Thermotectonic studies in the Paleoproterozoic Glennie domain, trans-Hudson orogen, Canada

Abstract

The Glennie domain of the Trans-Hudson Orogen (THO) is characterized by Paleoproterozoic island arc volcanogenic assemblages and granitoid rocks thrust as sheets over the Archean Saskatchewan craton prior to terminal collision between the Archean Rae-Hearne and Superior cratons. Four discrete deformation events have been recorded in the domain. The D1 and D2 events are associated with the southwestward-directed imbrication of Paleoproterozoic allochthons over the Saskatchewan craton, while the D3 and D4 events are associated with terminal collision and transpression, respectively. Discernable metamorphic episodes are associated with the D2 and D3 events, with peak thermal metamorphism during D3. Using INVEQ thermobarometry, metamorphic conditions during D3 in the Santoy Lake area were ca. 655–705°C and 6.1–7.3 kbar and ca. 530–595°C and 3.2–4.8 kbar for the Brownell Lake area. 40Ar/ 39Ar hornblende and biotite ages suggest the Santoy Lake area remained above ca. 490°C until ca. 1720 Ma, when it underwent rapid cooling through the biotite Ar closure temperature of ca. 330°C. 40Ar/ 39Ar biotite ages from the Brownell Lake area suggest moderate cooling from peak thermal metamorphism at ca. 1810–1755 Ma, when it passed through the ca. 310°C biotite Ar closure temperature. Differences between cooling rates for the two areas are interpreted as differential exhumation of smaller lithotectonic blocks bound by domain-wide, deep-crustal faults and shear zones. Zircon Pb-evaporation ages of variably deformed granitoid rocks from the Santoy Lake area show that the D2 event occurred after ca. 1857 Ma. The oldest granitoid in the Santoy Lake area provides a minimum age of mafic volcanism in the area of ca. 1886 Ma, as well as a significant hiatus (ca. 50 Ma) between deposition of the two supracrustal assemblages in the domain.