摘要:

R-mode factor analysis, discrimant analysis, trend surface, and canonical trend surface analyses are applied to the 42 variables measured for 171 Precambrian igneous and high grade metamorphic rocks, sampled in deep drill holes in the western Canada sedimentary basin. Low-grade metasedimentary rocks and post-Hudsonian diabase intrusives are excluded. The four strongest R-mode factors are related to processes of regional metamorphism. These are: potassium metasomatism, shearing with the development of secondary foliation, chloritization, and mylonization. Potassium metasomatism appears mainly to be later than the three other processes.Regional lineaments in the western Shield, identified from tectonic, gravity, and magnetic maps, when combined with trend surface maps from drill hole data, suggest southwestward extensions of major lithologic tectonic units of the Churchill province. The fivefold division of the subsurface Precambrian includes, from north lo south: I—Liard block (Slave and Bear provinces, in part), II—Athabasca mobile belt (restricted). III—Cree Lake – Calgary belt, IV—Kisseynew–Sweetgrass belt, and V—Superior province (Assiniboia block, restricted).The two major Phanerozoic crustal flexures in the Western Canada basin, the Peace River arch and the Williston basin, correspond to canonical trend surface highs and lows, respectively. Their persistent isostatic tendencies are linked to differing Hudsonian metamorphic histories.A depletion of trace metal content, which accompanies shearing, can be traced diagonally across northern Alberta. The southwestward projection of this belt matches the portion of the Canadian Cordillera barren of major ore deposits.

ISSN:0008-4077    

DOI:10.1139/e76-001

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The Oxford Dolomite of southeastern Ontario is considered to be equivalent to the Ogdensburg Dolomite of northern New York State. The Oxford Formation is redefined in terms of its lithology, distribution, thickness, sedimentary environment, and age.A series of representative sections can be correlated with wells drilled in southeastern Ontario. The formation rests disconformably upon the March Formation (Tremadocian) and is overlain disconformably by Middle Ordovician (Chazyan) sediments. The lower contact of the formation is widely exposed, but the upper contact is known only from boreholes.Lithologies are not distinctive; a lower division in which quartz sand is abundant and an upper division in which it is rare or absent can be recognized. The total thickness of the formation is not known; however, a minimum thickness of 605 ft (184.5 m) is present in a well near Williamsburg, Ontario. Conodont faunas indicate that the age of the Oxford is Lower Arenig and the disconformity at the base of the formation marks the base of the Arenig series in the Ottawa – St. Lawrence Lowlands.

ISSN:0008-4077    

DOI:10.1139/e76-002

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The lowlands adjacent to the Red River Valley were flooded whenever Quaternary glaciation dammed the northward-draining river systems of the region. The most recent impoundment, referred to as Lake Agassiz, began shortly before 13 500 years BP, as late Wisconsinan ice retreated northward in the Valley for the last time. In southern Manitoba, three fine-grained lacustrine units, numerous beach deposits, and an extensive area of fluvio-lacustrine (deltaic) sediment were deposited in and around the main depositional center of the Lake Agassiz basin during the life of the lake.The oldest offshore deposit of Lake Agassiz (Unit 1) is a silty clay containing ice-rafted clasts of till, clayey silt, and rock. Most of the silty and sandy sediment of the Assiniboine Delta also was deposited at this time. A readvance of ice into the northern and eastern Lake Agassiz basin, about 9800 years ago, caused a new influx of ice-rafted sediment into the offshore silty clays of southern Manitoba. Clast-rich Unit 2 was deposited at this time along the northern and eastern margins of the basin. When the ice retreated from the area shortly after 9800 years BP, lake levels dropped, and siltier, better laminated, and relatively clast-free Unit 3 was deposited. Units 1, 2, and 3 in southern Manitoba are correlated, respectively, with the Brenna Formation, lower part of the Sherack Formation, and upper part of the Sherack Formation of Lake Agassiz in North Dakota and Minnesota. Lake Agassiz deposition continued in southern Manitoba until after 8700 years BP.

ISSN:0008-4077    

DOI:10.1139/e76-003

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Conodonts have been recovered from highly deformed limestone and calcareous argillite in Palaeozoic and Mesozoic successions near the western border of the Shuswap Metamorphic Complex. Presently known biostratigraphic sequences indicate that the Eagle Bay Formation of the Mount Ida Group is in part Mississippian in age, and likely correlative with the Slide Mountain and Milford Groups. In addition, part of the succession previously mapped as Cache Creek Group in the Vernon area is now known to be Late Triassic in age, and can be correlated with the Sicamous Formation of the Mount Ida Group, the Nicola Group, and the Slocan Group. The Upper Triassic succession was affected by deformation and metamorphism associated with development of the Shuswap Metamorphic Complex.

ISSN:0008-4077    

DOI:10.1139/e76-004

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The fold-axis is the eigenvector associated with the smallest eigenvalue of a symmetrical 3 × 3 matrix of direction cosines of poles to the folded surface, only if the fold is cylindrical. Cylindricity can be tested using either a χ2or an F test. Sections showing the traces of macroscopic surfaces and of the axial plane may be constructed with the aid of computer plots that show the projection of each outcrop as well as the trace of the folded surface. The orientation of the axial plane can be calculated from the orientations of the fold-axis and the trace of the axial plane on a section normal to the fold-axis. These numerical procedures are illustrated by an analysis of four folds from the Rocky Mountains.

