Spatial and Temporal Thermal Variations in Deformed and Denudated Foreland-Fold-and-Thrust Belt – A Case Study from the Southern Canadian Cordillera

N.J. Hardebol^1,2 and J.-P. Callot^1
1Institut Français du Pétrole – Rueil-Malmaison, France
²Faculty of Earth and Life Sciences, Vrije Universiteit – Amsterdam, The Netherlands

The study of spatial and temporal variations in the geothermal field during ongoing deformation has received much attention in extensional, but less in compressional tectonic regime. For extensional settings, basin subsidence and burial history studies advanced with the recognition of the effect of thermal perturbation induced by stretching (McKenzie, 1978) and subsequently with coupled basin-scale litho-astenosphere geodynamic modeling (e.g. Cloetingh et al., 1995; Huismans et al., 2001). In contrast, in compressional settings, orogenic loading, denudation and foreland sedimentation are recognised as the main controlling factors for the burial history, but the interaction of such phenomena and its impact on the thermal field within the growing orogen is still debated. Thus the focus of this combined field-data and modeling oriented study is to relate thermal field and deformation history for a proper appraisal of the burial-exhumation path at various scales.

The thermal evolution of the southern Canadian Foreland fold-and-thrust Belt (FFTB; SW Alberta – SE British Columbia) forms the locus of this study. Understanding the thermal history is the key to a proper appraisal of burial and exhumation history from organic maturity ranks (OMR) and fission track studies, in a setting that is subjected to a perturbed thermal field affected by both tectonic and sedimentary burial. The FFTB is located at the transition between a thermally stable North American Craton to the east and Proterozoic-Palaeozoic inverted passive margin. The Cordillera hinterland in the west marks at present a zone of significant thinning of the lithosphere expressed by enhanced surface heat flow values and strong denudation both in the belt and in the foreland basin.

A compilation of literature with newly acquired surface and borehole OMR constrain 1D and 2D, conceptual and realistic thermo-kinematic modelling of burial-exhumation history scenarios. This study especially illustrates the interplay of sedimentary versus tectonic burial (i.e. by thrustsheet stacking) for deducing pre-, syn and post deformation thermal and organic maturation pathways. Our results show that synorogenic exhumation (4-6 km) confined to thrustsheet emplacement in the deformed FFTB is superimposed by a second episode of large wavelength exhumation involving also the entire former foredeep. Plotting OMR onto structural and restored cross-sections facilitate the definition of thermo-tectonic provinces and estimation of paleo-geothermal gradients used as first order boundary conditions for thermo-kinematics modeling. Spatial and temporal variations of the FFTB’s thermal field are governed primarily by the interplay of heat conduction, convection from fluid flow and advection by rock displacement. Thereby, recorded thermal gradient variations during the main phase of thin-skinned contraction tend to be limited to the deformational prism itself. Potential heat flow fluctuations which originate from changes in crustal and mantle heat source become apparent only after the removal of these confined yet therefore not less significant perturbation. This thermal signal from the mantle is important in the context of dynamic induced topography that has potentially affected the exhumation of the FFTB waning into the more distal undeformed foreland.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands