Repository logo
 

Metamorphic evolution of the Great Slave Lake shear zone

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Goddard, RM 
Wallis, D 
Hansen, LN 
Martel, E 

Abstract

jats:titleAbstract</jats:title>jats:pThe Palaeoproterozoic Great Slave Lake shear zone (GSLsz) is a crustal‐scale strike‐slip structure, with a total length of >1,000 km and a width of ~25 km, that separates the Archean Rae and Slave cratons. The range of metamorphic rocks now exposed at the surface encompasses granulite facies mylonite through to lower‐greenschist facies ultramylonite and cataclasite, providing a potential type example of fault‐zone structure in the middle and lower crust. However, the metamorphic evolution of the units remains poorly quantified, hindering detailed structural and tectonic interpretations. Here, we use phase equilibria modelling and thermobarometry to determine the metamorphic conditions recorded by pelitic, mafic and felsic GSLsz mylonites. Samples from the entire range of granulite–greenschist facies units preserve evidence for nested clockwise pressure–temperature paths that are consistent with a single orogenic cycle. Our findings indicate that the northern Rae margin underwent pervasive crustal thickening with peak pressures in metasedimentary rocks reaching ~1.1 GPa. The crustal thermal gradient at the onset of thickening was ~650°C/GPa, whereas the final stages of equilibrium recorded by fine‐grained matrix minerals in all samples collectively define a metamorphic field gradient of ~1,000°C/GPa. Deformation microstructures are consistent with the main phase of dextral shear having been synchronous with or following peak metamorphism. The history of metamorphism and exhumation of the GSLsz is consistent with the Sibson–Scholz model for shear zones, with a narrowing of the deforming zone and the progressive overprinting of higher‐grade assemblages during exhumation through shallower crustal levels.</jats:p>

Description

Keywords

mylonite, phase equilibria modelling, shear zone, thermometry

Journal Title

Journal of Metamorphic Geology

Conference Name

Journal ISSN

0263-4929
1525-1314

Volume Title

39

Publisher

Wiley

Rights

All rights reserved