ISSN:0008-4077    

DOI:10.1139/e76-005

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Fold structures in Cambro-Ordovician schists of the Stoke Mountain complex are compared with similar structures in adjacent Middle Ordovician and Siluro-Devonian slaty rocks. Schistosity in the complex lies parallel to the axial surfaces of obscure F1folds. F2isoclines in the schistosity and first generation isoclinal folds in bedding within the Siluro-Devonian rocks are essentially coplanar and coaxial; both are steeply inclined and plunge dominantly northeast. Parallel folds in Middle Ordovician and younger rocks apparently pass upward into Siluro-Devonian strata. Hence the F2folds are plausibly correlated with those in the Siluro-Devonian rocks, which are of Acadian (mid-Devonian) age. Nevertheless, the steeply inclined F2-type folds in the Middle Ordovician rocks can be traced northeast along the Appalachians to localities where they are truncated by an angular unconformity beneath Siluro-Devonian rocks. It is evident that here the folds are not Acadian but late Ordovician (Taconic) structures.The conflicting evidence as to the age of the F2-type folds, which is not resolved by radiometric data, casts doubt on both local and regional correlations based on fold form and orientation.

ISSN:0008-4077    

DOI:10.1139/e76-006

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

As part of studies of anorthosites from the northern hemisphere, the paleomagnetism of two anorthosite inliers at Indian Head and Steel Mountain in western Newfoundland is described. The six sites at Indian Head retain a stable remanent magnetization and yield a paleomagnetic pole at 8 °S, 157½° E(δp = 15°, δm = 20°). This is close to poles for anorthositic and other rock units from within the Grenville Province that represent magnetization of age 1000 m. y., suggesting that there is no relative rotation between western Newfoundland and the southeastern part of the Canadian Shield, at least since the time of the Grenville orogeny. The ten sites at Steel Mountain also retain a stable magnetization, which yields a paleomagnetic pole at 22½° S, 41 °W (δp = 8°, δm = 14°). This position is closer to lower Paleozoic poles from Newfoundland and thus probably represents a lower Paleozoic magnetization.

ISSN:0008-4077    

DOI:10.1139/e76-007

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A 10 km wide, subcircular body of highly recrystallized anorthosite (meta-anorthosite) located north of La Tuque, Québec, is partially surrounded by an aureole of gneisses in the granulite facies. It is foliated near the edges, but lineated in the center. Pegmatites and mafic dikes were intruded into the anorthosite after the major phase of emplacement, but before a later, minor phase of deformation. Younger pegmatites post-date all deformation. The pluton appears to have been emplaced like a hot diapir, possibly during the Grenvillian thermostructural event.

ISSN:0008-4077    

DOI:10.1139/e76-008

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

An earthquake occurred at 10 h 16 m 39 s GMT on 5 July 1972 in close proximity to the west coast of Vancouver Island, near 49.5 °N and 127.2 °W. Its magnitude (mb) was 5.7 and the hypocenter was near the middle of the crust. A well defined P nodal solution has a pressure axis with a north-south orientation and a tension axis with an east-west orientation. The preferred nodal plane suggests right lateral strike-slip faulting on a near vertical fault, striking in a north-northwest direction. The other nodal plane suggests that left lateral strike-slip faulting on a near vertical fault striking in an east-northeast direction is also a plausible solution. A field study with portable seismographs revealed that very few aftershocks were associated with this earthquake. The largest aftershock had a magnitude (ML) of 3.4. The distribution of intensity of the mainshock observed on Vancouver Island differs from that predicted by the intensity versus distance relation presently used for western Canada.

ISSN:0008-4077    

DOI:10.1139/e76-009

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Eight distinct facies have been defined in a 110 m thick section of the Lower Devonian Battery Point Sandstone near Gaspé, Québec. The first is a scoured surface overlain by massive sandstone with mudstone intraclasts. Facies A and B are trough cross-bedded sandstones, with poorly- and well-defined stratification, respectively. Facies C and D consist of large isolated, and smaller multiple, sets of planar cross-stratified sandstones, respectively. Facies E comprises large sandstone-filled scours, facies F comprises ripple cross stratified fine sandstones with interbedded mudstones, and facies G comprises sets of very low angle cross-stratified sandstones.The overall context of the Battery Point Sandstone, the presence of rootlets, and the abundance of trough and planar-tabular cross bedding, all suggest a generally fluvial environment of deposition. Analysis of the facies sequence and interpretation of the primary sedimentary structures suggest that channel development began by scouring, and deposition of an intraclast lag. Above this, the two trough cross bedded facies indicate unidirectional dune migration downchannel (vector mean direction 291°). The large planar tabular sets are associated with the trough cross bedded facies, but always show a large (almost 90°) paleoflow divergence, suggesting lateral movement of in-channel transverse bars. The smaller planar tabular sets occur higher topographically in the fluvial system, and the rippled silts and muds indicate vertical accretion. Because of the very high ratio of in-channel sandy facies to fine-grained vertical accretion facies, and because of the evidence of lateral migration of large in-channel bars, the Battery Point River appears to resemble modern braided systems more than meandering ones.

ISSN:0008-4077    

DOI:10.1139/e76-010

出版商:NRC Research Press    

年代:1976

数据来源: NRC