The Role of Structural Inheritance in Strain Localization During Continental Breakup: Examples From Australia, Canada and Greenland

Abstract

Basement terranes of Australia, Canada and Greenland are locally dominated by Archean cratons separated by Proterozoic orogenic belts. Archean blocks include the typical competent rounded cratons with minimal post-Archean reworking as well as large elongate blocks that have been reworked during Proterozoic assembly. The orogenic belts range in age from latest Archean to Neoproterozoic. A solid understanding of the composition and rheology of the basement terranes is critical in order to predict how the crust will behave during continental breakup. Potential field data highlight the characteristic patterns of cratons and orogenic belts worldwide. Basement terranes onshore have been mapped and studied in detail in areas where the basement outcrops, but basement geology is commonly buried by overlying basins or surficial material. Using potential field data, terranes can be mapped and their boundaries and major structures delineated by changes in structural fabric, orientation and/or magnitude of magnetic and gravity anomalies. Basement composition can also be mapped where basement is relatively shallow and data quality is sufficient. Current models for hyperextension tend to have a starting model consisting of horizontally layered crust that requires an initial structure to localize strain. Real continental crust is much more complex and more often has moderate to steeply dipping zones and structures. Using terrane mapping along continental margins, the relationship between hyperextended non-volcanic margins and inherited basement structure has been investigated. On the North West Shelf and Southern Margin of Australia the relationship between hyperextended crust and cratonic basement can be documented in both regions using combined potential field and deep seismic data. A similar relationship can also be recognized between the exposed Archean terranes of Canada and Greenland. When basement terranes are taken into account, strain localization is shown to focus on terrane boundaries. Partitioning is strongest on those boundaries with the greatest rheological contrast. Thus mantle exhumation on magma-poor margins is more likely to develop at the boundary of a craton or in narrow mobile belts between cratons where rheological contrast is the highest.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015