| Popis: |
The major fold pattern of the Chibougamau region in the Archean Abitibi Belt, Quebec, is the result of two fold phases. The principal F1-synclines first formed as subsiding fault troughs, and were shortened in NS direction and molded around volcanic centers that had been consolidated by large synvolcanic plutons; they have a general easterly direction but curve locally to the NE or SE. N-trending F1-folds are locally present in the anticlinoria and are thought to have been produced by the upwelling of basement gneiss and/or synvolcanic plutons. The F2-folds have rather regular easterly trends; their axial plane schistosity S2 is the predominant planar fabric element. Basin margin faults were transformed into east-trending thrust faults during the F1- and F2-folding. The superposed schistosities S3 and S4 are conjugate shear planes related to NS shortening. They and the kink bands produce only minor strain except at a few localities. Synkinematic and late kinematic diapiric plutons pierce the structural pattern. The F1-folds, derived from the paleogeographic pattern during the uplift of volcanic islands and during the subsidence of fault basins, may also be interpreted as diapiric. Thus, diapirism took place during the whole period of NS compression. ENE trending left-lateral shear belts and their associated first and second order faults, displaced the Kenoran structures in late Archean and early Proterozoic time. |
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