Rb/Sr Isochrons for some Precambrian Rocks in the Hanson Lake Area, Saskatchewan: Discussion

1971 ◽  
Vol 8 (1) ◽  
pp. 181-182
Author(s):  
R. Bruce Farquharson
Keyword(s):  
Lake Area ◽  
Precambrian Rocks

Pedogenesis of the Precambrian Rocks in the Hanson Lake Area, East-Central Saskatchewan

1971 ◽  
Vol 8 (7) ◽  
pp. 820-843
Author(s):  
J. W. Gaskarth
Keyword(s):  
Basal Part ◽  
Lake Area ◽  
Chemical Analyses ◽  
East Central ◽  
Precambrian Rocks ◽  
Metavolcanic Rocks ◽  
Orogenic Cycle ◽  
Silicate Rocks ◽  
Lower Group ◽  
Chemical Evidence

Precambrian rocks in the Hanson Lake area occur in two main groups. The first (Lower Group) consists of quartz dioritic rocks, migmatites, and agmatites which occur in two large anticlinal complexes. These rocks are overlain by and concordant with a complicated sequence of supracrustal rocks which comprise the second group (Upper Group). The basal part of the Upper Group is basaltic and the rest is made up of basaltic, andesitic, dacitic, and rhyolitic fragmental metavolcanic rocks, dacitic metalavas, calc-silicate rocks, and graywacke-type metasediments. Other rocks in the area include several bodies of intrusive granite, one of which has a mass of magnetite – amphibole – epidote rock associated with it, a body of metapyroxenite, and a number of apparently intrusive amphobolite bodies. Both beryliferous and non-beryliferous pegmatites are abundant and occur mainly within the rocks of the Lower Group.An interpretation of the petrogenesis, consistent with the available petrographic, structural, and chemical evidence (46 new chemical analyses are presented), suggests that the Upper and Lower Groups were originally parts of a conformable supracrustal sequence. The lower parts of the sequence (Lower Group) were migmatized, partially melted, and mobilized during a complicated orogenic cycle.

Rb/Sr isochrons for some Precambrian rocks in the Hanson Lake area, Saskatchewan

1970 ◽  
Vol 7 (2) ◽  
pp. 338-345 ◽  
Author(s):  
L. C. Coleman
Keyword(s):  
Analytical Data ◽  
Lake Area ◽  
Geological Evidence ◽  
Precambrian Rocks ◽  
Granite Intrusion

Rb–Sr whole rock analyses of rocks from the Hanson Lake area; Saskatchewan, combined with geological evidence suggest that there were three thermal events in that region during Precambrian time. During Archean time, a period of volcanism about 2520 m.y. ago was followed by a period of granite intrusion about 2445 m.y. ago. During Aphebian time, the rocks of the area were intruded by pegmatites about 1800 m.y. ago. If the analytical data alone are considered, the two earlier events should be considered as one that took place about 2425 m.y. ago.

Age of the Early Precambrian Rocks of the Saganaga Lake – Northern Light Lake Area, Ontario–Minnesota

1971 ◽  
Vol 8 (9) ◽  
pp. 1110-1124 ◽  
Author(s):  
G. N. Hanson ◽  
S. S. Goldich ◽  
J. G. Arth ◽  
D. H. Yardley
Keyword(s):  
Hydrothermal Alteration ◽  
Low Grade ◽  
Lake Area ◽  
Geologic History ◽  
Pyroclastic Material ◽  
Local Conditions ◽  
Precambrian Rocks ◽  
Sequence Of Events ◽  
Mineral Data ◽  
Volcanic Pile

Whole-rock Rb–Sr isochron and mineral ages from the Saganaga Lake – Northern Light Lake area on the Ontario–Minnesota boundary indicate a major orogeny at 2700 m.y. ago. The sequence of events reconstructed in the geologic history started with the eruption of a volcanic pile of flows and pyroclastic material. During metamorphism and folding the basalt flows were converted to amphibolite and an interlayered series to the Northern Light Gneiss, which is now principally trondhjemite with lesser amounts of amphibolite and metarhyolite. The greenstones and the Northern Light Gneiss were intruded by the Saganaga Granite (tonalite), and the tonalite and the Northern Light Gneiss, in turn, were intruded by a syenodioritic phase of the lcarus pluton.The whole-rock isochron ages for the Northern Light Gneiss, the Saganaga tonalite, and the lcarus pluton are 2740, 2710, and 2690 m.y., respectively. Large uncertainties are attached to these values because of the unfavorable Rb/Sr ratios, but the mineral data that include Rb–Sr, K–Ar, and U–Pb analyses, together with geologic observations, permit dating of the Saganaga tonalite at 2700 ± 50 m.y.Mineral ages from this study and some published by the Geological Survey of Canada cluster in the range from 2650 to 2600 m.y. ago and may indicate h low-grade event or an epeirogenetic effect that dates the time of uncovering and stabilization of the region. Mineral ages in the range from 2600 to 2400 m.y. and at approximately 1800 m.y. ago may be partially reset and probably reflect local conditions of faulting and shearing associated with hydrothermal alteration, later low-grade metamorphism, and possibly recent weathering. Similarly, faults and sheared zones probably were effective in localizing the intrusion of dikes that occurred at various times between 2700 and 1100 m.y. ago.

Sign in / Sign up

Export Citation Format

Share Document