Understanding the Relationship Between Structural Inheritance and Rift Related Magmatism on the Labrador Margin

Abstract

The process of continental breakup involves a complex and variable sequence of events beginning with a period of continental extension causing rifting, and eventually the initiation of seafloor spreading. Continental breakup in the Baffin Bay – Labrador Sea system reached variable degrees of maturity along the margin. Full oceanic spreading was initiated in the Labrador Sea and probably Baffin Bay, but the Davis Strait is dominated by continental crust. The amount of rifting and breakup-related magmatism is also variable with the most volcanic segment focused around the Davis Strait with abundant basalts both on and offshore, seaward dipping reflectors and mafic underplating inferred on velocity models. Structural inheritance may have influenced both the along-margin variation in the degree of magmatism and the variable manifestation of rifting in the Labrador Sea – Baffin Bay system. To gain insight into the role of pre-existing structures in continental breakup four weeks of fieldwork were undertaken around Makkovik in Labrador, Canada. The fieldwork focused on two subject areas; 1) establishing the chronology of structural events prior to continental breakup and 2) locating and characterising geological evidence for breakup-related magmatism. Our structural study produced a relative chronology of brittle deformation events between the Makkovik Orogen (1.9-1.7 Ga) and Mesozoic rifting. The data points to a sequence of sinistral and dextral brittle deformation events introducing heterogeneities into the pre-rift rocks, which crosscut the regional metamorphic fabric. Field observations of magmatism show that Mesozoic dykes are more elusive and spatially limited than previous work suggests. However magmatism contemporaneous with breakup processes is manifest in the form of a diatreme and associated dykes. The diatreme records a multiphase eruptive history, crosscut by melilitic dykes. An older dyke was intruded parallel to the basement mineral fabric, whereas a younger dyke crosscuts this fabric, potentially demonstrating the changing influence of the pre-existing fabric. The preliminary results indicate that the metamorphic mineral fabric and potentially the sequence of brittle deformation events prior to Mesozoic rifting have influenced the manifestation of rifting and magmatism. The aim is to now tie these deformation events to plate tectonic models, allowing us to attribute deformation styles to tectonic events and thus add a temporal framework.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016