils, tillites, and volcanic episodes, have been correlated with similar 'features' in late Precambrian sequences in other parts of the world where these 'features' have been dated isotopically. Some of the correlations are probable, others only possible as long-distance correlation involves an element of speculation.Conception Group sedimentation may have lasted from 710 m.y. ago, the possible age of the 'basal' conglomerate, to ca 600 m.y. ago, and possible ages for the Conception Group tillites and fossils (Mistaken Point fauna) are 670–715 m.y. and 610 to 630 m.y. respectively. Harbour Main volcanism began some 795 m.y. ago and continued until about 715 m.y. before present. These ages indicate a possible age-range for the late Precambrian of the Avalon Peninsula from ca 800 m.y. to 570 m.y. (age of base of Cambrian accepted here), a time span of ca 230 m.y. that is equivalent to the greater part of the Proterozoic Hadrynian Era.The soft-bodied metazoan fossils of the Conception Group Mistaken Point fauna are comparable to those of the Australian Ediacara fauna and related forms in other parts of the world. Conception Group tillites are correlated with glaciogenic deposits of the uppermost Precambrian ice age in central Australia, the Rybachiy Peninsula, U.S.S.R., and Scotland (Dalradian tillites). Harbour Main Group volcanics are correlated with part of the Coldbrook Group volcanic sequence, southern New Brunswick; the Fourchu Group and Morrison River Formation of southeast Cape Breton Island are believed younger, and possibly, the time equivalent of the upper part of the Musgravetown Group together with the Random Formation, western Avalon, although the possibility of the Morrison River Formation being Cambrian cannot be excluded. Correlation of Harbour Main volcanics with volcanics of late Precambrian age in the British Midlands is considered a possibility but remains conjectural.A single intrusive event is favored for emplacement of the Holyrood granite 607 ± 11 m.y. ago. This necessitates there having been older granite in the area to provide a source for the granite clasts in the Conception Group conglomerates and tillites. A second, less likely, alternative is that the Holyrood granite was emplaced over a substantial period by successive pulses of magma; the 607 m.y. age is then that of the last intrusion of magma.

Detrital Garnet and Muscovite in Late Precambrian Sandstone near St. John's, Newfoundland, and their Significance

1973 ◽  
Vol 10 (3) ◽  
pp. 430-432 ◽  
Author(s):  
V. S. Papezik
Keyword(s):  
Main Group ◽  
Precambrian Basement ◽  
Granitic Pluton ◽  
Late Precambrian ◽  
Lower Member ◽  
Western Flank ◽  
Basement Rocks ◽  
Avalon Peninsula

The lower member of the Signal Hill Formation of Late Precambrian age, a lithofeldspathic sandstone exposed near St. John's, Newfoundland, contains small but persistent amounts of garnet and muscovite. These minerals are not known to occur in rocks of the Harbour Main Group and the Holyrood granitic pluton of the Avalon Peninsula, previously considered to be the source of the Signal Hill sediments. As paleocurrent studies indicate a northeasterly provenance of the sediment it is suggested that the rock may have been derived from Precambrian gneissic and granitic basement, now covered by the ocean, similar to the Precambrian(?) basement rocks along the western flank of the Avalon Platform.

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.

Late Precambrian ignimbrites on the Avalon Peninsula, Newfoundland

1969 ◽  
Vol 6 (6) ◽  
pp. 1405-1414 ◽  
Author(s):  
V. S. Papezik
Keyword(s):  
Volcanic Belt ◽  
Main Group ◽  
Granitic Magma ◽  
Late Precambrian ◽  
Volcanic Pile ◽  
Avalon Peninsula

The predominantly volcanic Harbour Main Group of Late Precambrian age, forming a broad northerly trending belt in the central part of the Avalon Peninsula of Newfoundland, includes some well-developed ignimbrites. The ignimbrite sequence, best exposed in the western part of the volcanic belt, consists of ash-flow tuffs intercalated with tuff–breccias of various origins and minor volcanigenic sediments. Some of the ignimbrite sheets are densely welded, with distinct eutaxitic structures. Although the original glass is recrystallized, shard outlines are perfectly preserved and fragments of obsidian and perlite can be recognized; albite crystals are abundant, and quartz, augite, and biotite are present locally. The ignimbrites have been folded, faulted, and are now almost vertical. In composition, they range from rhyolites to dacites and are distinctly sodic.It is suggested that the ignimbrites may be derived from the gas-charged upper part of a granitic magma intruded into a pre-existing part of the Harbour Main volcanic pile; the lower, gas-poor part of the magma may have formed the present discordant "Holyrood batholith" of the Avalon Peninsula.

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