Structural Studies of the Killarney Igneous Complex, Ontario and Their Tectonic Implications

Abstract

<p>The Killarney Igneous Complex (KIC), one of a suite of plutons known as the Killarney Magmatic Belt along the Grenville Front Tectonic Zone (GFTZ), consists of granite, porphyry and volcanic rocks, forming a wedge between Huronian metasediments of the Southern Province and the Grenville Province gneisses.</p> <p>Structural analysis of micro- and meso-scopic structural features of the KIC suggests that a set of subparallel faults observed in the research area are thrusting faults with substantial dextral horizontal movement. Various kinematic indicators are examined and proved very useful in determining the sense of shear accommodated by the faults. Palaeopiezometry indicates that the differential stress related to the thrusting ranged from 85 MPa to 146 MPa, with average of 100 MPa and standard deviation of 15 MPa, similar to the results obtained from other major thrusting zones. Fault-slip analysis reveals that the maximum compressive stress responsible for the thrusting came from the WNW direction, supporting the tectonic model that these faults were imposed by the indentation of the Superior craton.</p> <p>Two fracture variations, namely, kinks and wedges, are found common in the KIC and are studied theoretically and practically. The study provides valuable insight into the palaeostress field and the regional structural development in the research area. Kink angles are found to be a reliable kinematic indicator, and are determined by the ratio of the effective shear stress and the effective normal stress acting on their parent fractures. Wedge angles are found to be the prime factor controlling the fracture patterns developed within wedges; the formation of wedges was associated with the development of main faults.</p> <p>These structural studies are integrated with previous work of geochronology into a tectonic model for the geological history of the KIC and the surrounding area. During the period of 1.75-1.65 Ga, the KIC was emplaced in a transtension zone due to the southeasterly indentation of the Superior craton or the northwesterly encroachment of the block of Grenville Province. After its emplacement, the KIC underwent two major compressional events: the first one imposed a regional foliation and lineation in the porphyry-volcaniclastic assemblages, at about 1.62 Ga; the second event, due to a renewed southeasterly indentation of the Superior craton or northwesterly encroachment of the Grenville Province, imposed the thrusting faults in the area, and effectively produced a transtension zone between the KIC and the Grenville Province, so providing the space and the thermal environment for the emplacement of the Bell Lake Granite (ca. 1.47 Ga).</p>