Pluton emplacement within an extensional transfer zone during dextral strike-slip faulting: an example from the late Archaean Abitibi Greenstone Belt

• Published in: Journal of structural geology 1998, Vol.20 (1), p.43-59
• Main Authors: Lacroix, S., Sawyer, E.W., Chown, E.H.
• Format: Article
• Language: English
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/S0191-8141(97)00071-0

The Lake Abitibi area within the late Archaean Abitibi Greenstone Belt exhibits an interlinked plutonic, structural and metamorphic evolution that may characterize segmented strike-slip faults at upper-to-mid-crustal levels. Along the major, southeastward propagating Macamic D 2 dextral strike-slip fault, Theological and preexisting D 1 structural heterogeneities induced the development of NNW-trending dextral-oblique splays which evolved into an extensional trailing fan and created an extensional, NNW-dipping stepover. Magma flowing upwards from deeper parts of the Macamic Fault spread towards the southeast at upper crustal levels along both the oblique-slip and extensional D 2 splays, and built several plutons in a pull-apart domain between 2696 and 2690 Ma. Different emplacement and material transfer mechanisms operated simultaneously in different parts of the system, including fault dilation and wedging, lateral expansion, wall-rock ductile flow and stoping. Transfer of movement between D 2 splays occurred under ductile conditions during syn-emplacement, amphibolite-grade metamorphism (500–700 °C). During cooling (< 2690 Ma), narrower brittle-ductile zones of greenschist-grade shearing were concentrated along the pluton-wall rock contacts, but the extensional stepover locked since both normal and reverse movements occurred along NNW-dipping faults. Pluton emplacement, contact metamorphism and propagation of D 2 faults appear to have been closely linked during the Superior Province-wide late transpressional event.