عنوان

Tectonic evolution of the Late Archean Pontiac Subprovince, Superior Province, Canada:

Number

TLpq194016914

.Language of Text, Soundtrack etc

انگلیسی

Title Proper

Tectonic evolution of the Late Archean Pontiac Subprovince, Superior Province, Canada:

General Material Designation

[Thesis]

First Statement of Responsibility

M. R. Ghassemi

Title Proper by Another Author

Structural, metamorphic, and geochronological studies

Subsequent Statement of Responsibility

K. Benn

Name of Publisher, Distributor, etc.

University of Ottawa (Canada)

Date of Publication, Distribution, etc.

1996

Specific Material Designation and Extent of Item

320

Dissertation or thesis details and type of degree

Ph.D.

Body granting the degree

University of Ottawa (Canada)

Text preceding or following the note

1996

Text of Note

The Pontiac Subprovince is a Late Archean (ca. 2.7 Ga) metasedimentary-metavolanic-granitoid-gneiss terrane situated along the southeastern margin of the Superior Province in Quebec. Detailed structural study of the northwestern part of this amphibolite facies metasedimentary belt has revealed a protracted history of deformation in Late Archean and Early Proterozoic time. An early contractional event (D) resulted in development of steep foliations now preserved as folded or straight relics within microlithons of S2 foliation. During this stage, the Cadillac-Larder Lake fault zone acted as a major fault zone along which greenstones for the Abitibi Subprovince were thrust over the Pontiac Subprovince. Regional metamorphism resulted from both thickening of the crust, and intrusion of voluminous I-type graintes. D2 structures record peak metamorphic high-temperature deformation of the crustal rocks during which large-scale D2 nappes moved towards the south-southeast. The basal thrust faults of these nappes are preserved as high-strain shear zones within the study area. Second order east-trending recumbent F2 folds, a penetrative S2 crenulation foliation, and a north-northwest-trending L2 elongation lineation are other important structures of this deformational event. A later D3 contractional event superimposed east-trending upright folds on all earlier structures. Extensional D4 structures are associated with reactivation of the Cadillac-Larder Lake fault zone as a normal fault zone, and are only recorded in or close to normal faults within this fault zone. Finally, brittle D5 thrust faults and kink structures are superimposed on all older structures in the northwestern Pontiac Subprovince. Gneisses of the Lac Opasatica area record pre-D penetrative structures that are not present within the other rock types of the study area. Increasing metamorphic grade from biotite zone to sillimanite zone is evident from north (the Cadillac-Larder Lake fault zone) to south in the study area, close to outcrops of the S-type granites. Thermobarometry of samples from the study area indicates that regional metamorphism of the rocks in the northwestern Pontiac Subprovince occurred at about 590C and 6.2 kbar. Investigation of the metamorphic and structural history of these Late Archean rocks suggests a clockwise PT path similar to that of Phanerozoic collisional belts. Ar/Ar age constraints from this study combined with other geochronologic indicate a slow cooling rate of about 2 to 6C/Ma, and reveal that temperatures as high as 350C and 280C were persistent in crustal rocks of the area until ca. 150 Ma after attainment of peak metamorphic conditions. (Abstract shortened by UMI.)

Earth sciences

Geology

Quebec

K. Benn

M. R. Ghassemi

Electronic name

p

[Thesis]

276903

a

Y