Structural development of angular volcanic belts in the Archean Slave Province

Abstract

Narrow belts of metavolcanics lying between metasediments and granitoid rocks in the southwestern part of the Archean Slave Province display a distinctive angular map pattern. Steep homoclinal segments, from 10 to over 50 km in length, change strike abruptly at "corners" as if defining large, open, angular folds. Structures near two corners in a belt are not, however, compatible with such folds. Examples include early-phase, layer-parallel foliations in directional sets that are interspersed with one set overprinting the other; mafic dykes of similar contrasting orientations interspersed within basal gneiss; and isoclines in metasediments that deflect rather than wrap around a corner. Additionally, late-phase foliations striking across corners indicate compression that tended to straighten rather than fold the belt.It is suggested that the angular volcanic belts and imposed structures reflect movements on long-lived, crustal-scale faults. A model of development is proposed in which synvolcanic, listric extensional faults and high-angle transfer faults were reactivated as upthrusts during regional compression. Consequent tilting of the volcanics in different directions formed the angular pattern of steep homoclines and guided the development of a succession of folds and foliations.